M⁺M³⁺₂As(HAsO₄)₆ (M⁺M³⁺ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO₆ octahedra

Abstract

The crystal structures of hydro­thermally synthesized (T = 493 K, 7 d) thallium(I) digallium arsenic(V) hexa­kis­[hydrogenarsenate(V)], TlGa₂As(HAsO₄)₆, caes­ium digallium arsenic(V) hexa­kis­[hydrogenarsenate(V)], CsGa₂As(HAsO₄)₆, and caesium dialuminium arsenic(V) hexa­kis­[hydrogenarsenate(V)], CsAl₂As(HAsO₄)₆, were solved by single-crystal X-ray diffraction. The three compounds are isotypic and adopt the structure type of RbAl₂As(HAsO₄)₆ (R\overline{3}c), which itself represents a modification of the RbFe(HPO₄)₂ structure type and consists of a tetra­hedral-octa­hedral framework in which the slightly disordered M⁺ cations are located in channels. The three new compounds contain AsO₆ octa­hedra assuming the topological role of M³+O₆ octa­hedra. The As-O bond lengths are among the shortest As-O bond lengths known so far in AsO₆ octa­hedra.