Programming Local Confinements in Crystalline Frameworks through Reticular Chemistry

Programming Local Confinements in Crystalline Frameworks through Reticular Chemistry | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Programming Local Confinements in Crystalline Frameworks through Reticular Chemistry Omar Farha, Xianhui Tang, Xiaoliang Wang, Zi-Ming Ye, Shengyi Su, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8090759/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Controlling chemical microenvironments within porous crystalline materials is central to advancing selective adsorption, separation, and catalytic processes, yet remains difficult to achieve in stable frameworks with precisely oriented functional sites. Here, we leverage reticular chemistry to program tunable confinement in triazolate metal–organic frameworks (MOFs) built from Kuratowski-type Zn5Cl4 nodes. Rational modulation of linker geometry targets the ith-d topology in which terminal Zn-bound groups point inward to define confined, chemically addressable pores. This design yields two isoreticular frameworks, NU-6000 and NU-6001, that preserve the overall topology while reconfiguring cage dimensions, apertures, and pore functionality through linker inversion. The frameworks are structurally well-defined and thermally stable beyond 525 °C, and post-synthetic chloride-to-hydroxide exchange installs dense, oriented Zn-OH arrays without loss of crystallinity, enabling strong yet reversible CO2 binding through bicarbonate formation. Single-crystal analysis of a CO2 adduct reveals a geometric accessibility rule in the smallest cage of NU-6000, where only a subset of inward-facing hydroxyls can bind to form bicarbonate, thereby setting an intrinsic upper bound to uptake that is dictated by cage architecture rather than linker count. Under this tunable local-confinement regime in NU-6000, the framework achieves high CO2 uptake across a broad low-pressure range, including at concentrations as low as 30 ppm, and attains a site utilization of 61.4 % at 420 ppm, representing the highest efficiency reported for MOFs under comparable conditions. This work establishes a generalizable approach for encoding functional confinement into robust crystalline frameworks, bridging molecular design with solid-state functionality for selective gas capture and other confinement-driven applications. Physical sciences/Chemistry/Materials chemistry/Metal–organic frameworks Physical sciences/Chemistry/Supramolecular chemistry/Crystal engineering Physical sciences/Materials science/Materials for energy and catalysis/Metal–organic frameworks Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Microenvironments in biological systems, such as the confined pockets of enzymes, are crucial to their extraordinary catalytic performance 1, 2, 3 . These highly organized spaces bring multiple functional groups or active sites into proximity, enabling synergistic interactions that deliver exceptional reaction rates and selectivity 4 . Although enzymes exhibit unparalleled catalytic efficiency 5 , their delicate structures make it challenging to maintain these functions under the harsher conditions typical of industrial processes 6 , motivating the search for stable, bio-inspired materials. Translating the principle of local confinement into a robust, crystalline scaffold, such as a metal-organic framework (MOF), offers an opportunity to recreate these synergistic microenvironments in solid materials 7, 8 (Fig. 1a). By rationally programming the spatial arrangement of functional groups within a stable framework, it becomes possible to design high-performance materials for applications including catalysis, guest-molecule capture, molecular recognition, and gas separation 9, 10, 11, 12, 13, 14, 15, 16, 17 . Despite the utility of this bio-inspired principle, constructing such finely tuned microenvironments within solid materials remains a formidable challenge 18 . Reticular chemistry, guided by the abstract concept of topology and centered on linking molecular building blocks through strong chemical bonds, provides the guidelines for assembling crystalline open frameworks with predetermined connectivity 19, 20 . This approach underpins the modular synthesis of porous materials such as MOFs and covalent organic frameworks (COFs), expanding the accessible landscape of compounds and functional materials 21, 22 . By decoupling framework connectivity from specific chemistries, reticular chemistry enables a given topology to be recreated with distinct linkers or metal nodes, offering a versatile platform for engineering local confinement with tailored chemical environments 23 . To date, most functional MOFs have been constructed from carboxylate linkers 24, 25 . Although these frameworks have delivered impressive performance across many applications, those built from 3d transition metals often suffer from limited stability under humidity, acidic, basic, or high-temperature conditions 26 . Heterocyclic linkers offer a promising route to address these limitations. Among them, triazole-based MOFs, such as MFU-4l, which features a Zn 5 Cl 4 secondary building unit (SBU), stand out for their exceptional stability and chemical versatility 27 . This SBU can undergo transmetalation of Zn with other transition metals (V, Fe, Co, Ni, Cu, Mo) 28, 29, 30, 31, 32, 33, 34, 35 and exchange of terminal ligands (Cl for Me, OH, NO 3 , H, SH) 9, 10, 12, 36, 37 while retaining the overall framework, offering a powerful platform for tailoring local environments and introducing biomimetic functionality. Yet, the diversity of known triazole-based MOFs remains strikingly narrow: beyond MFU-4 38 , MFU-4l 39 , CFA-1 40 , CFA-7 41 , CFA-19 42 , and a recent example of Zn 5 (OAc) 4 (TBTT) 2 , which employs a non-conjugated tritopic benzotriazole linker 43 , only a handful of structures have been reported over the past two decades. Developing reticular chemistry-based strategies to construct new MOFs from Kuratowski-type building blocks 40 , with topologies that enable local confinements, would greatly expand this family’s structural diversity and enable the precise tuning of local environments for enhanced performance across a range of potential applications. From a geometric and topological perspective, the Zn 5 Cl 4 SBU adopts T d symmetry with a connectivity of six 44 , making it a geometric analog of the Zn 4 O cluster in the prototypical carboxylate-based MOF-5 45 (Fig. 1b). Based on the Kuratoski-type SBUs, triazole-based MOFs such as MFU-4 and MFU-4l are isoreticular to MOF-5 and the IRMOF series 46 with pcu topology, while CFA-1 is isoreticular to Zn 4 (μ 4 -O)[(Metrz- p ba) 2 m Ph] 3 47 with acs topology. Both cases provide a strategy for constructing Zn 5 Cl 4 SBU-based MOFs by topology transfer from Zn 4 O SBU MOFs. On the other hand, in both cases, only a single type of ditopic linker connects the metal clusters, resulting in one type of cavity. Bringing cluster nodes together to create local confinement usually comes at the expense of overall porosity, potentially limiting the diffusion of the guest molecules. Frameworks with multiple types of cages can overcome this challenge by using one type of cage for local confinement while leaving the other cages for diffusion and porosity. Achieving these architectures requires moving beyond frameworks with only one type of connectivity; introducing linkers with multiple connectivities opens access to otherwise unattainable nets. For example, in the Zn 4 O-carboxylate MOF family, MOF-905 48 and MOF-205 49 adopt the ith-d topology with two distinct cage types, arising from the combination of tritopic and ditopic linkers. Inspired by this design, we introduced two additional tritopic linkers into the MFU-4 system, which contains Zn 5 Cl 4 nodes and the original ditopic BBTA (1,5-dihydrobenzo[1,2-d:4,5-d']bis([1,2,3]triazole) linker, yielding two new Zn 5 Cl 4 -triazole MOFs with ith-d topology, NU-6000 and NU-6001 . These represent the first examples of triazole-based MOFs with this topology, expanding the structural diversity accessible to this class of frameworks. NU-6000 and NU-6001 not only adopt desirable topologies analogous to MOF-205 but also display remarkable thermal stability and tunable sorption behavior through post-synthetic modification that replaces terminal chlorides with hydroxides. Moreover, altering the dihedral angle between the triazole plane and the C 3 axis of the tritopic linker affords the same overall topology but generates distinct local confinements within the pores. In NU-6000 , the co-planar geometry of TPHTA directs the formation of two types of cages: a smaller cage with Zn sites oriented inward, creating confined environments that can promote synergistic interactions, and a larger cage lacking closely positioned metal sites. In contrast, NU-6001 , which is constructed from the tritopic TPTTA linker that adopts a 90° dihedral angle, contains two cages of similar size without closely spaced metal centers. Hydroxyl-substituted versions of NU-6000 show a pronounced enhancement of CO 2 uptake at low concentrations, attributed to local interactions between the -CO 3 H moiety on one Zn site and -OH groups on adjacent Zn sites through hydrogen bonding interactions. In NU-6001 , such synergistic interactions are absent, highlighting how reticular design strategies can be used to tune local confinement and reactivity within triazole-based MOFs. Results and discussion Synthesis and structural characterization . Two triazole-based ligands, 6,11-dihydro-1H-triphenyleno[2,3-d:6,7-d':10,11-d'']tris([1,2,3]triazole) ( TPHTA) and 7,13-dihydro-1H-9,10-dihydro-9,10-[1,2]benzenoanthraceno[2,3-d:7,8-d':12,13-d'']-tris([1,2,3]triazole) ( TPTTA) , were synthesized based on planar triphenylene and stereoscopic triptycene backbones, respectively. These linkers were combined with BBTA and ZnCl 2 to yield NU-6000 and NU-6001 , respectively, in N , N -dimethylformamide (DMF) at 140 °C for 3 days. 3D micro-electron diffraction (micro-ED) analysis reveals that both frameworks adopt the ith-d topology with Zn 5 Cl 4 nodes and formulas [(Zn 5 Cl 4 ) 3 ( TPHTA ) 4 ( BBTA ) 3 ] ( NU-6000 ) and [(Zn 5 Cl 4 ) 3 ( TPTTA ) 4 ( BBTA ) 3 ] ( NU-6001 ). Their phase purity was confirmed by comparing their experimental and simulated PXRD patterns. (Fig. 3a,d). Thermogravimetric analysis (TGA) revealed that in NU-6000 and NU-6001 , the solvent molecules, methanol and water are removed between 50 and 150 °C, with decomposition beginning at approximately 500 °C under air (Supplementary Fig. 32 and 33). Variable-temperature powder X-ray diffraction (VT-PXRD) analysis confirms that both materials maintain crystallinity up to 525 °C (Fig. 3b,e). Their permanent porosities were evaluated by gas sorption isotherms after exchanging the solvent to methanol and then activating under a dynamic vacuum at 200 °C, as shown in Fig. 3c,f. Despite its high crystallinity, NU-6000 exhibits minimal N 2 uptake at 77 K, which is attributed to the small pore apertures. Therefore, CO 2 , which has a smaller kinetic diameter (3.3 Å), was used to probe the accessible porosity of NU-6000 at 195 K (Supplementary Fig. 36), yielding a Brunauer-Emmett-Teller (BET) area of 980 m 2 /g, and the pore volume of 0.64 cm 3 /g is given by water sorption isotherm (Supplementary Fig. 37). In comparison, NU-6001 exhibits higher porosity, with a BET area of 1230 m 2 /g and a pore volume of 0.68 cm 3 /g, giving rise to a typical type I isotherm (Supplementary Fig. 38). The BET areas and pore volumes of NU-6000 and NU-6001 are both approximately equal to their calculated values, suggesting that the guest molecules are successfully removed from these frameworks under the employed activation conditions. Structure analysis and description. Micro-ED analysis demonstrates that NU-6000 crystallizes in the cubic space group Pm-3n , and the asymmetric unit contains one-sixth TPHTA , one-fourth BBTA , and one-fourth T d symmetrical pentanuclear [Zn 5 Cl 4 ] 6+ secondary building units. Each [Zn 5 Cl 4 ] 6+ node adopts an octahedral geometry, which is similar to the Zn 4 O node in MOF-5, with the basal plane defined by four triazoles from four linkers TPHTA , and the axial positions are occupied by two BBTA (Supplementary Fig. 14a). In NU-6000 , each TPHTA coordinates to three [Zn 5 Cl 4 ] 6+ units through three triazole groups (Supplementary Fig. 14c), and each BBTA coordinates to two [Zn 5 Cl 4 ] 6+ units through two triazole groups (Supplementary Fig. 14b). The ditopic and tritopic ligands link the [Zn 5 Cl 4 ] clusters to generate an ith-d network with 2,3,6 connectivity (Fig. 2a). To illustrate the three-dimensional pore architecture of NU-6000 , we carried out natural tiling with 3dt software 50, 51 . The analysis shows a 3-periodic network composed of two tile types and characterized by a transitivity of [2212] (Fig. 2d). The NU-6000 features two distinct cages: Cage 1 is a small cavity with a window of approximately 0.35 nm, where four chloride ions are positioned inward. The Cl···Cl distances are 4.8 and 3.8 Å, indicating a confined opening that plays a key role in the gas adsorption behavior of NU-6000 . Cage 2 is significantly larger, measuring approximately 1.9 nm in diameter with a 0.35 nm aperture. Calculations using PLATON show that NU-6000 has approximately 61.6% of the total volume occupied by anions and solvents. 52 By rotating the coordinated arms of the linkers by 90° along the triazole direction (Supplementary Fig. 13), the isoreticular MOF NU-6001 was obtained under the same conditions as NU-6000 . NU-6001 (Fig. 1d) also crystallizes in the cubic space group Pm-3n, with one-sixth TPTTA , one-fourth BBTA , and one-fourth T d symmetrical pentanuclear [Zn 5 Cl 4 ] 6+ SBUs occupying the asymmetric unit. Each [Zn 5 Cl 4 ] cluster adopts an octahedral coordination geometry, with the equatorial plane defined by four triazole donors from four distinct TPTTA linkers, and the axial positions occupied by two BBTA linkers (Supplementary Fig. 18a). Each TPTTA ligand bridges three [Zn 5 Cl 4 ] 6+ nodes through its three triazole groups (Supplementary Fig. 18c), while each BBTA linker connects two [Zn 5 Cl 4 ] 6+ clusters via two triazole donors (Supplementary Fig. 18b). The topology of NU-6001 , like that of NU-6000 , is classified as the known 2,3,6-connected ith-d net with the same tiling features (Fig. 2a). In the 3D framework, two types of cages are formed with a diameter of ~1.4 nm (Cage 1) and ∼1.0 nm (Cage 2) (Supplementary Fig. 20). Notably, all 12 chloride atoms point inward toward Cage 1, which can potentially influence guest uptake. The extended 3D porous framework (Fig. 1d and Supplementary Fig. 19) exhibits ~61.3% free volume. 