The effect of heterocyclic S,S’-ligands on the electrochemical properties of some cobalt(III) complexes in acid

Abstract

Eight mixed-ligand cobalt(III) complexes with the macrocyclic amine 1,4,8,11-tetraazacyclotetradecane (cyclam) and a heterocyclic dithiocarbamate (Rdtc-)i.e., morpholine-(Morphdtc), thiomorpholine- (Timdtc), piperazine-(Pzdtc), N-methylpiperazine-(Mepzdtc), piperidine- (Pipdtc), 2-, 3- or 4-methylpiperidine-(2-, 3- and 4-Mepipdtc) carbodithionato-S,S ions, of the general formula [Co(cyclam)Rdtc](ClO4)2, were investigated in deoxygenated 0.1 MHClO4 solutions. Cyclic voltammetry data at a glassy carbon (GC) electrode demonstrate a redox reaction of cobalt(III) from the complexes at potentials strongly influenced by the presence of different heterocyclic Rdtc- ligands. In this respect, the complexes were separated into two groups: the first, with a heteroatom O, S or N in the heterocyclic ring, and the second, with a methyl group on the piperidine ring of the Rdtc- ligand. Anodic polarization of an Fe electrode in the presence of the complexes shows their influence not only on the dissolution of iron but also on the hydrogen evolution reactions and on this basis complexes the complexes could be divided into the same two groups. It was found that the weaker the inhibiting effect of the free heterocyclic amines is, the significantly higher is the efficiency of the corresponding complexes.

Osam mešovito-ligandnih kompleksa kobalta(III) sa makrocikličnim aminom 1,4,8,11-tetraazaciklotetradekanom (cyclam) i heterocikličnim ditiokarbamatima (Rdtc-) t.j., morfolin-(Morphdtc), tiomorfolin-(Timdtc), piperazin-(Pzdtc), N-metilpiperazin-(Mepzdtc), piperidin-(Pipdtc), 2-, 3- ili 4-metilpiperidin- (2-, 3- i 4-Mepipdtc) karboditionato-S,S jonima, opšte formule [Co(cyclam)Rdtc)](ClO4)2 , ispitano je u 0,1 M HClO4 rastvoru na elektrodi od staklastog ugljenika i gvožđa. Ciklična voltametrija na elektrodi od staklastog ugljenika pokazala je da dolazi do redoks reakcije kobalt(III) jona iz kompleksa. Različiti heterociklični Rdtc- ligandi utiču na vrednost potencijala ove redoks reakcije. Na osnovu ovih vrednosti kompleksi se mogu podeliti u dve grupe: jednu sa heteroatomom u heterocikličnom prstenu i drugu sa metil-grupom na piperidinskom prstenu Rdtc- liganda. Anodna polarizacija gvožđa u prisustvu kompleksa pokazala je njihov uticaj ne samo na reakciju rastvaranja metala već i na reakciju izdvajanja vodonika. Rezultati su pokazali da što je slabiji inhibitorski efekat heterocikličnog amina to je veći uticaj odgovarajućeg kompleksa.