Schwingungsspektren und Normalkoordinatenanalyse der Acetatohalogenodimetallate M2(O2CCH3)4X2, M = Re, Tc; X = CI, Br/Vibrational Spectra and Normal Coordinate Analysis of Acetatohalogenodimetalates M2(O2CCH3)4X2, M = Re, Tc; X = Cl, Br

Abstract

Abstract The orange-red Tc2(O2CCH3)4Br2 has been prepared for the first time by reaction of [Tc2Br8]2- with glacial acetic acid and acetic anhydride. The IR and Raman spectra have been recorded at 80 K and are compared with those of the analogous compounds Tc2(O2CCH3)4Cl2, Re2(O2CCH3)4Cl2 and Re2(O2CCH3)4Br2. The assignment according to the point group D4h is supported by normal coordinate analysis based on a general valence force field. The quadruple M - M bond is stabilized by the bridging acetato and destabilized by the axial halogeno ligands. The valence force constants fd(MM) are determined to 3,96-4,08 mdyn/Å. The interaction constants fdd(MM/MX), fdd(MM/MO) and fdα (MM/MMO) are about three times higher for the technetates as compared with the rhenates. The stronger interaction between oppo­site bonds in the equatorial ligand sphere is revealed by the stretching interaction constants fdd', which are about two times higher than fdd for M - O bonds at right angles. The strong coupling of the ring co-ordinates implies extensive mixing of the M - O valence and deformation modes. The electronic spectra of Tc2(O2CCH3)4X2, agree with those of the corresponding Re compounds.