Knowledge Bank

The complexes $Cl2(OH)2ReReCl2(PH3)2$ and $Re2Cl8-2$ were studied. Atomic basis sets were optimized for rhenium, chlorine, oxygen, and phosphorus for use with Christiansen relativistic effective core potentials. Recently the COLUMBUS graphical unitary group approach multi-configuration self-consistent field (MCSCF) program was modified to incorporate these potentials. Hartree-Fock and MCSCF calculations for these complexes were performed on the ground state and several excited states. Spin-orbit splittings of these states were found using a double group spin-orbit configuration interaction (CI) program. The known quadruple rhenium-rhenium bond was investigated and, as previously shown, was not found at the Hartree-Fock level. A MCSCF calculation on the ground state of the complexes showed this quadruple bond. The criteria chosen for the discription of the bonds were the molecular orbital and CI coefficients. The lowest excited state for these complexes was found to be a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}A1$, $\delta -\delta \ast$ state with spin-orbit coupling of the order of 50 $cm-1$. Two other important excited states, for which calculations are proceeding, are the $\delta -\delta \ast$ singlet state and a ligand-metal charge transfer state.