Gotowa bibliografia na temat „Non-transition Metals - Poly-dentate Ligands”

N-heterocyclic carbenes (NHCs) have generated much interest for use as versatile metal-coordinating groups, since they were first synthesized by Arduengo and coworkers in 1991. NHC molecules can be considered as L-type ligands, because they share their non-bonding electron pairs with the σ-accepting orbital of transition metals, and this endows them with strong coordination interactions. NHC-appended molecules have recently been actively exploited as potentially effective ligands for the surface passivation of various colloidal nanomaterials. We investigate the coordination interactions between a few representative colloidal nanocrystals, including gold nanoparticles (AuNPs) and luminescent quantum dots (QDs), and a NHC-based polymer ligand. The latter presents multiple NHC groups and several short poly (ethylene glycol) (PEG) chains as solubilizing blocks. We find that our NHC-decorated ligands rapidly coordinate onto both sets of nanocrystals, which we attribute to their soft Lewis base nature. These ideally match the soft Lewis acid character of transition metal colloid surfaces, promoting strong coordination bonding through soft‐soft interaction. We combine NMR spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy supplemented with dynamic light scattering to characterize the nature of the binding interactions. Furthermore, the long-term stability of the NHC-stabilized nanocolloids have been tested after phase transfer to water, a highly challenging chemical venue for such groups, due to the moisture sensitive nature of NHC molecules. Data show that our NHC-polymer-stabilized AuNPs and QDs exhibit long-term colloidal stability in buffer media while preserving their optical and fluorescing properties, with no sign of degradation or aggregation build up for at least one year of storage. We will discuss the ligand design and synthesis, characterization of the polymer-stabilized nanocrystals under various conditions, with a particular focus on the beneficial effects of ligand multi-coordination interactions onto the nanocolloid surfaces.

A variety of transition metal complexes involving picolylcyanoacetamides (pica = NCCH2CONH-R; R = 2-picolyl- (2pica), 3-picolyl- (3pica), 4-picolyl- (4pica)) and thiocyanate have been synthesised and their solid-state structures have been determined. The complexes were all obtained from reactions between the corresponding metals salts and pica ligands with sodium thiocyanate under ambient conditions. Both 3pica and 4pica coordinate to the metal solely through the nitrogen atom of the picolyl group and form discrete tetrahedral [M(NCS)2(pica)2] (3pica; M = Mn, Zn; 4pica; M = Co) and octahedral [M(NCS)2(3pica)4] (M = Co, Fe, Ni) complexes. In addition, one-dimensional N,S-thiocyanate-bridged coordination polymers poly-[M(µ-NCS)2(pica)2] (3pica; M = Cd; 4pica; M = Co, Cd) were obtained. The ligand 2pica gave the discrete octahedral complexes [Co(NCS)2(2pica)2] and [Cd(NO3)2(2pica)2] in which 2pica chelates in a bidentate fashion through its picolyl and carbonyl groups. Magnetic susceptibility measurements on the cobalt(ii) complexes were performed and showed short-range antiferromagnetic coupling for the [Co(NCS)2(4pica)2]n 1D polymer.

Novel organoboron polymers containing transition metals (Ni, Pd, Pt) and pyrazaboles in the main chain were prepared by Cu-catalyzed coupling polymerization. The Ni- and Pt-containing polymers showed MLCT (metal-to-ligand charge transfer) absorption, whereas the Pd-containing polymer did not demonstrate the absorption. Only the Pd-containing polymer exhibited the emission spectrum with a vibronic structure. These differences in the optical properties were studied in detail.

