Elucidation of the Off-Center Displaced Mo in Octahedral Coordination in BaMoO.

The detailed crystal structure as well as the heat capacity at low temperature and standard entropy of BaMoO are reported for the first time. High-resolution X-ray and neutron diffraction were employed to reveal the structural features of this compound. BaMoO has a six-coordinated Mo and a strongly negative excess volume with respect to the binary oxides. X-ray absorption near edge structure (XANES) spectroscopy at the Mo K-edge shows Mo to be in the oxidation state 6+. The pre-edge peak in the XANES spectrum indicates a distorted octahedral environment, in line with the results from diffraction studies and FDMNES calculations. The standard entropy and heat capacity of BaMoO at 298.15 K, determined with a thermal-relaxation technique, are calculated to be respectively 223.2 ± 7 and 184.7 ± 5 J·K·mol. The obtained thermodynamic properties are discussed in the context of the literature reports on molybdate compounds.