Stoichiometric control of guest‐recognition of self‐assembled palladium(II)‐based supramolecular architectures

We report flexible [Pd(L)2]2+ complexes where there is self‐recognition, driven by π ‐ π interactions between electron‐rich aromatic arms and the cationic regions they are tethered to. This self‐recognition hampers the association of these molecules with aromatic molecular targets in solution. In one case, this complex can be reversibly converted to an ‘open’ [Pd2(L)2]4+ macrocycle through introduction of more metal ion. This is accomplished by the ligand having two bidentate binding sites: a 2‐pyridyl‐1,2,3‐triazole site, and a bis‐1,2,3‐triazole site. Due to favourable hydrogen bonding, the 2‐pyridyl‐1,2,3‐triazole units reliably coordinate in the [Pd(L)2]2+ complex to control speciation: a second equivalent of Pd(II) is required to enforce coordination to bis‐triazole sites and form the macrocycle. The macrocycle interacts with a molecular substrate with higher affinity. In this fashion we are able to use stoichiometry to reversibly switch between two different species and regulate guest binding.