title: An investigation of polyhedral deformation in two mixed-metal diarsenates: SrZnAs₂O₇ and BaCuAs₂O₇.
abstract: Two isostructural diarsenates, SrZnAs2O7 (strontium zinc diarsenate), (I), and BaCuAs2O7 [barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The three-dimensional open-framework crystal structure consists of corner-sharing M2O5 (M2 = Zn or Cu) square pyramids and diarsenate (As2O7) groups. Each As2O7 group shares its five corners with five different M2O5 square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine-coordinated M1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of the M1O9, M2O5 and As2O7 groups of known isostructural diarsenates, adopting the general formula M1(II)M2(II)As2O7 (M1(II) = Sr, Ba, Pb; M2(II) = Mg, Co, Cu, Zn) and crystallizing in the space group P2₁/n, are presented and discussed.
authors.affiliation: University of Belgrade, Faculty of Mining and Geology, Laboratory of Crystallography, Đušina 7, 11000 Belgrade, Serbia.
authors.forename: Sabina
authors.initials: S
authors.lastname: Kovač
authors.affiliation: University of Belgrade, Faculty of Mining and Geology, Laboratory of Crystallography, Đušina 7, 11000 Belgrade, Serbia.
authors.forename: Ljiljana
authors.initials: L
authors.lastname: Karanović
authors.affiliation: Universität Wien, Institut für Mineralogie und Kristallographie, Althansstrasse 14, A-1090 Vienna, Austria.
authors.forename: Tamara
authors.initials: T
authors.lastname: Đorđević
keywords: X-ray diffraction; barium–copper; crystal structure; diarsenates; hydrothermal synthesis; polyhedral deformation; strontium–zinc