The electrochemical behavior of microcrystals of the [C(60)subset of(p-benzyl-calix[5]arene)(2)]. 8toluene (referred to as C(60)subset of L-2) encapsulation complex adhered to electrode surfaces in contact with CH3CN (electrolyte) has been studied using cyclic voltammetric and microgravimetric techniques. Six successive one-electron reduction processes, of which the first two have chemically reversible characteristics, are observed at a glassy carbon electrode when large Bu4N+ cations are used as the electrolyte, although dissolution of the reduced solid into the bulk solution also accompanies the reduction processes. Under the same conditions but with an electrolyte containing much smaller Li+, Na+, or Ba2+ cations, all reduction processes were found to be chemically irreversible, These chemically reversible/irreversible reduction processes are attributed to the reversible/irreversible intercalation processes of large/small electrolyte cations into the lattice of C(60)subset of L-2 crystals. In EPR studies, the g values of 2.0020 +/- 0.0002 at 293 K and 2.0022 +/- 0.0002 at 77 K found for reduced solid [C(60)subset of L-2](.-) containing Ba2+ cations suggest that significant fullerene structure distortion is present in this one-electron-reduced form of solid. Magnetic measurements indicated that extensive unpaired electron delocalization may occur within the structure of this reduced [C(60)subset of L-2](.-) solid and that the reduced solid is relatively stable in air. Data show that the interactions between C-60 and the calix[5]arene to form an encapsulation complex are sufficiently strong that free one-electron-reduced C-60 anions are not produced even during the course of reduction, as is the case with previously studied C-60 host-guest complexes.