NH4[BAsO4F] - A new layer fluoro-boroarsenate with a silicate related topology

The fluoro-boroarsenate NH4[BAsO4F] has been obtained by the melt reaction of NH4H2AsO4, B(OH)3 and LiBF4. The dry reaction mixture, in a 3:3:2 ratio, was treated at 240 °C for 14 days. After cooling to room temperature and washing with hot water, the product was isolated as colourless crystals and powder. The crystal structure was determined by single-crystal X-ray diffraction. The structure consists of [BAsO4F]– layers, separated by ammonium ions, having a unique orientation pattern of the tetrahedra forming the constituent six-membered rings. The topology of the fluoro-boroarsenate layer is related to those of the silicate δ-Na2Si2O5 and the borophosphate Mg(H2O)2[B2P2O8(OH)2]·H2O. NH4[BAsO4F] was further characterised by powder X-ray diffraction, IR spectroscopy and EDX analyses.