Interfacial Electron Transfer to the Zeolite-Encapsulated Methylviologen Acceptor from Various Carbonylmanganate Donors. Shape Selectivity of Cations in Mediating Electron Conduction through the Zeolite Framework

摘要

The series of (one-electron) reductions of methylviologen (MY2*) intercalated into zeolite-Y by various carbonylmanganate donors [C~+Mn(CO)4L~-, L = CO, P(OPh)_3] are very selective and highly dependent on the size/ shape of the counterion C~+, although the same electron transfers carried out (homogeneously) in solution always occur spontaneously, trregardless of C~+. For example, the complete reduction of MV~(2+) extensively doped into zeolite-Y proceeds rapidly and quantitatively when the Na~+ salts of the carbonylmanganates are employed as the reductants, but only to a very limited extent (1%) when the large PPN~+ [bis(triphenylphosphine)iminium] salts of the carbonylmanganates are employed. The medium-size tetraethylammonium (TEA~+) salt of Mn(CO)_4P(OPh)_3~-slowly effects an intermediate conversion (80%). Based on the fact that the large phosphite-substituted Mn(CO)4P(OPh)r donor cannot enter the supercage of zeolite-Y, we propose interfacial electron transfer from the carbonylmanganate to theMV~(2+) acceptor to occur only at the zeolite periphery. Importantly, the strong dependence of the further progress of the redox reaction with decreasing size of the cation C~+ (i.e., shape selectivity) predicts that electron conduction throughout the zeolite framework requires the simultaneous transport of these cations in order to effect the complete reduction of all the encapsulated MV~(2+), as presented in Chart 5.