Precision pore engineering via fit-topology assembly in a Zn-porphyrin MOF for selective C₂H₂ capture

Abstract

The topology-guided design of porphyrin-based metal–organic frameworks (PMOFs) with tailored ultramicroporosity (<7 Å) remains a formidable challenge, as conventional strategies often fail to balance structural rigidity with precise pore confinement. To address this limitation, we propose a dual-ligand coordination approach, integrating Zn²⁺-porphyrin chelation and triazole-mediated SBU assembly, to construct Zn-TCPP-dmtrz—a novel PMOF featuring a unique fit topology for C₂H₂/CO₂ separation. Unlike traditional PMOFs with oversized pores (e.g., Al/Y-TCPP), this strategy exploits the synergistic coordination of tetrakis(4-carboxyphenyl)porphyrin (TCPP) and 3,5-dimethyl-1,2,4-triazole (dmtrz) to compress pore apertures to 6.3 × 6.8 Å, closely matching the molecular dimensions of the C₂H₂ molecule. The resulting ultramicroporous channels, reinforced by staggered porphyrin planes and hydrophobic methyl groups, exhibit high C₂H₂ uptake (4.30 mmol g⁻¹) and a separation potential (ΔQ = 1.62 mmol g⁻¹) under ambient conditions, outperforming existing PMOFs. Crucially, the framework retains structural integrity under high humidity (90% RH) and cyclic adsorption–desorption, with a low regeneration energy barrier (Q_st = 28.5 kJ mol⁻¹). Computational studies attribute the selectivity to confinement-enhanced van der Waals interactions and electrostatic alignment at the porphyrin-Zn interface and methyl-decorated channels. This work establishes a topology-driven pore engineering strategy for PMOFs, advancing the design of next-generation adsorbents for challenging gas separations.

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1. Introduction

Metal–organic frameworks (MOFs) are a versatile class of crystalline porous materials assembled from metal ions or clusters and multitopic organic ligands into periodic architectures.^1–3 Their modularity not only affords ultrahigh surface areas and permanent porosity but also enables precise control over pore structures and functionalities.^4–6 These attributes have made MOFs attractive candidates for applications in gas storage and separation,^7–9 heterogeneous catalysis,^10,11 and chemical sensing.¹² One of the fundamental challenges in this field is the translation of structural diversity into rationally designed pore systems capable of delivering predictable adsorption properties and effective separation of small molecules with closely similar physicochemical characteristics.

The network topology of a MOF provides a critical link between local coordination environments and global material properties.^13,14 While metal–ligand coordination defines primary connectivity, the resulting topology dictates the dimensionality of channels, the continuity of pore windows, and the overall packing density of the framework.¹⁵ These features directly impact how guest molecules are confined and interact within the pore space.^16–18 Even subtle variations in connectivity or linker orientation can reshape pore apertures, reorganize channels, and ultimately transform adsorption behavior.^19,20 Accordingly, rational topology engineering, guided by reticular chemistry principles, has become an effective strategy for constructing MOFs with precisely tuned pore systems.²¹

Such considerations are particularly important for the separation of small gas molecules with similar physicochemical properties. Acetylene (C₂H₂) and carbon dioxide (CO₂), for example, both have kinetic diameters of ∼3.3 Å and similar polarizabilities, making size-based discrimination extremely challenging.^22,23 Their quadrupole moments, however, differ substantially (C₂H₂: −29 × 10⁻⁴⁰ C m²; CO₂: −14 × 10⁻⁴⁰ C m²), offering an opportunity for frameworks with confined pores and well-distributed adsorption sites to selectively recognize one molecule over the other.^24–26 Topology-directed pore confinement thus provides a powerful means to amplify such differences, enabling MOFs to achieve separation performance that cannot be obtained through simple surface functionalization.^27,28

