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Double-Bridging Increases the Stability of Zinc(II) Metal–Organic Cages
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Cite this: J. Am. Chem. Soc. 2024, 146, 45, 30958–30965
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https://doi.org/10.1021/jacs.4c09742
Published November 4, 2024

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Abstract

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A key feature of coordination cages is the dynamic nature of their coordinative bonds, which facilitates the synthesis of complex polyhedral structures and their post-assembly modification. However, this dynamic nature can limit cage stability. Increasing cage robustness is important for real-world use cases. Here we introduce a double-bridging strategy to increase cage stability, where designed pairs of bifunctional subcomponents combine to generate rectangular tetratopic ligands within pseudo-cubic Zn8L6 cages. These cages withstand transmetalation, the addition of competing ligands, and nucleophilic imines, under conditions where their single-bridged congeners decompose. Our approach not only increases the stability and robustness of the cages while maintaining their polyhedral structure, but also enables the incorporation of additional functional units in proximity to the cavity. The double-bridging strategy also facilitates the synthesis of larger cages, which are inaccessible as single-bridged congeners.

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Introduction

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Molecular capsules have proved useful in applications that include separation and purification, (1,2) sensing, (3,4) storage of reactive compounds, (5−7) and (photo)catalysis. (8−12) The functionality of these capsules in solution complements the solid-state applications of porous networks, such as metal–organic frameworks. (13,14) Subcomponent self-assembly, where ligands and capsule assemble from smaller subunits during the same overall process, has enabled the rapid preparation of structurally complex polyhedral capsules with little synthetic effort. (15−19) Such capsules can be tailored through subcomponent exchange or other post-assembly modifications. (20−24) The dynamic nature of the coordination bonds that hold these structures together provides advantages in their synthesis and applications, but these dynamic linkages also limit capsule stability. For example, competing ligands can degrade cages by extracting their metal ions. The labile imine bonds formed within ligands during subcomponent self-assembly are also susceptible to acid- or base-catalyzed hydrolysis. (25) This property can limit the application potential of coordination cages in real-world scenarios, which can require low cage concentrations or high stability in complex solutions with potentially interfering species, such as ligands and metal ions.
One approach to increasing cage stability is to use metal–ligand combinations with intrinsically stable coordination bonds. Metals in high oxidation states, such as ZrIV or CoIII, or 4d and especially 5d metals such as PtII, thus generate more stable cages. (26−30) However, the slow dynamic exchange of coordination bonds can impede cage formation, as less stable structures become kinetically trapped, requiring strategies such as post-assembly oxidation, dynamic covalent approach, or harsh reaction conditions. (31−35) Most strategies for stabilizing coordination bonds are based on matching the softness/hardness of the metal and ligand donor, (36) optimization of the coordination geometry, (37,38) and enhancing the Lewis acidity/basicity of the metal ion/ligand. (39,40) These strategies can also provide control over dynamic ligand or subcomponent exchange, which is often based on the introduction of labile bonds such as imines. (20,25,40−47) Another well-investigated approach to stabilize coordination cages is based on strategic entropy gain, for example by using high-topicity ligands, leading to preorganization. (48−50) For instance, capping cages increases the density of connections that bind them together, increasing their stability. (51−54)
In this work, we demonstrate the stabilization of pyridyl-imine-based Zn8L6 coordination cages through double-bridging their edges. These cages were constructed from a dialdehyde subcomponent that provides a novel vertex coordination geometry upon imine condensation. This arrangement contrasts with other pyridyl-imine-based cages (55−57) because of the unique orientations of the aniline units within the product structure. This geometry positions the aniline residues of these imines so that cross-linking between ligands is possible when certain dianilines are added. The resulting double-bridged ligands thus chelate four zinc ions instead of two─their topicity increases from 2 to 4 going from the cubic to the pseudo-cubic framework. This increase in topicity increases the robustness of the cage, enhancing its application potential. The double-bridging approach also enabled the assembly of a larger pseudo-cubic cage, which could not be obtained as the single-bridged version.

Results and Discussion

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Self-Assembly and Characterization of Single- and Double-Bridged Cages

Subcomponent A (Figure 1) was synthesized via Pd-catalyzed Suzuki–Miyaura cross-coupling as detailed in the Supporting Information (Figures S1–S3, pages 2–4 in the SI). Heating subcomponent A (1.5 equiv), p-toluidine (3.0 equiv), and zinc(II) bis(trifluoromethylsulfonyl)imide (Zn(NTf2)2, 1 equiv) in acetonitrile gave cubic [Zn8L12]16+ cage 1. The 1H NMR spectrum of 1 was consistent with a highly symmetrical species, as only one set of ligand signals was obtained (Figures S11, S12). Further NMR experiments (Figures S13–S16) enabled the assignment of the peaks as shown in Figures 1 and S11. While the pyridyl, imine and methyl protons gave sharp peaks in the 1H NMR spectrum, the signals of the phenylene protons e, f and g were broad and overlapping. Upon increasing the temperature, the signals become sharper, consistent with restricted rotational motion of the phenylene groups at room temperature (Figure S17). The nuclear overhauser effect spectroscopy (NOESY) NMR spectrum of 1 indicated through-space interactions between protons h, e and c, confirming that the tolyl groups point toward each other on the faces of the cube (Figures S18, S19). This arrangement contrasts with other pyridyl-imine-based cages, whose vertices bear externally oriented substituents (Figure S20). (15,56,57)

Figure 1

Figure 1. Subcomponent self-assembly of A, p-toluidine, and Zn(NTf2)2, to form O-symmetric Zn8L12 cube 1. Protons are assigned according to 1D and 2D NMR spectra (Figures S11–S16). Only the Λ8 enantiomer is shown. Hydrogen atoms and counteranions are omitted for clarity.

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Crystals of 1 suitable for single-crystal X-ray diffraction were obtained by vapor diffusion of benzene into an acetonitrile solution of 1 containing excess KSbF6 (see Figures 1 and S71, with details given on SI pages 43–45). As shown in Figure 1, the crystal structure obtained was consistent with the solution-state configuration of the tolyl substituents observed by NOESY, with each tolyl group at 90° to its nearest neighbors on the respective cage face. Cage 1 thus exhibits O point symmetry, with all metal ions within a cage exhibiting the same Λ- or Δ-handedness, and both cage enantiomers present in the crystal.
Diffusion ordered spectroscopy (DOSY) NMR spectra verified the formation of a single species with a solvodynamic radius of 18.4 Å (Figure S21). The radius exceeds the value of 14.1 Å based upon the crystal structure (Figure S71). As the experimental radius remained unchanged upon concentration increase from 0.2 to 0.8 mM, we infer that aggregation is not responsible for the larger-than-expected radius observed in solution (Figure S22). The increased solvodynamic radius might be a consequence of interactions between 1 and counteranions or solvent molecules. In contrast to previously reported pyridyl-imine cages, the charged metal centers of 1 are more exposed to the external environment, with less shielding by the ligands.
In the 19F NMR spectrum of 1, two signals at −78.6 and −80.4 ppm were observed, consistent with the binding of a Tf2N– anion in slow exchange on the NMR time scale (Figure S23). Heteronuclear Overhauser enhancement spectroscopy (HOESY) experiments confirmed 1H–19F through-space interactions between the encapsulated Tf2N– and the tolyl substituents at the faces of cage 1 (Figure S24). We were not able to prepare 1 from Zn(OTf)2 or Zn(BF4)2 under similar reaction conditions, suggesting that the encapsulated Tf2N– anion exercised a stabilizing effect. CH–π interactions between neighboring p-tolyl groups may also serve to stabilize the framework of 1, as we were unable to synthesize cage 1 with aniline in place of p-toluidine under the same reaction conditions.
High resolution electrospray ionization mass spectrometry (ESI-MS) confirmed the presence of cubic cage 1 in solution (Figures S25, S26). However, cage fragmentation could only be prevented by applying very mild MS conditions, consistent with low stability of 1 in the mass spectrometer. Even under mild MS conditions, many ions attributable to fragments of 1 were observed (Figure S25).
The novel vertex motif of 1, which orients its tolyl substituents parallel to the cage faces, suggested the possibility of double-bridging the cage faces by linking them with dianilines. The reaction of subcomponent A (1.5 equiv) and 2,7-diaminofluorene (1.5 equiv) with Zn(NTf2)2 (1.1 equiv) in acetonitrile in a microwave reactor produced double-bridged [Zn8L′6]16+ pseudo-cube 2 (Figure 2 top). NMR spectra of 2 confirmed the formation of a single high-symmetry species and enabled assignment of its 1H NMR spectrum (Figures S27–S33). HR-ESI-MS (Figures S41–S43) measurements confirmed its composition.

Figure 2

Figure 2. Self-assembly of double-bridged zinc(II) cages based on subcomponent A. (Top) Self-assembly of subcomponents A, 2,7-diaminofluorene, and Zn(NTf2)2, forming achiral double-bridged Zn8L′6 cage 2 (illustrated as a schematic model and the crystal structure of Th-symmetric 2•(PF6)16). Cage 2 was also formed through reaction of 1 with 2,7-diaminofluorene. (Bottom) Self-assembly of subcomponents A and 2,7-diaminofluorenone with Zn(NTf2)2, forming achiral double-bridged Zn8L″6 3 (illustrated as a schematic model and a model based on GFN2-xTB calculations). Proton assignments are derived from NMR spectra (Figures S27−S33, S44−S48). Hydrogen atoms and counteranions are omitted for clarity.

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The double-bridging in cage 2 fundamentally alters its stereochemistry. In contrast to singly bridged 1, the extra ligand bridges in 2 enforce a 1:1 mixture of Δ and Λ handed metal centers, in which every zinc(II) center has nearest neighbors of the opposite handedness, as shown in Figure 2. Single crystals of 2 suitable for X-ray diffraction analysis were obtained by vapor diffusion of diethyl ether into an acetonitrile solution of 2 containing excess TBA+PF6– (see Figures 2 and S72, with details given on SI pages 43–46). The crystal structure confirmed the alternating Λ- and Δ-handedness of the metal centers, resulting in achiral Th symmetry.
In the NOESY NMR spectrum of 2, a through-space interaction was observed between the protons b and h, but not between c and h (Figures S34, S35). These observations confirm the locked state of the fluorene unit, whose bent geometry prevents free rotation. Furthermore, CH–π interactions between the fluorene unit and the phenyl unit prevent free rotation of the phenyl unit and result in splitting of the aromatic protons e and i. As proton i is pointing toward the fluorene unit, it is strongly shielded by its ring current, leading to a pronounced upfield shift with Δδ = 5 ppm. Upon temperature increase, the increased rotational freedom results in broadening of the two proton signals e and i and shifts them closer to each other (Figure S36). Furthermore, even upon temperature increase to 368 K in deuterated nitromethane solution, convergence into a single sharp signal was not observed (Figure S37). These observations indicate that the solution structure of 2 is isomorphous to the crystal structure.
DOSY NMR gave results consistent with the presence of a single species with a solvodynamic radius of 19.7 Å (Figure S38). As with 1, the solvodynamic radius was concentration-independent and exceeds the radius of 14.1 Å determined from the crystal structure (Figures S39, S72). The solution and solid-state radii of 1 and 2 are nearly identical, confirming that double-bridging impacted the cage framework symmetry, but not its size. In contrast to 1, only one Tf2N– signal, which is slightly shifted compared to a TBA+Tf2N– control sample, was observed in the 19F NMR spectrum of 2 (Figure S40), indicating fast exchange of this anion between bulk solution and the cage cavity.
As the fluorene CH2 protons point toward the cage window and cavity, we inferred that alteration at the CH2 position of the fluorene unit might enable endohedral functionalization, thus changing the size and properties of the cage cavity and windows. We therefore prepared the derivative 2,7-diamino-9-fluorenone (Figures S4, S5, pages 4, 5 in the SI), and combined it with subcomponent A and Zn(NTf2)2 in acetonitrile in a microwave reactor (Figure 2 bottom). The formation of double-bridged [Zn8L″6]16+ pseudo-cube 3 was confirmed by NMR and ESI-MS experiments (Figures S44–S56).
We were not able to obtain crystals of 3 suitable for single-crystal X-ray diffraction, despite numerous attempts. We therefore optimized its structure using GFN2-xTB calculations, which produced a geometry very similar to the X-ray structure of cage 2, as is evident when the two are overlaid (Figure S57). The calculated structure suggests that the carbonyl oxygen significantly impacts the size and polarity of the cage windows and cavity (Figures 2 and S57).
To confirm the transferability of the double-bridging strategy to other cages, we prepared extended subcomponent B (Figures 3, S6–S10, pages 6–9 in the SI). A larger single-bridged pseudo-cube similar to 1 was not obtained when B and p-toluidine were mixed with Zn(NTf2)2 under the same conditions used for the formation of 1. However, the reaction of subcomponent B (1.5 equiv), 4,4″-diamino-p-terphenyl (1.5 equiv), and zinc(II) bis(trifluoromethylsulfonyl)imide (Zn(NTf2)2, 1.1 equiv) in acetonitrile in a microwave reactor resulted in the formation of the extended double-bridged [Zn8L‴6](NTf2)16 pseudo-cube 4 (Figure 3), as confirmed by HR-ESI-MS (Figures S67–S70), single-crystal X-ray diffraction, and NMR, as detailed below.

Figure 3

Figure 3. Self-assembly of double-bridged zinc(II) cages based on subcomponent B. (Top) No cage formation was observed upon reaction of the subcomponents B and p-toluidine with Zn(NTf2)2 under similar conditions. (Bottom) The self-assembly of subcomponents B and 4,4″-diamino-p-terphenyl with Zn(NTf2)2, forming Th-symmetric double-bridged Zn8L‴6 cage 4, illustrated as a schematic model and view of the crystal structure of the (tetrakis(4-fluorophenyl)borate) salt. Proton assignments are derived from NMR spectra (Figures S58–S62 in the Supporting Information). Hydrogen atoms and counteranions are omitted for clarity.

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Single crystals of 4 were obtained by vapor diffusion of benzene into an acetonitrile solution of 4 containing excess sodium (tetrakis(4-fluorophenyl)borate). The X-ray structure of 4 confirmed the formation of a Th symmetric cage (see Figures 3 and S73, with details given on SI pages 43–47).
Solution NMR characterization (Figures S58–S62) gave results consistent with the X-ray structure. We infer the mutual proximity of the aromatic hydrogens of the double-bridged edges to result in restricted rotational freedom in solution, which led to a broadening of the proton signals in the 1H NMR spectrum. This proximity was confirmed by NOESY measurements (Figure S63). At elevated temperatures, increased rotational freedom resulted in a sharpening of the phenylene proton signals (Figure S64). DOSY NMR measurements confirmed the presence of a single species with a solvodynamic radius of 22.9 Å (Figure S65). As with the DOSY measurements of 1, 2, and 3, the experimentally determined solvodynamic radius exceeded the radius of 17.6 Å determined from the crystal structure of 4 (Figure S73). Here too we attribute this observation to an extended solvent/anion shell, due to metal charge exposure to the external environment. As with 2 and 3, only one Tf2N– signal was observed in the 19F NMR spectrum of 4, consistent with a poorly enclosed cage cavity (Figure S66).

