Spectroscopic ͑Raman, NMR, impedance spectroscopy͒, and thermal ͓differential scanning calorimetry ͑DSC͔͒ techniques have been used to study the solvation mechanism of lithium ions in ethylene carbonate ͑EC͒-propylene carbonate ͑PC͒ concentrated solutions. For values of N ϭ͓Li ϩ ͔/͓ECϩPC͔р0.2 all the cations are solvated by ϳ4 solvent molecules and interaction chiefly takes place between Li ϩ and the ring oxygens. For NϾ0.2 a part of Li ϩ ions begins to form complexes with two solvent molecules ͑sandwich configuration͒. At NХ0.5 nearly all cations are complexed, and a crystalline compound is formed at room temperature. For higher values of N a reassociation of the salt takes place.
A complex of p-tert-butylcalix [4]arene and chloroform has been prepared and characterized in the solid state using, for the Ðrst time for any calixarene complex, the Rietveld powder XRD method, as well as variable-temperature 2H and 13C solid-state NMR. The 2H NMR spectra are composed of a central isotropic peak, attributed to a small fraction of in the free motion regime inside the crystal lattice, and a CDCl 3 quadrupolar powder pattern. 2H spinÈlattice relaxation times lead to activation energies for the molecular motion of 4.9 ^0.5 and 6.0 ^0.6 kJ mol~1 for the two spectral components, respectively. The temperature dependence of the static 2H spectra shows a very unusual increase in the e †ective quadrupolar coupling constant with temperature, caused by the change in the geometry of the complex. We show that the complexation is caused by weak dispersion interactions. The 13C MAS NMR spectrum of the guest molecule changes upon prolonged heating, while thermal analysis conÐrms the presence of an exothermic transition attributed to an intermediate state before the choroform is released.
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