Solvent- and Concentration-Induced Topological Transformation of a Ruthenium(II)-Based Trigonal Prism to a Triply Interlocked [2] Catenane

Synthesis of interlocked supramolecular cages has been a growing field of interest due to their structural diversity. Herein, we report the template-free synthesis of a Ru(II) triply interlocked [2] catenane using coordination-driven self-assembly. The self-assembly of a triazine-based tripyridyl donor <b>L</b> (2,4,6-tris(5-(pyridin-4-yl)thiophen-3-yl)-1,3,5-triazine) with a dinuclear Ru(II) acceptor <b>M</b> (Ru₂(dhnq)(η⁶-<i>p</i>-cymene)₂)(CF₃SO₃)₂) yielded two distinct structures depending on the solvent and concentration. In methanol, a triply interlocked metalla [2] catenane (<b>MC2</b>) was formed, whereas in nitromethane, a non-interlocked cage (<b>MC1</b>) was obtained. The non-interlocked cage <b>MC1</b> was gradually converted to <b>MC2</b> in nitromethane by the increase in the concentration of cage <b>MC1</b> from 0.5 to 9 mM. The interlocked cage (<b>MC2</b>) was stable after formation and was unaffected by the change in concentration. Notably, the free cage (<b>MC1</b>) exhibited host-guest interactions with polycyclic aromatic aldehydes, stabilizing the non-interlocked structure even at higher concentrations. In contrast, the triply interlocked [2] catenane (<b>MC2</b>) remains stable due to self-penetration and does not encapsulate guest molecules. This work showcases the stimuli-induced irreversible structural transformation of a triangular prismatic cage to its triply interlocked [2] catenane by employing metal-ligand coordination chemistry.