Extraction and DFT study on the complexation of H 3O + with hexaethyl p- tert-butylcalix[6]arene hexaacetate

Abstract

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H 3O +(aq) + 1· Na +(nb) ⇆ 1·H 3O +(nb) + Na +(aq) taking place in the two-phase water–nitrobenzene system ( 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (H 3O +, 1·Na +) = −0.6 ± 0.1. Further, the stability constant of the 1·H 3O + complex in water saturated nitrobenzene was calculated for a temperature of 25 °C as log β nb ( 1·H 3O +) = 6.8 ± 0. 2. By using quantum mechanical DFT calculations, the most probable structure of the 1·H 3O + complex species was predicted. In this complex, the hydroxonium ion H 3O + is bound partly to three carbonyl oxygen atoms by strong hydrogen bonds and partly to three alternate phenoxy oxygens by somewhat weaker hydrogen bonds.