Synthesis, electronic spectroscopy, electrochemistry and catalytic activity of a new Co (II) complex of 1,4,8,11-tetraaza[14]annulene derivative

A new Co (II) complex of 6,13-disubstituted 1,4,8,11-tetraaza[14]annulene derivative has been synthesized by template condensation reaction of 2-(1-quinolinium-1-yl) trimethinium salt (B) with 1,2-diaminopyridine in the presence of Co (II) acetate in DMF. The electrochemical behavior of the metal complex showed a CoII/CoI redox couple at about −0.99 V vs. Ag/Ag+ in DMF solvent. Axial ligation of N-donor ligands such as pyridine and imidazole was found to shift the reduction potential of CoII/CoI to more negative potential. The binding of N-donor axial ligands to the metal complex was monitored by measuring changes at about 458 nm (maximun absorption of the metal complex) and shifts in the CoII/CoI redox couple potential upon addition of various concentrations of the N-donor axial ligand. Results showed that the number of axial ligand molecules bound to the metal complex is ≈1 and the oxidized state of cobalt (CoII) is more stabilized than the reduced state (CoI) in the presence of the axial ligand. The metal complex also showed catalytic activity toward hydrogen peroxide decomposition in the presence of the N-donor axial ligand.