Ring-in-ring complexes typically suffer from limited stability, as the interactions between the inner and outer macrocycles rely predominantly on nondirectional van der Waals forces or directional hydrogen bonding alone. To address this limitation, we identified a novel stabilization strategy based on the mortise-and-tenon principle from the crystal structure of assembly Rh-1. In this architecture, the three characteristic cavities inherent in the classic ring-in-ring framework are defined as the "mortise", while a one-dimensional molecular chain is rationally designed to act as the complementary "tenon". Through precise insertion of the tenon into the mortise, dense and continuous π-π stacking interactions as well as extensive van der Waals contact surfaces are successfully established within the ring-in-ring skeleton. Such directional and efficient molecular packing significantly strengthens the overall intermolecular forces, thereby substantially increasing the dissociation energy barrier. Furthermore, structurally analogous complex Ir-1 can be readily synthesized using the same assembly protocol. Guided by the pseudo-mortise-and-tenon platform, we further constructed molecular figure-eight knots, Rh-2 and Ir-2, and metalla[2]catenanes, Rh-3 and Ir-3, by judiciously tuning the folding angle and length of the organic bridging ligands.

A flexible tetradentate ligand, L,1,2,4,5-tetrakis((pyridin-4-ylthio)methyl)benzene, was designed to precisely construct topologically distinct handcuff-shaped molecules 1,2 and Double-Z cage 1 through coordination-driven self-assembly with building blocks (B1-B3). In particular, the size of the conjugated surfaces of B1-B3 and hydrogen bond-accepting properties of anions play critical roles in influencing the resulting topology, as supported by single-crystal X-ray diffraction (SCXRD), electrostatic potential (ESP), and independent gradient model (IGM) calculations. BF4- anions favored the formation of handcuff-shaped structures with smaller conjugated building blocks B1 and B2, while Double-Z Cage 1 with a larger conjugated building block B3. Intriguingly, when BF4- is replaced with OTf-, the stronger electron-donating and hydrogen bond-accepting capabilities of OTf- induce a topological transformation from Handcuff 2 to Double-Z Cage 3. Specifically, Handcuff 1 and Double-Z Cage 1 correspond to Handcuff 3 and Double-Z Cage 2, respectively, demonstrating how anion identity influences the final topology for similar building blocks. Furthermore, a remarkable in situ topological transformation from Handcuff 2 to Double-Z Cage 3 was achieved under mild conditions with the addition of KOTf to Handcuff 2, as confirmed by real-time 1H NMR monitoring. This work offers promising avenues for designing responsive molecular materials with tailored topologies.

ABSTRACT Low‐symmetry mechanically interlocked molecules (MIMs) remain challenging targets because of their anisotropic structures and synthetic complexity. We devised a self‐sorting strategy employing two unsymmetric flexible bidentate ligands, L ab and L cd , which co‐assemble with two size‐differentiated rigid chelating building blocks and half‐sandwich organometallic units. This approach yields three discrete topologies with high orientational fidelity: a Solomon link (), a figure‐eight knot (4 1 ), and a trefoil (3 1 ) knot, enabling systematic investigation of oriented entanglements. Notably, we successfully implemented a “MIM‐to‐MIM” strategy that enables the transformation between fully interlocked molecular species, representing the first example in which both reactants and products are discrete MIMs. Through either this interlocked molecular fusion process or completely integrative self‐sorting of mixed unsymmetric components, a heteroleptic Solomon link was constructed in a non‐statistical manner. The outcome highlights how diverse noncovalent interactions, the conformational adaptability of ligands, and geometric complementarity cooperate to direct complex self‐sorting behavior in unpredictable, non‐rigid mixed‐assembly systems.

The synthesis of molecular topology beyond conventional symmetric knots remains a formidable challenge. Here, we report the first synthesis of the molecular 8_5 knot—a low-symmetry, representative pretzel knot with eight crossing points—via coordination-driven self-assembly. This knot was assembled from eight 4-azaindolyl ligand strands (L) and eight binuclear metal blocks (E1-Rh). These components intertwine in three-dimensional space in an alternating up-and-down fashion, forming a closed loop featuring eight crossings. Successful construction of this elusive 8_5 knot relies on our newly developed 4-azaindolyl ligand strand, whose unique electronic and steric properties enable tunable topological organisation. Exploiting this ligand design, we further systematically synthesized two 5_1 torus knots in high yields by tuning the size of the binuclear metal motifs, thereby validating the platform's broad applicability. This study fills a key gap concerning low-symmetry eight-crossing molecular knots and establishes a versatile route to accessing diverse molecular topologies.

