Literatura académica sobre el tema "Boron-Nitrogen Compounds"

Abstract Atropisomerism owing to hindered rotation about the N-aryl bond is observed in 4,5-diethyl-2,2,3-trimethyl-1-(o-trifluormethyl)phenyl-2,5-dihydro-1H-1,2,5-azasila-(2) and -azastanna-boroles (5). The compounds 2 and 5 are characterized by elemental analysis, mass spectra and 1H, 11B, 13 C, 29Si and119Sn NMR. The ortho-trifluoromethyl group serves as an additional NMR spectroscopic probe because of “through space” 19F-1H and 19F-13C spin spin coupling. Compound 5 is the first derivative of a 2,5-dihydro-1H-1,2,5-azastannaborol.

The boron and nitrogen nuclear quadrupole double resonance spectra of several ring compounds with transannular boron-nitrogen bonds are reported. The electron donation from nitrogen to boron as seen by their quadrupole coupling parallels the boron-nitrogen bond lengths. One of the compounds exhibits a transannular valence topomerisation between two identical boron-nitrogen pairs in solution which is frozen in the solid state but may possibly exist in a preformed state of this equilibrium from its quadrupole coupling. The oxygen-boron π-bond in boroxines, whose extent is deduced from the quadrupole coupling in one of the compounds with a boroxine-like structure at boron and in (PhBO)3, is approximately half as strong as the nitrogen-boron π-bond in borazine.

Wood fiber and its products are modified to increase fire and bio-resistance. The best results are achieved by using modifiers that enter into chemical interaction with the hydroxylated substrate, forming the organic matrix of the materials. The purpose of the research described in the article was to study the possibility of using boron-nitrogen compounds to modify cellulose and cellulose-containing materials to improve the performance, bio- and fire-protective properties of construction materials, as well as to optimize the consumption of boron-nitrogen compounds. As a result of the research, it was found that the boron-nitrogen compounds used in the compositions developed here chemically interact with hydroxyl groups at the C6-atom of cellulose. The chemical interaction of boron-nitrogen compounds with cellulose is an inter-crystalline process occurring without destruction of the crystal structure of the substrate since the modifier molecules bind with the more accessible hydroxyl groups of the amorphous regions of cellulose. Thus, surface modification with boron-nitrogen compounds does not result in accelerated aging of cellulose-containing materials and loss of strength but, on the contrary, increases the durability of wooden structures.

Boron possesses the second greatest heating value of any element that can be adopted as an energetic material in the processing of propellants and explosives. It has become the first choice as a high energy fuel for solid fuel-rich propellants because of its advantages of high theoretical combustion heat. In the actual condition, the combustion efficiency of boron-containing fuel-rich propellants is low, and the potential energy of boron cannot be fully utilized. The compound containing-boron can be used as a new way to improve the combustion efficiency of fuel-rich propellants. In this paper, the progress in the synthesis of energetic borides is reviewed from the perspectives of molecular design, synthesis strategy and route optimization. The situation of the synthesis methods of energetic borides (nitrogen-rich boron esters, poly(azole)borates, nitroboranes, nitrogen-rich borazines and azide boron compounds) is reviewed. The research focus and development trend of various boron compounds are analyzed, and the potential application prospect in the propellant is investigated.

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2007.
In this study, ten selected boron-nitrogen compounds and three borane carbonyl complexes were investigated by a number of computational methods. It is well known that the B-N dative bond is shorter in the solid state than in the gas phase. The B-CO distance, on the other hand, displays the opposite effect. Quantum mechanical techniques at the Hartree-Fock, Møller-Plesset second-order and Density Functional Theory level were used to calculate the geometries of the isolated molecules and to compare them with those found in molecular clusters built to model the solid state. It was found that calculated geometries were very sensitive to the choice of the basis set. The effects of dipole-dipole interactions were further investigated by applying an external electric field with varying strength to isolated molecules, and by replacing the central molecule in a cluster with a different compound. The B-N bond was found to respond much more to the applied field than the B-CO bond. An effort was made to correlate the lengthening or shortening of the dative bond to the strength of the crystal field, the latter being calculated classically from point charges. Unfortunately, large differences were noted between the charges calculated with common methods like Mulliken or Merz-Kollman-Singh. Furthermore, an analysis of 67 crystal structures taken from the Cambridge Structural Database did not reveal a correlation between the length of the B-N bond and the crystal field calculated with Charge Equilibration charges. Finally, a valence force field was developed for H3N-BH3. It was shown that a much better fit of the vibrational spectrum can be obtained if the B-N stretching mode is assigned to the 603 cm-1 band rather than the peak observed at 968 cm-1.

