New carbide clusters in the cobalt sub-group. Part III. Crystallographic characterization of the hydroxonium salt of tetradeca-µ-carbonyl-dicarbidotetradecacarbonyl-polyhedro-pentadecarhodate(1–)

Abstract

The trtle compound crystallizes in the orthorhombic space group Pbcn, with cell constants a= 15.N (2). b= 17.34(2). c= 18.85(2)Å, Z= 4. The structure was determined by direct methods from X-ray single-crystai counter data and refined by least-squares calculations to R 0.0267 for 2 387 significant reflections.

The [Rh₁₅(CO)₂₈C₂]^– anion has precise C₂ symmetry idealizable to C_2v. The Rh₁₅ metal atom cluster can be described as a centted and tetracapped pentagonal prism in which the central atom is twelve-co-ordinated in a non-crystallographicfashion, with Rh–Rh distances ranging from 2.738 to 3.332(3)Å. The two carbide-atoms occupy octahedral cavities, mean Rh–C 2.04 Å. The carbonyl ligands are bound on the cluster surface, fourteen linearly and fourteen edge-bridging such that all the metal atoms are thrice-connected to the ligands. The molecular architecture is discussed and a growth mechanism of the cluster is proposed.