Synthesis, crystal structure, and characterization (vibrational and solid-state 31P MAS NMR spectroscopy) of the high-temperature modification of calcium catena-polyphosphate(V)

The metastable high-temperature modification of calcium catena-polyphosphate, alpha-Ca(PO3)(2), was obtained by quenching the recrystallized sample from a temperature shortly below the melting. point. The novel crystal structure [Cc, Z = 16, a = 13.6835(14) angstrom, b = 19.981(2) angstrom, c = 6.7535(7) angstrom, beta = 94.514(2)degrees, V = 1840.7(3) angstrom(3), 4929 structure factors, 326 parameters, R[F-2 > 2 sigma(F-2)] = 0.0561] was determined from a combined X-ray diffraction and solid-state P-31 NMR study. The unit cell features a pseudoinversion center. The structure contains 4 Ca, 8 P, and-24 O atoms in the asymmetric unit and is composed of two different kinds of polyphosphate chains, with one helical chain running with a periodicity P of 12 parallel to [101], whereas the second chain is corrugated and directed parallel to [001] with a periodicity P of 4. P-31 chemical shift parameters were determined for all eight phosphorus positions, and peaks were assigned to the two different polyphosphate chains. alpha-(CaPO3)(2) was further characterized by IR and Raman spectroscopy.