Synthesis and inclusion behavior of a heterotritopic receptor based on hexahomotrioxacalixarene†
A heterotritopic hexahomotrioxacalixarene receptor with the capability of binding two alkali metals and a transition metal in a cooperative fashion was synthesized. The binding model was investigated by using 1H NMR titration experiments in CDCl3–CD3CN (10 : 1, v/v), and the results revealed that the transition metal was bound at the upper rim and the alkali metals at the lower and upper rims. Interestingly, the alkali metal ions Li+ and Na+ bind at the lower and upper rim respectively depending on the dimensions of the alkali metal ions versus the size of the cavities formed by the calixarene derivative. The hexahomotrioxacalixarene receptor acts as a heterotritopic receptor, binding with the transition metal ion Ag+ and the alkali metals ions Li+ and Na+. These findings were not applicable to other different sized alkali metals, such as K+ and Cs+.