Porphyrin-based MOFs (PMOFs) represent a promising but underexplored platform for implementing this concept. The rigid, square-planar geometry of porphyrin ligands promotes ordered frameworks, while their π-conjugated cores impart stability and tunability.^29,30 Among them, tetrakis(4-carboxyphenyl)porphyrin (TCPP) has been most widely employed, as its four carboxylate groups readily coordinate with high-valent metals.^31,32 However, when combined with metals such as Al³⁺ or Y³⁺, TCPP typically forms frameworks with large one-dimensional channels (>10 Å).^33,34 These structures are chemically stable but suffer from loose packing and oversized pore apertures, thereby limiting their ability to discriminate between small molecules. Attempts with transition metals such as Zn²⁺ or Cu²⁺ can, in principle, yield more compact frameworks since these metals can also coordinate to the porphyrin core.^35,36 Nevertheless, most reported transition-metal PMOFs crystallize as layered structures or interpenetrated networks, leading to limited porosity and reduced tunability.^37–39 Traditional single-ligand PMOFs (e.g., Al- and Y-TCPP) therefore produce loosely packed frameworks with large pore apertures, whereas the dual-ligand approach, by introducing an auxiliary triazole ligand, converts TCPP into a 5-connected node and directs the assembly of densely packed frameworks with compressed pore windows (Scheme 1).

Scheme 1 Topology-directed dual-ligand strategy for pore-window compression in porphyrinic MOFs.

Building on this rationale, short N-donor linkers such as imidazoles and triazoles provide an effective means of stabilizing high-connectivity secondary building units (SBUs), suppressing interpenetration, and guiding frameworks toward compact topologies.^40–42 Integrating such linkers with porphyrins offers a powerful means to merge the rigidity of porphyrins with tunable pore confinement, yet this dual-ligand approach has rarely been applied in porphyrinic systems. In this work, we report a new PMOF, Zn-TCPP-dmtrz, synthesized from Zn²⁺, TCPP, and 3,5-dimethyl-1,2,4-triazole (dmtrz). The introduction of dmtrz converts TCPP into a 5-connected node, which, together with Zn SBUs, directs the formation of a distinctive (5,10)-connected fit topology. The resulting framework is densely packed and features one-dimensional rectangular channels with ultramicroporous apertures of 6.3 × 6.8 Å. Compared with conventional Al- and Y-TCPP analogues, this design compresses pore size and enhances confinement, enabling more effective recognition of C₂H₂ relative to CO₂. Static adsorption isotherms at 298 K and 1 bar reveal preferential C₂H₂ uptake (4.30 mmol g⁻¹) over CO₂ (2.61 mmol g⁻¹), with a separation potential (ΔQ) of 1.6 mmol g⁻¹ for equimolar C₂H₂/CO₂ mixtures—substantially higher than conventional TCPP-based MOFs. Dynamic breakthrough experiments demonstrate stable C₂H₂/CO₂ separation over 5 cycles, while static adsorption–desorption tests confirm full retention of capacity after 10 cycles, underscoring the framework's robust recyclability. Even under high humidity (90% RH), Zn-TCPP-dmtrz preserves its separation performance without noticeable degradation. The relatively low initial isosteric heat of adsorption (28.5 kJ mol⁻¹ for C₂H₂) suggests facile regeneration, a critical advantage for industrial applications. Moreover, Grand Canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations reveal that C₂H₂ molecules preferentially adsorb at the porphyrin-Zn interface, where confinement-enhanced van der Waals interactions dominate. This work pioneers a topology-guided design strategy for PMOFs, demonstrating how coordination-driven pore compression can unlock their potential for precision gas separations.

2. Results and discussion

Zn-TCPP-dmtrz was synthesized through a solvothermal reaction of Zn(NO₃)₂·6H₂O, TCPP, and dmtrz in a mixed solution of N,N-dimethylformamide (DMF), water, and a minimal amount of HNO₃ at 140 °C for 72 hours, yielding black-purple block-shaped crystals. Single-crystal X-ray diffraction (SCXRD) studies reveal that the structure of Zn-TCPP-dmtrz belongs to the monoclinic crystal system and C2 space group (Table S1). Structural analysis identifies three distinct Zn²⁺ coordination environments (Fig. 1a and S1): the first Zn center adopts a five-coordinate geometry, ligated by three oxygen atoms from two carboxylate groups of adjacent TCPP ligands, one nitrogen atom from a dmtrz ligand, and one oxygen atom from a μ₃-OH group; the second Zn center exhibits a six-coordinate octahedral geometry, coordinated to four carboxylate oxygen atoms from four distinct TCPP ligands and two μ₃-OH oxygen atoms; and the third Zn center is chelated within the porphyrin macrocycle, coordinating to four nitrogen atoms of the porphyrin core and axially binding to a nitrogen atom from a dmtrz ligand, forming a five-coordinate square pyramidal geometry. This unusual axial coordination mode at the porphyrin center arises directly from the dense packing of the framework. The assembly of a pentanuclear Zn cluster—comprising four five-coordinate Zn ions and one six-coordinate Zn ion (Fig. 1a)—shortens the interlayer distance between adjacent porphyrin planes, sterically hindering ligand binding at the opposite axial site (Fig. 1b). Consequently, the porphyrin-chelated Zn center adopts an asymmetric five-coordinate geometry, bonding exclusively to a single dmtrz ligand. This multimodal coordination strategy drives the formation of two distinct secondary building units (SBUs) (Fig. 1a and b): a pentanuclear Zn cluster acting as a 10-connected node through linkages to eight TCPP carboxylates and two dmtrz ligands, and a 5-connected TCPP unit formed by the porphyrin-chelated Zn center, which bridges four carboxylate-linked Zn clusters and one axial dmtrz ligand. The interconnection of these SBUs, mediated by tritopic dmtrz spacers, generates a three-dimensional framework with a novel (5,10)-connected fit topology in porous coordination polymers (Fig. 1c), marking the first example of this topology in metal–organic frameworks. The framework features unidirectional rectangular channels along the c-axis (Fig. 1d and e), with pore dimensions of 6.3 × 6.8 Å, as determined by Connolly surface analysis (Fig. 1f). Notably, the staggered arrangement of porphyrin planes and Zn clusters at all four channel corners (Fig. 1e) creates a confined ultramicroporous environment, distinct from conventional PMOFs, where partial corner occupation by elongated metal-carboxylate chains or vertically aligned porphyrins leads to larger apertures. This asymmetric distribution of SBUs compresses the pore aperture into the ultramicroporous regime while introducing a diverse chemical environment: the π-conjugated porphyrin walls enhance the van der Waals interactions with C₂H₂, facilitating its selective adsorption in C₂H₂/CO₂ mixtures, while the hydrophobic methyl groups of dmtrz ligands project into the channels, minimizing competitive H₂O adsorption that could otherwise interfere with the C₂H₂ recognition.

Fig. 1 (a) The structure of the building blocks of Zn-TCPP-dmtrz and the corresponding polyhedral model; (b) polyhedral simplification of the SBUs; (c) the (5,10)-connected fit topology of Zn-TCPP-dmtrz; (d) 3D framework of Zn-TCPP-dmtrz along the c-axis; (e) polyhedral view of the framework structure; (f) Connolly surface representation of the pores in Zn-TCPP-dmtrz. Color code: Zn, light blue; O, red; N, blue; C, gray; H, white.

