Vibrational studies of compounds with multiple molybdenum-molybdenum and rhenium-rhenium bonds

A detailed study of the possible force fields for M2X8 anions (M = MO or Re; X = halide or carboxylate) has shown a definite difference in metal-metal stretching force constant between the molybdenum halides (FMMca. 3.5 mdyn Å–1) and the other molecules (FMMca. 4.5 mdyn Å–1). This suggests that δ bonds play a significant part in the metal–metal bond strength for the rhenium compounds and for the molybdenum carboxylates, but probably not for the molybdenum halides.