Hexacarbonylocta(.mu.3-sulfido)hexacobalt.cntdot.tris(octasulfur). Structure, bonding, and vibrational analysis of an exceptionally electron-rich carbonyl cluster

The title complex is the main product of the room-temperature reaction between Co2(CO)8 and sulfur. Its crystals are monoclinic, space group C2/c, with a = 20.456 (4) A, b = 12.385 (4) A, c = 17.600 (5) A, 6 = 90.94 (2)O, and Z = 4. The structure was solved by the heavy-atom method and refined by full-matrix least-squares techniques to the conventional R(Fo) value of 0.048 for 3395 reflections having F > 6a(F). The structure of the cluster can be described as a CO, octahedron (mean COCO distance 2.81 A) inserted in a SB cube (mean nonbonded S.-S distance 3.09 A). Each sulfur atom caps the triangular Co, faces, and one CO group is terminally bonded to each cobalt atom. The idealized symmetry is Oh. The SB rings are distant enough from the molecules of the cluster to exclude any chemical interaction between them. A qualitative description of the bonding (49 accessible MOs to accommodate the 98 valence electrons) is compared with that of the common octahedral metal clusters (43 MOs and 86 valence electrons). Detailed calculations on similar molecular complexes (Cp.&(p&) and solid-state structures ('Chevrel phases") give insights to a qualitative understanding of the chemical and structural properties of the cluster. The analysis of the FT-infrared and Raman spectra leads to an assignment of the main vibrational modes of the coordinated CO groups (C-O and Co-CO stretch and Co-C-0 deformation) and of the Co6SBc ore (Co-S and Co-Co stretch).