Light‐Triggered High‐Affinity Binding of Tetramethylammonium over Potassium Ions by [18]crown‐6 in a Tetrahedral Anion Cage

An azobenzene‐functionalized bis‐bis(urea) ligand (Lazo) and phosphate anion assemble to give the first photoactive “aniono” constructs, tetrahedron (A4L6) and helicate (A2L3), which readily undergo interconversion through cis‐trans isomerization of the azo group under irradiation/heating. Most strikingly, the tetrahedral cage can accommodate an [18]crown‐6 molecule, which can capture two tetramethylammonium (TMA+) ions with an unusually high affinity, even capable of replacing K+ in [K([18]crown‐6)]+ to form a {(TMA)2⊂ ([18]crown‐6)}⊂ cage “Russian doll” structure. Thus, the current work may provide a model for the light‐driven binding and exchange of the biologically important K+ and TMA+ ions. Anion‐coordination‐driven assembly from an azobenzene‐functionalized bis‐bis(urea) ligand (Lazo) with phosphate anion affords the first photoactive A4L6‐type tetrahedral cage. The tetrahedral cage can reversibly trap two TMA+ cations and one [18]crown‐6 molecule with an unusually high affinity accompanied by the release/capture of K+ ion from [K([18]crown‐6)]+ under irradiation/heating.