Electrochemical, spectroelectrochemical, and pyridine binding properties of tetrathia macrocycle-bridged dimeric cobalt phthalocyanine

Tetrathia macrocycle-bridged dimeric cobalt phthalocyanine, [(RS) ₆CoPc]₂CR where R=C₆H₁₃, CR=[1,4,7,10-tetrathia-(12-crown-4)], was investigated electrochemically and spectroelectrochemically. Pyridine binding properties of the complex were also investigated by spectrophotometric technique in the solution of dichloromethane. The neutral complex undergoes two quasi-reversible two-electron-oxidations and two quasi-reversible two-electron-reductions in CH₂Cl₂ containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The half-wave potentials for oxidation of the hexylthio substituted complex are located at E_1/2=0.65 and 1.28 V, while the two reductions are located at E _1/2=-0.38 and -1.37 V vs. SCE. These potentials of the complex show little or no difference compared to those of unsubstituted CoPc and other SR substituted phthalocyanines under the same experimental condition, thus suggesting the weak electron-donating properties of the peripheral hexylthio substituents on the phthalocyanine rings. Evaluation of the well-defined UV-Vis spectra of the neutral complex and its electrochemically oxidized and reduced, {[(RS)₆Co(2+)Pc(-)]₂CR}²⁺, {[(RS) ₆Co(+)Pc(2-)]₂CR}^2-, and {[(RS) ₈Co(+)Pc(3-)]₂CR}^4-, species obtained with applied potentials in thin layer cell showed that neutral and mono-oxidized species remained its highly aggregation properties while mono- and doubly reduced complexes behave as monomeric form in the solution as a result of a weak coupling effect. The complex was also investigated as to pyridine-binding ability in dichloromethane/pyridine mixtures. Spectroscopic changes were monitored by UV-Vis spectrophotometry where the Q band of the neutral complex resulted in an increase in intensity, which was associated with the formation of pyridine mono-adduct for binuclear cobalt phthalocyanine complex, [(RS) ₆CoPc]₂CR.