52 Typically, isoreticular MOFs are designed by changing the length or width of linkers or through post-synthetic modification of the framework. However, it has not been previously reported that flipping the coordinated arms of the linkers (Supplementary Fig. 13) can invert the entire framework to yield an isoreticular structure. In MOFs constructed from carboxylates or pyridyl linkers, these linkers can freely rotate about single bonds even after coordination to SBUs. As a result, the entire framework does not invert, even when the linker core is rotated, and this rotational flexibility facilitates framework formation by allowing the linker to self-adapt to the coordination geometry of the nodes. In contrast, for triazole-based linkers in which the triazole group is conjugated with the core skeleton, rotation along the arm direction is restricted. The triazole groups must coordinate to the [Zn 5 Cl 4 ] 6+ nodes at specific angles defined by the three coordinated sites between the linker and node. Therefore, triazole-based MOFs constructed by conjugated linkers require not only a suitable geometric match between linker and node coordination modes, but also a topology compatible with this configuration. These stringent geometric and electronic requirements have so far limited the diversity of triazole-based MOFs. Accordingly, in this work, the entire frameworks of NU-6000 or NU-6001 must invert as the linker inverts, especially the tritopic linker, reflecting the transformation between the planar TPHTA and the stereoscopic TPTTA . On the [Zn 5 Cl 4 ] 6+ node, the opposing coordination sites along any axis of the T d symmetric node are separated by 90°, precisely matching the rotation angle between TPHTA and TPTTA . This geometric match between linker flipping and [Zn 5 Cl 4 ] 6+ node coordination orientation enables the formation of two distinct yet isoreticular frameworks, NU-6000 and NU-6001 . Despite the significant difference in spatial configuration between the planar TPHTA and the twisted TPTTA , both linkers assemble with the same node while preserving the overall ith-d topology. The rigid coordination geometry of the triazole groups, combined with the symmetric yet angular nature of the [Zn 5 Cl 4 ] 6+ node, thus enforces a global inversion of the framework upon switching between TPHTA and TPTTA . This phenomenon of framework inversion induced by linker flipping represents a new level of structural control in MOF design, where topological isoreticularity is maintained not through linker flexibility but through precise geometric alignment. It also highlights the critical interplay between linker rigidity and node symmetry in governing framework propagation, particularly in systems built from multidentate, conjugated triazole linkers. CO 2 adsorption. Building upon this structural insight, we next sought to investigate how the distinct pore architectures and internal environments of NU-6000 and NU-6001 influence their gas adsorption behavior, with a particular focus on CO 2 capture. Although these two MOFs are isoreticular and share the same underlying topology, the difference in linker geometry, with TPHTA being planar and TPTTA stereoscopic, leads to notably different cage dimensions, aperture sizes, and chloride-ion orientations. In NU-6000 , the tight apertures (~0.35 nm) and inward-facing chloride ions create a highly confined microporous environment, which is expected to impose significant kinetic restrictions on gas diffusion, especially for larger gas molecules. Conversely, NU-6001 features larger cages and more accessible pore windows, offering enhanced molecular accessibility while retaining the same chemical composition and node-linker connectivity. Given these structural distinctions, we imagined that the frameworks would exhibit markedly different sorption behaviors, despite their isoreticular relationship. To validate these hypotheses, we conducted a series of gas adsorption experiments under controlled conditions, with emphasis on CO 2 sorption at room temperature, to quantitatively assess how framework inversion affects guest accessibility and storage capacity. In particular, we anticipated that NU-6001 would demonstrate higher CO 2 uptake and more rapid adsorption kinetics due to its larger, less sterically hindered pore system, whereas NU-6000 might exhibit selective adsorption toward smaller gas molecules, such as CO 2 , owing to its narrow aperture and potential for strong electrostatic interactions with the exposed chloride ions. In addition, we performed post-synthetic modifications to NU-6000 and NU-6001 to exchange the terminal chloride ions with terminal hydroxide groups, which we anticipated would improve the CO 2 capture performance of these materials. First, NU-6000- HCO 3 and NU-6001 -HCO 3 were prepared by soaking NU-6000 and NU-6001 in aqueous solutions of NaHCO 3 , followed by subsequent washing with water and organic solvents. 37 After heating at 200 °C under vacuum for 2 h, NU-6000-OH and NU-6001-OH were obtained and confirmed by crystal structure (Fig. 5a-c and Supplementary Fig. 24) and DFITS (Fig. 5e,f and Supplementary Fig. 43 and 44). PXRD patterns of the ligand-exchanged MOFs closely match those of NU-6000 and NU-6001 , confirming that the post-synthetic modifications do not cause any major structural changes (Fig. 3a,b). Moreover, the disappearance of Cl 2p signals in the X-ray photoelectron spectra (XPS) indicates nearly quantitative exchange of chloride regardless of the post-synthesis linker exchange method used (Supplementary Fig. 39 and 40). The parent frameworks NU-6000 and NU-6001 display smooth, nearly linear CO 2 uptakes up to 1 bar (Fig. 4a), characteristic of physisorption. Across the whole pressure range, NU-6000-OH adsorbs more CO 2 than NU-6001-OH . At low CO 2 partial pressures, the chemisorptive interactions between CO 2 and the Zn-OH functional groups dominate, resulting in steep CO 2 uptake at low pressures (1-10 mbar, 0.1-1% CO 2 ) and ultra-low pressures (20 mbar), however, NU-6000-OH shows similar or slightly greater capacities than NU-6001-OH . For instance, NU-6000-OH adsorbs ~2.1 mmol/g and NU-6001-OH reaches ~1.7 mmol/g (Fig. 4b) at 298 K and 150 mbar, representative of post-combustion streams. This trend highlights the significant effect of pore confinement in the physisorption MOF series, besides chemical binding sites. 53, 54, 55 Under lower CO 2 concentrations in which the driving force is minimal and site efficiency becomes limiting, NU-6000-OH achieves 1.2 mmol/g at 0.4 mbar, comparable to NbOFFIVE-1-Ni (~1.3 mmol/g) 56 and below chemisorptive amine-functionalized benchmarks such as Mg 2 (dobpdc)(en) 0.33 (~2.8 mmol/g) 57 and Mg 2 (dobdc)(N 2 H 4 ) 1.8 (~3.9 mmol/g) 58 . Notably, this level is reached without pendant amines, offering a chemically robust alternative that mitigates known amine-deactivation pathways while preserving high low-pressure uptake. The contrast between NU-6000-OH and NU-6001-OH (0.32 mmol/g) underscores the role of linker geometry and aperture tuning in raising the fraction of sites that react with CO 2 at 420 ppm. Due to the small cavity size of Cage 1 in NU-6000-OH , only two of the four Zn-OH groups oriented toward the cavity (geometrically accessible), at most, can chemically bind with CO 2 to form HCO 3 - , as can be clearly observed from the single-crystal structure of NU-6000-OH after CO 2 binding (Fig. 5c). In the field of direct air capture (DAC, 420 ppm CO 2 ), the performance of an adsorbent is determined not only by the number of chemically active sites (site loading), but also by the fraction of these sites that can react with CO 2 under low-concentration conditions, known as the site efficiency. Numerous studies 59 have shown that even when MOFs are functionalized with a high density of hydroxyl, amine, or other CO 2 -philic groups, only a limited proportion of these sites participate in the formation of bicarbonates or carbamates during DAC. Typical conversion ratio of reacted CO 2 per site (site efficiency) ranges from 5% to 40%. For example, the mono-hydroxyl functionalized CFA-1-OH 37 exhibits a site efficiency of 34.6%, while Ni-CFA-1-OH 60 improves this to 41.5%. In contrast, MFU-4-OH and MFU-4l-OH, which both feature [Zn 5 Cl 4 ] 6+ nodes, utilize only 10.9% and 8.2% of their available sites for CO 2 binding, respectively. Similarly, amine-functionalized MIL-101(Cr)-TAEA 61 or MOF-808-Lys 62 have site efficiencies below 20%. This means that most chemical adsorption sites remain “idle” under DAC conditions, limiting the practical CO 2 capture capacity. Unlike many MOFs where virtually all nominal sites are accessible under working conditions, steric confinement in NU-6000-OH imposes an upper bound of two opposing –OH groups per cavity as geometrically accessible sites. Under DAC-relevant conditions (0.4 mbar CO 2 ), 61.4% of these accessible sites are actually engaged by CO 2 (per-accessible-site engagement), corresponding to 30.7% relative to all nominal –OH sites. This confinement-controlled limitation of accessible sites leads to a 61.4% per-accessible-site engagement, surpassing prior reports for chemisorption-based MOFs in the ultra-dilute regime. (Fig. 4c) 37, 54, 57, 58, 60, 61, 62, 63, 64, 65 . This performance is attributed to an extreme spatial confinement effect. By precisely tuning the pore aperture and the spatial arrangement of functional sites, CO 2 molecules entering the pore channels are effectively directed to the reactive centers. As a result, the majority of functional sites can chemically bind CO 2 . This design concept not only maximizes CO 2 uptake capacity, but also provides a new paradigm for developing high-efficiency, low-cost, and scalable adsorbents for DAC applications. In the ultra-dilute regime (~30 ppm CO 2 ), relevant to tail-end polishing of high-purity gas streams and to the local ultra-low CO 2 partial pressures encountered near the adsorption front in air contactors, adsorption performance is governed less by nominal site density than by intrinsic binding affinity and site efficiency. Under such conditions, where the driving force for adsorption is minimal, most porous materials operate near their baseline capacity. Remarkably, NU-6000-OH maintains measurable uptake across a wide pressure range, from industrially relevant 150 mbar (~15% CO 2 , flue gas) down to 0.4 mbar (~420 ppm, air) and retains exceptional performance even at 0.03 mbar (~30 ppm). The sustained uptake of 1.1 mmol/g at 30 ppm CO 2 demonstrates that the chemisorptive Zn–OH sites in NU-6000-OH are both sufficiently strong and readily accessible, reflecting the intended coupling between functional-site density and aperture-level mass transport. By contrast, the parent NU-6000 and its isostructural analogue NU-6001 exhibit negligible CO 2 uptake in the low- and ultra-low-pressure regions, confirming that hydroxyl functionalization is essential for generating active Zn–HCO 3 binding sites in NU-6000-OH and NU-6001-OH . Isosteric heat of adsorption ( Q st). CO 2 adsorption isotherms were collected over 288-308 K, and the isosteric heat of adsorption ( Q st) was obtained as a function of loading (n) from the Clausius-Clapeyron relation (Fig. 4d, Supplementary Fig. 41, and 42). For the parent frameworks NU-6000 and NU-6001 , Qst values fall within the physisorption regime and remain essentially constant with loading. NU-6000 shows a modest decrease from ~30 kJ/mol at very low n to a plateau of ~23-24 kJ/mol, while NU-6001 exhibits a slight monotonic increase toward ~23 kJ/mol across the measured range. These trends are consistent with pore filling on predominantly dispersive sites and a relatively homogeneous adsorption landscape in the parent materials. In contrast, the -OH-modified analogs display pronounced loading-dependent Qst values. NU-6001-OH rises to a maximum of ~75 kJ/mol at n = 0.6-0.7 mmol/g and then decays toward ~20 kJ/mol as pores fill. NU-6000-OH shows an apparent anomaly at the lowest coverages (nonphysical negative Qst with large uncertainty), followed by a sharp peak of ~95 kJ/mol near n = 1.1-1.2 mmol/g and a gradual decline to ~30 kJ/mol at higher loading. The shaded envelopes indicate sizeable uncertainties at low pressure. The observed maxima (~75-90 kJ/mol) point to a strong, likely chemisorptive interaction introduced by the -OH functionality (e.g., bicarbonate/carbamate-like binding or cooperative H-bonding at basic sites), while the return to ~20-30 kJ/mol at higher n reflects a transition to weaker, physisorptive processes. Practically, such strong initial binding benefits trace-level capture but implies higher regeneration energy; beyond loadings of ~1 mmol/g, adsorption is dominated by weaker interactions that require lower regeneration energies to desorb. Dynamic Breakthrough and Competitive CO 2 Capture under Humidity. Based on the superior CO 2 uptake of NU-6000-OH at room temperature, we next assessed how the pre-configured Zn-OH microenvironments translate into dynamic separation under flow conditions. To this end, dynamic breakthrough experiments were conducted under 1 vol% and 15 vol% CO 2 /N 2 feeds, each tested under dry, 50% relative humidity (RH), and 90% RH conditions to quantify the influence of water on adsorption properties (Fig. 4e,f). For 1 vol% CO 2 /N 2 , NU-6000-OH exhibits the earliest breakthrough under dry conditions, showing a steep mass-transfer front at 411 min/g, corresponding to a CO 2 adsorption capacity of 0.40 mmol/g (single-component isotherm capacity at 0.01 bar