STUDIES OF COBALT(III) AND CHROMIUM(III), AMMINE, AQUO AND CHLORO COMPLEXES BY NIR-FT-RAMAN SPECTROSCOPY

$^{1.}$ Y. Chen, D. H. Christensen, O. F. Nielsen and E. Pedersen, J. Mol. Structure, in press (1993) $^{2.}$ T. W. Swaddle, P. J. Craig and P. M. Boorman, Spectrochim. Acta, 26A, 1559 (1970)Author Institution: Department of Chemistry, Laboratory V. H. C. \O orsted Institute, Copenhagen University; Department of Chemistry, Laboratory V. H. C. \O orsted Institute, Haldor Topsoe A/S.Studies of the complexes with the general formula $[M(NH_{3})_{5}L]^{p+}$ where $M = Co(III); Cr(III); L = NH_{3}, H_{2}O, OH, CI$, were carried out in both the solid state (powder) and aqueous solutions by Fourier transform-(FT)-Raman spectroscopy employing near-infrared (NIR) laser excitation ( 1064 nm). So far very few Raman spectra have been reported for the strongly colored cobalt(III) and chromium(III) $complexes^{1.2}$. The Raman spectra of the complexes including some deuterated species will be presented. The observed Raman frequencies were all assigned in the skeleton vibrational region under the assumption of $O_{2}$ or $C_{4}$ symmetry. Force constants of a general valence force field were fitted to the experimental frequencies. For the stretching force constants of the metal-nitrogen $(f_{MN})$, and metal-oxygen $(f_{MN})$, and metal-chloro $(f_{MN})$ we observed that $f_{coN}$ was larger than $f_{Cr-N}$, and $f_{Co-*}$ and $f_{Co-*}$ for cobalt(II) compounds were both smaller than the corresponding force constants calculated for chromium(III) compounds