The phase purity and structural integrity of Zn-TCPP-dmtrz are confirmed by powder X-ray diffraction (PXRD, Fig. S2). The experimental patterns of both the as-synthesized and activated samples closely match the simulated pattern derived from single-crystal data. Scanning electron microscopy (SEM) images, presented in Fig. S3a, reveal uniform block-shaped particles with sizes ranging from 50 to 100 μm. Elemental mapping via SEM-EDX (Fig. S3b) shows a homogeneous distribution of C, N, O, and Zn across the framework, which is further confirmed by X-ray photoelectron spectroscopy (XPS) data (Fig. S4). According to the single-crystal X-ray diffraction results (CCDC 2410049) and the XPS elemental composition, the molecular formula of Zn-TCPP-dmtrz is determined to be Zn₇(μ₃-OH)₂(TCPP)₂(dmtrz)₂(DMF)₂. The XPS analysis confirms the presence of Zn²⁺, with a binding energy of 1021.9 eV for the Zn 2p_3/2 peak, and provides information about the coordination environment of nitrogen species, including triazole N at 399.8 eV and pyrrolic N at 401.7 eV (Fig. S5).⁴³ Fourier-transform infrared spectroscopy (FT-IR, Fig. S6) reveals characteristic peaks at 1119.5 and 1347.0 cm⁻¹ corresponding to C–N stretching vibrations of the porphyrin ring, at 989.2 cm⁻¹ for N–N stretching in dmtrz ligands, and at 531.4 and 429.7 cm⁻¹ for Zn–O and Zn–N bonds, respectively.⁴⁴ The N₂ adsorption isotherm at 77 K (Fig. S7) exhibits a type I adsorption curve, characteristic of microporous materials, with a calculated Brunauer–Emmett–Teller (BET) surface area of 829 m² g⁻¹ and a pore volume of 0.34 cm³ g⁻¹. Non-local density functional theory (NLDFT) calculations show a narrow pore size distribution centered at 0.5–0.8 nm, which aligns well with the crystallographic pore dimensions. Thermogravimetric analysis (TGA, Fig. S8) shows that the framework remains stable up to 380 °C before decomposition begins, demonstrating its excellent thermal stability. Overall, these comprehensive characterization studies confirm the successful synthesis of Zn-TCPP-dmtrz as a highly crystalline, thermally stable, and ultramicroporous material, making it suitable for gas separation applications.

Inspired by its ultramicroporous characteristics, the adsorption performance and separation potential of Zn-TCPP-dmtrz for C₂H₂ and CO₂ are systematically examined. As shown in Fig. 2a, single-component adsorption isotherms for both gases are measured at various temperatures using a BSD-660M sorption analyzer (BSD Instruments). The results clearly indicate a stronger affinity for C₂H₂ than for CO₂ under identical conditions. Specifically, at 298 K and 1 bar, Zn-TCPP-dmtrz exhibits a C₂H₂ adsorption capacity of 4.30 mmol g⁻¹, outperforming several well-established porous materials, such as SOFOUR-TEPE-Zn (3.98 mmol g⁻¹),⁴⁵ ZJU-74 (3.83 mmol g⁻¹),⁴⁶ JNU-1 (3.35 mmol g⁻¹),⁴⁷ Zn-bpy-DLmal (3.10 mmol g⁻¹),⁴⁸ and NKMOF-1-Ni (2.74 mmol g⁻¹)⁴⁹ (Table S4). In contrast, the CO₂ uptake is considerably lower, with Zn-TCPP-dmtrz adsorbing only 2.61 mmol g⁻¹ under the same conditions. Furthermore, when the temperature is adjusted to 283 K or 313 K, the C₂H₂ uptake remains significantly higher than that of CO₂ at both temperatures, reaffirming the stronger interaction between C₂H₂ and the framework. To better understand the differences in C₂H₂ and CO₂ adsorption behavior across TCPP-based adsorbents, we synthesize seven different TCPP-based PMOFs incorporating various metals, comparing their C₂H₂ and CO₂ adsorption performance with that of Zn-TCPP-dmtrz (Fig. S9–S17). Among these materials, Al-TCPP shows the highest C₂H₂ uptake (3.89 mmol g⁻¹), but it is still lower than that of Zn-TCPP-dmtrz, while most of the other PMOFs, such as Y-TCPP, demonstrate much lower capacities due to the larger pore size weakening the interactions with C₂H₂. Interestingly, Al-TCPP and In-TCPP also exhibit relatively strong CO₂ adsorption capacities, further distinguishing Zn-TCPP-dmtrz for its superior C₂H₂/CO₂ adsorption capacity difference, highlighting its significant potential for C₂H₂/CO₂ separation.

