Tetranuclear Ru Complex Linked via Redox-Active Azobis(bipyridine) Ligands as a Redox-Responsive Photoswitch Aminoethanethiolate or L-Cysteinate

The UV-vis spectroelectrochemical properties of S-bridged tricobalt(III) complexes [CoIII{CoIII(aet or L-cys)3}2]^3+ or ^3- and dicobalt(III) complexes [CoIII{CoIII (aet or L-cys)3}(dien)]^3+ or 0 (aet = 2-aminoethanethiolate, L-cys = L-cysteinate, dien = diethylenetriamine) were investigated using a thin-layer quartz cell with a platinum mesh working electrode. The absorption spectroelectrochemical measurements for the tricobalt(III) complexes indicated that a two-electron reduction proceeds through pseudo two-steps, CoIIICoIIICoIII (right arrow) CoIIICoIICoIII (right arrow) CoIIICoIICoII for the aet complex, while through pseudo one-step for the L-cys complex. The CD spectroelectrochemical measurements demonstrated that the optically active isomer ((delta)(delta) form) of the aet tricobalt(III) complex loses chirality during the oneelectron reduction, whereas the (delta)LLL(delta)LLL isomer of the L-cys tricobalt(III) complex is reduced with an inversion of configuration, to form the (lambda)LLL(lambda)LLL isomer. The (lambda)LLL(lambda)LLL isomer is reduced with a retention of configuration. The aet and L-cys dicobalt(III) complexes were converted to the corresponding tricobalt(III) complexes by electrochemical reduction, accompanied by the release of the Co(II) ion and dien ligand. It was also elucidated that this conversion occurred with a retention of configuration.