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Solid-State Crystal-to-Crystal Phase Transitions and Reversible Structure–Temperature Behavior of Phosphovanadomolybdic Acid, H5PV2Mo10O40

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posted on 20.01.2015, 00:00 by Delina Barats-Damatov, Linda J. W. Shimon, Yishay Feldman, Tatyana Bendikov, Ronny Neumann
The crystal packing and secondary structure of H5PV2Mo12O40 was followed by careful X-ray diffraction studies that revealed four unique structures and three solid phase transitions at temperatures between 25 and 55 °C, with loss of solvated water and concomitant contraction of the volume and increase of the packing density. Above 60 °C H5PV2Mo12O40 becomes amorphous and then anhydrous although the polyoxometalate cluster is stable indefinitely up to 300 °C. Above this temperature, combined IR, Raman, XRD, and XPS measurements show the decomposition of H5PV2Mo12O40 to crystalline MoO3 and probably amorphous vanadium oxide and vanadylphosphate, the latter appearing to cover the surface of MoO3. Importantly, H5PV2Mo12O40 can be easily recovered by dissolution in water at 80 °C.