Rozprawy doktorskie na temat „Metallo Supramolecular Self-assembly”

Self-assembly processes were used to construct supramolecular architectures based on metal-ligand interactions. The structures formed strongly depend on the used metal ion, the ligand type, the chosen counter ion and solvent as well as on the experimental conditions. The focus of the studies was the design of multifunctional N-donor ligands and the characterization of their complexing and structural properties. This work was divided into three distinct main parts: The bis(2-pyridylimine), the bis(2-hydroxyaryl) imine and the tripodal imine / amine ligand approach. In the first part a series of bis(2-pyridylimine) derivatives having different linking elements were employed as building blocks for novel supramolecular architectures. Reaction of individual d-block metal salts with these ligands has led to the isolation of coordination polymers, a metallamacrocycle, double-stranded helicates, triple-stranded helicates as well as of circular meso-helicates. The nature of the spacer in the Schiff base ligands, the noncovalent weak interactions, such as hydrogen bond, face-to-face π-π and edge-to-face CH-π interactions, are all important factors influencing the architecture of the final products. Topological control of the assembly process of the hexanuclear meso-helicates is clearly associated with the bidentate coordination of the sulfate anion which directs the formation of a double- rather than a triple-stranded helicate around the octahedrally coordinated Cu(II). Surprisingly, the variation of the linker function in the ligands, which significantly changes the linking angle of the pyridylimine strands, has only a little influence of the resulting structure. Also the use of a mixture of ligands does not influence the meso-helicate topology; the result is the symmetrically mixed meso-helicate. The new iron(II) triple helicate [Fe2(L5)3](PF6)4 14 {L5 = bis[4-(2-pyridylmethyleneimino)phenyl]-1,1-cyclohexane} in its chloride form binds strongly to DNA as confirmed by induced circular dichroism signals in both the metal-to-ligand charge transfer (MLCT) and in-ligand bands of the helicate. The induced CD spectrum gives some evidence that [Fe2(L5)3]4+ interacts with the DNA in a single binding mode, which is consistent with major groove binding. The cytotoxicity of the new iron(II) triple helicate 14 was evaluated on human lung cancer A549 cells and compared with that of cisplatin and that of the previously reported iron(II) triple helicate [Fe2(L1)3]4+{L1 = bis[4-(2-pyridylmethyleneimino)phenyl]methane}. The first results show some distinguishing features for 14 obviously caused by the existing structural differences of the complexes. In the second part of the thesis, novel uranyl complexes of the bis(2-hydroxyaryl) imine ligands have been synthesized and characterized. 1D coordination polymers and mononuclear structures were formed. In all complexes a distorted hexagonal bipyramidal coordination geometry around the uranyl centre is observed. The imine nitrogen atoms of the ligands do not bind to the metal centre but interact strongly with the hydroxy group via H-bonding. DFT calculations made with L8 ( α,α’-Bis(salicylimino)-m-xylene) are in good agreement with the X-ray crystal structure data. Liquid-liquid extraction studies involving selected ligands and Eu(III) or U(VI) indicate remarkably high selectivity for U(VI) over Eu(III) at weak acidic pH conditions. We believe that the study made opens up new possibilities for uranyl ion extraction which could be interesting in view of the treatment of nuclear waste. In the third part of the thesis, a series of multifunctional tripodal ligands with different N-donor centres were used for U(VI) and lanthanide, Nd(III), Eu(III) and Yb(III), binding and extraction. Reaction of these metal ions with selected tripodal ligands afforded complexes which were characterized by ESI mass spectroscopy. The complex composition was found to be 1:1 in all cases. The extraction behaviour of the tripodal ligands towards Eu(III) and U(VI) was studied both in the absence and presence of octanoic acid as co-ligand using the extraction system Eu(NO3)3 or UO2(NO3)2–buffer–H2O/ ligand–CHCl3. These separation systems show a remarkably high selectivity for U(VI) over Eu(III). It is interesting to note that the addition of the octanoic acid to the extraction system leads to high synergistic effects. A series of Eu(III) extraction experiments were done to clarify the composition of the extracted complexes. The results clearly point to the formation of various species with changing composition.

Supramolecular self-assembly on metallic surfaces is the ideal playground for studying a variety of physical and chemical phenomena. Adsorbed molecules will diffuse and self-organise to form assemblies dictated by their functionalities, while the more or less pronounced metal reactivity will accordingly affect both the supramolecular patterns and the interfacial chemistry. Besides structural aspects, electronic properties are central in determining the energy level alignment at the heterojunction and, thus, the performance of organic-based devices. Notably, charge reorganisation at the metal-organic interface will produce surface dipoles, whose effect is to add electrostatic repulsion to the dispersion-driven supramolecular self-assembly and to change the work function of the surface. Herein, the relation between charge migration (i.e., the creation of surface dipoles) and molecular self-assembly is addressed by studying the behaviour of on-purpose designed molecular units on selected metals. We will show that choosing the substrate on the basis of its work function can selectively allow or inhibit the transfer of charge from the organic material to the electrode. When charge transfer occurs, the growing supramolecular structures exhibit a phase modulation driven by the presence of competing interactions. Moreover, the introduction of reactive moieties in formerly inert tectons will be identified as a suitable strategy for promoting the formation of interfacial dipoles upon surface-mediated chemical reactions. Our work paves the way for a more rational approach to the design of metal-organic systems, as we speculate that charge transfer effects and surface chemistry can be predicted at the stage of molecular design, at variance with the current trial and error approach used in the field of organic electronics. This thesis is based on multiscale theoretical modelling of selected metalmolecule couples and it is the result of a fruitful collaboration with the groups of Prof Davide Bonifazi (Université de Namur) and Prof Giovanni Costantini (University of Warwick).

Thesis (Ph.D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Marcus Weck; Committee Member: Bunz, Uwe; Committee Member: Collard, David; Committee Member: Jones, Christopher; Committee Member: Payne, Christine

xvii, 147 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
Supramolecular chemistry is a relatively new and exciting field offering chemists simplistic approaches to generating complex assemblies through strategically designed ligands. Much like the many spectacular examples of supramolecular assemblies in nature, so too are chemists able to construct large, elegant assemblies with carefully designed ligands which bind preferentially to target metal ions of choice. An important concept of supramolecular chemistry, often subtle and overlooked, is secondary bonding interactions (SBIs) which in some cases, act as the glue to hold supramolecular assemblies together. This dissertation examines SBIs in a number of systems involving the pnictogen elements of arsenic and antimony as well as aromatic interactions in self-assembled monolayers. The first half of this dissertation is an introduction to the concepts of supramolecular chemistry and secondary bonding interactions and how they are used in the self-assembly process in the Darren Johnson laboratory. Chapter I describes how secondary bonding interactions between arsenic and aryl ring systems and antimony and aryl ring systems assist with the assembly process. Chapter II is a continuation of the discussion of SBIs but focuses on the interactions between arsenic and heteroatoms. The second half of this dissertation will describe work performed in collaboration with Pacific Northwest National Laboratory (PNNL) in Richland, WA. This work was performed under the guidance of Dr. R. Shane Addleman in conjunction with Professor Darren W. Johnson of the University of Oregon. This portion describes novel systems for use in heavy metal ion remediation from natural and unnatural water sources. Chapters III-V describe functionalized mesoporous silica for use in heavy metal uptake from contaminated water sources. Chapter V describes a new technology invented during this internship at PNNL which utilizes weak bonding interactions between aryl ring systems to produce regenerable green materials for toxic metal binding. This work is ongoing in the Darren Johnson lab. This dissertation includes my previously published and co-authored material.
Committee in charge: Michael Haley, Chairperson, Chemistry; Darren Johnson, Member, Chemistry; Shih-Yuan Liu, Member, Chemistry; James Hutchison, Member, Chemistry; Eric Johnson, Outside Member, Biology

Despite the prevalence of supramolecular architectures derived from metal-ligand or hydrogen-bonding interactions, few studies have focused on the simultaneous use of these two strategies to form discrete metal-ligand hydrogen-bonded (MLHB) assemblies. The design, synthesis, and characterization of 2-quinolone based hybrid subunits, 7-DPQ and 5-PYQ, that contain phosphine and pyridyl metal binding sites, respectively, is reported. Both subunits give two-fold symmetric hydrogen-bonded tectons that assemble with metal precursors to give hybrid MLHB structures. Treatment of [Cp*RhCl2]2 with the 7-DPQ subunit yields hybrid MLHB assemblies with closed topology. 1H diffusion ordered spectroscopy experiments established the stability of the structures in solution, and the measured hydrodynamic radii match those determined crystallographically, suggesting that the closed topology is maintained in solution and the solid state. In order to further explore possible MLHB architectures and test the selectivity boundaries of our quinolone-based subunits we report the selective assembly of 5-PYQ with mono- and bis-platinated anthracene precursors. Addition of 5-PYQ to [1-trans-Pt(PEt3)2NO3]-8-chloroanthracene yielded a hybrid MLHB structure with preorganization for a hybrid MLHB polymer. Despite the systems preorganization for the hybrid polymeric structure the assembly of 5-PYQ with 1,8-bis(trans-Pt(PEt3)2NO3)anthracene selects only for one discrete closed self-assembled macrocycle. The strong π-π stacking interactions of the 5-PYQ subunits erode the hydrogen-bonding fidelity to favor ambidentate coordination modes of 5-PYQ and give the non-hybrid macrocycle. In the course of investigating the intricacies of hybrid MLHB supramolecular structures we observed that, in addition to metal-ligand and hydrogen-bond interactions, the π-π stacking interactions of the 7-DPQ and 5-PYQ subunits played a critical role in determining the final assemblies. In fact, the prominent π-π interactions were typically found to be more favorable than the quinolone interligand hydrogen-bonding interactions. These results contribute to the overall knowledge of the design principles, synthesis, characterization, and fundamental assembly trends when exploiting both hydrogen-bonding and metal-ligand interactions to form stable supramolecular architectures. These studies have provided the foundation for expanding the accessible space of supramolecular chemistry to include rationally designed hybrid MLHB systems to give structures that more closely mimic the complex supramolecular systems observed in Nature. This dissertation includes both previously published/unpublished and co-authored material.
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The aim of this PhD thesis is the development of new metodologies for surface anchoring of molecular and supramolecular systems for applications in molecular electronics and photonics, and for preparation of devices for molecular recognition. The systems are made up, as usually, of hybrid systems, divided in two parts, a molecular one and a solid support. The molecular part performs the desired function, while the solid support (metal or semiconductor on which the molecules are bound) allows to conjunct its properties with molecular system properties and, moreover, to help the correct orientation of the molecules at the surface. Such systems were compositionally and structurally characterized by means of surface analysis techniques, as time of flight of secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The nodal point of this research work, so, is surface functionalization. Many kind of surface were used, in particular oxides like silicon oxide and quartz (as model systems), transparent semiconductor oxides like indium tin oxide (ITO), and metal surfaces like gold. Such surfaces were functionalized by means of a bottom up approach, in particular the formation of a self-assembled monolayer (SAM), based on the chemisorpion of molecules bearing suitable functional groups. For oxide surfaces, molecules for SAM formation were characterized by a phosphonate as surface active group, able to form monolayer exploiting zirconium-phosphate-phosphonate (ZP) chemistry. For gold surface, instead, the surface active group was a thiol. Functional molecules adopted for this purpose, bear a terpyridine group as tail. Such ligand was chosen because the chelant moiety 2,2 :6 ,2 -terpyridine (Tpy) is one of the most exploited because of the very high affinity for bivalent metal ions, and the ability to form stereospecific, achiral, and octhaedrical complexes. Mono- and bis-terpyridine based metal ion complexes were prepared in order to obtain, by means of a step-wise approach, multilayer systems that can be seen as assembled molecular wires. In particular conjucated polyphenilenic ligands properties were exploited. Moreover, great efforts were made in order to obtain systems for the construction of devices for molecular recognition. With this aim, attention was focused on gold surface funtionalization to anchor on it, on one hand oligonucleotides chains, on the other hand, supramolecular systems called pseudo-rotaxanes . Oligonucleotide sequences anchoring was carried out in order to have information about the possibility that probe and targed oligonucleotides chains could react depending on them complementarity, studing this process by hybridization directly in situ. Pseudo-rotaxanes assembly, was very interesting because it was possible, for the first time, to carry out complexation of molecular building blocks (host and guest) directly on surface, instead of in solution.

We have designed and synthesized a fluorescent, self-assembled molecular square containing a highly fluorescent well known flurophore boradiazaindacene (BODIPY) dye. Pt(II) complexes were used to hold together BODIPY derivatives and give the right angle to form the square structure. Usage of BODIPY fluorophore is very important on such structures because its variety of superior properties. BODIPY is a well studied fluorophore in our group and it is known that this self assembled square can be easily modified to any area of use it is needed.

