Reticular synthesis of a pcu-b framework: digital reticular chemistry for anisotropic modulation and multicomponent integration

Abstract

The introduction of “heterogeneity within order” to metal–organic frameworks (MOFs) commonly leads to an increase in structural complexity, posing the question of whether it is possible to spatially arrange multiple components in a simple network. Here, we focus on the integration of quaternary components into a simple pcu-b (primitive cubic unit-biparticle) network using a [Zn₄O]-core cluster and paddle-wheel secondary building units (SBUs) alongside organic linkers. We systematically explore a design space of over 180 candidate configurations, identifying an optimal structure that balances synthetic feasibility and functional potential. Experimental validation confirmed the successful synthesis of the predicted framework, named MAC-5, which exhibits unique anisotropic modulation enabled by the controlled spatial arrangement of distinct Zn₄O(COO)₄(NN)₂ and paddle-wheel SBUs. Extending this approach, we synthesized a series of iso-reticular analogues, presenting the tailored multiple functions from different multicomponent frameworks. The hetero-SBU arrangement of MAC-5 enhanced the thermal and chemical stabilities and enabled programmable metal doping that defies expectations in pcu-based systems. This work establishes a reticular chemistry approach to engineering functional complexity within simple network topologies, providing a blueprint for the rational design of multicomponent MOFs with tailored properties.

---

Introduction

A fascinating objective in chemistry is to synthesize compounds with underlying simple structures, yet which are capable of performing multiple, tailorable functions. Achieving this goal requires the integration of various components into a framework that retains simplicity while enabling the desired properties. Multicomponent metal–organic frameworks (MOFs) are a prime example, as they involve the spatial arrangement of different building units in an ordered crystalline network.^1–3 Owing to the compositionally encoded chemical and physical properties, the integration of multiple components in reticulated space would endow the fundamental structures with unique multiple functionalities.^4,5 Synergistic interactions between distinct components enable unprecedented properties for adsorption, separation, catalysis and photoluminescence applications.^6,7 Balancing the functionality of MOFs with structural integrity is also challenging in terms of practical applications. A notable example is MOF-5, one of the most iconic prototype structures, which suffers from poor water stability, despite its high porosity.⁸ The Zn₄O(COO)₆ clusters in MOF-5 are particularly susceptible to hydrolytic attack, leading to rapid degradation of the framework upon exposure to moisture. To address this limitation, researchers have turned to the principles of reticular chemistry. Multicomponent MOFs could be used to design materials that meet the requirements of topological simplicity, functional complexity and enhanced structural integrity.^9–12 However, as the heterogeneity of the components increases, the simplicity of the underlying networks often gives way to greater structural complexity. This raises the question of the accommodation of multiple components within a simple, ordered network.^13,14

MOF-5 is constructed using Zn₄O(COO)₆ as a 6-connected octahedral node with 1,4-benzenedicarboxylate (bdc) linkers, which represent simple three-dimensional primitive cubic unit (pcu) networks. Even within this ‘simple’ structural space, diversity is created by simply varying the parameters pertaining to the composition, size, linkage, and connectivity of the building units to make different structures.^15–18 Furthermore, a new level of diversity can be achieved by applying variations to one or more components within a single network.¹⁹ Incorporating a tritopic ligand leads to a ternary system of UMCM-1 underlying a (3,6)-connected muo net.²⁰ By introducing azolate ligands and combining them with carboxylate ligands, new 6-connected [Zn₄O]-core derivatives can be formed. The azolate group serves in μ_1,2-coordinated mode, and can substitute one to six positions of the carboxylate groups to form Zn₄O(COO)₆ analogues of Zn₄O(COO)₅(NN), Zn₄O(COO)₄(NN)₂, Zn₄O(COO)₃(NN)₃ and Zn₄O(NN)₆.^21,22 However, as the complexity of the components increases, network design becomes more challenging and leads to difficulties in maintaining a simple pcu topology.^23,24 Introducing azolate ligands often results in quaternary systems with complex network topologies, such as tap, tub, ott, umt, and ith-d.²⁵Zn(bdc)(dabco)_0.5 is another well-known prototype structure with a pcu network, built from paddle-wheel units as 6-connected octahedral nodes, with bdc and dabco serving as linear linkers.^26,27 Our previous studies have revealed a series of structures composed of paddle-wheel and azolate-dinuclear units, where the equatorial plane consists of four η₁-coordinated carboxylate groups, and the axial position is occupied by two μ_1,2-coordinated azolate groups.^28–32 This encouraged us to explore the potential of accommodating both [Zn₄O]-derived clusters and paddle-wheel SBUs within a single pcu-b framework.

