New M (+), M (3+)-arsenates – the framework structures of AgM (3+)(HAsO(4))(2) (M (3+) = Al, Ga) and M (+)GaAs(2)O(7) (M (+) = Na, Ag)

The crystal structures of hydro­thermally synthesized silver(I) aluminium bis­[hydrogen arsenate(V)], AgAl(HAsO(4))(2), silver(I) gallium bis­[hydrogen arsenate(V)], AgGa(HAsO(4))(2), silver gallium diarsenate(V), AgGaAs(2)O(7), and sodium gallium diarsenate(V), NaGaAs(2)O(7), 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(HAsO(4))(2), which is characterized by a three-dimensional anionic framework of corner-sharing alternating M (3+)O(6) octa­hedra (M = Al, Ga) and singly protonated AsO(4) 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 NaAlAs(2)O(7) structure type, characterized by an anionic framework topology built of M (3+)O(6) 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 As(2)O(7) groups.