CO 2 : 1.30 mmol/g). This behavior indicates rapid uptake and largely reversible binding at the oriented –OH arrays. Introducing 50% RH shifts the breakthrough to a later time (477 min/g; 0.44 mmol/g) while preserving a narrow mass-transfer zone, revealing a humidity-assisted enhancement of dynamic capacity. This effect arises from water molecules anchored onto the Zn–OH sites, mediating the formation of a bicarbonate-like CO 2 adduct through cooperative hydrogen bonding, which was confirmed by DFT calculation (Fig. 5d and Supplementary Figs. 47–52). The confined hydration remains discontinuous, preventing the development of a percolated water network and preserving diffusion pathways. At 90% RH, the breakthrough is further delayed (517 min/g; 0.49 mmol/g), and the bed approaches saturation more gradually as excess water begins to compete with CO 2 for –OH sites. When the CO 2 feed concentration is increased to 15%, the higher driving force accelerates saturation and shifts the breakthrough to earlier times. Under dry conditions, the front remains sharp at 78 min/g, corresponding to a CO 2 adsorption capacity of 1.37 mmol/g (single-component isotherm capacity at 0.15 bar CO 2 : 2.11 mmol/g), and the bed productivity rises accordingly. Introducing 50% RH extends the breakthrough to 94 min/g (1.61 mmol/g) while maintaining a narrow mass-transfer zone, indicating that a thin hydration layer promotes reversible CO 2 activation without impeding transport. At 90% RH, the breakthrough occurs at an intermediate time (86 min/g; 1.49 mmol/g), reflecting partial pore occupation by water that modestly reduces access to the –OH sites. These capacities are lower than those expected from single-component isotherm measurements, likely because non-equilibrium flow conditions limit complete utilization of the pore volume. In addition, diffusional resistance and partial mass-transfer inefficiencies under dynamic operation can further reduce the accessible adsorption capacity compared to static equilibrium measurements. Unlike state-of-the-art CO 2 -capture MOFs such as MAF-X27ox, 65 CFA-1, 60 or MOF-74 derivatives, 66, 67 whose CO 2 chemisorption behavior is either humidity-insensitive or strongly humidity-dependent but structurally fragile, NU-6000-OH exhibits enhanced CO 2 adsorption under humid conditions, and its confined Zn–OH arrays enable cooperative yet stable hydration that enhances reversible CO 2 activation without compromising framework integrity, achieving humidity tolerance and capacity enhancement simultaneously. This humidity-tolerant and reversible chemisorption mechanism demonstrates how local geometric confinement can balance water compatibility and CO 2 reactivity, offering a rational pathway toward sorbents that maintain strong CO 2 uptake under realistic humid conditions. Diffuse-reflectance IR spectroscopy (DRIFTS). DRIFTS confirms that both NU-6000-OH and NU-6001-OH capture CO 2 at framework hydroxyl sites through bicarbonate formation (Fig. 5d,e, Supplementary Fig. 43 and 44). At room temperature, NU-6000-OH shows new bands at 1471, 1614, and 1655 cm -1 , while NU-6001-OH displays bands at 1505, 1634, and 1650 cm -1 . Features in the 1610-1655 cm -1 range are assigned to the asymmetric C-O stretch of bicarbonate, and the bands near 1470-1505 cm -1 fall within the region of the symmetric C-O stretch and the O-H-O bending vibration, which together indicate hydrogen-bond-stabilized Zn-O 2 COH species with a likely bidentate coordination at the hydroxyl sites. The high-frequency O-H region tracks the thermal evolution of these adducts. For NU-6000-OH , CO 2 binding gives a hydrogen-bonded O-H stretch at 3607 cm -1 ; heating under dry N 2 weakens this feature and produces a band at 3665 cm -1 while a band at 3676 cm -1 grows; with further heating, only the sharp 3676 cm -1 peak remains, consistent with complete bicarbonate removal and recovery of isolated Zn-OH species. NU-6001-OH follows the same sequence and ultimately shows a single high-frequency O-H stretch at 3688 cm -1 , also diagnostic of isolated Zn-OH sites after bicarbonate decomposition. The concurrent decay of the bicarbonate C-O bands and the reappearance of the free O-H bands demonstrate a reversible process in which CO 2 forms bicarbonate at ambient conditions and is released upon thermal regeneration, restoring the active hydroxyl sites. Thermal swing adsorption-desorption experiments. We conducted thermal-swing adsorption-desorption (TSAD) measurements to evaluate adsorption kinetics, regeneration temperature, and cyclic stability of the sorbents. Under a gas mixture of 15 vol% CO 2 / N 2 , with adsorption near 298 K and thermal regeneration at 200 °C, both NU-6000-OH and NU-6001-OH show robust performance with only slight decreases in capacity over 50 adsorption-desorption runs (Supplementary Fig. 45 and 46). NU-6000-OH reaches ~8.8 wt% at 298 K (2 mmol/g) and maintains a slightly higher steady-state uptake (7.5 wt%, 1.7 mmol/g), whereas NU-6001-OH starts at ~1.9 mmol/g (~8.4 wt%) and stabilizes at ~1.4 mmol/g (~6.2 wt%) by the end of cycling, giving a modestly lower capacity than NU-6000-OH . For both frameworks, TSAD uptakes are higher than those inferred from single-component isotherms at comparable CO 2 partial pressures, which is commonly observed for MOF sorbents, likely due to temperature-swing re-exposure of high-energy sites together with minor multicomponent/kinetic effects. In absolute terms, the simulated-flue gas performance of these hydroxylated MOFs exceeds that of Mg 2 (dobdc)-mmen (4.6 wt%) but remains below that of Mg 2 (dobpdc)en (11.8 wt%), confirming good cyclability and CO 2 TSAD performance for NU-6000-OH . Determination of the binding domains for adsorbed CO 2 . The binding domains of CO 2 in NU-6000-OH were elucidated through micro-ED analysis, in situ DRIFTS measurements, and complementary DFT simulations. Structural refinement of activated NU-6000-OH reveals the complete removal of guest solvent molecules and full exposure of four μ 2 -OH groups lining the internal surface of each small cage, forming an array of open Zn-OH sites with well-defined orientation (Supplementary Fig. 25). Micro-ED analysis of CO 2 -loaded NU-6000-OH (Fig. 5a) reveals partial conversion of the Zn-bound hydroxyl groups into bicarbonate species upon CO 2 chemisorption. Within each Zn 5 Cl 4 node, one Zn center exhibits positional disorder between two coordination modes, Zn-OH and Zn-OCO 2 H, indicating that only a fraction of the hydroxyl sites participates in the formation of HCO 3 - while the remainder retain the terminal -OH groups. The coexistence of these two motifs at a single Zn site reflects the dynamic equilibrium established during CO 2 uptake and desorption. Considering the experimentally measured adsorption capacity, we infer that only two of the four Zn-OH sites in Cage 1 are involved in CO 2 binding, with the other two remaining unreacted. This mixed configuration yields an energetically favorable arrangement within the confined microcavity, minimizing steric congestion and allowing cooperative stabilization of the bound CO 2 molecules through adjacent hydrogen-bond networks (O···O = 2.8–3.4 Å). The structural disorder between Zn-OH and Zn-HCO 3 motifs thus represents a crystallographic snapshot of the chemisorption process and provides direct evidence for the reversible transformation between hydroxyl and bicarbonate species under mild conditions. To further elucidate the cooperative chemisorption behavior observed experimentally, DFT calculations were performed for NU-6000-OH models containing one, two, three, and four chemisorbed CO 2 molecules per small cage (Fig. 5c). The optimized structures are summarized in Supplementary Fig. 47–52. Upon uptake of one CO 2 molecule (Supplementary Fig. 48), the framework (1-HCO 3 ) predominantly stabilizes a bicarbonate species with Gibbs free energy (Δ G ) = −61.3 kJ/mol. When two CO 2 molecules are present, the ortho configuration (2-HCO 3 - o ) yields a mixed bicarbonate–carbonate pair with steric repulsion and distortion of the hydrogen-bond geometry result in Δ G = −54.2 kJ/mol (Supplementary Fig. 49), whereas the para configuration (2-HCO 3 - p ) favors the formation of two carbonate units; in this case, the terminal –OH group is converted to H 2 O, which in turn participates in a locally ordered cyclic hydrogen-bonding network. In this configuration with two opposite bicarbonates across the cage window displays a low energy (Δ G = −145.8 kJ/mol), stabilized by the cyclic hydrogen-bonded network formed by two directional hydrogen bonds (O···H = ~1.4 Å) linking the Zn–OH 2 and Zn–CO 3 units (Supplementary Fig. 50). Among these configurations, the structure containing three bicarbonate species (3-HCO 3 ) exhibits a cooperative environment forms comprising bicarbonate, carbonate, and water species with the lowest Δ G (−149.2 kJ/mol), where a cyclic hydrogen-bonded network is formed with neighboring Zn–OH groups and adjacent bicarbonates, generating an extended cooperative O···H···O array within the confined cavity (Supplementary Fig. 51). By contrast, when four CO 2 molecules are introduced, the system (4-HCO 3 ) reverts predominantly to bicarbonate formation because of steric effect and display a Δ G = −125.1 kJ/mol (Supplementary Fig. 52). The thermodynamic distinction between the 3-HCO 3 and 2-HCO 3 - p configurations is marginal in the idealized static model. Consideration of gas diffusion constraints, steric accessibility, and gating barrier during stepwise adsorption within the pore suggests that the opposite-pair di-bicarbonate configuration (2-HCO 3 - p ) is the most plausible adsorption state under experimental conditions. This model aligns with the single-crystal structure of CO 2 -loaded NU-6000-OH , which shows partial conversion of Zn–OH to Zn–HCO 3 and approximately two CO 2 molecules bound per cage. Collectively, these results indicate that CO 2 uptake in NU-6000-OH proceeds through cooperative hydrogen-bonding interactions among symmetrically aligned hydroxyl sites, where the formation of a locally ordered hydrogen-bond network stabilizes carbonate-rich intermediates and achieves an optimal balance between strong binding and reversible regeneration. This mechanistic picture aligns with the breakthrough measurements, where water markedly enhances CO 2 capture under flow, confirming that hydration-assisted hydrogen-bond networks facilitate CO 2 activation and stabilization in NU-6000-OH . Conclusion Through reticular chemistry, we have established a strategy for designing MOFs with tunable chemical microenvironments within their pores. Starting from a known Kuratowski-type Zn 5 Cl 4 secondary building unit, we rationally modified linker geometry to target the ith-d topology in which terminal Zn-bound groups are oriented toward the cage interior to create confined, chemically addressable spaces. This design enabled the construction of an isoreticular pair of triazolate MOFs, NU-6000 and NU-6001 , where flipping the coordinated arms of rigid, mixed triazole linkers aligns with node symmetry to preserve the overall topology while reprogramming cage size, aperture, and inward functionality. These frameworks are structurally well-defined and thermally robust above 525 °C, as confirmed by VT-PXRD, TGA, and CO 2 sorption isotherm measurements. Post-synthetic Cl - /OH - exchange introduces dense, oriented Zn-OH arrays that mediate strong yet reversible CO 2 binding through bicarbonate formation, achieving a site utilization efficiency of 61.4%, which is the highest among MOFs reported under DAC conditions. Beyond overcoming long-standing synthetic challenges in the Zn 5 Cl 4 -triazolate family, this work establishes a transferable design principle for engineering chemically robust, permanently porous materials with preconfigured microenvironments. More broadly, this tunable confinement strategy offers a generalizable platform for gas separation, selective adsorption, and confined catalysis, where control over local geometry and functionality can be leveraged to direct molecular recognition and reactivity within well-defined crystalline pores. Declarations Data availability Detailed synthetic procedures, NMR spectra, X-ray crystallographic structures, TGA curves, UV-Vis spectra, Raman spectra, and crystal data (PDF) are provided in the Supplementary Information. Meanwhile, the X-ray crystallographic data have also been deposited at the Cambridge Crystallographic Data Center (CCDC), which can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk. Author information Notes The authors declare the following competing financial interest(s): O.K.F. has a financial interest in Numat Technologies, a startup company that is seeking to commercialize MOFs. Acknowledgment This research was supported by the Catalyst Design for Decarbonization Center, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under grant DE-SC0023383 for synthesis and characterization of metal–organic frameworks. 