Sulphur-enriched thiacalix[4]arenes in the cone conformation: Synthesis, crystal structures and cation binding properties

The synthesis and crystal structure of p-tert-butylthia- and p-tert-butylcalix[4]arene derivatives 1-7 substituted at the narrow rim by diethylthiophosphate ester groups, -PS(OEt)₂ are reported. In these compounds the phosphorus atoms are directly attached to the phenolic O atoms of the calix units and the S atoms of the thiophosphate may serve as a two-electron donor to a metal ion. Their crystal structures were solved, which revealed their cone conformation. Their cation-binding properties have been established by liquid-liquid extraction of metal picrates from water into dichloromethane and stability constant determination in acetonitrile using UV-absorption spectrophotometry. Quantitative extraction was achieved for Ag⁺ (%E = 99) with the tetra-substituted thiacalix[4]arene derivative. The complexes were found to be of 1:1 stoichiometry and the location of the metal cations was shown to be nearby the sulphur atoms by ¹H NMR.