Synthesis of two modifications of NH4 2SeO4 H3PO4 and their crystal structure as probed by x ray and neutron diffraction

The alpha and beta modifications of NH 4 2 SeO 4 H 3 PO 4 are obtained by crystallization from aqueous solution of NH 4 2 SeO 4 and H 3 PO 4 at room temperature and 60 degrees C, respectively. X ray and neutron diffraction analysis of alpha NH 4 2 SeO 4 H 3 PO 4 shows that the hydrogen atom distribution in the crystal structure corresponds to the occurrence of SeO 4 2 bicharged anions and H 3 PO 4 molecules. A similar distribution, but with a less intricate system of hydrogen bonds, is also found by X ray crystallography for beta NH 4 2 SeO 4 H 3 PO 4 . The crystal structures of alkali metal and ammonium biselenophosphates and bisulfophosphates are compared