Novel non-toxic and environmentally friendly pyrotechnic formulations have been developed and investigated. A series of nitrogen-rich metal salts and energetic boron-based compounds have been synthesized, characterized and tested as red, green and blue colorants in pyrotechnic compositions.

Replacing nonpolar homodiatomic C=C unit in a fully carbon -conjugated system with an isoelectronic polar heterodiatomic B-N fragment is an active area of research. The first BN/CC isosterism was demonstrated seven decades ago. In the following decades, a significant amount of research effort has been devoted to understand the nature of chemical bonding between boron and nitrogen. Although, BN/CC isosterism is known for seven decades, surprisingly, the knowledge about the solid-state structure and optical properties of aminoboranes are scarce in literature. In modern days luminescent materials find numerous applications in display and lighting technologies, security systems, sensing and biological investigations. Thus, the main goal of this thesis is the design and development of novel aminoborane based organic materials that exhibit bright luminescence in the solid state. By exploiting BN/CC isosterism, we have developed new materials which are prototypes and exhibit interesting properties such as aggregation-induced emission and stimuli-responsive luminescence characteristics. Boron-nitrogen chemistry not only provides a rational design for smart materials but also enhances our understanding of the structure-property correlations in the solid state. This thesis contains 7 chapters and the content of each chapter is described below. Chapter 1 The first chapter provides an introduction to the theme of the thesis and presents a general review of boron based donor-acceptor systems with special emphasis on BN/CC isosterism. Replacement of C=C units by an isoelectronic B–N units in acyclic/cyclic π-systems and their potential applications in various fields are discussed. In addition, advances in the new frontier areas, such as aggregation-induced emission, mechanochromism and triboluminescence are discussed in brief. Chapter 2 The second chapter deals with the general experimental techniques and synthetic procedures utilized in this work. Chapter 3 Replacing homodiatomic C=C in polyaryl systems with an isoelectronic heterodiatomic B─N unit is a powerful strategy for rational design and construction of novel materials with versatile properties. In chapter 3, we uncover for the first time the intriguing aggregation-induced emission enhancement (AIEE) properties of four tetra-arylaminoboranes (TAAB) 3.1-3.4 in which the C=C fragment of the tetra-arylethene molecule is replaced by the isoelectronic B─N unit. The dipole moments of these compounds are fine-tuned by judiciously placing amine donor(s) on the aryl groups attached to nitrogen. The optical properties are greatly influenced by the number of amine donor(s) on the B─N fragment. Compounds 3.1-3.4 are weakly emissive in dilute solutions, but are strongly emissive in aggregated/condensed state. Compounds with strong amine donor(s) on B─N fragment exhibit reversible mechanofluorochromism. The experimental observations are corroborated by quantum mechanical calculations. Chapter 4 The synthesis, structure and intriguing optical characteristics of four new polyaromatic aminoboranes (4.1-4.4) bearing bis(mesityl)boron (Mes2B) as electron accepting unit(s) and diphenylamine (Ph2N) as electron donating unit(s) are reported in this chapter. These compounds are strongly fluorescent in the solid state. Crystalline samples of 4.1 and triarylborane decorated aminoboranes 4.3 and 4.4 were found to be blue emitters in the solid state. Compounds 4.1 and 4.2 showed aggregation-induced emission (AIE) and aggregation-induced emission color switching, respectively, while 4.3 and 4.4 exhibited aggregation-induced emission enhancement. Compounds 4.1 and 4.2 showed fascinating mechanofluorochromism upon grinding and such fluorescence changes are due to a crystalline–amorphous phase transition, as confirmed by powder X-ray diffraction studies (PXRD). Interestingly, a ground sample of 4.2 was found to be stable and did not revert back upon removal of external stress even after the sample was kept over a long period of time under ambient conditions (more than 6 months). “IPC” was written on a substrate of 4.2, and the part that was touched showed fluorescence different from the rest of the substrate, which could be erased by heating. This result opens up the possibility of using 4.2 for rewritable data storage devices. The effect of steric and electronic factors on the optical properties of molecules was corroborated by DFT computational studies. Chapter 5 Development of metal-free room temperature organic phosphorescent materials is emerging as highly attractive technology; however, several challenges remain in this area. We report in this chapter a new BN system, tetraarylaminoborane tethered with vinylpyridene units (5.1) and its corresponding photodimerized product (5.2) obtained by [2+2] cycloaddition of olefinic bonds in a single crystal to single crystal (SCSC) transformation upon exposure to sun light within a very short time span of 1 hr. The reaction occurs in the solid state with complete conversion; however, there is no reaction in solution. The photodimerization is highly regioselective and irreversible under thermal conditions. Compounds 5.1 and 5.2 show distinct optical features in the solid state with contrast emission colours under UV light illumination and room temperature phosphorescence as confirmed by TRF measurements. DFT and TD-DFT calculations were performed to support the experimental observations. Chapter 6 This chapter deals with the synthesis of the molecular siblings 6.1 (10-(dimesitylboryl)phenothiazine) and 6.2 (10-(bis(2,6-dimethylphenyl)boryl)phenothiazine) with multifunctional characteristics such as aggregation-induced emission (AIE), triboluminescence (TL), mechanofluorochromism and temperature sensing. Though 6.1 and 6.2 are structurally similar, their optical characteristics are quite different. The emission characteristics of aggregates of 6.1 in 1:9 THF-water mixtures are sensitive to temperature while the aggregates of 6.2 are not so. Compound 6.1 showed luminescence color changes with mechanical stress, whereas 6.2 was insensitive to mechanical grinding. Relatively loose packing of 6.1 in the solid state makes it prone to mechanical forces and this could be a possible reason for its mechanofluorochromic properties. Crystals of 6.2 exhibited greenish yellow color triboluminescence (TL) when they were crushed with mild force. The polar non-centrosymmetric space group (R3c) of crystal 6.2 may be responsible for its TL behavior. No TL was observed for the crystals of 6.1 Chapter 7 Design, synthesis and structural characterization of borylated aryl amines, Mes2BAr {Ar = C6(CH3)4NR2 (7.1, 7.4); C6H4NR2 (7.2, 7.5); C6H3(NR2)2 (7.3, 7.6); R=H or CH3} and their optical properties are reported in this chapter. In these compounds, bright solid state emission with emission color tunability has been realized. The solid state luminescence characteristics of 7.1 and 7.3 are sensitive to mechanical stress with distinct emission color changes. Multiple strong intermolecular hydrogen bonds ((N-HN and N-H) accompanied by subtle conformational changes play a significant role in the piezochromic response. PXRD and FT-IR spectroscopic studies and insensitivity of substituted derivatives to mechanical stress support the above inference. Interestingly, compound 7.3 crystallized in two different polymorphic forms 7.3BP and 7.3GP, which showed distinct luminescence, i.e., green and blue color under UV light. Such changes are due to their distinct hydrogen-bond network assembly in the solid state. Quantum mechanical calculations are performed in order to corroborate the optical properties.

