Preparation, characterisation and complexation of a redox-active, soft-donor macrocycle

Two new redox-active macrocycles 2 and 3 have been prepared based on an 18-membered S4N2-donor ring conjugated to one or two CpCo(dithiolene) redox/chromophore units respectively. Cyclic voltammetry for 2 showed one reversible reduction process at -0.29 V and EPR spectroscopy of the reduced form indicated a significant degree of delocalisation of the unpaired electron. The compound 2 showed an intense low-energy absorption at 675 nm (in CH2Cl2) that was shown to shift to higher energy during electrochemical reduction. Interaction of 2 with guest Ag(I) ions was followed by monitoring changes in the electrochemical and spectroscopic behaviour with sequential additions of the guest metal ion and by electrochemistry at a silver electrode. UV/Vis spectroscopic results indicated a strong interaction of Ag(I) with 2 involving large changes in the electronic nature of the macrocycle chromophore. Cyclic voltammetry also indicated interaction between 2 and Ag(I) and suggested the involvement of a film containing 2 on the electrode surface.