M(HAsO)(HAsO) (M = Al, Ga) and In(HAsO)(HAsO): a new layer structure type and a new framework structure type containing the rare HAsO group.

The crystal structures of hydrothermally synthesized aluminium dihydrogen arsenate(V) dihydrogen diarsenate(V), Al(HAsO)(HAsO), gallium dihydrogen arsenate(V) dihydrogen diarsenate(V), Ga(HAsO)(HAsO), and diindium bis[dihydrogen arsenate(V)] bis[dihydrogen diarsenate(V)], In(HAsO)(HAsO), were determined from single-crystal X-ray diffraction data collected at room temperature. The first two compounds are representatives of a novel sheet structure type, whereas the third compound crystallizes in a novel framework structure. In all three structures, the basic building units are MO octahedra (M = Al, Ga, In) that are connected via one HAsO and two HAsO groups into chains, and further via HAsO groups into layers. In Al/Ga(HAsO)(HAsO), these layers are interconnected by weak-to-medium-strong hydrogen bonds. In In(HAsO)(HAsO), the HAsO groups link the chains in three dimensions, thus creating a framework topology, which is reinforced by weak-to-medium-strong hydrogen bonds. The three title arsenates represent the first compounds containing both HAsO and HAsO groups.