Electrochemical examination of mixed-ligand cobalt(III) complexes with tetraazamacrocyclic ligand and heterocyclic dithiocarbamates

摘要

Electrochemical stability of eight complexes of the general formula [Co(III)Rdtc(1-8)cyclam](ClO4)(2), where cyclam = 1,4,8,11-tetraazacyclotetradecane and Rdtc(-) (1-8) = 4-morpholine (Morphdtc), 4-thiomorpholine (Timdtc), 4-piperazine (Pzdtc), N-methyl piperazine (N-Mepzdtc), piperidine (Pipdtc), 2-, 3- or 4-methylpiperidine (2-, 3- or 4-Mepipdtc) dithiocarbamates, respectively, were studied. The substances were examined in aqueous NaClO4 solution and nonaqueous LiClO4 in CH3CN solution by cyclic voltammetry. In aqueous solution, macrocyclic ligand cyclam is characterized by the anodic peak at 0.95 V. The Rdtc(-) ligands have two anodic peaks, one in the region 0.25-0.30 V and the other in the 0.78-0.95 V region. Absence of these anodic peaks in the case of the complexes indicates that coordination to cobalt(III) stabilizes both cyclam and Rdtc(-) ligands, but reversible peaks in the range -0.68 to -0.78 V support the Co(III) redox reaction. In nonaqueous solutions cyclam has one anodic peak at 1.75 V. The ligands with heteroatom in the ring (Morphdtc, Timdtc, Pzdtc, N-Mepzdtc) have two anodic peaks, while the other four ligands (Pipdtc, 2-, 3- and 4-Mepipdtc) have only one anodic peak. In nonaqueous solution again, coordination to Co(III) ion stabilizes the Rdtc(-) ligands and contrary to aqueous solution no Co(III) redox reaction occurs, indicating a greater stability of the complexes in this media. Finally, the electrochemical results are compared with spectroscopic data obtained previously. [References: 30]