Crystal structure of sodium dihydrogen arsenate

Single crystals of the title compound, Na(H2AsO4), were obtained by partial neutralization of arsenic acid with sodium hydroxide in aqueous solution. The crystal structure of Na(H2AsO4) is isotypic with the phosphate analogue and the asymmetric unit consists of two sodium cations and two tetrahedral H2AsO4− anions. Each of the sodium cations is surrounded by six O atoms of five H2AsO4− groups, defining distorted octahedral coordination spheres. In the extended structure, the sodium cations and dihydrogen arsenate anions are arranged in the form of layers lying parallel to (010). Strong hydrogen bonds [range of O...O distances 2.500 (3)–2.643 (3) Å] between adjacent H2AsO4− anions are observed within and perpendicular to the layers. The isotypic structure of Na(H2PO4) is comparatively discussed.