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 (2 1 2 links), whereas the isoquinolinyl ligand produces molecular Borromean links (6 2 3 links). Intriguingly, when utilizing extended bithiophene segments, the pyridyl ligand forms Borromean rings (6 2 3 links), while isoquinolinyl counterparts produced a rare low-symmetry cyclic [3]catenane (6 3 3 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.

Investigating stimulus-responsive structural transformations of complex mechanically interlocked molecules (MIMs) is key to better understanding the dynamic behaviors of biological macromolecules. Herein, we integrated oxidation-reactive dibenzothiophene moieties into organic frameworks, which self-assembled with binuclear half-sandwich organometallic clips of varying lengths, achieving selective construction of a linear [3]catenane (413 metalla-link) and an exceptionally rare closed four-link chain (CFLC, 814 metalla-link), the latter representing a synthetically challenging, highly interlocked topology. Topological transformation of the linear [3]catenane into a metalla-macrocycle was driven by substantial steric repulsion induced by bulky sulfone groups upon full oxidation with 3-chloroperoxybenzoic acid. By contrast, the CFLC exhibited remarkable topological stability against oxidative modifications, consistently preserving 814 link topology throughout the sequential oxidation process despite in situ structural transformations, yielding sulfoxide- and sulfone-containing CFLC derivatives. All nonoxidized and oxidized supramolecular assemblies were comprehensively characterized using single-crystal X-ray diffraction, high-resolution electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy. This work unveils a new pathway for postsynthetic modification of MIMs and provides critical insights into chemically driven transformations of complex, higher-order interlocked architectures, with significant potential to mimic nature's sophisticated, dynamic molecular systems.

In this work, a 16-electron half-sandwich Ir(III) complex (Cp*Ir(OCN-Ph-Cl)C2B10H10, 2) featuring a bifunctional O,N-o-carborane ligand was synthesized, and its reactivity was thoroughly investigated. Further studies indicate that this complex could react with various donor ligands to achieve a stable 18-electron species. Interestingly, the obtained 16-electron complex 2 shows acid-base responsive behavior, namely reversible structural transformation between the 16-electron complex 2 and 18-electron complex 4 (Cp*IrCl(OCNH-Ph-Cl)C2B10H10) with different coordination configuration. This work describes in detail the different reaction processes of half-sandwich iridium complex and carborane ligand.

Achieving transformation between different types of topologies remains a challenge in supramolecular chemistry. Herein, sulfur oxidation was utilized as the stimuli to trigger topological transformations from knots to links. The process began with a thioether-type precursor, M (4(1) metallic knot), which was synthesized by self-assembling the sulfur-bridged ligand L with building block B in high yield. Following oxidation reactions, we successfully transformed the octanuclear 4(1) metallic knot (M) with four crossing points into a sulfoxide-type dodecanuclear metallic link (M-O) with six crossing points as an intermediate product, and then to a sulfone-type dodecanuclear metallic link (M-2O) with six crossing points, which achieves a dual leap in both metal nuclearity and crossing complexity. Remarkably, the key to the transformation lies in using the embedded S-centres of M as molecular triggers and stepwise oxidation (-S-->-S(O)-->-S(O)(2)-) enabled precise modulation of the geometric configuration of the sp(3) S-centres, drastically altering the range of accessible coordination vectors and inducing conformational self-adaptation among components. This strategy establishes a novel oxidation-mediated interconversion paradigm among complex topologies, offering new insights for designing dynamic molecular triggers in intelligent material systems.

Supported by chiral stationary phase high-performance liquid chromatography HPLC (CSP-HPLC), examples of chiral mechanically interlocked organic molecules, including knots, rotaxanes, and catenanes, have been reported. However, the exploration of stereoselective construction of chiral cationic complexes, particularly those induced by point chirality, has been notably limited due to the constraints posed by the type of chiral chromatographic columns and separation efficiency. To address this, we have developed a construction strategy for generating coconformational mechanically helical and topologically chiral [2]catenanes through the induction of point chirality. In this study, by adjusting the symmetry of the ligand, we have easily realized the efficient construction of high-yield crystalline coconformational mechanically helical and topologically chiral [2]catenanes. Moreover, within the enantiomerically pure chiral environment of molecular self-assembly driven by L-alanine and L-valine residues in bidentate ligands, the coconformational mechanically helical and topologically chiral [2]catenanes exist exclusively as a single enantiomer, thus eliminating the need for laborious CSP-HPLC separation from racemic mixtures. The generation of the opposite enantiomer can be realized by employing unsymmetrical ligands containing corresponding D-alanine and D-valine residues, as confirmed through single-crystal X-ray diffraction, elemental analysis, electrospray-ionization time-of-flight mass spectrometry, solution-state NMR spectroscopy, and circular dichroism spectroscopy.

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 pi-pi stacking, C-H center dot center dot center dot pi 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.