Multicomponent MOFs developed exciting artificial systems and introduced novel concepts, such as programmable pore architectures, structural flexibility, solid-state solution and ordered vacancies into the MOF field.³³ Recent advances in digital reticular chemistry (DRC) have opened up new opportunities for addressing these challenges.³⁴ By integrating computational predictions with artificial intelligence (AI)-assisted design, DRC provides a systematic approach to developing multicomponent frameworks with a higher degree of control by predicting the optimal arrangement of SBUs and linkers, and assessing the stability and potential properties of the resulting structures.³⁵ With the assistance of digital reticular chemistry, we aimed to investigate how these distinct building blocks could be accommodated together, paving the way for new possibilities in framework design. This approach greatly improves design precision and accelerates experimental validation.^36,37 In this study, we accurately simulated the reticular coding of [Zn₄O]-core clusters, alongside paddle-wheel units in a pcu-b network, and the actual synthetic possibilities were assessed. Experimental validation confirmed the successful synthesis of the predicted framework, named MAC-5, which exhibits unique anisotropic modulation enabled by the controlled spatial arrangement of distinct Zn₄O(COO)₄(NN)₂ and paddle-wheel SBUs. MAC-5 exhibited higher thermal and chemical stabilities than those of MOF-5 or Zn(bdc)(dabco)_0.5, which are built solely from Zn₄O and paddle-wheel units, respectively. We also synthesized a series of iso-reticular analogues and realized site-selective metal doping and anisotropic property modulation in a simple pcu-b framework.

Results and discussion

Computational design

In this work, we employed a computational tool known as ToBaCCo (topologically based crystal constructor), which was specifically designed to construct MOFs by using molecular building blocks and topological blueprints.^38,39pcu-b was selected as a template for this study. Although other 6-connected SBUs, such as V₃ trimers⁴⁰ or Zr₆ clusters,⁴¹ are computationally viable for forming pcu nets, their synthetic accessibility is often limited due to non-ideal 6-connected geometries. In contrast, both Zn₄O clusters and paddle-wheel SBUs are well established in the literature for reliably forming robust, high-symmetry pcu nets, as exemplified by MOF-5 and frameworks such as Zn(bdc)(dabco)_0.5. ToBaCCo's algorithm facilitates the automated generation of structures by systematic arrangements of zinc paddle-wheel units and [Zn₄O]-core analogies within a pcu framework. Initially, we isolated Zn₄O(COO)₆ and six other Zn-carboxylate-azolate SBUs along with zinc paddle-wheel units from the CIF files of MOF-5, Zn(BDC)(dabco)_0.5 and the FDM series.²² As shown in Scheme 1, these six SBUs are typical Zn4O_a SBU with six carboxylate groups; Zn4ONN_b with one substituted azolate group; Zn4ONN2_c with two adjacent azolate groups; Zn4ONN3_d and Zn4ONN3_e with three azolate groups in different configurations; and finally, Zn4ONN6 with all six groups being azolate. Notably, we identified an unreported Zn-carboxylate-azolate SBU, which contains two opposing substituted azolate groups and was added as Zn4ONN2_f. To streamline the selection of structures feasible for laboratory synthesis, we standardized the linkers to phenyl groups, focusing solely on the arrangement of nodes in a pcu network. This approach enables the generation of thousands of potential framework combinations through different assembly patterns. Structures generated solely from Zn₄O units and Zn-carboxylate-azolate derivatives, such as MOF-5 and FDM-1,²² were not considered in this study, as our primary focus was on the potential for multicomponent construction. After systematic screening to eliminate duplicate structures, we identified over 400 unique architectures. Among these, approximately 186 variants adopt a pcu-b topology with a well-defined alternating sequence of paddle-wheel and [Zn₄O]-derived SBUs. Seven representative structures were geometrically and energetically optimized using Material Studio software. The simulated structures are shown in Fig. S1. Considering experimental feasibility, we then deduced the necessary linkers (ligands) for syntheses. Only three cases could be realized using just two linkers: the Zn4O_a-paddle-wheel, Zn4ONN6-paddle-wheel, and Zn4ONN2_f-paddle-wheel structures (highlighted by red, purple, and green lines, respectively). The synthesis of other mixed-SBU structures would require more than three different linkers. Such asymmetric configurations are inherently less probable and pose significant challenges for laboratory implementation. The Zn4O_a-paddle-wheel structure was achievable with terephthalic acid and pyridine-4-carboxylic acid, while the highly symmetric Zn4ONN6 SBU could incorporate paddle-wheel units through a combination of triazole derivatives and pyrazole-carboxylic acid linkers, consistent with previous work.^42,43 Notably, among the lower-symmetry Zn-carboxylate-azolate derivatives, only the Zn4ONN2_f-paddle-wheel proved synthetically accessible with two linkers, specifically terephthalic acid and a triazole-based ligand. Considering laboratory synthesizability, the Zn4ONN2_f-paddle-wheel structure emerges as the most promising candidate for new synthesis.

