Naturally Asymmetric Plant Polyphenol Linkers Enable Robust Metal-Organic Frameworks with Built-In Structural Heterogeneity

Naturally Asymmetric Plant Polyphenol Linkers Enable Robust Metal-Organic Frameworks with Built-In Structural Heterogeneity | 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 Naturally Asymmetric Plant Polyphenol Linkers Enable Robust Metal-Organic Frameworks with Built-In Structural Heterogeneity Jiaojiao Shang, Zijun Zhu, Tong Shao, Lantao He, Jun Deng, Yang Chu, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9550934/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Metal–organic frameworks (MOFs) have been built largely on geometrically regular linkers, whereas asymmetric molecules have received far less attention. Such asymmetric linkers offer a unique opportunity to encode structural heterogeneity, coordinatively unsaturated sites, and chemically differentiated pores directly at the molecular design stage. However, their structural complexity often makes periodic frameworks assembly and structure determination more challenging. Here, we show that haematoxylin, a naturally occurring plant polyphenol with two chemically inequivalent catechol coordination sites, can serve as an intrinsically asymmetric linker for constructing a crystalline bismuth framework, SCU-1. Despite the low symmetry of the linker, SCU-1 can be synthesized in water with good scalability and retains long-range order. Structural modelling, electron diffraction, powder diffraction refinement, thermogravimetric compositional analysis, and low-angle diffraction collectively support a structurally heterogeneous framework associated with asymmetric coordination behavior. At the same time, strong Bi-phenolate chelation, rod-like inorganic building units, and hydrogen-bond reinforcement endow SCU-1 with exceptional robustness, allowing it to remain crystalline from pH 1 to 13, in diverse aqueous and organic media, and up to 450°C under N 2 . The resulting ultramicroporous phenolic framework exhibits strong CO 2 affinity, with a dominant pore feature of ~ 5 Å and a calculated binding energy of − 87.5 kJ mol − 1 , arising from cooperative confinement and multipoint host–guest interactions. Under visible light, SCU-1 further enables additive-free photocatalytic CO 2 conversion in water, favoring ethanol formation at 50.13 µmol g − 1 h − 1 . These findings establish naturally asymmetric phytochemicals as an underexplored linker platform for creating robust MOFs with structural heterogeneity and functional CO 2 -binding microenvironments. Physical sciences/Chemistry/Supramolecular chemistry/Self-assembly Physical sciences/Materials science/Nanoscale materials/Organic–inorganic nanostructures Physical sciences/Chemistry/Green chemistry/Sustainability Physical sciences/Chemistry/Coordination chemistry/Organometallic chemistry/Ligands Asymmetric linker Plant polyphenol Bismuth-based MOF Structural heterogeneity CO2 photoreduction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Metal–organic frameworks (MOFs) derive their structural diversity from the combination of inorganic nodes and organic linkers. However, the vast majority of crystalline MOFs have been constructed from geometrically regular ligands, because symmetry facilitates predictable network formation, supports long-range order, and simplifies crystallographic analysis 1 – 5 . Although this design logic has been central to the success of reticular chemistry 4 , 6 , it also narrows the range of accessible molecular building blocks and limits opportunities to introduce local disorder, heterogeneous pore environments, and structurally complex frameworks 7 – 9 . This limitation is becoming increasingly relevant as MOF research moves beyond defect-free crystals toward framework heterogeneity as a functional design element 10 – 12 . Defect engineering, low-symmetry ligands, and heterogeneous pores have all emerged as effective routes to tune adsorption and catalysist 8 , 13 , 14 . Yet most current strategies either modify conventional frameworks or rely on synthetically tailored ligands 8 , 13 , 15 . For example, Dincă and co-workers used a symmetry-reduction strategy to construct an amorphous MOF containing locally ordered MOF-74 domains 16 . These studies clearly demonstrate that lowering linker symmetry can generate new structural features and functions. They also highlight a fundamental challenge: asymmetric linkers generally complicate topology prediction, hinder the growth of high-quality single crystals, and make structural determination difficult 17 . Moreover, most asymmetric linkers explored to date have been derived from synthetic chemistry 13 , 15 – 17 . Although effective, such ligands may suffer from limited chemical stability and may not be ideal for applications that demand low cost, environmental compatibility, or biological safety 18 , 19 . By contrast, intrinsically asymmetric molecules from nature remain largely unexplored in the construction of crystalline MOFs, despite their potential to provide complex coordination environments and diverse pores. Developing asymmetric linkers that combine structural complexity, strong metal-binding ability, and favorable biocompatibility, therefore, remains an important challenge in MOF chemistry. Plant polyphenols are especially attractive candidates for addressing this challenge. These molecules are renewable, low-cost, and rich in metal-binding and secondary interaction motifs 20 – 23 . Their phenolic hydroxyl groups can strongly chelate metal ions, often producing robust coordination architectures, while their multiple hydrogen-bonding and π-interaction sites can enrich host–guest interactions within pores 24 , 25 . Nevertheless, plant polyphenols explored in frameworks construction have so far been largely restricted to highly symmetric molecules 20 . It remains unclear whether intrinsically asymmetric plant polyphenols can act as framework linkers and introduce local heterogeneity without disrupting long-range order. Such molecules are highly appealing because their non-equivalent coordination sites could create local structural heterogeneity, whereas strong metal-phenolate bonding could preserve framework integrity. This combination suggests a promising route to crystalline MOFs that unite structural complexity with high robustness. Here, we use haematoxylin (HMT), a naturally occurring plant polyphenol containing two electronically distinct catechol coordination sites, to construct a bismuth-based