Electronic Structure and Molecular Properties of the Mixed Rhenium-Molybdenum [Re6-x Mo x S8(CN)6]q-, (x=0 to 6) Clusters

Relativistic density functional calculations including scalar and spin-orbit effects via the ZORA approximation and including solvent effects were carried out on the [Re6S8(CN)(6)](4-), [Re5MoS8(CN)(6)](5-), [Re4Mo2S8(CN)(6)](5-), [Re3Mo3S8(CN)(6)](5-), [Re2Mo4S8(CN)(6)](5-), [ReMo5S8(CN)(6)](5-) and [Mo6S8(CN)(6)](6-) clusters. By increasing the replacement of each Re atom with Mo atoms we find that for x > 2 the HOMO-LUMO gap decreases significantly. The calculated gap of the [Re3Mo3S8(CN)(6)](5-), [Re2Mo4S8(CN)(6)](5-) and [ReMo5S8(CN)(6)](5-) clusters is similar to the calculated and observed gap of the superconducting PbMo6S8 Chevrel phases. The current calculations also indicates that the electronic similarities of the lowest excited states of the semiconducting 24e [Re5MoS8(CN)(6)](5-) and 23e [Re4Mo2S8(CN)(6)](5-) clusters with the strongly luminescent 24e [Re6S8(CN)(6)](4-) cluster, suggest that these mixed metal clusters might be luminescent.