Structure and conformational equilibrium of new thiacalix[4]arene derivatives

Density functional theory was used to study the structure and conformational equilibrium of tetraaminothiacalix[4]arene (1) and tetramercaptothiacalix[4]arene (2), which are expected to open a new area of host–guest chemistry. All the calculations predict the cone as the most stable conformer for both compounds, which is in good agreement with an earlier theoretical study on the parent thiacalix[4]arene. It is shown that different substituents at the lower rim do not affect the stability ordering. The intramolecular bonding between hydrogen atoms and sulfur bridges seems to be a dominant factor in stabilizing all the conformers rather than hydrogen bonds between the groups of the lower rim.