Under the section on “Soil Aeration” (Chapter 4), it was explained that all living plants respire. This is the process where oxygen is used to burn food into carbon dioxide and water. Now we will consider another process used by green plants to manufacture their own food called “photosynthesis,” In photosynthesis, carbon dioxide and water are used along with light energy in the plant cell chloroplasts (containing chlorophyll) to produce their own food (carbohydrates) with oxygen produced as a by-product: Although this seems to be the opposite process from respiration, yet there are differences. Note that light energy and chlorophyll are required in photosynthesis. Chlorophyll is the green coloring matter in plants. There are, at present, seventeen (17) elements that plants need to grow and complete their life cycle. These are called “essential elements” or “nutrients.” Usually an essential element cannot be completely replaced by any other element. There are also four (4) other elements, although not essential, that help plants to grow better. These are called “functional” or “metabolic.” To remember all of these elements a memory aid, a mnemonic (the first letter is silent) has been devised. The 21 elements used by plants, carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium (K), nitrogen (N), sulfur (S), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), molybdenum (Mo), vanadium (V), boron (B), silicon (Si), chlorine (Cl), and sodium (Na), can be listed in their chemical abbreavtions with the mnemonic below: The elements carbon, hydrogen, and oxygen can be considered nonmineral elements, as these are obtained by plants from air and water (O2, CO2, and H2O) and not from the soil. Plants use these three elements to form simple carbohydrates from which large amounts of more complex plant compounds (about 95% of plant tissue) are formed. There is little control of these elements by man, except for water. Supplemental CO2 has been provided to plants to increase photosynthesis by using solid CO2 (dry ice), hut this has not proved economical.