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

Abstract

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.

Graphical Abstract

Complexes of M(II) with 3-methylpyrazole as ligand were prepared at ambient temperature using MCl₂ metal salts (M = Cu, Co, Pd, and Zn). Reactions led to the formation of octahedral (Cu, Co), square-planar (Pd), and tetrahedral (Zn) mononuclear complexes. All reactions were straightforward and no appreciable amount of side products was detected. X-ray structures were determined for all the complexes. The cyclic voltammetric investigations indicate the involvement of proton during electron transfer reactions of these complexes.

Keywords:

• 3-Methylpyrazole
• M(II) complexes
• X-ray structures
• Electrochemistry

Acknowledgements

S.A.K. is grateful to Higher Education Commission (HEC) Pakistan for fellowship under “5000 indigenous PhD scholarships” at the University of Malakand and a six month fellowship under the “International Research Support Initiative Program” IRSIP as a graduate research trainee, Anorganische Chemie II, Universität Bayreuth, Bayreuth, Germany. We are also thankful to an anonymous reviewer for his valuable suggestions.