Theoretical and experimental determination of the crystal structures of cesium-molybdenum chloride

We herein report the structure-property relationships of the octahedral molybdenum metal cluster compound, Cs-2[Mo6Cl14]. Using purified samples, we attempted to determine if Cs-2[Mo6Cl14] possesses crystalline polarity. Heat treatment was performed prior to characterization to remove impurities, as X-ray powder diffraction and Fourier transformation infrared spectroscopy studies suggested the unit cell of Cs-2[Mo6Cl14] expanded with the insertion of water molecules and/or hydroxyl moieties. Geometry optimization and total energy calculations by density functional theory calculations were conducted to determine whether Cs-2[Mo6Cl14] crystallizes in centrosymmetric (P (3) over bar 1c) or non-centrosymmetric (P31c) space groups. Furthermore, the results of the optical studies, along with the absence of a second harmonic generation, and the observation of a strong third harmonic generation, supported the hypothesis that inversion symmetry exists in the Cs-2[Mo6Cl14] lattice. The space group of Cs-2[Mo6Cl14] was therefore identified as P (3) over bar 1c symmetry. (C) 2016 The Japan Society of Applied Physics