New M(+), M(3+)-arsenates - the framework structures of AgM(3+)(HAsO4)2 (M(3+) = Al, Ga) and M(+)GaAs2O7 (M(+) = Na, Ag).

The crystal structures of hydro-thermally 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 M(3+)O6 octa-hedra (M = Al, Ga) and singly protonated AsO4 tetra-hedra. Inter-secting 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 M(3+)O6 octa-hedra (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.