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Supplementary Files NU6001checkcif.pdf Checkcif NU6000HCO3.pdf Checkcif NU6000checkcif.pdf Checkcif NU6001.cif Crystal information file NU6000.cif Crystal information file NU6000OHcheckcif.pdf Checkcif NU6000OH.cif Crystal information file NU6000HCO3.cif Crystal information file SINatMaterTangxhNU600020251110.docx Supplementary Information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8090759","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":548786598,"identity":"446c7ea8-61e5-4a21-9d32-b3eee6104cf7","order_by":0,"name":"Omar Farha","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+klEQVRIiWNgGAWjYFACxgcMjA0MciAmM5IwMw7lYDkDkBZjkOZmEJ+HWC2JDURr4WdgZvxcucMufTt77/PHhW029vbsvc8eMFRYgwzBCiQbmJklz55Jzt3Zc9yweWZbWmIPz3FzA4Yz6Ti1GNx/f0CysY05d8ONNMZm3m2HE3gk0tgkGNsO49ZygJn5Z2NbfboBRMt/ex75Z0At//BqYQPacjgBquUAY48EG1BLA24tQL+wWTa2HTfccOYY42zef8mJPWeADks4lm6MSwswxJhvNrZVyxscb2P4zHPGzp69/RibxIcaa1lcWnCABNKUj4JRMApGwShAAwB7mVMgLuSzBwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-9904-9845","institution":"Northwestern University","correspondingAuthor":true,"prefix":"","firstName":"Omar","middleName":"","lastName":"Farha","suffix":""},{"id":548786599,"identity":"7739f27a-6d09-4a29-aa67-1de5d531ca77","order_by":1,"name":"Xianhui Tang","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Xianhui","middleName":"","lastName":"Tang","suffix":""},{"id":548786600,"identity":"8e84d811-78f5-4944-9d44-75e8adad693b","order_by":2,"name":"Xiaoliang Wang","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Xiaoliang","middleName":"","lastName":"Wang","suffix":""},{"id":548786602,"identity":"478bb18f-bebf-41d2-9514-e1473254ba6d","order_by":3,"name":"Zi-Ming Ye","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Zi-Ming","middleName":"","lastName":"Ye","suffix":""},{"id":548786605,"identity":"572f616c-3316-49cd-b809-910cc70dcfe7","order_by":4,"name":"Shengyi Su","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Shengyi","middleName":"","lastName":"Su","suffix":""},{"id":548786607,"identity":"2efaf467-05c2-43c9-89c6-c059c40b3eb2","order_by":5,"name":"Julian Magdalenski","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Julian","middleName":"","lastName":"Magdalenski","suffix":""},{"id":548786608,"identity":"30832968-9bfc-416a-8bb2-58c9de618710","order_by":6,"name":"Bang Hou","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Bang","middleName":"","lastName":"Hou","suffix":""},{"id":548786609,"identity":"08b27f8d-f59d-40b1-a5fe-4509860f10b7","order_by":7,"name":"Timothy Li","email":"","orcid":"","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Timothy","middleName":"","lastName":"Li","suffix":""},{"id":548786610,"identity":"753e2119-7be5-4329-abd4-eb1882a5bec0","order_by":8,"name":"Kent Kirlikovali","email":"","orcid":"https://orcid.org/0000-0001-8329-1015","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Kent","middleName":"","lastName":"Kirlikovali","suffix":""},{"id":548786611,"identity":"f8d3b952-f0e6-41d1-890e-3976462a5bc8","order_by":9,"name":"Nathan Gianneschi","email":"","orcid":"https://orcid.org/0000-0001-9945-5475","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Nathan","middleName":"","lastName":"Gianneschi","suffix":""},{"id":548786612,"identity":"586ec2d1-8602-4177-87d3-994b6cd731ba","order_by":10,"name":"Haomiao Xie","email":"","orcid":"https://orcid.org/0000-0001-7688-6571","institution":"Northwestern University","correspondingAuthor":false,"prefix":"","firstName":"Haomiao","middleName":"","lastName":"Xie","suffix":""}],"badges":[],"createdAt":"2025-11-12 00:55:44","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8090759/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8090759/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":97249324,"identity":"0d0e0beb-4676-49d5-bcaa-ff75006e340d","added_by":"auto","created_at":"2025-12-02 13:12:11","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":116172,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Local confinements of enzyme TEV protease with catalytic triad of an aspartate (acid), histidine (base), and cysteine (nucleophile) residues (red) in its active site (Left); Local confinements of cage in MOF with Zn-OH toward cavity (right). \u003cstrong\u003e(b)\u003c/strong\u003e The evolution of MOFs based on Zn\u003csub\u003e4\u003c/sub\u003eO and Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e nodes involves a transfer between the \u003cstrong\u003epcu\u003c/strong\u003e topology and the \u003cstrong\u003eith-d\u003c/strong\u003e topology.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/fa16c00c65f63502eab266c6.jpg"},{"id":97192512,"identity":"74a088a7-e318-4be7-9955-9ff34324a14b","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":186015,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea)\u003c/strong\u003e \u003cstrong\u003eith-d\u003c/strong\u003e topology nets. \u003cstrong\u003e(b) \u003c/strong\u003e3D single-crystal X-ray structure of \u003cstrong\u003eNU-6000\u003c/strong\u003ealong \u003cem\u003ec\u003c/em\u003e axis. \u003cstrong\u003e(c\u003c/strong\u003e) Tetrahedral cages in \u003cstrong\u003eNU-6000\u003c/strong\u003e contain four chlorides oriented toward the cavity. (\u003cstrong\u003ed)\u003c/strong\u003e Topological representation of the underlying \u003cstrong\u003eith-d \u003c/strong\u003enet in \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e as a natural tiling with transitivity [2212]. \u003cstrong\u003e(e) \u003c/strong\u003e3D single-crystal X-ray structure of \u003cstrong\u003eNU-6001\u003c/strong\u003e. \u003cstrong\u003e(f\u003c/strong\u003e) Octahedral cages in \u003cstrong\u003eNU-6001\u003c/strong\u003econtain twelve chlorides oriented toward the cavity.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/fa5accbf45956774dbaf85c2.jpg"},{"id":97192514,"identity":"2b3d874c-fb9c-44e8-9056-522576ad7465","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":157694,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;\u003cstrong\u003e(a)\u003c/strong\u003e PXRD patterns of the simulated, pristine, and thermally activated \u003cstrong\u003eNU-6000\u003c/strong\u003e, as well as the samples after CO\u003csub\u003e2\u003c/sub\u003e sorption. \u003cstrong\u003e(b)\u003c/strong\u003e VT-PXRD for \u003cstrong\u003eNU-6000\u003c/strong\u003e from 25 to 525 °C. \u003cstrong\u003e(c)\u003c/strong\u003e CO\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms of \u003cstrong\u003eNU-6000\u003c/strong\u003e at 195 K after activation at 250 °C, 350 °C, and 450 °C, respectively. \u003cstrong\u003e(d)\u003c/strong\u003e PXRD patterns of the simulated, pristine, and thermally activated \u003cstrong\u003eNU-6001\u003c/strong\u003e, as well as the samples after N\u003csub\u003e2\u003c/sub\u003e sorption. \u003cstrong\u003e(e)\u003c/strong\u003e VT-PXRD for \u003cstrong\u003eNU-6001\u003c/strong\u003e from 25 to 525 °C. \u003cstrong\u003e(f)\u003c/strong\u003e CO\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms of \u003cstrong\u003eNU-6001\u003c/strong\u003e at 195 K after activation at 160 °C, 250 °C, 350 °C, 400 °C, and 450 °C, respectively.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/cdb6a148784b354a43cb0425.jpg"},{"id":97250894,"identity":"9ca35ce7-6b67-45cf-abaf-19cc8b40143f","added_by":"auto","created_at":"2025-12-02 13:15:34","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":135257,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e. CO\u003csub\u003e2\u003c/sub\u003e adsorption isotherms of \u003cstrong\u003eNU-6000\u003c/strong\u003e, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e, \u003cstrong\u003eNU-6001\u003c/strong\u003e, and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e up to 1 bar at 298 K. \u003cstrong\u003e(b)\u003c/strong\u003e The CO\u003csub\u003e2\u003c/sub\u003e adsorption isotherm of \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e in the low-pressure and ultra-low-pressure region. \u003cstrong\u003e(c)\u003c/strong\u003e Site efficiency and CO\u003csub\u003e2\u003c/sub\u003e uptake of \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e compared with\u003cstrong\u003e \u003c/strong\u003erepresentative MOFs at 0.4 mbar and 298 K.\u003cstrong\u003e (d)\u003c/strong\u003e Isosteric heat of adsorption (Qst) for \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e as a function of the amount of CO\u003csub\u003e2\u003c/sub\u003e adsorbed (n). The shaded area represents the uncertainty calculated from the linear fit of the isosteres (see Supporting Information). Breakthrough curves of \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e with 1% \u003cstrong\u003e(e)\u003c/strong\u003e and 15% \u003cstrong\u003e(f)\u003c/strong\u003e CO\u003csub\u003e2\u003c/sub\u003e in N\u003csub\u003e2\u003c/sub\u003e at 298 K under dry and different wet conditions.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/2ef1ee1cf19b3c3817986f74.jpg"},{"id":97250925,"identity":"7fa877c0-5d21-45fe-a68c-f14a620976c2","added_by":"auto","created_at":"2025-12-02 13:15:38","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":134517,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Single crystal structure of \u003cstrong\u003eNU-6000-HCO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e. \u003cstrong\u003e(b)\u003c/strong\u003e Hydroxyl and bicarbonate crystallographic disorder are present on the nodes of \u003cstrong\u003eNU-6000/6001\u003c/strong\u003e. \u003cstrong\u003e(c)\u003c/strong\u003e Two HOCO\u003csub\u003e2\u003c/sub\u003e and OH groups are oriented toward the cage cavity. \u003cstrong\u003e(d)\u003c/strong\u003e DFT optimized structures of \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e with different amounts of CO\u003csub\u003e2\u003c/sub\u003e molecules. Evolution of the IR spectrum of \u003cstrong\u003e(e)\u003c/strong\u003e \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003e(f)\u003c/strong\u003e \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e upon heating under N\u003csub\u003e2\u003c/sub\u003e atmosphere. (Blue: N; Red: O; Gray: C; Black: H; Pale blue: Zn; Yellow ellipsoids: cavity of Cage 2).\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/5e5849e8ecf742a9d47c1a68.jpg"},{"id":97367039,"identity":"ca54f038-8a6b-40a8-99f0-a7caed7e8261","added_by":"auto","created_at":"2025-12-03 16:15:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2386231,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/d9cc16b6-6530-4905-a1d1-d73021ed5b29.pdf"},{"id":97192517,"identity":"65a03580-3d1a-4400-9b25-74cd93b00049","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":185985,"visible":true,"origin":"","legend":"Checkcif","description":"","filename":"NU6001checkcif.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/2725197f7c02f7f7dea34461.pdf"},{"id":97250622,"identity":"0f4c8341-b5a3-42d7-b82f-14780f64a855","added_by":"auto","created_at":"2025-12-02 13:14:50","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":152501,"visible":true,"origin":"","legend":"Checkcif","description":"","filename":"NU6000HCO3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/bf07f8eccad7e3628d38b716.pdf"},{"id":97249328,"identity":"efbb6725-994a-4089-ba3c-cda303b5645a","added_by":"auto","created_at":"2025-12-02 13:12:11","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":135046,"visible":true,"origin":"","legend":"Checkcif","description":"","filename":"NU6000checkcif.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/a8bb533109993a06a7a1402d.pdf"},{"id":97192522,"identity":"83e8028c-089f-4fec-8430-0ebe8acb1417","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"cif","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":1369032,"visible":true,"origin":"","legend":"Crystal information file","description":"","filename":"NU6001.cif","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/2773bdfe4df191e271d2c82e.cif"},{"id":97192521,"identity":"7f390eb4-0cdf-4bd2-b93d-2675c2a31e67","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"cif","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":2881193,"visible":true,"origin":"","legend":"Crystal information file","description":"","filename":"NU6000.cif","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/669ff4131541d68b8dcb6019.cif"},{"id":97192520,"identity":"ddf652c0-325d-4428-9972-5ac84172ce34","added_by":"auto","created_at":"2025-12-01 20:18:52","extension":"pdf","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":140042,"visible":true,"origin":"","legend":"Checkcif","description":"","filename":"NU6000OHcheckcif.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/ae251a1dc81ff391d19be451.pdf"},{"id":97192523,"identity":"ac3e8704-6c21-482f-8bd5-b0a2cc665b99","added_by":"auto","created_at":"2025-12-01 20:18:53","extension":"cif","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":3971052,"visible":true,"origin":"","legend":"Crystal information file","description":"","filename":"NU6000OH.cif","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/f11b40ba8c8f3f7b4a78cabf.cif"},{"id":97249355,"identity":"a2b76f62-f1ed-4ca7-99ab-e8c9b0b78614","added_by":"auto","created_at":"2025-12-02 13:12:18","extension":"cif","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":4504046,"visible":true,"origin":"","legend":"Crystal information file","description":"","filename":"NU6000HCO3.cif","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/1722fe53ffb4afd8b7b176c4.cif"},{"id":97192525,"identity":"4ee67db0-4628-4186-adab-f37dbf43fb51","added_by":"auto","created_at":"2025-12-01 20:18:53","extension":"docx","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":10711717,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SINatMaterTangxhNU600020251110.docx","url":"https://assets-eu.researchsquare.com/files/rs-8090759/v1/45f2faae0d1c4a115488f390.