Electrochemical, EPR, and magnetic studies on microcrystals of the [C₆⊂(p-BenzyI-calix[5]arene)₂]·8toluene and its one-electron-reduced encapsulation complex

The electrochemical behavior of microcrystals of the [C₆₀⊂(p-benzyl-calix[5]arene)₂]·8toluene (referred to as C₆₀⊂L₂) 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 C₆₀⊂L₂ 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 [C₆₀⊂L₂]^·- 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 [C₆₀⊂L₂]^·- solid and that the reduced solid is relatively stable in air. Data show that the interactions between C⁶⁰ and the calix[5]arene to form an encapsulation complex are sufficiently strong that free one-electron-reduced CM anions are not produced even during the course of reduction, as is the case with previously studied CM host-guest complexes.