Alkali metal ion complexes of functionalised calixarenes – competition between pendent arm and anion bonding to sodium

Abstract

Determination of the crystal structure of the acetonitrile inclusate of the complex formed between sodium trifluoromethanesulfonate (triflate, CF₃SO₃⁻) and the narrow-rim functionalised calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,27-di(phenylmethoxy)-26,28-di(2′-methoxyethoxy)calix[4]arene, has shown, somewhat unexpectedly, that the diether pendent arms do not chelate the sodium cation, although coordination of all four phenolic oxygen atoms does draw the calixarene into a nearly symmetrical cone form, consistent with conclusions drawn earlier from solution ¹H NMR data. Crystals of C₆₄H₈₀O₆·NaO₃S.CF₃·CH₃CN obtained from acetonitrile solvent are monoclinic, C2/c, a structure determination at ‘low’ temperature (153 K) resolving several difficulties encountered in earlier attempts to analyse data acquired at ∼295 K, and indicative of an interesting temperature dependence of substituent and anion orientations.