Intercalation of dicarboxylate anions into a Zn-Al-Cl layered double hydroxide: microcalorimetric determination of the enthalpies of anion exchange

The enthalpies of anion exchange in a chloride-intercalated zinc aluminium layered double hydroxide (LDH) in suspension in water have been studied at 25degreesC. The heat effects associated with the exchange of the chloride anions for dicarboxylate anions (oxalate, succinate, adipate and tartrate) have been determined by titration microcalorimetry for different amounts of LDH. Except for tartrate, the exchange processes are endothermic, in contrast to the exchange processes involving only inorganic anions. The enthalpies of exchange vary linearly with the number of carbon atoms, suggesting that the intercalated dicarboxylate anions are perpendicular to the layers. The energetic parameters show, for the first time, hydrophobic interactions between the CH2 groups of the parallel succinate or adipate anions and hydrogen bonding between the OH groups of the parallel tartrate anions.