Crystal structure of 1,3-alternate 25,26,27,28-tetra(tert-butoxyethoxy)calix[4]arene: a selective Ag+ extractant

Alkylation of calix[4]arene by 2-tert-butoxyethyl bromide led to the tetraa lkylated calix[4]arene in the 1,3-alternate, the conformation of which has been established by X-ray crystallography. This spatial structure included a cavity potentially useful for host-guest complexes achieved with metal ca tions, especially with Ag+. The title compound crystallizes in the monoclin ic space group Cc with cell constants a = 29.901(2), b = 8.139(1), c = 22.2 64(3) Angstrom, alpha = 90 degrees, beta = 117.08(1)degrees and gamma = 90 degrees. This conformer represents an example for Ag+-tunneling across an a romatic cavity. This behaviour could lead to important implications with re gard to the metal cation-pi interaction expected for metal transport throug h ion channels, metal inclusion in fullerenes, intercalation of metal catio ns into graphites, etc.