M3+(H2AsO4)(H2As2O7) (M3+ = Al, Ga) and In2(H2AsO4)2(H2As2O7)2: a new layer structure type and a new framework structure type containing the rare H2As2O72− group

Abstract

The crystal structures of hydrothermally synthesized aluminium dihydrogen arsenate(V) dihydrogen diarsenate(V), Al(H2AsO4)(H2As2O7), gallium dihydrogen arsenate(V) dihydrogen diarsenate(V), Ga(H2AsO4)(H2As2O7), and diindium bis[dihydrogen arsenate(V)] bis[dihydrogen diarsenate(V)], In2(H2AsO4)2(H2As2O7)2, 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 M3+O6 octahedra (M = Al, Ga, In) that are connected via one H2AsO4- and two H2As2O72- groups into chains, and further via H2As2O72- groups into layers. In Al/Ga(H2AsO4)(H2As2O7), these layers are interconnected by weak-tomedium-strong hydrogen bonds. In In2(H2AsO4)2(H2As2O7)2, the H2As2O72- 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 H2AsO4- and H2As2O72- groups.