Theoretical study on the structure and conformational features of distally dibromo-dipropoxythiacalix[4]arene derivatives and their Zn2+ complexes

A comparative DFT study of distally dibromo-dipropoxythiacalix[4]arene and dipropoxythiacalix[4]arene was performed. The hydrogen bonds OH O at the lower rim play an important role in stabilizing all the conformers, and cone is predicted to be the most stable. The structure and energetic ordering of the conformers are not affected by the bromination at upper rim. The inclusion of the solvent effect keeps the energetic orderings unchanged, but leads to a reduction in the energy gaps between conformers. Concerning the 1:1 neutral Zn²⁺ complexes, only one binding mode was found which presented the metal ion coordinated to four oxygen atoms at lower rim. This is in good agreement with our previous study on the Zn²⁺ complex with thiacalix[4]arene carrying opposite phenolate groups. The results thus support the idea that the position of the phenolate groups at lower rim is crucial to define the structural binding mode pattern of metal complexes.