Synthesis and Structure of a Calcium Polyphosphate with a Unique Criss-Cross Arrangement of Helical Phosphate Chains
datasetposted on 06.09.2005, 00:00 by Lauren E. Jackson, Benson M. Kariuki, Mark E. Smith, Jake E. Barralet, Adrian J. Wright
We report here the facile synthesis and structural characterization of γ-Ca(PO3)2, a novel polymorph of calcium polyphosphate. The single-step synthesis of this potential biomaterial was achieved using flux methods at 250 °C, yielding a single-phase product stable at room temperature. Single-crystal X-ray diffraction determined the structure to be of monoclinic symmetry (a = 9.5669(2) Å, b = 9.5023(2) Å, c = 10.3717(3) Å, and β = 93.474(2)°, space group Cc), with layers of helical polyphosphate chains directed alternately along the  and [−110] unit cell directions to produce a unique arrangement of criss-cross polyphosphate layers separated by calcium ions. Further structural characterization by MAS-NMR and FT-IR was found to be consistent with this structure. Thermal studies indicated that γ-Ca(PO3)2 is stable up to 690 °C, whereupon it irreversibly converts to the β-Ca(PO3)2 polymorph.