From the viewpoint of crystal engineering, the construction of crystalline polymeric materials requires a rational choice of organic bridging ligands for the self-assembly process. Multicarboxylate ligands are of particular interest due to their strong coordination activity towards metal ions, as well as their various coordination modes and versatile conformations. The structural chemistry of dicarboxylate-based coordination polymers of transition metals has been developed through the grafting of N-containing organic linkers into carboxylate-bridged transition metal networks. A new luminescent two-dimensional zinc(II) coordination polymer containing bridging 2,2-dimethylsuccinate and 4,4′-bipyridine ligands, namely poly[[aqua(μ2-4,4′-bipyridine-κ2N:N′)bis(μ3-2,2-dimethylbutanedioato)-κ4O1,O1′:O4:O4′;κ5O1:O1,O4:O4,O4′-dizinc(II)] dihydrate], {[Zn2(C6H8O4)2(C10H8N2)(H2O)]·2H2O}n, has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction and elemental, IR and thermogravimetric analyses. In the structure, the 2,2-dimethylsuccinate ligands link linear tetranuclear ZnIIsubunits into one-dimensional chains along thecaxis. 4,4′-Bipyridine acts as a tethering ligand expanding these one-dimensional chains into a two-dimensional layered structure. Hydrogen-bonding interactions between the water molecules (both coordinated and free) and carboxylate O atoms strengthen the packing of the layers. Furthermore, the luminescence properties of the complex were investigated. The compound exhibits a blue photoluminescence in the solid state at room temperature and may be a good candidate for potential hybrid inorganic–organic photoactive materials.

The ligand BTIM (1,2,4,5-tetrakis(4,5-dihydro-imidazol-2-yl)benzene) reacts with cobalt(II) salts to form two series of complexes. The 1:1, dinuclear, metallocyclic derivatives [Co2(BTIM)2X2]X2 (X = Cl (I), Br (II)) involve two bis-dentate ligands in a metallocyclic structure with a large unoccupied cavity. The 2:1, binuclear derivatives [Co2(BTIM)X4] (X = Cl (III), Br (IV)) involve two metals bound to a single, bis-bidentate ligand. The crystal and molecular structures of II and III are reported. Compound II crystallized in the monoclinic system, space group P21/c, with a = 13.642(6) Å, b = 11.560(3) Å, c = 18.406(7) Å, β = 101.73(3)° and four formula units per unit cell. Refinement by full-matrix least squares gave final residuals of R = 0.060 and Rw = 0.062. Compound III crystallized in the triclinic system, space group [Formula: see text], with a = 8.367(2) Å, b = 14.254(3) Å, c = 7.649(2) Å, α = 100.99(2)°, β = 101.44(2)°, γ = 106.85(1)° and one formula per unit cell. Refinement by full-matrix least squares gave final residuals of R = 0.052 and Rw = 0.045. In the metallocyclic structure (II) the square-pyramidal cobalt(II) centres are separated by 7.599(4) Å, while in the 2:1 derivative the two tetrahedral cobalt(II) centres have a much larger separation (8.736(3) Å).

Reduction of VCl3(THF)3(THF is tetrahydrofuran) and NbCl4(THF)2by alkali metal pyrene radical anion salts in THF affords the paramagnetic sandwich complexes bis[(1,2,3,3a,10a,10b-η)-pyrene]vanadium(0), [V(C16H10)2], and bis[(1,2,3,3a,10a,10b-η)-pyrene]niobium(0), [Nb(C16H10)2]. Treatment of tris(naphthalene)titanate(2−) with pyrene provides the isoelectronic titanium species, isolated as an (18-crown-6)potassium salt, namelycatena-poly[[(18-crown-6)potassium]-μ-[(1,2-η:1,2,3,3a,10a,10b-η)-pyrene]-titanate(−I)-μ-[(1,2,3,3a,10a,10b-η:6,7-η)-pyrene]], {[K(C12H24O6)][Ti(C16H10)2]}n. The first two compounds have very similar packing, with neighboring molecules arranged orthogonally to one another, such that aromatic donor–acceptor interactions are likely responsible for the specific arrangement. The asymmetric unit contains a half-occupancy metal center η6-coordinated to one pyrene ligand, with the fullM(pyrene)2molecule generated by a crystallographic inversion center. In the titanium compound, the cations and anions are in alternating contact throughout the crystal structure, in one-dimensional chains along the [101] direction. As in the other two compounds, the asymmetric unit contains a half-occupancy Ti atom η6-coordinated to one pyrene ligand. Additionally, the asymmetric unit contains one half of an (18-crown-6)potassium cation, located on a crystallographic inversion center coincident with the K atom. The full formula units are generated by those inversion centers. In all three structures, the pyrene ligands are eclipsed and sandwich the metals in one of two inversion-related sites. These species are of interest as the first isolable homoleptic pyrene transition metal complexes to be described in the scientific literature.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006.
Prof. Will Rees, Committee Member ; Prof. Charles Liotta, Committee Member ; Prof. David Collard, Committee Member ; Prof. Marcus Weck, Committee Chair ; Prof. Kent Barefield, Committee Member.