In this research project, reduction or complete elimination of organic solvents is explored in the synthesis of cyclic imides using a technique that brings reagents into favorable position to react. Cocrystal Controlled Solid-State Synthesis (C3Sy3), takes advantage of supramolecular interactions such as hydrogen bonding and π-π stacking to form a cocrystal which can sequential be heated to complete the condensation reaction and produce a desirable product. Twenty-five successful condensation reactions result in high and clean yield. C3Sy3 of cyclic imides with auxiliary hydrogen bonding moieties like carboxylic acid, carboxylate or pyridyl groups are amenable to form additional solid-state materials. These moieties are useful in forming coordinate covalent bonds with metal cations. Using these C3Sy3 synthesized molecules as ligands, various Metal-Organic Materials (MOMs) are self-assembled. These MOMs offer unique qualities owing to the properties of the cyclic imides. With the addition of accessible carbonyl groups, they may participate as hydrogen bond acceptors or hydrophilic groups. Various degrees of rotation of N-phenyl substituents around the imide plane allow for structural flexibility as a route to supramolecular isomers in MOMs. The ease in imide synthesis may allow the fast scale-up of these ligands for industrial application. Similar ligands are generally synthesized by cross-coupling or substitution reactions that require expensive catalyst and various organic solvents. Metal-organic materials are a class of compounds amenable to crystal engineering owing to the directional coordinate covalent bonds between metal or metal clusters and organic ligands. They are characterized by X-ray diffraction, spectroscopy, volumetric and gravimetric analysis. The C3Sy3 imides were used to construct various MOMs, from discrete nanostructures to extended 3-periodic frameworks that possess viable internal space for applications pertaining to porous materials. Structural characterization by single crystal X-ray diffraction and structure-function relations are addressed. Gas sorption experiments show that many of these materials are structurally robust and retain crystallinity after evacuation. Ion exchange and guest uptake experiments using the synthesized materials demonstrate their potential as agents for sequestration. The bottom-up synthesis of metal-organics materials is leading the field of crystal engineering with built-in properties, showing promise by combining attributes from both inorganic and organic components.

Understanding the supramolecular interactions governing the self-assembly of molecular building blocks upon surfaces is fundamental to the design of new devices such as sensors or catalysts. Successful heterogeneous enantioselective catalysts have relied upon the adsorption of ‘chiral modifiers’, usually chiral amino acids, onto reactive metal surfaces. One of the most researched examples is the hydrogenation of β-ketoesters using nickel-based catalysts. The stability of the chiral modifiers upon catalyst surfaces is a major obstacle to the industrial scale-up of this reaction. In this study, the replacement of conventional modifiers with porous, chiral and functionalised self-assembled networks is investigated. Perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and melamine (1,3,5-triazine,-2,4,6-triamine) have been shown to form hydrogen bonded networks on Ag-Si(111)√3x√3R30° in ultra-high vacuum (UHV) and Au(111) substrates in UHV and ambient conditions, these networks are capable of hosting guest molecules. These networks are investigated further in this study. In UHV, the behaviour of the components and network formation on Ni(111) is probed using scanning tunnelling microscopy (STM) and temperature-programmed desorption (TPD). The stability of the PTCDI-melamine network on Au(111) was analysed using TPD. Metal coordination interactions between each of the network components and nickel upon the Au(111) surface were examined by STM before testing the ability of the network to act as a template for metal growth. Finally, a number of polymerisation reactions are investigated with a view to replacing chiral modifiers with porous, chiral, functionalised covalent networks. Periodic covalent networks should possess the greater chemical and thermal stability required for more widespread use. In UHV and ambient conditions, STM is used to monitor the progress of surface-confined reactions on Au(111) and characterise the resultant covalent structures.

Metallosupramolecular chemistry involves the construction of nanoscale molecular assemblies by reacting metal atoms with bridging organic ligands. The metal atoms act as a type of molecular ‘glue’ binding together the organic ligands in specific orientations. Thus, appropriate combinations of metal ions and ligands lead to the controlled self-assembly of interesting one-, two- and three-dimensional molecular aggregates. This thesis details the preparation of a range of novel flexible bridging heterocyclic ligands using conventional organic synthesis, and then explores their reactions with a variety of transition metal precursors. By varying the nature of the organic ligand and the transition metal precursor, new and exciting supramolecular topologies and architectures can be formed. A total of forty-eight ligands were synthesised in this work, forty-seven of which are new compounds. The majority of the ligands synthesised were based around commercially available bisphenol cores. All forty-eight of the ligands had nitrogen heterocyclic groups as coordinating units. The ligands discussed in this thesis can be divided into three main sections. The first involves the synthesis and coordination chemistry of two-armed ligands based around the Bisphenol A, Bisphenol Z and Bisphenol AP cores. The second section describes the synthesis and coordination chemistry of the larger Bisphenol P and Bisphenol M based two-armed bridging ligands. The third section describes the synthesis and coordination chemistry of various multi-substituted ligands, including tripodal ligands based around a trisphenol core, four-armed ligands and six-armed ligands. The two-armed bisphenol based ligands proved very successful as synthons in metallosupramolecular chemistry and produced many products with a variety of different metal atoms. The complexes characterised included discrete dimeric products, coordination polymers and a number of helicates, including a dinuclear quadruply-stranded helicate. Multi-armed ligands are topical, because they have multiple coordination sites that are capable of binding and bridging multiple metal atoms. Such coordination can lead to the construction of cage-like species and complicated networks. A series of three-armed ligands based around a trisphenol core were synthesised with the intention to use these to form such species on coordination with appropriate metal salts. Indeed, one of the products of self-assembly was an interesting M₃L₂ cage. Various other multi-armed ligands were also investigated. The ligands and complexes in this thesis were characterised by a variety of structural techniques, such as ¹H NMR, ¹³C NMR, mass spectrometry, elemental analysis and X-ray crystallography when crystals were obtained. The crystal structures of twenty-seven ligands and forty-three complexes are described.

Les foldamères d’oligoquinoline carboxamide forment des structures hélicoïdales en solution et dans le solide. Ces structures sont stabilisées par liaisons hydrogène, empilement aromatique et interactions électrostatiques. Dans une première partie de ce manuscrit, les fonctions amide connectant les unités quinolines ont été substituées par des fonctions vinylène, isostères de celles-ci. Ces composés quinolynènes-vinylènes, seuls, forment principalement des structures étendues en solution. Toutefois lorsque ces nouvelles unités sont en faible proportion au sein de l’oligomères contenant principalement de connections amides, des architectures hélicoïdales ont pu être obtenues. Dans une seconde partie, des ions Cu (II) ont été introduits au centre des hélices d’oligoquinoline carboxamide. Ces ions sont liés aux atomes d’azote des quinolines, et à ceux des fonctions amides après leur déprotonation. Une organisation linéaire de ces ions a été observée dans le solide. L’auto-assemblage d’hélices, en faisceaux, par empilement aromatique d’unités acridines portées par les chaines latérales a été entrepris dans une troisième partie de ce manuscrit. De faibles associations ont pu être mises en évidence en solution. Dans le solide ces interactions, bien que faibles, ont permis le contrôle de l’organisation des hélices dans le cristal. Dans une dernière partie de ce manuscrit, la coordination de métaux a été utilisée afin de permettre l’assemblage d’hélices d’oligoquinoline carboxamide. Des ligands acridine et pyridine ont été fixés sur la périphérie de l’hélice de façon à permettre la coordination par des métaux de transition tel que le palladium (II). Ces assemblages d’hélices induits par le palladium, ont été caractérisés par RMN en solution et par diffraction des rayons X dans le solide
Oligo-quinolinecarboxamide foldamers form stable helical structures in solution and in the solid state. These helices are stabilized by hydrogen bonds, π-π stacking and electrostatic interactions. In a first part of this manuscript, vinyl functions have been introduced as isosteres of amides. The resulting quinolylene-vinylene oligomers form mainly extended structures in solution. Helical folded conformations can nevertheless be stabilized by attaching two segments of oligoamides at both ends of an oligoquinolylene-vinylene. In a second part, copper (II) ions have been loaded into the single helices of quinolinecarboxamide foldamers. The copper (II) ions coordinate the nitrogen atoms of the quinoline units and also deprotonated amide nitrogen atoms. A one dimensional alignment of the copper (II) ions was observed in the solid state. In a third part, acridine functionalized foldamers were prepared in order to test their self-assembly into bundles through interactions between aromatic functions at the exterior of helices. Associations of the acridine functionalized oligoamides are weak in organic solution. In contrast, in the solid state, interactions between helices are mainly governed by acridine units. In a fourth part, metal coordination has been used to promote helix-helix assembly of quinoline oligoamides foldamers. Acridine and pyridine rings have been attached on the side chains of these oligomers to allow coordination with metals, palladium (II) in this case. The helix-helix assembly of quinoline oligoamides by palladium coordination has been confirmed by NMR and x-ray diffraction

碩士
國立臺灣大學
化學研究所
104
In supramolecular chemistry, constructing a well-defined three-dimensional cage has attracted more and more attention. Herein, we explore the possibility of exterior functionalization for the self-assembled cages. A series of tritopic terpyridine-based ligands with various exterior functionalities was used to construct metallo-supramolecular cages. To investigate the self-assembly behavior of the predesigned tritopic ligand system, ligands with simple hydroxyl and alkyl substituents were synthesized and complexed with Cd(II) and Zn(II) ions to give supramolecular cubic cages that were well characterized by 1H-NMR, ESI-MS, and electron microscopes. Besides, changing connected positions between the terpyridine moieties and the central core to generate a bent version of the tritopic ligand was successfully used for constructing a smaller supramolecular structure, demonstrating a simple method to build variant metallo-supramolecular structures. To date, the polymer solar cells (PSCs) with P3HT and PCBM as an active layer suffer from a severe lifetime problem, which is partly caused by the macrophase separation from the aggregation of PCBM with time. Based on our new findings, the tritopic terpyridine-based ligand decorated with pendant fullerene groups was successfully synthesized and self-assembled into a functional metallocage via coordination. In addition, the fullerene-functionalized cage was used as a supramolecular crosslinker to alleviate the macrophase aggregation caused by the migration of the C60 acceptor, which significantly improved the stability of organic photovoltaics.

碩士
國立臺灣大學
化學研究所
104
Molecular self-assembly using metal-ligand coordinative interaction has drawn much attention in recent years. Utilizing non-covalent interactions provides a facile way to construct large and complicated 2D/3D structures in contrast with the conventional organic chemistry. Moreover, incorporation of orthogonal host-guest and metal-coordination interactions into supramolecular structures will enhance their structural complexity and impart additional functions. In this research, we designed and synthesized a series of metallo-supramolecular cages possessing multiple (tpy = terpyridine) connections and ion–dipole interaction sites (i.e., crown ethers), which functioned orthogonally to each other. It was found that a decrease in the size of crown ethers leaded to a decrease in the flexibility, and thus various thermodynamic products were formed. To further study these metallo-supramolecular cages, we investigated the interactions between the crown ethers and the predesigned secondary ammonium ions. The 1:1 inclusion complex formed by the cage assembly and the multivalent ammonium salt was successfully achieved in MeCN and further characterized by NMR spectroscopy and ESI mass spectrometry. The formation of a metallo-supramolecular rotaxane based on the inclusion compound was explored as well.

