Electrochemical, EPR, and magnetic studies on microcrystals of the [C-60 subset of (p-benzyl-calix[5]arene)(2)]center dot 8toluene and its one-electron-reduced encapsulation complex
Am. Bond et al., Electrochemical, EPR, and magnetic studies on microcrystals of the [C-60 subset of (p-benzyl-calix[5]arene)(2)]center dot 8toluene and its one-electron-reduced encapsulation complex, J PHYS CH B, 104(34), 2000, pp. 8129-8137
The electrochemical behavior of microcrystals of the [C(60)subset of(p-benz
yl-calix[5]arene)(2)]. 8toluene (referred to as C(60)subset of L-2) encapsu
lation complex adhered to electrode surfaces in contact with CH3CN (electro
lyte) has been studied using cyclic voltammetric and microgravimetric techn
iques. Six successive one-electron reduction processes, of which the first
two have chemically reversible characteristics, are observed at a glassy ca
rbon electrode when large Bu4N+ cations are used as the electrolyte, althou
gh 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/irre
versible 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(6
0)subset of L-2](.-) containing Ba2+ cations suggest that significant fulle
rene structure distortion is present in this one-electron-reduced form of s
olid. Magnetic measurements indicated that extensive unpaired electron delo
calization 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 en
capsulation 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.