Structural and Mechanistic Studies of the Dehydration of MoO2PO3OH•H2O and the In situ Identification of Two New Molybdenum Phosphates

We report investigations into the dehydration pathway of the precursor material MoO2-PO3OH center dot H2O to gamma-(MoO2)(2)P2O7. The reaction occurs in three distinct stages via the formation of two new previously unidentified molybdenum phosphate phases, beta-MoOP3O4 and delta-(MoO2)(2)P2O7. Conditions for the isolation of these phases were identified by a whole powder pattern fitting technique to follow phase evolution versus time and temperature and later verified by full Rietveld refinement. Structural refinement of beta-MoOPO4 was performed against X-ray and neutron data. The new phase has lattice parameters a = 7.4043(3) angstrom, b = 7.2128(3) angstrom, c = 7.2876(3) angstrom, beta = 118.346(2)degrees, and volume 342.53(3) angstrom(3) at room temperature, containing 7 unique atoms in space group Cc. delta-(MoO2)(2)P2O7 forms on slowly heating the precursor material to 793 K. Lattice parameters at room temperature are a = 16.2213(11) angstrom, b = 3.8936(3) angstrom, and c = 6.2772(4) angstrom and volume 396.46(5) angstrom(3), in space group C222(1). A transformation mechanism is proposed for the dehydration. Lithium intercalation into layered delta-(MoO2)(2)P2O7 has been shown.