NICKEL(II) AND MANGANESE(II) COMPLEXES OF SUBSTITUTED PHENANTHROLINE LIGANDS

The synthesis and characterization of nickel(II) and manganese(II) com plexes of substituted 1,10-phenanthroline ligands are described.; The ligands include 2,9-di(o-tolyl)-1,10-phen (dtphen), 2,9-di(2-methoxyph enyl)-1,10-phen (dmophen), 2,9-di(2-ethoxyphenyl)-1,10-phen (deophen), 2-(o-tolyl)-1,10-phen (tphen), 2-(2-ethoxyphenyl)-1,10-phen (eophen) and 2,9-bis(N-pyrazolylmethyl)1,10-phen (bpmp). 1:1 Metal-to-ligand co mplexes have been isolated with dmophen and bpmp, and 1:2 metal-to-lig and complexes have been isolated with all ligands except bpmp. The str ucture of 1:1 nickel(II) complex with dmophen has been determined by t hree-dimensional X-ray diffraction methods. The complex [Ni(dmophen)Cl 2], [NiC26H20N2O2Cl2], crstallizes in the space group Pccn of theortho rhombic system with eight molecules in a cell of dimensions a = 14.572 (3), b = 16.741(3) and c = 19.209(4) angstrom. The structure has been refined to a final value of the crystallographic R factor of 0.0427 ba sed on 2618 observed independent reflections. There are two crystallog raphically independent, but geometrically very similar, molecules in t he cell, each lying on a twofold axis. The complex is roughly tetrahed ral, the coordination being provided by two ligand phen nitrogen atoms and by two chloride ions. Electrochemical data for the 1:2 complexes suggest that the M(II) <-> M(I) electron transfer process is essential ly metal localized, but that the M(I) <-> M(0) electron transfer proce ss is ligand localized. Moreover, the electrochemical results demonstr ate that the 2,9-di(o-substituted phenyl)-1,10-phen ligands are able t o stabilize lower oxidation states, and that ligand binding to the red uced metal ion prevents its dissociation into free ligand and metal.