Ion association and solvation behavior of tetraalkylammonium iodides in binary mixtures of dichloromethane plus N,N-dimethylformamide probed by a conductometric study

Precise measurements on electrical conductances of tetraalkylammonium iodides, R4NI (R = n-butyl to n-heptyl), in different mass% (0-100) of dichloromethane (DCM) + N,N-dimethylformamide (DMF) at 298.15 K have been performed. Limiting molar conductances (Lambda(0)), association constants (K-A) and co-sphere diameter (R) for ion-pair formation in the mixed solvent mixtures have been evaluated using the Fuoss conductance-concentration equation. However, the deviation of the conductometric curves (Lambda versus root c) from linearity for the electrolytes in 100 mass% of DCM indicated triple ion formation, and therefore corresponding conductance data have been analyzed by the Fuoss-Kraus theory of triple ions. Limiting ionic molar conductances lambda(+/-)(0) have been calculated by the reference electrolyte method along with a numerical evaluation of ion pair and triple ion formation constants (K-P approximate to K-A and K-T). The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents.