Interaction of Cesium Ions with Calix[4]arene-bis(t-octylbenzo-18-crown-6): NMR and Theoretical Study

Using H-1, C-13, and Cs-133 NMR spectra, it is shown that calix[4]arene-bis (t-octylbenzo-18-crown-6) (L) forms complexes with one (L center dot Cs+) and two (L center dot 2Cs(+)) Cs+ ions offered by cesium bis(1,2-dicarbollide) cobaltate (CsDCC) in nitrobenzene-d(5). The ions interact with all six oxygen atoms in the crown-ether ring and the pi electrons of the calixarene aromatic moieties. According to extraction technique, the stability constant of the first complex is log beta(nb)(L center dot Cs+) = 8.8 +/- 0.1. According to Cs-133 NMR spectra, the value of the equilibrium constant of the second complex is log K-nb((2))(L center dot 2Cs(+)) = 6.3 +/- 0.2, i.e., its stabilization constant is log beta(nb)(L center dot 2Cs(+)) = 15.1 +/- 0.3. Self-diffusion measurements by H-1 pulsed-field gradient (PFG) NMR combined with density functional theory (DFT) calculations suggest that one DCC- ion is tightly associated with L center dot Cs+, decreasing its positive charge and consequently stabilizing the second complex, L center dot 2Cs(+). Using a saturation-transfer Cs-133 NMR technique, the correlation times tau(ex) of chemical exchange between L center dot Cs+ and L center dot 2Cs(+) as welt as between L center dot 2Cs(+) and free Cs+ ions were determined as 33.6 and 29.2 ms, respectively.