X-Ray Charge Densities and Chemical Bonding

Author(s):  
Philip Coppens

This book deals with the electron density distribution in molecules and solids as obtained experimentally by X-ray diffraction. It is a comprehensive treatment of the methods involved, and the interpretation of the experimental results in terms of chemical bonding and intermolecular interactions. Inorganic and organic solids, as well as metals, are covered in the chapters dealing with specific systems. As a whole, this monograph is especially appealing because of its broad interface with numerous disciplines. Accurate X-ray diffraction intensities contain fundamental information on the charge distribution in crystals, which can be compared directly with theoretical results, and used to derive other physical properties, such as electrostatic moments, the electrostatic potential and lattice energies, which are accessible by spectroscopic and thermodynamic measurements. Consequently, the work will be of great interest to a broad range of crystallographers and physical scientists.

Author(s):  
John Meurig Thomas

A non-mathematical account of the discovery of X-ray diffraction by von Laue and its use as a new kind of high-resolution microscopy by W. L. Bragg is given. There follows a simple explanation of how the electron densities in various regions of any molecule that can be crystallized can be retrieved from its X-ray diffraction pattern. Also, it is explained how the molecular weight of the molecule can be determined from straightforward measurements of the diffraction and the density of the crystal. The identity of the elements in a crystal, as well as the nature of the chemical bonding between them, may also be derived from measurement of the electron density distribution within it. The importance of Bragg’s Law, relating X-ray pattern to interatomic distance, is demonstrated, and initial applications of it by Bragg and Pauling are given.


Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4227
Author(s):  
Alessandro Cossard ◽  
Silvia Casassa ◽  
Carlo Gatti ◽  
Jacques K. Desmarais ◽  
Alessandro Erba

The chemistry of f-electrons in lanthanide and actinide materials is yet to be fully rationalized. Quantum-mechanical simulations can provide useful complementary insight to that obtained from experiments. The quantum theory of atoms in molecules and crystals (QTAIMAC), through thorough topological analysis of the electron density (often complemented by that of its Laplacian) constitutes a general and robust theoretical framework to analyze chemical bonding features from a computed wave function. Here, we present the extension of the Topond module (previously limited to work in terms of s-, p- and d-type basis functions only) of the Crystal program to f- and g-type basis functions within the linear combination of atomic orbitals (LCAO) approach. This allows for an effective QTAIMAC analysis of chemical bonding of lanthanide and actinide materials. The new implemented algorithms are applied to the analysis of the spatial distribution of the electron density and its Laplacian of the cesium uranyl chloride, Cs2UO2Cl4, crystal. Discrepancies between the present theoretical description of chemical bonding and that obtained from a previously reconstructed electron density by experimental X-ray diffraction are illustrated and discussed.


Author(s):  
Marieta Muresan-Pop ◽  
Sergiu Macavei ◽  
Alexandru Turza ◽  
Gheorghe Borodi

Four new solvates of the anti-HIV compound etravirine [systematic name: 4-({6-amino-5-bromo-2-[(4-cyanophenyl)amino]pyrimidin-4-yl}oxy)-3,5-dimethylbenzonitrile, C20H15BrN6O] with dimethyl sulfoxide (C2H6OS, two distinct monosolvates), 1,4-dioxane (C4H8O2, the 0.75-solvate) and N,N-dimethylacetamide (C4H9NO, the monosolvate), which exhibit conversion to the same anhydrous etravirine phase upon desolvation, and a stable etravirinium oxalate salt {6-amino-5-bromo-4-(4-cyano-2,6-dimethylphenoxy)-2-[(4-cyanophenyl)amino]pyrimidin-1-ium hemioxalate, C20H16BrN6O+·0.5C2O4 2−} were obtained. The crystal structures were solved by single-crystal X-ray diffraction and analyzed by powder X-ray diffraction, and the intermolecular interactions were explored by Hirshfeld surface analysis. Lattice energies were evaluated using the atom–atom force field Coulomb–London–Pauli (AA CLP) approximation, which distributes the total energy as four separate contributions: Coulombic, polarization, dispersion and repulsion. The formation of the solvates and the oxalate salt was further characterized by thermal analysis and IR spectroscopy.


2019 ◽  
Vol 2019 (6) ◽  
pp. 875-884 ◽  
Author(s):  
Maxim G. Chegerev ◽  
Alexandr V. Piskunov ◽  
Kseniya V. Tsys ◽  
Andrey G. Starikov ◽  
Klaus Jurkschat ◽  
...  

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