Computational study of calix[4]arene derivatives and complexation with Zn

High level DFT was applied to study structure and conformational equilibrium of amino and mercaptocalix4]arenes possessing methylene groups or sulfur atoms at their four junctions. All the calculations point to cone and 1,3-alternate as the most stable conformers for sulfur and methylene bridged compounds, respectively. The presence of four sulfur atoms in place of the methylene bridges can lead to novel features in the complexation with transition metals. The host–guest 1:1 complexes between Zn²⁺ and each conformer of tetraaminothiacalix4]arene were also investigated at the same DFT level. The four nitrogens of amino groups play a dominant role in the interaction with Zn²⁺ via distorted tetrahedral coordination for 1,3-alternate, or distorted square planar for partial cone and 1,2-alternate. On the other hand, the 2:1 complexes with cone show that the sulfur bridges can also bind Zn²⁺ and contribute to form two sets of five-membered chelated rings with two N donor atoms.