Structures and properties of solvated and unsolvated isopropyl functionalised calix[4]arenes

The tetra-iso-propyl ethers of calix[4]arene and p-t-butylcalix[4]arene have been isolated in the cone conformation, and structurally characterized as chloroform solvates. Thermogravimetric analysis demonstrated that the parent iso-propylcalix[4]arene solvate is significantly more stable than the p-t-butylcalix[4]arene analogue, retaining the solvent up to a temperature of of 125 °C. It was found that the calix[4]arene ether sublimes at atmospheric pressure, and solvent-free crystals appropriate for structure determination were produced at reduced pressure. The p-t-butylcalix[4]arene ether was also isolated without solvent in the lattice, but in this case the calixarene was crystallized from acetone, as sublimation did not produce crystals of sufficient quality