Intramolecular d10-d10 Interactions in a Ni6C(CO)9(AuPPh3)4 Bimetallic Nickel-Gold Carbide Carbonyl Cluster

The Ni6C(CO)(9)(AuPPh3)(4) bimetallic carbide carbonyl duster was obtained from the reaction of [Ni9C(CO)(17)](2-) with Au(PPh3)Cl. It contains a rare carbon-centered (distorted) Ni6C octahedral core decorated by four Au(PPh3) fragments. These are mu(3)-bonded to four contiguous Ni-3-triangular faces and display weak intramolecular Au center dot center dot center dot Au d(10)-d(10) interactions. The cluster has been characterized in the solid state on two different solvato crystals, i.e., Ni6C(CO)(9)(AuPPh3)(4)center dot THF and Ni6C(CO)(9)(AuPPh3)(4)center dot THF center dot 0.5C(6)H(14). The two solvates show some interesting differences concerning the weak Au center dot center dot center dot Au contacts. Density functional theory calculations have demonstrated that the presence of the two isomers is related to solid-state packing effects and not to the existence of two double minima in the potential energy surface. This, in turn, confirms that Au center dot center dot center dot Au d(10)-d(10) interactions are rather soft and thus influenced also by weak van der Waals forces because of the interaction of the duster with the cocrystallized solvent molecules.