Crystal structure analysis, quantum chemistry

DFT calculations were performed on Mo dinitrogen, hydra-zido(2-) and hydrazidium complexes. The calculations are based on available X-ray crystal structures, simplifying the phosphine ligands by PH3 groups. Vibrational spectroscopic data were then evaluated with a quantum chemistry-assisted normal coordinate analysis (QCA-NCA) which involves calculation of the / matrix by DFT and subsequent fitting of important force constants to match selected experimentally observed frequencies, in particular v(NN), v(MN), and 8(MNN) (M = Mo, W). Furthermore time-dependent (TD-) DFT was employed to calculate electronic transitions, which were then compared to experimental UVATs absorption spectra (16). As a result, a close check of the quality of the quantum chemical calculations was obtained. This allowed us to employ these calculations as well as to understand the chemical reactivity of the intermediates of N2 fixation (cf. Section III). 

The basic theories of physics - classical mechanics and electromagnetism, relativity theory, quantum mechanics, statistical mechanics, quantum electrodynamics - support the theoretical apparatus which is used in molecular sciences. Quantum mechanics plays a particular role in theoretical chemistry, providing the basis for the valence theories which allow to interpret the structure of molecules and for the spectroscopic models employed in the determination of structural information from spectral patterns. Indeed, Quantum Chemistry often appears synonymous with Theoretical Chemistry it will, therefore, constitute a major part of this book series. However, the scope of the series will also include other areas of theoretical chemistry, such as mathematical chemistry (which involves the use of algebra and topology in the analysis of molecular structures and reactions) molecular mechanics, molecular dynamics and chemical thermodynamics, which play an important role in rationalizing the geometric and electronic structures of molecular assemblies and polymers, clusters and crystals surface, interface, solvent and solid-state effects excited-state dynamics, reactive collisions, and chemical reactions. 

Labarre JF (1978) Conformational Analysis in Inorganic Chemistry Semi-Empirical Quantum Calculation vs. Experiment 35 1-35 hammers M, Follmann H (1983) The Ribonucleotide Reductases A Unique Group of Metallo-enzymes Essential for Cell Proliferation. 54 27-91 Le Brun NE, Thomson AJ, Moore GR (1997) Metal Centres of Bacterioferritins or Non-Heam-Iron-Containing Cytochromes (>557. 88 103-138 Leciejewicz J, Alcock NW, Kemp TJ (1995) Carboxylato Complexes of the Uranyl Ion Effects of Ligand Size and Coordinat. Geometry Upon Molecular and Crystal Structure. 82 43-84 Lecomte C, see Guilard R (1987) 64 205-268 Lee YJ, see Scheldt WR (1987) 64 1-70 Lehmann H, see Schultz H (1991) 74 41-146... 

In a nutshell, the book amalgamates an analysis of the earlier works of great professors such as Sommerfeld, Slater, Landau and Feynman in a methodological, informative and epistemological way with practical and computational applications. The volumes are layered such that each can be used either individually or in combination with the other volumes. For instance, each volimie reviews quantum chemistry from its level as quantum formalisms in Volume I, as atomic structure and properties in Volume II, as detailed molecular bonding in Volume III, as crystal/solid state (electronic) in Volimie IV, and as pharmacophore activity targeting specific bindings in Voliune V. 

The Wiberg indices (4.137) and atomic covalence (4.140) are called the local properties of the electronic structure of periodic systems. These properties also include AO populations, atomic charges (electrovalencies) and total atomic valences [97]. The analysis of the local properties of the electronic structure in molecular quantum chemistry is very popular as it gives useful information about the chemical bonding. The local properties of the electronic structure of crystals are considered in more detail in Chap. 9. The above consideration holds for the density matrix of the basic domain of the crystal that is, it is assumed that the number N of primitive cells in this domain is so large that the introduction of cyclic boundary conditions virtnaUy does not affect the density matrix of the infinite crystal. 

Phosphazene chemistry is covered separately elsewhere within this volume but three notable papers involving theoretical and computational chemistry methods have been reported. Non-empirical RHF/6-31G and MP2/6-31G quantum chemical methods have been used to calculate the molecular structure of two trichlorophosphazenes (8) and (9). The corresponding geometric parameters obtained from the calculations were compared with XRD analysis data previously reported in the literature. Conformational differences between the two molecules, previously found by XRD analysis of the crystals, were confirmed by non-empirical quantum chemical calculations on the molecules in the free state and the features of their geometry were discussed. A DFT study of the structural organization and infrared spectra of hexakis 4-iV -dichloro(thio)phosphonyl-A -methyl-dia-zobenzene cyclotriphosphazene, a phosphorus-containing dendrimer built... 

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