Peripheral Templation-Modulated Interconversion between an A₄L₆ Tetrahedral Anion Cage and A₂L₃ Triple Helicate with Guest Capture/Release

An anion-coordination-based A₄L₆ (“A” denotes anion and “L” is ligand) tetrahedral cage was constructed by a C₂-symmetric bis-bis(urea) ligand and phosphate anion, which showed reversible interconversion with the A₂L₃ triple helicate as a response to the template, concentration, or solvent. Notably, an unusual “peripheral” templation was found to be critical to stabilize the tetrahedral structure. This peripheral effect was utilized to assemble an “empty” A₄L₆ cage that allows the multi-stimuli-controlled capture/release of biologically important species such as choline and acetylcholine.