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Stability constants and derived Gibbs energies and enthalpies and entropies of complexation of alkali−metal cations and macrocycles (18-crown-6 and ethyl p-tert-butylcalix(6)arenehexanoate) in benzonitrile at 298.15 K derived from titration calorimetry (macro and micro) are first reported. These data are compared with those previously reported for cryptand 222 and these cations in this solvent. A “peak” selectivity is observed for the complexation of the calix(6)arene ester and alkali metal cations with a monotonic increase in stability from lithium to potassium followed by a decrease from the latter to rubidium. This behavior is analogous to that shown for cation binding involving 18-crown-6 and cryptand 222. Similar to the process of complex formation involving these ligands, that involving the calix(6)arene ester and these metal cations is enthalpy controlled with an exothermic maximum for the potassium cation. Among the ligands considered, thermodynamic data involving cation−calix(6)arene ester interactions are characterized by a lower enthalpic stability (less exothermic) and a more favorable entropy (except for K+) than corresponding data involving cryptand 222 or indeed 18-crown-6. These results are analysed in terms of solute−solvent interactions reflected on the solution thermodynamic data of the free and the complexed electrolytes and the ligand in benzonitrile. Standard enthalpies of solution of macrocycles and their sodium and potassium salts in benzonitrile measured calorimetrically are discussed in relation to (i) corresponding data for the uncomplexed salts and (ii) previously reported data for sodium and potassium cryptate salts in various solvents. Enthalpies of coordination referred to the process in the solid state for eighteen systems involving sodium and potassium coronates, cryptates, and calix(6)arenates are derived and whenever possible these are discussed on the basis of (i) available X-ray crystallographic data and (ii) the anion effect on the coordination process.

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No abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract