Redox active liquid membranes: transport of electrons across a dichloromethane layer mediated by the [CoIIIL1X2]+-[CoIIL1X2] cobalt redox system (L1 = 1-hexadecyl-1,4,8,11-tetraazacyclotetradecane, X = Cl or ClO4)

Lipophilic [CoIIILCl2]Cl (L = 1-hexadecyl-1,4,8,11-tetraazacyclotetradecane) can transport electrons, through the CoIII-CoII redox change, from an aq. phase contg. CrII to an aq. phase contg. the mild oxidizing agents FeIII or [NiIIIL1]3+ (L1 = 1,4,8,11-tetraazacyclotetradecane), in aq. HCl, across a bulk CH2Cl2 membrane. The transport of electrons, to which a counter transport of Cl- is coupled, implies that the potential assocd. with the [CoIIILCl2]Cl + e- → CoIILCl2 + Cl- half-reaction (-0.60 V vs. ferrocenium-ferrocene, measured in a CH2Cl2 soln., 0.1 mol dm-3 in NBu4Cl) should lie between that assocd. with the aq. CrIII-CrII couple and that assocd with the aq. Q-Q- couple (Q = FeIII or [NiIIIL1]3+). Replacement of Cl- by ClO4- stops the electron transport from CrII to FeIII or [NiIIIL1]3+. This is ascribed to the esp. high potential assocd. with the [CoIIIL(ClO4)2]ClO4 + e- → CoIIL(ClO4)2 + ClO4- half-reaction. CoIIL(ClO4)2 in a CH2Cl2 soln., covered by a layer of aq. HClO4, is not oxidized even by bubbling O2. This complex can transport electrons, across the bulk CH2Cl2 membrane, from aq. CrII only to the strong oxidizing agent CeIV in aq. HClO4.