MOF (SCU-1) synthesized in aqueous acetic acid and accessible at an enlarged scale (Fig. 1 A). Structural modelling combined with electron diffraction and powder diffraction refinement supports a tetragonal framework with one-dimensional channels and rod-like bismuth oxo subunits. HMT is a typical nonplanar and chiral molecule that provides an intrinsically asymmetric coordination. Quantum-chemical analysis further reveals pronounced site differentiation in HMT, with one catechol unit showing an order-of-magnitude higher reactivity toward Bi 3+ coordination than the other, although both sites are accessible (Fig. 1 B). These features indicate that HMT is a naturally low-symmetry linker capable of encoding coordination inequivalence and framework heterogeneity during assembly. The strong Bi–phenolate chelation enables this heterogeneity to be accommodated without loss of crystallinity or robustness. As a result, SCU-1 combines exceptional stability with ultramicroporosity. This pore enables strong CO 2 binding through confinement-enhanced, multipoint host–guest interactions and further supports visible-light-driven photocatalytic CO 2 conversion (Figs. 1 C–E). This work establishes naturally asymmetric plant polyphenols as a viable linker platform for robust MOFs with built-in structural heterogeneity and interaction-rich pore microenvironments, and it provides a new strategy for expanding MOF chemistry beyond conventional symmetry-guided linker design. Results and Discussion Synthesis and frameworks construction of SCU-1 SCU-1 was synthesized by hydrothermal treatment of an aqueous suspension of bismuth nitrate and haematoxylin (HMT) for 36 h. The material could also be prepared under ambient-pressure reflux conditions, indicating that framework formation does not depend on a narrow solvothermal window. Phase purity and synthetic reproducibility were markedly improved by the addition of acetic acid as a modulator (6 vol%, pH ≈ 2.3). Notably, this acidity is comparable to that of common household vinegar, highlighting the mild and practical nature of the synthetic conditions. Solvent screening showed that ethanol and acetone did not yield crystalline products, whereas DMF led to a distinct reaction pathway in which Bi 3+ was reduced to Bi nanocrystals dispersed within an HMT-Bi matrix (Figures S1 and S2). Although this material lies beyond the scope of the present study, it further illustrates the rich coordination and redox chemistry of HMT towards bismuth and suggests that this phytochemical may also be useful for constructing uniformly dispersed Bi nanocrystal composites. The frameworks of SCU-1 consist of rod-like inorganic building units (IBUs) aligned along the c-axis and interconnected by HMT linkers to generate a three-dimensional network featuring one-dimensional channels along the same direction (Fig. 2 A). The coordination between Bi 3+ ions and the ortho-hydroxy groups of HMT promotes the formation of rod-like metal subunits, which further assemble into nanorod crystals with diameters of approximately 100 nm (Fig. 2 B). Structure determination was complicated by the intrinsic asymmetry of the HMT ligand. Despite extensive optimization of the synthetic conditions, crystals large enough for single-crystal X-ray diffraction could not be obtained. Only microcrystals were formed, and their local disorder along the c axis prevented direct structure solution by 3D electron diffraction (3DED). Nevertheless, the combination of 3DED, indexed diffraction patterns, and PXRD refinement provides strong evidence for a well-defined long-range ordered framework. Indexing of the 3DED data yielded unit-cell parameters consistent with those of SU-101 (Fig. 2 C, Table S1) 26 , and the refined PXRD pattern shows excellent agreement with a structural model derived from SU-101 (Figs. 2 D–F and Table S2). On this basis, SCU-1 was modelled in the tetragonal space group P4 2 (no. 77) with unit-cell constants a = b = 18.967 Å and c = 5.666 Å. Powder X-ray diffraction (PXRD) further confirmed the phase purity of SCU-1 and demonstrated excellent consistency between samples prepared via hydrothermal and reflux methods (Fig. 2 F). High isolated yields were achieved on both small (30 mL, 79%, 0.35 g) and larger scales (600 mL, 72%, 5.66 g), highlighting the scalability of this system using a renewable phytochemical linker. This result is particularly notable given that intrinsically asymmetric natural molecules are typically considered difficult to incorporate into crystalline MOF architectures due to their irregular coordination geometries and reduced predictability in long-range ordering. Structurally, each repeating unit contains one HMT anion and two Bi 3+ cations. Each Bi 3+ adopts an octahedral coordination geometry defined by six oxygen donors originating from coordinated water molecules, µ 4 -oxygen atoms, and the ortho-hydroxy groups of HMT, resulting in a charge-neutral framework with the composition Bi 2 O(H 2 O) 2 (C 16 H 10 O 6 ) (Figure S3). Within the coordination environment, one phenolate group of HMT binds to a single Bi 3+ center, while the other bridges two Bi 3+ ions along the rod-like IBU (Figure S4). In addition, non-coordinated water molecules located within the one-dimensional channels, along with neighboring coordinated water molecules, phenolic hydroxyl oxygen, hydroxyl oxygen, and pyran oxygen atoms, form multiple hydrogen-bonding interactions with distances ranging from 2.8 to 3.4 Å, indicating that SCU-1 possesses multiple host–guest interaction sites (Figure S5). The nonplanar geometry of the HMT ligand imposes significant steric confinement in the ab plane, leading to relatively narrow pore apertures. Although this geometric constraint reduces the accessible surface area, it is expected to enhance size-selective adsorption and separation through spatial confinement effects (Figs. 2 G, 1 B). To simplify the structural description, a topological analysis was conducted using the node-deconstruction approach proposed by Michael O'Keeffe and Omar Yaghi 27 . The nodes are linked to neighboring vertices along the rod, giving a 6-connected node. When the connections between adjacent rods through HMT anions are considered, the overall frameworks can be described as a uninodal 7-connected svd net (Fig. 2 H, I). Effect of linker asymmetry on framework formation Understanding how linker asymmetry affects periodic framework formation is a central aim of this study. To examine the site selectivity of HMT coordination, high-level