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Dittrich B.,Institute For Anorganische Und Angewandte Chemie | Matta C.F.,Mount Saint Vincent University | Matta C.F.,Dalhousie University | Matta C.F.,Saint Marys University, Halifax
IUCrJ | Year: 2014

This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug-receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug-receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography. Source

Lubben J.,University of Gottingen | Volkmann C.,University of Gottingen | Edwards A.,Australian Nuclear Science and Technology Organisation | Morgenroth W.,Goethe University Frankfurt | And 3 more authors.
Acta Crystallographica Section A: Foundations and Advances | Year: 2014

The temperature dependence of H-Uiso in N-acetyl-l-4- hydroxyproline monohydrate is investigated. Imposing a constant temperature-independent multiplier of 1.2 or 1.5 for the riding hydrogen model is found to be inaccurate, and severely underestimates H-Uiso below 100K. Neutron diffraction data at temperatures of 9, 150, 200 and 250K provide benchmark results for this study. X-ray diffraction data to high resolution, collected at temperatures of 9, 30, 50, 75, 100, 150, 200 and 250K (synchrotron and home source), reproduce neutron results only when evaluated by aspherical-atom refinement models, since these take into account bonding and lone-pair electron density; both invariom and Hirshfeld-atom refinement models enable a more precise determination of the magnitude of H-atom displacements than independent-atom model refinements. Experimental efforts are complemented by computing displacement parameters following the TLS+ONIOM approach. A satisfactory agreement between all approaches is found. © 2014 International Union of Crystallography. Source

Asrial,Otto Von Guericke University of Magdeburg | Olbrich F.,Institute For Anorganische Und Angewandte Chemie | Spoida M.,Otto Von Guericke University of Magdeburg | Fischer A.,Otto Von Guericke University of Magdeburg | Edelmann F.T.,Otto Von Guericke University of Magdeburg
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2011

The first triorganotin(IV) pentacyanopropenides, [R3Sn(H 2O)2][C3(CN)5] (R = Me (2), nBu (3), Ph (4) were prepared by treatment of Ag[C3(CN)5] (1) with equimolar amounts of R3SnCl in reagent grade THF. In a similar manner, dark red [R3Sn(H2O)2][N{C(CN)C(CN) 2}2] (6) containing the hexacyanoazapentadienyl anion was prepared in 55 % yield. The molecular structure of [Ph3Sn(H 2O)2][C3(CN)5] (4) was determined by X-ray diffraction. The crystal structure consists of separated trigonal-bipyramidal [Ph3Sn(H2O)2]+ cations and nearly planar [C3(CN)5]- anions which are linked through O-H⋯N hydrogen bonds to give a three-dimensional network. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Lubben J.,Institute For Anorganische Und Angewandte Chemie | Bourhis L.J.,Bruker | Dittrich B.,Institute For Anorganische Und Angewandte Chemie | Dittrich B.,Heinrich Heine University Dusseldorf
Journal of Applied Crystallography | Year: 2015

Invariom partitioning and notation are used to estimate anisotropic hydrogen displacements for incorporation in crystallographic refinement models. Optimized structures of the generalized invariom database and their frequency computations provide the information required: frequencies are converted to internal atomic displacements and combined with the results of a TLS (translation-libration-screw) fit of experimental non-hydrogen anisotropic displacement parameters to estimate those of H atoms. Comparison with TLS+ONIOM and neutron diffraction results for four example structures where high-resolution X-ray and neutron data are available show that electron density transferability rules established in the invariom approach are also suitable for streamlining the transfer of atomic vibrations. A new segmented-body TLS analysis program called APD-Toolkit has been coded to overcome technical limitations of the established program THMA. The influence of incorporating hydrogen anisotropic displacement parameters on conventional refinement is assessed. © 2015 International Union of Crystallography. Source

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