Stability and Robustness Investigations

Double-bridging leads to an increase in ligand topicity. This increase should stabilize a coordination cage due to a higher density of linkages holding the structure together, requiring more bonds to be broken in order to disrupt the structure. (58) In contrast to previous cases, (43) the novel vertex geometry generated by dialdehydes A and B facilitates vertex bridging without disrupting the polyhedral framework of the metal–organic cage. To gauge the effects of double-bridging on cage stability, the conversion from 1 to 2 was investigated experimentally and computationally. Upon addition of 12 equiv 2,7-diaminofluorene to cage 1 and heating at 70 °C over 20 h, complete conversion from 1 to 2 was observed (Figures 4 and S74). In contrast, the conversion of 2 to 1 was not observed even upon addition of 200 equiv of p-toluidine and prolonged heating (Figures 4 and S75). These observations indicate that cage 2 is thermodynamically favored over cage 1. As the conversion from 1 to 2 results in a change in electronic structure, this process could be followed by UV–vis spectroscopy (Figures S76, S77). While increasing the temperature increased both reaction rates and conversion, substitution did not follow straightforward first or second order rate laws (Figure S77, right). Furthermore, addition of a smaller amount of 2,7-diaminofluorene resulted in a mixture of cage 1 and 2, and the observation of undefined intermediates (Figure S78).

Figure 4

Figure 4. Comparison of the stabilities of cages 1 and 2. 1 converted into 2 upon addition of 2,7-diaminofluorene (12 equiv), whereas conversion of 2 to 1 was not observed even upon addition of 200 equiv p-toluidine. After conversion from 1 to 2, the sample was washed with Et2O to remove free p-toluidine and minor impurities. The spectrum before washing is given in Figure S74 in the Supporting Information.

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To investigate the thermodynamic driving force for the conversion of 1 to 2 in detail and gain a deeper understanding of the effect of double-bridging on the stability of the cages, semiempirical quantum mechanical calculations were performed (structures based on GFN2-xTB calculations are given in Figures S79, S80, with details given on SI pages 51–53). The optimized structures were very similar to the crystal structures of 1 and 2. Calculations at both the GFN2-xTB and DFT level indicated that 1 is enthalpically favored over 2. Nevertheless, the entropic contribution outweighs the enthalpic term, leading to a driving force for the conversion from 1 to 2 of ΔG = −30.39 kcal mol–1 (ΔH = 101.40 kcal mol–1), TΔS = 131.70 kcal mol–1 (r2SCAN-3c//GFN2-xTB).
Cage 2 is also more rigid than 1, as confirmed by molecular dynamics (MD) simulations (details on SI pages 53–55) using a classical force-field, where cage 1 was found to collapse. The cage framework was maintained only when intramolecular noncovalent interactions were better described using the GFN2-xTB approach. In contrast, 2 remained rigid in all the simulations. Molecular flexibility is qualitatively correlated with atomic movement over a given time interval, as indicated by larger integrated atomic displacement, a high average Cartesian coordinate root-mean-square deviation, or low fluctuation in total energy during MD simulation. For all the metrics considered, 2 consistently exhibited greater rigidity than 1 (Table S4, Figure S82).
We next sought to investigate whether the stability increase through double-bridging also translates to greater robustness against chemical stimuli. Cages 1 and 2 were exposed to various such stimuli chosen for their relevance to real-world applications. Upon addition of 12 equiv of aniline, decomposition of cage 1 was observed, while cage 2 remained intact even following the addition of 100 equiv of aniline (Figures S83, S84). The effect of salt addition was then investigated through addition of TBA+TfO–. While cage 1 decomposed upon addition of 20 equiv of this salt, cage 2 remained intact in the presence of 30 equiv of TBA+TfO– (Figures S85, S86). Cage resistance to transmetalation was investigated upon addition of Fe(NTf2)2, as the iron(II) congeners of 1 and 2 were not obtained by direct self-assembly. Addition of 8 equiv Fe(NTf2)2 to a solution of cage 1 resulted in an immediate color change to produce a purple solution, consistent with the formation of low-spin iron(II) pyridyl-imine complexes. (59) Decomposition of 1 was further confirmed by 1H NMR (Figure S87). In contrast, following the addition of 24 equiv of Fe(NTf2)2 to a solution of 2, no color change was observed, and the 1H NMR spectrum confirmed that cage 2 remained intact (Figure S88). Cage tolerance toward added ligands was investigated by the addition of neat deuterated DMSO, which can form [Zn(DMSO)6]2+ with zinc(II). (60) As in other cases, (61,62) the low stability of 1 resulted in full decomposition at 7 vol % DMSO, while 2 stayed intact even in 33 vol % DMSO (Figures S89, S90). Furthermore, cage 2 exhibited a higher thermal stability in the solid state compared to cage 1 (Figures S91, S92). We conclude that the greater stability of 2 compared to 1 is based on increased topicity, and thus preorganization, of the tetratopic ligands of 2.

Host–Guest Chemistry

The host–guest chemistry of all cages was investigated by the addition of 10 equiv of an anionic guest─BF4−, PF6−, TfO−, BPh4F− (tetrakis(4-fluorophenyl)borate), and BPh4CF3− (tetrakis[3,5-bis(trifluoromethyl)phenyl]-borate)─to a solution of the host. Even though cage 1 exhibited decomposition upon addition of larger amounts of salts, addition of 10 equiv of one of these anions did not result in decomposition (Figure S93). While the addition of the largest anionic guest BPh4CF3– did not result in any shifts of the signals, the addition of BPh4F– resulted in small shifts of all proton signals. In contrast, the addition of the smaller anionic guests BF4–, PF6–, or TfO– only affected the signals of protons e and f, hinting at localization of interactions of the small anions at the cage faces (Figure S94). Similar interactions were also observed for NTf2– (Figure S24).
Cage 2 bound all of the tested anionic guests except for BPh4CF3– (Figure S95). The addition of 10 equiv of one of the small anions BF4–, PF6–, or TfO– resulted in shifts of the 1H NMR signals of protons c and j, which point toward the cage cavity. We thus conclude that these anions with van der Waals volumes between 53.2 to 84.3 Å3 bind within the 353.9 Å3 cavity of 2 (Figure S96). (63) In contrast, the addition of BPh4F–, with a van der Waals volume of 358.2 Å3, results in shifts of protons g and h, consistent with exterior binding of the anion at the cage windows. The presence of two binding sites that are selective for specific guests permits the simultaneous binding of BF4– and BPh4F– in the interior and exterior binding sites, respectively. This behavior is reflected in shifts of both the c/j and g/h protons upon simultaneous addition of both guests. Detailed investigation of the host–guest binding by NMR titration experiments, including determination of the binding constants, proved challenging due to the limited solubility of cage 2 following addition of BF4–, PF6–, or TfO–, which resulted in precipitation of the cage upon anion exchange. Furthermore, the lack of a suitable chromophore within 2 prevented the determination of host–guest isotherms and the associated binding constants by UV–vis titration measurements.
Host–guest experiments with congener 3 indicated that only the addition of BPh4F– resulted in NMR shifts of protons g and h, indicating exterior binding on the cage window, as with cage 2 (Figure S97). The addition of BF4–, PF6–, or TfO– did not lead to significant NMR shifts, indicating a lack of interaction. This result indicates that the incorporation of a carbonyl oxygen prevents encapsulation of small anionic guests, despite the similarity of the framework of 3 to that of 2 (Figure S98). Cage 4 exhibited weak interactions between BPh4F– and the edges of the pseudo-cube, as evidenced by small NMR shifts of protons e and f (Figure S99). We attribute the lack of guest binding to the porous architecture of cage 4 (Figure S100).

Conclusion

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Our approach─the double-bridging strategy─facilitates the formation of highly robust self-assembled zinc(II) metal–organic cages. This strategy is based on a novel dialdehyde subcomponent that produces a vertex motif in which substituents point toward the cage faces, enabling covalent bridging to increase ligand topicity. WAlthough the architecture is not affected by double-bridging, the cage chirality is transformed from point group O to achiral Th. Our strategy permits the introduction of functional groups in proximity to the cage cavity, influencing host–guest binding. The topicity increase through double-bridging enhances the cage stability sufficiently to enable the preparation of a large double-bridged cage that could not be obtained as its single-bridged congener. Double-bridged metal–organic cages did not decompose upon treatment with chemical stimuli that destroyed their single-bridged congeners, withstanding transmetalation, the addition of competing ligands and anilines. This thermodynamic and kinetic stability is crucial for the application of metal–organic cages in real-world scenarios, for instance in the purification of industrially relevant molecules out of complex reaction mixtures. (2,64) The application of the double-bridging strategy in other metal–organic cage systems thus appears very promising, potentially creating new use cases for these systems by increasing their robustness, while simultaneously offering a new route to endofunctionalisation.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.4c09742.

  • (1) General Information (2) Synthesis and Characterization of Subcomponents (3) Subcomponent Self-Assembly (4) Single-crystal X-ray Diffraction (5) Conversion from 1 to 2 (6) Robustness Investigations of 1 and 2 (7) Host–Guest Experiments (PDF)

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CCDC 2362227–2362229 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Author Information

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  • Corresponding Author
  • Authors
    • Hannah Kurz - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
    • Paula C. P. Teeuwen - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.;  Orcidhttps://orcid.org/0000-0002-2571-8161
    • Tanya K. Ronson - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.;  Orcidhttps://orcid.org/0000-0002-6917-3685
    • Jack B. Hoffman - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
    • Philipp Pracht - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.;  Orcidhttps://orcid.org/0000-0002-8495-9504
    • David J. Wales - Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
  • Funding

    This study was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) (EP/T031603/1 and EP/S024220/1). H.K. thanks the Alexander von Humboldt Foundation and the Isaac Newton Trust. P.P. thanks the Alexander von Humboldt Foundation

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We thank Diamond Light Source for synchrotron beamtime on Beamline I19 (CY29890) and the NMR service of the Yusuf Hamied Department of Chemistry at the University of Cambridge.

Abbreviations

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NMR

nuclear magnetic resonance

NOESY

nuclear overhauser effect spectroscopy

DOSY

diffusion ordered spectroscopy

HOESY

heteronuclear overhauser enhancement spectroscopy

HR-ESI-MS

high resolution electrospray ionization mass spectrometry

DFT

density functional theory

MD

molecular dynamics

H

enthalpy

T

temperature

S

entropy

equiv

equivalents

DMSO

dimethyl sulfoxide

TBA+

tetrabutylammonium

Tf2N–

(trifluoromethylsulfonyl)imide

OTf–

trifluoromethanesulfonate

BPh4F–

(tetrakis(4-fluorophenyl)borate)

BPh4CF3–

(tetrakis[3,5-bis(trifluoromethyl)phenyl]-borate)

