EFFECTS OF ELECTRONEGATIVE SUBSTITUENTS OF ANIONS ON ION-PAIR FORMATION .2. THE TEMPERATURE-DEPENDENCE OF CONDUCTIVITY OF LITHIUM TRIFLUOROACETATE AND LITHIUM DIFLUOROACETATE SOLUTIONS IN PROPYLENE CARBONATE

The interpretation of the molar conductivity of lithium trifluoroaceta te and lithium difluoroacetate solutions in propylene carbonate obtain ed from precise measurements at temperatures 238.15 less than or equal to T/K less than or equal to 308.15 in the concentration range 7 < 10 (4) c/mol dm(-3) < 90 requires the consideration of ion-pair and unila teral triple-ion formation despite the high permittivity of the solven t. Association constants and triple-anion formation constants strongly increase at decreasing temperature, in accordance with the assumption of strong non-Coulombic effects. At all temperatures the association constants of lithium trifluoroacetate are lower than those of lithium difluoroacetate, revealing the electron withdrawing effect of the subs tituent decreasing the charge density on the oxygen atoms. Traces of w ater increase the conductivity of the solution, showing that water sel ectively solvates the lithium ion.