Scheme 1 Schematic framework with pcu-b topology using zinc paddle-wheels and Zn₄O-derived SBUs and the deduced linkers based on the structures.

Synthesis and structural validation

Guided by these simulated results, we then prepared a series of quaternary-component iso-reticular frameworks constructed from Zn₄O derivative Zn4ONN2_f and paddle-wheel SBUs using terephthalic acid and triazole derivatives. Block crystals of the basic MOF formulated as Zn₂(Zn₄O)(BDC)₃(dmtrz)₂ (named MAC-5) were isolated by solvothermal reaction of Zn(NO₃)₂, 1,4-benzenedicarboxylate acid (H₂bdc) and 3,5-dimethyl-1H-1,2,4-triazole (Hdmtrz). Single crystal X-ray diffraction (SCXRD) analysis reveals that it crystallizes in the tetragonal space group I-4 with a = b = 16.78 Å, and c = 17.13 Å (Table S1). As shown in Fig. 1, the six-connected octahedral node of Zn₄O(COO)₄(dmtrz)₂, that is Zn4ONN2_f, is observed. Four μ_1,2-carboxylate groups from four bdc ligands that take up the equatorial plane of the octahedral node, and two dmtrz ligands in μ_1,2-connected mode occupy the axial positions. The carboxylate group present at the other end of the bdc ligand coordinates to the zinc paddle-wheel unit, similar to that in Zn(bdc)(dabco)_0.5. The bdc-directed alternating arrangement of Zn₄O and paddle-wheel results in a 2D (4,4) grid in the ab-plane. Conversely, a dmtrz ligand bridges Zn₄O and paddle-wheel units along the c-axis, generating a 3D pcu-b-type framework, in which all Zn₄O units are spatially separated by six paddle-wheel units and vice versa. The solvent-accessible volume per unit cell was calculated to be approximately 65.0%. After activation, the accessible porosity was confirmed by N₂ adsorption at 77 K (Fig. S2a), which showed a type-I isotherm with a BET surface area of ca. 1691 m² g⁻¹. MAC-5 exhibits an intermediate BET surface area between those of Zn(bdc)(dabco)_0.5 (1450 m² g⁻¹) and MOF-5 (2900 m² g⁻¹), as expected from their respective layer distances and ligand sizes (Fig. S3). MAC-5 also shows promising gas adsorption for H₂, CO₂, CH₄ and CH₂CH₂ (Fig. S2b).

Fig. 1 (a) Zinc paddle-wheel, Zn4ONN2_f SBUs and two kinds of linkers in MAC-5; (b) the 3-D structures of MAC-5; (c) pcu-b topology.

Thermal and chemical stabilities

We then tested the thermal and chemical stabilities of MAC-5. MOF-5 and Zn(bdc)(dabco)_0.5 were used as references because of their framework similarity. Despite a relatively low BET surface area, MAC-5 exhibits a constructional advantage inherited from the component heterogeneity. Thermogravimetric analysis (TGA) shows its thermo-decomposition temperature to be around 410 °C (Fig. S2c), like that of MOF-5 but higher than that of Zn(bdc)(dabco)_0.5. Variable-temperature powder X-ray diffraction (VT-PXRD) studies revealed that MAC-5 shows no obvious changes as the temperature increases to 180 °C under ambient conditions (Fig. 2). In contrast, both MOF-5 and Zn(bdc)(dabco)_0.5 exhibit obvious peak shifts assigned to their own typical crystal phase transformation. In addition, the framework integrity of MAC-5 in common solvents was also confirmed (Fig. S2d). We attribute the stability to component heterogeneity, where: (i) the alternating sequences of rigid Zn₄O and flexible paddle-wheel units stabilize the pcu-type framework by suppressing the breathing behavior typically induced by homogeneous flexible paddle-wheel assemblies. (ii) the introduction of μ_1,2-dmtrz ligands into Zn₄O consolidates the octahedral node, lowering its susceptibility to attack by water. In conclusion, the synergistic effect of these two SBUs in the pcu-b matrix enhanced the stability of the MAC-5 structure, which shows outstanding rigidity to remain stable both in air and humid conditions beyond those of single components.

Fig. 2 (a) VT-PXRD patterns of (a) MOF-5; (b) MAC-5; (c) Zn(bdc)(dabco)_0.5.

