New carbide clusters in the cobalt sub-group. Part 6. Crystallographic characterization of the tetramethylammonium salt of the paramagnetic anion carbidohexa-µ-carbonyl-octacarbonyl-polyhedro-hexa-cobaltate(1–)

Abstract

The title complex crystallizes in the triclinic space group P with unit-cell dimensions a= 12.17(1), b= 13.28(1), c= 8.67(1)Å, α= 97.78(8)°, β= 89.93(8)°, γ= 98.93(8)°, and Z= 2. The structure has been solved from X-ray single-crystal counter data and refined by least-squares calculations to R= 0.07 for 1 689 significant diffraction intensities. The [Co₆C(CO)₁₄]^– paramagnetic anion contains 87 valence electrons and the metal atom cluster is a distorted octahedron of C_2v idealized symmetry. The Co–Co distances are in the range 2.53–2.92 Å, indicating the antibonding character of the extra electron. The carbide atom is located in the cluster cavity with average Co–C distance 1.90 Å. The carbonyl ligands are bonded edge-bridging (six) and terminally (eight), and conform to the cluster symmetry. The uneven lengthenings of the Co–Co interactions and the ligand stereochemistry give evidence that the unpaired electron is essentially located outside the cluster in front of the longest Co–Co edge.