Dynamic Open Coordination Cage from Nonsymmetrical Imidazole–Pyridine Ditopic Ligands for Turn‐On/Off Anion Binding

This work demonstrates a new nonconventional ligand design, imidazole/pyridine‐based nonsymmetrical ditopic ligands ( 1 and 1 S ), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd 2+ at a 1:4 molar ratio, 1 and 1 S initially form mononuclear PdL 4 complexes (Pd 2+ ( 1 ) 4 and Pd 2+ ( 1 S ) 4 ) without formation of a cage. The PdL 4 complexes undergo a stoichiometrically controlled structural transition to Pd 2 L 4 open cages ((Pd 2+ ) 2 ( 1 ) 4 and (Pd 2+ ) 2 ( 1 S ) 4 ) capable of anion binding, leading to turn‐on anion binding. The structural transitions between the Pd 2 L 4 open cage and the PdL 4 complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1 S to the (Pd 2+ ) 2 ( 1 S ) 4 open cage holding a guest anion ((Pd 2+ ) 2 ( 1 S ) 4 ⋅G − ) enables the structural transition to the Pd 2+ ( 1 S ) 4 complex, which does not have a cage and thus causes the release of the guest anion (Pd 2+ ( 1 S ) 4 +G − ).