Electroswitchable binding of [Co(dipy)3]3+ and [Fe(dipy)3]2+n-sulfonato(thia)calix[4]arenas

The methods of cyclic voltammetry, electrolysis, and spectrophotometry were used to study electrochemical properties of (TCAS + Fe3+ + dipy), (CCAS + Fe3+ + dipy), and (CCAS + Fe3+ + [Co(dipy)3]3+) triple systems (where TCAS is n-sulfonatothiacalix[4]arene, CCAS is tetracarboxylate n-sulfonatocalix[4]arene, and dipy = α,α′-dipyridyl) in an aqueous solution. One-electron reduction of Fe(III) in the (TCAS + Fe3+ + dipy) system at pH 2.5 results in electroswitching of iron ions from the lower TCAS ring to the upper ([Fe(dipy)3]2+). Reverse electrochemical switching of the system is impossible due to mediator ([Fe(dipy)3]2+/3+) oxidation of TCAS. Reverse electroswitching of Fe(III) ions from unbound to bound state as ([Fe(dipy)3]2+) with CCAS has been revealed in the system (CCAS + Fe3+ + dipy) (pH 1.7) upon single-electron transfer, whereas reversible electroswitching by the upper rim of CCAS from one complex ion ([Co(dipy)3]3+) to another ([Fe(dipy)3]2+) has been demonstrated in the system ([Co(dipy)3]3+ + CCAS + Fe3+ upon double-electron transfer. In all systems, electric switching was accompanied by synchronous color switching.