Probing the gas-phase stability of the (X = Cl, Br) and (X = Cl, Y = Br, n = 1–3) metal–metal bond complexes

The prototypical metal–metal multiple bonded molecule, Re 2 Cl 8 2 - , and the brominated analogues, Re 2 Br 8 2 - and Re 2 X n Y 8 - n 2 - (X = Cl, Y = Br, n = 1–3) have been prepared using electrospray ionization and investigated using low-energy collision-induced dissociation in a quadrupole ion-trap. Each of the dianions studied here decays via ionic fragmentation (i.e. loss of a halide ion) upon resonance excitation in the ion-trap, and comparison of the collision energies for activated decay reveal that the Re–Cl bond is stronger than Re–Br. CASSCF(8, 8)/LANL2DZ calculations of the ionic fragmentation potential energy surfaces of Re 2 Cl 8 2 - and Re 2 Br 8 2 - are presented to support the experimental results.