Thermodynamics of Bolaform Electrolytes. III. Partial and Apparent Molal Volumes in H2O and D2O1

The apparent, phi(v), and partial, (V) over bar (2), molal volumes of a series of homologous bis-tetraalkylammonium bromides have been determined in H2O and D2O at 25 degrees C from precision density measurements carried out with a buoyancy density meter and a dilatometer. The Debye-Huckel theoretical limiting slope for phi(v) and (V) over bar (2) as a function of the square root of molar concentration is approached for all of the salts studied. The concentration dependence of phi(v) and (V) over bar (2) is anomalously large and negative in both solvents, with the deviations being less negative in D2O than in H2O. The bolaform salts have larger (V) over bar degrees(2) values in H2O than in D2O, contrary to the observed behavior of R4NX salts. Possible origins of the solvent isotope effects observed are discussed in terms of structural and cavity contributions to the measured volumes. A comparison of thermodynamic transfer functions ( H2O -> D2O) for Et4NBr and the corresponding bolaform analog appropriate in the consideration of cation-cation pairing of Et4N+ ions shows inconclusive evidence for the support of the cation pair theory.