Tuesday, October 09, 2007

Hiyam's Journal Update

Chem. Mater., 19 (21), 5067 -5073, 2007.
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, -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) Å, b = 19.981(2) Å, c = 6.7535(7) Å, = 94.514(2), V = 1840.7(3) Å3, 4929 structure factors, 326 parameters, R[F2 > 2(F2)] = 0.0561] was determined from a combined X-ray diffraction and solid-state 31P 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. 31P chemical shift parameters were determined for all eight phosphorus positions, and peaks were assigned to the two different polyphosphate chains. -(CaPO3)2 was further characterized by IR and Raman spectroscopy.

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