(NH4)Ga(HAsO4)2 and TlAl(HAsO4)2 - two new RbFe(HPO4)2-type M + M 3+ arsenates

Abstract

The crystal structures of hydrothermally synthesized (T = 493 K, 7–9 d) ammonium gallium bis[hydrogen arsenate(V)], (NH4)Ga(HAsO4)2, and thallium aluminium bis[hydrogen arsenate(V)], TlAl(HAsO4)2, were solved by single-crystal X-ray diffraction. Both compounds crystallize in the common RbFe(HPO4)2 structure type (R\overline{3}c) and share the same tetrahedral–octahedral framework topology that houses the M + cations in its channels. One of the two Tl sites is slightly offset from its ideal position. Strong O—H...O hydrogen bonds strengthen the network.