Reorientation of Mo-co-ordinated water molecules in high-hydrogen-content oxide bronzes H1.7MoO3 and H2.0MoO3. A neutron scattering study

Abstract

Variable-temperature incoherent quasielastic neutron scattering (QENS) measurements have been used to investigate motions of hydrogenic species in the oxide bronzes H_1.7MoO₃ and H_2.0MoO₃. In both phases there are distinct (slowly exchanging) populations of H undergoing reorientational (those present in Mo-co-ordinated H₂O) and self-diffusive (those present in Mo-co-ordinated hydroxyl) motions. In H_1.7MoO₃ the H₂O molecules undergo four-fold reorientation [E_a= 26 ± 3 kJ mol^–1, log (τ_res⁰/s)=–14.4 ± 0.7] about the Mo—O bond. In H_2.0MoO₃, reorientation of H₂O is restricted to a 180° flip about the bisector of the H—O—H bond angle.