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 C3v, 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 C3v 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.