Raman and infrared spectroscopic and theoretical studies of dinuclear rhenium and osmium complexes, M 2(O 2CCH 3) 4X 2 (M = Re, Os; X = Cl, Br)

Abstract

Infrared, far-infrared and Raman spectra of Re 2(O 2CCH 3) 4X 2 (X = Cl, Br) and Re 2(O 2CCD 3) 4Cl 2 have been recorded. Assignments of the vibrational spectra of Os 2(O 2CCH 3) 4Cl 2 and its deuterated derivative have been completed together with the Re complexes on the basis of normal-coordinate analysis. Force constant calculation was made for the acetate ion as well as for a four-atomic unit (with the CH 3 and CD 3 groups considered as point masses) using optimized masses of 16.7, 17.8, 20.5 and 21.6 for 12CH 3, 13CH 3, 12CD 3 and 13CD 3 groups, respectively. The force constants of the acetate ion have been adopted to the starting force field of the M 2(O 2CCH 3) 4X 2 type complexes. The metal–halide (0.889, 0.997 and 1.286 N cm −1) and metal–metal stretching (3.32, 3.34 and 3.57 N cm −1) force constants were obtained for Re 2(O 2CCH 3) 4Cl 2Re 2(O 2CCH 3) 4Br 2 and Os 2(O 2CCH 3) 4Cl 2 complexes, respectively. It was shown that the so-called diatomic approximation in most cases overestimates the M–M stretching force constants by 30–40%. Much better correlation has been obtained to fit these force constants, which produced values very close to those obtained by full normal-coordinate calculations. The Re–Re stretching force constants showed a reasonable correlation with the Re–Re bond distances for 18 rhenium complexes.