Extensive electrochemical measurements of the kinetic parameters for electron transfer in aqueous bis(1,4,7-trithiacyclononane)copper(II) ([CuII(TTCN)2]) and its Cu(I) analog have been carried out at a glassy carbon electrode. Our studies have shown that the [CuII(TTCN)2]/[CuI(TTCN)2] system follows an ECEC square mechanism rather than just simple electron transfer as suggested previously. Unlike the octahedral Cu(II) complex, [Cu(TTCN)2]PF6 crystallizes with two independent formula units in space group P21/n of the monoclinic system with unit cell dimensions a = 8.608 (3) Å, b = 31.041 (8) Å, c = 16.008 (4) Å, and β = 90.88 (2)°. The two molecular units have distorted tetrahedral CuS4 coordination spheres with monodentate and tridentate TTCN ligands. The mondentate ligands have a unique conformation for the TTCN moiety with Cu(I) coordinated differently in each of the two independent [CuI(TTCN)2] units. The ring conformation, however, remains the same. The uncoordinated sulfur atoms on the monodentate TTCN ligand can coordinate to a metal ion added to the solution, and this ligand ultimately reverts to a tridentate ligand with the standard endodentate [3 3 3] conformation of the TTCN moiety. The transient trinuclear complex with added Cu(II) can be detected both electrochemically and spectrophotometrically. Electrochemical oxidation of [CuI(TTCN)2] and reduction of [CuII(TTCN)2] both occur rapidly, but in both cases, the electron transfer is followed by chemical steps. These chemical steps are the conformational reorganization of the monodentate TTCN ligand into the tridentate [3 3 3] conformer and the reverse of this process, respectively. Digital simulations of the cyclic voltammetric data for the kinetic parameters of both the [CuII(TTCN)2]/[CuI(TTCN)2] system and the entire mechanism of the interaction between [CuI(TTCN)2] and Cu(II) followed by the subsequent reduction of the intermediate have been carried out.
ASJC Scopus subject areas
- Colloid and Surface Chemistry