No abstract

The densities of divalent transition-metal perchlorates in N,N-dimethylformamide have been measured over the whole composition range at (283.15, 293.15, 298.15, 303.15, 313.15, 323.15, and 333.15) K. From these densities, apparent molar volumes and partial molar volumes of the salts at infinite dilution as well as the expansibilities have been evaluated. The apparent molar isentropic compressibilities of transition-metal perchlorates in DMF have been determined from sound velocity data obtained at 298.15 K.

Densities and heat capacities of various 1:1 and higher-charged electrolytes have been measured in N,N-dimethylformamide (DMF) at 25 degrees C using a series-connected flow densimeter and Picker calorimeter. Standard molar volumes V (o) and isobaric heat capacities C p (o) derived from these data were split into their ionic contributions using the tetraphenylphosphonium tetraphenylborate (TPTB) reference electrolyte assumption. The values so obtained have enabled a meaningful separation of the effects of cationic size and charge for the first time in a nonaqueous solvent. As in water, V (o)(M (n+) ) values in DMF are markedly more negative for higher-charged cations due to increasing electrostriction of the solvent. In contrast, ionic charge has a much smaller effect on C p (o)(M (n+) ) in DMF than in water. Ionic volumes in DMF show the expected dependence on size but those of small monatomic monovalent cations and anions imply a significant difference in accessibility of the electron donor and acceptor sites on the DMF molecule. Ionic heat capacities in DMF show a relatively weak dependence on ionic size that, when corrected for charge, is opposite to that in water. Both V (o)(R 4N (+)) and C p (o)(R 4N (+)) in DMF show the usual linear dependence on carbon number but differ from their values in aqueous solution due to the absence of hydrophobic interactions in DMF.

Densities of solutions of sodium tetraphenylborate, tetraphenylphosphonium bromide, sodium bromide, and sodium perchlorate solutions in N,N-dimethylacetamide and N,N-dimethylformamide have been measured over the concentration range of (0.015 to 0.40) mol‚kg -1 at temperatures between T ) 283.15 K and T ) 333.15 K. From densities, apparent molar volumes and partial molar volumes of the salts at infinite dilution as well as the expansibilities have been evaluated. Moreover, the apparent molar isentropic compressibility of all electrolytes has been determined from sound velocity measurements at T ) 298.15 K. The limiting apparent molar compressibilities have been discussed in terms of possible methods of splitting them into ionic contributions.