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.