Self–assembly has long been attracting chemists’ attention because it can yield fascinating supramolecular architectures in a single step. More precisely, metal–ligand coordination–driven self–assembly has stood out as an efficient methodology in this paradigm due to simple design principle and high predictability of the final molecular architectures. Moreover, one can envisage hierarchical nanoscopic molecular architectures with a vast range of size, shape and functionality via this methodology. Two–component self–assembly (involving one type of donor and one type of acceptor) is relatively easy to monitor and a widely used protocol. Whereas, multicomponent self–assembly (involving more than one types of donors/or acceptors) is too complex due to the possibility of formation of several products. The prime advantage of multicomponent self–assembly lies in one–pot construction of topologically complicated multifunctional architectures. Template– induced multicomponent self–assembly of discrete architectures is recently investigated to some extent. But, template–free multicomponent self–assembly of discrete architectures is rare in the literature. Physico–chemical property of a self–assembled product is coded in the functional groups present in its precursor building units. Functional supramolecular architectures have important applications in many potential fields such as chemosensing, drug delivery, supramolecular catalysis, etc. Porphyrin, pyrazole, imidazole, etc. functionalized organic molecules are hydrophilic as well as hydrophobic in nature. Introduction of such functionality in building units can lead to amphiphilic supramolecular complexes. Therefore, such complexes can be employed as hosts for versatile guests, or as molecular reactors for various chemical reactions. In general, counter ions block the cavity of ionic molecular architectures. Thus, when ionic molecular architectures are employed as hosts, they cannot fully provide their cavity towards guest molecules. In contrast, neutral molecular complexes are expected to be better hosts. It is well known that alkenyl/alkynyl heavy metal complexes exhibit efficient chemoluminescence due to facile metal to ligand charge transfer (MLCT). Hence, such complexes can be employed as efficient chemosensors towards the detection of electron deficient molecules such as nitroaromatics which are the chemical signatures of many powerful explosives. In these regards, a considerable effort is being paid recently to design and construct various functional supramolecular architectures. Symmetry and rigidity of building units increase predictability of the final product in self– assembly. In this regard, symmetric; rigid Pd(II)/Pt(II)–based acceptors and polypyridyl donors are explored extensively in metal–ligand coordination–driven self–assembly. In contrast to rigidity, flexibility endows building units to adopt thermodynamically most stable conformer/architecture. Hence, same set of building units can render different conformers/architectures in presence of different templates for the sake of suitable host–guest interactions. Contrary to high symmetry, asymmetry in building units leads to molecular architectures with polar environments. But, due to the possibility of formation of several isomeric products from the self–assembly involving such building units, it is difficult to monitor the reaction and purify the products. Hence, designing appropriate synthetic routes which can lead to formation of single isomeric products possessing flexible/asymmetric building units is a challenge to synthetic chemists. Investigations incorporated in the present thesis are focused to design and construct various 2D/3D discrete supramolecular architectures employing self–assembly of mainly Pd(II)/Pt(II) acceptors with N/O donors. Elemental analyses, IR/NMR/UV–Vis/fluorescence/mass spectroscopy and single crystal X–ray diffraction analysis are among prime techniques employed for characterization of the reported architectures. For a few cases, powder X–ray diffraction (PXRD) analysis and density functional theory (DFT) calculations are also carried out. CHAPTER 1 of the thesis provides a brief general introduction to self–assembly and supramolecular chemistry. It emphasizes on the metal–ligand coordination–driven self–assembly approach towards the construction of a library of 2D/3D supramolecular architectures. CHAPTER 2 describes formation of a series of template–induced and template–free discrete 3D Pd(II) molecular prisms via multicomponent self–assembly. Because of the possibility of formation of several products, multicomponent self–assembly is difficult to monitor. For example, several molecular architectures are expected from a three–component self–assembly involving a 90° acceptor [ca. cis–blocked Pd(II)], a 120° tritopic donor [ca. benzene–1,3,5– tricaboxylate (tma)] and a 180° donor [ca. 4,4'–bipyridine (4,4'–bpy) or pyrazine (pz)]. Interestingly, treatment of cis–(tmen)Pd(NO3)2 [tmen = N,N,N′,N′–tetramethylethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in mainly a nanoscopic molecular trigonal prism [{(tmen)Pd}6(bpy)3(tma)2](NO3)6 (1) with three 4,4'–bpy pillars, two tma caps and six cis–(tmen)Pd connectors (Scheme 1). Scheme 1: Schematic representation of the formation of multicomponent self–assembled molecular trigonal prisms 1, 2 and 3. Surprisingly, the same reaction in presence of benzene–1,3,5–tricaboxylic acid (H3tma) as guest yielded exclusively the guest–encapsulated analogous molecular prism [{(tmen)Pd}6(bpy)3(tma)2(H3tma)2](NO3)6 (2; Scheme 1). It is also presented how variation of steric crowding at connectors (acceptors) influenced final outcomes. Self–assembly of cis– (en)Pd(NO3)2 [en = ethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in a triply interlocked nanoscopic 3D coordination cage [{(en)Pd}6(bpy)3(tma)2]2(NO3)12 (3; Scheme 1). It is also shown that above trend is followed even upon changing the pillar length from 4,4'–bpy to pz. Aromatic –stacking interactions amog tma caps as well as among 4,4'–bpy pillars provided considerable stability to interlocked archirecture 3. Steric crowding due to the methyl groups in cis–(tmen)Pd connectors hindered intercalation and hence led to non–interlocked architecture 1. As expected, similar self–assembly using moderately crowded acceptor cis–(pn)Pd(NO3)2 [pn = 1,2–diaminopropane] with same donors 4,4'–bpy and K3tma resulted in a mixture of analogous triply interlocked and non– interlocked architectures in solution though it was found to be only triply interlocked architecture in solid state. Interestingly, irrespective of the steric crowding of the blocking amines, self– assembly in presence of H3tma as guest preferred exclusive formation of guest–encapsulated prisms of type 2 (Scheme 1). This is due to considerable stabilazation via aromatic –stacking interactions amog tma caps and H3tma guests. Formation of guest–free discrete molecular prisms (such as 1) and triply interlocked coordination cages (such as 3) were confirmed by spectroscopic and single crystal X–ray diffraction analyses. Whereas, formation of guest– encapsulated discrete molecular prisms (such as 2) was established by DOSY, ROESY 2D NMR spectroscpic study in conjunction with energy optimized geometry analysis. CHAPTER 3 reports design and syntheses of a series of porphyrin functionalized nanoscopic 3D molecular open prisms. Self–assembly of a C4 –symmetric tetratopic donor with a 90° ditopic acceptor can, in principle, lead to several architectures such as trigonal; tetragonal; pentagonal; hexagonal; etc. open prisms, closed cube or 1D oligomers. Both of 1,5,10,15–tetrakis(4– 12 pyridyl)porphyrin (L) and 1,5,10,15–tetrakis(3–pyridyl)porphyrin (L) possess pseudo C4 – 1 symmetry. Surprisingly, treatment of Lwith the 90° ditopic acceptor cis–(dppf)Pt(OTf)2 [dppf = diphenylphosphinoferrocene, OTf = trifluoromethanesulphonate] yielded exclusively an 1 unprecedented [6 + 12] self–assembled hexagonal open prism [(dppf)12Pt12L6](OTf)24 (4; Scheme 2). Scheme 2: Schematic representation of formation of [6 + 12] self–assembled molecular hexagonal open prism 4 and its Zn(II) embedded complex 4a. 2 In contrast, [3 + 6] self–assembled trigonal open prisms are adopted upon self–assembly of Lwith Pd(II)–based 90° ditopic acceptors. These complexes show facile incorporation of Zn(II) ions into porphyrin N4 –pockets. Moreover, they incorporate high microporosity in solid state and they are amphiphilic in nature due to porphyrin functionality. One of the trigonal open prisms revealed its considerably high adsorbate–adsorbent affinity towards non–polar gas such as N2 and protic solvent vapors such as water, methanol and ethanol. Formation of hexagonal and trigonal open prisms is fully authenticated by spectroscopic and single crystal X–ray diffraction analyses. CHAPTER 4 describes design and synthesis of a pyrazole functionalized flexible donor (L) and its self–assembly towards the construction of three nanoscopic 3D supramolecular discrete cages 5–7 (Scheme 3). Scheme 3: Schematic representation of formation of [4 + 6] self–assembled molecular double–square 5 and [2 + 3] self–assembled molecular trigonal bipyramids 6–7. 3 Due to flexibility, Lcan adopt different conformations and hence several isomeric architectures 3 are expected upon self–assembly. For example, self–assembly of Lwith a rigid ditopic 90° acceptor can lead to trigonal bipyramid (TBP), double–square, adamantanoid or truncated 3 tetrahedron. Treatment of Lwith cis–(tmen)Pd(NO3)2 yielded a [4 + 6] self–assembled double–3 square [(tmen)6Pd6L4](NO3)12 (5; Scheme 3). Much to our surprise, replacement of cis– (tmen)Pd(NO3)2 with CuCl2 or AgOTf yielded [2 + 3] self–assembled molecular TBP 33 [Cu3Cl6L2] (6) or [Ag3L2](OTf)3 (7), respectively (Scheme 3). CHAPTER 5 presents study of self–assembly involving flexible asymmetric donors and rigid 4 symmetric 90° acceptors. Three ambidentate donors 5–pyrimidinecarboxylate (L), nicotinate–56 N–oxide (L) and isonicotinate–N–oxide (L) were employed in self–assembly with symmetric rigid 90° acceptors cis–(dppf)M(OTf)2 [M = Pd(II)/Pt(II)]. Due to flexibility and different 464 connectivity of these donors L–L, several linkage isomers are expected. Treatment of Lwith cis–(dppf)M(OTf)2 in 1 : 1 molar ratio resulted in exclusive formation of single linkage isomeric 4 [3 + 3] self–assembled symmetric molecular triangles [(dppf)3M3L3](OTf)3 (8: M = Pd and 9: M = Pt), where the donors connected to metal centers in head–to–tailfashion (Scheme 4). Similar 56 reactions of Land Lwith cis–(dppf)M(OTf)2 resulted in self–sorting of [2 + 2] self–assembled molecular rhomboids 10–13 (Scheme 4). Exclusive self–selection of single linkage isomeric architectures 8, 9, 10 and 12 was fully established by spectroscopic as well as single crystal X– ray diffraction analyses. Though we could not obtain suitable X–ray diffraction quality single crystals of 11 and 13, exclusive formation of single isomeric [2 + 2] self–assembled rhomboids 131 was established by multinuclear NMR (H and P) in conjunction with ESI–MS spectroscopic studies. Scheme 4: Schematic representation of formation of complexes 8–13. Part A of the CHAPTER 6 describes how two neutral organometallic mononuclear chelates are formed upon treatment of disodium fumarate (,–unsaturated dicarboxylate) with cis– (dppf)Pd/Pt(OTf)2 at ambient conditions. Reaction of 90acceptors cis–(dppf)Pd/Pt(OTf)2 with fumarate is expected to result in [4 + 4] self–sorted molecular squares/or [2 + 2] self–sorted molecular rhomboids (Scheme 5). To our surprise, the above reactions led to an unusual reduction of C–C double bond followed by concomitant formation of mononuclear chelates [M(dppf)(C4H4O4)] (M = Pd for 14 and Pt for 15) via coordination with one of the carboxylate oxygen atoms and –carbon to metal centers (Scheme 5). Scheme 5: Schematic representation of formation of the complexes 14–15. Part B of the CHAPTER 6 describes design and synthesis of a novel shape selective “clip” 1 shaped bimetallic Pd(II) acceptor Mand its self–assembly with disodium fumarate to construct a neutral tetrametallic Pd(II) supramolecular rectangle 16 (Scheme 6, left). Similarly, a shape selective 180° bimetallic Pd(II) acceptor was also synthesized and employed in self–assembly with several “clip” shaped organic donors to achieve several cationic tetrametallic Pd(II) supramolecular rectangles. Scheme 6: Schematic representation of the formation of neutral Pd4 (left) and Pd2 (right) molecular rectangles. Moreover, synthesis of a neutral bimetallic Pd(II) molecular rectangle 17 via one–pot reaction of trans–(PEt3)2PdCl2 with 1,8–diethynylanthracene (Scheme 6, right) is also presented herein. These –electron rich rectangles exhibit prominent chemoluminescence. Chemosensitivity of these complexes towards the detection of electron deficient nitroaromatics via fluorescence study is also discussed in details in this section. (Pl refer the abstract file for figures).

