We report investigations into the dehydration pathway of the precursor material MoO2PO3OH·H2O to γ-(MoO2)2P2O7. The reaction occurs in three distinct stages via the formation of two new previously unidentified molybdenum phosphate phases, β-MoOPO4 and δ-(MoO2)2P2O7. 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 β-MoOPO4 was performed against X-ray and neutron data. The new phase has lattice parameters a = 7.4043(3) Å, b = 7.2128(3) Å, c = 7.2876(3) Å, β = 118.346(2)°, and volume 342.53(3) Å3 at room temperature, containing 7 unique atoms in space group Cc. δ-(MoO2)2P2O7 forms on slowly heating the precursor material to 793 K. Lattice parameters at room temperature are a = 16.2213(11) Å, b = 3.8936(3) Å, and c = 6.2772(4) Å and volume 396.46(5) Å3, in space group C2221. A transformation mechanism is proposed for the dehydration. Lithium intercalation into layered δ-(MoO2)2P2O7 has been shown.

Structural and Mechanistic Studies of the Dehydration of MoO 2 PO 3 OH·H 2 O and the in situ Identification of Two New MolybdenumPhosphates. -The dehydration pathway of the title material to γ-(MoO2)2P2O7 is monitored by variable-temperature XRD. The reaction occurs via the formation of two new phases, β-MoOPO4 (I) and δ-(MoO2)2P2O7 (II). The blue compound (I) is isolated by heating the precursor material at 553 K for 60 min. It crystallizes in the monoclinic space group Cc. The three-dimensional structure is formed by corner-sharing MoO6 octahedra and PO4 tetrahedra. Pale gray (II) is synthesized by heating the precursor at 793 K for 0.1 h. It crystallizes in the orthorhombic space group C2221. The structure contains octahedral MoO6 and corner--sharing P2O7 groups. The layered phase undergoes Li intercalation. δ-Lix(MoO2)2P2O7 (x = 1.11) crystallizes in the space group C222 1 . -(LISTER, S. E.; RIXOM, V.