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Experimental Charge-density Studies (experimental + charge-density_studies)
Selected AbstractsTowards the best model for H atoms in experimental charge-density refinementACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2009Anna A. Hoser The consequences of different treatments of H atoms in experimental charge-density studies are discussed. Geometric and topological parameters obtained after applying four different H-atom models in multipolar refinement on high-resolution X-ray data only were compared with the results obtained for a reference joint high-resolution X-ray/neutron refinement. The geometry and the topological critical point and integrated parameters closest to the reference values were obtained after a mixed refinement (high-order refinement of heavy atoms, low-angle refinement of H atoms and elongation of the X,H distance to the average neutron bond lengths) supplemented by an estimation of the anisotropic thermal motions of H atoms using the SHADE program. Such a procedure works very well even for strong hydrogen bonds. The worst fit to the reference results for both critical point and integrated parameters was obtained when only the standardization to the average neutron X,H distances was applied. The non-H-atom parameters are also systematically influenced by the H-atom modeling. In order to compare topological and integrated properties calculated for H and non-H atoms in multipolar refinement when there are no neutron data, the same treatment of H atoms (ideally the mixed refinement + estimated anisotropic atomic displacement parameters for H atoms) should be applied. [source] Bond catastrophes in rhodium complexes: experimental charge-density studies of [Rh(C7H8)(PtBu3)Cl] and [Rh(C7H8)(PCy3)Cl]ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Hazel A. Sparkes Rhodium complexes have potential uses in both catalysis and promoting the cleavage of C,C bonds. In order to further our understanding of these species and their potential applications, it is vital to obtain insight into the bonding within the species, particularly the Rh,C interactions, and to this end experimental charge-density studies have been undertaken on the title complexes. High-resolution single-crystal datasets to sin,,/, = 1.06,Å,1 were obtained at 100,K and analysed using Bader's `Atoms in Molecules' (AIM) approach. The results of the studies have provided unique insights into the bonding involving rhodium and highlight the importance of undertaking such investigations for transition metal compounds. [source] Trans -cinnamic acid and coumarin-3-carboxylic acid: experimental charge-density studies to shed light on [2,+,2] cycloaddition reactionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009Judith A. K. Howard As part of an ongoing series of experimental charge-density investigations into the intra- and intermolecular interactions present in compounds which undergo solid-state [2,+,2] cycloaddition reactions, the charge-density analyses of trans -cinnamic acid and coumarin-3-carboxylic acid are reported. Thus, high-resolution single-crystal X-ray diffraction data were recorded at 100,K for trans -cinnamic acid (sin,,/,max = 1.03,Å,1) and coumarin-3-carboxylic acid (sin,,/,max = 1.19,Å,1). In addition to the anticipated O,H...O hydrogen bonds weak C,H...O interactions were identified in both structures along with very weak intermolecular interactions between pairs of molecules that undergo solid-state [2,+,2] cycloaddition reactions upon irradiation. [source] | ||||||||||