quantum chemical calculations were first performed to evaluate the Gibbs free energies (ΔG) of binding between Bi 3+ and the two catechol coordination sites of HMT. The HMT molecule contains two catechol groups in distinct local environments: one attached to a fused five-membered ring (A ring) and the other to a pyran ring (B ring). HOMO analysis shows a clear difference in electron density between the two catechol units, with the A ring displaying a higher electron density and therefore a stronger coordination tendency (Fig. 3 A). This trend is supported by condensed Fukui function and dual descriptor analyses, which show that the electron density on the phenolic oxygen atoms of the A ring is approximately one order of magnitude higher than that of the B ring (Table S3). The corresponding binding thermodynamics further support this site selectivity. We next evaluated site selectivity using ΔG I *, which describes ligand binding strength. As shown in Fig. 3 B, site selectivity is predicted for Bi 3+ –HMT complexes, with coordination at the A ring favored by approximately 4.7 kJ mol – 1 relative to the B ring. This energy difference corresponds to a selectivity of about 4.2:1 at 120°C between the two sites. Importantly, the Gibbs free energy changes associated with chelating coordination at both sites are negative, indicating that chelation between Bi 3+ and either catechol group is thermodynamically favorable. As a result, both coordination modes can lead to the formation of the S3 motif, which subsequently self-assembles into the infinite periodic frameworks of SCU-1. These results demonstrate that differences in local chemical environments do not prevent the formation of periodic frameworks, provided that the linker structure is compatible with the coordination geometry of the node, highlighting the potential of such asymmetric linkers for Bio-MOF design. In addition, previous studies have shown that MOFs constructed from catechol- or pyrogallol-based linkers often display high structural stability 12 , 35 (Figure S9), further supporting the potential of polyphenols with chelating phenolate motifs as robust MOF linkers. Physicochemical characterization and frameworks robustness The thermal stability of MOF materials is a key consideration for their practical applications. To evaluate the thermal stability of SCU-1, thermogravimetric analysis (TGA) was performed under air and revealed three distinct stages of degradation (Fig. 4 A). The initial mass loss in the 35–95°C range corresponds to the evacuation of free guest H 2 O trapped in the pores. The subsequent mass loss up to approximately 190°C is assigned to the removal of two Bi-coordinated water molecules. The final stage, below 360°C, corresponds to decomposition of the organic linker and oxidation of the organic component, consistent with the known thermal behavior of phenolic MOFs. Additionally, TGA of SCU-1 agrees with the proposed sum formula. The stepwise weight loss and complete combustion of the organic content in the final stage allowed us to estimate the contents of guest molecules, coordinated H 2 O, HMT ligands, and residual Bi. Notably, in an ideal defect-free framework, the Bi:HMT ratio should be 2:1, whereas the TGA-derived value is 1.87:1. This deviation suggests a degree of node loss in the framework. Consistent with this interpretation, low-angle PXRD shows a broad diffraction feature, indicating the presence of nanoregions with missing metal nodes (Figure S10). Variable-temperature PXRD further confirms the high thermal stability of SCU-1. In air, structural changes become evident above 190°C, consistent with oxidation of the phenolic groups (Fig. 4 B). Under N 2 , however, SCU-1 retains its framework structure up to 450°C, demonstrating excellent thermal robustness (Fig. 4 B). This stability can be understood from several structural features. First, Bi 3+ in this system assembles into compact rod-like IBUs, which are known to impart high structural robustness (Fig. 4 C). Second, the ortho-hydroxy groups of HMT form five-membered chelate rings with Bi 3+ ions, with Bi–O bond lengths of approximately 2.1–2.2 Å, indicating deprotonation of the phenolic hydroxyls before coordination. These shorter bond lengths suggest stronger bonding compared to carboxylate-Bi coordination (typically 2.4–2.8 Å), contributing to the enhanced stability of the MOF (Fig. 4 D). In addition, the distance between the phenolic hydroxyl groups on the pyran rings of two adjacent HMT molecules in the ab plane is 2.8 Å, indicating hydrogen bonding between the HMT linkers and further stabilizing the structure (Fig. 4 E). Chemical stability is equally important for practical applications, especially under aqueous conditions. SCU-1 retains its crystallinity after 24 h in water, phosphate-buffered saline (PBS), and cell culture medium (RPMI 1640), indicating strong resistance to common coordinating species and biologically relevant media (Fig. 5 A). The acid–base tolerance of SCU-1 was further examined by exposure to aqueous H 2 SO 4 and NaOH solutions over a wide pH range. As shown in Fig. 5 B, the frameworks remain intact from pH 1 to 13. In concentrated sulfuric acid (pH = 0), SCU-1 undergoes complete decomposition. At pH ≥ 14, framework collapse is likely caused by the oxidation of phenolic hydroxyl groups under strongly alkaline conditions. The stability of SCU-1 was further examined in fourteen commonly used catalytic solvents and reagents, including aromatic and aliphatic hydrocarbons, halogenated hydrocarbons, alcohols, ethers, esters, and ketones. Stability tests were carried out at room temperature and at 80°C for 24 h. As shown in Figs. 5 C and 5 D, SCU-1 remains stable in all of these media except formic acid and acetic acid. The HOMO energy distributions and condensed Fukui functions indicate that the carbonyl oxygen atoms of formic acid and acetic acid have strong coordination ability and can compete with the phenolic oxygen atoms of HMT for Bi 3+ centers, thereby destabilizing the framework (Figs. 5 E, F). Formic acid shows nearly twice the coordination activity of acetic acid, consistent with its stronger destabilizing effect. After immersion in formic acid at 80°C for 24 h, both SCU-1 and bismuth nitrate were converted into the same bismuth triformate phase, which strongly supports this interpretation (Figure S11). Since bismuth-based materials have attracted growing interest in CO 2 reduction catalysis, we also evaluated the stability of SCU-1 under