Synthesis, characterization and crystal structure analysis of an open-framework zirconium phosphate

A series of syntheses in the HF–ZrO2–P2O5–pyridine–H2O system have been performed in an attempt to synthesize novel materials with open zirconium phosphate framework structures. One of the resulting products, designated ZrPOF–pyr (∣(C5H6N)4(H2O)2 ∣ [Zr12P16O60(OH)4F8]), has been characterized by XRD, SEM and TG-DTA, and its crystal structure determined from powder diffraction data using direct methods (Pnnm, a = 19.1595(2) Å, b = 15.1428(1) Å, c = 6.61804(6) Å). The framework structure, consisting of corner sharing ZrO6, ZrO5F, ZrO4F2 octahedra and PO4 and PO3OH tetrahedra, proved to be identical to that of ∣(C5H16N2)2(H2O)6 ∣ [Zr12P16O60(OH)4F8], which had been reported previously. In both structures, the terminal P–OH group is disordered. The non-framework species (pyridinium ion and water molecule) could be located in the channels of the framework. Structure solution was also performed using a charge-flipping algorithm, which makes no symmetry assumptions, to verify that the P–OH disorder is inherent to the material and not a result of an incorrectly assumed space group. The phase is thermally stable to 450 °C, but transforms to another phase at higher temperatures.