Fig. 2 (a) C₂H₂ and CO₂ adsorption isotherms of Zn-TCPP-dmtrz at 283–313 K; (b) comparison of C₂H₂ and CO₂ uptake at 298 K and 1 bar for Zn-TCPP-dmtrz and other TCPP-based PMOFs; (c) C₂H₂ adsorption isotherms of Zn-TCPP-dmtrz for 10-cycle tests at 298 K; (d) separation potential (ΔQ) curves and comparison of Zn-TCPP-dmtrz with other TCPP-based PMOFs for a 50 : 50 C₂H₂/CO₂ mixture at 298 K; (e) Q_st of C₂H₂ and CO₂ for Zn-TCPP-dmtrz; (f) comparison plot for Q_st of C₂H₂ and C₂H₂ uptake at 1 bar and 298 K.

The stability and regeneration potential of Zn-TCPP-dmtrz are evaluated through 10 adsorption–desorption cycles for both C₂H₂ and CO₂ (Fig. 2c and S18). The results indicate that the adsorption capacities are well-maintained, confirming excellent cycling stability. To further assess its separation capability, we employ the Ideal Adsorbed Solution Theory (IAST) to calculate the selectivity for C₂H₂/CO₂ (50/50). The dual-site Langmuir (DSL) model fits the adsorption isotherms with high precision (Fig. S11–S17, S19 and Table S2), and the IAST selectivity for C₂H₂/CO₂ at 298 K and 1 bar is 2.63 for Zn-TCPP-dmtrz, outperforming other TCPP-based PMOFs such as In-TCPP (2.39), Y-TCPP (1.77), and Al-TCPP (1.07) (Fig. S20). Furthermore, the maximum recoverable C₂H₂ from a C₂H₂/CO₂ mixture, represented by the separation potential (ΔQ), is calculated to be 1.62 mmol g⁻¹ for Zn-TCPP-dmtrz, which is significantly higher than other PMOFs, including In-TCPP (1.10 mmol g⁻¹) (Fig. 2d). This highlights the exceptional potential of Zn-TCPP-dmtrz for efficient C₂H₂ selectivity and purification. Additionally, the adsorption heat (Q_st), indicative of the binding affinity between the framework and the guest molecules, is determined using adsorption isotherms at different temperatures and fitted with the Virial equation (Fig. S11–S17, S21, and Table S3). The Q_st for C₂H₂ is 28.5 kJ mol⁻¹ at low loading, demonstrating that Zn-TCPP-dmtrz allows for energy-efficient regeneration (<30 kJ mol⁻¹), whereas the Q_st for CO₂ is 25.0 kJ mol⁻¹. The noticeable difference in Q_st supports the preferential adsorption of C₂H₂, providing moderate C₂H₂/CO₂ selectivity. Despite other PMOFs having similarly low binding energies for C₂H₂, their low adsorption capacities limit their performance in C₂H₂/CO₂ separation. In contrast, Zn-TCPP-dmtrz, as a representative of a fit-topology PMOF, combines high C₂H₂ adsorption capacity and excellent regeneration potential, making it a promising candidate for C₂H₂ purification with lower energy consumption compared to other PMOFs and conventional adsorbents (Fig. 2f).

