The hexanuclear rhenium cluster ions Re6S8X64- (X = Cl, Br, I):: Are these clusters luminescent?

Dirac molecular orbital calculations on the octahedral rhenium clusters Re6S8X64- (where X=Cl, Br, I) are reported. The calculated relativistic molecular orbitals indicate that the manifold of closely spaced unoccupied energy levels are mainly localized on the octahedral rhenium core with some contributions from the mu(3)-S ligands, while all the cluster highest occupied molecular orbitals are largely centered on the terminal halide ligands. All three hexanuclear rhenium cluster ions have singlet ground state (spanning the Gamma(6)(+) symmetry) and are therefore diamagnetic. They have the same ground state and excited state features as the intensely luminescent W6Cl142- cluster ion. The calculated charge distributions indicate that these clusters could be formulated as: Re6-0.21S8-0.16Cl6-0.24,Re6-0.23S8-0.17Br6-0.21 and Re6-0.26S8-0.26I6-0.12, respectively. (C) 1999 American Institute of Physics. [S0021-9606(99)30204-X].