Iso-reticular syntheses and anisotropic modulation

As a quaternary-component MOF within a simple net, MAC-5 shows more possibilities for anisotropic modulation of the organic linkers by iso-reticular synthesis, which leads to the isolation of MAC-5-II to MAC-5-VIII (Fig. 3). The synthetic details are listed in SI, experimental section. All these iso-reticular products were structurally confirmed by SCXRD (Table S2). The 3-D structures of MAC-5-II to MAC-5-VIII are shown in Fig. S4. For this quaternary-component system, replacement of dmtrz by 3,5-diethyl-1H-1,2,4-triazole (detrz) and 3,5-dipropyl-1H-1,2,4-triazole (dptrz), respectively, provides tailored modulation along the c-axis of the pcu-b type framework, while leaving the pore surface on the ab-plane unchanged in MAC-5-II and MAC-5-III. Conversely, replacement of bdc by 1,4-biphenyldicarboxylate (bpdc) and 2′,5′-dimethyl-terphenyldicarboxylate (dmtpdc), respectively, while keeping dmtrz unchanged along the c-axis, provides tailored modulation on the ab-plane in MAC-5-V and MAC-5-VI. Employing the anisotropic advantage, tailored modulation synchronously along the c-axis and on the ab-plane leads to the generation of MAC-5-IV, MAC-5-VII and MAC-5-VIII. As the carboxylic acid ligands elongate, the MAC-5-V to MAC-5-VIII structures exhibit twofold interpenetration, accompanied by a reduction in pore aperture and accessible free volume. Bulk-phase purity, thermal stability, and surface area were evaluated via PXRD, TGA, and N₂ sorption analyses (Fig. S5–S8). PXRD after solvent immersion and variable-temperature PXRD patterns reveal that MAC-5-II to MAC-5-VII maintain solvent stability and thermal stability comparable to those of MAC-5. While MAC-5-II and MAC-5-VI undergo phase transformation at 180 °C, likely due to the instability of the F-substituted ligand and interpenetration-induced structural displacement, respectively. Hysteresis loops were observed in the N₂ adsorption isotherms of MAC-5-II, -III, and -IV, which correspond to the replacement of methyl groups by larger ethyl and propyl functional groups. These bulkier groups introduce a gating effect at the pore apertures. The apertures open under a certain pressure during adsorption, but the restricted movement of bulkier groups delays their closure during desorption, resulting in a hysteresis loop. In contrast, MAC-5-V, -VI, and -VII, which incorporate long-chain linkers, maintain permanently open pores, leading to hysteresis-free curves. MAC-5-VIII exhibits a large, non-closing hysteresis loop due to framework collapse. N₂ sorption data (Table S3) indicate that the experimental BET surface areas agree very well with the calculated values. Conventional iso-reticular synthesis of pcu-type frameworks with binary components typically yields only isotropic 3D matrix modulation.⁴⁴ While the multivariate MOF (MTV-MOF) strategy enables anisotropic modulation, it often compromises the integrity of the chemical sequence, complicating precise structural characterization.² In this context, we demonstrate a breakthrough approach that enhances component heterogeneity within a simple architecture, providing a novel pathway for tailored anisotropic modulation while preserving crystallinity with well-defined chemical ordering.

Fig. 3 The iso-structures of MAC-5 to MAC-5-VIII.

