Acta Crystallographica Section C

Crystal Structure Communications

Volume 61, Part 9 (September 2005)

inorganic compounds

Acta Cryst. (2005). C61, i90-i93 [doi:10.1107/S0108270105023243]

CsGa(H_1.5AsO₄)₂(H₂AsO₄) and isotypic CsCr(H_1.5AsO₄)₂(H₂AsO₄): decorated kröhnkite-like chains in two unusual hydrogen arsenates

K. Schwendtner and U. Kolitsch

Abstract: Hydrothermally synthesized caesium gallium(III) hydrogen arsenate(V), CsGa(H_1.5AsO₄)₂(H₂AsO₄), (I), and isotypic caesium chromium(III) hydrogen arsenate(V), CsCr(H_1.5AsO₄)₂(H₂AsO₄), (II), represent a new structure type and stoichiometry among M^I-M^III hydrogen arsenates. The crystal structure, determined from single-crystal X-ray diffraction data, is based on an infinite octahedral-tetrahedral chain and can be described as a decorated kröhnkite-like chain. The chains extend parallel to [100] and are separated by ten-coordinated Cs atoms. The hydrogen-bonding scheme comprises one very short symmetry-restricted hydrogen bond, with OO distances of 2.519 (4) and 2.508 (4) Å in (I) and (II), respectively, and two further medium-strong hydrogen bonds, all of which reinforce the connections between adjacent chains. The average Ga-O and Cr-O bond lengths are 1.973 (15) and 1.980 (13) Å, respectively, and the average As-O bond lengths in the two protonated arsenate groups lie within a very narrow range [1.690 (18)-1.69 (3) Å]. The Cs atom is located on a centre of inversion, while the M^III and As2 atoms lie on twofold axes. Relationships to CaBa₂(HPO₄)₂(H₂PO₄)₂ and other compounds containing decorated kröhnkite-type or kröhnkite-like chains are discussed.

Formula: CsGa(H_1.5AsO₄)₂(H₂AsO₄) and CsCr(H_1.5AsO₄)₂(H₂AsO₄)


	Structure factor file (CIF format) (113.6 kbytes) Contains datablock I

	Structure factor file (CIF format) (94.5 kbytes) Contains datablock II

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