Elucidation\nof the Off-Center Displaced Mo in Octahedral\nCoordination in Ba<sub>2</sub>MoO<sub>5</sub>

The detailed crystal\nstructure as well as the heat capacity\nat\nlow temperature and standard entropy of Ba<sub>2</sub>MoO<sub>5</sub> are reported for the first time. High-resolution X-ray and neutron\ndiffraction were employed to reveal the structural features of this\ncompound. Ba<sub>2</sub>MoO<sub>5</sub> has a six-coordinated Mo and\na strongly negative excess volume with respect to the binary oxides.\nX-ray absorption near edge structure (XANES) spectroscopy at the Mo\nK-edge shows Mo to be in the oxidation state 6+. The pre-edge peak\nin the XANES spectrum indicates a distorted octahedral environment,\nin line with the results from diffraction studies and FDMNES calculations.\nThe standard entropy and heat capacity of Ba<sub>2</sub>MoO<sub>5</sub> at 298.15 K, determined with a thermal-relaxation technique, are\ncalculated to be respectively 223.2 ± 7 and 184.7 ± 5 J·K<sup>–1</sup>·mol<sup>–1</sup>. The obtained thermodynamic\nproperties are discussed in the context of the literature reports\non molybdate compounds.