Ligand-directed topological engineering: self-assembly of cyclic <sc>[3]catenane</sc> (6<sub>3</sub><sup>3</sup>), Borromean rings (6<sub>2</sub><sup>3</sup>), and Hopf links (2<sub>1</sub><sup>2</sup>)
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The 6-isoquinolinyl system was incorporated into mechanically interlocked molecules (MIMs) syntheses for comparative analysis of its assembly behavior with 4-pyridyl-based coordination ligands, where a coordination-driven self-assembly strategy by half-sandwich Cp*Rh units was employed to construct diverse molecular links. The pyridyl ligand, adorned with thiophene moieties, assembles into [2]catenanes (212 links), whereas the isoquinolinyl ligand produces molecular Borromean links (623 links). Intriguingly, when utilizing extended bithiophene segments, the pyridyl ligand forms Borromean rings (623 links), while isoquinolinyl counterparts produced a rare low-symmetry cyclic [3]catenane (633 topology). The results were confirmed through single-crystal X-ray diffraction analysis, nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight mass spectrometry (ESI-TOF/MS) experiments. Synergistic π-π stacking, C–H···π interactions, and solvophobic effects governed the complex self-assembly system, with independent gradient model (IGM) analyses and solvent-accessible surface area (SASA) calculations providing atomistic insights into the pathway selectivity of distinct topological links.