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Programming Local Confinements in Crystalline Frameworks through Reticular Chemistry","fulltext":[{"header":"Main","content":"\u003cp\u003eMicroenvironments in biological systems, such as the confined pockets of enzymes, are crucial to their extraordinary catalytic performance\u003csup\u003e1, 2, 3\u003c/sup\u003e. These highly organized spaces bring multiple functional groups or active sites into proximity, enabling synergistic interactions that deliver exceptional reaction rates and selectivity\u003csup\u003e4\u003c/sup\u003e. Although enzymes exhibit unparalleled catalytic efficiency\u003csup\u003e5\u003c/sup\u003e, their delicate structures make it challenging to maintain these functions under the harsher conditions typical of industrial processes\u003csup\u003e6\u003c/sup\u003e, motivating the search for stable, bio-inspired materials. Translating the principle of local confinement into a robust, crystalline scaffold, such as a metal-organic framework (MOF), offers an opportunity to recreate these synergistic microenvironments in solid materials\u003csup\u003e7, 8\u003c/sup\u003e (Fig. 1a). By rationally programming the spatial arrangement of functional groups within a stable framework, it becomes possible to design high-performance materials for applications including catalysis, guest-molecule capture, molecular recognition, and gas separation\u003csup\u003e9, 10, 11, 12, 13, 14, 15, 16, 17\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eDespite the utility of this bio-inspired principle, constructing such finely tuned microenvironments within solid materials remains a formidable challenge\u003csup\u003e18\u003c/sup\u003e. Reticular chemistry, guided by the abstract concept of topology and centered on linking molecular building blocks through strong chemical bonds, provides the guidelines for assembling crystalline open frameworks with predetermined connectivity\u003csup\u003e19, 20\u003c/sup\u003e. This approach underpins the modular synthesis of porous materials such as MOFs and covalent organic frameworks (COFs), expanding the accessible landscape of compounds and functional materials\u003csup\u003e21, 22\u003c/sup\u003e. By decoupling framework connectivity from specific chemistries, reticular chemistry enables a given topology to be recreated with distinct linkers or metal nodes, offering a versatile platform for engineering local confinement with tailored chemical environments\u003csup\u003e23\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTo date, most functional MOFs have been constructed from carboxylate linkers\u003csup\u003e24, 25\u003c/sup\u003e. Although these frameworks have delivered impressive performance across many applications, those built from 3d transition metals often suffer from limited stability under humidity, acidic, basic, or high-temperature conditions\u003csup\u003e26\u003c/sup\u003e. Heterocyclic linkers offer a promising route to address these limitations. Among them, triazole-based MOFs, such as MFU-4l, which features a Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e secondary building unit (SBU), stand out for their exceptional stability and chemical versatility\u003csup\u003e27\u003c/sup\u003e. This SBU can undergo transmetalation of Zn with other transition metals (V, Fe, Co, Ni, Cu, Mo) \u003csup\u003e28, 29, 30, 31, 32, 33, 34, 35\u003c/sup\u003e and exchange of terminal ligands (Cl for Me, OH, NO\u003csub\u003e3\u003c/sub\u003e, H, SH)\u003csup\u003e9, 10, 12, 36, 37\u003c/sup\u003e while retaining the overall framework, offering a powerful platform for tailoring local environments and introducing biomimetic functionality. Yet, the diversity of known triazole-based MOFs remains strikingly narrow: beyond MFU-4\u003csup\u003e38\u003c/sup\u003e, MFU-4l\u003csup\u003e39\u003c/sup\u003e, CFA-1\u003csup\u003e40\u003c/sup\u003e, CFA-7\u003csup\u003e41\u003c/sup\u003e, CFA-19\u003csup\u003e42\u003c/sup\u003e, and a recent example of Zn\u003csub\u003e5\u003c/sub\u003e(OAc)\u003csub\u003e4\u003c/sub\u003e(TBTT)\u003csub\u003e2\u003c/sub\u003e, which employs a non-conjugated tritopic benzotriazole linker\u003csup\u003e43\u003c/sup\u003e, only a handful of structures have been reported over the past two decades. Developing reticular chemistry-based strategies to construct new MOFs from Kuratowski-type building blocks\u003csup\u003e40\u003c/sup\u003e, with topologies that enable local confinements, would greatly expand this family\u0026rsquo;s structural diversity and enable the precise tuning of local environments for enhanced performance across a range of potential applications.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFrom a geometric and topological perspective, the Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e SBU adopts T\u003cem\u003e\u003csub\u003ed\u003c/sub\u003e\u003c/em\u003e symmetry with a connectivity of six\u003csup\u003e44\u003c/sup\u003e, making it a geometric analog of the Zn\u003csub\u003e4\u003c/sub\u003eO cluster in the prototypical carboxylate-based MOF-5\u003csup\u003e45\u003c/sup\u003e (Fig. 1b). Based on the Kuratoski-type SBUs, triazole-based MOFs such as MFU-4 and MFU-4l are isoreticular to MOF-5 and the IRMOF series\u003csup\u003e46\u003c/sup\u003e with \u003cstrong\u003epcu\u003c/strong\u003e topology, while CFA-1 is isoreticular to Zn\u003csub\u003e4\u003c/sub\u003e(\u0026mu;\u003csub\u003e4\u003c/sub\u003e-O)[(Metrz-\u003cem\u003ep\u003c/em\u003eba)\u003csub\u003e2\u003c/sub\u003e\u003cem\u003em\u003c/em\u003ePh]\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e47\u003c/sup\u003e with \u003cstrong\u003eacs\u003c/strong\u003e topology. Both cases provide a strategy for constructing Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e SBU-based MOFs by topology transfer from Zn\u003csub\u003e4\u003c/sub\u003eO SBU MOFs. On the other hand,\u0026nbsp;in both cases, only a single type of ditopic linker connects the metal clusters, resulting\u0026nbsp;in one type of cavity. Bringing cluster nodes together to create local confinement usually comes at the expense of overall porosity, potentially limiting the diffusion of the guest molecules. Frameworks with multiple types of cages can overcome this challenge by using one type of cage for local confinement while leaving the other cages for diffusion and porosity.\u0026nbsp;Achieving these architectures requires moving beyond frameworks with only one type of connectivity; introducing linkers with multiple connectivities opens access to otherwise unattainable nets.\u0026nbsp;For example, in the Zn\u003csub\u003e4\u003c/sub\u003eO-carboxylate MOF family, MOF-905\u003csup\u003e48\u003c/sup\u003e and MOF-205\u003csup\u003e49\u003c/sup\u003e adopt the \u003cstrong\u003eith-d\u003c/strong\u003e topology with two distinct cage types, arising from the combination of tritopic and ditopic linkers.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eInspired by this design, we introduced two additional tritopic linkers into the MFU-4 system, which contains Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e nodes and the original ditopic \u003cstrong\u003eBBTA\u003c/strong\u003e (1,5-dihydrobenzo[1,2-d:4,5-d\u0026apos;]bis([1,2,3]triazole) linker, yielding two new Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e-triazole MOFs with \u003cstrong\u003eith-d\u003c/strong\u003e topology, \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e. These represent the first examples of triazole-based MOFs with this topology, expanding the structural diversity accessible to this class of frameworks. \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e not only adopt desirable topologies analogous to MOF-205 but also display remarkable thermal stability and tunable sorption behavior through post-synthetic modification that replaces terminal chlorides with hydroxides. Moreover, altering the dihedral angle between the triazole plane and the \u003cem\u003eC\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e axis of the tritopic linker affords the same overall topology but generates distinct local confinements within the pores. In \u003cstrong\u003eNU-6000\u003c/strong\u003e, the co-planar geometry of \u003cstrong\u003eTPHTA\u003c/strong\u003e directs the formation of two types of cages: a smaller cage with Zn sites oriented inward, creating confined environments that can promote synergistic interactions, and a larger cage lacking closely positioned metal sites. In contrast, \u003cstrong\u003eNU-6001\u003c/strong\u003e, which is constructed from the tritopic \u003cstrong\u003eTPTTA\u003c/strong\u003e linker that adopts a 90\u0026deg; dihedral angle, contains two cages of similar size without closely spaced metal centers. Hydroxyl-substituted versions of \u003cstrong\u003eNU-6000\u003c/strong\u003e show a pronounced enhancement of CO\u003csub\u003e2\u003c/sub\u003e uptake at low concentrations, attributed to local interactions between the -CO\u003csub\u003e3\u003c/sub\u003eH moiety on one Zn site and -OH groups on adjacent Zn sites through hydrogen bonding interactions. In \u003cstrong\u003eNU-6001\u003c/strong\u003e, such synergistic interactions are absent, highlighting how reticular design strategies can be used to tune local confinement and reactivity within triazole-based MOFs.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003eSynthesis and\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003estructural\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003echaracterization\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTwo triazole-based ligands, 6,11-dihydro-1H-triphenyleno[2,3-d:6,7-d\u0026apos;:10,11-d\u0026apos;\u0026apos;]tris([1,2,3]triazole) (\u003cstrong\u003eTPHTA)\u003c/strong\u003e and 7,13-dihydro-1H-9,10-dihydro-9,10-[1,2]benzenoanthraceno[2,3-d:7,8-d\u0026apos;:12,13-d\u0026apos;\u0026apos;]-tris([1,2,3]triazole) (\u003cstrong\u003eTPTTA)\u003c/strong\u003e, were synthesized based on planar triphenylene and stereoscopic triptycene backbones, respectively. These linkers were combined with \u003cstrong\u003eBBTA\u003c/strong\u003e and ZnCl\u003csub\u003e2\u003c/sub\u003e to yield \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e, respectively, in \u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide (DMF) at 140 \u0026deg;C for 3 days. 3D micro-electron diffraction (micro-ED) analysis reveals that both frameworks adopt the \u003cstrong\u003eith-d\u003c/strong\u003e topology with Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e nodes and formulas [(Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e(\u003cstrong\u003eTPHTA\u003c/strong\u003e)\u003csub\u003e4\u003c/sub\u003e(\u003cstrong\u003eBBTA\u003c/strong\u003e)\u003csub\u003e3\u003c/sub\u003e] (\u003cstrong\u003eNU-6000\u003c/strong\u003e) and [(Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e(\u003cstrong\u003eTPTTA\u003c/strong\u003e)\u003csub\u003e4\u003c/sub\u003e(\u003cstrong\u003eBBTA\u003c/strong\u003e)\u003csub\u003e3\u003c/sub\u003e] (\u003cstrong\u003eNU-6001\u003c/strong\u003e). Their phase purity was confirmed by comparing their experimental and simulated PXRD patterns. (Fig. 3a,d). Thermogravimetric analysis (TGA) revealed that in \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e, the solvent molecules, methanol and water are removed between 50 and 150 \u0026deg;C, with decomposition beginning at approximately 500 \u0026deg;C under air (Supplementary Fig. 32 and 33). Variable-temperature powder X-ray diffraction (VT-PXRD) analysis confirms that both materials maintain crystallinity up to 525 \u0026deg;C (Fig. 3b,e). Their permanent porosities were evaluated by gas sorption isotherms after exchanging the solvent to methanol and then activating under a dynamic vacuum at 200 \u0026deg;C, as shown in Fig. 3c,f. Despite its high crystallinity, \u003cstrong\u003eNU-6000\u003c/strong\u003e exhibits minimal N\u003csub\u003e2\u003c/sub\u003e uptake at 77 K, which is attributed to the small pore apertures. Therefore, CO\u003csub\u003e2\u003c/sub\u003e, which has a smaller kinetic diameter (3.3 \u0026Aring;), was used to probe the accessible porosity of \u003cstrong\u003eNU-6000\u003c/strong\u003e at 195 K (Supplementary Fig. 36), yielding a Brunauer-Emmett-Teller (BET) area of 980 m\u003csup\u003e2\u003c/sup\u003e/g, and the pore volume of 0.64 cm\u003csup\u003e3\u003c/sup\u003e/g is given by water sorption isotherm (Supplementary Fig. 37). In comparison, \u003cstrong\u003eNU-6001\u003c/strong\u003e exhibits higher porosity, with a BET area of 1230 m\u003csup\u003e2\u003c/sup\u003e/g and a pore volume of 0.68 cm\u003csup\u003e3\u003c/sup\u003e/g, giving rise to a typical type I isotherm (Supplementary Fig. 38). The BET areas and pore volumes of \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e are both approximately equal to their calculated values, suggesting that the guest molecules are successfully removed from these frameworks under the employed activation conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStructure analysis and description.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMicro-ED analysis demonstrates that \u003cstrong\u003eNU-6000\u003c/strong\u003e crystallizes in the cubic space group \u003cem\u003ePm-3n\u003c/em\u003e, and the asymmetric unit contains one-sixth \u003cstrong\u003eTPHTA\u003c/strong\u003e, one-fourth \u003cstrong\u003eBBTA\u003c/strong\u003e, and one-fourth T\u003cem\u003e\u003csub\u003ed\u003c/sub\u003e\u003c/em\u003e symmetrical pentanuclear [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e secondary building units. Each [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e node adopts an octahedral geometry, which is similar to the Zn\u003csub\u003e4\u003c/sub\u003eO node in MOF-5, with the basal plane defined by four triazoles from four linkers \u003cstrong\u003eTPHTA\u003c/strong\u003e,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eand the axial positions are occupied by two \u003cstrong\u003eBBTA\u003c/strong\u003e (Supplementary Fig. 14a). In \u003cstrong\u003eNU-6000\u003c/strong\u003e, each \u003cstrong\u003eTPHTA\u003c/strong\u003e coordinates to three [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e units through three triazole groups (Supplementary Fig. 14c), and each \u003cstrong\u003eBBTA\u003c/strong\u003e coordinates to two [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e units through two triazole groups (Supplementary Fig. 14b). The ditopic and tritopic ligands link the [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e] clusters to generate an \u003cstrong\u003eith-d\u003c/strong\u003e network with 2,3,6 connectivity (Fig. 2a). To illustrate the three-dimensional pore architecture of \u003cstrong\u003eNU-6000\u003c/strong\u003e, we carried out natural tiling with 3dt software\u003csup\u003e50, 51\u003c/sup\u003e. The analysis shows a 3-periodic network composed of two tile types and characterized by a transitivity of [2212] (Fig. 2d). The \u003cstrong\u003eNU-6000\u003c/strong\u003e features two distinct cages: Cage 1 is a small cavity with a window of approximately 0.35 nm, where four chloride ions are positioned inward. The Cl\u0026middot;\u0026middot;\u0026middot;Cl distances are 4.8 and 3.8 \u0026Aring;, indicating a confined opening that plays a key role in the gas adsorption behavior of \u003cstrong\u003eNU-6000\u003c/strong\u003e. Cage 2 is significantly larger, measuring approximately 1.9 nm in diameter with a 0.35 nm aperture. Calculations using PLATON show that \u003cstrong\u003eNU-6000\u003c/strong\u003e has approximately 61.6% of the total volume occupied by anions and solvents.\u003cstrong\u003e\u003csup\u003e52\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBy rotating the coordinated arms of the linkers by 90\u0026deg; along the triazole direction (Supplementary Fig. 13), the isoreticular MOF \u003cstrong\u003eNU-6001\u003c/strong\u003e was obtained under the same conditions as \u003cstrong\u003eNU-6000\u003c/strong\u003e. \u003cstrong\u003eNU-6001\u003c/strong\u003e (Fig. 1d) also crystallizes in the cubic space group \u003cem\u003ePm-3n,\u003c/em\u003e with one-sixth \u003cstrong\u003eTPTTA\u003c/strong\u003e, one-fourth \u003cstrong\u003eBBTA\u003c/strong\u003e, and one-fourth T\u003cem\u003e\u003csub\u003ed\u003c/sub\u003e\u003c/em\u003e symmetrical pentanuclear [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e SBUs occupying the asymmetric unit. Each [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e] cluster adopts an octahedral coordination geometry, with the equatorial plane defined by four triazole donors from four distinct \u003cstrong\u003eTPTTA\u003c/strong\u003e linkers, and the axial positions occupied by two \u003cstrong\u003eBBTA\u003c/strong\u003e linkers (Supplementary Fig. 18a). Each \u003cstrong\u003eTPTTA\u003c/strong\u003e ligand bridges three [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e nodes through its three triazole groups (Supplementary Fig. 18c), while each \u003cstrong\u003eBBTA\u003c/strong\u003e linker connects two [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e clusters via two triazole donors (Supplementary Fig. 18b). The topology of \u003cstrong\u003eNU-6001\u003c/strong\u003e, like that of \u003cstrong\u003eNU-6000\u003c/strong\u003e, is classified as the known 2,3,6-connected \u003cstrong\u003eith-d\u003c/strong\u003e net with the same tiling features (Fig. 2a). In the 3D framework, two types of cages are formed with a diameter of ~1.4 nm (Cage 1) and \u0026sim;1.0 nm (Cage 2) (Supplementary Fig. 20). Notably, all 12 chloride atoms point inward toward Cage 1, which can potentially influence guest uptake. The extended 3D porous framework (Fig. 1d and Supplementary Fig. 19) exhibits ~61.3% free volume.\u003csup\u003e52\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTypically, isoreticular MOFs are designed by changing the length or width of linkers or through post-synthetic modification of the framework. However, it has not been previously reported that flipping the coordinated arms of the linkers (Supplementary Fig.\u0026nbsp;13)\u0026nbsp;can invert the entire framework to yield an isoreticular structure. In MOFs constructed from carboxylates or pyridyl linkers, these linkers can freely rotate about single bonds even after coordination to SBUs. As a result, the entire framework does not invert, even when the linker core is rotated, and this rotational flexibility facilitates framework formation\u0026nbsp;by allowing the linker to self-adapt to the coordination geometry of the nodes. In contrast, for triazole-based linkers in which the triazole group is conjugated with the core skeleton, rotation along the arm direction is restricted.\u0026nbsp;The triazole groups must coordinate to the\u0026nbsp;[Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e nodes at specific angles defined by the three coordinated sites between the linker and node. Therefore, triazole-based MOFs constructed by conjugated linkers require not only a suitable geometric match between linker and node coordination modes, but also a topology compatible with this configuration. These stringent geometric and electronic requirements have so far limited the diversity of triazole-based MOFs.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Accordingly, in this work, the entire frameworks of \u003cstrong\u003eNU-6000\u003c/strong\u003e or \u003cstrong\u003eNU-6001\u003c/strong\u003e must invert as the linker inverts, especially the tritopic linker, reflecting the transformation between the planar \u003cstrong\u003eTPHTA\u003c/strong\u003e and the stereoscopic \u003cstrong\u003eTPTTA\u003c/strong\u003e. On the [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e node, the opposing coordination sites along any axis of the T\u003cem\u003e\u003csub\u003ed\u003c/sub\u003e\u003c/em\u003e symmetric node are separated by 90\u0026deg;, precisely matching the rotation angle between \u003cstrong\u003eTPHTA\u003c/strong\u003e and \u003cstrong\u003eTPTTA\u003c/strong\u003e. This geometric match between linker flipping and [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e node coordination orientation enables the formation of two distinct yet isoreticular frameworks, \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e. Despite the significant difference in spatial configuration between the planar \u003cstrong\u003eTPHTA\u003c/strong\u003e and the twisted \u003cstrong\u003eTPTTA\u003c/strong\u003e, both linkers assemble with the same node while preserving the overall \u003cstrong\u003eith-d\u003c/strong\u003e topology. The rigid coordination geometry of the triazole groups, combined with the symmetric yet angular nature of the [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e node, thus enforces a global inversion of the framework upon switching between \u003cstrong\u003eTPHTA\u003c/strong\u003e and \u003cstrong\u003eTPTTA\u003c/strong\u003e. This phenomenon of framework inversion induced by linker flipping represents a new level of structural control in MOF design, where topological isoreticularity is maintained not through linker flexibility but through precise geometric alignment. It also highlights the critical interplay between linker rigidity and node symmetry in governing framework propagation, particularly in systems built from multidentate, conjugated triazole linkers.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eadsorption.\u003c/strong\u003e Building upon this structural insight, we next sought to investigate how the distinct pore architectures and internal environments of \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e influence their gas adsorption behavior, with a particular focus on CO\u003csub\u003e2\u003c/sub\u003e capture. Although these two MOFs are isoreticular and share the same underlying topology, the difference in linker geometry, with \u003cstrong\u003eTPHTA\u003c/strong\u003e being planar and \u003cstrong\u003eTPTTA\u003c/strong\u003e stereoscopic, leads to notably different cage dimensions, aperture sizes, and chloride-ion orientations. In \u003cstrong\u003eNU-6000\u003c/strong\u003e, the tight apertures (~0.35 nm) and inward-facing chloride ions create a highly confined microporous environment, which is expected to impose significant kinetic restrictions on gas diffusion, especially for larger gas molecules. Conversely, \u003cstrong\u003eNU-6001\u003c/strong\u003e features larger cages and more accessible pore windows, offering enhanced molecular accessibility while retaining the same chemical composition and node-linker connectivity.\u003c/p\u003e\n\u003cp\u003eGiven these structural distinctions, we imagined that the frameworks would exhibit markedly different sorption behaviors, despite their isoreticular relationship. To validate these hypotheses, we conducted a series of gas adsorption experiments under controlled conditions, with emphasis on CO\u003csub\u003e2\u003c/sub\u003e sorption at room temperature, to quantitatively assess how framework inversion affects guest accessibility and storage capacity.\u003cins cite=\"mailto:Kent%20Kirlikovali\" datetime=\"2025-11-07T14:50\"\u003e\u0026nbsp;\u003c/ins\u003eIn particular, we anticipated that \u003cstrong\u003eNU-6001\u003c/strong\u003e would demonstrate higher CO\u003csub\u003e2\u003c/sub\u003e uptake and more rapid adsorption kinetics due to its larger, less sterically hindered pore system, whereas \u003cstrong\u003eNU-6000\u003c/strong\u003e might exhibit selective adsorption toward smaller gas molecules, such as CO\u003csub\u003e2\u003c/sub\u003e, owing to its narrow aperture and potential for strong electrostatic interactions with the exposed chloride ions. In addition, we performed post-synthetic modifications to \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e to exchange the terminal chloride ions with terminal hydroxide groups, which we anticipated would improve the CO\u003csub\u003e2\u003c/sub\u003e capture performance of these materials. First, \u003cstrong\u003eNU-6000-\u003c/strong\u003e\u003cstrong\u003eHCO\u003csub\u003e3\u003c/sub\u003e\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e\u003cstrong\u003e-HCO\u003csub\u003e3\u003c/sub\u003e\u003c/strong\u003e were prepared by soaking \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e in aqueous solutions of NaHCO\u003csub\u003e3\u003c/sub\u003e, followed by subsequent washing with water and organic solvents.\u003csup\u003e37\u003c/sup\u003e After heating at 200 \u0026deg;C under vacuum for 2 h, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e were obtained and confirmed by crystal structure (Fig. 5a-c and Supplementary Fig. 24) and DFITS (Fig. 5e,f and Supplementary Fig. 43 and 44). PXRD patterns of the ligand-exchanged MOFs closely match those of \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e, confirming that the post-synthetic modifications do not cause any major structural changes (Fig. 3a,b). Moreover, the disappearance of Cl 2p signals in the X-ray photoelectron spectra (XPS) indicates nearly quantitative exchange of chloride regardless of the post-synthesis linker exchange method used (Supplementary Fig. 39 and 40).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe parent frameworks \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e display smooth, nearly linear CO\u003csub\u003e2\u003c/sub\u003e uptakes up to 1 bar (Fig. 4a), characteristic of physisorption. Across the whole pressure range, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e adsorbs more CO\u003csub\u003e2\u003c/sub\u003e than \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e. At low CO\u003csub\u003e2\u003c/sub\u003e partial pressures, the chemisorptive interactions between CO\u003csub\u003e2\u003c/sub\u003e and the Zn-OH functional groups dominate, resulting in steep CO\u003csub\u003e2\u003c/sub\u003e uptake at low pressures (1-10 mbar, 0.1-1% CO\u003csub\u003e2\u003c/sub\u003e) and ultra-low pressures (\u0026lt;0.02 mbar, 0.1% CO\u003csub\u003e2\u003c/sub\u003e) in both \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e (Fig. 4a). At higher pressures (\u0026gt;20 mbar), however, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e shows similar or slightly greater capacities than \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e. For instance, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e adsorbs ~2.1 mmol/g and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e reaches ~1.7 mmol/g (Fig. 4b) at 298 K and 150 mbar, representative of post-combustion streams. This trend highlights the significant effect of pore confinement in the physisorption MOF series, besides chemical binding sites.\u003csup\u003e53, 54, 55\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUnder lower CO\u003csub\u003e2\u003c/sub\u003e concentrations in which the driving force is minimal and site efficiency becomes limiting, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e achieves 1.2 mmol/g at 0.4 mbar, comparable to NbOFFIVE-1-Ni (~1.3 mmol/g)\u003csup\u003e56\u003c/sup\u003e and below chemisorptive amine-functionalized benchmarks such as Mg\u003csub\u003e2\u003c/sub\u003e(dobpdc)(en)\u003csub\u003e0.33\u003c/sub\u003e (~2.8 mmol/g)\u003csup\u003e57\u003c/sup\u003e and Mg\u003csub\u003e2\u003c/sub\u003e(dobdc)(N\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e1.8\u003c/sub\u003e (~3.9 mmol/g)\u003csup\u003e58\u003c/sup\u003e. Notably, this level is reached without pendant amines, offering a chemically robust alternative that mitigates known amine-deactivation pathways while preserving high low-pressure uptake. The contrast between \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e (0.32 mmol/g) underscores the role of linker geometry and aperture tuning in raising the fraction of sites that react with CO\u003csub\u003e2\u003c/sub\u003e at 420 ppm. Due to the small cavity size of Cage 1 in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e, only two of the four Zn-OH groups oriented toward the cavity\u0026nbsp;(geometrically accessible), at most, can chemically bind with CO\u003csub\u003e2\u003c/sub\u003e to form HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, as can be clearly observed from the single-crystal structure of \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e after CO\u003csub\u003e2\u003c/sub\u003e binding (Fig. 5c).