Interactions of the aromatic cavity of rigid calix[4]arene cone conformers with acid CH3 and CH2 containing guests in apolar solvents

The effect of the acidity of CH groups within the guests on the binding ability of the aromatic cavity of rigid cone conformers of p-tert-butylcalix[4]arene toward guests containing acid CH3 and CH2 groups have been investigated in apolar media by 1H NMR spectroscopy. In CDCl3 and/or CCl4, CH3Y and CH2XY guests show different binding modes. In particular the acidity of the CH2XY guests strongly affects the binding efficiency whereas the guest acidity does not seem the sole parameter in determining the stability of the complexes with CH3Y guests. With methylene containing guests, the polarizability of the X and Y groups strongly affect the binding process and the ΔG0 of complexation is linearly correlated with both pKa and polarizability of the guests. Solid state structures of sodium and potassium complexes of tetrakisdiethylamide of p-tert-butylcalix[4]arene⊃CH3CN complexes are discussed.