The Borromean link, characterized by structural integrity and aesthetic beauty, represents one of the most intriguing entanglements. Most Borromean links consist of three identical macrocycles, and there are few examples of links constructed from trimeric cages. Here, by selecting a tetrapyridyl ligand derived from dibenzo-18-crown-6 and two binuclear building units, we construct two high-yield molecular-cage-based Borromean links comprised of over 1,100 non-hydrogen atoms, in particular, 24 rhodium(III)/iridium(III) and six sodium(I) ions. Facilitated by multiple aromatic stacking interactions between components, three identical coordination cages are found to be linked with a Borromean link topology. These structures are confirmed by X-ray crystallographic analysis, detailed nuclear magnetic resonance spectroscopy, electrospray ionization-time-of-flight/mass spectrometry and elemental analysis. The cage-based Borromean links constructed in this work using coordination cages rather than rectangles have enriched the kinds of Borromean links, and the bottom-up synthetic strategy has provided additional insights into the design and synthesis of more sophisticated architectures. Molecular Borromean links are typically composed of trimeric macrocycles, but their construction with three cages remains scarce. Here, a bottom-up strategy is developed to achieve the rational and efficient construction of metallocage-based Borromean links.

Achieving transformation between different types of topologies remains a challenge in supramolecular chemistry. Herein, sulfur oxidation was utilized as the stimuli to trigger topological transformations from knots to links. The process began with a thioether-type precursor, M (41 metallic knot), which was synthesized by self-assembling the sulfur-bridged ligand L with building block B in high yield. Following oxidation reactions, we successfully transformed the octanuclear 41 metallic knot (M) with four crossing points into a sulfoxide-type dodecanuclear 6 3 2 $6_3^2$ metallic link (M-O) with six crossing points as an intermediate product, and then to a sulfone-type dodecanuclear 6 3 2 $6_3^2$ metallic link (M-2O) with six crossing points, which achieves a dual leap in both metal nuclearity and crossing complexity. Remarkably, the key to the transformation lies in using the embedded S-centres of M as molecular triggers and stepwise oxidation (-S-→-S(O)-→-S(O)2-) enabled precise modulation of the geometric configuration of the sp3 S-centres, drastically altering the range of accessible coordination vectors and inducing conformational self-adaptation among components. This strategy establishes a novel oxidation-mediated interconversion paradigm among complex topologies, offering new insights for designing dynamic molecular triggers in intelligent material systems.

Mechanically interlocked molecules (MIMs) have unique properties with broad applications, yet constructing both knotted and linked topologies from the same ligand remains challenging due to their distinct geometric demands. To address this, we design and synthesize a conformationally adaptive ligand 4,7-bis(3-(pyridin-4-yl) phenyl) benzo[c][1,2,5]thiadiazole (L1) with a tunable torsional angle theta of N1-C1-C2-N2 ranging from 7.5 degrees to 108.9 degrees. Utilizing coordination-driven self-assembly at ambient temperature, L1 selectively assembles with binuclear half-sandwich units Rh-B1, Rh-B2, Rh-B3, and Rh-B4 featuring Cp*RhIII (Cp* = ]5-pentamethylcyclopentadienyl) into distinct topologies: Solomon links Rh-1, trefoil knots Rh-2, molecular tweezers Rh3, and Rh-4, respectively. Crucially, the self-adaptability of ligand L1 directs topology formation through programming different combination of noncovalent interactions (it-it stacking, CH & ctdot;it interaction, and lone pair-it interaction), thus navigating divergent assembly pathways by conformational switching, as evidenced by X-ray crystallography analysis, independent gradient model (IGM) analysis, detailed nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization time-of-flight/mass spectrometry (ESI-TOF/MS). This strategy can also be extended to construct Cp*IrIII analogs (Solomon links Ir-1, trefoil knots Ir-2, molecular tweezers Ir-3 and Ir-4), demonstrating metal-independent control and achieving intricate topologies in a high yield.

Despite substantial advancements in the synthesis of mechanically interlocked molecules (MIMs), achieving the efficient construction of higher‐order links remains a formidable challenge. Herein, we report the highly efficient one‐step directed construction of a series of unprecedented molecular closed four‐link chains (84 1 metalla‐links), achieved through the synergistic assembly of coordination‐driven and aromatic stacking interactions involving binuclear rhodium/iridium precursors and bidentate benzothiadiazole derivative ligands. Meanwhile, modulating the substituent positions of the pyridine groups in bidentate ligand resulted in a change in the topological structure, leading to the formation of two molecular Borromean links (63 2metalla‐links). The molecular configurations of abovementioned metalla‐links were clearly identified through mass spectrometry, NMR, and single‐crystal X‐ray diffraction. Furthermore, the structural transformation between the molecular Borromean links and corresponding monocycles was achieved through concentration effects, as validated by solution‐state NMR spectroscopy investigations.

