Structural and electrochemical diversity of Cu(II), Co(II) and Ni(II) naphthoyl hydrazonoates: Electropolymerizable copper chains

Abstract

Copper(II), cobalt(II) and nickel(II) complexes incorporating 3-hydroxy-2-naphthoyl hydrazone (HLL) have been prepared: nanometer-sized metallopolymeric chains [Cu(μ-LL)2]n as well as octahedral monomers [Co(LL)2(L)2] (L=H2O, pyridine) and [Ni(LL)2(L)2] (L=H2O, thf). Their structural diversity both in the solid state and solution, evidenced by single-crystal X-ray diffraction and dynamic light scattering, fundamentally affects their electrochemical behavior. Contrary to monomeric nickel and cobalt complexes, 1-D polymeric copper complex forms aggregates (ca. 750nm in size) in solution and undergoes a unique cathodic electropolymerization that results in the formation of a conducting film on Pt electrode. The plausible mechanism of its formation, based on the preorganization present in the 1-D structure of the copper(II) complex, is proposed.