Effect of temperature on the molar conductivity of aqueous solutions of sodium and calcium fullerenehexamalonates, Th-C66(COONa)12 and Th-C66((COO)2Ca)6

Abstract

Electrical conductivity measurements on aqueous solutions of the sodium and calcium salts of fullerenehexamalonic acid, C₆₆(COONa)₁₂ and C₆₆((COO)₂Ca)₆, were carried out at four temperatures: 5, 15, 25 and 35°C, and in the concentration range from about 0.04 to 0.0001 mol (COO⁻) dm⁻³. Few measurements were also performed at 25°C on mixed solutions of C₆₆(COONa)₁₂ and C₆₆((COO)₂Ca)₆. The limiting equivalent conductivities of the fullerenehexamalonate anion were estimated: Λ₀[1//₁₂C₆₆(COO⁻)₁₂] = 68.9, 91.4, 115.4 and 137.2 Ω⁻¹ cm² mol⁻¹, respectively, at the temperatures of our measurements. Walden's product for the fullerenehexamalonate anion is practically independent of the temperature and is close to the theoretical value predicted by the Stokes' law. Following the idea of association of counterions with the macroion we estimated the values of the molar conductivity of the fullerene macroion constituent and its transport number, assuming for the fraction of apparently free counterions the theoretical values based on the solution of the Poisson–Boltzmann equation for the spherical cell model. A reasonable concentration dependence of these properties has been observed.