Acta Crystallographica Section C

Crystal Structure Communications

Volume 60, Part 12 (December 2004)

Acta Cryst. (2004). C60, i113-i116    [doi:10.1107/S0108270104026368]

K₂[HCr₂AsO₁₀]: redetermination of phase II and the predicted structure of phase I

T. J. R. Weakley, E. R. Ylvisaker, R. J. Yager, P. Wu, P. Photinos and S. C. Abrahams

Abstract: Our prediction that phase II of dipotassium hydrogen chromatoarsenate, K₂[HCr₂AsO₁₀], is ferroelectric, based on the analysis of the atomic coordinates by Averbuch-Pouchot, Durif & Guitel [Acta Cryst. (1978), B34, 3725-3727], led to an independent redetermination of the structure using two separate crystals. The resulting improved accuracy allows the inference that the H atom is located in the hydrogen bonds of length 2.555  (5)  Å which form between the terminal O atoms of shared AsO₃OH tetrahedra in adjacent HCr₂AsO₁₀^2- ions. The largest atomic displacement of 0.586  Å between phase II and the predicted paraelectric phase I is by these two O atoms. The H atoms form helices of radius 0.60  Å about the 3₁ or 3₂ axes. Normal probability analysis reveals systematic error in seven or more of the earlier atomic coordinates.

Formula: Two crystals phases of K₂[HCr₂AsO₁₀]

Online 11 November 2004

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