New M⁺, M³⁺-arsenates - the framework structures of AgM³⁺(HAsO₄)₂ (M³⁺ = Al, Ga) and M⁺GaAs₂O₇ (M⁺ = Na, Ag)

Abstract

The crystal structures of hydro­thermally synthesized silver(I) aluminium bis­[hydrogen arsenate(V)], AgAl(HAsO₄)₂, silver(I) gallium bis­[hydrogen arsenate(V)], AgGa(HAsO₄)₂, silver gallium diarsenate(V), AgGaAs₂O₇, and sodium gallium diarsenate(V), NaGaAs₂O₇, were determined from single-crystal X-ray diffraction data collected at room temperature. The first two compounds are representatives of the MCV-3 structure type known for KSc(HAsO₄)₂, which is characterized by a three-dimensional anionic framework of corner-sharing alternating M³⁺O₆ octa­hedra (M = Al, Ga) and singly protonated AsO₄ tetra­hedra. Inter­secting channels parallel to [101] and [110] host the Ag⁺ cations, which are positionally disordered in the Ga compound, but not in the Al compound. The hydrogen bonds are relatively strong, with O...O donor-acceptor distances of 2.6262 (17) and 2.6240 (19) Å for the Al and Ga compounds, respectively. The two diarsenate compounds are representatives of the NaAlAs₂O₇ structure type, characterized by an anionic framework topology built of M³⁺O₆ octa­hedra (M = Al, Ga) sharing corners with diarsenate groups, and M⁺ cations (M = Ag) hosted in the voids of the framework. Both structures are characterized by a staggered conformation of the As₂O₇ groups.