photocatalytic conditions. Triethanolamine (TEA), a common CO 2 -reduction additive, often decomposes MOFs because of its strong coordinating amino and hydroxyl groups. In contrast, SCU-1 remains crystalline after 24 h in 0.5% TEA and under xenon lamp irradiation (Fig. 5 G). Overall, the chemical stability of SCU-1 appears to be superior to that of benchmark BioMOFs such as CD-MOFs 28 and Bio-MOF-1 29 . To further evaluate the intrinsic properties of this material, we examined its biocompatibility, sulfur tolerance, and colloidal behavior. In vitro cytotoxicity tests using the B16 melanoma cell line showed that neither SCU-1 nor its constituent components inhibited cell growth even at concentrations up to 1000 µg mL − 1 (Figure S12). Because sulfur-containing molecules often destabilize MOFs by competing with linkers for metal coordination, the stability of SCU-1 was also tested in aqueous solutions of L-cysteine and L-cystine. As shown in Figure S13, SCU-1 retains its structural integrity after 24 h, demonstrating its robustness under sulfur-rich conditions. In addition to chemical stability, surface charge and colloidal stability can significantly affect interactions between materials and various biological structures or drug molecules. We further investigated the surface chemistry of SCU-1 in both complete cell culture medium (RPMI) and water. As shown in Figure S14, SCU-1 exhibited a negative surface charge, suggesting its potential for electrostatic interactions with positively charged molecules. The reduced absolute value of the zeta potential in RPMI is attributed to protein adsorption from the culture medium. These results further demonstrate the unusual robustness of SCU-1 under biologically relevant conditions. Porosity and CO-binding microenvironment The porosity of SCU-1 was investigated by combining theoretical and experimental analyses. The ideal framework was analyzed using the Zeo + + program with N 2 as the probe sorbate. The pore-size distribution indicates that the ideal structure contains a dominant pore size of approximately 5 Å (Fig. 6 A). The theoretical surface area was calculated to be 231 m 2 g − 1 , which reflects the narrow channel aperture (~ 2.8 Å) that limits diffusion of N 2 molecules. Experimental N 2 sorption at 77 K, after activation at 150°C under vacuum for 10 h, confirmed the presence of permanent porosity in SCU-1. The adsorption isotherm displays a type IV profile according to the IUPAC classification, indicating the coexistence of micropores and mesopores (Fig. 6 B). The Brunauer–Emmett–Teller (BET) surface area is 181 m 2 g − 1 , slightly lower than the theoretical value. This difference is consistent with the presence of structural defects, which may partially merge micropores into mesopores and thereby reduce the accessible surface area. The pore-size distribution derived from N 2 sorption is consistent with this interpretation (Fig. 6 C). To exclude possible interference from the quadrupole moment of N 2 , additional adsorption experiments were performed with Ar at 87 K. As shown in Figures S15 and S16, the adsorption behavior and pore-size distribution were similar to those obtained with N 2 , supporting the same structural interpretation. However, because of the kinetic diameter limitations of both N 2 and Ar, ultramicropores of about 5 Å cannot be fully resolved using these gases. We therefore carried out CO 2 sorption measurements at 273 K (Figure S17). The resulting pore-size distribution shows a clear microporous feature centered at 5.4 Å (Fig. 6 D), in excellent agreement with the crystallographic model and thus providing independent support for the proposed pore structure. Given that only a limited number of porous Bi-based MOFs have been reported, we further compared SCU-1 with representative Bi-MOFs in terms of thermal stability, BET surface area, and ligand cost (Fig. 6 E) 26 , 30 – 37 . SCU-1 combines high thermal stability, appreciable surface area, and low linker cost, which together support its potential practical value. The selective adsorption of CO 2 by SCU-1 was then examined under conditions relevant to gas separation. As shown in Fig. 6 F, SCU-1 displays a stronger affinity for CO 2 than for N 2 or CH 4 . This result indicates that the framework provides not only geometric confinement but also a favorable chemical environment for CO 2 . To understand this, grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations were used to identify the preferred adsorption sites and the corresponding host–guest interactions. At low loading, CO 2 preferentially accumulates at the center of the small pores of SCU-1 (Fig. 6 G). DFT optimization of the adsorption configurations shows that all tested starting positions converge to the same host–guest structure (Figure S18), indicating a well-defined preferred adsorption configuration. Notably, the diameter of the small pores in SCU-1 is approximately 5 Å, only slightly larger than the kinetic diameter of CO 2 (3.3 Å). This close size match creates a strong confinement effect, allowing each CO 2 molecule to be surrounded by multiple non-covalent interactions within the pore. Specifically, the oxygen atoms of CO 2 participate in O–H···O and C–H···O hydrogen bonds with framework hydroxyl groups, with intermolecular distances of 2.4, 2.7, and 3.3 Å. In addition, the electropositive carbon atom of CO 2 forms close contacts with framework oxygen atoms at distances of 2.7 and 3.7 Å, consistent with Lewis acid–base interactions (Fig. 6 H). In agreement with these structural features, the calculated adsorption energy reaches approximately − 87.5 kJ mol − 1 . These results show that the strong affinity of SCU-1 for CO 2 arises from the combined effects of pore confinement and multiple host–guest interactions within the phenolic pore environment. Visible-light-driven CO conversion Given the known photocatalytic and electrocatalytic activity of Bi-based materials towards CO 2 reduction, we next investigated whether SCU-1 could function as a photocatalyst under visible light. Photocatalytic CO 2 reduction was conducted in water under 50 kPa CO 2 and simulated solar irradiation (AM 1.5 G, 100 mW cm − 2 ), without any added sacrificial agents or photosensitizers. As shown in Fig. 7 A, SCU-1 produced C 2 H 5 OH, CH 3 OH, and HCOOH, with ethanol as the major product at a rate of 50.13 µmol g − 1 h − 1 . HPLC analysis indicated that formic acid, methanol, and ethanol were the only detectable liquid products (Figure S19), and the 