Herein, we perform a topological transformation by guest induction, converting [2]catenane Rh-1 into the Rh-3 molecular figure-of-eight. The transformation involves the interaction of longer π-acceptor half-sandwich RhIII bimetallic building block B1 [(Cp*Rh)2(TPPHZ)](OTf)4 and π-donor bipyridyl ligands 4,4′-bis((pyridin-4-ylthio)methyl)-1,1′-biphenyl with four molecules of pyrene under ambient temperature in high yields. Intriguingly, despite the involvement of a single pyrene molecule in modifying [2]catenane Rh-2 by transitioning B1 to B2, the underlying skeleton of Rh-2 remains unaltered. Furthermore, we explored the application of these substances before and after the reaction for near-infrared (NIR) photothermal conversion. Through meticulous structural analysis, the π–π stacking interactions play a pivotal role in stabilizing the abovementioned structures, enhancing the nonradiative transitions and initiating photothermal conversion in solution. Based on the results, the introduction of pyrene significantly intensified the π–π stacking interactions but diminished the electron density between the adjacent NDI units, leading to a decrease in the NIR photothermal conversion efficiency (from 58.29

Mechanically interlocked molecules (MIMs) exhibit unique properties and functions arising from their structural entanglement, features of which are absent in their individual components. However, synthesizing topologically complex architectures, particularly those with topological chirality, remains a significant challenge due to the lack of general methods for controlled entanglement. Herein, we report the stereoselective synthesis of a 24-metal-center topologically chiral [6]catenane featuring 18 crossings ( link), representing one of the most intricate MIMs constructed to date. This complex architecture was achieved in high yield (71%) via one-step coordination-driven self-assembly of 12 chiral semirigid bidentate ligands and 12 conjugated binuclear half-sandwich organometallic clips. Critically, chirality transfer from enantiopure ligands enabled exclusive formation of topological enantiomer pairs ( Rh-1 S / Rh-1 R ), each containing four topologically chiral stereogenic units—three cyclic [3]catenane components and one closed three-link chain component. The self-assembly is synergistically directed by integrated noncovalent interactions (sevenfold π–π stacking, hydrogen bonding, and solvophobic effects), as unambiguously confirmed by single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. This design strategy, incorporating tailored noncovalent interaction sites in building blocks, provides a viable approach for synthesizing other structurally complex topologically chiral MIMs.

Achieving transformation between different types of topologies remains a challenge in supramolecular chemistry. Herein, sulfur oxidation was utilized as the stimuli to trigger topological transformations from knots to links. The process began with a thioether‐type precursor, M (4 1 metallic knot), which was synthesized by self‐assembling the sulfur‐bridged ligand L with building block B in high yield. Following oxidation reactions, we successfully transformed the octanuclear 4 1 metallic knot ( M ) with four crossing points into a sulfoxide‐type dodecanuclear metallic link ( M‐O ) with six crossing points as an intermediate product, and then to a sulfone‐type dodecanuclear metallic link ( M‐2O ) with six crossing points, which achieves a dual leap in both metal nuclearity and crossing complexity. Remarkably, the key to the transformation lies in using the embedded S‐centres of M as molecular triggers and stepwise oxidation (‐S‐→‐S(O)‐→‐S(O) 2 ‐) enabled precise modulation of the geometric configuration of the sp 3 S‐centres, drastically altering the range of accessible coordination vectors and inducing conformational self‐adaptation among components. This strategy establishes a novel oxidation‐mediated interconversion paradigm among complex topologies, offering new insights for designing dynamic molecular triggers in intelligent material systems.

Realizing topological transformation through supramolecular fusion is particularly challenging, as the self-assembly of disparate components often results in the orthogonal assembly of building blocks into distinct structures rather than the formation of a heteroleptic architecture. This study introduces a topological transformation, transitioning from a figure-eight knot (41 knot) to a Solomon link (412 link) through a supramolecular fusion process. By employing two structurally similar amino acid ligands (L1 and L3) of varying lengths as bridge ligands, we obtained figure-eight knot 1 and a molecular tweezer-like compound 3 when individually complexed with binuclear Cp*Rh acceptor B1. Our results revealed that subtle modifications to bridge ligands can lead to dramatic changes in their structures and recognition properties. Moreover, we successfully achieved the targeted formation of a heteroleptic Solomon link 4 by blending figure-eight knot 1 and compound 3 in a 1:1 ratio without the need for templates. This procedure effortlessly converted the 41 knot into a 412 link, thus marking a significant advancement in the topological transformation. This work not only marks the construction of the first heteroleptic Solomon link comprising two distinct metallamacrocycles but also demonstrates a process of supramolecular fusion-based topological transformation involving three distinct topological structures.