Location of hydrogen atoms in hydronium jarosite

Spratt, Henry J., Avdeev, Maxim, Pfrunder, Michael C., McMurtrie, John, Rintoul, Llewellyn, & Martens, Wayde N. (2014) Location of hydrogen atoms in hydronium jarosite. Physics and Chemistry of Minerals, 41(7), pp. 505-517.

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Various models for the crystal structure of hydronium jarosite were determined from Rietveld refinements against neutron powder diffraction patterns collected at ambient temperature and also single-crystal X-ray diffraction data. The possibility of a lower symmetry space group for hydronium jarosite that has been suggested by the literature was investigated. It was found the space group is best described as R3¯m, the same for other jarosite minerals. The hydronium oxygen atom was found to occupy the 3¯m site (3a Wyckoff site). Inadequately refined hydronium bond angles and bond distances without the use of restraints are due to thermal motion and disorder of the hydronium hydrogen atoms across numerous orientations. However, the acquired data do not permit a precise determination of these orientations; the main feature up/down disorder of hydronium is clear. Thus, the highest symmetry model with the least disorder necessary to explain all data was chosen: The hydronium hydrogen atoms were modeled to occupy an m (18 h Wyckoff site) with 50 % fractional occupancy, leading to disorder across two orientations. A rigid body description of the hydronium ion rotated by 60° with H–O–H bond angles of 112° and O–H distances of 0.96 Å was optimal. This rigid body refinement suggests that hydrogen bonds between hydronium hydrogen atoms and basal sulfate oxygen atoms are not predominant. Instead, hydrogen bonds are formed between hydronium hydrogen atoms and hydroxyl oxygen atoms. The structure of hydronium alunite is expected to be similar given that alunite supergroup minerals are isostructural.

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ID Code: 70616
Item Type: Journal Article
Refereed: Yes
Keywords: Hydronium jarosite, Neutron diffraction, Crystal structure, Orientational disorder, Rietveld refinement, Hydrogen location
DOI: 10.1007/s00269-014-0661-5
ISSN: 1432-2021
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > PHYSICAL CHEMISTRY (INCL. STRUCTURAL) (030600) > Structural Chemistry and Spectroscopy (030606)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2014 Springer-Verlag Berlin Heidelberg
Copyright Statement: The final publication is available at Springer via http://dx.doi.org/10.1007/s00269-014-0661-5
Deposited On: 29 Apr 2014 23:50
Last Modified: 11 Feb 2015 00:41

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