| Abstract
| - The metastable high-temperature modification of calcium catena-polyphosphate, α-Ca(PO3)2, wasobtained 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) Å3, 4929 structure factors, 326 parameters, R[F2> 2σ(F2)] = 0.0561] wasdetermined from a combined X-ray diffraction and solid-state 31P NMR study. The unit cell features apseudoinversion center. The structure contains 4 Ca, 8 P, and 24 O atoms in the asymmetric unit and iscomposed of two different kinds of polyphosphate chains, with one helical chain running with a periodicityP of 12 parallel to [101], whereas the second chain is corrugated and directed parallel to [001] with aperiodicity P of 4. 31P chemical shift parameters were determined for all eight phosphorus positions, andpeaks were assigned to the two different polyphosphate chains. α-(CaPO3)2 was further characterized byIR and Raman spectroscopy.
- The metastable polymorph α-Ca(PO3)2 exists in a narrow temperature range shortly below the melting point. The noncentrosymmetric crystal structure was determined from a combined X-ray diffraction and solid-state 31P MAS NMR study. Two different kinds of polyphosphate chains are present in the structure, viz., one helical chain with a repeating unit of 12 PO4 tetrahedra and a second corrugated chain with a repeating unit of 4 PO4 tetrahedra.
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