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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 100 K. Neutron diffraction data at temperatures of 9, 150, 200 and 250 K 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 250 K (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.
|Number of pages||8|
|Journal||Acta Crystallographica. Section A: Foundations of Crystallography|
|Publication status||Published - 2014|
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Seeing Chemical Reactions: Electron Pairing and Energetics Along Pseudo-Reaction Pathways From High-Resolution X-Ray Diffraction Data
1/01/11 → 31/12/13