Octahedro octahedra and tetrahedra. II. Tetra- to heptanuclear carbonyl(cyano)chromato, -molybdato and -tungstato complexes of 3d metals

Abstract

A series of mostly homoleptic supercomplexes has been synthesized and characterized in which a central metalloid (Si IV, Ge IV, Sn IV) or (3d) metal (Cr III, Mn II, Fe II, Co II, Ni II, Cu I, Zn II) is surrounded by up to six ‘ligand complexes’ [NCM′(CO) 5] − (M′Cr o, Mo o, W o). X-ray structures are reported for the heptanuclear six-coordinate (NEt 4) 2[Si{NCCr(CO) 5} 6] ( 1a) (‘octahedro octahedron’), the hexanuclear five-coordinate (NEt 4) 3[Ni{NCW(CO) 5} 5] ( 8c) and the (heteroleptic) tetranuclear four-coordinate (NEt 4) 2[Co(Cl){NCCr(CO) 5} 3] ( 7d), the most striking feature being the co-existence in all complex anions of linear and distinctly bent M′ C  N  M linkages. An approximately square-pyramidal coordination sphere is established for the nickel ion in 8c. Generally, the peripheral atoms and groups (oxygen, methyl) are found in rather ill-defined positions due to their high thermal motion. In the spectrochemical series, a position slightly above NCS − (i.e. towards the stronger end) is deduced for the [NCM′(CO) 5] − (A) ligands from VisUV spectra. Negative FAB mass spectra reveal the presence in the matrix of the cluster anions [MA 3] −, [MA 4, NEt 4] − ([CuA 2] −, [CuA 3, Cu] −). Thermolysis of 7a and 10a proceeds in two steps with loss of, initially, Cr(CO) 6 followed by CO and HCN as established by mass chromatography.