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    Emissive Platinum(II) Cages with Reverse Fluorescence Resonance Energy Transfer for Multiple Sensing
    Zhang, Zeyuan; Zhao, Zhengqing; Wu, Lianwei; Lu, Shuai; Ling, Sanliang; Li, Guoping; Xu, Letian; Ma, Lingzhi; Hou, Yali; Wang, Xingchen; Li, Xiaopeng; He, Gang; Wang, Kai; Zou, Bo; Zhang, Mingming
    Journal of the American Chemical Society (2020), 142 (5), 2592-2600CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    It is quite challenging to realize fluorescence resonance energy transfer (FRET) between 2 chromophores with specific positions and directions. Through the self-assembly of 2 carefully selected fluorescent ligands via metal-coordination interactions, 2 tetragonal prismatic Pt(II) cages with a reverse FRET process between their faces and pillars were prepd. Bearing different responses to external stimuli, these 2 emissive ligands are able to tune the FRET process, thus making the cages sensitive to solvents, pressure, and temp. These cages could distinguish structurally similar alcs. such as n-BuOH, Me3COH, and i-BuOH. They showed decreased emission with bathochromic shifts under high pressure. They exhibited a remarkable ratiometric response to temp. over a wide range (223-353 K) with high sensitivity. By plotting the ratio of the max. emission (I600/I480) of metallacage 4b against the temp., the slope reaches 0.072, which is among the highest values for ratiometric fluorescent thermometers reported so far. This work offers a strategy to manipulate the FRET efficiency in emissive supramol. coordination complexes and paves the way for the future design and prepn. of smart emissive materials with external stimuli responsiveness.
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  4. 4
    Gemen, J.; Ahrens, J.; Shimon, L. J. W.; Klajn, R. Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage. J. Am. Chem. Soc. 2020, 142 (41), 17721– 17729,  DOI: 10.1021/jacs.0c08589
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    4
    Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage
    Gemen, Julius; Ahrens, Johannes; Shimon, Linda J. W.; Klajn, Rafal
    Journal of the American Chemical Society (2020), 142 (41), 17721-17729CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Aggregation of org. mols. can drastically affect their physicochem. properties. For instance, the optical properties of BODIPY dyes are inherently related to the degree of aggregation and the mutual orientation of BODIPY units within these aggregates. Whereas the noncovalent aggregation of various BODIPY dyes has been studied in diverse media, the ill-defined nature of these aggregates has made it difficult to elucidate the structure-property relationships. Here, we studied the encapsulation of three structurally simple BODIPY derivs. within the hydrophobic cavity of a water-sol., flexible PdII6L4 coordination cage. The cavity size allowed for the selective encapsulation of two dye mols., irresp. of the substitution pattern on the BODIPY core. Working with a model, a pentamethyl-substituted deriv., authors found that the mutual orientation of two BODIPY units in the cage's cavity was remarkably similar to that in the cryst. state of the free dye, allowing to isolate and characterize the smallest possible noncovalent H-type BODIPY aggregate, namely, an H-dimer. Interestingly, a CF3-substituted BODIPY, known for forming J-type aggregates, was also encapsulated as an H-dimer. Taking advantage of the dynamic nature of encapsulation, they developed a system in which reversible switching between H- and J-aggregates can be induced for multiple cycles simply by addn. and subsequent destruction of the cage. Authors expected that the ability to rapidly and reversibly manipulate the optical properties of supramol. inclusion complexes in aq. media will open up avenues for developing detection systems that operate within biol. environments.
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  5. 5
    Dong, V. M.; Fiedler, D.; Carl, B.; Bergman, R. G.; Raymond, K. N. Molecular Recognition and Stabilization of Iminium Ions in Water. J. Am. Chem. Soc. 2006, 128 (45), 14464– 14465,  DOI: 10.1021/ja0657915
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    5
    Molecular Recognition and Stabilization of Iminium Ions in Water
    Dong, Vy M.; Fiedler, Dorothea; Carl, Barbara; Bergman, Robert G.; Raymond, Kenneth N.
    Journal of the American Chemical Society (2006), 128 (45), 14464-14465CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Iminium ions are known to exist only transiently in aq. soln. due to their high reactivity toward hydrolysis. In this communication, we report on the generation and stabilization of iminium ions in aq. soln. via mol. encapsulation using a K12Ga4L6 host. Our studies revealed that a tetrahedral host can encapsulate a variety of iminium cations in a mol. recognition process that is selective based on the charge, hydrophobicity, size, and shape of the guest.
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  6. 6
    Yamashina, M.; Sei, Y.; Akita, M.; Yoshizawa, M. Safe Storage of Radical Initiators within a Polyaromatic Nanocapsule. Nat. Commun. 2014, 5 (1), 4662,  DOI: 10.1038/ncomms5662
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    6
    Safe storage of radical initiators within a polyaromatic nanocapsule
    Yamashina, Masahiro; Sei, Yoshihisa; Akita, Munetaka; Yoshizawa, Michito
    Nature Communications (2014), 5 (), 4662CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    2,2'-Azobisisobutyronitrile and its derivs. are std. reagents for polymer and org. synthesis that generate radical species on stimuli by light or heat. Radical initiators like the azo compds. are unstable so that they should be kept in the dark at low temp. to avoid photochem. and thermal decompn. as well as accidental explosion. Here we report the spontaneous and quant. encapsulation of the radical initiators by a supramol. nanocapsule in aq. soln. We demonstrate the remarkable stability of the initiators toward light and heat in the well-defined cavity shielded by the polyarom. capsule shell. The incarcerated and stabilized initiators can be directly utilized for the radical polymn. of olefins on spontaneous release of the initiators from the capsule under the reaction conditions.
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  7. 7
    Mal, P.; Breiner, B.; Rissanen, K.; Nitschke, J. R. White Phosphorus Is Air-Stable Within a Self-Assembled Tetrahedral Capsule. Science 2009, 324 (5935), 1697– 1699,  DOI: 10.1126/science.1175313
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    7
    White Phosphorus Is Air-Stable Within a Self-Assembled Tetrahedral Capsule
    Mal, Prasenjit; Breiner, Boris; Rissanen, Kari; Nitschke, Jonathan R.
    Science (Washington, DC, United States) (2009), 324 (5935), 1697-1699CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    The air-sensitive nature of white phosphorus underlies its destructive effect as a munition; tetrahedral P4 mols. readily react with atm. dioxygen, leading this form of the element to spontaneously combust upon exposure to air. Here, hydrophobic P4 mols. are rendered air-stable and water-sol. within the hydrophobic hollows of self-assembled tetrahedral container mols., [Fe4L6]4- (L = 4,4'-bis(2-pyridylmethyleneamino)-1,1'-biphenyl-2,2'-disulfonate), which form in water from simple org. subcomponents and iron(II) ions. The host-guest complex with P4 was characterized by x-ray crystallog. This stabilization is not achieved through hermetic exclusion of O2 but rather by constriction of individual P4 mols.; the addn. of oxygen atoms to P4 would gave oxidized species too large for their containers. The phosphorus can be released in controlled fashion without disrupting the cage by adding the competing guest benzene.
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  8. 8
    Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Functional Molecular Flasks: New Properties and Reactions within Discrete, Self-Assembled Hosts. Angew. Chem., Int. Ed. 2009, 48 (19), 3418– 3438,  DOI: 10.1002/anie.200805340
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    8
    Functional Molecular Flasks: New Properties and Reactions within Discrete, Self-Assembled Hosts
    Yoshizawa, Michito; Klosterman, Jeremy K.; Fujita, Makoto
    Angewandte Chemie, International Edition (2009), 48 (19), 3418-3438CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Self-assembled hosts applied as "mol. flasks" can alter and control the reactivity and properties of mols. encapsulated within their well-defined, confined spaces. A variety of functional hosts of differing sizes, shapes, and utility have been prepd. by using the facile and modular concepts of self-assembly. The application of self-assembled hosts as "mol. flasks" has pptd. a surge of interest in the reactivity and properties of mols. within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepd. This Review briefly highlights the various mol. flasks synthesized before focusing on their use as functional mol. containers-specifically for the encapsulation of guest mols. to either engender unusual reactions or unique chem. phenomena. Such self-assembled cavities now constitute a new phase of chem., which cannot be achieved in the conventional solid, liq., and gas phases.
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  9. 9
    Hong, C. M.; Morimoto, M.; Kapustin, E. A.; Alzakhem, N.; Bergman, R. G.; Raymond, K. N.; Toste, F. D. Deconvoluting the Role of Charge in a Supramolecular Catalyst. J. Am. Chem. Soc. 2018, 140 (21), 6591– 6595,  DOI: 10.1021/jacs.8b01701
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    9
    Deconvoluting the Role of Charge in a Supramolecular Catalyst
    Hong, Cynthia M.; Morimoto, Mariko; Kapustin, Eugene A.; Alzakhem, Nicola; Bergman, Robert G.; Raymond, Kenneth N.; Toste, F. Dean
    Journal of the American Chemical Society (2018), 140 (21), 6591-6595CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We have demonstrated that the microenvironment of a highly anionic supramol. catalyst can mimic the active sites of enzymes and impart rate accelerations of a million-fold or more. However, these microenvironments can be challenging to study, esp. in the context of understanding which specific features of the catalyst are responsible for its high performance. We report here the development of an exptl. mechanistic probe consisting of two isostructural catalysts. When examd. in parallel transformations, the behavior of these catalysts provides insight relevant to the importance of anionic host charge on reactivity. These two catalysts exhibit similar host-substrate interactions, but feature a significant difference in overall anionic charge (12- and 8-). Within these systems, we compare the effect of constrictive binding in a net neutral aza-Cope rearrangement. We then demonstrate how the magnitude of anionic host charge has an exceptional influence on the reaction rates for a Nazarov cyclization, evidenced by an impressive 680-fold change in reaction rate as a consequence of a 33% redn. in catalyst charge.
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  10. 10
    Jiao, J.; Tan, C.; Li, Z.; Liu, Y.; Han, X.; Cui, Y. Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions. J. Am. Chem. Soc. 2018, 140 (6), 2251– 2259,  DOI: 10.1021/jacs.7b11679
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    10
    Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions
    Jiao, Jingjing; Tan, Chunxia; Li, Zijian; Liu, Yan; Han, Xing; Cui, Yong
    Journal of the American Chemical Society (2018), 140 (6), 2251-2259CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Supramol. nanoreactors featuring multiple catalytically active sites are of great importance, esp. for asym. catalysis, and are yet challenging to construct. Here we report the design and assembly of five chiral single- and mixed-linker tetrahedral coordination cages using six dicarboxylate ligands derived-from enantiopure Mn(salen), Cr(salen) and/or Fe(salen) as linear linkers and four Cp3Zr3 clusters as three-connected vertices. The formation of these cages was confirmed by a variety of techniques including single-crystal and powder X-ray diffraction, inductively coupled plasma optical emission spectrometer, quadrupole-time-of-flight mass spectrometry and energy dispersive X-ray spectrometry. The cages feature a nanoscale hydrophobic cavity decorated with the same or different catalytically active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen) species is shown to be an efficient supramol. catalyst for sequential asym. alkene epoxidn./epoxide ring-opening reactions with up to 99.9% ee. The cage catalyst demonstrates improved activity and enantioselectivity over the free catalysts owing to stabilization of catalytically active metallosalen units and concn. of reactants within the cavity. Manipulation of catalytic org. linkers in cages can control the activities and selectivities, which may provide new opportunities for the design and assembly of novel functional supramol. architectures.
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  11. 11
    Wang, J.-S.; Wu, K.; Yin, C.; Li, K.; Huang, Y.; Ruan, J.; Feng, X.; Hu, P.; Su, C.-Y. Cage-Confined Photocatalysis for Wide-Scope Unusually Selective [2 + 2] Cycloaddition through Visible-Light Triplet Sensitization. Nat. Commun. 2020, 11 (1), 4675,  DOI: 10.1038/s41467-020-18487-5
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  12. 12
    Ham, R.; Nielsen, C. J.; Pullen, S.; Reek, J. N. H. Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis. Chem. Rev. 2023, 123 (9), 5225– 5261,  DOI: 10.1021/acs.chemrev.2c00759
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    12
    Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis
    Ham, Rens; Nielsen, C. Jasslie; Pullen, Sonja; Reek, Joost N. H.
    Chemical Reviews (Washington, DC, United States) (2023), 123 (9), 5225-5261CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Since sunlight is the most abundant energy source on earth it has huge potential for practical applications ranging from sustainable energy supply to light driven chem. From a chem. perspective, excited states generated by light make thermodynamically uphill reactions possible, which forms the basis for energy storage into fuels. In addn., with light, open shell species can be generated which open up new reaction pathways in org. synthesis. Crucial are photosensitizers, which absorb light and transfer energy to substrates by various mechanisms; processes that highly depend on the distance between the mols. involved. Supramol. coordination cages are well studied and synthetically accessible reaction vessels with single cavities for guest binding, which ensures close proximity of different components. Due to high modularity of their size, shape, and nature of metal centers and ligands, cages are ideal platforms to exploit preorganization in photocatalysis. Herein we focus on the application of supramol. cages for photocatalysis in artificial photosynthesis and in org. photo(redox) catalysis. Finally, a brief overview of immobilization strategies for supramol. cages provides tools for implementing cages into devices. This review provides inspiration for future design of photocatalytic supramol. host-guest systems, and their application in producing solar fuels and complex org. mols.
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  13. 13
    Pilgrim, B. S.; Champness, N. R. Metal-Organic Frameworks and Metal-Organic Cages─A Perspective. ChemPlusChem 2020, 85 (8), 1842– 1856,  DOI: 10.1002/cplu.202000408
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  14. 14
    Percástegui, E. G.; Ronson, T. K.; Nitschke, J. R. Design and Applications of Water-Soluble Coordination Cages. Chem. Rev. 2020, 120 (24), 13480– 13544,  DOI: 10.1021/acs.chemrev.0c00672
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    14
    Design and Applications of Water-Soluble Coordination Cages
    Percastegui, Edmundo G.; Ronson, Tanya K.; Nitschke, Jonathan R.
    Chemical Reviews (Washington, DC, United States) (2020), 120 (24), 13480-13544CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Compartmentalization of the aq. space within a cell is necessary for life. In similar fashion to the nanometer scale compartments in living systems, synthetic water-sol. coordination cages (WSCCs) can isolate guest mols. and host chem. transformations. Such cages thus show promise in biol., medical, environmental, and industrial domains. This review highlights examples of three-dimensional synthetic WSCCs, offering perspectives so as to enhance their design and applications. Strategies are presented that address key challenges for the prepn. of coordination cages that are sol. and stable in water. The peculiarities of guest binding in aq. media are examd., highlighting amplified binding in water, changing guest properties, and the recognition of specific mol. targets. The properties of WSCC hosts assocd. with biomedical applications, and their use as vessels to carry out chem. reactions in water, are also presented. These examples sketch a blueprint for the prepn. of new metal-org. containers for use in aq. soln., as well as guidelines for the engineering of new applications in water.
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  15. 15
    Zhang, D.; Ronson, T. K.; Nitschke, J. R. Functional Capsules via Subcomponent Self-Assembly. Acc. Chem. Res. 2018, 51 (10), 2423– 2436,  DOI: 10.1021/acs.accounts.8b00303
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    15
    Functional Capsules via Subcomponent Self-Assembly
    Zhang, Dawei; Ronson, Tanya K.; Nitschke, Jonathan R.
    Accounts of Chemical Research (2018), 51 (10), 2423-2436CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    Coordination-driven self-assembly can produce large, sym., hollow cages that are synthetically easy to access. The functions provided by these aesthetically attractive structures provide a driving force for their development, enabling practical applications. For instance, cages have provided new methods of mol. recognition, chirality sensing, sepns., stabilization of reactive species, and catalysis. We have fruitfully employed subcomponent self-assembly to prep. metal-org. capsules from simple building blocks via the simultaneous formation of dynamic coordinative (N→metal) and covalent (N=C) bonds. Design strategies employ multidentate pyridyl-imine ligands to define either the edges or the faces of polyhedral structures. Octahedral metal ions, such as FeII, CoII, NiII, ZnII and CdII constitute the vertices. The generality of this technique has enabled the prepn. of capsules with diverse three-dimensional structures. This Account will highlight how fundamental investigations into the host-guest chem. of capsules prepd. through subcomponent self-assembly have led to the design of useful functions and new applications. We start by discussing simple host-guest systems, involving a single capsule, and continue to systems that include multiple capsules and guests, whose interactions give rise to complex functional behavior. Many of the capsules presented herein bind varied neutral guests, including arom. or aliph. mols., biomols. and fullerenes. Binding selectivity is influenced by solvent effects, weak noncovalent interactions between hosts and guests, and the size, shape, flexibility and degree of surface enclosure of the inner spaces of the capsules. Some hosts were able to adaptively rearrange structurally, or express a different ratio of cage diastereomers to optimize the guest binding ability of the system. In other cases, the bound guest could be either protected from degrdn. or catalytically transformed through encapsulation. Other capsules bind anions, most often in org. solvents and occasionally in water. Complexation is usually driven by a combination of electrostatic interactions, hydrogen bonding and coordination to addnl. metal centers. Anion binding can also induce cage diastereomeric reconfiguration in a similar manner to some neutral guests, illustrating the general ability of subcomponent self-assembled capsules to respond to stimuli due to their dynamic nature. Capsules have been developed as supramol. extractants for the selective removal of anions from water, and as channels for transporting anions through planar lipid bilayers and into vesicles. Different capsules may work together, allowing for functions more complex than those achievable within single host-guest systems. Incorporation of stimuli-responsive capsules into multi-cage systems allows individual capsules within the network to be addressed and may allow signals to be passed between network members. We first present strategies to achieve selective guest binding and controlled guest release using mixts. of capsules with varied affinities for guests and different stabilities towards external stimuli. We then discuss strategies to sep. capsules with encapsulated cargos via selective phase transfer, where the solvent affinities of capsules change as a result of anion exchange or post-assembly modification. The knowledge gained from these multi-cage systems may lead to the design of synthetic systems able to perform complex tasks in biomimetic fashion, paving the way for new supramol. technologies to address practical problems.
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  16. 16
    Moree, L. K.; Faulkner, L. A. V.; Crowley, J. D. Heterometallic Cages: Synthesis and Applications. Chem. Soc. Rev. 2024, 53 (1), 25– 46,  DOI: 10.1039/D3CS00690E
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    Hardy, M.; Lützen, A. Frontispiece: Better Together: Functional Heterobimetallic Macrocyclic and Cage-like Assemblies. Chem.─Eur. J. 2020, 26 (59), 13332– 13346,  DOI: 10.1002/chem.202085962
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    There is no corresponding record for this reference.
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    Davies, J. A.; Ronson, T. K.; Nitschke, J. R. Triamine and Tetramine Edge-Length Matching Drives Heteroleptic Triangular and Tetragonal Prism Assembly. J. Am. Chem. Soc. 2024, 146 (8), 5215– 5223,  DOI: 10.1021/jacs.3c11320
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  19. 19
    Speakman, N. M. A.; Heard, A. W.; Nitschke, J. R. A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]Anes and Selectively Bind Fluorinated Steroids. J. Am. Chem. Soc. 2024, 146 (15), 10234– 10239,  DOI: 10.1021/jacs.4c00257
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  20. 20
    Benchimol, E.; Nguyen, B.-N. T.; Ronson, T. K.; Nitschke, J. R. Transformation Networks of Metal–Organic Cages Controlled by Chemical Stimuli. Chem. Soc. Rev. 2022, 51 (12), 5101– 5135,  DOI: 10.1039/D0CS00801J
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    20
    Transformation networks of metal-organic cages controlled by chemical stimuli
    Benchimol, Elie; Nguyen, Bao-Nguyen T.; Ronson, Tanya K.; Nitschke, Jonathan R.
    Chemical Society Reviews (2022), 51 (12), 5101-5135CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    The flexibility of biomols. enables them to adapt and transform as a result of signals received from the external environment, expressing different functions in different contexts. In similar fashion, coordination cages can undergo stimuli-triggered transformations owing to the dynamic nature of the metal-ligand bonds that hold them together. Different types of stimuli can trigger dynamic reconfiguration of these metal-org. assemblies, to switch on or off desired functionalities. Such adaptable systems are of interest for applications in switchable catalysis, selective mol. recognition or as transformable materials. This review highlights recent advances in the transformation of cages using chem. stimuli, providing a catalog of reported strategies to transform cages and thus allow the creation of new architectures. Firstly we focus on strategies for transformation through the introduction of new cage components, which trigger reconstitution of the initial set of components. Secondly we summarize conversions triggered by external stimuli such as guests, concn., solvent or pH, highlighting the adaptation processes that coordination cages can undergo. Finally, systems capable of responding to multiple stimuli are described. Such systems constitute composite chem. networks with the potential for more complex behavior. We aim to offer new perspectives on how to design transformation networks, in order to shed light on signal-driven transformation processes that lead to the prepn. of new functional metal-org. architectures.