To evaluate the practical C₂H₂/CO₂ separation performance of Zn-TCPP-dmtrz, dynamic breakthrough measurements are carried out at 298 K on a fixed-bed column packed with the activated PMOF and fed with a 50 : 50 C₂H₂/CO₂ mixture at 2 mL min⁻¹ (Fig. 3a). CO₂ elutes first at 12.3 min g⁻¹, affording 9.08 cm³ g⁻¹ of 99.95% pure CO₂, whereas C₂H₂ remains on the column until 23.5 min g⁻¹, yielding a dynamic uptake of 41.22 cm³ g⁻¹ (61.1% of the 298 K isotherm capacity). In contrast, Y-TCPP demonstrates weak interactions with C₂H₂, resulting in a shorter breakthrough time for C₂H₂ (9.1 min g⁻¹), and although Al-TCPP delays C₂H₂ breakthrough to 16.4 min g⁻¹, its CO₂ elution at 19.8 min g⁻¹ does not precede C₂H₂, precluding direct recovery of high-purity CO₂. Since C₂H₂ is recovered during desorption, the regeneration step is assessed by purging the saturated column with He (10 mL min⁻¹) at 333 K (Fig. 3b, S22 and S23). Zn-TCPP-dmtrz releases CO₂ completely within 4 min g⁻¹, enabling collection of C₂H₂ at >99.5% purity with a yield of 29.80 cm³ g⁻¹ (72.3% of the dynamic uptake), whereas Y-TCPP desorbs both gases rapidly—resulting in only 5.00 cm³ g⁻¹ C₂H₂—and Al-TCPP shows no selective C₂H₂ recovery (Fig. 3c). To probe operational feasibility, breakthrough tests under varied flow rates (3 and 5 mL min⁻¹; Fig. 3d) and temperatures (283 and 313 K; Fig. S24) maintain one-step high-purity CO₂ elution. Finally, Zn-TCPP-dmtrz retains its separation performance over five consecutive cycles without detectable change (Fig. 3e), and exhibits outstanding moisture resilience: after six months of air exposure, 48 h at 90% RH, or 24 h water immersion, PXRD patterns and 77 K N₂ isotherms show unchanged crystallinity and BET surface area (Fig. S25), and humid-condition breakthrough (Fig. 3f) yields identical elution profiles—attributable to the hydrophobic methylated triazole groups—underscoring its recyclability and stability under realistic conditions.

Fig. 3 Dynamic breakthrough and regeneration performance of Zn-TCPP-dmtrz and comparison with other PMOFs for C₂H₂/CO₂ (50 : 50, v/v) at 298 K: (a) breakthrough curves of Zn-TCPP-dmtrz, Al-TCPP and Y-TCPP at 2 mL min⁻¹; (b) desorption profiles of C₂H₂ and CO₂ from Zn-TCPP-dmtrz during He purge (10 mL min⁻¹) at 333 K; (c) comparison of C₂H₂ dynamic uptake and productivity among the three PMOFs; (d) breakthrough curves of Zn-TCPP-dmtrz at flow rates of 3 and 5 mL min⁻¹; (e) five consecutive breakthrough cycles for the 50 : 50 C₂H₂/CO₂ mixture; and (f) breakthrough behavior of Zn-TCPP-dmtrz under dry and humid (∼90% RH) conditions.

To gain deeper insights into the underlying mechanism of C₂H₂/CO₂ separation in Zn-TCPP-dmtrz, grand canonical Monte Carlo (GCMC) simulations and dispersion-corrected density functional theory (DFT-D) calculations are employed to probe the binding sites and interaction strengths of both gases within the framework. GCMC results reveal distinct density distributions for C₂H₂ and CO₂ within the confined pore architecture (Fig. 4a and d). Both gases localize near the porphyrin walls, aromatic rings, and alkyl-functionalized channels, but C₂H₂ exhibits significantly higher adsorption density, consistent with experimental uptake trends. Two primary adsorption sites for C₂H₂ are identified: Site I is situated near symmetrically arranged SBUs formed by TCPP porphyrin rings and dmtrz ligands, where C₂H₂ engages in multiple interactions, including hydrogen bonding between the H atoms of C₂H₂ and both the carboxylate O atoms of TCPP and the methyl H atoms of dmtrz (H⋯O and H⋯H distances ∼4.0 Å) (Fig. 4b). Simultaneously, the C atoms of C₂H₂ form electrostatic interactions (C^δ−⋯H^δ+) with aromatic H atoms (3.79–4.07 Å). Site II, located near the bilayered porphyrin region adjacent to the 10-connected Zn₅ clusters, allows C₂H₂ to form multiple C^δ−⋯H^δ+ interactions with pyrrole moieties (3.21–3.98 Å) and engage in H⋯π interactions with the benzene rings (3.68 Å), as shown in Fig. 4c. In comparison, CO₂ occupies analogous regions (Fig. 4e and f) but interacts via weaker and fewer non-directional van der Waals forces. At Site I, CO₂ forms contacts (3.42–4.08 Å) between its O atoms and aromatic/pyrrolic H atoms, while at Site II, interactions are limited to distances of 3.57–3.99 Å. DFT-D calculations corroborate these observations: the binding energies for C₂H₂ at Sites I and II are 30.5 and 28.0 kJ mol⁻¹, respectively, significantly exceeding those for CO₂ (26.6 and 26.2 kJ mol⁻¹). These findings underscore the critical role of the densely packed π-conjugated porphyrin arrays and alkyl moieties within the ultramicroporous channels in Zn-TCPP-dmtrz, which enable enhanced C₂H₂-framework recognition through the synergistic interplay of hydrogen bonding, electrostatic complementarity, and confinement-enhanced van der Waals interactions, thereby boosting its separation performance. The results highlight the topology-guided structural design principles for developing PMOF-based materials for challenging gas separations.

Fig. 4 Simulated adsorption density maps of (a) C₂H₂ and (d) CO₂ in Zn-TCPP-dmtrz at 298 K and 1 bar; binding configurations of C₂H₂ at (b) Site I and (c) Site II; and binding configurations of CO₂ at (e) Site I and (f) Site II. Color code: Zn-light blue, O-red, C (framework)-gray, N-blue, H-white, C (in C₂H₂)-yellow, C (in CO₂)-pink.

3. Conclusions

In summary, this study presents a strategic advancement in PMOF design by integrating Zn²⁺ coordination and dual-ligand assembly to construct an ultramicroporous architecture (6.3 × 6.8 Å) with tailored pore confinement for efficient C₂H₂/CO₂ separation. Distinct from conventional PMOFs (e.g., Al- and Y-TCPP) with enlarged apertures, the Zn-TCPP-dmtrz framework adopts a novel fit topology—enabled by porphyrin chelation and triazole-mediated SBU densification—which achieves pore channels optimized for C₂H₂ accommodation. This structural design enhances host–guest interactions while maintaining framework stability, resulting in superior C₂H₂ uptake (4.30 mmol g⁻¹) and separation potential (ΔQ = 1.62 mmol g⁻¹) at 298 K and 1 bar, outperforming existing PMOFs in both selectivity (2.63) and regenerability (Q_st = 28.5 kJ mol⁻¹). Computational analyses reveal that staggered porphyrin planes and methyl-functionalized channels synergistically amplify C₂H₂ recognition through van der Waals and electrostatic interactions—mechanisms unattainable in PMOFs with less confined geometries. Remarkable moisture resistance and cycling stability further validate its practical feasibility. By demonstrating the effectiveness of topology-driven pore engineering in PMOFs, this work expands the scope of precision adsorbent design for gas mixtures with near–identical properties, offering a blueprint for future studies to extend this strategy to other industrially relevant separations.

Author contributions

Zhenliang Zhu performed the methodology, data curation, and writing – original draft; Jianfei Xiao contributed to methodology and formal analysis; Min Zhang was involved in formal analysis; Yaoqi Huang contributed to methodology and writing – review & editing; Shaojun Yuan supervised the project, acquired funding, and contributed to project administration, resources, and writing – review & editing.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary Information is available. See DOI: https://doi.org/10.1039/d5sc07319g.

Acknowledgements

The authors would like to acknowledge the financial support provided by the National Natural Science Foundation of China (22578284) and Beijing Welltrailing Science and Technology Co., Ltd (contact no. 2025510005000242) to provide financial support for this study. They also express their gratitude to Dr Ji Li and Mr Pan Wu from the Engineering Teaching Center, School of Chemical Engineering, Sichuan University, for their support in conducting the measurements using the BSD-MAB Analyzer. Furthermore, the authors would like to thank Dr Yingming Zhu from the Institute of New Energy and Low Carbon Technology, Sichuan University, for assistance with the XRD characterization. Additionally, the authors extend their gratitude to Mr Sheng Liu from Scientific Compass (https://www.shiyanjia.com/) for providing invaluable assistance with the single crystal structure determination.

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