Water-soluble fullerenes.: 3.: Alkali salts of fullerenehexamalonic acid Th-C66(COOH)12

The electrical conductivity, the osmotic coefficient, the apparent molar volume, and the enthalpy of dilution of aqueous solutions of the lithium and cesium salts of fullerenehexarnalonic acid, C-66(COOH)(12), were measured at 25 degreesC in a wide concentration range. The data for the sodium salt published previously were included for comparison. 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 numbers in solutions of the three alkali fullerenchexamalonates, 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. The mean value of the limiting molar conductivity of the macroion constituent was Lambda(0) [1/12 C-66 (COO-)(12)] = (104.8 +/- 5) Omega(-1) cm(2) mol(-1). The curves of the apparent molar volumes and the enthalpies of dilution display minima at low concentrations, a finding which is characteristic for hydrolyzing electrolytes. Comparison of experimental data with predictions of the spherical cell model shows a semiquantitative agreement.