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    Luo, D.; Zhu, X.; Zhou, X.; Li, D. Covalent Post-Synthetic Modification of Metal-Organic Cages: Concepts and Recent Progress. Chem.─Eur. J. 2024, 30 (24), e202400020  DOI: 10.1002/chem.202400020
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    Liu, J.; Wang, Z.; Cheng, P.; Zaworotko, M. J.; Chen, Y.; Zhang, Z. Post-Synthetic Modifications of Metal–Organic Cages. Nat. Rev. Chem 2022, 6 (5), 339– 356,  DOI: 10.1038/s41570-022-00380-y
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    Zhou, L.-P.; Feng, X.-S.; Hu, S.-J.; Sun, Q.-F. Controlled Self-Assembly, Isomerism, and Guest Uptake/Release of Charge-Reversible Lanthanide–Organic Octahedral Cages. J. Am. Chem. Soc. 2023, 145 (32), 17845– 17855,  DOI: 10.1021/jacs.3c04921
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    Sivalingam, V.; Parbin, M.; Krishnaswamy, S.; Chand, D. K. Cage-To-Cage Transformations in Self-Assembled Coordination Cages Using “Acid/Base” or “Guest Binding-Induced Strain” as Stimuli. Angew. Chem., Int. Ed. 2024, 63 (23), e202403711  DOI: 10.1002/anie.202403711
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    Belowich, M. E.; Stoddart, J. F. Dynamic Imine Chemistry. Chem. Soc. Rev. 2012, 41 (6), 2003– 2024,  DOI: 10.1039/c2cs15305j
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    Dynamic imine chemistry
    Belowich, Matthew E.; Stoddart, J. Fraser
    Chemical Society Reviews (2012), 41 (6), 2003-2024CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Formation of an imine-from an amine and an aldehyde-is a reversible reaction which operates under thermodn. control such that the formation of kinetically competitive intermediates are, in the fullness of time, replaced by the thermodynamically most stable product(s). For this fundamental reason, the imine bond has emerged as an extraordinarily diverse and useful 1 in the hands of synthetic chemists. Imine bond formation is 1 of a handful of reactions which define a discipline known as dynamic covalent chem. (DCC), which is now employed widely in the construction of exotic mols. and extended structures on account of the inherent proof-reading' and error-checking' assocd. with these reversible reactions. While both supramol. chem. and DCC operate under the regime of reversibility, DCC has the added advantage of constructing robust mols. on account of the formation of covalent bonds rather than fragile supermols. resulting from noncovalent bonding interactions. However, these products tend to require more time to form-sometimes days or even months-but their formation can often be catalyzed. In this manner, highly sym. mols. and extended structures can be prepd. from relatively simple precursors. When DCC is used in conjunction with template-directed protocols-which rely on the use of noncovalent bonding interactions between mol. building blocks to preorganise them into certain relative geometries as a prelude to the formation of covalent bonds under equil. control-an addnl. level of control of structure and topol. arises which offers a disarmingly simple way of constructing mech.-interlocked mols., such as rotaxanes, catenanes, Borromean rings, and Solomon knots. This tutorial review focuses on the use of dynamic imine bonds in the construction of compds. and products formed with and without the aid of addnl. templates. While synthesis under thermodn. control is giving the field of chem. topol. a new lease of life, it is also providing access to an endless array of new materials that are, in many circumstances, simply not accessible using more traditional synthetic methodologies where kinetic control rules the roost. One of the most endearing qualities of chem. is its ability to reinvent itself to create its own object, as Berthelot 1st pointed out a century and a half ago.
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  26. 26
    Liu, G.; Di Yuan, Y.; Wang, J.; Cheng, Y.; Peh, S. B.; Wang, Y.; Qian, Y.; Dong, J.; Yuan, D.; Zhao, D. Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal–Organic Cages. J. Am. Chem. Soc. 2018, 140 (20), 6231– 6234,  DOI: 10.1021/jacs.8b03517
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    26
    Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal-Organic Cages
    Liu, Guoliang; Di Yuan, Yi; Wang, Jian; Cheng, Youdong; Peh, Shing Bo; Wang, Yuxiang; Qian, Yuhong; Dong, Jinqiao; Yuan, Daqiang; Zhao, Dan
    Journal of the American Chemical Society (2018), 140 (20), 6231-6234CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Metal-org. cages (MOCs) are discrete mol. assemblies formed by coordination bonds between metal nodes and org. ligands. The application of MOCs has been greatly limited due to their poor stability, esp. in aq. solns. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aq. solns. with acidic, neutral, and weak basic conditions. In addn., we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NH2, highlighting the excellent stability and versatility of Zr-MOCs as a new type of mol. platform for various applications.
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    Zhang, Y.-W.; Bai, S.; Wang, Y.-Y.; Han, Y.-F. A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors. J. Am. Chem. Soc. 2020, 142 (31), 13614– 13621,  DOI: 10.1021/jacs.0c06470
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    27
    A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors
    Zhang, Ya-Wen; Bai, Sha; Wang, Yao-Yu; Han, Ying-Feng
    Journal of the American Chemical Society (2020), 142 (31), 13614-13621CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Three-dimensional (3D) triply interlocked catenanes are a family of chem. topologies that consist of two identical, mech. interlocked coordination cage components with intriguingly complex structures. Although only a few successful constructions of 3-dimensional interlocked catenanes were achieved to date via metal-mediated assembly, these complex structures have thus far only been targeted by metal-N/O coordination techniques. Here, taking advantage of rational ligand design, the authors report the efficient construction of 3-dimensional triply interlocked [2]catenanes [Ag3L2]2, wherein the metal ions exclusively form bonds to N-heterocyclic carbene (NHC) units, and their subsequent transmetalation to the corresponding [Au3L2]2 Au analogs. The formation and transmetalation reactions proceed under mild conditions and are generally applicable. Characterization techniques were applied to confirm the formation and structure of the desired 3-dimensional triply interlocked architectures: multinuclear NMR spectroscopy, ESI-MS, and single-crystal x-ray diffraction anal. The solid-state structure of [Ag3(1a)2]2(PF6)6 unambiguously confirms the existence of a 3-dimensional catenane that consists of two identical, mech. interlocked trinuclear hexacarbene cage components. The interlocking of two 3-dimensional cages into a [2]catenane is driven by the efficient π···π stacking of triazine-triazine stacks with cooperative interactions between imidazo[1,5-a]pyridine subunits. Notably, the triply interlocked organometallic cages exhibit good stability toward various org. solvents, concns., and temps., and no disassembly occurred in the presence of coronene or pyrene. The future construction of mech. interlocked architectures using metal-carbene bonds rather than metal-N bonds may provide assemblies with interesting properties for as-yet-unimagined applications in fields such as sensors and mol. elec. conductors.
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  28. 28
    El-Sayed, E.-S. M.; Yuan, Y. D.; Zhao, D.; Yuan, D. Zirconium Metal–Organic Cages: Synthesis and Applications. Acc. Chem. Res. 2022, 55 (11), 1546– 1560,  DOI: 10.1021/acs.accounts.1c00654
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    Sun, Y.; Chen, C.; Liu, J.; Stang, P. J. Recent Developments in the Construction and Applications of Platinum-Based Metallacycles and Metallacages via Coordination. Chem. Soc. Rev. 2020, 49 (12), 3889– 3919,  DOI: 10.1039/D0CS00038H
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    Recent developments in the construction and applications of platinum-based metallacycles and metallacages via coordination
    Sun, Yan; Chen, Chongyi; Liu, Jianbo; Stang, Peter J.
    Chemical Society Reviews (2020), 49 (12), 3889-3919CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    Coordination-driven suprastructures have attracted much interest due to their unique properties. Among these structures, platinum-based architectures have been broadly studied due to their facile prepn. The resultant two- or three-dimensional (2D or 3D) systems have many advantages over their precursors, such as improved emission tuning, sensitivity as sensors, and capture and release of guests, and they have been applied in biomedical diagnosis as well as in catalysis. Herein, we review the recent results related to platinum-based coordination-driven self-assembly (CDSA), and the text is organized to emphasizes both the synthesis of new metallacycles and metallacages and their various applications.
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    Zhang, B.; Lee, H.; Holstein, J. J.; Clever, G. H. Shape-Complementary Multicomponent Assembly of Low-Symmetry Co(III) Salphen-Based Coordination Cages. Angew. Chem., Int. Ed. 2024, 63 (24), e202404682  DOI: 10.1002/anie.202404682
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    Symmers, P. R.; Burke, M. J.; August, D. P.; Thomson, P. I. T.; Nichol, G. S.; Warren, M. R.; Campbell, C. J.; Lusby, P. J. Non-Equilibrium Cobalt(III) “Click” Capsules. Chem. Sci. 2015, 6 (1), 756– 760,  DOI: 10.1039/C4SC03036B
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    Non-equilibrium cobalt(III) "click" capsules
    Symmers, P. R.; Burke, M. J.; August, D. P.; Thomson, P. I. T.; Nichol, G. S.; Warren, M. R.; Campbell, C. J.; Lusby, P. J.
    Chemical Science (2015), 6 (1), 756-760CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Cobalt(III) tetrahedral capsules were prepd. using an assembly-followed-by-oxidn. protocol from a Co(II) precursor and a readily derivatizable pyridyl-triazole ligand system. Expts. designed to probe the constitutional dynamics show that these architectures are in a nonequil. state. A preliminary study into the host-guest chem. of a water-sol. deriv. shows it can bind and differentiate a range of different neutral org. mols. The stability of this ensemble also permits the study of guest-binding at high salt concns.
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    Su, P.; Zhang, W.; Guo, C.; Liu, H.; Xiong, C.; Tang, R.; He, C.; Chen, Z.; Yu, X.; Wang, H.; Li, X. Constructing Ultrastable Metallo-Cages via In Situ Deprotonation/Oxidation of Dynamic Supramolecular Assemblies. J. Am. Chem. Soc. 2023, 145 (33), 18607– 18622,  DOI: 10.1021/jacs.3c06211
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    Yamashita, K.; Sato, K.; Kawano, M.; Fujita, M. Photo-Induced Self-Assembly of Pt(II)-Linked Rings and Cages via the Photo- labilization of a Pt(II)−Py Bond. New J. Chem. 2009, 33 (2), 264,  DOI: 10.1039/b817713a
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    Bobylev, E. O.; Poole, D. A.; De Bruin, B.; Reek, J. N. H. How to Prepare Kinetically Stable Self-assembled Pt12L24 Nanocages While Circumventing Kinetic Traps. Chem.─Eur. J. 2021, 27 (49), 12667– 12674,  DOI: 10.1002/chem.202101931
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    van Hilst, Q. V. C.; Pearcy, A. C.; Preston, D.; Wright, L. J.; Hartinger, C. G.; Brooks, H. J. L.; Crowley, J. D. A Dynamic Covalent Approach to [PtnL2n]2n+ Cages. Chem. Commun. 2024, 60 (32), 4302– 4305,  DOI: 10.1039/D4CC00323C
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    Hamisu, A. M.; Ariffin, A.; Wibowo, A. C. Cation Exchange in Metal-Organic Frameworks (MOFs): The Hard-Soft Acid-Base (HSAB) Principle Appraisal. Inorg. Chim. Acta 2020, 511, 119801,  DOI: 10.1016/j.ica.2020.119801
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    Cation exchange in metal-organic frameworks (MOFs): The hard-soft acid-base (HSAB) principle appraisal
    Hamisu, Aliyu M.; Ariffin, Azhar; Wibowo, Arief C.
    Inorganica Chimica Acta (2020), 511 (), 119801CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
    A review. Cation exchange in Metal-Org. Frameworks (MOFs) is an emerging synthetic pathway for modifying chem. compns. and has been expansively investigated. It has been an important tool for leveraging novel functional MOFs that otherwise have not been achieved via the conventional technique. Yet, the governing phys. and chem. factors responsible for this occurrence are not clearly understood. The most encountered interpretations are related with the presence of open metal sites, coordinated solvent or lattice distortion tolerance. There is no unifying concept that gives a detailed insight on some common observations in cation exchanged MOFs, e.g. why some MOFs can undergo complete and reversible cation exchange, complete but irreversible, partial exchange, and in some cases, they do not exchange. Other puzzles include, why certain cation can exchange others while some cannot, why exchange can proceed in certain solvents but fails in others. Herein, we qual. demonstrate how the concept of Hard-Soft Acid-Base principle allows a plethora of reported exptl. observations dealing with cation exchange at the SBUs of MOFs could be reasonably explained. This review is intended to provide rationalization of cation exchange behaviors in both stable and labile MOFs, based on the hardness or softness of cations and ligands, effect of solvents, temp. and exchange period using the HSAB principle's point of view. Authors hope that this review may lead to a deeper understanding of the cation exchange behavior in MOFs, which in turns allow chemists to use it as a predictive tool for engineering novel functional MOFs with the required complexities.
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    Pullen, S.; Tessarolo, J.; Clever, G. H. Increasing Structural and Functional Complexity in Self-Assembled Coordination Cages. Chem. Sci. 2021, 12 (21), 7269– 7293,  DOI: 10.1039/D1SC01226F
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    Increasing structural and functional complexity in self-assembled coordination cages
    Pullen, Sonja; Tessarolo, Jacopo; Clever, Guido H.
    Chemical Science (2021), 12 (21), 7269-7293CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Progress in metallo-supramol. chem. creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centers or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction center. Combining several functionalities without creating statistical mixts., however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.
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    Wu, K.; Benchimol, E.; Baksi, A.; Clever, G. H. Non-Statistical Assembly of Multicomponent [Pd2ABCD] Cages. Nat. Chem. 2024, 16 (4), 584– 591,  DOI: 10.1038/s41557-023-01415-7
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    Kurz, H.; Schötz, K.; Papadopoulos, I.; Heinemann, F. W.; Maid, H.; Guldi, D. M.; Köhler, A.; Hörner, G.; Weber, B. A Fluorescence-Detected Coordination-Induced Spin State Switch. J. Am. Chem. Soc. 2021, 143 (9), 3466– 3480,  DOI: 10.1021/jacs.0c12568
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    Bandi, S.; Chand, D. K. Cage-to-Cage Cascade Transformations. Chem.─Eur. J. 2016, 22 (30), 10330– 10335,  DOI: 10.1002/chem.201602039
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    Samanta, D.; Mukherjee, P. S. Component Selection in the Self-Assembly of Palladium(II) Nanocages and Cage-to-Cage Transformations. Chem.─Eur. J. 2014, 20 (39), 12483– 12492,  DOI: 10.1002/chem.201402553
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    Preston, D.; Barnsley, J. E.; Gordon, K. C.; Crowley, J. D. Controlled Formation of Heteroleptic [Pd2(La)2(Lb)2]4+ Cages. J. Am. Chem. Soc. 2016, 138 (33), 10578– 10585,  DOI: 10.1021/jacs.6b05629
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    Controlled Formation of Heteroleptic [Pd2(La)2(Lb)2]4+ Cages
    Preston, Dan; Barnsley, Jonathan E.; Gordon, Keith C.; Crowley, James D.
    Journal of the American Chemical Society (2016), 138 (33), 10578-10585CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Metallosupramol. architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, mol. recognition, and sensing. For the most part these achievements have been made with high-symmetry metallosupramol. architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallosupramol. architectures that are made up of multiple different ligands and/or metals ions to obtain more complex systems with new properties. Herein the addn. of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis(pyridin-3-ylethynyl)pyridine (2A-tripy), to a soln. of the [Pd2(tripy)4]4+ cage resulted in the clean generation of a heteroleptic [Pd2(tripy)2(2A-tripy)2]4+ architecture. The formation of the mixed-ligand cage [Pd2(tripy)2(2A-tripy)2]4+ was confirmed using 1H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resoln. electrospray ionization mass spectrometry. D. functional theory calcns. suggested the cis isomer was more stable that the trans isomer. Addnl., the calcns. indicated that the heteroleptic palladium(II) cages are kinetically metastable intermediates rather than the thermodn. product of the reaction. Competition expts. supported that finding and showed the cages are long-lived in soln. at room temp. Finally, the addn. of 2A-tripy to a range of preformed [Pd2(Ltripy)4]4+ cages cleanly generated the mixed-ligand systems. Three other systems displaying different exo and endo functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized heteroleptic cis-[Pd2(La)2(Lb)2]4+ cages.
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    Zhang, D.; Ronson, T. K.; Xu, L.; Nitschke, J. R. Transformation Network Culminating in a Heteroleptic Cd6L6L′2 Twisted Trigonal Prism. J. Am. Chem. Soc. 2020, 142 (20), 9152– 9157,  DOI: 10.1021/jacs.0c03798
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    Transformation Network Culminating in a Heteroleptic Cd6L6L'2 Twisted Trigonal Prism
    Zhang, Dawei; Ronson, Tanya K.; Xu, Lin; Nitschke, Jonathan R.
    Journal of the American Chemical Society (2020), 142 (20), 9152-9157CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Transformations between three-dimensional metallosupramol. assemblies can enable switching between the different functions of these structures. Here authors report a network of such transformations, based upon a subcomponent displacement strategy. The flow through this network is directed by the relative reactivities of different amines, aldehydes, and di(2-pyridyl)ketone. The network provides access to an unprecedented heteroleptic Cd6L6L'2 twisted trigonal prism. The principles underpinning this network thus allow for the design of diverse structural transformations, converting one helicate into another, a helicate into a tetrahedron, a tetrahedron into a different tetrahedron, and a tetrahedron into the new trigonal prismatic structure type. The selective conversion from one host to another also enabled the uptake of a desired guest from a mixt. of guests.
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    McConnell, A. J.; Aitchison, C. M.; Grommet, A. B.; Nitschke, J. R. Subcomponent Exchange Transforms an FeII4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System. J. Am. Chem. Soc. 2017, 139 (18), 6294– 6297,  DOI: 10.1021/jacs.7b01478
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    Subcomponent Exchange Transforms an FeII4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System
    McConnell, Anna J.; Aitchison, Catherine M.; Grommet, Angela B.; Nitschke, Jonathan R.
    Journal of the American Chemical Society (2017), 139 (18), 6294-6297CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage's FeII centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addn. of p-anisidine to a mixt. of high-spin 1 and previously-reported low-spin FeII4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addn. of 2-formylpyridine to an identical mixt. of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addn. of 2-formylpyridine thus modulated the system's behavior, fundamentally altering its response to the subsequent signal p-anisidine.
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    Huang, Y.; Lu, Y.; Zhang, X.; Liu, C.; Ruan, J.; Qin, Y.; Cao, Z.; Jiang, J.; Xu, H.; Su, C. Dynamic Stereochemistry of M8Pd6 Supramolecular Cages Based on Metal-Center Lability for Differential Chiral Induction, Resolution, and Recognition. Angew. Chem. Int. Ed. 2024, 63 (2), e202315053  DOI: 10.1002/anie.202315053
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    Vardhan, H.; Mehta, A.; Nath, I.; Verpoort, F. Dynamic Imine Chemistry in Metal–Organic Polyhedra. RSC Adv. 2015, 5 (82), 67011– 67030,  DOI: 10.1039/C5RA10801B
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    Meng, W.; Ronson, T. K.; Clegg, J. K.; Nitschke, J. R. Transformations within a Network of Cadmium Architectures. Angew. Chem., Int. Ed. 2013, 52 (3), 1017– 1021,  DOI: 10.1002/anie.201206990
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    Davies, J. A.; Tarzia, A.; Ronson, T. K.; Auras, F.; Jelfs, K. E.; Nitschke, J. R. Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn8L6 Self-Assembled Structures. Angew. Chem., Int. Ed. 2023, 62 (10), e202217987  DOI: 10.1002/anie.202217987
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    Percástegui, E. G.; Mosquera, J.; Nitschke, J. R. Anion Exchange Renders Hydrophobic Capsules and Cargoes Water-Soluble. Angew. Chem., Int. Ed. 2017, 56 (31), 9136– 9140,  DOI: 10.1002/anie.201705093
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    Anion Exchange Renders Hydrophobic Capsules and Cargoes Water-Soluble
    Percastegui, Edmundo G.; Mosquera, Jesus; Nitschke, Jonathan R.
    Angewandte Chemie, International Edition (2017), 56 (31), 9136-9140CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Control over the soly. properties of container mols. is a central challenge in host-guest chem. Herein we present a simple anion-exchange protocol that allows the dissoln. in water of various hydrophobic metal-org. container mols. prepd. by iron(II)-templated subcomponent self-assembly. Our process involved the exchange of less hydrophilic trifluoromethanesulfonate anions for hydrophilic sulfate; the resulting water-sol. cages could be rendered water-insol. through reverse anion exchange. Notably, this strategy allowed cargoes within capsules, including polycyclic arom. compds. and complex org. drugs, to be brought into water. Hydrophobic effects appeared to enhance binding, as many of these cargoes were not bound in non-aq. media. Studies of the scope of this method revealed that cages contg. tetratopic and tritopic ligands were more stable in water, whereas cages with ditopic ligands disassembled.
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    He, D.; Ji, H.; Liu, T.; Yang, M.; Clowes, R.; Little, M. A.; Liu, M.; Cooper, A. I. Self-Assembly of Chiral Porous Metal–Organic Polyhedra from Trianglsalen Macrocycles. J. Am. Chem. Soc. 2024, 146 (25), 17438– 17445,  DOI: 10.1021/jacs.4c04928
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    Dworzak, M. R.; Deegan, M. M.; Yap, G. P. A.; Bloch, E. D. Synthesis and Characterization of an Isoreticular Family of Calixarene-Capped Porous Coordination Cages. Inorg. Chem. 2021, 60 (8), 5607– 5616,  DOI: 10.1021/acs.inorgchem.0c03554
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    Zenka, M.; Preinl, J.; Pertermann, E.; Lützen, A.; Tiefenbacher, K. A Water- and Base-Stable Iminopyridine-Based Cage That Can Bind Larger Organic Anions. Eur. J. Inorg. Chem. 2023, 26 (15), e202300110  DOI: 10.1002/ejic.202300110
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  • Abstract

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    Figure 1

    Figure 1. Subcomponent self-assembly of A, p-toluidine, and Zn(NTf2)2, to form O-symmetric Zn8L12 cube 1. Protons are assigned according to 1D and 2D NMR spectra (Figures S11–S16). Only the Λ8 enantiomer is shown. Hydrogen atoms and counteranions are omitted for clarity.

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    Figure 2

    Figure 2. Self-assembly of double-bridged zinc(II) cages based on subcomponent A. (Top) Self-assembly of subcomponents A, 2,7-diaminofluorene, and Zn(NTf2)2, forming achiral double-bridged Zn8L′6 cage 2 (illustrated as a schematic model and the crystal structure of Th-symmetric 2•(PF6)16). Cage 2 was also formed through reaction of 1 with 2,7-diaminofluorene. (Bottom) Self-assembly of subcomponents A and 2,7-diaminofluorenone with Zn(NTf2)2, forming achiral double-bridged Zn8L″6 3 (illustrated as a schematic model and a model based on GFN2-xTB calculations). Proton assignments are derived from NMR spectra (Figures S27−S33, S44−S48). Hydrogen atoms and counteranions are omitted for clarity.

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    Figure 3

    Figure 3. Self-assembly of double-bridged zinc(II) cages based on subcomponent B. (Top) No cage formation was observed upon reaction of the subcomponents B and p-toluidine with Zn(NTf2)2 under similar conditions. (Bottom) The self-assembly of subcomponents B and 4,4″-diamino-p-terphenyl with Zn(NTf2)2, forming Th-symmetric double-bridged Zn8L‴6 cage 4, illustrated as a schematic model and view of the crystal structure of the (tetrakis(4-fluorophenyl)borate) salt. Proton assignments are derived from NMR spectra (Figures S58–S62 in the Supporting Information). Hydrogen atoms and counteranions are omitted for clarity.

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    Figure 4

    Figure 4. Comparison of the stabilities of cages 1 and 2. 1 converted into 2 upon addition of 2,7-diaminofluorene (12 equiv), whereas conversion of 2 to 1 was not observed even upon addition of 200 equiv p-toluidine. After conversion from 1 to 2, the sample was washed with Et2O to remove free p-toluidine and minor impurities. The spectrum before washing is given in Figure S74 in the Supporting Information.

