NEW ROUTE TO BIMETALLIC IMIDAZOLATE-BRIDGED COMPLEXES .6. STRUCTURAL AND MAGNETIC CONSEQUENCES OF STERIC EFFECTS IN MONONUCLEAR AND DINUCLEAR NICKEL(II) AND COPPER(II) COMPLEXES INVOLVING 4-METHYLIMIDAZOLE AS LIGAND

The syntheses of (4(5)-methylimidazole)(7-amino-4-methyl-5-aza-3-hepten-2-onato(1-))metal(II)(1+) complexes [metal(II) being nickel(II) and copper(II)] are described. X-ray diffraction and NMR data show that, in both cases, the adjacent isomer (where the methyl group is near the metal ion) is practically missing from the reaction mixture. The remote isomer (methyl group away from the metal ion) of the copper(II) complex crystallizes in the triclinic space group P1BAR (No. 2) with two formula weights in a cell having the dimensions a = 9.184 (1) angstrom, b = 12.828 (2) angstrom, c = 7.627 (1) angstrom, alpha = 94.64 (1)-degrees, beta = 105.84 (1)-degrees, and gamma = 106.75 (1)-degrees. The related dinuclear complexes (mu-5-methylimidazolato)bis(7-amino-4-methyl-5-aza-3-hepten-2-onato(1-))dimetal(II)(1+) have been obtained. The dinickel complex II(a)-4(5) Me crystallizes in the monoclinic space group P2(1)/n (No. 14) with formula weights in the cell having the dimensions a = 15.910 (2) angstrom, b = 9.769 (1) angstrom, c = 15.979 (2) angstrom, and beta = 100.31 (2)-degrees. The most interesting result of this structural study is that the coordination plane of one metal ion is nearly orthogonal to the mean plane of the rest of the molecule. Static susceptibility measurements point to an antiferromagnetic exchange interaction of 2J = -68 cm-1 in the case of the dicopper complex. The mononuclear and dinuclear nickel complexes, which are diamagnetic in the solid state and in noncoordinating solvents, become paramagnetic in the presence of an excess of pyridine. H-1 NMR data seem to indicate that, for the dinickel complex, a modification of the geometry toward coplanarity is needed before adduct formation.