title: K2[HCr2AsO10]: redetermination of phase II and the predicted structure of phase I.
abstract: Our prediction that phase II of dipotassium hydrogen chromatoarsenate, K(2)[HCr(2)AsO(10)], 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) angstroms which form between the terminal O atoms of shared AsO(3)OH tetrahedra in adjacent HCr(2)AsO(10)(2-) ions. The largest atomic displacement of 0.586 angstroms between phase II and the predicted paraelectric phase I is by these two O atoms. The H atoms form helices of radius approximately 0.60 A about the 3(1) or 3(2) axes. Normal probability analysis reveals systematic error in seven or more of the earlier atomic coordinates.
authors.affiliation: Department of Chemistry, University of Oregon, Eugene, OR 97403, USA.
authors.forename: T J R
authors.initials: TJ
authors.lastname: Weakley
authors.forename: E R
authors.initials: ER
authors.lastname: Ylvisaker
authors.forename: R J
authors.initials: RJ
authors.lastname: Yager
authors.forename: P
authors.initials: P
authors.lastname: Wu
authors.forename: P
authors.initials: P
authors.lastname: Photinos
authors.forename: S C
authors.initials: SC
authors.lastname: Abrahams