Contrasting Structure and Bonding of a Copper-Rich and a Zinc-Rich Intermetalloid Cu/Zn Cluster

Reaction of the Cu­(I) sources, [Cu₅]­(Mes)₅ and [(ⁱDipp)­CuO^tBu] (Mes = mesityl; ⁱDipp = 1,3-bis­(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene) with the Zn­(I) complex [Zn₂]­(Cp*)₂ leads to a mixture of intermetallic Cu/Zn clusters with a distribution of species that is dependent on the stoichiometric ratio of the reactants, the reaction time, as well as the temperature. Systematic and careful investigation of the product mixtures rendered the isolation of two new clusters possible, i.e., the Zn-rich, red cluster 1, [CuZn₁₀]­(Cp*)₇ = [Cu­(ZnZnCp*)₃(ZnCp*)₄], as well as the Cu-rich, dark-green cluster 2 [Cu₁₀Zn₂]­(Mes)₆(Cp*)₂. Structure and bonding of these two species was rationalized with the help of density functional theory calculations. Whereas 1 can be viewed as an 18-electron Cu center coordinated to four ZnCp* and three ZnZnCp* one-electron ligands (with some interligand bonding interaction), compound 2 is better to be described as a six-electron superatom cluster. This unusual electron count is associated with a prolate distortion from a spherical superatom structure. This unexpected situation is likely to be associated with the ZnCp* capping units that offer the possibility to strongly bind to the top and the bottom of the cluster in addition to the bridging mesityl ligands stabilizing the Cu core of the cluster.