To confirm the tailored anisotropic modulation, we then verified the differential metal-doping behaviours of Zn₄O-derived architectures compared to paddle-wheel motifs in MAC-5. Anisotropic modulation of the SBUs was consequently exemplified by in situ doping of metal cations, which leads to the isolation of bi-metallic MAC-5-ZnM (M = Co, Cu, Ni, Mn) and tri-metallic MAC-5-ZnM₁M₂ (M₁, M₂ = Co, Cu, Ni, Mn). As shown in Fig. S9, the distinctive colours between MAC-5 and its Co/Cu-substituted analogues can be clearly observed from optical photographs. The morphology of doped MAC-5 remains as tetragonal prismatic crystals with dimensions of approximately 10 × 10 × 30 μm. The XPS spectra also confirmed successful metal doping. A slight shift in the Zn binding energy before and after doping suggests electronic interactions between the metal nodes. Both Co and Cu are present in their characteristic +2 oxidation states (Fig. S10). Metal-doped MOF-5 and Zn(bdc)(dabco)_0.5 were also synthesized for comparison. Their structures remain unchanged after doping, as identified by PXRD patterns (Fig. S11 and S12). The doping ratios were confirmed by ICP-OES, as shown in Tables S4 and S5. This showed that Co(II) was preferably incorporated in the Zn₄O(COO)₆ SBU in the MOF-5 structure compared to the other three cations. Conversely, in the Zn(BDC)(dabco)_0.5 structure, the doping amount of Cu(II) is the highest among the metal cations. The MAC-5-ZnM structure exhibited even doping of Co(II), Mn(II) and Ni(II). Thus, MAC-5 simultaneously provides Zn₄O clusters and paddle-wheel SBUs, making it an ideal platform for dual incorporation. The bi-metal-doping results confirmed that the doping amount of Co(II) is nine times that of Cu(II) in MOF-5-ZnCoCu, and the doping amount of Cu(II) is almost 30 times that of Co(II) in Zn(bdc)(dabco)_0.5-ZnCoCu. While the MAC-5-ZnCoCu structure exhibited nearly equimolar doping of Co(II) and Cu(II). We hypothesize that the distinct coordination geometries preferred by different metal ions may govern their differential incorporation efficiencies into these SBUs. To verify the anisotropic metal-doping, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) analyses of metal-doped MAC-5, MOF-5 and Zn(bdc)(dabco)_0.5 were further carried out. As shown in Fig. 4a, MOF-5-ZnCo shows two absorption peaks at 497 and 527 nm, both arising from transitions of octahedrally coordinated Oh symmetry Co(II).⁴⁵MAC-5-ZnCo displays two similar absorption peaks at 493 nm and 526 nm, also resulting from d → d* transitions of the outermost d⁷ electrons of Co(II). The presence of octahedrally coordinated Co(II) was optically observed from the sample before activation (Fig. S13), which was attributed to the transition from the 4-coordinated Co(II) on the substituted Zn₄O-cluster, as shown in Fig. 4b. In contrast, the UV-vis spectrum of Zn(bdc)(dabco)_0.5-ZnCo shows three absorption peaks at 533 nm, 592 nm, and 780 nm, corresponding to transitions of five-coordinated Co(II) with wheel-spoke-like C_4v symmetry.⁴⁶ The UV-vis spectrum of MOF-5-ZnCu (Fig. 4c) exhibits a broad absorption band in the range of 600–680 nm, which originates from the d → d* transitions of the outermost d⁹ electrons of Cu(II). This can be attributed to d-electron transitions in octahedrally coordinated Oh symmetry Cu(II) within the metal tetranuclear clusters.⁴⁵ In contrast, the UV-vis spectrum of Zn(bdc)(dabco)_0.5-ZnCu shows an absorption peak at 720 nm, resulting from d-electron transitions in five-coordinated Cu(II) with wheel-spoke-like C_4v symmetry.⁴⁷ Similarly, the spectrum of MAC-5-ZnCu displays an absorption peak at 750 nm, which arises from d-electron transitions in five-coordinated Cu(II) with C_4v symmetry.⁴⁵ The observed similar absorption bands of MAC-5-ZnCo and MOF-5-ZnCo as well as those of MAC-5-ZnCu and Zn(bdc)(dabco)_0.5-ZnCu indicate that the doped Co preferentially takes the Zn position of Zn₄O, while the doped Cu favours substitution of the Zn position of the paddle-wheel unit.

Fig. 4 Solid UV-vis spectra of (a) Co-doped samples; (c) Cu-doped samples; (d) CoCu-doped samples and (b) the transition between 4- and 6-coordinated Co(II) in MAC-5.

The UV-vis spectrum of MAC-5-ZnCoCu (Fig. 4d) exhibits characteristic peaks corresponding to both octahedrally coordinated (Oh symmetry) Co(II) at 493 nm and 526 nm (as seen in MAC-5-ZnCo) and five-coordinated (C_4v symmetry) Cu(II) at 750 nm (observed in MAC-5-ZnCu), demonstrating that the in situ metal-doping strategy successfully incorporates both Co(II) and Cu(II) into the MAC-5 framework containing multiple secondary building units (SBUs). MOF-5-ZnCoCu and Zn(bdc)(dabco)_0.5-ZnCoCu show only the characteristic peaks of octahedral Co(II) and five-coordinated Cu(II), respectively. This indicates that, when co-doping Co(II) and Cu(II) into MOF structures with single-type SBUs, only metal ions whose coordination geometry matches the SBU configuration of the host framework can be effectively incorporated. These results highlight that the enhanced component heterogeneity within the simple net architecture of MAC-5 creates multiple host sites for anisotropic metal-doping, surpassing conventional frameworks with homogeneous SBUs. This unique feature enables spatially selective doping, offering the potential for programmable metal-sequence engineering and precise structural control in modular framework design.

Conclusions

In summary, guided by reticular synthesis, units of Zn₄O(COO)₄(NN)₂ and paddle-wheels were translated into the crystalline solid MAC-5, resulting in ordered heterogeneity within a simple pcu-b network. This shows a superior framework stability to that of MOF-5 or Zn(bdc)(dabco)_0.5, which are built solely of Zn₄O and paddle-wheel units, respectively. The iso-reticular chemistry of MAC-5 demonstrated how crystalline heterogeneity enables modulation of anisotropic pore texture while maintaining structural order. Remarkably, anisotropic metal substitution in MAC-5 produces a unique competitive inclusion behaviour within the pcu-b network, which may open up new avenues for systematically engineering crystalline heterogeneity to tailor functional properties for adsorption, catalysis, and bioapplications.

Author contributions

Xiaoming Lv, Yichen Yao and Jiaxing Zhu performed the experiments and analysed the results. Yun Ling and Yaming Zhou designed and supervised the project. Zhenxia Chen performed the structural simulation and wrote the manuscript.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

Data supporting this article have been included in the supplementary information (SI). Supplementary information: details of syntheses, crystallographic data, additional figures and tables. See DOI: https://doi.org/10.1039/d5qm00561b.

CCDC 2471318–2471325 contain the supplementary crystallographic data for this paper.^48a–h

Acknowledgements

This work was funded by Shanghai Municipal Education Commission Program (Grant no. 24KXZNA03), National Natural Science Foundation of China (no. 22275037) and Shanghai “Science and Technology Innovation Action Plan” Intergovernmental International Science and Technology Cooperation Program (no. 22520713700).

Notes and references

1. W. T. Xu, B. B. Tu, Q. Liu, Y. F. Shu, C. C. Liang, C. S. Diercks, O. M. Yaghi, Y. B. Zhang, H. X. Deng and Q. W. Li, Anisotropic reticular chemistry, Nat. Rev. Mater., 2020, 5, 764–779.
2. T. M. O. Popp and O. M. Yaghi, Sequence-Dependent Materials, Acc. Chem. Res., 2017, 50, 532–534.
3. H. Furukawa, K. E. Cordova, M. O'Keeffe and O. M. Yaghi, The Chemistry and Applications of Metal-Organic Frameworks, Science, 2013, 341, 974.
4. L. Y. Chen, H. F. Wang, C. X. Li and Q. Xu, Bimetallic metal-organic frameworks and their derivatives, Chem. Sci., 2020, 11, 5369–5403.
5. S. M. Cohen, Modifying MOFs: new chemistry, new materials, Chem. Sci., 2010, 1, 32–36.
6. H. Furukawa, U. Müller and O. M. Yaghi, Heterogeneity within Order in Metal-Organic Frameworks, Angew. Chem., Int. Ed., 2015, 54, 3417–3430.
7. C. Janiak, Engineering coordination polymers towards applications, Dalton Trans., 2003, 2781–2804.
8. M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O'Keeffe and O. M. Yaghi, Systematic design of pore size and functionality in isoreticular MOFs and their application in methane storage, Science, 2002, 295, 469–472.
9. A. Dutta, Y. Pan, J. Q. Liu and A. Kumar, Multicomponent isoreticular metal-organic frameworks: Principles, current status and challenges, Coord. Chem. Rev., 2021, 445, 214074.
10. M. Viciano-Chumillas, X. Y. Liu, A. Leyva-Pérez, D. Armentano, J. Ferrando-Soria and E. Pardo, Mixed component metal-organic frameworks: Heterogeneity and complexity at the service of application performances, Coord. Chem. Rev., 2022, 451, 214273.
11. Q. Q. Pang, B. B. Tu and Q. W. Li, Metal-organic frameworks with multicomponents in order, Coord. Chem. Rev., 2019, 388, 107–125.
12. R. Freund, S. Canossa, S. M. Cohen, W. Yan, H. X. Deng, V. Guillerm, M. Eddaoudi, D. G. Madden, D. Fairen-Jimenez, H. Lyu, L. K. Macreadie, Z. Ji, Y. Y. Zhang, B. Wang, F. Haase, C. Wöll, O. Zaremba, J. Andreo, S. Wuttke and C. S. Diercks, 25 Years of Reticular Chemistry, Angew. Chem., Int. Ed., 2021, 60, 23946–23974.
13. P. F. Muldoon, C. Liu, C. C. Miller, S. B. Koby, A. G. Jarvi, T. Y. Luo, S. Saxena, M. O'Keeffe and N. L. Rosi, Programmable topology in new families of heterobimetallic metal-organic frameworks, J. Am. Chem. Soc., 2018, 140, 6194–6198.
14. M. Kim, J. F. Cahill, Y. X. Su, K. A. Prather and S. M. Cohen, Postsynthetic ligand exchange as a route to functionalization of 'inert' metal-organic frameworks, Chem. Sci., 2012, 3, 126–130.
15. B. B. Tu, Q. Q. Pang, E. L. Ning, W. Q. Yan, Y. Qi, D. F. Wu and Q. W. Li, Heterogeneity within a Mesoporous Metal-Organic Framework with Three Distinct Metal-Containing Building Units, J. Am. Chem. Soc., 2015, 137, 13456–13459.
16. S. Yuan, J. S. Qin, J. L. Li, L. Huang, L. Feng, Y. Fang, C. Lollar, J. D. Pang, L. L. Zhang, D. Sun, A. Alsalme, T. Cagin and H. C. Zhou, Retrosynthesis of multi-component metal-organic frameworks, Nat. Commun., 2018, 9, 808.
17. T. W. Liu, Q. Nguyen, A. B. Dieng and D. A. Gómez-Gualdrón, Diversity-driven, efficient exploration of a MOF design space to optimize MOF properties, Chem. Sci., 2024, 15, 18903–18919.
18. W. Gschwind, G. Nagy, D. Primetzhofer and S. Ott, Optimizing post-synthetic metal incorporation in mixed-linker MOFs: insights from metalation studies on bipyridine-containing UiO-67 single crystals, Dalton Trans., 2024, 53, 14779–14785.
19. A. K. Cheetham, C. N. R. Rao and R. K. Feller, Structural diversity and chemical trends in hybrid inorganic-organic framework materials, Chem. Commun., 2006, 4780–4795.
20. K. Koh, A. G. Wong-Foy and A. J. Matzger, A crystalline mesoporous coordination copolymer with high microporosity, Angew. Chem., Int. Ed., 2008, 47, 677–680.
21. L. J. Liu, K. Konstas, M. R. Hill and S. G. Telfer, Programmed Pore Architectures in Modular Quaternary Metal-Organic Frameworks, J. Am. Chem. Soc., 2013, 135, 17731–17734.
22. B. B. Tu, Q. Q. Pang, H. S. Xu, X. M. Li, Y. L. Wang, Z. Ma, L. H. Weng and Q. W. Li, Reversible Redox Activity in Multicomponent Metal-Organic Frameworks Constructed from Trinuclear Copper Pyrazolate Building Blocks, J. Am. Chem. Soc., 2017, 139, 7998–8007.
23. J. R. Li, Y. Tao, Q. Yu and X. H. Bu, A pcu-type metal-organic framework with spindle [Zn₇(OH)₈]⁶⁺ cluster as secondary building units, Chem. Commun., 2007, 1527–1529.
24. Y. W. He, Z. H. Li, Z. M. Soilis, G. F. He and N. L. Rosi, Modulator approach for the design and synthesis of anisotropic multi-domain metal-organic frameworks, Chem. Sci., 2025, 16, 7442–7449.
25. L. Feng, K. Y. Wang, J. Willman and H. C. Zhou, Hierarchy in Metal-Organic Frameworks, ACS Cent. Sci., 2020, 6, 359–367.
26. H. Chun, D. N. Dybtsev, H. Kim and K. Kim, Synthesis, X-ray crystal structures, and gas sorption properties of pillared square grid nets based on paddle-wheel motifs: Implications for hydrogen storage in porous materials, Chem. – Eur. J., 2005, 11, 3521–3529.
27. J. D. Pang, S. Yuan, J. S. Qin, M. Y. Wu, C. T. Lollar, J. L. Li, N. Huang, B. Li, P. Zhang and H. C. Zhou, Enhancing Pore-Environment Complexity Using a Trapezoidal Linker: Toward Stepwise Assembly of Multivariate Quinary Metal-Organic Frameworks, J. Am. Chem. Soc., 2018, 140, 12328–12332.
28. W. Y. Dan, Z. X. Chen, Y. Ling, Y. Jia, Y. T. Yang, X. F. Liu and M. L. Deng, Discovery of two predictable (3,18)-connected topologies based on Wells-Dawson type cages for the design of porous metal phosphonocarboxylate frameworks, Dalton Trans., 2024, 53, 7734–7741.
29. M. L. Deng, F. L. Yang, P. Yang, Z. X. Li, J. Y. Sun, Y. T. Yang, Z. X. Chen, L. H. Weng, Y. Ling and Y. M. Zhou, A Series of Metal-Organic Frameworks Built of Triazolate-Trinuclear and Paddlewheel Units: Solid-Solution Framework Approach for Optimizing CO₂ Adsorption and Separation, Cryst. Growth Des., 2015, 15, 5794–5801.
30. J. X. Zhu, J. Y. Chen, T. Z. Qiu, M. L. Deng, Q. S. Zheng, Z. X. Chen, Y. Ling and Y. M. Zhou, Cobalt substitution in a flexible metal-organic framework: modulating a soft paddle-wheel unit for tunable gate-opening adsorption, Dalton Trans., 2019, 48, 7100–7104.
31. J. X. Zhu, Y. Yu, H. C. Fan, H. Q. Cai, Z. X. Chen, L. H. Weng, Y. Ling and Y. M. Zhou, Precise regulating synergistic effect in metal-organic framework for stepwise-controlled adsorption, Inorg. Chem. Front., 2021, 8, 1666–1674.
32. Y. Ling, F. L. Yang, M. L. Deng, Z. X. Chen, X. F. Liu, L. H. Weng and Y. M. Zhou, Novel Iso-Reticular Zn(II) Metal-Organic Frameworks constructed by Trinuclear-Triangular and Paddle-Wheel Units: Synthesis, Structure and Gas Adsorption, Dalton Trans., 2012, 41, 4007–4011.
33. B. B. Tu, Q. Q. Pang, D. F. Wu, Y. N. Song, L. H. Weng and Q. W. Li, Ordered Vacancies and Their Chemistry in Metal Organic Frameworks, J. Am. Chem. Soc., 2014, 136, 14465–14471.
34. H. Lyu, Z. Ji, S. Wuttke and O. M. Yaghi, Digital Reticular Chemistry, Chem, 2020, 6, 2219–2241.
35. K. M. Jablonka, A. S. Rosen, A. S. Krishnapriyan and B. Smit, An Ecosystem for Digital Reticular Chemistry, ACS Cent. Sci., 2023, 9, 563–581.
36. X. Y. Wu and J. W. Jiang, Precision-engineered metal-organic frameworks: fine-tuning reverse topological structure prediction and design, Chem. Sci., 2024, 15, 16467–16479.
37. Z. Y. Song, S. P. Lu, S. S. Cheng, H. J. Li, H. Y. Gao, Z. M. Liu, Y. Q. Su, W. Q. Li, Y. J. Ji, X. Jin and G. Wang, Accelerated screening of water-stable MOF structures using the digital reticular chemistry method, J. Mater. Chem. A, 2025, 13, 17087–17101.
38. Y. J. Colón, D. A. Gómez-Gualdrón and R. Q. Snurr, Topologically Guided, Automated Construction of Metal-Organic Frameworks and Their Evaluation for Energy-Related Applications, Cryst. Growth Des., 2017, 17, 5801–5810.
39. R. Anderson and D. A. Gómez-Gualdrón, Increasing topological diversity during computational synthesis of porous crystals: how and why, CrystEngComm, 2019, 21, 1653–1665.
40. K. Barthelet, D. Riou and G. Ferey, [VIII(H₂O)]₃O(O₂CC₆H₄CO₂)₃·(Cl, ₉H₂O) (MIL-59): A rare example of vanadocarboxylate with a magnetically frustrated three-dimensional hybrid framework, Chem. Commun., 2002, 1492–1493.
41. H. Furukawa, F. Gandara, Y. B. Zhang, J. C. Jiang, W. L. Queen, M. R. Hudson and O. M. Yaghi, Water Adsorption in Porous Metal-Organic Frameworks and Related Materials, J. Am. Chem. Soc., 2014, 136, 4369–4381.
42. M. L. Deng, P. Yang, X. F. Liu, B. Xia, Z. X. Chen, Y. Ling, L. H. Weng, Y. M. Zhou and J. Y. Sun, End-End Connection Pattern of Trinuclear-Triangular Copper Cluster for Construction of Two Metal-Organic Frameworks: Syntheses, Structures, Magnetic and Gas Adsorption Properties, Cryst. Growth Des., 2015, 15, 1526–1534.
43. S. Kouser, A. Hezam and S. A. Khanum, Synthesis, characterization, and catalytic activity of zinc-isonicotinic acid MOF, J. Mol. Struct., 2025, 1321.
44. D. J. Tranchemontagne, J. R. Hunt and O. M. Yaghi, Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-177, MOF-199, and IRMOF-0, Tetrahedron, 2008, 64, 8553–8557.
45. O. G. Holmes and D. S. McClure, Optical Spectra of Hydrated Ions of the Transition Metals, J. Chem. Phys., 1957, 26, 1686–1694.
46. J. A. Larrabee, C. M. Alessi, E. T. Asiedu, J. O. Cook, K. R. Hoerning, L. J. Klingler, G. S. Okin, S. G. Santee and T. L. Volkert, Magnetic circular dichroism spectroscopy as a probe of geometric and electronic structure of Cobalt(II)- substituted proteins: Ground-state zero-field splitting as a coordination number indicator, J. Am. Chem. Soc., 1997, 119, 4182–4196.
47. H. Adams, N. A. Bailey, C. O. R. Debarbarin, D. E. Fenton and O. Y. He, Heteroleptic tripodal complexes of copper(II) – toward a synthetic model for the active-site in galactose-oxidase, Dalton Trans., 1995, 2323–2331.
48. (a) CCDC 2471318: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nyly5; (b) CCDC 2471319: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nylz6; (c) CCDC 2471320: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym08; (d) CCDC 2471321: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym19; (e) CCDC 2471322: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym2b; (f) CCDC 2471323: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym3c; (g) CCDC 2471324: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym4d; (h) CCDC 2471325: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2nym5f.

---