Pyridine as axial ligand on the [Mo6Cl8]4+ core switches off luminescence

TDDFT calculations including scalar, spin–orbit and solvent effects were carried out on [Mo6Cl8Cl6]2−, and [Mo6Cl8(py)6]4+ clusters. The calculations indicate that the contribution of the axial pyridine ligands in the active lowest unoccupied molecular orbitals which are involved in the higher intensity transitions in the [Mo6Cl8(py)6]4+ cluster are significant (∼31%). This situation differs from all the luminescent [M6X8L6] clusters, where most of the closely spaced excited states are located in the [M6X8]q+ core. Thus, the pyridine axial ligands switch off the cluster luminescence.