Electrochemical study of copper chloride complexes in the RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

The electrochemistry of copper(I) and copper(II) chloride complexes in the RTIL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMPTf2N, has been studied with constant current electrolysis and cyclic staircase voltammetry at temperatures between 21.0 and 96.0 °C and in different concentrations of chloride. The chloride concentration was controlled by addition of 1-butyl-1-methylpyrrolidinium chloride, BMPCl. An important finding is the evidence of a three-coordinated complex, Cu(I)Cl32− which has not been found in organic chloroaluminates without a significant increase in temperature. Two Cu(I) species were found at molar ratios of [Cl−]/[Cu] < 4. The kinetic parameters for the quasi-reversible Cu(I)–Cu(II) electron transfer were obtained with non-linear fitting. Successful fits required that the charge transfer coefficients for the reduction of Cu(II) (α) and oxidation of Cu(I) (β) did not sum up to unity, i.e. α + β ≠ 1. This result was interpreted using Tsallis non-extensive thermostatistics.