A symmetry interaction approach to [M2L2]4+ metallocycles and their self-catenanes.

The use of stimuli to induce reversible structural transformations in metallosupramolecular systems is of keen interest to chemists seeking to mimic the way that Nature effects conformational changes in biological machinery. While a wide array of stimuli have been deployed towards this end, stoichiometric changes have only been explored in a handful of examples. Furthermore, switching has generally been between only two distinct states. Here we use a simple 2‐(1‐(pyridine‐4‐methyl)‐1H‐1,2,3‐triazol‐4‐yl)pyridine “click” ligand in combination with PdII in various stoichiometries and concentrations to quantitatively access and cycle between three distinct species: a [PdL2]2+ monomer, a [Pd2L2]4+ dimer, and a [Pd9L12]18+ cage.

While Nature often controls supramolecular processes through regulation giving multiple levels of activity, synthetic metallosupramolecular systems have generally been binary (e.g. on/off) when they have control over molecular recognition events,...