CATION CALIXARENE INTERACTIONS - TETRAALKYLAMMONIUM CATION-BINDING BYCALIXARENE ANIONS

Syntheses of a number of tetraalkylammonium derivatives of various cal ix[n]arenes (n = 4, 6, 8) have been conducted by reacting the tetraalk ylammonium hydroxides with the parent calixarenes. H-1 NMR studies in acetone and dimethylsulfoxide (DMSO) solvents have shown that cation i nclusion by the anionic calixarenes occurs in some cases for only the tetramethyl- and tetraethylammonium cations, indicating that different forms of ion association must occur in solution. The nature of cation -anion interactions in the solid tetraethylammonium salts of the monoa nions of p-tert-butylcalix[4]arene (L2) and its dihomooxa analogue (L3 ) has been explored by room temperature single-crystal X-ray studies o f the two salts and the parent ligand L3, all recrystallised variously solvated from acetonitrile. In both solid salts, columnar arrays of a lternating cations and anions are found: in the dihomooxa ligand (L3) salt, the cations are captured within the ligand cup, forming contact ion pairs, the column comprising stacks of these. By contrast, the col umnar array found in the parent ligand (L2) salt consists of discrete moieties, with the anion cavity occupied by acetonitrile. The free (ne utral) ligand L3, as its acetonitrile monosolvate, contains the aceton itrile within the ligand cavity also. The structure determination of t he unsubstituted calix[4]arene ligand, L1, is recorded as its 1/3 acet onitrile solvate, with location of all phenolic hydrogen atoms bridgin g their associated oxygen atoms; the acetonitrile in this case simply occupies a lattice void, as in the isomorphous acetone solvate.