Bonding and Electronic Structure of Cluster Assemblies with Metal Carbonyls*

Understanding the factors controlling the band gap energies of cluster-assembled materials is an important step towards creating nano-assemblies with tailored properties. To this end, we have investigated the band gap energies of cluster assemblies involving arsenic clusters bound to metal carbonyl charge-transfer complexes, [As$_{7}$M(CO)$_{3}$]$^{3-}$ M = Cr, Mo, W. The binding of a single charge-transfer complex is shown to have a small effect on the band gap energy as the arsenic lone pair orbital and metal carbonyl orbitals are closely aligned in energy, resulting in a gap similar to the original cluster. The band gap energy is also found to be insensitive to the architecture of the assembled material. In the case where two charge-transfer complexes are bound to the cluster, the bottom of the conduction band is shown to be localized on a solvent molecule bound to the metal carbonyl.