Self–assembly has long been attracting chemists’ attention because it can yield fascinating supramolecular architectures in a single step. More precisely, metal–ligand coordination–driven self–assembly has stood out as an efficient methodology in this paradigm due to simple design principle and high predictability of the final molecular architectures. Moreover, one can envisage hierarchical nanoscopic molecular architectures with a vast range of size, shape and functionality via this methodology. Two–component self–assembly (involving one type of donor and one type of acceptor) is relatively easy to monitor and a widely used protocol. Whereas, multicomponent self–assembly (involving more than one types of donors/or acceptors) is too complex due to the possibility of formation of several products. The prime advantage of multicomponent self–assembly lies in one–pot construction of topologically complicated multifunctional architectures. Template– induced multicomponent self–assembly of discrete architectures is recently investigated to some extent. But, template–free multicomponent self–assembly of discrete architectures is rare in the literature. Physico–chemical property of a self–assembled product is coded in the functional groups present in its precursor building units. Functional supramolecular architectures have important applications in many potential fields such as chemosensing, drug delivery, supramolecular catalysis, etc. Porphyrin, pyrazole, imidazole, etc. functionalized organic molecules are hydrophilic as well as hydrophobic in nature. Introduction of such functionality in building units can lead to amphiphilic supramolecular complexes. Therefore, such complexes can be employed as hosts for versatile guests, or as molecular reactors for various chemical reactions. In general, counter ions block the cavity of ionic molecular architectures. Thus, when ionic molecular architectures are employed as hosts, they cannot fully provide their cavity towards guest molecules. In contrast, neutral molecular complexes are expected to be better hosts. It is well known that alkenyl/alkynyl heavy metal complexes exhibit efficient chemoluminescence due to facile metal to ligand charge transfer (MLCT). Hence, such complexes can be employed as efficient chemosensors towards the detection of electron deficient molecules such as nitroaromatics which are the chemical signatures of many powerful explosives. In these regards, a considerable effort is being paid recently to design and construct various functional supramolecular architectures. Symmetry and rigidity of building units increase predictability of the final product in self– assembly. In this regard, symmetric; rigid Pd(II)/Pt(II)–based acceptors and polypyridyl donors are explored extensively in metal–ligand coordination–driven self–assembly. In contrast to rigidity, flexibility endows building units to adopt thermodynamically most stable conformer/architecture. Hence, same set of building units can render different conformers/architectures in presence of different templates for the sake of suitable host–guest interactions. Contrary to high symmetry, asymmetry in building units leads to molecular architectures with polar environments. But, due to the possibility of formation of several isomeric products from the self–assembly involving such building units, it is difficult to monitor the reaction and purify the products. Hence, designing appropriate synthetic routes which can lead to formation of single isomeric products possessing flexible/asymmetric building units is a challenge to synthetic chemists. Investigations incorporated in the present thesis are focused to design and construct various 2D/3D discrete supramolecular architectures employing self–assembly of mainly Pd(II)/Pt(II) acceptors with N/O donors. Elemental analyses, IR/NMR/UV–Vis/fluorescence/mass spectroscopy and single crystal X–ray diffraction analysis are among prime techniques employed for characterization of the reported architectures. For a few cases, powder X–ray diffraction (PXRD) analysis and density functional theory (DFT) calculations are also carried out. CHAPTER 1 of the thesis provides a brief general introduction to self–assembly and supramolecular chemistry. It emphasizes on the metal–ligand coordination–driven self–assembly approach towards the construction of a library of 2D/3D supramolecular architectures. CHAPTER 2 describes formation of a series of template–induced and template–free discrete 3D Pd(II) molecular prisms via multicomponent self–assembly. Because of the possibility of formation of several products, multicomponent self–assembly is difficult to monitor. For example, several molecular architectures are expected from a three–component self–assembly involving a 90° acceptor [ca. cis–blocked Pd(II)], a 120° tritopic donor [ca. benzene–1,3,5– tricaboxylate (tma)] and a 180° donor [ca. 4,4'–bipyridine (4,4'–bpy) or pyrazine (pz)]. Interestingly, treatment of cis–(tmen)Pd(NO3)2 [tmen = N,N,N′,N′–tetramethylethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in mainly a nanoscopic molecular trigonal prism [{(tmen)Pd}6(bpy)3(tma)2](NO3)6 (1) with three 4,4'–bpy pillars, two tma caps and six cis–(tmen)Pd connectors (Scheme 1). Scheme 1: Schematic representation of the formation of multicomponent self–assembled molecular trigonal prisms 1, 2 and 3. Surprisingly, the same reaction in presence of benzene–1,3,5–tricaboxylic acid (H3tma) as guest yielded exclusively the guest–encapsulated analogous molecular prism [{(tmen)Pd}6(bpy)3(tma)2(H3tma)2](NO3)6 (2; Scheme 1). It is also presented how variation of steric crowding at connectors (acceptors) influenced final outcomes. Self–assembly of cis– (en)Pd(NO3)2 [en = ethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in a triply interlocked nanoscopic 3D coordination cage [{(en)Pd}6(bpy)3(tma)2]2(NO3)12 (3; Scheme 1). It is also shown that above trend is followed even upon changing the pillar length from 4,4'–bpy to pz. Aromatic –stacking interactions amog tma caps as well as among 4,4'–bpy pillars provided considerable stability to interlocked archirecture 3. Steric crowding due to the methyl groups in cis–(tmen)Pd connectors hindered intercalation and hence led to non–interlocked architecture 1. As expected, similar self–assembly using moderately crowded acceptor cis–(pn)Pd(NO3)2 [pn = 1,2–diaminopropane] with same donors 4,4'–bpy and K3tma resulted in a mixture of analogous triply interlocked and non– interlocked architectures in solution though it was found to be only triply interlocked architecture in solid state. Interestingly, irrespective of the steric crowding of the blocking amines, self– assembly in presence of H3tma as guest preferred exclusive formation of guest–encapsulated prisms of type 2 (Scheme 1). This is due to considerable stabilazation via aromatic –stacking interactions amog tma caps and H3tma guests. Formation of guest–free discrete molecular prisms (such as 1) and triply interlocked coordination cages (such as 3) were confirmed by spectroscopic and single crystal X–ray diffraction analyses. Whereas, formation of guest– encapsulated discrete molecular prisms (such as 2) was established by DOSY, ROESY 2D NMR spectroscpic study in conjunction with energy optimized geometry analysis. CHAPTER 3 reports design and syntheses of a series of porphyrin functionalized nanoscopic 3D molecular open prisms. Self–assembly of a C4 –symmetric tetratopic donor with a 90° ditopic acceptor can, in principle, lead to several architectures such as trigonal; tetragonal; pentagonal; hexagonal; etc. open prisms, closed cube or 1D oligomers. Both of 1,5,10,15–tetrakis(4– 12 pyridyl)porphyrin (L) and 1,5,10,15–tetrakis(3–pyridyl)porphyrin (L) possess pseudo C4 – 1 symmetry. Surprisingly, treatment of Lwith the 90° ditopic acceptor cis–(dppf)Pt(OTf)2 [dppf = diphenylphosphinoferrocene, OTf = trifluoromethanesulphonate] yielded exclusively an 1 unprecedented [6 + 12] self–assembled hexagonal open prism [(dppf)12Pt12L6](OTf)24 (4; Scheme 2). Scheme 2: Schematic representation of formation of [6 + 12] self–assembled molecular hexagonal open prism 4 and its Zn(II) embedded complex 4a. 2 In contrast, [3 + 6] self–assembled trigonal open prisms are adopted upon self–assembly of Lwith Pd(II)–based 90° ditopic acceptors. These complexes show facile incorporation of Zn(II) ions into porphyrin N4 –pockets. Moreover, they incorporate high microporosity in solid state and they are amphiphilic in nature due to porphyrin functionality. One of the trigonal open prisms revealed its considerably high adsorbate–adsorbent affinity towards non–polar gas such as N2 and protic solvent vapors such as water, methanol and ethanol. Formation of hexagonal and trigonal open prisms is fully authenticated by spectroscopic and single crystal X–ray diffraction analyses. CHAPTER 4 describes design and synthesis of a pyrazole functionalized flexible donor (L) and its self–assembly towards the construction of three nanoscopic 3D supramolecular discrete cages 5–7 (Scheme 3). Scheme 3: Schematic representation of formation of [4 + 6] self–assembled molecular double–square 5 and [2 + 3] self–assembled molecular trigonal bipyramids 6–7. 3 Due to flexibility, Lcan adopt different conformations and hence several isomeric architectures 3 are expected upon self–assembly. For example, self–assembly of Lwith a rigid ditopic 90° acceptor can lead to trigonal bipyramid (TBP), double–square, adamantanoid or truncated 3 tetrahedron. Treatment of Lwith cis–(tmen)Pd(NO3)2 yielded a [4 + 6] self–assembled double–3 square [(tmen)6Pd6L4](NO3)12 (5; Scheme 3). Much to our surprise, replacement of cis– (tmen)Pd(NO3)2 with CuCl2 or AgOTf yielded [2 + 3] self–assembled molecular TBP 33 [Cu3Cl6L2] (6) or [Ag3L2](OTf)3 (7), respectively (Scheme 3). CHAPTER 5 presents study of self–assembly involving flexible asymmetric donors and rigid 4 symmetric 90° acceptors. Three ambidentate donors 5–pyrimidinecarboxylate (L), nicotinate–56 N–oxide (L) and isonicotinate–N–oxide (L) were employed in self–assembly with symmetric rigid 90° acceptors cis–(dppf)M(OTf)2 [M = Pd(II)/Pt(II)]. Due to flexibility and different 464 connectivity of these donors L–L, several linkage isomers are expected. Treatment of Lwith cis–(dppf)M(OTf)2 in 1 : 1 molar ratio resulted in exclusive formation of single linkage isomeric 4 [3 + 3] self–assembled symmetric molecular triangles [(dppf)3M3L3](OTf)3 (8: M = Pd and 9: M = Pt), where the donors connected to metal centers in head–to–tailfashion (Scheme 4). Similar 56 reactions of Land Lwith cis–(dppf)M(OTf)2 resulted in self–sorting of [2 + 2] self–assembled molecular rhomboids 10–13 (Scheme 4). Exclusive self–selection of single linkage isomeric architectures 8, 9, 10 and 12 was fully established by spectroscopic as well as single crystal X– ray diffraction analyses. Though we could not obtain suitable X–ray diffraction quality single crystals of 11 and 13, exclusive formation of single isomeric [2 + 2] self–assembled rhomboids 131 was established by multinuclear NMR (H and P) in conjunction with ESI–MS spectroscopic studies. Scheme 4: Schematic representation of formation of complexes 8–13. Part A of the CHAPTER 6 describes how two neutral organometallic mononuclear chelates are formed upon treatment of disodium fumarate (,–unsaturated dicarboxylate) with cis– (dppf)Pd/Pt(OTf)2 at ambient conditions. Reaction of 90acceptors cis–(dppf)Pd/Pt(OTf)2 with fumarate is expected to result in [4 + 4] self–sorted molecular squares/or [2 + 2] self–sorted molecular rhomboids (Scheme 5). To our surprise, the above reactions led to an unusual reduction of C–C double bond followed by concomitant formation of mononuclear chelates [M(dppf)(C4H4O4)] (M = Pd for 14 and Pt for 15) via coordination with one of the carboxylate oxygen atoms and –carbon to metal centers (Scheme 5). Scheme 5: Schematic representation of formation of the complexes 14–15. Part B of the CHAPTER 6 describes design and synthesis of a novel shape selective “clip” 1 shaped bimetallic Pd(II) acceptor Mand its self–assembly with disodium fumarate to construct a neutral tetrametallic Pd(II) supramolecular rectangle 16 (Scheme 6, left). Similarly, a shape selective 180° bimetallic Pd(II) acceptor was also synthesized and employed in self–assembly with several “clip” shaped organic donors to achieve several cationic tetrametallic Pd(II) supramolecular rectangles. Scheme 6: Schematic representation of the formation of neutral Pd4 (left) and Pd2 (right) molecular rectangles. Moreover, synthesis of a neutral bimetallic Pd(II) molecular rectangle 17 via one–pot reaction of trans–(PEt3)2PdCl2 with 1,8–diethynylanthracene (Scheme 6, right) is also presented herein. These –electron rich rectangles exhibit prominent chemoluminescence. Chemosensitivity of these complexes towards the detection of electron deficient nitroaromatics via fluorescence study is also discussed in details in this section. (Pl refer the abstract file for figures).

2005/2006
The term Nanotechnology is used to describe a variety of techniques to fabricate materials and devices at the nanoscale. Nano-techniques include those used for fabrication of nanowires, those used in semiconductor fabrication such as deep ultraviolet and electron beam lithography, focused ion beam machining, nanoimprint lithography, atomic layer deposition, molecular vapor deposition, and the ones including molecular self-assembly techniques. All these methods are still being developed and not all of them were devised with the sole purpose of creating devices for nanotechnology. A number of physical phenomena become noticeably pronounced as the system size decreases. These include statistical effects, as well as quantum effects, where the electronic properties of solids are altered if the particle size is greatly reduced. There are also effects which never come into play by going from macro to micro dimensions, while they become dominant when the nanometer scale is reached. Furthermore nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of all these effects. Traditional disciplines can be re-interpreted as specific applications of nanotechnology. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices with atomicscale control. Modern synthetic chemistry has reached the point where it is possible to prepare small molecules of almost any (stable) structure. Methods exist today to produce a wide variety of useful chemicals. A branch of nanotechnology, relevant to the present thesis work, is looking for methods to assemble single molecules into supramolecular assemblies arranged in a well defined manner. These approaches use molecular self-assembly and supramolecular chemistry to automatically arrange the single molecules into interesting and potentially useful structures. The scanning tunneling microscope (STM) is a non-optical microscope that scans an electrical probe (the tip) over a conductive surface to be imaged. It allows scientists to visualize regions of high electron density at the atomic scale, and hence infer the position of individual atoms and molecules on a material surface. STM is specially suited for the study of the self-assembly of molecules deposited on conductive substrates because it provides direct insight into the assembled structures. However, the STM images are often insufficient for a complete description of the phenomena, and computer simulations offer a complementary approach that can effectively integrate the experiments . The theoretical investigation of the molecular self-assembly aims at the understanding of the mechanisms that are involved in the assemblies formatiom. In particular the atomistic simulation can provide information on the geometry of the stable structures, the nature and the intensity of the interactions as well as on the dynamical processes. In this thesis, a combination of first principles and classical molecular dynamics simulations is used to shed light on the self-assembly of some organic molecules deposited on noble metal substrates. Three cases are discussed, the self-assembly of TMA and BTA molecules on Ag(111) and the self-assembly of an oxalic amide derivative on Au(111). When TMA and BTA molecules are deposited onto a silver surface at a temperature lower than room temperature they form a regular 2D honeycomb network featuring double hydrogen bonds between carboxylic groups. Even if this bonding makes the network very stable, when these systems are annealed to higher temperatures they undergo some irreversible phase transition into closer-packed supramolecular arrangements. Namely, the TMA has a transition from honeycomb to a high coverage “quartet” structure and the BTA has two transtions: from honeycomb to unidimensional stripes and from here to a closed-packed monolayer. A combination of experimental and theoretical techniques allowed us to identify the stepwise deprotonation of the carboxylic acid groups as the driving force driving the phase transitions. Our theoretical investigation targeted the electrostatic interaction involved in the formation of the various phases revealing that a depolarisation of the molecular ions occurs as a consequence of the deprotonation process. Therefore, the repulsive contribution arising from the interaction of negatively charged molecules can be overcome by the attractive hydrogen bond interaction involving the deprotonated carboxylic groups, thus resulting in a stable closed-packed arrangement. Rather remarkably, this exemplifies how higher-coverage phases can be obtained at each step of a series of phase transitions in a supramolecular assembled system, despite the increasing temperature and the increasing electrostatic repulsive energy cost accompanying deprotonation. The oxalic amide derivative molecules arranges themselves in linear chains both in the molecular solid and when adsorbed on a gold surface. However the intermolecular distance and the geometry of the chains are different in these two cases. Various relaxed bonding structure between molecules in the chains have been calculated from first principles in the present work. The rationale of the different linkage behaviour between molecules in the two situations described have also been investigated: the interaction with the substrate appears to be the main cause for the particular rearrangement observed in the chains. Both experimental observations and theoretical predictions indicate that a conformational change involving the rotation of the phenyl rings of the monomers is necessary for chain formation.

