Crystal structures of two modifications of sodium pentahydrogendiphosphateNaH5(PO4)(2)

Two crystalline modifications of NaH5(PO4)(2) are obtained by the reaction of Na2CO3 with an excess of orthophosphoric acid. The crystal structures of alpha- and beta-NaH5(PO4)(2) are determined by X-ray diffraction analysis. The crystal data are a = 8.484(4) Angstrom, b = 7.842(3) Angstrom, c = 10. 353(4) Angstrom, beta = 90.50(3)degrees, V = 689.3(3) Angstrom(3), space gr oup P2(1)/c, Z = 4, and R-1 = 0.0250 for the alpha modification and a = 7.1 27(2) Angstrom, b = 13.346(4) Angstrom, c = 7.177(2) Angstrom, beta = 95.5( 2)degrees, V = 679.5(3) Angstrom(3), space group P2(1)/c, Z = 4, and R-1 = 0.0232 for the beta modification. Based of the hydrogen-bond system, the fo rmulas of the alpha and beta modifications can be represented as Na(H2PO4)( H3PO4) and Na[H(H2PO4)(2)], respectively. They correspond to the stable and metastable forms of the compound. (C) 2000 MAIK "Nauka/Interperiodica".