Poly-N-isopropylacrylamide (PNIPAM) gels grafted to redox-active metal monomers undergo sudden expansion-contraction activity in response to change in environmental conditions, such as temperature, pH, ion concentration, and oxidation states of the metal. The relevance of these conditions to biological systems has garnered attention for PNIPAM-based polymer as potential biomedical materials. Candidate transition metal monomers containing ruthenium and nickel cores were designed and synthesized for copolymerization with NIPAM and cross-linker methylene-bis-acrylamide in order to attain metallopolymer microspheres with a high percentage of metal incorporation. Synthesis of 4-vinyl-4'-methyl-2,2'-bipyridine (vmbpy) was optimized from literature procedures for usage in the metal-containing monomers. Metal-containing monomers were then synthesized, purified, and characterized using electrospray ionization mass spectrometry (ESI-MS), proton nuclear magnetic resonance ( 1 H-NMR), X-ray diffraction, Ultraviolet-Visible light (UV-Vis) spectroscopy, and spectrofluorometry. While the Ru complex was pure and exhibited interesting photochemical properties, lability of the ligands on the Ni monomers resulted in complication of their synthesis. Polymer microspheres of poly(NIPAM-co-vmbpy), the cross-linked copolymer constructed from NIPAM and vmbpy monomers, were synthesized from modified emulsion polymerization procedures. Experimental setup parameters and conditions—such as the methods of injection of initiator and stirring, the time duration for incubating the emulsion, and the initiation temperature—were varied to assess their influences on the material properties of the final product. The polymers were tested for size and morphological uniformity by dynamic light scattering (DLS) and scanning electron microscopy (SEM). While varying the method of initiator injection had no measurable effect on the product, strong mechanical stirring and incubation of the polymer emulsion for 15-25 minutes at 71 °C procured similar polymer products. Consistent properties ensured the polymers' suitability for further material development. Preliminary morphological and spectroscopic characterization was conducted of metallopolymers made from Ru and Ni grafted to PNIPAM. Metallopolymers containing polypyridyl Ru cores exhibited desirable spectroscopic properties and spherical morphology.

