Probing the electronic structure and metal-metal bond of Re2Cl82- in the gas phase

Re2Cl82-, the classical metal complex with a metal-metal multiple bond, was observed in the gas phase for the first time using electrospray. Photodetachment photoelectron spectroscopy (PES) was used to probe its electronic structure, metal-metal bonding, and gas-phase molecular properties. The PES spectra provide a unique and direct picture about the occupied molecular orbitals (MOs) of Re2Cl82-. Detachments from the metal-metal and metaI-ligand bonding MOs were clearly observed and distinguished We found that the metal-metal bonding MOs from the d orbitals (delta, pi, and sigma) have low electron binding energies and yielded three well-resolved detachment bands. The metal-ligand or pure Ligand MOs all have higher binding energies and give congested PES features. The ground state of Re2Cl82- with a configuration of ...sigma(2)pi(2)delta(2) and a formal quadruple Re-Re bond is unequivocally confirmed. The PES spectra yielded a 1.00 eV adiabatic binding energy for the second excess electron in the doubly charged anion. The magnitude of the intramolecular Coulomb repulsion was estimated to be similar to 2.3 eV using photon-energy-dependent PES spectra. Despite its electronic stability, Re2Cl82- was found to be metastable against the loss of a Cl- in the gas phase, suggesting that the Re-Cl bond strength is less than 2.3 eV.