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Revision of the crystal structure of ulrichite, CaCu2+(UO2)(PO4)2·4H2O

Published online by Cambridge University Press:  05 July 2018

U. Kolitsch  and
G. Giester
U. Kolitsch*
Affiliation:
Institut für Mineralogie und Kristallographie, Universität Wien, Geozentrum, Althanstr. 14, A-1090 Wien, Austria
G. Giester
Affiliation:
Institut für Mineralogie und Kristallographie, Universität Wien, Geozentrum, Althanstr. 14, A-1090 Wien, Austria
*
*E-mail: uwe.kolitsch@univie.ac.at
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Abstract

The crystal structure of ulrichite, CaCu2+(UO2)(PO4)2·4H2O (space group P21/c, a = 12.784(3), b = 6.996(1), c = 13.007(3)Å, β = 91.92(1)°, V = 1162.7(4)Å3, Z = 4) was redetermined using X-ray diffraction data measured from a twinned crystal with Mo-Kα radiation and a CCD area detector (2510 unique reflections with Fo > 4σ(Fo), R1 = 8.8%). Ulrichite crystallizes in space group P21/c rather than C2/m reported previously. The newly determined atomic positions give reasonable coordination polyhedra. One unique Ca atom is irregularly coordinated by eight O atoms (<Ca–O> = 2.46 Å). One unique U atom shows a {2+5} coordination with characteristic bond angles and lengths (1.806(11)Å, 1.842(12)Å and five bonds between 2.252(15) and 2.441(11)Å). Furthermore, the structure contains groups in which strongly elongated CuO6 ‘octahedra’ (also describable as CuO4 squares) are corner-linked to two PO4 tetrahedra via two opposite, equatorial O atoms. Edge- and corner-sharing UO7, CaO8 and PO4 polyhedra form heteropolyhedral sheets parallel to (001) that are linked to adjacent sheets via the CuO6 ‘octahedra’ and hydrogen bonds.

Keywords

ulrichitecrystal structuretwinninguraniumphosphates
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 6 , December 2001 , pp. 717 - 724
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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