Y. Israeli et C. Detellier, COMPLEXATION OF THE SODIUM-CATION BY A CALIX[4]ARENE TETRAESTER IN SOLUTION - FORMATION OF A 2 1 CALIXARENE/SODIUM COMPLEX/, JOURNAL OF PHYSICAL CHEMISTRY B, 101(10), 1997, pp. 1897-1901
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)met
hoxy)cal (1) was studied by H-1 and Na-23 NMR in a 50:50 v:v mixture o
f deuteriated acetonitrile and deuteriated chloroform. A 1:1 complex w
as formed, in very slow exchange, both on the H-1 and on the Na-23 NMR
time scales, with solvated calixarene and sodium cation, respectively
. From H-1 NMR 2D exchange spectroscopy experiments and Na-23 NMR line
width analysis, an upper limit of the rate constant for the dissociat
ion of the 1:1 complex was estimated to be 3 Hz. A 2:1 calixarene:sodi
um complex in fast exchange with the 1:1 complex was evidenced by Na-2
3 NMR. The characteristic Na-23 NMR line widths of the 1:1 and of the
2:1 complexes, determined at several temperatures, were linearly relat
ed, with a slope of 1.8 +/- 0.2. This corresponds to a reorientational
correlation time, characteristic of the Na-23 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 format
ion of the 2:1 complex could be estimated: Delta H degrees = -16 +/- 5
kJ mol(-1) and Delta S degrees = -28 +/- 17 J K-1 mol(-1). It is spec
ulated that this complex could be an intermediate in the pathway of th
e exchange of sodium cations between 1:1 complexes in solution.