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Proton disorder in dehydrated hemimorphite - IR spectroscopy and X-ray structure refinement at low and ambient temperatures

Libowitzky, Eugen and Kohler, Thomas and Armbruster, Thomas and Rossman, George R. (1997) Proton disorder in dehydrated hemimorphite - IR spectroscopy and X-ray structure refinement at low and ambient temperatures. European Journal of Mineralogy, 9 (4). pp. 803-810. ISSN 0935-1221.

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Polarized IR absorption spectra of dehydrated hemimorphite single-crystals [Zn_4Si_2O_7(OH)_2] were recorded between 82 and 373 K. The crystal structure, including the proton positions, was refined in space group Imml from single-crystal X-ray data measured at 110 and 298 K. Both methods, as well as electrostatic and crystal chemical considerations, show that the protons of the hydroxide groups are disordered in the structural channels. One proton is located at the line between two O3 atoms (O3•••O3' = 2.99-3.02 Å) thus building up a weak H bond. The corresponding O-H stretching band occurs at ~3530 cm^(-1) and is polarized parallel to ɑ. Due to proton-proton repulsion, the O-H vector of the other H atom deviates from the O3—O3' line. As a consequence, the corresponding IR stretching vibration is observed at ~3600 cm^(-1) and components of this band occur parallel to ɑ and c. The disorder is also reflected by the large anisotropic displacement parameter U_(33) of the O3 atom. To test for a possible low-temperature phase transition (similar to that in natural hemimorphite), birefringence values were determined in (010) and (001) sections between 83 and 373 K. However, the smooth curves do not indicate a transition. This is explained by the lack of an additional proton acceptor (05 of the water molecule in hemimorphite) in the dehydrated phase.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1997 E. Schweizerbart'sche Verlagsbuchhandlung. Received 12 July 1996. Accepted 13 January 1997. Thanks are due to Jung Kim for help with preliminary IR measurements on dehydrated hemimorphite. E.L. appreciates financial support from the "Fonds zur Förderung der wissenschaftlichen Forschung, Austria" during an "Erwin Schrödinger" fellowship, project J01098-GEO. GRR acknowledges support from the National Science Foundation, grant EAR 9218980. The comments of referees K. Langer (Berlin) and A. Eriksson (Uppsala) helped to improve the quality of the manuscript.
Group:UNSPECIFIED, UNSPECIFIED, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Fonds zur Förderung der wissenschaftlichen ForschungUNSPECIFIED
Erwin Schrödinger FellowshipJ01098-GEO
NSFEAR 9218980
Subject Keywords:dehydrated hemimorphite, infrared spectroscopy, crystal structure, proton disorder.
Issue or Number:4
Record Number:CaltechAUTHORS:20130501-152430435
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Official Citation: Eugen Libowitzky, Thomas Kohler, Thomas Armbruster, and George R. Rossman Proton disorder in dehydrated hemimorphite; IR spectroscopy and X-ray structure refinement at low and ambient temperatures Eur J Mineral, August 1997, v. 9, p. 803-810
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38219
Deposited By: Ruth Sustaita
Deposited On:01 May 2013 22:47
Last Modified:03 Oct 2019 04:55

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