Enhanced electrostatic interactions for selective and controllable permeation of ionic species at a monolayer of self-assembled dicationic nickel complex

Abstract

Abstract Electrodic reactions of solution-dissolved ionic redox probes were carried out at a self-assembled monolayer (SAM) and mixed monolayers of {dinickel(II) (2,2-bis(1,3,5,8,12-pentaazacyclotetradec-3-yl)-diethyl disulfide) perchlorate}, 1 , on polycrystalline Au electrodes. Electrostatic repulsive interaction between the dicationic nickel(II) redox center of the SAM of 1 and the solution-dissolved [Ru(NH 3 ) 6 ] 3+ complex inhibits this complex from undergoing electrodic reaction, e.g. the peak-to-peak separation (Δ E p ) of the cyclic voltammogram (CV) for the [Ru(NH 3 ) 6 ] 3+/2+ couple in a 20 mM NaNO 3 solution is more than 600 mV, which is much larger than that (60 mV) at the bare Au electrode. On the other hand, the redox reaction of electroactive anions, [W(CN) 8 ] 3−/4− and [Fe(CN) 6 ] 3−/4− redox couples, occurs at the SAM of 1 without any inhibition such as that for the [Ru(NH 3 ) 6 ] 3+/2+ couple. A reversible redox wave was observed for the [W(CN) 8 ] 3−/4− redox couple at the SAM of 1 with the Δ E p value of 69 mV; but at a bare Au electrode, a quasi-reversible redox wave with Δ E p =270 mV was obtained. Such different electrodic reactions of the highly positively and negatively charged redox probes at the SAM of 1 possessing a short alkyl chain (its carbon number is 2) were explained as being due solely to the electrostatic interactions between the SAM of 1 and the redox probes in solution. The results obtained here illustrate the selective and controllable permeation of electroactive cations and anions at the monolayer electrodes.