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

Electrochemical stability of eight complexes of the general formula [Co(III )Rdtc(1-8)cyclam](ClO4)(2), where cyclam = 1,4,8,11-tetraazacyclotetradecan e 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, respe ctively, were studied. The substances were examined in aqueous NaClO4 solut ion and nonaqueous LiClO4 in CH3CN solution by cyclic voltammetry. In aqueo us 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 0.2 5-0.30 V and the other in the 0.78-0.95 V region. Absence of these anodic p eaks in the case of the complexes indicates that coordination to cobalt(III ) stabilizes both cyclam and Rdtc(-) ligands, but reversible peaks in the r ange -0.68 to -0.78 V support the Co(III) redox reaction. In nonaqueous sol utions 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 anodi c peak. In nonaqueous solution again, coordination to Co(III) ion stabilize s the Rdtc(-) ligands and contrary to aqueous solution no Co(III) redox rea ction occurs, indicating a greater stability of the complexes in this media . Finally, the electrochemical results are compared with spectroscopic data obtained previously.