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 1S), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd2+ at a 1:4 molar ratio, 1 and 1S initially form mononuclear PdL4 complexes (Pd2+(1)4 and Pd2+(1S)4) without formation of a cage. The PdL4 complexes undergo a stoichiometrically controlled structural transition to Pd2L4 open cages ((Pd2+)2(1)4 and (Pd2+)2(1S)4) capable of anion binding, leading to turn‐on anion binding. The structural transitions between the Pd2L4 open cage and the PdL4 complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1S to the (Pd2+)2(1S)4 open cage holding a guest anion ((Pd2+)2(1S)4⋅G−) enables the structural transition to the Pd2+(1S)4 complex, which does not have a cage and thus causes the release of the guest anion (Pd2+(1S)4+G−). Switchability: Nonsymmetrical ditopic ligands (L) drive the formation of a dynamic Pd2L4 open cage that is capable of turn‐on/off anion binding through stoichiometry‐driven structural transitions of the host cage.