Synthesis, structure and alkali metal ion binding properties of a podand polyether derived from calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,27-di(phenylmethoxy)-26,28-di(2'- methoxyethoxy)-calix[4]arene

The ligand 5,11,17,23-tetra-t-butyl-25,27-di(phenylmethoxy)-26,28-di(2-methoxyethoxy)calix[4]arene, designed as an analogue of some calixcrown species in order to evaluate possible origins of their selectivity in alkali metal ion binding, has been synthesised and structurally characterised by X-ray crystallography. The crystals are monoclinic, P2(1)/n, a = 15.940(6), b = 19.388(5), c = 20.020(5) Angstrom, beta = 109.10(2) deg., Z = 4, conventional R on \F\ being 0.073 for 3454 independent, 'observed' (I > 3 sigma(I)) reflections. H-1-NMR studies in 1:1 CD3CN/CDCl3 solvent have shown that the ligand exerts a strong preference for the lighter alkali metal ions (Li+ and Na+) contrary to the binding behaviour of known calixcrowns. This may reflect interactions restricted to the lower rim donor atoms without concomitant interaction with the calixarene pi-electrons, perhaps because the latter interactions are substituted by those with the benzyl group pi-electrons.