Electronic structure and molecular properties of the mixed rhenium-molybdenum [Re_6-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-, [Re ₄Mo₂S₈(CN)₆]^5-, [Re ₃Mo₃S₈(CN)₆]^5-, [Re ₂Mo₄S₈(CN)₆]^5-, [ReMo₅S₈(CN)₆]^5- and [Mo ₆S₈(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 [Re ₃Mo₃S₈(CN)₆]^5-, [Re ₂Mo₄S₈(CN)₆]^5- and [ReMo₅S₈(CN)₆]^5- clusters is similar to the calculated and observed gap of the superconducting PbMo ₆S₈ 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.