Three new vic-dioxime ligands:: Synthesis, characterization, spectroscopy, and redox properties of their mononuclear nickel(II) complexes

Nickel(II) complexes with three new vic-dioxime reagents, N-(ethyl-4-amino-l-piperidine carboxylate)phenylglyoxime (L2H2), N-(ethyl-4-amino- 1-piperidine carboxylate)glyoxime (L2H2) and N,N'-bis(ethyl-4-amino-1-piperidine carboxylate)glyoxime (L3H2), have been prepared. Mononuclear nickel(II) complexes with a metal/ligand ratio of 1:2 were prepared using Ni(II) salt. All these nickel(II) complexes are nonelectrolytes as shown by their molar conductivities (Lambda(M)) in DMF solution at 10(-3) M concentration. The ligands are soluble in common solvents such as DMSO, DMF, CHCl3, and C2H5OH. The ligands and their Ni(II) complexes were characterized by elemental analyses, FT-IR, UV-visible, H-1 NMR, 13 C NMR, magnetic susceptibility measurements, cyclic voltammetry, and molar conductivities (Am). The cyclic voltammetric measurements show that [Ni(L1H)(2)] and [Ni(L2H)(2)]complexes exhibit almost similar electrochemical behavior, with two reduction and two oxidation processes based on either metals or oxime moities, while [Ni(L3H)(2)center dot 2H(2)O] complex displays irreversible, with one reduction and one oxidation processes based on oxime moity. This main difference could be attributed to the highly polarized [Ni(L3H)(2)center dot 2H(2)O] complex that has four carboxylate groups attached to piperidine on the oxime moieties. (c) 2007 Wiley Periodicals, Inc.