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

Abstract

Electrochemical stability of eight complexes of the general formula [co 111 Rdtc(1-8)cyclam](ClO 4 ) 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 NaClO 4 solution and nonaqueous LiClO 4 in CH 3 CN 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.