Over the past few decades, supramolecular self-assembly has become an alternative synthetic tool for constructing targeted discrete molecular architectures. Among various interactions, metal-ligand coordination has attracted great attention owing to high bond enthalpy (15−50 Kcal/mol) and predictable directionality. The basic principle of metal-ligand directed self-assembly relies on the proper designing of information encoded rigid complementary building units (a transition metal based acceptor and a multidentate organic donor) that self-recognize themselves in a chemically reasonable way (depends on their bite angle and symmetry) during self-assembly process. As far as acceptor units are concerned, Pd(II) and Pt(II) metal-based cis-blocked 90° acceptors have so far been used greatly for the construction of a library of 2D/3D discrete supramolecular architectures due to their rigid square planar geometry and kinetic lability. However, in some cases the efforts to design finite supramolecular architectures using a cis-blocked 90° acceptor in combination with a bulky donor ligand were unsuccessful, which may be due to the steric demands of donor ligand. Moreover, the resulted assemblies from such cis-blocked 90° building unit are mostly non-fluorescent in nature and limit the possibility of using them as chemosensors for various practical applications. Unlike that of rigid square-planar Pt(II) and Pd(II)-metal based building blocks, the use of other transition metal-based building units for the construction of discrete nanoscopic molecular architectures are known to lesser extent, mainly because of their versatile coordination geometries. However, some of the half-sandwiched piano-stool complexes of late transition metals like Ru, Os, Ir and Rh are known to maintain the stable octahedral geometry under various reaction conditions. Moreover, the self-assembly using redox active transition metal-based building units may lead to redox active assemblies. On the other hand, symmetrical rigid donors have been widely used as the favorite choices for the purpose of constructing desired product mainly due to their predictable directionality. Flexible linkers are not predictable in their directionality during self-assembly process and thus results mostly in undesired polymeric products. Furthermore, metal-ligand directed self-assembly provides opportunity to introduce multifunctionality in a single step within/onto the final supramolecular architectures. Among various functional groups, the incorporation of unsaturated ethynyl functionality is expected to enrich the final assemblies to be π-electron-rich and the attachment of ethynyl functionality with heavy transition metal ions are known to be luminescent in nature due to the facile metal to ligand charge transfer (MLCT). Hence, the final supramolecular complexes can be used as potential fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signature of most of the commercially available explosives. The main thrust of the present investigation is focused on the judicious design and syntheses of multifaceted 2D/3D supramolecular architectures of finite shapes, sizes and functionality using Pt(II)/Ru(II) based “shape-selective” organometallic building blocks and investigation of their application as chemosensors. CHAPTER 1 of the thesis presents a general review on the core concepts of self-assembly and supramolecular chemistry. In particular, it underlines the importance of metal-ligand directional bonding approach for designing a vast plethora of discrete 2D/3D supramolecular architectures with tremendous variation in topology. CHAPTER 2 describes the design and syntheses of a series of 2D metallamacrocycles using carbazole-functionalized shape-selective 90° building units. A new Pt2II organometallic 90° acceptor 3,6-bis[trans-Pt(PEt3)2(NO3)(ethynyl)]carbazole (M1) containing ethynyl functionality is synthesized via Sonagashira coupling reaction and characterized. The combination of M1 with three different flexible ditopic donors (L1−L3) afforded [2 + 2] self-assembled molecular squares (1−3), respectively [where L1 = 1,3-bis(4-pyridyl)isophthalamide; L2 = 1,3-bis(3-pyridyl)isophthalamide; L3 = 1,2-bis(4-pyridyl)ethane] (Scheme 1). Scheme 1: Schematic presentation of the formation of a series of [2 + 2] self-assembled molecular squares. An equimolar (1:1) combination of same acceptor M1 with rigid linear ditopic donors (L4-L5) yielded [4 + 4] self-assembled octanuclear molecular squares 4 and 5, respectively [L4 = 4,4’-bipyridine; L5 = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar reaction of M1 with an amide-based unsymmetrical linear flexible ditopic donor L6 resulted in the formation a [2 + 2] self-sorted molecular rhomboid (6a) as a single product [L6 = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboids, triangles and squares) due to different connectivity of the ambidentate linker, the formation of a single and symmetrical molecular rhomboid 6a as an exclusive product is an interesting observation. This chapter also presents the synthesis and characterization of a complementary 90° dipyridyl donor 3,6-bis(4-pyridylethynyl)carbazole (L7). Stoichiometric combination of L7 with several PdII/PtII-based 90° acceptors (M2−M4) yielded [2 + 2] self-assembled molecular “bowl” shaped macrocycles (7−9) respectively, in good yields [M2 = cis-(dppf)Pd(CF3SO3)2; M3 = cis-(dppf)Pt(CF3SO3)2; M4 = cis-(tmen)Pd(NO3)2]. All these newly synthesized macrocycles were characterized by various spectroscopic techniques and molecular structures of some of them were confirmed by single crystal X-ray diffraction analysis. In addition to their syntheses and characterization, fluorescence chemosensing ability for various analytes was investigated. Macrocycle 1 is a system composed of amide-based receptor units and carbazole-based fluorophore moieties. The fluorescence study of 1 elicited a dramatic enhancement in the fluorescence intensity upon gradual addition of P2O74- anion in DMF/H2O solvent mixture, whereas similar titration under identical condition with other anions like F-, ClO4-, and H2PO4- did not show such change. Hence, molecular square 1 can be used as selective fluorescence sensor for pyrophosphate (P2O74-) anion. Due to their extended π-conjugation, macrocycles 3-4 were used as fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signatures of many commercially available explosives. The fluorescence study showed a marked quenching of initial fluorescence intensity of the macrocycles(3-4) upon gradual addition of picric acid (PA) and they exhibited large fluorescence quenching responses with high selectivity for nitroaromatics among various other electron deficient aromatic compounds tested. As macrocycle 7 has large concave aromatic surface, it was utilized as a suitable host for large convex guest such as fullerene C60. The fluorescence quenching titration study suggested that macrocycle 7 forms a stable ~1:1 host-guest complex with C60 and the calculated association constant (KSV) is 1.0 × 105 M-1. CHAPTER 3 presents two-component coordination-driven self-assembly of a series of [2 + 2] molecular rectangles and a [2 + 4] self-assembled molecular tetragonal prism. An equimolar combination of pre-designed linear PtII2-acceptors M5−M6 separately with three different “clip” donors (L2, L8−L9) led to the formation of [2 + 2] self-assembled tetranuclear cationic molecular rectangles (10−15), respectively [M5 = 1,4-bis[trans-Pt(PEt3)2(NO3)(ethynyl)] benzene; M6 = 4,4’-bis[trans-Pt(PEt3)2(CF3SO3)(ethynyl)]biphenyl; L8 = 1,3-bis(3-pyridyl)ethynylbenzene; L9 = 1,8-bis(4-pyridyl)ethynylanthracene]. Rectangles 10-15 showed strong fluorescence in solution owing to their extended π-conjugation. Amide-functionalized rectangle 10 was used as a macrocyclic receptor for dicarboxylic acids. Solution state fluorescence study showed that rectangle 10 selectively binds (KSV = 1.4 × 104 M-1) with maleic acid by subsequent enhancement in emission intensity and addition of other analogous aliphatic dicarboxylic acids such as fumaric, succinic, adipic, mesaconic and itaconic acids causes no change in the emission spectra; thereby demonstrated its potential use as macrocyclic receptor in sensor applications. Since rectangle 15 is enriched with π-conjugation, it was examined as a fluorescence sensor for electron-deficient nitroaromatics such as picric acid, which is often considered as a secondary chemical explosive. The fluorescence study of 15 showed a significant quenching of initial emission intensity upon titrating with picric acid (PA) and it exhibited the largest fluorescence quenching response with high selectivity for picric acid. Scheme 2: Schematic representation of formation of [2 + 4] self-assembled of molecular tetragonal prism. This chapter also describes two-component coordination [2 + 4] self-assembly of a pyrene-based PtII8 tetragonal prism (16) as shown in Scheme 2, using a newly designed tetratopic organometallic acceptor (M7; 1,3,6,8-tetrakis[trans-Pt(PEt3)2(NO3)(ethynyl)]pyrene) in combination with an amide-based “clip” donor (L2) and propensity of this prism (16) as a selective fluorescence sensor for nitroaromatic explosives has been examined both in solution as well as in thin-film. CHAPTER 4 reports the synthesis and structural characterization of a series of Ru(II)-based bi-and tetra-nuclear metallamacrocycles and hexanuclear trigonal prismatic cages. In principle, the self-assembly of a “clip” acceptor with an asymmetrical ditopic donor is expected to give two different linkage isomeric (head-to-tail and head-to-head) molecular rectangles because of different bond connectivity of the donor. However, the equimolar combination of half-sandwiched p-cymene binuclear Ru(II)-based “clip” acceptors (M8−M9) and an amide-based ambidentate donor (L6) resulted in the self-sorting of single linkage (head-to-tail) isomeric rectangles 17−18 as only products, respectively [M8 = [Ru2(μ-η4-C2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2; M9 = [Ru2(μ- η4-C6H2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2]. Molecular structures of these head-to-tail linkage isomeric rectangles were unambiguously proved by single crystal X-ray diffraction analysis. Likewise, the self-assembly of oxalato-bridged Ru(II) acceptor M8 with a rigid dipyridyl “clip” donor L8 yielded a tetranuclear cationic pincer complex 19, while a similar reaction of M8 with an anthracene-functionalized “clip” donor L9 having shorter distance (between their reactive sites) compared to L8 led to the formation of [1 + 1] self-assembled macrocycle 20. This chapter also represents the design and synthesis of two hexanuclear trigonal prismatic cages (21−22) from the self-assembly of a π-electron rich tripyridyl donor (L10; 1,3,5-tris(4-pyridylethynyl)benzene) in combination with binuclear acceptors M8 and M9, respectively (Scheme 3). Formation of these prismatic cages was initially characterized using various spectroscopic techniques and the molecular structure of oxalato-bridged prism 21 was confirmed by single crystal X-ray diffraction analysis. In addition to the structural characterization, the pincer complex 19 and trigonal prismatic cages 21−22 were used as fluorescence sensors for nitroaromatic explosives owing to their large internal porosity and their π-electron rich nature. Scheme 3: Schematic representation of the formation of [3 + 2] self-assembled trigonal prismatic cage. CHAPTER 5 covers the syntheses of a few discrete metallamacrocycles using flexible imidazole/carboxylate based donors instead of much widely employed polypyridyl donors. The metal-ligand directed self-assembly of oxalato-bridged acceptor M8 and an imidazole-based tetratopic donor (L11; 1,2,4,5-tetrakis(imidazol-1-yl)benzene) in methanol afforded [2 + 1] self-assembled tetranuclear macrocycle 23. Conversely, the similar combination of L11 with 2,5-dihydroxy-1,4-benzoquinonato-bridged binuclear complex (M9) in 1:2 molar ratio in methanol resulted in an octanuclear cage 24. Both the complexes (23−24) were isolated as their triflate salts in high yields and were characterized by various spectroscopic methods including single crystal X-ray diffraction analysis. Scheme 4: Schematic representation of formation of an octanuclear incomplete Ru(II) open prism via ruthenium-oxygen coordination driven self-assembly. This chapter also explains the self-sorting of an unusual octanuclear incomplete prism [Ru8(η6-p-cymene)8(tma)2(μ-η4-C2O4)2(OMe)4](CF3SO3)2 (25) via ruthenium-oxygen coordination driven self-assembly of building block M8 and sodium benzene-1,3,5-tricarboxylate (L12) (Scheme 4). Electronic absorption study indicated that prism 25 exhibited a remarkable shape-selective binding affinity for 1,3,5-trihydroxybenzene (phluoroglucinol) via multiple hydrogen bonding interactions and such shape-selective binding was confirmed by single crystal X-ray diffraction analysis. (For figures pl see the abstract file)

