SYNTHESIS AND CHARACTERIZATION OF MIXED-LIGAND NICKEL(II) CHELATES OFBETA-DIONES AND ALPHA-DIIMINES - CRYSTAL AND MOLECULAR-STRUCTURE OF (NI(NCUP)(2)ETACET]CLO4

A series of new nickel(II) perchlorate complexes containing an alpha-d iimine(enR) and the anion of a beta-dione (1,3-ketoenol or 1,3-ketoest er, beta H) was prepared and characterized. The composition and the ov erall structure of the new chelates depend on ligand concentration, on steric and electronic effects induced by substituents within the liga nds and the ability of the perchlorate group to coordinate. The IR and electronic excitation spectra of [Ni(enR)(2)beta]ClO4 and [Ni(enR)bet a(O2ClO2)] indicate, in conjunction with other physicochemical measure ments, bidentate coordination of the ligands and replacement of the (O ,O') perchlorato group by basic solvents. The structure of the new che lates was further supported by an X-ray structure analysis of [Ni(ncup )(2)Etacet]ClO4, where ncup denotes neocuproine and Etacet the anion o f the ethyl acetoacetate (orthorhombic, space group Pc2(1)n, a = 14.08 7(5), b = 14.713(5) and c = 15.952(5) Angstrom, Z = 4). The coordinati on sphere of nickel is a distorted octahedron, arised from the chromop hore NiN4O2, in which the base is favored by three neocuproine nitroge ns and one Etacet oxygen. The apical sites are occupied by the remaini ng oxygen and nitrogen atoms, one from Etacet and one from neocuproine respectively.