The nature of ligands coordinated to the metal ion mostly determines the properties of the inorganic, organometallic or bioinorganic model compounds. The pyrazole is one of the most studied heterocyclic aromatic compounds in coordination chemistry as single ligand or incorporated in polidentate ligands, such as in poly(pyrazolyl)borates (‘scorpionates'), poly(pyrazolyl)alkanes, etc. The great versatility of the pyrazole allows the formation of several ligands with different functionalizations, which mainly influence the geometry and nuclearity of the diverse coordination complexes afforded by the reaction of the pyrazole-based chelating ligands and a metal ion. Another of the most studied heterocyclic aromatic compounds in coordination chemistry is an analogue of pyrazole with two non-adjacent nitrogen atoms, the imidazole, which represents the main structure of the most common and studied N-Heterocyclic carbenes (NHCs), in particular the imidazol‐2‐ylidenes. These general informations arouse curiosity in main features and reactivity, synthesis and coordination modes, potential and ensured applications of various N-donor ligands, such as poly(pyrazolyl)borates or scorpionates, their isoelectronic and isosteric neutral analogues poly(pyrazolyl)alkanes and N-heterocyclic carbenes, presented, thus, in detail, in Chapter 1. The focus on the electronic and steric properties, the coordinating behaviour and several applications of scorpionates metal complexes, the state-of-art on coordination chemistry and reactivity of the poly(pyrazolyl)alkanes derivatives, the advantages of NHCs over phosphines, including ease of handling, minimal toxicity and powerful electron-donating properties, as enhanced stability of their transition metal complexes, which lead to the synthesis of highly active derivatives in homogeneous catalysis, anticipate the research work of this thesis on the nitrogen pyrazole- and imidazole-based ligands and their organometallic compounds. Beginning from Chapter 2, which describes the aims of the research work, all the chapters are divided in four sub-chapters. In the first sub-chapter differently halogen substituted bis- and tris-(pyrazolyl)borate ligands (BpBr3, TpBr3 and TpiPr,4Br) are compared in terms of electron-donor character through their interactions with various ruthenium(II) arene dimers, as also through electrochemical studies. Interestingly, an unexpected dinuclear ionic compound accounted for by its low thermodynamic stability, confirmed by theoretical calculations at the DFT level, due to steric reasons. The second sub-chapter is centered on the synthesis, characterization and crystal structure of the complexes of the second-lowest steric hindrance scorpionate ligand, TpTn, towards CuI, CuII, ZnII and CdII acceptors. A remarkable coordinative aspect of this ligand is pointed out, as well as the thermal and air stability of the relative complexes, confirmed by thermogravimetric and differential thermal analysis (TGA-DTA). By contrast, the interaction between TpTn and PtI2 proceeded through ligand decomposition, affording a monomeric complex. In the third sub-chapter, the varying, different stoichiometries and the N,N-chelating coordination modes of the bis(pyrazolyl)methanes, in particular of the two indazolyl-based regio-isomeric ligands, L1, bis(1H-indazol-1-yl)methane, and L2, bis(2H-indazol-2-yl)methane, toward XI group metal centers are studied. The synthesis and full characterization of analogous adducts of both regio-isomers allow a systematic comparison of their structural and spectral features, depending on the regio-isomeric ligand and counter-ion used, and the reaction conditions employed. The synthesis and characterization of a new series of stable, cationic gold(I/III) NHC complexes, as well as their catalytic activity in five well-established organic gold-mediated transformations, performed at the University of Strasbourg, under guidance of Director of Research Pierre Braunstein and coworkers (Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Universita'© de Strasbourg, France) is described in the fourth sub-chapter. Interestingly, various attempts to synthesize gold(III) NHC bis- or tris-pyridine complexes, as also the comparative behaviour of NHCs respect to phosphine ligands, are presented. Going further on the thesis structure, all the general procedures and experimental data are reported in Chapter 3, while the discussion and elaboration of the results are described in Chapter 4. Concluding remarks and future perspectives are discussed in Chapter 5, whereas all the references and some notes are given in Chapter 6. In Annexes section, the Curriculum Vitae, the List of Pubblications and the Contributions to Congresses are presented.

In this study we synthesized and characterized new complexes containing ((isophthalohyrazide ) N,N (1,3-dithioformylphthalamide)) ligand which prepared from reaction between phathalic acid with thiosemicarbazied in the rate of (2:2) presence of the hydraulic acid with some transition metal (Cr(III),Mn(II),Fe(II), Co(II),Ni(II), Cu(II), Zn(II)). Elemental analyses, FTIR (Fourier transform infrared) and UV-vis spectral investigations, magnetic measurement, conductivity measurement, and 1HNMR for the ligand (L) and some of the complexes have all been used to characterize the complexes. The complexes' stoichiometry has been determined from analytical data to be (1:2) (metal: ligand), and conductance results show that they are (1:2) electrolyte.The electronic spectra and magnetic measurements indicate that the type of complexes [M(L)]Cl2 and [M(L)]Cl3 have a tetrahedral environment around the metal ions.