Stable and Metastable Self‐Assembled Rings based on trans ‐chelated Pd II

In contrast to the large number of self‐assembled ring and cage structures based on cis ‐chelated square‐planar metal complexes as connecting nodes, the use of trans ‐chelated square‐planar building blocks is vastly underrepresented in supramolecular coordination chemistry. We here report of a strategy for the formation of self‐assembled ring structures based on the trans ‐chelating ligand 1, 2‐bis(2‐pyridylethinyl)‐benzene coordinated to Pd II in a 1:1 fashion and bis‐monodentate pyridyl bridging ligands. Depending on the angle between the two N ‐donor functionalities of the bridging ligands, three‐ or two‐membered rings are quantitatively formed in solution. Whereas the former species show a high thermodynamic stability, the latter rings are of only kinetic stability if the bridging ligand is also able to form a coordination cage as an alternative product. The assembly and transformation of the supramolecular structures was characterized by 1 H NMR spectroscopy and high‐resolution FTICR‐ESI mass spectrometry, augmented by semiempiric PM6 geometry optimizations.