Air-Tight Three-Electrode Design of Coaxial Electrochemical-EPR Cell for Redox Studies at Low Temperatures

The weak point of the original Allendoerfer electrochemical-EPR cell has been the reference electrode, placed outside the space-limited electrolysis cavity or not used at all in experiments at low temperatures. We present here an elegant solution to this problem, based on a modified air-tight design of an Allendoerfer cell equipped with a silver-wire pseudoreference electrode. The cell performance is demonstrated on one-electron electrochemical oxidation of heterocyclic 3,6-diphenyl-1,2-dithiine and one-electron reduction of 6-methyl-6-phenylfulvene and the pseudo-octahedral complex fac-[Re(benzyl)(CO)3(dmb)] (dmb = 4,4'-dimethyl-2,2'-bipyridine). In the latter case, the EPR spectrum of the radical anion [Re(benzyl)(CO)3(dmb)]•- points to predominant localization of the unpaired electron on the dmb ligand, in agreement with UV-VIS and IR spectroelectrochemical data.