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, α-Ca(PO 3 ) 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) Å, b = 19.981(2) Å, c = 6.7535(7) Å, β = 94.514(2)°, V = 1840.7(3) Å 3, 4929 structure factors, 326 parameters, R [ F 2 > 2σ( F 2 )] = 0.0561] was determined from a combined X-ray diffraction and solid-state 31 P 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. 31 P chemical shift parameters were determined for all eight phosphorus positions, and peaks were assigned to the two different polyphosphate chains. α-(CaPO 3 ) 2 was further characterized by IR and Raman spectroscopy.