Iridium-nickel mixed-metal carbonyl clusters. Part 2. Synthesis and chemical behaviour of [IrNi8(CO)18]3-. Crystal and molecular structure of [NBu4]3[IrNi8(CO)18]

The mixed-metal carbonyl cluster [IrNi8(CO)18]3- was obtained by treating [Ni6(CO)12]2- with [Ir(CO)2Cl2]- in MeCN (molar ratio 2:1). It is rapidly degraded by carbon monoxide, at room temperature and atmospheric pressure, to [Ni5(CO)12]2-, [Ni(CO)4] and [Ir(CO)4]-. The salt [NBu4]3[IrNi8(μ-CO)9(CO) 9] crystallizes in the monoclinic space group C2/c, with a = 20.525(9), b = 18.877(5), c = 42.713(4), β = 95.13(2)°, and Z = 8. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least squares to R = 0.045 and R′ = 0.054 for 4545 independent reflections having I > 3.0σ(I). The cluster consists of three almost parallel stacked triangles; the central unit contains the iridium atom, which achieves the highest metal-metal connectivity by rotating and translating the internal triangle. Each metal atom is bonded to one terminal CO and each intratriangular edge is spanned by one bridging carbonyl ligand. Average bond distances are Ir-Niinter 2.945, Ir-Niintra 2.522, Ni-Niinter 2.891 and Ni-Niintra 2.401 Å.