Anionic germanium polycobalt carbonyl clusters. Part 3. Preparation and structures of [NEt4][Ge2Co7(CO)21] and [NEt4][Ge{Co7(CO)20}]; two large clusters incorporating tetrahedral GeCo3 units

Abstract

Reactions of the [Ge{Co₅(CO)₁₆}]^– cluster have given rise to two new germanium–polycobalt cluster anions, characterised as their NEt₄⁺ salts by X-ray crystallography. The complex [NEt₄][Ge₂Co₇(CO)₂₁](1a) forms triclinic crystals, space group P, with a= 13.085(2), b= 19.712(7). c= 12.220(8)Å, α= 109.10(3), β= 92.60(2), γ= 129.32(3)°, and Z= 2. The structure was solved by direct methods and refined to R=R′= 0.046 for 2 076 reflections with l > 3σ(l). The anion (1) consists of two –GeCo₃(CO)₉ units bonded mutually trans about a trigonal planar Co(CO)₃ group, giving idealised C_3v, symmetry. For [NEt₄][Ge{Co₇(CO)₂₀}](2a). crystals are monoclinic, space group P2₁/c, with a= l2.761(7), b= 18.415(3), c= 17.675(4)Å, β= 102.91(3)°, and Z= 4. The structure was refined to R= 0.077, R′= 0.074, for 1 123 reflections with I > 2σ(I). The anion (2) is a derivative of the C_3v structure of [Co₄(CO)₁₂] with the axial carbonyl ligand of one basal cobalt replaced by a –GeCo₃-(CO)_9^– fragment. The Co₄ tetrahedron is disordered.