1 H NMR spectrum further confirmed the presence of C 2 H 5 OH, CH 3 OH, and HCOOH in the liquid-phase products (Fig. 7 C). No products were detected under Ar, confirming that CO 2 is the sole carbon source under the reaction conditions. Compared with representative Bi-based catalysts reported to date, SCU-1 shows a competitive ethanol production rate under visible light even without post-synthetic modification (Table S4). It is also notable that this activity is observed in pure water, without sacrificial agents or carbonate-containing media. The photocatalytic activity of SCU-1 can be understood in light of the adsorption results discussed above. The pore surface provides multiple interaction sites for CO 2 , and the resulting strong adsorption energy promotes local enrichment of CO 2 near the catalytic sites. At the same time, the porous framework ensures that these sites remain accessible, thereby facilitating contact between the substrate and the active centers. To assess durability, SCU-1 was subjected to four consecutive photocatalytic cycles. No obvious loss of activity was observed after the fourth cycle (Fig. 7 B), and both PXRD and SEM confirmed that the framework structure and morphology were retained after the reaction (Figures S20A and S20B). These results demonstrate that SCU-1 combines photocatalytic activity with good operational stability. To evaluate the thermodynamic feasibility of this process, the optical and electronic properties of SCU-1 were examined. UV-vis diffuse reflectance spectra show broad absorption across the visible region, with a maximum near 570 nm, indicating effective light harvesting by the plant polyphenol-Bi coordination (Fig. 7 D). Based on Tauc plot analysis derived from the UV-vis spectra, the energy gap (E g ) of SCU-1 was determined to be 1.87 eV. Mott-Schottky measurements conducted at different frequencies show positive slopes for the sample, confirming its n-type semiconductor behavior (Fig. 7 E). On this basis, the conduction band minimum (E CB ) and valence band maximum (E VB ) of SCU-1 were calculated to be − 0.62 V and 1.25 V versus the NHE, respectively (Fig. 7 F). These band-edge positions indicate that SCU-1 is thermodynamically capable of driving CO 2 reduction coupled with H 2 O oxidation under light irradiation. Conclusions In summary, we show that haematoxylin, a natural asymmetric plant polyphenol, can serve as a linker for the construction of a crystalline bismuth-based MOF. Despite the low symmetry of the linker, SCU-1 retains long-range order and can be synthesized under aqueous acidic conditions with good scalability. Structural analysis and theoretical calculations show that the intrinsic coordination asymmetry of haematoxylin creates framework heterogeneity without disrupting long-range order. These findings also reveal the potential of intrinsically asymmetric plant polyphenols to serve as linkers for robust MOFs with intrinsic structural heterogeneity. In SCU-1, linker asymmetry is not merely a structural feature but also contributes to the properties of the material. Strong Bi-phenolate chelation, rod-like inorganic building units, and hydrogen-bonding interactions confer exceptional thermal and chemical robustness, while the resulting ultramicroporous phenolic environment enables strong CO 2 binding through combined confinement and multipoint host–guest interactions, and supports visible-light-driven CO 2 conversion in water. More broadly, this work expands the linker space of MOF chemistry beyond symmetry-compatible molecules and shows that intrinsically asymmetric plant polyphenols can be used to construct robust porous frameworks with built-in structural heterogeneity and interaction-rich pore microenvironments. Methods Chemicals All chemicals and reagents were used as obtained without further purification unless otherwise mentioned. Bismuth(III) nitrate pentahydrate (Bi(NO 3 ) 3 ·5H 2 O, 99.995% metals basis), HMT (99%, HPLC), acetic acid, L-cysteine, L-cystine, triethanolamine, formic acid, N,N-dimethylformamide, dimethyl sulfoxide, acetone, acetonitrile, cyclohexanone, dichloromethane, 1,4-dioxane, ethyl acetate, methanol, N-methylpyrrolidone, tetrahydrofuran, toluene were purchased from Titan (China). MTT Cell Proliferation and Cytotoxicity Assay Kit (MTT) was purchased from Beyotime (China). Roswell Park Memorial Institute (RPMI), phosphate-buffered saline (PBS), and normal saline were purchased from Gibco (USA). High-purity Milli-Q (MQ) water with a resistivity of 18.2 MΩ cm was obtained from an inline Millipore RiOs/Origin water purification system. Synthesis In a typical synthesis, 45.3 mg of reagent-grade HMT (0.15 mmol) and 145.5 mg of bismuth(III) nitrate pentahydrate (0.3 mmol) were separately dissolved in 7.5 mL of acetic acid aqueous solution (6 vol.% acetic acid, made from glacial acetic acid), then mixed in a Teflon autoclave reactor (25 mL) for hydrothermal treatment at 120°C. After 36 h, the obtained product was collected by centrifugation (8000 rpm for 8 min) and washed with water and ethanol. Yield (after washing with water and ethanol, then drying overnight at 60°C): 0.175 g (79% of theoretical yield). Larger batches of SCU-1 were synthesized using 1.71 g of HMT (6 mmol) and 5.82 g bismuth(III) nitrate pentahydrate (12 mmol), which was added to a Teflon autoclave reactor (1 L) containing 600 mL of a water and acetic acid mixture (6 vol.% acetic acid) for hydrothermal treatment at 120°C. After 36 h, it was placed in an oven at 60°C overnight. Yield after washing with water and ethanol, then drying overnight at 60°C: 5.66 g (72% of theoretical yield). The phase purity of both materials was confirmed by PXRD and elemental analysis. Atmospheric reflux method:​​ 90.6 mg of reagent-grade HMT (0.3 mmol) and 291 mg of bismuth(III) nitrate pentahydrate (0.6 mmol) were separately dissolved in 15 mL of an acetic acid aqueous solution (6 vol.