Spectral studies, cyclic voltammetry and synthesis of cobalt(II) and ruthenium(III) complexes with symmetric and asymmetric ring containing membered N 2S 2, N 4, and N 5 donor macrocyclic ligands

Abstract

Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO 3, SCN and SO 4) with macrocyclic ligands L 1, L 2 and L 3 having N 2S 2, N 4 and N 5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru–N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L 1 is more effective electron donors to ruthenium than of L 2 and L 3. Electronic spectral properties also show that the sulphur donor atom of L 1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal–ligand bonds tend to be weaker than third-row transition metal–ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to π-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism.