Syntheses of three-dimensional catenanes under kinetic control

A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]anes and Selectively Bind Fluorinated Steroids

Simple organic ligands can self-assemble with metal ions to generate metal-organic cages, whose cavities bind guests selectively. This binding may enable new methods of chemical separation or sensing, among other useful functions. Here we report the preparation of a CuI6L4 pseudo-octahedral metal-organic cage, the ligands of which self-assemble from simple organic building blocks. Temperature, solvent, and the presence of different guests governed which structure predominated from a dynamic mixture of cage diastereomers with different arrangements of right- or left-handed metal vertices. Dissolution in dimethyl sulfoxide or the binding of tetrahedral guests led to a chiral tetrahedral T-symmetric framework, whereas low temperatures favored the achiral S4-symmetric diastereomer. Tetrahedral guests with long arms were encapsulated to form mechanically bonded suit[4]anes, with guest arms protruding out through host windows. The cage was also observed to bind fluorinated steroids, an important class of drug molecules, but not non-fluorinated steroids, providing the basis for new separation processes.

Chiral Truxene-Based Self-Assembled Cages: Triple Interlocking and Supramolecular Chirogenesis

Incorporating chiral elements in host-guest systems currently attracts much attention because of the major impact such structures may have in a wide range of applications, from pharmaceuticals to materials science and beyond. Moreover, the development of multi-responsive and -functional systems is highly desirable since they offer numerous benefits. In this context, we describe herein the construction of a metal-driven self-assembled cage that associates a chiral truxene-based ligand and a bis-ruthenium complex. The maximum separation between both facing chiral units in the assembly is fixed by the intermetallic distance within the lateral bis-ruthenium complex (8.4 Å). The resulting chiral cavity was shown to encapsulate polyaromatic guest molecules, but also to afford a chiral triply interlocked [2]catenane structure. The formation of the latter occurs at high concentration, while its disassembly could be achieved by the addition of a planar achiral molecule. Interestingly the planar achiral molecule exhibits induced circular dichroism signature when trapped within the chiral cavity, thus demonstrating the ability of the cage to induce supramolecular chirogenesis.

Spontaneous and Selective Macrocyclization in Nitroaldol Reaction Systems

Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-β-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.

Self-Assembly of Cluster-Mediated 3D Catenanes with Size-Specific Recognition Behavior

Although interlocked three-dimensional molecules display unique properties associated with their spatial structures, their synthesis and study of their host-guest properties remain challenging. We report the formation of a novel [2]catenane, [Et4N]@[(Tp*WS3Cu3Cl)2(cis-bpype)3]2(OTf)5 ([Et4N][1](OTf)5), by self-assembly of the cluster node [Tp*WS3Cu3Cl]+ and the organic linker (Z)-1,2-diphenyl-1,2-bis(4-(pyridin-4-yl)phenyl)ethene (cis-bpype). Single-crystal X-ray and NMR analyses established that [1]4+ is formed by the interpenetration of two cluster-organic cages. Unique cation-in-cation host-guest complexes were observed with this catenane. The crystalline, empty catenane was formed by taking advantage of the electrostatic repulsion-induced weak binding of the host. Encapsulation experiments also reveal that the empty catenane can adaptively encapsulate cations such as [Et4N]+ and [Pr4N]+ in the cross cavity but is unable to encapsulate [Bu4N]+ and [Me4N]+, although the size of the latter is compatible with that of the cavity. Theoretical calculations and volume analysis allow to unravel the ingenious role of catenane structures and the interplay between electrostatic repulsion and attractive noncovalent interactions for size-specific recognition behavior in host-guest systems involving species with similar electric charges.

Molecular Recognition of Aromatics in Spherical Nanocages

In general, due to the lack of efficient specific molecular interactions, achieving host-guest molecular recognition inside large and neutral metal-organic cages (MOCs) is challenging. Preferential molecular recognition of aromatics using the internal binding sites of interlocked icosahedral (i. e., spherical) M12 L8 MOCs within poly-[n]-catenane (1) is reported. The guest absorption was monitored directly in the solid-state by consecutive single-crystal-to-single-crystal (SCSC) reactions in a gas-solid environment, in single-crystal X-ray diffraction (SC-XRD) experiments. The preferential guest uptake was corroborated by density functional theory (DFT) calculations by determining the host-guest interaction energy (Ehost-guest ) with a nitrobenzene (NB)≫p-xylene (p-xy)≫o-dichlorobenzene (o-DCB) trend (i. e., from 44 to 25 kcal mol-1 ), assessing the XRD outcomes. Combining SC-XRD, DFT and solid-state 13 C NMR, the exceptional stability of the M12 L8 cages, together with the guest exchange/release properties were rationalized by considering the presence of mechanical bonds (efficient π-π interactions) and by the pyridine's rotor-like behaviour (with 3 kcal mol-1 rotational energy barrier). The structure-function properties of M12 L8 makes 1 a potential candidate in the field of molecular sensors.