% acetic acid, prepared from glacial acetic acid). The mixtures were then combined in a 50 mL round-bottom flask and refluxed at 100°C for 36 h. The contents were then washed and left to dry at ambient conditions. Structure determination and characterization Scanning electron microscopy (SEM) SEM images and energy dispersive spectroscopy (EDS) mapping were conducted on a scanning electron microscope (ZEISS Gemini 300). Transmission electron microscopy (TEM) TEM images were acquired by Tecnai G2 F20 S-TWIN with an operation voltage of 200 kV. 3D electron diffraction (3DED) The crystal powder was drop-casted onto a copper grid (R1.2/1.3, QUANTIFOIL), and the grid was plunged into liquid nitrogen rapidly. The grid was then transferred to the Fischione 2550 cryo holder and TEM at liquid nitrogen temperature (77 K). The cRED data were collected on a JEOL 2100-plus TEM equipped with a MerelinEM detector under 200 kV acceleration voltage and installed with DiffProAcquire data collection software (software developed by the ReadCrystal Tech Co.). The tilting range depends on the location of the crystals on the grid. For the sample, 85 electron diffraction patterns were collected with the tilting angle ranging from − 54.98° to 18.50°. Each frame was collected with an exposure time of 1 s, resulting in a 1.07° wedge per frame. According to the 3DED data, the indexed unit cell parameters indicate that SCU-1 has an identical unit cell to SU-101 along all three crystallographic axes 26 . Powder X-ray diffraction (PXRD) The powder diffraction data of SCU-1 were measured at room temperature on a Rigaku Ultima IV, in the 2θ range 1–40°. The system is equipped with a Ge(111) monochromator producing Cu Kα1 radiation (λ = 1.54060 Å) and a LynxEye detector. The refinement of the electron-diffraction model against high-resolution PXRD data was carried out in GSAS II 38 . Topological analysis of the SCU-1 framework was carried out using the software package ToposPro 39 . Model building The structural model of the SCU-1 was developed using the Materials Studio software suite. Initially, the lattice was constructed based on the P1 space group, with the a and b lattice parameters set to 19.110 Å. These parameters were determined by measuring the center-to-center distances between the vertices of SU-101 26 . The model underwent geometry optimization using the Forcite module, which employs Universal force fields and Ewald summations to ensure accurate structural refinement. Computational details Coordination structure of the SCU-1 All complexes were optimized using the Perdew-Burke-Ernzerhof hybrid functional (PBE0) method and Def2-SVP basis set with Grimme’s DFT-D3(BJ) empirical dispersion correction by the Gaussian 16 package 40 . The single-point energy calculations were performed using the Def2-TZVP basis set. Harmonic vibrational frequency calculations were carried out at the same level to confirm that imaginary frequency is absent in the molecules, i.e., they are located at the minima of the potential energy surface. Moreover, water has been introduced as an implicit solvent by the SMD (Solvation model density) solvation model. The HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of these complexes were obtained by combining Multiwfn 3.8 40 and VMD 1.9.3 41 software, whose input files were extracted from a Gaussian checkpoint file. The condensed Fukui function and condensed dual descriptor were computed via Multiwfn, employing Hirshfeld charges for assessment 42 , 43 . Solution-phase Gibbs free energies were then calculated using the “direct method” 44 . For systems that undergo large geometry changes upon solvation, the direct method affords energetics that are superior to those obtained using (gas phase to solution) thermocycles 44 . Given the high partial charges on atoms within these metal complexes, significant geometry changes upon solvation (in water) would be anticipated. The default standard state used within the Gaussian 16 package for entropic components (even in a SMD solvent field) is based on the statistical mechanics for an ideal gas (evaluated at 1 atm of pressure and 25°C). Thus, appropriate standard state corrections were applied to ensure all binding energies were calculated at a standard state for solutes in solution (of 1 mol L − 1 and 120°C). This correction takes the following form. $$\:{\text{ΔG}}^{\text{1atm→1M}}\text{=ΔmRTln[}\frac{\text{RT}}{\text{P}}]$$ Here, Δm is the change in moles upon reaction, R is the ideal gas constant (8.3145 J mol – 1 K – 1 ), T is the temperature of interest at which the Gibbs free energy is also evaluated (typically 393.15 K), and P is pressure (101.325 kPa = 1 atm). For reactions that either generate or consume water (i.e., reactions where water is a product or reagent), a further state correction is required. The standard state for any liquid is the pure substance at 1 atm of pressure, so the standard state of liquid water should be [H 2 O] = 55.5 mol L − 1 (rather than 1 mol L − 1 for an aqueous solute). Gibbs free energies for reactions involving water as a reagent must be further corrected by adding the following additional term: $$\:{{\Delta\:}\text{G}}^{1\text{M}\to\:55.5\text{M}}=-\text{n}\text{R}\text{T}\text{l}\text{n}\left[{\text{H}}_{2}\text{O}\right]$$ Here, n is the number of moles of water acting as a reagent. Conversely, for reactions that generate water as a product, Gibbs free energies are corrected by the following term: $$\:{{\Delta\:}\text{G}}^{1\text{M}\to\:55.5\text{M}}=+\text{n}\text{R}\text{T}\text{l}\text{n}\left[{\text{H}}_{2}\text{O}\right]$$ Within standard continuum solvation models, solvation energies are profoundly influenced by the overall charge of the metal‒ligand (ML) complex as well as the coordination number (CN) and oxidation/spin state of the metal ion 45 , 46 . These issues can be resolved by constructing isodesmic proton-transfer reactions, taking the A-ring reaction as an example: I: \(\:{\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{6}\right]}^{3+}+\text{H}\text{M}\text{T}={\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{4}\right(\text{H}\text{M}\text{T}-\text{A}\left)\right]}^{3+}+2{\text{H}}_{2}\text{O}\) II: \(\:{\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{4}\right(\text{H}\text{M}\text{T}-\text{A}\left)\right]}^{3+}+{\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{4}{\left(\text{O}\text{H}\right)}_{2}\right]}^{+}={\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{4}{(\text{H}\text{M}\text{T}-\text{A})}^{2-}\right]}^{+}+{\left[\text{B}\text{i}{\left({\text{H}}_{2}\text{O}\right)}_{6}\right]}^{3+}\) ΔG* = ΔG I + ΔG II ΔG* corr = ΔG* + Δ𝐺 1atm→1M + 2Δ𝐺 1M→55.5M Grand Canonical Monte Carlo (GCMC) Classical GCMC simulations are performed using the RASPA 47 software to calculate the adsorption uptake of CO 2 within SCU-1 structures at 50 kPa, 298 K. The structures of the SCU-1 were treated as rigid frameworks during the simulations. The Monte Carlo moves in the GCMC simulations, including translational, rotational, addition/deletion, reinsertion, and identity change moves, were tried with