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

Abstract

Using 1H, 13C, and 133Cs NMR spectra, it is shown that calix[4]arene-bis (t-octylbenzo-18-crown-6) (L) forms complexes with one (L 3 Csþ) and two (L 3 2Csþ) Csþ ions offered by cesium bis(1,2-dicarbollide) cobaltate (CsDCC) in nitrobenzene-d5. The ions interact with all six oxygen atoms in the crown-ether ring and the π electrons of the calixarene aromatic moieties. According to extraction technique, the stability constant of the first complex is log βnb(L 3 Csþ) = 8.8 ( 0.1. According to 133Cs NMR spectra, the value of the equilibrium constant of the second complex is log Knb (2)(L 3 2Csþ) = 6.3(0.2, i.e., its stabilization constant is log βnb(L 3 2Csþ) = 15.1 ( 0.3. Self-diffusion measurements by 1H pulsed-field gradient (PFG) NMRcombined with density functional theory (DFT) calculations suggest that one DCC ion is tightly associated with L 3 Csþ, decreasing its positive charge and consequently stabilizing the second complex, L 3 2Csþ. Using a saturation-transfer 133Cs NMR technique, the correlation times τex of chemical exchange between L 3 Csþ and L 3 2Csþ as well as between L 3 2Csþ and free Csþ ions were determined as 33.6 and 29.2 ms, respectively.