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the field of direct air capture (DAC, 420 ppm CO\u003csub\u003e2\u003c/sub\u003e), the performance of an adsorbent is determined not only by the number of chemically active sites (site loading), but also by the fraction of these sites that can react with CO\u003csub\u003e2\u003c/sub\u003e under low-concentration conditions, known as the site efficiency. Numerous studies\u003csup\u003e59\u003c/sup\u003e have shown that even when MOFs are functionalized with a high density of hydroxyl, amine, or other CO\u003csub\u003e2\u003c/sub\u003e-philic groups, only a limited proportion of these sites participate in the formation of bicarbonates or carbamates during DAC. Typical conversion ratio of reacted CO\u003csub\u003e2\u003c/sub\u003e per site (site efficiency) ranges from 5% to 40%. For example, the mono-hydroxyl functionalized CFA-1-OH\u003csup\u003e37\u003c/sup\u003e exhibits a site efficiency of 34.6%, while Ni-CFA-1-OH\u003csup\u003e60\u003c/sup\u003e improves this to 41.5%. In contrast, MFU-4-OH and MFU-4l-OH, which both feature [Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e6+\u003c/sup\u003e nodes, utilize only 10.9% and 8.2% of their available sites for CO\u003csub\u003e2\u003c/sub\u003e binding, respectively. Similarly, amine-functionalized MIL-101(Cr)-TAEA\u003csup\u003e61\u003c/sup\u003e or MOF-808-Lys\u003csup\u003e62\u003c/sup\u003e have site efficiencies below 20%. This means that most chemical adsorption sites remain \u0026ldquo;idle\u0026rdquo; under DAC conditions, limiting the practical CO\u003csub\u003e2\u003c/sub\u003e capture capacity. Unlike many MOFs where virtually all nominal sites are accessible under working conditions, steric confinement in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e imposes an upper bound of two opposing \u0026ndash;OH groups per cavity as geometrically accessible sites. Under DAC-relevant conditions (0.4 mbar CO\u003csub\u003e2\u003c/sub\u003e), 61.4% of these accessible sites are actually engaged by CO\u003csub\u003e2\u003c/sub\u003e (per-accessible-site engagement), corresponding to 30.7% relative to all nominal \u0026ndash;OH sites. This confinement-controlled limitation of accessible sites leads to a 61.4% per-accessible-site engagement, surpassing prior reports for chemisorption-based MOFs in the ultra-dilute regime. (Fig. 4c)\u003csup\u003e37, 54, 57, 58, 60, 61, 62, 63, 64, 65\u003c/sup\u003e. This performance is attributed to an extreme spatial confinement effect. By precisely tuning the pore aperture and the spatial arrangement of functional sites, CO\u003csub\u003e2\u003c/sub\u003e molecules entering the pore channels are effectively directed to the reactive centers. As a result, the majority of functional sites can chemically bind CO\u003csub\u003e2\u003c/sub\u003e. This design concept not only maximizes CO\u003csub\u003e2\u003c/sub\u003e uptake capacity, but also provides a new paradigm for developing high-efficiency, low-cost, and scalable adsorbents for DAC applications.\u003c/p\u003e\n\u003cp\u003eIn the ultra-dilute regime (~30 ppm CO\u003csub\u003e2\u003c/sub\u003e), relevant to tail-end polishing of high-purity gas streams and to the local ultra-low CO\u003csub\u003e2\u003c/sub\u003e partial pressures encountered near the adsorption front in air contactors, adsorption performance is governed less by nominal site density than by intrinsic binding affinity and site efficiency. Under such conditions, where the driving force for adsorption is minimal, most porous materials operate near their baseline capacity. Remarkably, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e maintains measurable uptake across a wide pressure range, from industrially relevant 150 mbar (~15% CO\u003csub\u003e2\u003c/sub\u003e, flue gas) down to 0.4 mbar (~420 ppm, air) and retains exceptional performance even at 0.03 mbar (~30 ppm). The sustained uptake of 1.1 mmol/g at 30 ppm CO\u003csub\u003e2\u003c/sub\u003e demonstrates that the chemisorptive Zn\u0026ndash;OH sites in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e are both sufficiently strong and readily accessible, reflecting the intended coupling between functional-site density and aperture-level mass transport. By contrast, the parent \u003cstrong\u003eNU-6000\u003c/strong\u003e and its isostructural analogue \u003cstrong\u003eNU-6001\u003c/strong\u003e exhibit negligible CO\u003csub\u003e2\u003c/sub\u003e uptake in the low- and ultra-low-pressure regions, confirming that hydroxyl functionalization is essential for generating active Zn\u0026ndash;HCO\u003csub\u003e3\u003c/sub\u003e binding sites in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIsosteric heat of adsorption (\u003cem\u003eQ\u003c/em\u003est).\u0026nbsp;\u003c/strong\u003eCO\u003csub\u003e2\u003c/sub\u003e adsorption isotherms were collected over 288-308 K, and the isosteric heat of adsorption (\u003cem\u003eQ\u003c/em\u003est) was obtained as a function of loading (n) from the Clausius-Clapeyron relation (Fig. 4d, Supplementary Fig. 41, and 42). For the parent frameworks \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e, Qst values fall within the physisorption regime and remain essentially constant with loading. \u003cstrong\u003eNU-6000\u003c/strong\u003e shows a modest decrease from ~30 kJ/mol at very low n to a plateau of ~23-24 kJ/mol, while \u003cstrong\u003eNU-6001\u003c/strong\u003e exhibits a slight monotonic increase toward ~23 kJ/mol across the measured range. These trends are consistent with pore filling on predominantly dispersive sites and a relatively homogeneous adsorption landscape in the parent materials. In contrast, the -OH-modified analogs display pronounced loading-dependent Qst values. \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e rises to a maximum of ~75 kJ/mol at n = 0.6-0.7 mmol/g and then decays toward ~20 kJ/mol as pores fill. \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e shows an apparent anomaly at the lowest coverages (nonphysical negative Qst with large uncertainty), followed by a sharp peak of ~95 kJ/mol near n = 1.1-1.2 mmol/g and a gradual decline to ~30 kJ/mol at higher loading. The shaded envelopes indicate sizeable uncertainties at low pressure. The observed maxima (~75-90 kJ/mol) point to a strong, likely chemisorptive interaction introduced by the -OH functionality (e.g., bicarbonate/carbamate-like binding or cooperative H-bonding at basic sites), while the return to ~20-30 kJ/mol at higher n reflects a transition to weaker, physisorptive processes. Practically, such strong initial binding benefits trace-level capture but implies higher regeneration energy; beyond loadings of ~1 mmol/g, adsorption is dominated by weaker interactions that require lower regeneration energies to desorb.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDynamic Breakthrough and Competitive CO\u003csub\u003e2\u003c/sub\u003e Capture under Humidity.\u003c/strong\u003e Based on the superior CO\u003csub\u003e2\u003c/sub\u003e uptake of \u003cstrong\u003eNU-6000-OH\u0026nbsp;\u003c/strong\u003eat room temperature, we next assessed how the pre-configured Zn-OH microenvironments translate into dynamic separation under flow conditions. To this end, dynamic breakthrough experiments were conducted under 1 vol% and 15 vol% CO\u003csub\u003e2\u003c/sub\u003e/N\u003csub\u003e2\u003c/sub\u003e feeds, each tested under dry, 50% relative humidity (RH), and 90% RH conditions to quantify the influence of water on adsorption properties (Fig. 4e,f). For 1 vol% CO\u003csub\u003e2\u003c/sub\u003e/N\u003csub\u003e2\u003c/sub\u003e, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e exhibits the earliest breakthrough under dry conditions, showing a steep mass-transfer front at 411 min/g, corresponding to a CO\u003csub\u003e2\u003c/sub\u003e adsorption capacity of 0.40 mmol/g (single-component isotherm capacity at 0.01 bar CO\u003csub\u003e2\u003c/sub\u003e: 1.30 mmol/g). This behavior indicates rapid uptake and largely reversible binding at the oriented \u0026ndash;OH arrays. Introducing 50% RH shifts the breakthrough to a later time (477 min/g; 0.44\u0026nbsp;mmol/g) while preserving a narrow mass-transfer zone, revealing a humidity-assisted enhancement of dynamic capacity. This effect arises from water molecules\u0026nbsp;anchored onto the Zn\u0026ndash;OH sites, mediating the formation of a bicarbonate-like CO\u003csub\u003e2\u003c/sub\u003e adduct through cooperative hydrogen bonding, which was confirmed by DFT calculation (Fig. 5d and Supplementary Figs. 47\u0026ndash;52). The confined hydration remains discontinuous, preventing the development of a percolated water network and preserving diffusion pathways. At 90% RH, the breakthrough is further delayed (517 min/g; 0.49 mmol/g), and the bed approaches saturation more gradually as excess water begins to compete with CO\u003csub\u003e2\u003c/sub\u003e for \u0026ndash;OH sites.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhen the CO\u003csub\u003e2\u003c/sub\u003e feed concentration is increased to 15%, the higher driving force accelerates saturation and shifts the breakthrough to earlier times. Under dry conditions, the front remains sharp at 78 min/g, corresponding to a CO\u003csub\u003e2\u003c/sub\u003e adsorption capacity of 1.37 mmol/g (single-component isotherm capacity at 0.15 bar CO\u003csub\u003e2\u003c/sub\u003e: 2.11 mmol/g), and the bed productivity rises accordingly. Introducing 50% RH extends the breakthrough to 94 min/g (1.61 mmol/g) while maintaining a narrow mass-transfer zone, indicating that a thin hydration layer promotes reversible CO\u003csub\u003e2\u003c/sub\u003e activation without impeding transport. At 90% RH, the breakthrough occurs at an intermediate time (86 min/g; 1.49 mmol/g), reflecting partial pore occupation by water that modestly reduces access to the \u0026ndash;OH sites.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThese capacities are lower than those expected from single-component isotherm measurements, likely because non-equilibrium flow conditions limit complete utilization of the pore volume. In addition, diffusional resistance and partial mass-transfer inefficiencies under dynamic operation can further reduce the accessible adsorption capacity compared to static equilibrium measurements. Unlike state-of-the-art CO\u003csub\u003e2\u003c/sub\u003e-capture MOFs such as MAF-X27ox,\u003csup\u003e65\u003c/sup\u003e CFA-1,\u003csup\u003e60\u003c/sup\u003e or MOF-74 derivatives,\u003csup\u003e66, 67\u003c/sup\u003e whose CO\u003csub\u003e2\u003c/sub\u003e chemisorption behavior is either humidity-insensitive or strongly humidity-dependent but structurally fragile, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e exhibits enhanced CO\u003csub\u003e2\u003c/sub\u003e adsorption under humid conditions, and its confined Zn\u0026ndash;OH arrays enable cooperative yet stable hydration that enhances reversible CO\u003csub\u003e2\u003c/sub\u003e activation without compromising framework integrity, achieving humidity tolerance and capacity enhancement simultaneously. This humidity-tolerant and reversible chemisorption mechanism demonstrates how local geometric confinement can balance water compatibility and CO\u003csub\u003e2\u003c/sub\u003e reactivity, offering a rational pathway toward sorbents that maintain strong CO\u003csub\u003e2\u003c/sub\u003e uptake under realistic humid conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDiffuse-reflectance IR spectroscopy (DRIFTS).\u003c/strong\u003e DRIFTS confirms that both \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e capture CO\u003csub\u003e2\u003c/sub\u003e at framework hydroxyl sites through bicarbonate formation (Fig. 5d,e, Supplementary Fig. 43 and 44). At room temperature, \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e shows new bands at 1471, 1614, and 1655 cm\u003csup\u003e-1\u003c/sup\u003e, while \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e displays bands at 1505, 1634, and 1650 cm\u003csup\u003e-1\u003c/sup\u003e. Features in the 1610-1655 cm\u003csup\u003e-1\u003c/sup\u003e range are assigned to the asymmetric C-O stretch of bicarbonate, and the bands near 1470-1505 cm\u003csup\u003e-1\u003c/sup\u003e fall within the region of the symmetric C-O stretch and the O-H-O bending vibration, which together indicate hydrogen-bond-stabilized Zn-O\u003csub\u003e2\u003c/sub\u003eCOH species with a likely bidentate coordination at the hydroxyl sites. The high-frequency O-H region tracks the thermal evolution of these adducts. For \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e, CO\u003csub\u003e2\u003c/sub\u003e binding gives a hydrogen-bonded O-H stretch at 3607 cm\u003csup\u003e-1\u003c/sup\u003e; heating under dry N\u003csub\u003e2\u003c/sub\u003e weakens this feature and produces a band at 3665 cm\u003csup\u003e-1\u003c/sup\u003e while a band at 3676 cm\u003csup\u003e-1\u003c/sup\u003e grows; with further heating, only the sharp 3676 cm\u003csup\u003e-1\u003c/sup\u003e peak remains, consistent with complete bicarbonate removal and recovery of isolated Zn-OH species. \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e follows the same sequence and ultimately shows a single high-frequency O-H stretch at 3688 cm\u003csup\u003e-1\u003c/sup\u003e, also diagnostic of isolated Zn-OH sites after bicarbonate decomposition. The concurrent decay of the bicarbonate C-O bands and the reappearance of the free O-H bands demonstrate a reversible process in which CO\u003csub\u003e2\u003c/sub\u003e forms bicarbonate at ambient conditions and is released upon thermal regeneration, restoring the active hydroxyl sites.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThermal swing adsorption-desorption experiments.\u003c/strong\u003e We conducted thermal-swing adsorption-desorption (TSAD) measurements to evaluate adsorption kinetics, regeneration temperature, and cyclic stability of the sorbents. Under a gas mixture of 15 vol% CO\u003csub\u003e2\u003c/sub\u003e/ N\u003csub\u003e2\u003c/sub\u003e, with adsorption near 298 K and thermal regeneration at 200 \u0026deg;C, both \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e and \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e show robust performance with only slight decreases in capacity over 50 adsorption-desorption runs (Supplementary Fig. 45 and 46). \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e reaches ~8.8 wt% at 298 K (2 mmol/g) and maintains a slightly higher steady-state uptake (7.5 wt%, 1.7 mmol/g), whereas \u003cstrong\u003eNU-6001-OH\u003c/strong\u003e starts at ~1.9 mmol/g (~8.4 wt%) and stabilizes at ~1.4 mmol/g (~6.2 wt%) by the end of cycling, giving a modestly lower capacity than \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e. For both frameworks, TSAD uptakes are higher than those inferred from single-component isotherms at comparable CO\u003csub\u003e2\u003c/sub\u003e partial pressures, which is commonly observed for MOF sorbents, likely due to temperature-swing re-exposure of high-energy sites together with minor multicomponent/kinetic effects. In absolute terms, the simulated-flue gas performance of these hydroxylated MOFs exceeds that of Mg\u003csub\u003e2\u003c/sub\u003e(dobdc)-mmen (4.6 wt%) but remains below that of Mg\u003csub\u003e2\u003c/sub\u003e(dobpdc)en (11.8 wt%), confirming good cyclability and CO\u003csub\u003e2\u003c/sub\u003e TSAD performance for \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetermination of the binding domains for adsorbed CO\u003csub\u003e2\u003c/sub\u003e.