Over the past few decades, supramolecular self-assembly has become an alternative synthetic tool for constructing targeted discrete molecular architectures. Among various interactions, metal-ligand coordination has attracted great attention owing to high bond enthalpy (15−50 Kcal/mol) and predictable directionality. The basic principle of metal-ligand directed self-assembly relies on the proper designing of information encoded rigid complementary building units (a transition metal based acceptor and a multidentate organic donor) that self-recognize themselves in a chemically reasonable way (depends on their bite angle and symmetry) during self-assembly process. As far as acceptor units are concerned, Pd(II) and Pt(II) metal-based cis-blocked 90° acceptors have so far been used greatly for the construction of a library of 2D/3D discrete supramolecular architectures due to their rigid square planar geometry and kinetic lability. However, in some cases the efforts to design finite supramolecular architectures using a cis-blocked 90° acceptor in combination with a bulky donor ligand were unsuccessful, which may be due to the steric demands of donor ligand. Moreover, the resulted assemblies from such cis-blocked 90° building unit are mostly non-fluorescent in nature and limit the possibility of using them as chemosensors for various practical applications. Unlike that of rigid square-planar Pt(II) and Pd(II)-metal based building blocks, the use of other transition metal-based building units for the construction of discrete nanoscopic molecular architectures are known to lesser extent, mainly because of their versatile coordination geometries. However, some of the half-sandwiched piano-stool complexes of late transition metals like Ru, Os, Ir and Rh are known to maintain the stable octahedral geometry under various reaction conditions. Moreover, the self-assembly using redox active transition metal-based building units may lead to redox active assemblies. On the other hand, symmetrical rigid donors have been widely used as the favorite choices for the purpose of constructing desired product mainly due to their predictable directionality. Flexible linkers are not predictable in their directionality during self-assembly process and thus results mostly in undesired polymeric products. Furthermore, metal-ligand directed self-assembly provides opportunity to introduce multifunctionality in a single step within/onto the final supramolecular architectures. Among various functional groups, the incorporation of unsaturated ethynyl functionality is expected to enrich the final assemblies to be π-electron-rich and the attachment of ethynyl functionality with heavy transition metal ions are known to be luminescent in nature due to the facile metal to ligand charge transfer (MLCT). Hence, the final supramolecular complexes can be used as potential fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signature of most of the commercially available explosives. The main thrust of the present investigation is focused on the judicious design and syntheses of multifaceted 2D/3D supramolecular architectures of finite shapes, sizes and functionality using Pt(II)/Ru(II) based “shape-selective” organometallic building blocks and investigation of their application as chemosensors. CHAPTER 1 of the thesis presents a general review on the core concepts of self-assembly and supramolecular chemistry. In particular, it underlines the importance of metal-ligand directional bonding approach for designing a vast plethora of discrete 2D/3D supramolecular architectures with tremendous variation in topology. CHAPTER 2 describes the design and syntheses of a series of 2D metallamacrocycles using carbazole-functionalized shape-selective 90° building units. A new Pt2II organometallic 90° acceptor 3,6-bis[trans-Pt(PEt3)2(NO3)(ethynyl)]carbazole (M1) containing ethynyl functionality is synthesized via Sonagashira coupling reaction and characterized. The combination of M1 with three different flexible ditopic donors (L1−L3) afforded [2 + 2] self-assembled molecular squares (1−3), respectively [where L1 = 1,3-bis(4-pyridyl)isophthalamide; L2 = 1,3-bis(3-pyridyl)isophthalamide; L3 = 1,2-bis(4-pyridyl)ethane] (Scheme 1). Scheme 1: Schematic presentation of the formation of a series of [2 + 2] self-assembled molecular squares. An equimolar (1:1) combination of same acceptor M1 with rigid linear ditopic donors (L4-L5) yielded [4 + 4] self-assembled octanuclear molecular squares 4 and 5, respectively [L4 = 4,4’-bipyridine; L5 = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar reaction of M1 with an amide-based unsymmetrical linear flexible ditopic donor L6 resulted in the formation a [2 + 2] self-sorted molecular rhomboid (6a) as a single product [L6 = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboids, triangles and squares) due to different connectivity of the ambidentate linker, the formation of a single and symmetrical molecular rhomboid 6a as an exclusive product is an interesting observation. This chapter also presents the synthesis and characterization of a complementary 90° dipyridyl donor 3,6-bis(4-pyridylethynyl)carbazole (L7). Stoichiometric combination of L7 with several PdII/PtII-based 90° acceptors (M2−M4) yielded [2 + 2] self-assembled molecular “bowl” shaped macrocycles (7−9) respectively, in good yields [M2 = cis-(dppf)Pd(CF3SO3)2; M3 = cis-(dppf)Pt(CF3SO3)2; M4 = cis-(tmen)Pd(NO3)2]. All these newly synthesized macrocycles were characterized by various spectroscopic techniques and molecular structures of some of them were confirmed by single crystal X-ray diffraction analysis. In addition to their syntheses and characterization, fluorescence chemosensing ability for various analytes was investigated. Macrocycle 1 is a system composed of amide-based receptor units and carbazole-based fluorophore moieties. The fluorescence study of 1 elicited a dramatic enhancement in the fluorescence intensity upon gradual addition of P2O74- anion in DMF/H2O solvent mixture, whereas similar titration under identical condition with other anions like F-, ClO4-, and H2PO4- did not show such change. Hence, molecular square 1 can be used as selective fluorescence sensor for pyrophosphate (P2O74-) anion. Due to their extended π-conjugation, macrocycles 3-4 were used as fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signatures of many commercially available explosives. The fluorescence study showed a marked quenching of initial fluorescence intensity of the macrocycles(3-4) upon gradual addition of picric acid (PA) and they exhibited large fluorescence quenching responses with high selectivity for nitroaromatics among various other electron deficient aromatic compounds tested. As macrocycle 7 has large concave aromatic surface, it was utilized as a suitable host for large convex guest such as fullerene C60. The fluorescence quenching titration study suggested that macrocycle 7 forms a stable ~1:1 host-guest complex with C60 and the calculated association constant (KSV) is 1.0 × 105 M-1. CHAPTER 3 presents two-component coordination-driven self-assembly of a series of [2 + 2] molecular rectangles and a [2 + 4] self-assembled molecular tetragonal prism. An equimolar combination of pre-designed linear PtII2-acceptors M5−M6 separately with three different “clip” donors (L2, L8−L9) led to the formation of [2 + 2] self-assembled tetranuclear cationic molecular rectangles (10−15), respectively [M5 = 1,4-bis[trans-Pt(PEt3)2(NO3)(ethynyl)] benzene; M6 = 4,4’-bis[trans-Pt(PEt3)2(CF3SO3)(ethynyl)]biphenyl; L8 = 1,3-bis(3-pyridyl)ethynylbenzene; L9 = 1,8-bis(4-pyridyl)ethynylanthracene]. Rectangles 10-15 showed strong fluorescence in solution owing to their extended π-conjugation. Amide-functionalized rectangle 10 was used as a macrocyclic receptor for dicarboxylic acids. Solution state fluorescence study showed that rectangle 10 selectively binds (KSV = 1.4 × 104 M-1) with maleic acid by subsequent enhancement in emission intensity and addition of other analogous aliphatic dicarboxylic acids such as fumaric, succinic, adipic, mesaconic and itaconic acids causes no change in the emission spectra; thereby demonstrated its potential use as macrocyclic receptor in sensor applications. Since rectangle 15 is enriched with π-conjugation, it was examined as a fluorescence sensor for electron-deficient nitroaromatics such as picric acid, which is often considered as a secondary chemical explosive. The fluorescence study of 15 showed a significant quenching of initial emission intensity upon titrating with picric acid (PA) and it exhibited the largest fluorescence quenching response with high selectivity for picric acid. Scheme 2: Schematic representation of formation of [2 + 4] self-assembled of molecular tetragonal prism. This chapter also describes two-component coordination [2 + 4] self-assembly of a pyrene-based PtII8 tetragonal prism (16) as shown in Scheme 2, using a newly designed tetratopic organometallic acceptor (M7; 1,3,6,8-tetrakis[trans-Pt(PEt3)2(NO3)(ethynyl)]pyrene) in combination with an amide-based “clip” donor (L2) and propensity of this prism (16) as a selective fluorescence sensor for nitroaromatic explosives has been examined both in solution as well as in thin-film. CHAPTER 4 reports the synthesis and structural characterization of a series of Ru(II)-based bi-and tetra-nuclear metallamacrocycles and hexanuclear trigonal prismatic cages. In principle, the self-assembly of a “clip” acceptor with an asymmetrical ditopic donor is expected to give two different linkage isomeric (head-to-tail and head-to-head) molecular rectangles because of different bond connectivity of the donor. However, the equimolar combination of half-sandwiched p-cymene binuclear Ru(II)-based “clip” acceptors (M8−M9) and an amide-based ambidentate donor (L6) resulted in the self-sorting of single linkage (head-to-tail) isomeric rectangles 17−18 as only products, respectively [M8 = [Ru2(μ-η4-C2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2; M9 = [Ru2(μ- η4-C6H2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2]. Molecular structures of these head-to-tail linkage isomeric rectangles were unambiguously proved by single crystal X-ray diffraction analysis. Likewise, the self-assembly of oxalato-bridged Ru(II) acceptor M8 with a rigid dipyridyl “clip” donor L8 yielded a tetranuclear cationic pincer complex 19, while a similar reaction of M8 with an anthracene-functionalized “clip” donor L9 having shorter distance (between their reactive sites) compared to L8 led to the formation of [1 + 1] self-assembled macrocycle 20. This chapter also represents the design and synthesis of two hexanuclear trigonal prismatic cages (21−22) from the self-assembly of a π-electron rich tripyridyl donor (L10; 1,3,5-tris(4-pyridylethynyl)benzene) in combination with binuclear acceptors M8 and M9, respectively (Scheme 3). Formation of these prismatic cages was initially characterized using various spectroscopic techniques and the molecular structure of oxalato-bridged prism 21 was confirmed by single crystal X-ray diffraction analysis. In addition to the structural characterization, the pincer complex 19 and trigonal prismatic cages 21−22 were used as fluorescence sensors for nitroaromatic explosives owing to their large internal porosity and their π-electron rich nature. Scheme 3: Schematic representation of the formation of [3 + 2] self-assembled trigonal prismatic cage. CHAPTER 5 covers the syntheses of a few discrete metallamacrocycles using flexible imidazole/carboxylate based donors instead of much widely employed polypyridyl donors. The metal-ligand directed self-assembly of oxalato-bridged acceptor M8 and an imidazole-based tetratopic donor (L11; 1,2,4,5-tetrakis(imidazol-1-yl)benzene) in methanol afforded [2 + 1] self-assembled tetranuclear macrocycle 23. Conversely, the similar combination of L11 with 2,5-dihydroxy-1,4-benzoquinonato-bridged binuclear complex (M9) in 1:2 molar ratio in methanol resulted in an octanuclear cage 24. Both the complexes (23−24) were isolated as their triflate salts in high yields and were characterized by various spectroscopic methods including single crystal X-ray diffraction analysis. Scheme 4: Schematic representation of formation of an octanuclear incomplete Ru(II) open prism via ruthenium-oxygen coordination driven self-assembly. This chapter also explains the self-sorting of an unusual octanuclear incomplete prism [Ru8(η6-p-cymene)8(tma)2(μ-η4-C2O4)2(OMe)4](CF3SO3)2 (25) via ruthenium-oxygen coordination driven self-assembly of building block M8 and sodium benzene-1,3,5-tricarboxylate (L12) (Scheme 4). Electronic absorption study indicated that prism 25 exhibited a remarkable shape-selective binding affinity for 1,3,5-trihydroxybenzene (phluoroglucinol) via multiple hydrogen bonding interactions and such shape-selective binding was confirmed by single crystal X-ray diffraction analysis. (For figures pl see the abstract file)

The work highlighted in this dissertation comprises of syntheses and characterizations of coordination driven supramolecular compounds. The synthesized complexes are characterized by IR spectroscopy, multinuclear NMR spectroscopy and single crystal structure determination. Chapter 2: In this chapter we attempted to make a three dimensional self-assembled cage by the reaction between N, N’, N’’- tris(3-pyridyl)trimesic amide a tritopic donor and Pt(II) based 90° ditopic acceptor cis-(dppe)Pt(II)(OTf)2 [dppe = 1,2-bis(diphenylphosphino)ethane]. It resulted in a trigonal bipyramidal structure. The cage was characterized by single crystal XRD and FT-IR spectra. Chapter 3: In this chapter we have reported the synthesis and characterization of two hereby unknown metal containing carboxylic acid ligands containing the Pt-ethynyl moiety. Also we have shown the preparation and structure analysis of a copper containing metal-organic framework incorporating one of the Pt-ethynyl containing carboxylic acid ligand. This has resulted in the formation of a very interesting hetero-metallic MOF which is quite uncommon in literature.

