SPECTROSCOPIC PROBING OF SITE SYMMETRY IN SOLIDS

Infrared (IR), electronic absorption and Raman spectroscopy are employ ed to probe the site symmetry, coordination geometry and structural ch anges in rare-earth complexes of high and low symmetry. The results of these studies are compared with X-ray data. Although unpolarized IR s pectra do not enable, a priori, determination of the site symmetry of an ion in a crystal, the spectra can be shown to be consistent with cr ystallographic data. In addition, IR spectra can be employed to indica te subtle changes in the distances of nuclei bonded to hydrogen, which are not available from X-ray data, as exemplified herein for P-H bond s in hypophosphite complexes. The use of electronic absorption spectra to explore the coordination geometry (rather than the site symmetry) of a complexed rare-earth ion is considered. Both the IR and electroni c absorption techniques are found to be useful in fingerprinting given structural types. Small perturbations on distant neighbours of a chro mophore may be silent in IR and Raman spectra, but significant in elec tronic absorption spectra. (C) 1997 Elsevier Science B.V.