\u0026nbsp;\u003c/strong\u003eThe binding domains of CO\u003csub\u003e2\u003c/sub\u003e in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e were elucidated through micro-ED analysis, \u003cem\u003ein situ\u003c/em\u003e DRIFTS measurements, and complementary DFT simulations. Structural refinement of activated \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e reveals the complete removal of guest solvent molecules and full exposure of four \u0026mu;\u003csub\u003e2\u003c/sub\u003e-OH groups lining the internal surface of each small cage, forming an array of open Zn-OH sites with well-defined orientation (Supplementary\u0026nbsp;Fig. 25). Micro-ED analysis of CO\u003csub\u003e2\u003c/sub\u003e-loaded \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e (Fig. 5a) reveals partial conversion of the Zn-bound hydroxyl groups into bicarbonate species upon CO\u003csub\u003e2\u003c/sub\u003e chemisorption. Within each Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e node, one Zn center exhibits positional disorder between two coordination modes, Zn-OH and Zn-OCO\u003csub\u003e2\u003c/sub\u003eH, indicating that only a fraction of the hydroxyl sites participates in the formation of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e while the remainder retain the terminal -OH groups. The coexistence of these two motifs at a single Zn site reflects the dynamic equilibrium established during CO\u003csub\u003e2\u003c/sub\u003e uptake and desorption. Considering the experimentally measured adsorption capacity, we infer that only two of the four Zn-OH sites in Cage 1 are involved in CO\u003csub\u003e2\u003c/sub\u003e binding, with the other two remaining unreacted. This mixed configuration yields an energetically favorable arrangement within the confined microcavity, minimizing steric congestion and allowing cooperative stabilization of the bound CO\u003csub\u003e2\u003c/sub\u003e molecules through adjacent hydrogen-bond networks (O\u0026middot;\u0026middot;\u0026middot;O = 2.8\u0026ndash;3.4 \u0026Aring;). The structural disorder between Zn-OH and Zn-HCO\u003csub\u003e3\u003c/sub\u003e motifs thus represents a crystallographic snapshot of the chemisorption process and provides direct evidence for the reversible transformation between hydroxyl and bicarbonate species under mild conditions.\u003c/p\u003e\n\u003cp\u003eTo further elucidate the cooperative chemisorption behavior observed experimentally, DFT calculations were performed for \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e models containing one, two, three, and four chemisorbed CO\u003csub\u003e2\u003c/sub\u003e molecules per small cage (Fig. 5c). The optimized structures are summarized in Supplementary Fig. 47\u0026ndash;52. Upon uptake of one CO\u003csub\u003e2\u003c/sub\u003e molecule (Supplementary Fig. 48), the framework (1-HCO\u003csub\u003e3\u003c/sub\u003e) predominantly stabilizes a bicarbonate species with Gibbs free energy (\u0026Delta;\u003cem\u003eG\u003c/em\u003e) = \u0026minus;61.3 kJ/mol. When two CO\u003csub\u003e2\u003c/sub\u003e molecules are present, the \u003cem\u003eortho\u003c/em\u003e configuration (2-HCO\u003csub\u003e3\u003c/sub\u003e-\u003cem\u003eo\u003c/em\u003e) yields a mixed bicarbonate\u0026ndash;carbonate pair with steric repulsion and distortion of the hydrogen-bond geometry result in \u0026Delta;\u003cem\u003eG\u003c/em\u003e = \u0026minus;54.2 kJ/mol (Supplementary Fig. 49), whereas the \u003cem\u003epara\u003c/em\u003e configuration (2-HCO\u003csub\u003e3\u003c/sub\u003e-\u003cem\u003ep\u003c/em\u003e) favors the formation of two carbonate units; in this case, the terminal \u0026ndash;OH group is converted to H\u003csub\u003e2\u003c/sub\u003eO, which in turn participates in a locally ordered cyclic hydrogen-bonding network. In this configuration with two opposite bicarbonates across the cage window displays a low energy (\u0026Delta;\u003cem\u003eG\u003c/em\u003e = \u0026minus;145.8 kJ/mol), stabilized by the cyclic hydrogen-bonded network formed by two directional hydrogen bonds (O\u0026middot;\u0026middot;\u0026middot;H = ~1.4 \u0026Aring;) linking the Zn\u0026ndash;OH\u003csub\u003e2\u003c/sub\u003e and Zn\u0026ndash;CO\u003csub\u003e3\u003c/sub\u003e units (Supplementary Fig. 50). Among these configurations, the structure containing three bicarbonate species (3-HCO\u003csub\u003e3\u003c/sub\u003e) exhibits a cooperative environment forms comprising bicarbonate, carbonate, and water species with the lowest \u0026Delta;\u003cem\u003eG\u0026nbsp;\u003c/em\u003e(\u0026minus;149.2 kJ/mol), where a cyclic hydrogen-bonded network is formed with neighboring Zn\u0026ndash;OH groups and adjacent bicarbonates, generating an extended cooperative O\u0026middot;\u0026middot;\u0026middot;H\u0026middot;\u0026middot;\u0026middot;O array within the confined cavity (Supplementary Fig. 51).\u0026nbsp;By contrast, when four CO\u003csub\u003e2\u003c/sub\u003e molecules are introduced, the system (4-HCO\u003csub\u003e3\u003c/sub\u003e) reverts predominantly to bicarbonate formation because of steric effect and display a \u0026Delta;\u003cem\u003eG\u0026nbsp;\u003c/em\u003e= \u0026minus;125.1 kJ/mol\u003csup\u003e\u0026nbsp;\u003c/sup\u003e(Supplementary Fig. 52).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe thermodynamic distinction between the 3-HCO\u003csub\u003e3\u003c/sub\u003e and 2-HCO\u003csub\u003e3\u003c/sub\u003e-\u003cem\u003ep\u003c/em\u003e configurations is marginal in the idealized static model. Consideration of gas diffusion constraints, steric accessibility, and gating barrier during stepwise adsorption within the pore suggests that the opposite-pair di-bicarbonate configuration (2-HCO\u003csub\u003e3\u003c/sub\u003e-\u003cem\u003ep\u003c/em\u003e) is the most plausible adsorption state under experimental conditions. This model aligns with the single-crystal structure of CO\u003csub\u003e2\u003c/sub\u003e-loaded \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e, which shows partial conversion of Zn\u0026ndash;OH to Zn\u0026ndash;HCO\u003csub\u003e3\u003c/sub\u003e and approximately two CO\u003csub\u003e2\u003c/sub\u003e molecules bound per cage. Collectively, these results indicate that CO\u003csub\u003e2\u003c/sub\u003e uptake in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e proceeds through cooperative hydrogen-bonding interactions among symmetrically aligned hydroxyl sites, where the formation of a locally ordered hydrogen-bond network stabilizes carbonate-rich intermediates and achieves an optimal balance between strong binding and reversible regeneration. This mechanistic picture aligns with the breakthrough measurements, where water markedly enhances CO\u003csub\u003e2\u003c/sub\u003e capture under flow, confirming that hydration-assisted hydrogen-bond networks facilitate CO\u003csub\u003e2\u003c/sub\u003e activation and stabilization in \u003cstrong\u003eNU-6000-OH\u003c/strong\u003e.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThrough reticular chemistry, we have established a strategy for designing MOFs with tunable chemical microenvironments within their pores. Starting from a known Kuratowski-type Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e secondary building unit, we rationally modified linker geometry to target the \u003cstrong\u003eith-d\u003c/strong\u003e topology in which terminal Zn-bound groups are oriented toward the cage interior to create confined, chemically addressable spaces. This design enabled the construction of an isoreticular pair of triazolate MOFs, \u003cstrong\u003eNU-6000\u003c/strong\u003e and \u003cstrong\u003eNU-6001\u003c/strong\u003e, where flipping the coordinated arms of rigid, mixed triazole linkers aligns with node symmetry to preserve the overall topology while reprogramming cage size, aperture, and inward functionality. These frameworks are structurally well-defined and thermally robust above 525 \u0026deg;C, as confirmed by VT-PXRD, TGA, and CO\u003csub\u003e2\u003c/sub\u003e sorption isotherm measurements. Post-synthetic Cl\u003csup\u003e-\u003c/sup\u003e/OH\u003csup\u003e-\u003c/sup\u003e exchange introduces dense, oriented Zn-OH arrays that mediate strong yet reversible CO\u003csub\u003e2\u003c/sub\u003e binding through bicarbonate formation, achieving a site utilization efficiency of 61.4%, which is the highest among MOFs reported under DAC conditions. Beyond overcoming long-standing synthetic challenges in the Zn\u003csub\u003e5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e-triazolate family, this work establishes a transferable design principle for engineering chemically robust, permanently porous materials with preconfigured microenvironments. More broadly, this tunable confinement strategy offers a generalizable platform for gas separation, selective adsorption, and confined catalysis, where control over local geometry and functionality can be leveraged to direct molecular recognition and reactivity within well-defined crystalline pores.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDetailed synthetic procedures, NMR spectra, X-ray crystallographic structures, TGA curves, UV-Vis spectra, Raman spectra, and crystal data (PDF) are provided in the Supplementary Information. Meanwhile, the X-ray crystallographic data have also been deposited at the Cambridge Crystallographic Data Center (CCDC), which can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNotes\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare the following competing financial interest(s): O.K.F. has a financial interest in Numat Technologies, a startup company that is seeking to commercialize MOFs.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Catalyst Design for Decarbonization Center, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under grant DE-SC0023383 for synthesis and characterization of metal\u0026ndash;organic frameworks. This research was supported by UL Research Institutes for separations studies. This work made use of the IMSERC (RRID: SCR_017874) Crystallography facility, NMR facility, and MS facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633) and Northwestern University. This work made use of the NUFAB facility (RRID: SCR_017779) of Northwestern University\u0026rsquo;s NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern\u0026rsquo;s MRSEC program (NSF DMR-2308691)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBuller, A.R., Townsend, C.A. 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The effect of water adsorption on the structure of the carboxylate containing metal\u0026ndash;organic frameworks Cu-BTC, Mg-MOF-74, and UiO-66. \u003cem\u003eJ\u003c/em\u003e\u003cem\u003e. \u003c/em\u003e\u003cem\u003eMater\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e\u003cem\u003e Chem\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e\u003cem\u003e A\u003c/em\u003e \u003cstrong\u003e1\u003c/strong\u003e, (2013).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8090759/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8090759/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Controlling chemical microenvironments within porous crystalline materials is central to advancing selective adsorption, separation, and catalytic processes, yet remains difficult to achieve in stable frameworks with precisely oriented functional sites. Here, we leverage reticular chemistry to program tunable confinement in triazolate metal–organic frameworks (MOFs) built from Kuratowski-type Zn5Cl4 nodes. Rational modulation of linker geometry targets the ith-d topology in which terminal Zn-bound groups point inward to define confined, chemically addressable pores. This design yields two isoreticular frameworks, NU-6000 and NU-6001, that preserve the overall topology while reconfiguring cage dimensions, apertures, and pore functionality through linker inversion. The frameworks are structurally well-defined and thermally stable beyond 525 °C, and post-synthetic chloride-to-hydroxide exchange installs dense, oriented Zn-OH arrays without loss of crystallinity, enabling strong yet reversible CO2 binding through bicarbonate formation. Single-crystal analysis of a CO2 adduct reveals a geometric accessibility rule in the smallest cage of NU-6000, where only a subset of inward-facing hydroxyls can bind to form bicarbonate, thereby setting an intrinsic upper bound to uptake that is dictated by cage architecture rather than linker count. Under this tunable local-confinement regime in NU-6000, the framework achieves high CO2 uptake across a broad low-pressure range, including at concentrations as low as 30 ppm, and attains a site utilization of 61.4 % at 420 ppm, representing the highest efficiency reported for MOFs under comparable conditions. This work establishes a generalizable approach for encoding functional confinement into robust crystalline frameworks, bridging molecular design with solid-state functionality for selective gas capture and other confinement-driven applications.","manuscriptTitle":"Programming Local Confinements in Crystalline Frameworks through Reticular Chemistry","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 20:18:48","doi":"10.21203/rs.3.rs-8090759/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-materials","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nmat","sideBox":"Learn more about [Nature Materials](http://www.nature.com/nmat/)","snPcode":"","submissionUrl":"","title":"Nature Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"62d98b0b-24af-49ff-8d07-9f5141f40fad","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":58397186,"name":"Physical sciences/Chemistry/Materials chemistry/Metal\u0026#x2013;organic frameworks"},{"id":58397187,"name":"Physical sciences/Chemistry/Supramolecular chemistry/Crystal engineering"},{"id":58397188,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Metal\u0026#x2013;organic frameworks"}],"tags":[],"updatedAt":"2026-05-01T07:45:30+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-01 20:18:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8090759","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8090759","identity":"rs-8090759","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}