The work highlighted in this dissertation comprises of syntheses and characterizations of coordination driven supramolecular compounds. The synthesized complexes are characterized by IR spectroscopy, multinuclear NMR spectroscopy and single crystal structure determination. Chapter 2: In this chapter we attempted to make a three dimensional self-assembled cage by the reaction between N, N’, N’’- tris(3-pyridyl)trimesic amide a tritopic donor and Pt(II) based 90° ditopic acceptor cis-(dppe)Pt(II)(OTf)2 [dppe = 1,2-bis(diphenylphosphino)ethane]. It resulted in a trigonal bipyramidal structure. The cage was characterized by single crystal XRD and FT-IR spectra. Chapter 3: In this chapter we have reported the synthesis and characterization of two hereby unknown metal containing carboxylic acid ligands containing the Pt-ethynyl moiety. Also we have shown the preparation and structure analysis of a copper containing metal-organic framework incorporating one of the Pt-ethynyl containing carboxylic acid ligand. This has resulted in the formation of a very interesting hetero-metallic MOF which is quite uncommon in literature.

Biological systems construct varieties of self-assembled architectures with incredible elegance and precession utilizing proteins as subunits to accomplish widespread functions. Inspired by natural systems, construction of artificial model systems with such sophistication and delicacy has become an intriguing field of research over the last two decades using so-called self-assembly process. Judiciously selected complementary building units encoded with specific chemical and structural information can be self-assembled into pre-programmed abiological architectures in a manner similar to biological self-assembly. In this regard, kinetically labile metal-ligand coordination has become an efficient and powerful protocol for the construction of highly intricate structures with specific topology and functionality due to its simple design principle, high bond enthalpy, and predictable directionality. Two-component self-assembly is very widely used methodology and easy to monitor. Recently, multi-component self-assembly has come up as an alternative and effective pathway to achieve complex architectures connecting more than two components in a single step. However, formation of selective single product from multicomponents is entropically unfavorable. Only a very few 3D architectures have been known, that are obtained from a mixture of ditopic and tri- or tetratopic donors with metal acceptors with or without employing templates. Development of template-free multicomponent architectures is still in its infancy. Strong tendency of Pd(II)/Pt(II) to attain square-planar geometry around the metal center and kinetically labile nature of Pd(II)/Pd(II)-N(pyridine) bonds made them chemists’ favourite to engineer desired supramolecular coordination architectures with structural resemblance to Platonic or Archimedean solids by employing symmetrical pyridyl donors due to their predictable directionality. In case of poly-imidazole donors, free rotation of C-N bond connecting imidazole and phenyl ring allows various dispositions of the donating nitrogen with respect to the aromatic backbone, and therefore, the structural topology of the architectures, made of poly-imidazole ligands becomes much more interesting as compared to symmetrical Platonic or Archimedean solids. The physico-chemical properties of self-assembled coordination cages depend on the structures of the complexes. Presence of large internal cavity surrounded by aromatic core, provides an excellent environment for the encapsulation of varieties of guest molecule or as nano-reactors for different organic transformations. Structural investigation in terms of packing interactions, solvent molecules, intermolecular channels can sometimes determine the property of such self-assembled materials as well. Presence of acidic water as well as H-bonded 3D-networks of water molecules in molecular pockets make them potential material for proton conduction. In addition, metal-ligand coordination offers opportunity to introduce new functionality through pre-synthetic modification of the building constituents to influence the property of the supramolecular systems. Incorporation of unsaturated ethynyl functionality attached to the heavy transition metal is expected to exhibit efficient luminescence due to the facile metal to ligand charge transfer (MLCT). Hence, the final assemblies can be employed as chemosensors for electron-deficient nitroaromatics, which are the chemical signature of many of the commercially available explosives. The present investigation is focused on design and construction of discrete, nanoscopic coordination cages with unusual structural topology employing mainly imidazole-based donors with Pd(II)/Pt(II) acceptors and their applications in catalysis, chemosensing, and proton conduction. CHAPTER 1 of the thesis provides a general introduction to self-assembly focusing on the importance and advantages of metal-ligand directional bonding approach towards the construction of supramolecular architectures with various structural topologies. This chapter also includes a brief review on the applications of such coordination cages in various fields especially as ‘molecular flask’ for the observation of unique chemical phenomena and unusual reactions. Part A of CHAPTER 2 describes the synthesis of a new hollow Pd6 water soluble cage [{(tmen)Pd}6(timb)4](NO3)12 (1) via two-component self-assembly of a triimidazole donor and 90° Pd(II) acceptor [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)benzene]. The assembly was successfully crystallized with a hydrophilic dianionic benzoquinone derivative (formed in situ by the decomposition of DDQ) as [{(tmen)Pd}6(timb)4](NO3)10()2(H2O)18 (3), and a hydrophobic sterically demanding aromatic aldehyde as [{(tmen)Pd}6(timb)4](NO3)12{()4a}2(H2O)27 (5a) [where 2H2 = 2,3-dichloro-5,6-dihydroxycyclohexa-2,5diene-1,4-dione, 4a = 1-pyrenecarboxaldehyde,  = exohedral and  = endohedral] to confirm the hydrophobic nature of the cavity. Experiments were carried out to show that the hydrophobic confined nanospace of the cage (1) catalyses the Knoevenagel condensation of a series of different aromatic monoaldehydes with active methylene compounds in ‘green’ aqueous medium. The Knoevenagel condensation reaction is basically a dehydration reaction because water is a by-product. So the presence of water should, in principle, promote the backward reaction as per Le Chatelier’s principle. In general, these reactions with organic substrates are not performed in water. However, difficulty has been overcome using hydrophobic cavity of the cage. It has also been established that the cavity of the cage also enhances the rate of Diels-Alder reaction of 9-hydroxymethylanthracene with N-phenylmaleimide/N-cyclohexylmaleimide. Figure 1. Catalytic Knoevenagel condensation and Diels-Alder reaction using hydrophobic cavity of the cage (1) in aqueous medium. Part B of CHAPTER 2 reports unique three-component self-assembly incorporating both tri- and tetra-topic donors. Until now, a very few 3D-architectures have been known that are obtained from self-assembly of ditopic and tri- or tetratopic donors with metal acceptors. Scheme 1. Three-component self-assembly of a Pd7 cage (1) from cis-blocked Pd(II) 90° acceptor (M), tri-imidazole (timb) and tetra-imidazole (tim) donors. Self-assembled multicomponent discrete architecture composed of both tri- and tetra-topic donors is yet to be reported due to difficulty in prediction of the final structure from the mixture of ligands having multiple donor sites. The first example of self-sorted Pd7 molecular boat [{(tmen)Pd}7(timb)2(tim)2](NO3)14(H2O)20 (1) [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)-benzene, tim = 1,2,4,5-tetrakis(1-imidazolyl)benzene] was synthesized via three-component self-assembly of cis-(tmen)Pd(NO3)2, tetra- (tim) and tri-topic donors (timb) in a 7:2:2 ratio. The cavity of this cage was also utilized as a nanoreactor for catalytic Knoevenagel condensations of a series of aromatic aldehydes with 1,3-dimethylbarbituric acid (e) and Meldrum’s acid (f) in aqueous media. CHAPTER 3 presents the results of an investigation on how simple variation of length and coordination mode of linear donors can self-discriminate into markedly different complex architectures, from Pd8 molecular swing [{(tmen)Pd}8(tim)2(bpy)4](NO3)16 (1) or [{(tmen)Pd}8(tim)2(stt)5](NO3)6 (2) to Pd6 molecular boat [{(tmen)Pd}6(tim)2(bpe/dpe/pin/dpb)2](NO3)12, (3/4/5/6). Also by enhancing denticity [bidentate to tridentate (ptp)] as well as introducing asymmetry, they self-sort into Pd7 molecular tent [{(tmen)Pd}7(tim)2(ptp)2](NO3)14 (7) by employing it in a self-assembly of cis-(tmen)Pd(NO3)2 and tetraimidazole (tim) donor [where tmen = N,N,N’,N’-tetramethylethylenediamine, bpy = 4,4’-bipyridyl, stt = sodium terephthalate, bpe = trans-1,2-bis(4-pyridyl)ethylene, dpe = 1,2-di(pyridin-4-yl)ethane, pin = N-(pyridin-4-yl)isonicotinamide, dpb = 1,4-di(pyridin-4-yl)benzene, ptp = 6'-(pyridin-4-yl)-3,4':2',4''-terpyridine, and tim = 1,2,4,5-tetrakis(1- imidazolyl)benzene]. In these cases, control of the geometrical principles and stereo-electronic preferences of the building units allowed the formation of such intricate architectures. Some of these assemblies represent first examples of such types of structures, and their formation would not be anticipated by taking into account only the geometry of the donor and acceptor building units. In addition to their direct structural confirmation using single crystal X-ray diffraction analysis, propensity of the assemblies (1 and 3) to form inclusion complexes with large guest like C60 in solution was also demonstrated by fluorescence quenching experiment. The high KSV values for both the assemblies 1 (1.0 × 10-5 M-1) and 2 (1.6 × 10-6 M-1) with C60 indicated the propensity of these assemblies to form complexes with C60 in solution. Furthermore, inspection of crystal packing of other five complexes (2 and 4 - 7) revealed the presence of water molecules H-bonded with NO3– (O-H···O=N) and 3D H-bonded networks of water in the intermolecular pockets. Interestingly, the present complexes (2 and 4 - 7) show high conductivity across low-humidity range at ambient temperature and achieve a conductivity of ~10-3 Scm-1 at 75% relative humidity and 296 K. These supra-molecular architectures represent a new generation of discrete materials that display high proton conductivity under ambient conditions with activation energy comparable to that of Nafion. Scheme 2. Exclusive formation of Pd8 molecular swings (1 and 2), Pd6 molecular boats (3-6), and Pd7 molecular tent (7) via self-sorting. CHAPTER 4 presents self-selection by synergistic effect of morphological information and coordination ability of the ligands through specific coordination interactional algorithms within dynamic supramolecular systems involving a tetratopic Pd(II) acceptor and three different pyridine- and imidazole-based donors (La - Lc) [La = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene, Lb = 1,3-di(1H-imidazol-1-yl)benzene, and Lc = tris(4-(1H-imidazol-1-yl)phenyl)amine]. Three different cages, ‘paddle wheel’ cluster Pd2(La)4(NO3)4 (2a), molecular barrel Pd3(Lb)6(NO3)6 (2b) and molecular sphere Pd6(Lc)8(NO3)12 (2c) were first synthesized via two-component self-assembly of a tetratopic Pd(II) acceptor (1) and individual pyridine- and imidazole-based donors (La - Lc). When all the four components were allowed to interact in a complex reaction mixture, only one out of three cages was isolated. The inherent dynamic nature of the kinetically labile coordination bond allows constitutional adaptation through component exchange in the competition experiment involving multiple constituents to self-organize into specific combination and thereby, achieve the thermodynamically most stable assembly. The preferential binding affinity towards a particular partner was also established by transforming a non-preferred cage to a preferred cage by the interaction with the appropriate ligand and thus, this represents the first examples of two-step cage-to-cage transformation through constitutional evolution of Figure 2. Cage-to-cage transformation from non-preferred cage to preferred cage upon treatment with appropriate ligand; and Nyquist plots of the complexes (2b and 2c) under 98% RH condition and ambient temparature. dynamic systems induced by both coordination ability and geometry of the ligand. Moreover, computational study further supported the fact that coordination interaction of imidazole moiety to Pd(II) is enthalpically more preferred compared to pyridine which drives the selection process. In addition, analysis of crystal packing of both the complexes (2b and 2c) indicated the presence of strong H-bonds between NO3- and water molecules; as well as H-bonded 3D-networks of water. Interestingly, both the complexes exhibit promising proton conductivity (10-5 to ca. 10-3 S cm-1) at ambient temperature under relative humidity of ~98% with low activation energy. CHAPTER 5 covers design and synthesis of new organometallic building block 1,3,5-tris(4-trans-Pt(PEt3)2I(ethynyl)phenyl)benzene (1) incorporating Pt-ethynyl functionality and [2 + 3] self-assembly of its nitrate analogue 1,3,5-tris(4-trans-Pt(PEt3)2(ONO2)(ethynyl)phenyl)benzene (2) with “clip” type bidentate donors (L1 – L3) separately afforded three trigonal prismatic architectures (3a – 3c), respectively (Scheme 3), Scheme 3. Schematic presentation of three different donors (L1 – L3) and a new planar tritopic acceptor (2) and their [3 + 2] self-assembly into trigonal prismatic architectures (3a - 3c). [L1 = N1,N3-di(pyridin-3-yl)isophthalamide; L2 = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene; L3 = 1,3-bis(pyridin-3-ylethynyl)benzene]. All these prisms were characterized and their shapes/sizes are predicted through geometry optimization employing molecular mechanics universal force field (MMUFF) simulation. The extended -conjugation including the presence of Pt-ethynyl functionality make them electron rich as well as luminescent in nature. As expected, cages 3b and 3c exhibit fluorescent quenching in solution upon addition of picric acid [PA], which is a common constituent of many explosives. Interestingly, the non-responsive nature of fluorescent intensity towards other electron-deficient nitro-aromatic explosives (NAEs) makes them promising selective sensors for PA with a detection limit deep down to ppb. Complexes 3b – c represent the first examples of molecular metallocages as selective sensors for picric acid. Furthermore, solid-state quenching of fluorescent intensity of the thin film of 3b upon exposure to saturated vapor of picric acid draws special attention for infield application.

