The first study about the relationship between the extractability of thiacalix[4]arene derivatives and the position of the coordination binding sites

Abstract

Three organic ionophores (2–4) based on the p-tert-butylthiacalix[4]arene backbone, blocked in the 1,3-alternate conformation, bearing two pyridyl coordinating moieties (ortho for 2, meta for 3 and para for 4), have been synthesized and characterized in the solid state. The solvent extraction experiments with the metal ions showed that the ability of these derivatives to complex with Ag⁺ appeared to be largely dependent on the position of the nitrogen atoms of the pyridyl ring. Two different complexation modes have been confirmed by ¹H NMR titration. Ionophore 2 armed with two pyridyl moieties, complexed with Ag⁺ cation through N⋯Ag⁺⋯S interactions; however, ionophore 3 and ionophore 4 complexed with Ag⁺ through metal–nitrogen (N⋯Ag⁺) interactions. The DFT computational studies were consistent with the experimental findings. These findings will provide us with an important rule to design an appropriate thiacalix[4]arene ionophore in the future. Another study on the possibility for application of ionophores 2–4 for the treatment of waste water containing Cr(VI) and Cr(III), showed that ionophore 3 was useful in the application of the solvent extraction method in selective treatment of waste water containing Cr(VI) and Cr(III) prior to discharge.