SUPERPARAMETERIZATION OF LOW-TEMPERATURE VIBRATIONAL DATA FOR LANTHANIDE HEXAHALIDE ANIONS

A complete dataset is presented for the modes of vibration of LnCl63- in CsNaLnCl6, from low temperature Raman and vibronic spectroscopy. Co nventional force constant calculations with this dataset are unsatisfa ctory since, although the datafits are quite good, the physical signif icance of the derived force constant parameters is not clear in all ca ses. A parameterization of 30 vibrational wavenumbers at a time, compr ising five datasets of six modes of vibration, enables the relative im portance of the GVFF interaction force constants to be ascertained. Th e trans stretch-stretch force constant is about 2.5 times larger than the cis interaction constant, and the angle-angle interaction constant s all have comparable magnitudes. However, the same ratios for the mag nitudes of the interaction force constants fail to provide a satisfact ory datafit for PrBr63- in Cs2NaPrBr6. This is attributed to the stron ger trans directing influence of the bromide ligand than the chloride ligand, and an increased ratio for the trans/cis stretching interactio n force constant provides a more satisfactory fit. Datasets are also p resented for LnF63- and CS2LiLnCl6. The nature of the cation A in Cs2A LnCl6 appreciably modifies the moiety mode vibrational wavenumbers.