Biological systems construct varieties of self-assembled architectures with incredible elegance and precession utilizing proteins as subunits to accomplish widespread functions. Inspired by natural systems, construction of artificial model systems with such sophistication and delicacy has become an intriguing field of research over the last two decades using so-called self-assembly process. Judiciously selected complementary building units encoded with specific chemical and structural information can be self-assembled into pre-programmed abiological architectures in a manner similar to biological self-assembly. In this regard, kinetically labile metal-ligand coordination has become an efficient and powerful protocol for the construction of highly intricate structures with specific topology and functionality due to its simple design principle, high bond enthalpy, and predictable directionality. Two-component self-assembly is very widely used methodology and easy to monitor. Recently, multi-component self-assembly has come up as an alternative and effective pathway to achieve complex architectures connecting more than two components in a single step. However, formation of selective single product from multicomponents is entropically unfavorable. Only a very few 3D architectures have been known, that are obtained from a mixture of ditopic and tri- or tetratopic donors with metal acceptors with or without employing templates. Development of template-free multicomponent architectures is still in its infancy. Strong tendency of Pd(II)/Pt(II) to attain square-planar geometry around the metal center and kinetically labile nature of Pd(II)/Pd(II)-N(pyridine) bonds made them chemists’ favourite to engineer desired supramolecular coordination architectures with structural resemblance to Platonic or Archimedean solids by employing symmetrical pyridyl donors due to their predictable directionality. In case of poly-imidazole donors, free rotation of C-N bond connecting imidazole and phenyl ring allows various dispositions of the donating nitrogen with respect to the aromatic backbone, and therefore, the structural topology of the architectures, made of poly-imidazole ligands becomes much more interesting as compared to symmetrical Platonic or Archimedean solids. The physico-chemical properties of self-assembled coordination cages depend on the structures of the complexes. Presence of large internal cavity surrounded by aromatic core, provides an excellent environment for the encapsulation of varieties of guest molecule or as nano-reactors for different organic transformations. Structural investigation in terms of packing interactions, solvent molecules, intermolecular channels can sometimes determine the property of such self-assembled materials as well. Presence of acidic water as well as H-bonded 3D-networks of water molecules in molecular pockets make them potential material for proton conduction. In addition, metal-ligand coordination offers opportunity to introduce new functionality through pre-synthetic modification of the building constituents to influence the property of the supramolecular systems. Incorporation of unsaturated ethynyl functionality attached to the heavy transition metal is expected to exhibit efficient luminescence due to the facile metal to ligand charge transfer (MLCT). Hence, the final assemblies can be employed as chemosensors for electron-deficient nitroaromatics, which are the chemical signature of many of the commercially available explosives. The present investigation is focused on design and construction of discrete, nanoscopic coordination cages with unusual structural topology employing mainly imidazole-based donors with Pd(II)/Pt(II) acceptors and their applications in catalysis, chemosensing, and proton conduction. CHAPTER 1 of the thesis provides a general introduction to self-assembly focusing on the importance and advantages of metal-ligand directional bonding approach towards the construction of supramolecular architectures with various structural topologies. This chapter also includes a brief review on the applications of such coordination cages in various fields especially as ‘molecular flask’ for the observation of unique chemical phenomena and unusual reactions. Part A of CHAPTER 2 describes the synthesis of a new hollow Pd6 water soluble cage [{(tmen)Pd}6(timb)4](NO3)12 (1) via two-component self-assembly of a triimidazole donor and 90° Pd(II) acceptor [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)benzene]. The assembly was successfully crystallized with a hydrophilic dianionic benzoquinone derivative (formed in situ by the decomposition of DDQ) as [{(tmen)Pd}6(timb)4](NO3)10()2(H2O)18 (3), and a hydrophobic sterically demanding aromatic aldehyde as [{(tmen)Pd}6(timb)4](NO3)12{()4a}2(H2O)27 (5a) [where 2H2 = 2,3-dichloro-5,6-dihydroxycyclohexa-2,5diene-1,4-dione, 4a = 1-pyrenecarboxaldehyde,  = exohedral and  = endohedral] to confirm the hydrophobic nature of the cavity. Experiments were carried out to show that the hydrophobic confined nanospace of the cage (1) catalyses the Knoevenagel condensation of a series of different aromatic monoaldehydes with active methylene compounds in ‘green’ aqueous medium. The Knoevenagel condensation reaction is basically a dehydration reaction because water is a by-product. So the presence of water should, in principle, promote the backward reaction as per Le Chatelier’s principle. In general, these reactions with organic substrates are not performed in water. However, difficulty has been overcome using hydrophobic cavity of the cage. It has also been established that the cavity of the cage also enhances the rate of Diels-Alder reaction of 9-hydroxymethylanthracene with N-phenylmaleimide/N-cyclohexylmaleimide. Figure 1. Catalytic Knoevenagel condensation and Diels-Alder reaction using hydrophobic cavity of the cage (1) in aqueous medium. Part B of CHAPTER 2 reports unique three-component self-assembly incorporating both tri- and tetra-topic donors. Until now, a very few 3D-architectures have been known that are obtained from self-assembly of ditopic and tri- or tetratopic donors with metal acceptors. Scheme 1. Three-component self-assembly of a Pd7 cage (1) from cis-blocked Pd(II) 90° acceptor (M), tri-imidazole (timb) and tetra-imidazole (tim) donors. Self-assembled multicomponent discrete architecture composed of both tri- and tetra-topic donors is yet to be reported due to difficulty in prediction of the final structure from the mixture of ligands having multiple donor sites. The first example of self-sorted Pd7 molecular boat [{(tmen)Pd}7(timb)2(tim)2](NO3)14(H2O)20 (1) [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)-benzene, tim = 1,2,4,5-tetrakis(1-imidazolyl)benzene] was synthesized via three-component self-assembly of cis-(tmen)Pd(NO3)2, tetra- (tim) and tri-topic donors (timb) in a 7:2:2 ratio. The cavity of this cage was also utilized as a nanoreactor for catalytic Knoevenagel condensations of a series of aromatic aldehydes with 1,3-dimethylbarbituric acid (e) and Meldrum’s acid (f) in aqueous media. CHAPTER 3 presents the results of an investigation on how simple variation of length and coordination mode of linear donors can self-discriminate into markedly different complex architectures, from Pd8 molecular swing [{(tmen)Pd}8(tim)2(bpy)4](NO3)16 (1) or [{(tmen)Pd}8(tim)2(stt)5](NO3)6 (2) to Pd6 molecular boat [{(tmen)Pd}6(tim)2(bpe/dpe/pin/dpb)2](NO3)12, (3/4/5/6). Also by enhancing denticity [bidentate to tridentate (ptp)] as well as introducing asymmetry, they self-sort into Pd7 molecular tent [{(tmen)Pd}7(tim)2(ptp)2](NO3)14 (7) by employing it in a self-assembly of cis-(tmen)Pd(NO3)2 and tetraimidazole (tim) donor [where tmen = N,N,N’,N’-tetramethylethylenediamine, bpy = 4,4’-bipyridyl, stt = sodium terephthalate, bpe = trans-1,2-bis(4-pyridyl)ethylene, dpe = 1,2-di(pyridin-4-yl)ethane, pin = N-(pyridin-4-yl)isonicotinamide, dpb = 1,4-di(pyridin-4-yl)benzene, ptp = 6'-(pyridin-4-yl)-3,4':2',4''-terpyridine, and tim = 1,2,4,5-tetrakis(1- imidazolyl)benzene]. In these cases, control of the geometrical principles and stereo-electronic preferences of the building units allowed the formation of such intricate architectures. Some of these assemblies represent first examples of such types of structures, and their formation would not be anticipated by taking into account only the geometry of the donor and acceptor building units. In addition to their direct structural confirmation using single crystal X-ray diffraction analysis, propensity of the assemblies (1 and 3) to form inclusion complexes with large guest like C60 in solution was also demonstrated by fluorescence quenching experiment. The high KSV values for both the assemblies 1 (1.0 × 10-5 M-1) and 2 (1.6 × 10-6 M-1) with C60 indicated the propensity of these assemblies to form complexes with C60 in solution. Furthermore, inspection of crystal packing of other five complexes (2 and 4 - 7) revealed the presence of water molecules H-bonded with NO3– (O-H···O=N) and 3D H-bonded networks of water in the intermolecular pockets. Interestingly, the present complexes (2 and 4 - 7) show high conductivity across low-humidity range at ambient temperature and achieve a conductivity of ~10-3 Scm-1 at 75% relative humidity and 296 K. These supra-molecular architectures represent a new generation of discrete materials that display high proton conductivity under ambient conditions with activation energy comparable to that of Nafion. Scheme 2. Exclusive formation of Pd8 molecular swings (1 and 2), Pd6 molecular boats (3-6), and Pd7 molecular tent (7) via self-sorting. CHAPTER 4 presents self-selection by synergistic effect of morphological information and coordination ability of the ligands through specific coordination interactional algorithms within dynamic supramolecular systems involving a tetratopic Pd(II) acceptor and three different pyridine- and imidazole-based donors (La - Lc) [La = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene, Lb = 1,3-di(1H-imidazol-1-yl)benzene, and Lc = tris(4-(1H-imidazol-1-yl)phenyl)amine]. Three different cages, ‘paddle wheel’ cluster Pd2(La)4(NO3)4 (2a), molecular barrel Pd3(Lb)6(NO3)6 (2b) and molecular sphere Pd6(Lc)8(NO3)12 (2c) were first synthesized via two-component self-assembly of a tetratopic Pd(II) acceptor (1) and individual pyridine- and imidazole-based donors (La - Lc). When all the four components were allowed to interact in a complex reaction mixture, only one out of three cages was isolated. The inherent dynamic nature of the kinetically labile coordination bond allows constitutional adaptation through component exchange in the competition experiment involving multiple constituents to self-organize into specific combination and thereby, achieve the thermodynamically most stable assembly. The preferential binding affinity towards a particular partner was also established by transforming a non-preferred cage to a preferred cage by the interaction with the appropriate ligand and thus, this represents the first examples of two-step cage-to-cage transformation through constitutional evolution of Figure 2. Cage-to-cage transformation from non-preferred cage to preferred cage upon treatment with appropriate ligand; and Nyquist plots of the complexes (2b and 2c) under 98% RH condition and ambient temparature. dynamic systems induced by both coordination ability and geometry of the ligand. Moreover, computational study further supported the fact that coordination interaction of imidazole moiety to Pd(II) is enthalpically more preferred compared to pyridine which drives the selection process. In addition, analysis of crystal packing of both the complexes (2b and 2c) indicated the presence of strong H-bonds between NO3- and water molecules; as well as H-bonded 3D-networks of water. Interestingly, both the complexes exhibit promising proton conductivity (10-5 to ca. 10-3 S cm-1) at ambient temperature under relative humidity of ~98% with low activation energy. CHAPTER 5 covers design and synthesis of new organometallic building block 1,3,5-tris(4-trans-Pt(PEt3)2I(ethynyl)phenyl)benzene (1) incorporating Pt-ethynyl functionality and [2 + 3] self-assembly of its nitrate analogue 1,3,5-tris(4-trans-Pt(PEt3)2(ONO2)(ethynyl)phenyl)benzene (2) with “clip” type bidentate donors (L1 – L3) separately afforded three trigonal prismatic architectures (3a – 3c), respectively (Scheme 3), Scheme 3. Schematic presentation of three different donors (L1 – L3) and a new planar tritopic acceptor (2) and their [3 + 2] self-assembly into trigonal prismatic architectures (3a - 3c). [L1 = N1,N3-di(pyridin-3-yl)isophthalamide; L2 = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene; L3 = 1,3-bis(pyridin-3-ylethynyl)benzene]. All these prisms were characterized and their shapes/sizes are predicted through geometry optimization employing molecular mechanics universal force field (MMUFF) simulation. The extended -conjugation including the presence of Pt-ethynyl functionality make them electron rich as well as luminescent in nature. As expected, cages 3b and 3c exhibit fluorescent quenching in solution upon addition of picric acid [PA], which is a common constituent of many explosives. Interestingly, the non-responsive nature of fluorescent intensity towards other electron-deficient nitro-aromatic explosives (NAEs) makes them promising selective sensors for PA with a detection limit deep down to ppb. Complexes 3b – c represent the first examples of molecular metallocages as selective sensors for picric acid. Furthermore, solid-state quenching of fluorescent intensity of the thin film of 3b upon exposure to saturated vapor of picric acid draws special attention for infield application.