Synthesis and Structure of a Calcium Polyphosphate with a Unique Criss-Cross Arrangement of Helical Phosphate Chains

We report here the facile synthesis and structural characterization of γ-Ca(PO 3 ) 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 [110] 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(PO 3 ) 2 is stable up to 690 °C, whereupon it irreversibly converts to the β-Ca(PO 3 ) 2 polymorph.