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      7
      White Phosphorus Is Air-Stable Within a Self-Assembled Tetrahedral Capsule
      Mal, Prasenjit; Breiner, Boris; Rissanen, Kari; Nitschke, Jonathan R.
      Science (Washington, DC, United States) (2009), 324 (5935), 1697-1699CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      The air-sensitive nature of white phosphorus underlies its destructive effect as a munition; tetrahedral P4 mols. readily react with atm. dioxygen, leading this form of the element to spontaneously combust upon exposure to air. Here, hydrophobic P4 mols. are rendered air-stable and water-sol. within the hydrophobic hollows of self-assembled tetrahedral container mols., [Fe4L6]4- (L = 4,4'-bis(2-pyridylmethyleneamino)-1,1'-biphenyl-2,2'-disulfonate), which form in water from simple org. subcomponents and iron(II) ions. The host-guest complex with P4 was characterized by x-ray crystallog. This stabilization is not achieved through hermetic exclusion of O2 but rather by constriction of individual P4 mols.; the addn. of oxygen atoms to P4 would gave oxidized species too large for their containers. The phosphorus can be released in controlled fashion without disrupting the cage by adding the competing guest benzene.
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    8. 8
      Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Functional Molecular Flasks: New Properties and Reactions within Discrete, Self-Assembled Hosts. Angew. Chem., Int. Ed. 2009, 48 (19), 3418– 3438,  DOI: 10.1002/anie.200805340
      8
      Functional Molecular Flasks: New Properties and Reactions within Discrete, Self-Assembled Hosts
      Yoshizawa, Michito; Klosterman, Jeremy K.; Fujita, Makoto
      Angewandte Chemie, International Edition (2009), 48 (19), 3418-3438CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Self-assembled hosts applied as "mol. flasks" can alter and control the reactivity and properties of mols. encapsulated within their well-defined, confined spaces. A variety of functional hosts of differing sizes, shapes, and utility have been prepd. by using the facile and modular concepts of self-assembly. The application of self-assembled hosts as "mol. flasks" has pptd. a surge of interest in the reactivity and properties of mols. within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepd. This Review briefly highlights the various mol. flasks synthesized before focusing on their use as functional mol. containers-specifically for the encapsulation of guest mols. to either engender unusual reactions or unique chem. phenomena. Such self-assembled cavities now constitute a new phase of chem., which cannot be achieved in the conventional solid, liq., and gas phases.
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    9. 9
      Hong, C. M.; Morimoto, M.; Kapustin, E. A.; Alzakhem, N.; Bergman, R. G.; Raymond, K. N.; Toste, F. D. Deconvoluting the Role of Charge in a Supramolecular Catalyst. J. Am. Chem. Soc. 2018, 140 (21), 6591– 6595,  DOI: 10.1021/jacs.8b01701
      9
      Deconvoluting the Role of Charge in a Supramolecular Catalyst
      Hong, Cynthia M.; Morimoto, Mariko; Kapustin, Eugene A.; Alzakhem, Nicola; Bergman, Robert G.; Raymond, Kenneth N.; Toste, F. Dean
      Journal of the American Chemical Society (2018), 140 (21), 6591-6595CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We have demonstrated that the microenvironment of a highly anionic supramol. catalyst can mimic the active sites of enzymes and impart rate accelerations of a million-fold or more. However, these microenvironments can be challenging to study, esp. in the context of understanding which specific features of the catalyst are responsible for its high performance. We report here the development of an exptl. mechanistic probe consisting of two isostructural catalysts. When examd. in parallel transformations, the behavior of these catalysts provides insight relevant to the importance of anionic host charge on reactivity. These two catalysts exhibit similar host-substrate interactions, but feature a significant difference in overall anionic charge (12- and 8-). Within these systems, we compare the effect of constrictive binding in a net neutral aza-Cope rearrangement. We then demonstrate how the magnitude of anionic host charge has an exceptional influence on the reaction rates for a Nazarov cyclization, evidenced by an impressive 680-fold change in reaction rate as a consequence of a 33% redn. in catalyst charge.
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    10. 10
      Jiao, J.; Tan, C.; Li, Z.; Liu, Y.; Han, X.; Cui, Y. Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions. J. Am. Chem. Soc. 2018, 140 (6), 2251– 2259,  DOI: 10.1021/jacs.7b11679
      10
      Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions
      Jiao, Jingjing; Tan, Chunxia; Li, Zijian; Liu, Yan; Han, Xing; Cui, Yong
      Journal of the American Chemical Society (2018), 140 (6), 2251-2259CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Supramol. nanoreactors featuring multiple catalytically active sites are of great importance, esp. for asym. catalysis, and are yet challenging to construct. Here we report the design and assembly of five chiral single- and mixed-linker tetrahedral coordination cages using six dicarboxylate ligands derived-from enantiopure Mn(salen), Cr(salen) and/or Fe(salen) as linear linkers and four Cp3Zr3 clusters as three-connected vertices. The formation of these cages was confirmed by a variety of techniques including single-crystal and powder X-ray diffraction, inductively coupled plasma optical emission spectrometer, quadrupole-time-of-flight mass spectrometry and energy dispersive X-ray spectrometry. The cages feature a nanoscale hydrophobic cavity decorated with the same or different catalytically active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen) species is shown to be an efficient supramol. catalyst for sequential asym. alkene epoxidn./epoxide ring-opening reactions with up to 99.9% ee. The cage catalyst demonstrates improved activity and enantioselectivity over the free catalysts owing to stabilization of catalytically active metallosalen units and concn. of reactants within the cavity. Manipulation of catalytic org. linkers in cages can control the activities and selectivities, which may provide new opportunities for the design and assembly of novel functional supramol. architectures.
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    11. 11
      Wang, J.-S.; Wu, K.; Yin, C.; Li, K.; Huang, Y.; Ruan, J.; Feng, X.; Hu, P.; Su, C.-Y. Cage-Confined Photocatalysis for Wide-Scope Unusually Selective [2 + 2] Cycloaddition through Visible-Light Triplet Sensitization. Nat. Commun. 2020, 11 (1), 4675,  DOI: 10.1038/s41467-020-18487-5
      There is no corresponding record for this reference.
    12. 12
      Ham, R.; Nielsen, C. J.; Pullen, S.; Reek, J. N. H. Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis. Chem. Rev. 2023, 123 (9), 5225– 5261,  DOI: 10.1021/acs.chemrev.2c00759
      12
      Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis
      Ham, Rens; Nielsen, C. Jasslie; Pullen, Sonja; Reek, Joost N. H.
      Chemical Reviews (Washington, DC, United States) (2023), 123 (9), 5225-5261CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Since sunlight is the most abundant energy source on earth it has huge potential for practical applications ranging from sustainable energy supply to light driven chem. From a chem. perspective, excited states generated by light make thermodynamically uphill reactions possible, which forms the basis for energy storage into fuels. In addn., with light, open shell species can be generated which open up new reaction pathways in org. synthesis. Crucial are photosensitizers, which absorb light and transfer energy to substrates by various mechanisms; processes that highly depend on the distance between the mols. involved. Supramol. coordination cages are well studied and synthetically accessible reaction vessels with single cavities for guest binding, which ensures close proximity of different components. Due to high modularity of their size, shape, and nature of metal centers and ligands, cages are ideal platforms to exploit preorganization in photocatalysis. Herein we focus on the application of supramol. cages for photocatalysis in artificial photosynthesis and in org. photo(redox) catalysis. Finally, a brief overview of immobilization strategies for supramol. cages provides tools for implementing cages into devices. This review provides inspiration for future design of photocatalytic supramol. host-guest systems, and their application in producing solar fuels and complex org. mols.
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    13. 13
      Pilgrim, B. S.; Champness, N. R. Metal-Organic Frameworks and Metal-Organic Cages─A Perspective. ChemPlusChem 2020, 85 (8), 1842– 1856,  DOI: 10.1002/cplu.202000408
      There is no corresponding record for this reference.
    14. 14
      Percástegui, E. G.; Ronson, T. K.; Nitschke, J. R. Design and Applications of Water-Soluble Coordination Cages. Chem. Rev. 2020, 120 (24), 13480– 13544,  DOI: 10.1021/acs.chemrev.0c00672
      14
      Design and Applications of Water-Soluble Coordination Cages
      Percastegui, Edmundo G.; Ronson, Tanya K.; Nitschke, Jonathan R.
      Chemical Reviews (Washington, DC, United States) (2020), 120 (24), 13480-13544CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Compartmentalization of the aq. space within a cell is necessary for life. In similar fashion to the nanometer scale compartments in living systems, synthetic water-sol. coordination cages (WSCCs) can isolate guest mols. and host chem. transformations. Such cages thus show promise in biol., medical, environmental, and industrial domains. This review highlights examples of three-dimensional synthetic WSCCs, offering perspectives so as to enhance their design and applications. Strategies are presented that address key challenges for the prepn. of coordination cages that are sol. and stable in water. The peculiarities of guest binding in aq. media are examd., highlighting amplified binding in water, changing guest properties, and the recognition of specific mol. targets. The properties of WSCC hosts assocd. with biomedical applications, and their use as vessels to carry out chem. reactions in water, are also presented. These examples sketch a blueprint for the prepn. of new metal-org. containers for use in aq. soln., as well as guidelines for the engineering of new applications in water.
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    15. 15
      Zhang, D.; Ronson, T. K.; Nitschke, J. R. Functional Capsules via Subcomponent Self-Assembly. Acc. Chem. Res. 2018, 51 (10), 2423– 2436,  DOI: 10.1021/acs.accounts.8b00303
      15
      Functional Capsules via Subcomponent Self-Assembly
      Zhang, Dawei; Ronson, Tanya K.; Nitschke, Jonathan R.
      Accounts of Chemical Research (2018), 51 (10), 2423-2436CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      Coordination-driven self-assembly can produce large, sym., hollow cages that are synthetically easy to access. The functions provided by these aesthetically attractive structures provide a driving force for their development, enabling practical applications. For instance, cages have provided new methods of mol. recognition, chirality sensing, sepns., stabilization of reactive species, and catalysis. We have fruitfully employed subcomponent self-assembly to prep. metal-org. capsules from simple building blocks via the simultaneous formation of dynamic coordinative (N→metal) and covalent (N=C) bonds. Design strategies employ multidentate pyridyl-imine ligands to define either the edges or the faces of polyhedral structures. Octahedral metal ions, such as FeII, CoII, NiII, ZnII and CdII constitute the vertices. The generality of this technique has enabled the prepn. of capsules with diverse three-dimensional structures. This Account will highlight how fundamental investigations into the host-guest chem. of capsules prepd. through subcomponent self-assembly have led to the design of useful functions and new applications. We start by discussing simple host-guest systems, involving a single capsule, and continue to systems that include multiple capsules and guests, whose interactions give rise to complex functional behavior. Many of the capsules presented herein bind varied neutral guests, including arom. or aliph. mols., biomols. and fullerenes. Binding selectivity is influenced by solvent effects, weak noncovalent interactions between hosts and guests, and the size, shape, flexibility and degree of surface enclosure of the inner spaces of the capsules. Some hosts were able to adaptively rearrange structurally, or express a different ratio of cage diastereomers to optimize the guest binding ability of the system. In other cases, the bound guest could be either protected from degrdn. or catalytically transformed through encapsulation. Other capsules bind anions, most often in org. solvents and occasionally in water. Complexation is usually driven by a combination of electrostatic interactions, hydrogen bonding and coordination to addnl. metal centers. Anion binding can also induce cage diastereomeric reconfiguration in a similar manner to some neutral guests, illustrating the general ability of subcomponent self-assembled capsules to respond to stimuli due to their dynamic nature. Capsules have been developed as supramol. extractants for the selective removal of anions from water, and as channels for transporting anions through planar lipid bilayers and into vesicles. Different capsules may work together, allowing for functions more complex than those achievable within single host-guest systems. Incorporation of stimuli-responsive capsules into multi-cage systems allows individual capsules within the network to be addressed and may allow signals to be passed between network members. We first present strategies to achieve selective guest binding and controlled guest release using mixts. of capsules with varied affinities for guests and different stabilities towards external stimuli. We then discuss strategies to sep. capsules with encapsulated cargos via selective phase transfer, where the solvent affinities of capsules change as a result of anion exchange or post-assembly modification. The knowledge gained from these multi-cage systems may lead to the design of synthetic systems able to perform complex tasks in biomimetic fashion, paving the way for new supramol. technologies to address practical problems.
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    16. 16
      Moree, L. K.; Faulkner, L. A. V.; Crowley, J. D. Heterometallic Cages: Synthesis and Applications. Chem. Soc. Rev. 2024, 53 (1), 25– 46,  DOI: 10.1039/D3CS00690E
      There is no corresponding record for this reference.
    17. 17
      Hardy, M.; Lützen, A. Frontispiece: Better Together: Functional Heterobimetallic Macrocyclic and Cage-like Assemblies. Chem.─Eur. J. 2020, 26 (59), 13332– 13346,  DOI: 10.1002/chem.202085962
      There is no corresponding record for this reference.
    18. 18
      Davies, J. A.; Ronson, T. K.; Nitschke, J. R. Triamine and Tetramine Edge-Length Matching Drives Heteroleptic Triangular and Tetragonal Prism Assembly. J. Am. Chem. Soc. 2024, 146 (8), 5215– 5223,  DOI: 10.1021/jacs.3c11320
      There is no corresponding record for this reference.
    19. 19
      Speakman, N. M. A.; Heard, A. W.; Nitschke, J. R. A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]Anes and Selectively Bind Fluorinated Steroids. J. Am. Chem. Soc. 2024, 146 (15), 10234– 10239,  DOI: 10.1021/jacs.4c00257
      There is no corresponding record for this reference.
    20. 20
      Benchimol, E.; Nguyen, B.-N. T.; Ronson, T. K.; Nitschke, J. R. Transformation Networks of Metal–Organic Cages Controlled by Chemical Stimuli. Chem. Soc. Rev. 2022, 51 (12), 5101– 5135,  DOI: 10.1039/D0CS00801J
      20
      Transformation networks of metal-organic cages controlled by chemical stimuli
      Benchimol, Elie; Nguyen, Bao-Nguyen T.; Ronson, Tanya K.; Nitschke, Jonathan R.
      Chemical Society Reviews (2022), 51 (12), 5101-5135CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      The flexibility of biomols. enables them to adapt and transform as a result of signals received from the external environment, expressing different functions in different contexts. In similar fashion, coordination cages can undergo stimuli-triggered transformations owing to the dynamic nature of the metal-ligand bonds that hold them together. Different types of stimuli can trigger dynamic reconfiguration of these metal-org. assemblies, to switch on or off desired functionalities. Such adaptable systems are of interest for applications in switchable catalysis, selective mol. recognition or as transformable materials. This review highlights recent advances in the transformation of cages using chem. stimuli, providing a catalog of reported strategies to transform cages and thus allow the creation of new architectures. Firstly we focus on strategies for transformation through the introduction of new cage components, which trigger reconstitution of the initial set of components. Secondly we summarize conversions triggered by external stimuli such as guests, concn., solvent or pH, highlighting the adaptation processes that coordination cages can undergo. Finally, systems capable of responding to multiple stimuli are described. Such systems constitute composite chem. networks with the potential for more complex behavior. We aim to offer new perspectives on how to design transformation networks, in order to shed light on signal-driven transformation processes that lead to the prepn. of new functional metal-org. architectures.
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    21. 21
      Luo, D.; Zhu, X.; Zhou, X.; Li, D. Covalent Post-Synthetic Modification of Metal-Organic Cages: Concepts and Recent Progress. Chem.─Eur. J. 2024, 30 (24), e202400020  DOI: 10.1002/chem.202400020
      There is no corresponding record for this reference.
    22. 22
      Liu, J.; Wang, Z.; Cheng, P.; Zaworotko, M. J.; Chen, Y.; Zhang, Z. Post-Synthetic Modifications of Metal–Organic Cages. Nat. Rev. Chem 2022, 6 (5), 339– 356,  DOI: 10.1038/s41570-022-00380-y
      There is no corresponding record for this reference.
    23. 23
      Zhou, L.-P.; Feng, X.-S.; Hu, S.-J.; Sun, Q.-F. Controlled Self-Assembly, Isomerism, and Guest Uptake/Release of Charge-Reversible Lanthanide–Organic Octahedral Cages. J. Am. Chem. Soc. 2023, 145 (32), 17845– 17855,  DOI: 10.1021/jacs.3c04921
