Anionic germanium polycobalt carbonyl clusters. Part 2. Preparation and structure of [NEt4][Ge{Co5(CO)16}], a cluster which contains five-co-ordinate germanium

Abstract

Addition of [Co(CO)₄]^– to [Ge{Co₄(CO)_n}](n= 16, 14, or 13) under mild conditions gives good yields of [Ge{Co₅(CO)₁₆}]^–. This forms crystals with NEt₄⁺ which are orthorhombic, space group Pn2₁a with a= 12.014(1), b= 36.938(4), c= 15.249(2), and Z= 8. The crystal structure was solved by direct methods and refined, with some difficulty due to pseudo-symmetry, to R= 0.088, R′= 0.081, for 1 590 unique reflections with F² > 2σ(F²). The anion has a GeCo₅ metal skeleton consisting of a GeCo₂ triangle and a GeCo₃ tetrahedron sharing a common apex at Ge. The five Ge–Co bond lengths vary from 2.33 to 2.51 Å. Three of the CO ligands on the GeCo₃ unit bridge the three Co–Co bonds, with two terminal CO groups on each Co atom. On the GeCo₂ moiety there are six terminal and one bridging carbonyls.