Vibronische Kopplung und dynamisch verzerrte Strukturen in Hexahalogenotelluraten(IV): Ergebnisse aus Tieftemperatur-Röntgenbeugungsuntersuchungen (300—160 K) und aus FTIR-spektroskopischen Experimenten (300—5 K) [1] / Vibronic Coupling and Dynamically Distorted Structures in Hexahalogenotellurates(IV): Low Temperatur X-Ray Diffraction (300—160 K) and FTIR-Spectroscopic (300—5 K) Results [1]

Abstract

Abstract From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX6 2- . A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A2TeX6 (A = Rb. Cs: X = Cl, Br) the averaged structure (m3̅m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar SnX6 2 compounds. Distortions therefore are very small and are evident from FTIR spectroscopic meas­urements only. Here very broad T1u-deformation vibration bands are observed down to tempera­tures <10 K without splitting: Astatically distorted species could not be frozen out. In contrast to XeF6 for TeX6 2- the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T1u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments.