New carbide clusters in the cobalt subgroup. Part 16. Preparation and structural characterization of µ6-carbido-penta-µ-carbonyl-octacarbonyl-octahedro-hexacobaltate(2–) as its tetraethylammonium salt

Abstract

The new anion [Co₆C(CO)₁₃]^2– has been prepared by refluxing a solution of [Co₆C(CO)₁₅]^2– in tetrahydrofuran under nitrogen; the loss of CO causes rearrangement of the metal cluster from trigonal prismatic to octahedral; the reaction is reversible, and on simple exposure to CO the starting anion is regenerated. The new anion has been characterized by single-crystal X-ray diffraction on the salt [NEt₄]₂[Co₆C(CO)₁₃] which crystallizes in the monoclinic space group C₂, with cell constants a= 20.750(2), b= 11.470(2), c= 16.097(2)Å, β= 91.968(3)°, and Z= 4. The structure has been solved from 6 066 reflections, collected by counter methods and refined by leastsquares calculations to R= 0.0295. The dianion possesses idealized C₂ symmetry and contains a distorted octahedron of cobalt atoms, whose cavity is occupied by the carbide atom. Five carbonyl ligands are bridging on opposite edges of the three octahedron equators, and eight are terminal. The dianion is not isostructural with the isoelectronic congener [Rh₆C(CO)₁₃]^2– thus showing a new way of arranging 13 CO ligands on an octahedral core of metal atoms.