High nuclearity carbonyl clusters of rhodium. Part 2. Crystal and molecular structure of the tetramethylammonium salt of dodeca-μ-carbonyl-dodecacarbonylhydrido-polyhedro-tridecarhodate(4-)-1- methylpyrrolidin-2-one (1/3)

The title compound, [N(CH3)4]4[Rh13H(CO) 24]·3C5H9NO, crystallises in the triclinic space group P1 with unit-cell dimensions a = 22.596(11), b = 14.263(7), c = 14.512(8) Å, α = 65.56(3), β = 107.58(4), γ = 100.86(5)°, and Z = 2. The structure has been solved by conventional Patterson and Fourier methods from single-crystal X-ray counter data and refined by least-squares methods to R 0.061 for 3 680 significant reflections. The anion, of idealised Cs symmetry, containing a centred twinned-cuboctahedron of metal atoms, is similar to that of the other members of the family [Rh13H5-n(CO)24]n- already studied. The mean value of the Rh-Rh bond lengths, ranging from 2.718(3) to 2.894(3) Å, is 2.782 Å. The Rh-C and C-O interactions for the 12 terminal and for the 12 edge-bridging CO groups have mean values of 1.80, 1.18, and 1.97, 1.21 Å, respectively. The hydride atom has been located in a semi-octahedral cavity, i.e. on a square face of the cluster, bisected by the ideal mirror plane.