      There is no corresponding record for this reference.
    24. 24
      Sivalingam, V.; Parbin, M.; Krishnaswamy, S.; Chand, D. K. Cage-To-Cage Transformations in Self-Assembled Coordination Cages Using “Acid/Base” or “Guest Binding-Induced Strain” as Stimuli. Angew. Chem., Int. Ed. 2024, 63 (23), e202403711  DOI: 10.1002/anie.202403711
      There is no corresponding record for this reference.
    25. 25
      Belowich, M. E.; Stoddart, J. F. Dynamic Imine Chemistry. Chem. Soc. Rev. 2012, 41 (6), 2003– 2024,  DOI: 10.1039/c2cs15305j
      25
      Dynamic imine chemistry
      Belowich, Matthew E.; Stoddart, J. Fraser
      Chemical Society Reviews (2012), 41 (6), 2003-2024CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Formation of an imine-from an amine and an aldehyde-is a reversible reaction which operates under thermodn. control such that the formation of kinetically competitive intermediates are, in the fullness of time, replaced by the thermodynamically most stable product(s). For this fundamental reason, the imine bond has emerged as an extraordinarily diverse and useful 1 in the hands of synthetic chemists. Imine bond formation is 1 of a handful of reactions which define a discipline known as dynamic covalent chem. (DCC), which is now employed widely in the construction of exotic mols. and extended structures on account of the inherent proof-reading' and error-checking' assocd. with these reversible reactions. While both supramol. chem. and DCC operate under the regime of reversibility, DCC has the added advantage of constructing robust mols. on account of the formation of covalent bonds rather than fragile supermols. resulting from noncovalent bonding interactions. However, these products tend to require more time to form-sometimes days or even months-but their formation can often be catalyzed. In this manner, highly sym. mols. and extended structures can be prepd. from relatively simple precursors. When DCC is used in conjunction with template-directed protocols-which rely on the use of noncovalent bonding interactions between mol. building blocks to preorganise them into certain relative geometries as a prelude to the formation of covalent bonds under equil. control-an addnl. level of control of structure and topol. arises which offers a disarmingly simple way of constructing mech.-interlocked mols., such as rotaxanes, catenanes, Borromean rings, and Solomon knots. This tutorial review focuses on the use of dynamic imine bonds in the construction of compds. and products formed with and without the aid of addnl. templates. While synthesis under thermodn. control is giving the field of chem. topol. a new lease of life, it is also providing access to an endless array of new materials that are, in many circumstances, simply not accessible using more traditional synthetic methodologies where kinetic control rules the roost. One of the most endearing qualities of chem. is its ability to reinvent itself to create its own object, as Berthelot 1st pointed out a century and a half ago.
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    26. 26
      Liu, G.; Di Yuan, Y.; Wang, J.; Cheng, Y.; Peh, S. B.; Wang, Y.; Qian, Y.; Dong, J.; Yuan, D.; Zhao, D. Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal–Organic Cages. J. Am. Chem. Soc. 2018, 140 (20), 6231– 6234,  DOI: 10.1021/jacs.8b03517
      26
      Process-Tracing Study on the Postassembly Modification of Highly Stable Zirconium Metal-Organic Cages
      Liu, Guoliang; Di Yuan, Yi; Wang, Jian; Cheng, Youdong; Peh, Shing Bo; Wang, Yuxiang; Qian, Yuhong; Dong, Jinqiao; Yuan, Daqiang; Zhao, Dan
      Journal of the American Chemical Society (2018), 140 (20), 6231-6234CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Metal-org. cages (MOCs) are discrete mol. assemblies formed by coordination bonds between metal nodes and org. ligands. The application of MOCs has been greatly limited due to their poor stability, esp. in aq. solns. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aq. solns. with acidic, neutral, and weak basic conditions. In addn., we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NH2, highlighting the excellent stability and versatility of Zr-MOCs as a new type of mol. platform for various applications.
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    27. 27
      Zhang, Y.-W.; Bai, S.; Wang, Y.-Y.; Han, Y.-F. A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors. J. Am. Chem. Soc. 2020, 142 (31), 13614– 13621,  DOI: 10.1021/jacs.0c06470
      27
      A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors
      Zhang, Ya-Wen; Bai, Sha; Wang, Yao-Yu; Han, Ying-Feng
      Journal of the American Chemical Society (2020), 142 (31), 13614-13621CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Three-dimensional (3D) triply interlocked catenanes are a family of chem. topologies that consist of two identical, mech. interlocked coordination cage components with intriguingly complex structures. Although only a few successful constructions of 3-dimensional interlocked catenanes were achieved to date via metal-mediated assembly, these complex structures have thus far only been targeted by metal-N/O coordination techniques. Here, taking advantage of rational ligand design, the authors report the efficient construction of 3-dimensional triply interlocked [2]catenanes [Ag3L2]2, wherein the metal ions exclusively form bonds to N-heterocyclic carbene (NHC) units, and their subsequent transmetalation to the corresponding [Au3L2]2 Au analogs. The formation and transmetalation reactions proceed under mild conditions and are generally applicable. Characterization techniques were applied to confirm the formation and structure of the desired 3-dimensional triply interlocked architectures: multinuclear NMR spectroscopy, ESI-MS, and single-crystal x-ray diffraction anal. The solid-state structure of [Ag3(1a)2]2(PF6)6 unambiguously confirms the existence of a 3-dimensional catenane that consists of two identical, mech. interlocked trinuclear hexacarbene cage components. The interlocking of two 3-dimensional cages into a [2]catenane is driven by the efficient π···π stacking of triazine-triazine stacks with cooperative interactions between imidazo[1,5-a]pyridine subunits. Notably, the triply interlocked organometallic cages exhibit good stability toward various org. solvents, concns., and temps., and no disassembly occurred in the presence of coronene or pyrene. The future construction of mech. interlocked architectures using metal-carbene bonds rather than metal-N bonds may provide assemblies with interesting properties for as-yet-unimagined applications in fields such as sensors and mol. elec. conductors.
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    28. 28
      El-Sayed, E.-S. M.; Yuan, Y. D.; Zhao, D.; Yuan, D. Zirconium Metal–Organic Cages: Synthesis and Applications. Acc. Chem. Res. 2022, 55 (11), 1546– 1560,  DOI: 10.1021/acs.accounts.1c00654
      There is no corresponding record for this reference.
    29. 29
      Sun, Y.; Chen, C.; Liu, J.; Stang, P. J. Recent Developments in the Construction and Applications of Platinum-Based Metallacycles and Metallacages via Coordination. Chem. Soc. Rev. 2020, 49 (12), 3889– 3919,  DOI: 10.1039/D0CS00038H
      29
      Recent developments in the construction and applications of platinum-based metallacycles and metallacages via coordination
      Sun, Yan; Chen, Chongyi; Liu, Jianbo; Stang, Peter J.
      Chemical Society Reviews (2020), 49 (12), 3889-3919CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Coordination-driven suprastructures have attracted much interest due to their unique properties. Among these structures, platinum-based architectures have been broadly studied due to their facile prepn. The resultant two- or three-dimensional (2D or 3D) systems have many advantages over their precursors, such as improved emission tuning, sensitivity as sensors, and capture and release of guests, and they have been applied in biomedical diagnosis as well as in catalysis. Herein, we review the recent results related to platinum-based coordination-driven self-assembly (CDSA), and the text is organized to emphasizes both the synthesis of new metallacycles and metallacages and their various applications.
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    30. 30
      Zhang, B.; Lee, H.; Holstein, J. J.; Clever, G. H. Shape-Complementary Multicomponent Assembly of Low-Symmetry Co(III) Salphen-Based Coordination Cages. Angew. Chem., Int. Ed. 2024, 63 (24), e202404682  DOI: 10.1002/anie.202404682
      There is no corresponding record for this reference.
    31. 31
      Symmers, P. R.; Burke, M. J.; August, D. P.; Thomson, P. I. T.; Nichol, G. S.; Warren, M. R.; Campbell, C. J.; Lusby, P. J. Non-Equilibrium Cobalt(III) “Click” Capsules. Chem. Sci. 2015, 6 (1), 756– 760,  DOI: 10.1039/C4SC03036B
      31
      Non-equilibrium cobalt(III) "click" capsules
      Symmers, P. R.; Burke, M. J.; August, D. P.; Thomson, P. I. T.; Nichol, G. S.; Warren, M. R.; Campbell, C. J.; Lusby, P. J.
      Chemical Science (2015), 6 (1), 756-760CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Cobalt(III) tetrahedral capsules were prepd. using an assembly-followed-by-oxidn. protocol from a Co(II) precursor and a readily derivatizable pyridyl-triazole ligand system. Expts. designed to probe the constitutional dynamics show that these architectures are in a nonequil. state. A preliminary study into the host-guest chem. of a water-sol. deriv. shows it can bind and differentiate a range of different neutral org. mols. The stability of this ensemble also permits the study of guest-binding at high salt concns.
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    32. 32
      Su, P.; Zhang, W.; Guo, C.; Liu, H.; Xiong, C.; Tang, R.; He, C.; Chen, Z.; Yu, X.; Wang, H.; Li, X. Constructing Ultrastable Metallo-Cages via In Situ Deprotonation/Oxidation of Dynamic Supramolecular Assemblies. J. Am. Chem. Soc. 2023, 145 (33), 18607– 18622,  DOI: 10.1021/jacs.3c06211
      There is no corresponding record for this reference.
    33. 33
      Yamashita, K.; Sato, K.; Kawano, M.; Fujita, M. Photo-Induced Self-Assembly of Pt(II)-Linked Rings and Cages via the Photo- labilization of a Pt(II)−Py Bond. New J. Chem. 2009, 33 (2), 264,  DOI: 10.1039/b817713a
      There is no corresponding record for this reference.
    34. 34
      Bobylev, E. O.; Poole, D. A.; De Bruin, B.; Reek, J. N. H. How to Prepare Kinetically Stable Self-assembled Pt12L24 Nanocages While Circumventing Kinetic Traps. Chem.─Eur. J. 2021, 27 (49), 12667– 12674,  DOI: 10.1002/chem.202101931
      There is no corresponding record for this reference.
    35. 35
      van Hilst, Q. V. C.; Pearcy, A. C.; Preston, D.; Wright, L. J.; Hartinger, C. G.; Brooks, H. J. L.; Crowley, J. D. A Dynamic Covalent Approach to [PtnL2n]2n+ Cages. Chem. Commun. 2024, 60 (32), 4302– 4305,  DOI: 10.1039/D4CC00323C
      There is no corresponding record for this reference.
    36. 36
      Hamisu, A. M.; Ariffin, A.; Wibowo, A. C. Cation Exchange in Metal-Organic Frameworks (MOFs): The Hard-Soft Acid-Base (HSAB) Principle Appraisal. Inorg. Chim. Acta 2020, 511, 119801,  DOI: 10.1016/j.ica.2020.119801
      36
      Cation exchange in metal-organic frameworks (MOFs): The hard-soft acid-base (HSAB) principle appraisal
      Hamisu, Aliyu M.; Ariffin, Azhar; Wibowo, Arief C.
      Inorganica Chimica Acta (2020), 511 (), 119801CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
      A review. Cation exchange in Metal-Org. Frameworks (MOFs) is an emerging synthetic pathway for modifying chem. compns. and has been expansively investigated. It has been an important tool for leveraging novel functional MOFs that otherwise have not been achieved via the conventional technique. Yet, the governing phys. and chem. factors responsible for this occurrence are not clearly understood. The most encountered interpretations are related with the presence of open metal sites, coordinated solvent or lattice distortion tolerance. There is no unifying concept that gives a detailed insight on some common observations in cation exchanged MOFs, e.g. why some MOFs can undergo complete and reversible cation exchange, complete but irreversible, partial exchange, and in some cases, they do not exchange. Other puzzles include, why certain cation can exchange others while some cannot, why exchange can proceed in certain solvents but fails in others. Herein, we qual. demonstrate how the concept of Hard-Soft Acid-Base principle allows a plethora of reported exptl. observations dealing with cation exchange at the SBUs of MOFs could be reasonably explained. This review is intended to provide rationalization of cation exchange behaviors in both stable and labile MOFs, based on the hardness or softness of cations and ligands, effect of solvents, temp. and exchange period using the HSAB principle's point of view. Authors hope that this review may lead to a deeper understanding of the cation exchange behavior in MOFs, which in turns allow chemists to use it as a predictive tool for engineering novel functional MOFs with the required complexities.
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    37. 37
      Pullen, S.; Tessarolo, J.; Clever, G. H. Increasing Structural and Functional Complexity in Self-Assembled Coordination Cages. Chem. Sci. 2021, 12 (21), 7269– 7293,  DOI: 10.1039/D1SC01226F
      37
      Increasing structural and functional complexity in self-assembled coordination cages
      Pullen, Sonja; Tessarolo, Jacopo; Clever, Guido H.
      Chemical Science (2021), 12 (21), 7269-7293CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Progress in metallo-supramol. chem. creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centers or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction center. Combining several functionalities without creating statistical mixts., however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.
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    38. 38
      Wu, K.; Benchimol, E.; Baksi, A.; Clever, G. H. Non-Statistical Assembly of Multicomponent [Pd2ABCD] Cages. Nat. Chem. 2024, 16 (4), 584– 591,  DOI: 10.1038/s41557-023-01415-7
      There is no corresponding record for this reference.
    39. 39
      Kurz, H.; Schötz, K.; Papadopoulos, I.; Heinemann, F. W.; Maid, H.; Guldi, D. M.; Köhler, A.; Hörner, G.; Weber, B. A Fluorescence-Detected Coordination-Induced Spin State Switch. J. Am. Chem. Soc. 2021, 143 (9), 3466– 3480,  DOI: 10.1021/jacs.0c12568
      There is no corresponding record for this reference.
    40. 40
      Bandi, S.; Chand, D. K. Cage-to-Cage Cascade Transformations. Chem.─Eur. J. 2016, 22 (30), 10330– 10335,  DOI: 10.1002/chem.201602039
      There is no corresponding record for this reference.
    41. 41
      Samanta, D.; Mukherjee, P. S. Component Selection in the Self-Assembly of Palladium(II) Nanocages and Cage-to-Cage Transformations. Chem.─Eur. J. 2014, 20 (39), 12483– 12492,  DOI: 10.1002/chem.201402553
      There is no corresponding record for this reference.
    42. 42
      Preston, D.; Barnsley, J. E.; Gordon, K. C.; Crowley, J. D. Controlled Formation of Heteroleptic [Pd2(La)2(Lb)2]4+ Cages. J. Am. Chem. Soc. 2016, 138 (33), 10578– 10585,  DOI: 10.1021/jacs.6b05629
      42
      Controlled Formation of Heteroleptic [Pd2(La)2(Lb)2]4+ Cages
      Preston, Dan; Barnsley, Jonathan E.; Gordon, Keith C.; Crowley, James D.
      Journal of the American Chemical Society (2016), 138 (33), 10578-10585CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Metallosupramol. architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, mol. recognition, and sensing. For the most part these achievements have been made with high-symmetry metallosupramol. architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallosupramol. architectures that are made up of multiple different ligands and/or metals ions to obtain more complex systems with new properties. Herein the addn. of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis(pyridin-3-ylethynyl)pyridine (2A-tripy), to a soln. of the [Pd2(tripy)4]4+ cage resulted in the clean generation of a heteroleptic [Pd2(tripy)2(2A-tripy)2]4+ architecture. The formation of the mixed-ligand cage [Pd2(tripy)2(2A-tripy)2]4+ was confirmed using 1H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resoln. electrospray ionization mass spectrometry. D. functional theory calcns. suggested the cis isomer was more stable that the trans isomer. Addnl., the calcns. indicated that the heteroleptic palladium(II) cages are kinetically metastable intermediates rather than the thermodn. product of the reaction. Competition expts. supported that finding and showed the cages are long-lived in soln. at room temp. Finally, the addn. of 2A-tripy to a range of preformed [Pd2(Ltripy)4]4+ cages cleanly generated the mixed-ligand systems. Three other systems displaying different exo and endo functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized heteroleptic cis-[Pd2(La)2(Lb)2]4+ cages.
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    43. 43
      Zhang, D.; Ronson, T. K.; Xu, L.; Nitschke, J. R. Transformation Network Culminating in a Heteroleptic Cd6L6L′2 Twisted Trigonal Prism. J. Am. Chem. Soc. 2020, 142 (20), 9152– 9157,  DOI: 10.1021/jacs.0c03798
      43
      Transformation Network Culminating in a Heteroleptic Cd6L6L'2 Twisted Trigonal Prism
      Zhang, Dawei; Ronson, Tanya K.; Xu, Lin; Nitschke, Jonathan R.
      Journal of the American Chemical Society (2020), 142 (20), 9152-9157CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Transformations between three-dimensional metallosupramol. assemblies can enable switching between the different functions of these structures. Here authors report a network of such transformations, based upon a subcomponent displacement strategy. The flow through this network is directed by the relative reactivities of different amines, aldehydes, and di(2-pyridyl)ketone. The network provides access to an unprecedented heteroleptic Cd6L6L'2 twisted trigonal prism. The principles underpinning this network thus allow for the design of diverse structural transformations, converting one helicate into another, a helicate into a tetrahedron, a tetrahedron into a different tetrahedron, and a tetrahedron into the new trigonal prismatic structure type. The selective conversion from one host to another also enabled the uptake of a desired guest from a mixt. of guests.
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    44. 44
