Journal ArticleDOI
Testing aspherical atom refinements on small-molecule data sets
N. K. Hansen,Philip Coppens +1 more
Reads0
Chats0
TLDR
In this paper, a generalized aspherical-atom formalism is used to refine X-ray data on silicon, tetracyanoethylene, p-nitropyridine N-oxide and ammonium thiocyanate.Abstract:
X-ray data on silicon, tetracyanoethylene, p-nitropyridine N-oxide and ammonium thiocyanate are refined with a generalized aspherical-atom formalism as introduced by Stewart, but modified to have a spherical valence more similar to the unperturbed HF valence shell. Several types of radial dependences of the multipole functions are tested and criteria are developed for judging the adequacy of the aspherical-atom refinement. The aspherical-atom model leads to a significant decrease in the least-squares error function, a reduction of features in the residual map, and an improvement in thermal parameters when comparison is made with the neutron results or when the rigid-bond postulate proposed by Hirshfeld is applied. Positional parameters are often improved except in the case of terminal atoms for which discrepancies, attributed to correlation between dipole-population and positional parameters, are sometimes observed. Deformation maps based on the aspherical-atom least-squares parameters contain less noise than X -- N maps and benefit from inclusion of calculated values of weak structure amplitudes in the summation. In the cases studied, deformation maps including terms beyond the experimental resolution do not yield additional information.read more
Citations
More filters
Journal ArticleDOI
Crystallographic Computing System JANA2006: General features
TL;DR: JANA2006 as discussed by the authors is a widely used program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/ powder diffraction or on electron diffraction.
Journal ArticleDOI
Hydrogen bond strengths revealed by topological analyses of experimentally observed electron densities
TL;DR: In this article, the topological properties of ρ(r) at the intermolecular critical points of 83 experimentally observed hydrogen bonds [X-H⋯O (X=C,N,O)], using accurate X-ray diffraction experiments, were analyzed.
Journal ArticleDOI
Chemical applications of X-ray charge-density analysis.
TL;DR: 4. Topological Analyses of Experimental Densities and Applications to Molecular Crystals 1599 1.
Journal ArticleDOI
Chemical bonding in transition metal carbonyl clusters: complementary analysis of theoretical and experimental electron densities
Piero Macchi,Angelo Sironi +1 more
TL;DR: In this paper, the electron density distribution in transition metal carbonyl clusters has been analyzed using the quantum theory of atoms in molecules and experimental determinations of electron density in metal-caroline clusters.