On the temperature dependence of H-U{sub iso} in the riding hydrogen model

Journal Article · Tue Jul 01 00:00:00 EDT 2014 · Acta crystallographica. Section A, Foundations and advances (Online)

DOI:https://doi.org/10.1107/S2053273314010626· OSTI ID:22351156

Lübben, Jens; Volkmann, Christian ^[1]; Grabowsky, Simon ^[2]; Edwards, Alison ^[3]; Morgenroth, Wolfgang ^[4]; Fabbiani, Francesca P. A. ^[5]; Sheldrick, George M. ^[1]; Dittrich, Birger ^[6]

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1. Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, D-37077 Göttingen (Germany)
2. School of Chemistry and Biochemistry, Stirling Highway 35, WA-6009 Crawley (Australia)
3. Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia)
4. Institut für Geowissenschaften, Abteilung Kristallographie, Goethe-Universität, Altenhöferallee 1, 60438 Frankfurt am Main (Germany)
5. GZG, Abteilung Kristallographie, Georg-August Universität, Goldschmidtstrasse 1, 37077 Göttingen (Germany)
6. Institut für Anorganische und Angewandte Chemie, Martin-Luther-King-Platz 6, 20146 Hamburg (Germany)

The temperature dependence of hydrogen U{sub iso} and parent U{sub eq} in the riding hydrogen model is investigated by neutron diffraction, aspherical-atom refinements and QM/MM and MO/MO cluster calculations. Fixed values of 1.2 or 1.5 appear to be underestimated, especially at temperatures below 100 K. The temperature dependence of H-U{sub iso} 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-U{sub iso} 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.

• OSTI ID: 22351156
• Journal Information: Acta crystallographica. Section A, Foundations and advances (Online), Journal Name: Acta crystallographica. Section A, Foundations and advances (Online) Journal Issue: Pt 4 Vol. 70; ISSN 2053-2733; ISSN ACSAD7
• Country of Publication: United Kingdom
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ATOMS
BENCHMARKS
BONDING
DENSITY
ELECTRON DENSITY
HYDROGEN
NEUTRON DIFFRACTION
NEUTRONS
RESOLUTION
SYNCHROTRON RADIATION
SYNCHROTRONS
TEMPERATURE DEPENDENCE
X-RAY DIFFRACTION