      McConnell, A. J.; Aitchison, C. M.; Grommet, A. B.; Nitschke, J. R. Subcomponent Exchange Transforms an FeII4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System. J. Am. Chem. Soc. 2017, 139 (18), 6294– 6297,  DOI: 10.1021/jacs.7b01478
      44
      Subcomponent Exchange Transforms an FeII4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System
      McConnell, Anna J.; Aitchison, Catherine M.; Grommet, Angela B.; Nitschke, Jonathan R.
      Journal of the American Chemical Society (2017), 139 (18), 6294-6297CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage's FeII centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addn. of p-anisidine to a mixt. of high-spin 1 and previously-reported low-spin FeII4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addn. of 2-formylpyridine to an identical mixt. of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addn. of 2-formylpyridine thus modulated the system's behavior, fundamentally altering its response to the subsequent signal p-anisidine.
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    45. 45
      Huang, Y.; Lu, Y.; Zhang, X.; Liu, C.; Ruan, J.; Qin, Y.; Cao, Z.; Jiang, J.; Xu, H.; Su, C. Dynamic Stereochemistry of M8Pd6 Supramolecular Cages Based on Metal-Center Lability for Differential Chiral Induction, Resolution, and Recognition. Angew. Chem. Int. Ed. 2024, 63 (2), e202315053  DOI: 10.1002/anie.202315053
      There is no corresponding record for this reference.
    46. 46
      Vardhan, H.; Mehta, A.; Nath, I.; Verpoort, F. Dynamic Imine Chemistry in Metal–Organic Polyhedra. RSC Adv. 2015, 5 (82), 67011– 67030,  DOI: 10.1039/C5RA10801B
      There is no corresponding record for this reference.
    47. 47
      Meng, W.; Ronson, T. K.; Clegg, J. K.; Nitschke, J. R. Transformations within a Network of Cadmium Architectures. Angew. Chem., Int. Ed. 2013, 52 (3), 1017– 1021,  DOI: 10.1002/anie.201206990
      There is no corresponding record for this reference.
    48. 48
      Davies, J. A.; Tarzia, A.; Ronson, T. K.; Auras, F.; Jelfs, K. E.; Nitschke, J. R. Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn8L6 Self-Assembled Structures. Angew. Chem., Int. Ed. 2023, 62 (10), e202217987  DOI: 10.1002/anie.202217987
      There is no corresponding record for this reference.
    49. 49
      Percástegui, E. G.; Mosquera, J.; Nitschke, J. R. Anion Exchange Renders Hydrophobic Capsules and Cargoes Water-Soluble. Angew. Chem., Int. Ed. 2017, 56 (31), 9136– 9140,  DOI: 10.1002/anie.201705093
      49
      Anion Exchange Renders Hydrophobic Capsules and Cargoes Water-Soluble
      Percastegui, Edmundo G.; Mosquera, Jesus; Nitschke, Jonathan R.
      Angewandte Chemie, International Edition (2017), 56 (31), 9136-9140CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Control over the soly. properties of container mols. is a central challenge in host-guest chem. Herein we present a simple anion-exchange protocol that allows the dissoln. in water of various hydrophobic metal-org. container mols. prepd. by iron(II)-templated subcomponent self-assembly. Our process involved the exchange of less hydrophilic trifluoromethanesulfonate anions for hydrophilic sulfate; the resulting water-sol. cages could be rendered water-insol. through reverse anion exchange. Notably, this strategy allowed cargoes within capsules, including polycyclic arom. compds. and complex org. drugs, to be brought into water. Hydrophobic effects appeared to enhance binding, as many of these cargoes were not bound in non-aq. media. Studies of the scope of this method revealed that cages contg. tetratopic and tritopic ligands were more stable in water, whereas cages with ditopic ligands disassembled.
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    50. 50
      He, D.; Ji, H.; Liu, T.; Yang, M.; Clowes, R.; Little, M. A.; Liu, M.; Cooper, A. I. Self-Assembly of Chiral Porous Metal–Organic Polyhedra from Trianglsalen Macrocycles. J. Am. Chem. Soc. 2024, 146 (25), 17438– 17445,  DOI: 10.1021/jacs.4c04928
      There is no corresponding record for this reference.
    51. 51
      Dworzak, M. R.; Deegan, M. M.; Yap, G. P. A.; Bloch, E. D. Synthesis and Characterization of an Isoreticular Family of Calixarene-Capped Porous Coordination Cages. Inorg. Chem. 2021, 60 (8), 5607– 5616,  DOI: 10.1021/acs.inorgchem.0c03554
      There is no corresponding record for this reference.
    52. 52
      Zenka, M.; Preinl, J.; Pertermann, E.; Lützen, A.; Tiefenbacher, K. A Water- and Base-Stable Iminopyridine-Based Cage That Can Bind Larger Organic Anions. Eur. J. Inorg. Chem. 2023, 26 (15), e202300110  DOI: 10.1002/ejic.202300110
      There is no corresponding record for this reference.
    53. 53
      Plajer, A. J.; Percástegui, E. G.; Santella, M.; Rizzuto, F. J.; Gan, Q.; Laursen, B. W.; Nitschke, J. R. Fluorometric Recognition of Nucleotides within a Water-Soluble Tetrahedral Capsule. Angew. Chem., Int. Ed. 2019, 58 (13), 4200– 4204,  DOI: 10.1002/anie.201814149
      53
      Fluorometric Recognition of Nucleotides within a Water-Soluble Tetrahedral Capsule
      Plajer, Alex J.; Percastegui, Edmundo G.; Santella, Marco; Rizzuto, Felix J.; Gan, Quan; Laursen, Bo W.; Nitschke, Jonathan R.
      Angewandte Chemie, International Edition (2019), 58 (13), 4200-4204CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The design of aq. probes and binders for complex, biol. relevant anions presents a key challenge in supramol. chem. Herein, a tetrahedral assembly with cationic faces and corners is reported that is capable of discriminating between anionic and neutral guests in water. Electrostatic repulsion between subcomponents can be overcome by the addn. of an anionic template, or generating a robust covalent framework by incorporating tris(2-aminoethyl)amine (TREN). The resultant TREN-capped, water-sol., fluorescent cage binds mono- and poly-phosphoric esters, including nucleotides. Its covalent skeleton renders it stable at micromolar concns. in water, enabling the fluorometric detection of biol. relevant guests in an aq. environment. Selective supramol. encapsulants, such as 1, could enable new sensing applications, such as recognition of toxins and drugs, under biol. conditions.
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    54. 54
      Takezawa, H.; Tabuchi, R.; Sunohara, H.; Fujita, M. Confinement of Water-Soluble Cationic Substrates in a Cationic Molecular Cage by Capping the Portals with Tripodal Anions. J. Am. Chem. Soc. 2020, 142 (42), 17919– 17922,  DOI: 10.1021/jacs.0c08835
      54
      Confinement of water-soluble cationic substrates in cationic molecular cage by capping portals with tripodal anions
      Takezawa, Hiroki; Tabuchi, Ryosuke; Sunohara, Haruka; Fujita, Makoto
      Journal of the American Chemical Society (2020), 142 (42), 17919-17922CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The ability of a cationic coordination cage to encapsulate mol. guests is enhanced by non-covalent capping of the cage portals with tripodal anions. The capped cage provides new cation binding sites at the portals, which enable accommodation of cationic substrates within the cationic cage. In addn., non-covalent capping allows neutral guests in the cage to be exchanged for cationic ones on demand.
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    55. 55
      Guo, S.; Zhan, W.-W.; Yang, F.-L.; Zhou, J.; Duan, Y.-H.; Zhang, D.; Yang, Y. Enantiopure Trigonal Bipyramidal Coordination Cages Templated by in Situ Self-Organized D2h-Symmetric Anions. Nat. Commun. 2024, 15 (1), 5628,  DOI: 10.1038/s41467-024-49964-w
      There is no corresponding record for this reference.
    56. 56
      Ma, S.; Smulders, M. M. J.; Hristova, Y. R.; Clegg, J. K.; Ronson, T. K.; Zarra, S.; Nitschke, J. R. Chain-Reaction Anion Exchange between Metal–Organic Cages. J. Am. Chem. Soc. 2013, 135 (15), 5678– 5684,  DOI: 10.1021/ja311882h
      56
      Chain-Reaction Anion Exchange between Metal-Organic Cages
      Ma, Shucong; Smulders, Maarten M. J.; Hristova, Yana R.; Clegg, Jack K.; Ronson, Tanya K.; Zarra, Salvatore; Nitschke, Jonathan R.
      Journal of the American Chemical Society (2013), 135 (15), 5678-5684CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Differential binding affinities for a set of anions were obsd. between larger [FeL6]8+(1; L = I) and smaller [Fe(L')6]8+ (2; L = II) tetrahedral metal-org. capsules in soln. A chem. network could thus be designed wherein the addn. of hexafluorophosphate could cause perchlorate to shift from capsule 2 to capsule 1 and triflimide to be ejected from capsule 1 into soln.
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    57. 57
      Browne, C.; Brenet, S.; Clegg, J. K.; Nitschke, J. R. Solvent-Dependent Host–Guest Chemistry of an Fe8L12 Cubic Capsule. Angew. Chem., Int. Ed. 2013, 52 (7), 1944– 1948,  DOI: 10.1002/anie.201208740
      There is no corresponding record for this reference.
    58. 58
      von Krbek, L. K. S.; Schalley, C. A.; Thordarson, P. Assessing Cooperativity in Supramolecular Systems. Chem. Soc. Rev. 2017, 46 (9), 2622– 2637,  DOI: 10.1039/C7CS00063D
      58
      Assessing cooperativity in supramolecular systems
      von Krbek, Larissa K. S.; Schalley, Christoph A.; Thordarson, Pall
      Chemical Society Reviews (2017), 46 (9), 2622-2637CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. This tutorial review summarises different aspects of cooperativity in supramol. complexes. We propose a systematic categorisation of cooperativity into cooperative aggregation, intermol. (allosteric) cooperativity, intramol. (chelate) cooperativity and interannular cooperativity and discuss approaches to quantify them thermodynamically using cooperativity factors. A brief summary of methods to det. the necessary thermodn. data is given with emphasis on isothermal titrn. calorimetry (ITC), a method still underrepresented in supramol. chem., which however offers some advantages over others. Finally, a discussion of very few selected examples, which highlight different aspects to illustrate why such an anal. is useful, rounds up this review.
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    59. 59
      Bolliger, J. L.; Belenguer, A. M.; Nitschke, J. R. Enantiopure Water-Soluble [Fe4L6] Cages: Host–Guest Chemistry and Catalytic Activity. Angew. Chem., Int. Ed. 2013, 52 (31), 7958– 7962,  DOI: 10.1002/anie.201302136
      There is no corresponding record for this reference.
    60. 60
      Sakiyama, H.; Abiko, T.; Ito, M.; Mitsuhashi, R.; Mikuriya, M.; Waki, K. Conformational Analysis of an Octahedral Zinc(II) Complex with Six Dimethylsulfoxide. Polyhedron 2016, 119, 512– 516,  DOI: 10.1016/j.poly.2016.09.039
      There is no corresponding record for this reference.
    61. 61
      Tateishi, T.; Takahashi, S.; Okazawa, A.; Martí-Centelles, V.; Wang, J.; Kojima, T.; Lusby, P. J.; Sato, H.; Hiraoka, S. Navigated Self-Assembly of a Pd2L4 Cage by Modulation of an Energy Landscape under Kinetic Control. J. Am. Chem. Soc. 2019, 141 (50), 19669– 19676,  DOI: 10.1021/jacs.9b07779
      61
      Navigated Self-Assembly of a Pd2L4 Cage by Modulation of an Energy Landscape under Kinetic Control
      Tateishi, Tomoki; Takahashi, Satoshi; Okazawa, Atsushi; Marti-Centelles, Vicente; Wang, Jianzhu; Kojima, Tatsuo; Lusby, Paul J.; Sato, Hirofumi; Hiraoka, Shuichi
      Journal of the American Chemical Society (2019), 141 (50), 19669-19676CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Kinetic control of mol. self-assembly remains difficult because of insufficient understanding of mol. self-assembly mechanisms. Here authors report the formation of a metastable [Pd2L4]4+ cage structure composed of naphthalene-based ditopic ligands (L) and Pd(II) ions in very high yield (99%) under kinetic control by modulating the energy landscape. When self-assembly occurs with anionic guests in weakly coordinating solvent then suitable intermediates and the metastable cage is formed. These conditions also prevent further transformation into the thermodynamically decompd. state. The cage formation pathways under kinetic control and the effect of the anions encapsulated on the self-assembly processes were investigated by QASAP (quant. anal. of self-assembly process) and NASAP (numerical anal. of self-assembly process). It was found that the self-assembly with a preferred guest (BF4-) proceeds through intermediates composed of no more components than the cage ([PdaLbXc]2a+ (a ≤ 2, b ≤ 4, X indicates a leaving ligand)) and that the final intramol. cage-closure step is the rate-detg. step. In contrast, a weaker guest (OTf-) causes the transient formation of intermediates composed of more components than the cage ([PdaLbXc]2a+ (a > 2, b > 4)), which are finally converted into the cage.
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    62. 62
      Díaz-Torres, R.; Alvarez, S. Coordinating Ability of Anions and Solvents towards Transition Metals and Lanthanides. Dalton Trans. 2011, 40 (40), 10742,  DOI: 10.1039/c1dt11000d
      62
      Coordinating ability of anions and solvents towards transition metals and lanthanides
      Diaz-Torres, Raul; Alvarez, Santiago
      Dalton Transactions (2011), 40 (40), 10742-10750CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      A scale that attempts to quantify the weakly coordinating character of a variety of solvents and anions is presented. For each group (solvent or anion), a coordinating ability index was calcd., based on the probability of it being coordinated in the presence of a transition metal atom, compared to the probability of finding it as a solvation mol. or as noncoordinating counterion in a crystal structure. The corresponding index is also defined for the same groups in the presence of lanthanides, and the similarities and differences are discussed.
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    63. 63
      Maglic, J. B.; Lavendomme, R. MoloVol: An Easy-to-Use Program for Analyzing Cavities, Volumes and Surface Areas of Chemical Structures. J. Appl. Crystallogr. 2022, 55 (4), 1033– 1044,  DOI: 10.1107/S1600576722004988
      There is no corresponding record for this reference.
    64. 64
      He, T.; Kong, X.-J.; Li, J.-R. Chemically Stable Metal–Organic Frameworks: Rational Construction and Application Expansion. Acc. Chem. Res. 2021, 54 (15), 3083– 3094,  DOI: 10.1021/acs.accounts.1c00280
      64
      Chemically Stable Metal-Organic Frameworks: Rational Construction and Application Expansion
      He, Tao; Kong, Xiang-Jing; Li, Jian-Rong
      Accounts of Chemical Research (2021), 54 (15), 3083-3094CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Metal-org. frameworks (MOFs) have been attracting tremendous attention owing to their great structural diversity and functional tunability. Despite numerous inherent merits and big progress in the fundamental research (synthesizing new compds., discovering new structures, testing assocd. properties, etc.), poor chem. stability of most MOFs severely hinders their involvement in practical applications, which is the final goal for developing new materials. Therefore, constructing new stable MOFs or stabilizing extant labile MOFs is quite important. As with them, some "potential" applications would come true and a lot of new applications under harsh conditions can be explored. Efficient strategies are being pursued to solve the stability problem of MOFs and thereby achieve and expand their applications. In this Account, we summarize the research advance in the design and synthesis of chem. stable MOFs, particularly those stable in acidic, basic, and aq. systems, as well as in the exploration of their applications in several expanding fields of environment, energy, and food safety, which have been dedicated in our lab over the past decade. The strategies for accessing stable MOFs can be classified into: (a) assembling high-valent metals (hard acid, such as Zr4+, Al3+) with carboxylate ligands (hard base) for acid-stable MOFs; (b) combining low-valent metals (soft acid, such as Co2+, Ni2+) and azolate ligands (soft base, such as pyrazolate) for alkali-resistant MOFs; (c) enhancing the connectivity of the building unit; (d) contracting or rigidifying the ligand; (e) increasing the hydrophobicity of the framework; and (f) substituting liable building units with stable ones (such as metal metathesis) to obtain robust MOFs. In addn., other factors, including the geometry and symmetry of building units, framework-framework interaction, and so forth, have also been taken into account in the design and synthesis of stable MOFs. On the basis of these approaches, the stability of resulting MOFs under corresponding conditions has been remarkably enhanced. With high chem. stability achieved, the MOFs have found many new and significant applications, aiming at addressing global challenges related to environmental pollution, energy shortage, and food safety. A series of stable MOFs have been constructed for detecting and eliminating contaminations. Various fluorescent MOFs were rationally customized to be powerful platforms for sensing hazardous targets in food and water, such as dioxins, antibiotics, veterinary drugs, and heavy metal ions. Some hydrophobic MOFs even showed effective and specific capture of low-concn. volatile org. compds. Novel MOFs with record-breaking acid/base/nucleophilic regent resistance have expanded their application scope under harsh conditions. BUT-8(Cr)A, as the most acid-stable MOF yet, showed reserved structural integrity in concd. H2SO4 and recorded high proton cond.; the most alkali-resistant MOF, PCN-601, retained crystallinity even in boiling satd. NaOH aq. soln., and such base-stable MOFs composed of non-noble metal clusters and poly pyrazolate ligands also demonstrated great potential in heterogeneous catalysis in alk./nucleophilic systems for the first time. It is believed that this Account will provide valuable refs. on stable MOFs' construction as well as application expansion toward harsh conditions, thereby being helpful to promote MOF materials to step from fundamental research to practical applications.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.4c09742.

    • (1) General Information (2) Synthesis and Characterization of Subcomponents (3) Subcomponent Self-Assembly (4) Single-crystal X-ray Diffraction (5) Conversion from 1 to 2 (6) Robustness Investigations of 1 and 2 (7) Host–Guest Experiments (PDF)

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    CCDC 2362227–2362229 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.


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