The hexanuclear rhenium cluster ions Re₆S₈X^4-₆ (X=Cl, Br, I): Are these clusters luminescent?

Dirac molecular orbital calculations on the octahedral rhenium clusters Re₆S₈X^4-₆ (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 μ₃-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 Γ^-₆ symmetry) and are therefore diamagnetic. They have the same ground state and excited state features as the intensely luminescent W₆Cl^2-₁₄ cluster ion. The calculated charge distributions indicate that these clusters could be formulated as: Re^-0.21₆S^-0.16₈Cl ^-0.24₆, Re^-0.23₆S^-0.17₈Br ^-0.21₆ and Re^-0.26₆S^-0.26₈I ^-0.12₆, respectively.