We report a microcalorimetry study of the association of various inorganic and organic cations with p-sulfonatocalix[4]arene at 298.15 K. First, we have studied the electrostatic attraction between host 1 and seven rare-earth-metal cations representative of the whole lanthanide series (La 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Dy 3+ and Yb 3+ ) in an acidic solution (pH 2). In order to compare the charge effects in the electrostatic interactions we have also studied the attraction between host 1 and two alkaline-earth-metal cations (Ca 2+ and Mg 2+ ). Next, we investigated the binding of a series of quaternary ammonium cations in an acidic solution (pH 2). For each system, both the apparent association constant and enthalpy of complexation have been extracted from the calorimetric data. In all cases, our results are consistent with the formation of 1 : 1 complexes. Whereas for the inorganic cations (alkaline-earthmetal and lanthanide cations) the association process is enthalpically unfavoured (∆ r H Њ>0) and entropically favoured (∆ r SЊ>0), the complexation is driven by a favourable enthalpy change for the organic cations. These thermodynamic properties show that the organic and inorganic cations bind in very different modes.

The layered double hydroxides (LDHs) Zn2Al(OH)6Cl·nH2O, Zn2Cr(OH)6Cl·nH2O, and Cu2Cr(OH)6Cl·nH2O have been shown to undergo staged intercalation reactions with succinate and tartrate anions. Monitoring the process in situ using energy-dispersive X-ray diffraction reveals the formation of second-stage intermediates caused by the filling of every second layer. Depending on the nature of the organic anion, the Bragg peaks of the second-stage intermediates and the fully organic exchanged materials emerge in two distinct sequences indicating two exchange pathways. For tartrate exchange, the fully exchanged material is not observed until the intermediate has gone through its maximum and the chloride precursor has disappeared completely, while for succinate exchange, the final state of intercalation and the second-stage intermediate simultaneously appear. Similar staging has previously been reported only for LiAl2(OH)6Cl·2H2O. These results demonstrate that staging in the intercalation of LDH does not involve a structural order of the host and cannot be explained by a tactoid mechanism.

The thermodynamic properties of anion exchange on a chloride-intercalated zinc-aluminium layered double hydroxide have been studied at 298.15 K. The heats for total exchange of Cl Ϫ for F Ϫ , Br Ϫ , I Ϫ , OH Ϫ , NO 3 Ϫ , and SO 4 2Ϫhave been determined by microcalorimetry and the standard molar enthalpies of these exchange reactions have been estimated. For the processes involving OH Ϫ and NO 3 Ϫ , the exchange isotherms have been determined using potentiometry in the former case and capillary ion analysis in the latter. The standard molar Gibbs free energy and entropy changes upon exchange of Cl Ϫ for OH Ϫ and exchange of Cl Ϫ for NO 3 Ϫ have been calculated as a function of the fraction of exchanged Cl Ϫ . These exchange processes appear to be entropy-driven, but the selectivity is controlled by the enthalpic contribution.

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