OCTAHEDRO OCTAHEDRA AND TETRAHEDRA .2. TETRANUCLEAR TO HEPTANUCLEAR CARBONYL(CYANO)CHROMATO, CARBONYL(CYANO) MOLYBDATO AND CARBONYL(CYANO) TUNGSTATO COMPLEXES OF 3D-METALS

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' = Cr0, Mo0, W0). X-ray structures are reported for the heptanuclear six-coordinate (NEt4)2[Si{NCCr(CO)5}6] (1a) ('octahedro octahedron'), the hexanuclear five-coordinate (NEt4)3[Ni{NCW(CO)5}5] (8c) and the (heteroleptic) tetranuclear four-coordinate (NEt4)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 [MA3]-, [MA4, NEt4]- ([CuA2]-, [CuA3, 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.