equal probability. A total of 1 × 10 5 steps was set for the initialization run, followed by a production run of another 1 × 10 6 steps. To describe adsorbate-adsorbate interactions, the UFF 48 force field was used for SCU-1 49 . CO 2 molecules, including charges and LJ parameters, are modeled using the EPM2 model 50 . In the calculations for each structure, a supercell comprising 2 × 2 × 5 unit cells for SCU-1 was used, ensuring the simulation box was at least twice the cutoff radius along each crystal direction. Nonbonded interactions are represented by the Lennard-Jones (LJ) potential with a cutoff radius of 12.9 Å. The partial atomic charges of the structures are calculated using the PACMOF package 51 . The long-range electrostatic interactions were processed by the Ewald summation method, while the Van Der Waals interactions were handled using the atom-based summation method. DFT of the CO 2 adsorption structure within the framework DFT calculations were performed using the Vienna Ab Initio Simulation Package (VASP) 52 , employing plane-wave basis sets and the projector augmented-wave (PAW) method. The exchange-correlation functional was approximated using the Perdew-Burke-Ernzerhof (PBE) parametrization within the generalized gradient approximation (GGA). Van der Waals interactions were accounted for using the DFT-D3 correction by Grimme. The energy cutoff was set to 450 eV, and Brillouin-zone integration was performed using a Monkhorst-Pack grid with a k-point mesh of 1×1×3. Structural optimizations were carried out until the maximum force on each atom was less than 0.02 eV Å – 1 , and energy convergence was set to 10 –5 eV. All structures were fully relaxed to the minimum energy configuration. Computational efficiency was further enhanced by enabling the automatic optimization of real-space projectors with an additional support grid. Stability TGA Thermogravimetric analysis data were gathered on a sample of SCU-1 using a TA Instruments Discovery TGA. The sample was put into a platinum crucible and heated in air from 35°C to 600°C with a heating rate of 10°C min – 1 . The empirical formula best matching the observed data was determined as Bi 2 O(H 2 O) 2 (C 16 H 10 O 6 )·H 2 O. Thermal stability The SCU-1 was calcined in a muffle furnace under air or in a tube furnace under nitrogen atmosphere for 10 hours, respectively, and then characterized by powder X-ray diffraction (PXRD). Stability in solvents and solutions For the stability tests, 30 mg of SCU-1 was added to a 10 mL glass vial fitted with a screw-cap. For every trial, 5 mL of each respective solvent or solution was added, and the resulting dispersion was stirred at room temperature or 80°C for 24 h. Stability in the presence of triethanolamine To assess the structural integrity of SCU-1 in the presence of triethanolamine, 30 mg of SCU-1 was dispersed in an aqueous triethanolamine solution (0.5% v/v) and maintained at 37°C with continuous stirring for 24 hours. The MOF was then recovered by centrifugation at 8000 rpm for 10 minutes. PXRD patterns were acquired after the powders were allowed to dry under ambient conditions. Stability in the presence of L-cysteine and L-cystine The integrity of SCU-1 in the presence of L-cysteine and L-cystine at 37°C was evaluated by preparing solutions with 5 mg mL – 1 of the material and each respective compound in water. The SCU-1 dispersions were then allowed to stir at 37°C for 24 h before the MOF was retrieved by centrifugation (8000 rpm, 10 min). PXRD patterns were acquired after the powders were allowed to dry under ambient conditions. Residual crystalline L-cystine can be observed in the sample previously immersed in a solution of L-cystine. pH-dependent stability For the pH-dependent stability tests, 20 mg of SCU-1 was immersed in 5 mL of stock solution, prepared from either NaOH or concentrated H 2 SO 4 , to obtain the desired pH. Stability in biorelevant media SCU-1 in PBS was prepared by dispersing the material in PBS solution (30 mg mL – 1 of SCU-1 in 0.01 M phosphate buffer, 0.0027 M KCl, 0.137 M NaCl, pH = 7.4) or cell culture medium (30 mg mL – 1 of SCU-1 in RPMI). Powder X-ray diffraction was collected on the pellet. The evolution of the SCU-1 ζ-potential was evaluated over time in the presence of diverse physiological media (aqueous solution (Milli-Q water) and cell culture media RPMI). Degradation mechanisms of SCU-1 by formic and acetic acids To probe the degradation mechanism, SCU-1 was initially treated with sulfuric acid at the same pH (0.5) as pure formic acid. The framework remained intact under these conditions, suggesting that structural collapse in formic/acetic acid likely arises from competition between the carboxylate groups of these acids and the phenolic hydroxyl groups of HMT for the Bi(III) nodes. Furthermore, exposure of SCU-1 to formic acid at 80°C yielded bismuth(III) triformate crystals, a common phase formed from the interaction of Bi(III) ions with formic acid. This phase was also obtained by dispersing bismuth nitrate directly in formic acid at 80°C, confirming that formic acid displaces HMT and coordinates with Bi(III), leading to the formation of the bismuth triformate salt. Porosity and sorption properties Simulated data Zeo + + Version 0.3 was used to determine cavity localization, connectivity, and volume in the crystal structure of SCU-1 52 . Experimental adsorption-desorption data Gas adsorption/desorption isotherms were recorded on a Micromeritics Tristar Ⅱ Plus 3030. Prior to the experiments, the samples were pretreated at 150°C under vacuum for 10 h. Nitrogen adsorption/desorption isotherms were recorded at liquid nitrogen temperature (–196°C). Argon adsorption/desorption isotherms were measured at liquid argon temperature (–186°C), using a liquid argon bath for temperature control. Nitrogen (N 2 ), carbon dioxide (CO 2 ), and methane (CH 4 ) adsorption-desorption isotherms were recorded at 0°C. An ice slurry bath was used as the temperature control for these experiments. Photocatalytic CO reduction test The CO 2 reduction experiments were conducted in a sealed Pyrex bottle, where a 20 mL glass dish was placed as the reactor. The reactor contained 3 mL of water and 20 mg of photocatalyst. Before irradiation, the reaction system was degassed to remove air and then refilled with high-purity CO 2 to a pressure of 50 kPa. The reaction was carried out under simulated solar irradiation using a 300 W Xe lamp equipped with an AM 1.5 G filter. The light intensity at the