Syntheses,molecular structure,and electrochemical investigations of cobalt(II), copper(II), palladium(II), and zinc(II) complexes with 3-methylpyrazole

Mononuclear complexes of 3-methylpyrazole with general formulas (3-Mepz)₄CuCl₂ (1), (3-Mepz)₄CoCl₂ (2), (3-Mepz)₂PdCl₂ (3), and (3-Mepz)₂ZnCl₂ (4) were prepared by reaction of the corresponding MCl₂ salt (M?=?Cu, Co, Pd, and Zn) with 3-methylpyrazole in appropriate amounts using acetonitrile as solvent at ambient temperature. The X-ray crystal structure determination reveals that 1 and 2 possess octahedral geometry, while 3 and 4 are square planar and tetrahedral, respectively. All the synthesized compounds have the MCl₂ fragment, thus making the synthesized compounds attractive synthons for further transformation. The cyclic voltammograms of the synthesized complexes were obtained and the voltammetric signatures of 1, 2, and 4 showed a single irreversible pH-dependent cathodic peak, while 3 has two reversible cathodic peaks. Involvement of protons accompanying the electron transfer processes was ascertained from differential pulse voltammetric results, indicating peak potential shift as a function of pH.