Synthesis and spectroscopic characterization of cobalt(II), nickel(II) and copper(II) complexes with 5-methyl-1-(2′-pyridyl)pyrazole-3-carboxylic acid and 5-methyl-1-(4′,6′-dimethyl-2′-pyrimidyl)pyrazole-3-carboxylic acid

Synthesis and characterization of cobalt(II), nickel(II) and coper(II) complexes with title ligands, 1 and 2 (abbreviated as PyPzCH and PymPzCH respectively) were carried out by elemental analyses, mass, IR and PMR spectral studies. Magnetic and electronic spectral features classify the reported bis.-chelates as six coordinated distorted octahedral ones. A comparative study of IR spectra between the ligands and the complexes indicate different denticity of the ligands. The neutral bidentate ligand 1 functions through pyrazolyl 2(N) and pyridyl 1'(N) (tertiary N atoms) and the ligand 2, in its zwitter ion form (achieved during complexation) exercises tridentate behaviour through pyrazolyl 2N, pyrimidyl 1'(N) (tertiary N atoms) and carboxylic acid oxygen. Hence, the different coordination environments viz. MN4X2 (M = Ni-II/Cu-II) for ligand 1 and MN4O2 (M = Co-II/Ni-II/Cu-II) for ligand 2 are indicated. Electrochemical studies of some of the Cu-II species demonstrate easy oxidative nature of Cu-II.