Chip-based in situ TEM investigation of structural thermal instability in aged layered cathode

Thermally induced oxygen release is an intrinsic structural instability in layered cathodes, which causes thermal runaway issues and becomes increasingly critical with the continuous improvement in energy density. Furthermore, thermal runaway events always occur in electrochemically aged cathodes, where the coupling of the thermal and electrochemical effect remains elusive. Herein, we report the anomalous segregation of cobalt metal in an aged LiCoO2 cathode, which is attributed to the local exposure of the high-energy (100) surface of LiCoO2 and weak interface Co-O dangling bonds significantly promoting the diffusion of Co. The presence of the LCO-Co interface severely aggregated the oxygen release in the form of dramatic Co growth. A unique particle-to-particle oxygen release pathway was also found, starting from the isolated high reduction areas induced by the cycling heterogeneity. This study provides atomistic insight into the robust coupling between the intrinsic structural instability and electrochemical cycling.

Kinetic trapping of 2,4,6-tris(4-pyridyl)benzene and ZnI2 into M12L8 poly-[n]-catenanes using solution and solid-state processes

Here, we show that in a supramolecular system with more than 20 building blocks forming large icosahedral M₁₂L₈ metal-organic cages (MOCs), using the instant synthesis method, it is possible to kinetically trap and control the formation of interlocking M₁₂L₈ nanocages, giving rare M₁₂L₈ TPB-ZnI₂ poly-[n]-catenane. The catenanes are obtained in a one-pot reaction, selectively as amorphous (a1) or crystalline states, as demonstrated by powder X-ray diffraction (powder XRD), thermogravimetric (TG) analysis and ¹H NMR. The 300 K M₁₂L₈ poly-[n]-catenane single crystal X-ray diffraction (SC-XRD) structure including nitrobenzene (1) indicates strong guest binding with the large M₁₂L₈ cage (i.e., internal volume ca. 2600 ų), allowing its structural resolution. Conversely, slow self-assembly (5 days) leads to a mixture of the M₁₂L₈ poly-[n]-catenane and a new TPB-ZnI₂ (2) coordination polymer (i.e., thermodynamic product), as revealed by SC-XRD. The neat grinding solid-state synthesis also yields amorphous M₁₂L₈ poly-[n]-catenane (a1'), but not coordination polymers, selectively in 15 min. The dynamic behavior of the M₁₂L₈ poly-[n]-catenanes demonstrated by the amorphous-to-crystalline transformation upon the uptake of ortho-, meta- and para-xylenes shows the potential of M₁₂L₈ poly-[n]-catenanes as functional materials in molecular separation. Finally, combining SC-XRD of 1 and DFT calculations specific for the solid-state, the role of the guests in the stability of the 1D chains of M₁₂L₈ nanocages is reported. Energy interactions such as interaction energies (E), lattice energies (E*), host-guest energies (E_host-guest) and guest-guest energies (E_guest-guest) were analysed considering the X-ray structure with and without the nitrobenzene guest. Not only the synthetic control achieved in the synthesis of the M₁₂L₈ MOCs but also their dynamic behavior either in the crystalline or amorphous phase are sufficient to raise scientific interest in areas ranging from fundamental to applied sides of chemistry and material sciences.

Stereoselective Construction of Chiral Linear [3]Catenanes and [2]Catenanes

We have successfully constructed a chiral linear [3]catenane stereoselectively by coordination-driven self-assembly using a ditopic monodentate ligand containing l-valine residues with a binuclear half-sandwich organometallic rhodium(III) unit. Furthermore, by increasing the steric hindrance of the amino acid residues in the ligand, a chiral [2]catenane was obtained, which can be regarded as the factor catenane of the chiral linear [3]catenane from a topological viewpoint. Notably, the resulting molecular catenanes all exhibit complex coconformational mechanical helical chirality and planar chirality ascribed to the point chirality of the ligands. Linear [3]catenanes and [2]catenanes with the opposite chirality can be obtained by using ligands containing the corresponding d-amino acid residues, which have been confirmed by single-crystal X-ray diffraction, NMR, mass spectrometry, and circular dichroism spectroscopy.

Single‐Walled Carbon Nanotubes Encapsulated within Metallacycles

Mechanically interlocked derivatives of carbon nanotubes (MINTs) are interesting nanotube products since they show high stability without altering the carbon nanotube structure. So far, MINTs have been synthesized using ring‐closing metathesis, disulfide exchange reaction, H‐bonding or direct threading with macrocycles. Here, we describe the encapsulation of single‐walled carbon nanotubes within a palladium‐based metallosquare. The formation of MINTs was confirmed by a variety of techniques, including high‐resolution transmission electron microscopy. We find the making of these MINTs is remarkably sensitive to structural variations of the metallo‐assemblies. When a metallosquare with a cavity of appropriate shape and size is used, the formation of the MINT proceeds successfully by both templated clipping and direct threading. Our studies also show indications on how supramolecular coordination complexes can help expand the potential applications of MINTs.