Synthesis, characterization, spectroscopic and electrochemical investigation of 2-aminopyridine-3-carboxylic acid copper(II) complexes with diimine

Three mixed- ligand copper(II)-organic coordination compounds were synthesized by using 2-aminopyridine-3-carboxylic acid (2-APCA) as a primary ligand while the aromatic diimines, viz., 2,2′-bipyridine (2,2′-bipy), 1,10-phenanthroline (1,10-phen) and 2,9-dimethyl-1,10-phenanthroline (dmp) as secondary ligands in aqueous/ nonaqueous media. These complexes are formulated as: [Cu(2-APCA)(bipy)(ONO2)] 1; [Cu(2-APCA)(phen)(H2O)](NO3) 2, and [Cu(2-APCA)2(dmp)(H2O)](NO3) 3. All these complexes (1–3) have been characterized by elemental analysis, molar conductance measurements, FT-IR, UV–Visible spectroscopic technique, room temperature magnetic susceptibility measurements, TGA and DSC of these complexes also done. Molar conductance measurements have been carried out in DMSO and DMF, complexes 1 and 3 correspond to non-electrolyte and complex 2 represents monocationic nature. The redox properties of the all these complexes were extensively investigated by electrochemical method using cyclic voltammetry (CV). The electrochemical behavior of complex 3, involving dmp as the secondary ligand is different from rest of two mixed-ligand Cu(II) complexes. Based on these studies, a square-pyramidal coordination geometry around the Cu(II) ion has been proposed in solid complexes (1–3). In DMSO and DMF solutions, complexes 1, 2 and 3 possess distorted octahedral geometry due to solvent coordination.