The synthesis, crystal structure and vibrational spectra of α-Sr(PO3)2 containing an unusual catena-polyphosphate helix

The phosphate alpha-Sr(PO3)(2) was synthesised as a single-phase crystalline powder starting from strontium carbonate and phosphorous acid at a temperature of 1150 K. alpha-Sr(PO3)(2) crystallises in a novel structure type in which helical PO3- catena-polyphosphate ions interpenetrate a substructure of Sr2+ closely related to cubic diamond (Sr-4(PO3)(8), P2(1), Z = 2, a = 735.37(8), b = 1868.2(2), c = 735.81(8) pm, beta = 90.021(9)degrees). The catena-polyphosphate chains form helices running along [0 10]. Their chain-periodicity is 16 and the length of the repeating unit complies with b = 1868 pm, the chain stretching factor amounts to f(s) = 0.48 and the pitch to radius ratio is xi = 2.49. The vibrational spectra of alpha-Sr(PO3)(2) are also reported. (c) 2005 Elsevier SAS. All rights reserved.