Alkali-metal ion complexes of the calixarenes. Part 1. Caesium bonding in calix[4]arene systems

Abstract

A crystal structure determination on the monocaesium derivative of bis(homooxa)-p-tert-butylcalix[4]arene (L²), [Cs(L²– H)(OH₂)₃]·xH₂O (x≈ 3)[orthorhombic, Pmnb, a= 26.666(5), b= 15.928(4), c= 11.499(9)Å, Z= 4, R= 0.071 for 1500 ‘observed’ reflections] showed that the caesium may be considered to be involved in polyhapto interactions with carbon atoms in two of the four phenyl rings as well as co-ordination to two phenolic oxygens, the ether oxygen and three water molecules. The nature of the polyhapto aromatic interactions seems to be similar to that of those previously observed as the exclusive mode of calixarene binding in the caesium complex of the monoanion of p-tert-butylcalix[4]arene. Both complexes can be described as cation inclusion compounds, and the retention of this solid-state structure in some solvents is associated with very low-field ¹³³Cs nuclear magnetic resonances. On the basis of ¹³³Cs NMR spectra, it can be concluded that a series of calix[4]arenes bridged at the upper rim by an aliphatic chain –(CH₂)_n– also forms inclusion complexes with Cs⁺ for n= 7–10, in accord with Cs⁺ transport studies previously reported for a similar series.