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Complexation of the Sodium Cation by a Calix[4]arene Tetraester in Solution. Formation of a 2:1 Calixarene:Sodium Complex

1997; American Chemical Society; Volume: 101; Issue: 10 Linguagem: Inglês

10.1021/jp962538q

1520-6106

Yaël Israëli, Christian Detellier,

Supramolecular Chemistry and Complexes

The complexation of the sodium cation by a calix[4]arene tetraester, 5,11,17,23-tetra-p-tert-butyl-25,26,27, 28-tetrakis((ethoxycarbonyl)methoxy)calix[4]arene (1) was studied by 1H and 23Na NMR in a 50:50 v:v mixture of deuteriated acetonitrile and deuteriated chloroform. A 1:1 complex was formed, in very slow exchange, both on the 1H and on the 23Na NMR time scales, with solvated calixarene and sodium cation, respectively. From 1H NMR 2D exchange spectroscopy experiments and 23Na NMR line width analysis, an upper limit of the rate constant for the dissociation of the 1:1 complex was estimated to be 3 Hz. A 2:1 calixarene:sodium complex in fast exchange with the 1:1 complex was evidenced by 23Na NMR. The characteristic 23Na NMR line widths of the 1:1 and of the 2:1 complexes, determined at several temperatures, were linearly related, with a slope of 1.8 ± 0.2. This corresponds to a reorientational correlation time, characteristic of the 23Na quadrupolar relaxation, twice as large in the case of the 2:1 complex than in the case of the 1:1 complex. The standard enthalpy and the standard entropy of formation of the 2:1 complex could be estimated: ΔH° = −16 ± 5 kJ mol-1 and ΔS° = −28 ± 17 J K-1 mol-1. It is speculated that this complex could be an intermediate in the pathway of the exchange of sodium cations between 1:1 complexes in solution.