Theoretical study of thiacalix[4]arene derivatives and their zinc(II) complexes

Abstract

The four typical conformers of thiacalix[4]arene and sulfonylcalix[4]arene derivatives have been studied using the density functional theory (DFT) at B3LYP/6-31G(d) level of theory. The most stable conformer is found to be cone for thiacalix[4]arene derivatives and 1.3-alternate for sulfonylcalix[4]arene derivatives in which an intramolecular hydrogen bond plays an important factor for the conformational stability. Effect of solvents, i.e., water, chloroform and dichloromethane on stability of sulfonylcalix[4]arene derivatives has been computer using the CPCM salvation model combined with DFT method. It is found that all solvents are slightly effect to their stability. The interconversion between cone and partial cone conformers found in each derivative has been predicted at B3LYP/6-31G(d) level of theory. It is clearly seen that bridge types of calix[4]arene show a strongly effect to the interconversion whereas the interconversion barrier of sulfonyl (-SO[superscript2-]) bridges of sulfonylcalix[4]arene derivatives is higher than that of sulfur (-S-) bridges of thiacalix[4]arene derivatives approximately twice times. The complexations between zinc(II) ion and the cone conformer of thiacalix[4]arene and sulfonylcalix[4]arene derivatives have been investigated at B3LYP/6-31G(d) level of theory. The result shows that all of complexations are an exothermic process. Furthermore, the complexation between the Zinci(II) ion and thiacalix[4]arene yields the highest energy which results from the metal-ligand charge transfer (MLCT) effect found on its complex. The host – guest complex of thiacalix[4]arene (tatbtc4a) and calix[4]arene (tatbc4a) receptors with a series of carboxylate guest (acetate, oxalate, malonate, succinate, glutarate, adipate, and pimelate) has been studied using the ONIOM(B3LYP/6-31G(d):AM1) method. All optimized structures are carried out by the B3LYP/6-31G(d) single point calculation. The relative stabilities of the tatbtc4a and tatbc4a complexes with carboxylates in order are malonate > oxalate > succinate > glutarate and oxalate > malonate > succinate > glutarate > adipate > pimelate, respectively.