ION-SOLVENT INTERACTION - EFFECTS OF ADDED POLAR COMPOUNDS ON THE CONDUCTANCES OF LITHIUM, SODIUM, AND TRI-NORMAL-BUTYLAMMONIUM PICRATES IN TETRAHYDROFURAN AT 25-DEGREES-C

The conductances of lithium picrate have been measured at 25°C as a function of salt concentration in tetrahydrofuran (THF) with and w ithout small amounts (up to 0.01 M) of added hexamethylphosphoric triantide (HMPA), dimethyl sulfoxide (Me2SO), and dimethylformamide (DMF). The conductances of sodium picrate and of tri-n-butylammonium picrate have been measured as a function of salt concentration in pure THF and in the presence of added HMPA. Values of ion pair dissociation constants, KDfor each of the salt-ligand systems have been derived from these data using estimated values of the limiting equivalent conductances. A0. The values of KDincrease linearly (except for NaPi-HMPA) with increasing addend concentration. These increases are interpreted as being due to cation-ligand complex formation. The equilibrium constants, K1+, for cation-ligand complex formation have been calculated and are found to be 17000 M-lfor HMPA with Li+, 140 M-1for Me2SO with Li+. 50 M-1for DMF with Li+. 430 M-1for HMPA with Na+, and 880 M-lfor HMPA with Bu3NH+In conjunction with other results in the literature, it is shown that the exchanges of one ligand for another on these cations are independent of the surrounding solvent to a good first approximation. A strong correlation is found between the standard free energies of exchange of one ligand for another on a cation and the standard free energy of transfer of that cation from one ligand as solvent to the other ligand as solvent. © 1979, American Chemical Society. All rights reserved.