Molecular structure in correlation with electrochemical properties of mixed-ligand cobalt(III) complexes

Four mixed-ligand cobalt(III) complexes (1–4) of the general formula [Co(Rdtc)cyclam](ClO4)2 and [Co(Rac)cyclam](ClO4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane; Rdtc = thiomorpholine-(Timdtc) or 2-methylpiperidine-(2-Mepipdtc) dithiocarbamates; Rac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato (Hfac) or 2,2,6,6-tetramethyl-3,5-heptanedionato (Tmhd), respectively) were electro­chemically examined on a glassy carbon and an iron electrode in perchloric acid solution. The obtained results showed the influence of these complexes on hydrogen evolution, the oxygen reduction reaction and iron dissolution. The exhibited effects of the complexes on these reactions depend on structure related to the bidentate dithiocarbamato or b-diketonato ligand. The electrochemical properties of the complexes were correlated with molecular structure and parameters derived from spectral analysis and molecular modeling

Comparative electrochemical study of some cobalt(III) and cobalt(II) complexes with azamacrocycles and b-diketonato ligands

The electrochemical properties of eight mixed-ligand cobalt(III) and cobalt(II) complexes of the general formulas [CoIII(Rac)cyclam](ClO4)2 (1)(4) and [Co2II(Rac)tpmc](ClO4)3 (5)(8) were studied. The substances were investigated in aqueous NaClO4 solution and non-aqueous LiClO4/CH3CN solution by cyclic voltammetry at a glassy carbon electrode. In aqueous solution, cyclam and Rac ligands being soluble in water undergo anodic oxidation. Coordination to Co(III) in complexes 14, stabilizes these ligands but reversible peaks in catohodic region indicate the redox reaction CoIII/CoII ion. In the case of the binuclear Co(II) complexes 58, peaks recorded on the CVs represent oxidation of the bridged Rac ligand. The complexes examined influence the cathodic reaction of hydrogen evolution in aqueous solutions by shifting its potential to more negative values and its current is increased. In non-aqueous solution the CVs of the ligands show irreversible anodic peaks for cyclam, tpmc and for the Rac ligands soluble in acetonitrile. The absence of any peaks in the case of the investigated complexes 14 indicates that coordination to Co(III) stabilizes both the cyclam and Rac ligands. Cyclic voltammograms of the complexes 58 show oxidation processes of the Rac ligand and Co(II) ions but the absence of a highly anodic peak of the coordinated macrocycle tpmc shows its stabilization. Contrary to in aqueous solution, the redox reaction Co(III)/Co(II) does not occur in acetonitrate indicating a higher stability of the complexes 14 in this media in comparison with the binuclear cobalt(II)-tpmc complexes 58

Thermal stability and kinetic studies of new cobalt(III) complexes with a tetraazamacrocyclic and dithiocarbamate ligands

The thermal properties of four cobalt(III) complexes with cyclam (1,4,8,11-tetraazacyclotetradecane) and the heterocyclic dithiocarbamates Rdtc(-) [2-, 3-, 4-methylpiperidine (2-, 3-, 4-Mepipdtc(-)) or 4-thiomorpholine (Timdtc(-)) dithiocarbamates], of the general formula [Co(Rdtc)cyclam](ClO4)(2), have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal decomposition pathways of these complexes were also proposed. The following thermal stability order can be recognized for the examined complexes. depending on the position of the methyl group on the piperidine ring coordinating dithiocarbamates 2- GT 3- GT 4 -Mepipdtc(-). Generally, the same order was found to affect the decrease in kinetic and activation parameters.Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavi