The isotypic family of the diarsenates MM′As2O7 (M = Sr, Ba; M′ = Cd, Hg)

Abstract

Abstract The diarsenates MM′As2O7 (M = Sr, Ba; M′ = Cd, Hg) were prepared under hydrothermal conditions (~200 °C, autogenous pressure), starting from As2O5 and the corresponding metal oxides or precursor compounds thereof in aqueous solutions. Structure analyses on the basis of single crystal X-ray data revealed the four structures to be isotypic. They are the first diarsenates to crystallize in the triclinic BaZnP2O7 structure type (space group P1̅, Z = 2, a ≈ 5.8 Å, b ≈ 7.3 Å, c ≈ 7.6 Å, α ≈ 101°, β ≈ 91°, γ ≈ 98°). All related MM′As2O7 diarsenates reported so far (M = Sr, Ba, Pb; M′ = Mg, Co, Cu, Zn) crystallize in the monoclinic α-Ca2P2O7 structure type (P21/n, Z = 4). Hence, the size of the divalent M′ cation determines which of the two structure types is adopted.