New carbide clusters in the cobalt sub-group. Part 4. Synthesis and crystallographic characterization of µ3-carbonyl-deca-µ-carbonyl-di-carbidotetradecacarbonyl-polyhedra-dodecarhodium

Abstract

The title complex crystallizes in the orthorhombic space group P2₁2₁2₁ with unit-cell dimensions a= 18.695(4), b= 18.604(4), c= 11 605(2)Å, and Z= 4. The structure has been determined by direct methods from X-ray single-crystal counter data and refined by least-squares calculations to R 0.037 for 3 450 significant diffraction intensities. The complex [Rh₁₂C₂(CO)₂₅] is asymmetric and the metal-atom cluster is an irregular closed polyhedron which can be described in terms of layer packing of atoms (mean Rh–Rh 2.79 Å). The carbide carbon atoms occupy an irregular cavity as a C₂ unit [C–C 1.48(2)Å]; there are 14 Rh–C(carbide) contacts, nine short and five long (means 2.22 and 2.58 Å respectively). Of the carbonyl ligands, 14 are terminal, 10 are edge-bridging, and one is face-bridging.