Ion association and solvation of perchlorate salts in N,N-dimethylformamide and N,N-dimethylacetamide

Abstract

The results of dielec. relaxation expts. on solns. of LiClO4, NaClO4 and Bu4NClO4 in N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA), performed at 25 °C in the frequency range 0.2 ≤ ν/GHz ≤ 89 are presented. For all electrolytes, a solute relaxation process due to ion pairs is obsd. in addn. to the solvent relaxation. The alkali salts form predominantly solvent-shared ion pairs in DMF and DMA, whereas contact ion pairs are obsd. for Bu4NClO4. In all cases, the rate of ion-pair formation is nearly diffusion-controlled. Effective solvation nos. were deduced from the solvent dispersion amplitude. Data suggest that the anion-solvent interactions are weak, whereas the alkali ions form a well-defined primary solvation shell. Interestingly, irrotational bonding of solvent mols. by Bu4N+ is obsd., possibly due to steric interactions.