reactor position was calibrated to 100 mW cm – 2 (Perfectlight Labsolar6A). The gaseous product was detected by an online gas chromatograph (GC 2014, Shimadzu) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) in series, which was used to quantify the produced gases during the photocatalytic reaction. Upon completion of the reaction, the liquid phase was collected, filtered, and analyzed by high-performance liquid chromatography (HPLC). Photoelectrochemical test An electrochemical workstation (PGSTAT30, Autolab) was equipped to perform photoelectrochemical studies. The three-electrode configuration was adopted, where the prepared electrode (SCU-1) served as the working electrode, the Pt sheet as the counter electrode, and the Ag/AgCl as the reference electrode. The electrolyte solution was prepared by dissolving Na 2 SO 4 in water (0.1 mol L – 1 ). Mott-Schottky plots were conducted at frequencies of 500, 1500, and 2500 Hz. Declarations Data availability Data supporting the findings of this investigation are available from the Article and its Supplementary Information. Author information Authors and Affiliations 1 College of Biomass Science and Engineering, Sichuan University, Chengdu, Sichuan 610065, China Zijun Zhu, Tong Shao, Lantao He, Shaojian Lin, Jianwu Lan, Jiaojiao Shang 2 School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China Jun Deng, Yang Chu, Xuemei Zhou 3 National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, Chengdu, Sichuan 610065, China Jiajing Zhou, Jiaojiao Shang Contributions The original idea was conceived by Z.Z.; the choice of organic linkers was made by Z.Z.; the synthesis of SCU-1 was performed by Z.Z.; MOF structure elucidation, performance investigation, and related data analysis were carried out by Z.Z., L.H., T.S., and J.S.; photocatalytic CO 2 reduction experiments were conducted by Z.Z., J.D., and Y.C.; X.Z., J.S., S.L., J.Z., and J.L. provided critical guidance throughout the project; J.S. supervised the overall research; all authors have reviewed and approved the final manuscript. Corresponding authors Correspondence to Jiaojiao Shang. Ethics declarations Competing interests The authors declare no competing interests. Acknowledgements This work was supported by the Institutional Research Fund from Sichuan University (Grant No. 2024SCUQJTX020) and the Science and Technology Project of Tibet Autonomous Region (Grant No. XZ202301YD0027C). The authors extend their gratitude to Dr. Zheng (from ReadCrystal Biotechnology) for providing invaluable assistance with the 3DED analysis. We thank A. Ken Inge (Stockholm University) for scientific discussions and encouragement. We thank the Theoretical and Computational Chemistry Team (from Scientific Compass www.shiyanjia.com ) for providing invaluable assistance. References Marsh C, Shearer GC, Knight BT, Paul-Taylor J, Burrows AD (2021) Supramolecular aspects of biomolecule interactions in metal-organic frameworks. 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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-9550934","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":633105317,"identity":"167e00bb-8f37-4995-b6d2-90ee16b57f50","order_by":0,"name":"Jiaojiao Shang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYBACxmYgIcHAkABiP4CIJRCvhdmAKC0wAFLGJkGUFuZ25ocPLBjq8vhnt1+r/FFzmIGfPceA4ecOfA5jMzaQYDhcLHHnTNltnmOHGSR73hgw9p7B6xczCQmGA4kNN3LSbjM2HGYwuJFjwMzYhk8L+zeglrrE+UAthT+BWuwJa+EB2cKcuOFG+jEGXpAtEoS1FBtIGBxO3Hgjh1ma51g6j8SZZwUHe/FoMew/vvGxREVd4rwb6Q8//qixluNvT9744Cc+LQ3AgJYAxyEPhAQRB3BrYGCQBznuA5jJ/gCfwlEwCkbBKBjBAAAEq05UN0YguwAAAABJRU5ErkJggg==","orcid":"","institution":"Sichuan Universuty","correspondingAuthor":true,"prefix":"","firstName":"Jiaojiao","middleName":"","lastName":"Shang","suffix":""},{"id":633105318,"identity":"dfec0b17-acfa-435e-bdf9-48b29345c5a3","order_by":1,"name":"Zijun Zhu","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Zijun","middleName":"","lastName":"Zhu","suffix":""},{"id":633105319,"identity":"fb15b5ba-26a8-421e-9db4-81e43b1acfb3","order_by":2,"name":"Tong Shao","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Tong","middleName":"","lastName":"Shao","suffix":""},{"id":633105320,"identity":"779ee588-b395-4ec8-9fdb-6d3696f683c9","order_by":3,"name":"Lantao He","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Lantao","middleName":"","lastName":"He","suffix":""},{"id":633105321,"identity":"fab3437a-e97d-4356-a975-3bb604437f41","order_by":4,"name":"Jun Deng","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Deng","suffix":""},{"id":633105322,"identity":"e9fabfff-7211-4783-8fa0-214cf6ed6697","order_by":5,"name":"Yang Chu","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Yang","middleName":"","lastName":"Chu","suffix":""},{"id":633105323,"identity":"a7778765-eb52-48c9-9a35-e73b8876042b","order_by":6,"name":"Xuemei Zhou","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Xuemei","middleName":"","lastName":"Zhou","suffix":""},{"id":633105324,"identity":"473ef40a-739a-4f97-8676-1dd1d9fd22f0","order_by":7,"name":"Jiajing Zhou","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Jiajing","middleName":"","lastName":"Zhou","suffix":""},{"id":633105325,"identity":"8407bae3-5459-4295-9173-2c12b9b8eb05","order_by":8,"name":"Shaojian Lin","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Shaojian","middleName":"","lastName":"Lin","suffix":""},{"id":633105326,"identity":"6532ab62-702c-4533-8118-1957d899fe9e","order_by":9,"name":"Jianwu Lan","email":"","orcid":"","institution":"Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Jianwu","middleName":"","lastName":"Lan","suffix":""}],"badges":[],"createdAt":"2026-04-28 08:30:54","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9550934/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9550934/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108482202,"identity":"a2563ef8-be50-480c-a30b-fad0b313fd6f","added_by":"auto","created_at":"2026-05-05 08:17:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1407762,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Self-assembly mechanism of SCU-1, illustrating the coordination building units, the formation of rod-like inorganic building units (IBUs), their extension mode, synthetic conditions, and the microstructure. (B) Intrinsic structural characteristics of the HMT linker, highlighting its asymmetric and nonplanar geometry, as well as the defect features and spatial confinement effects induced in the frameworks. (C) Proposed CO\u003csub\u003e2\u003c/sub\u003e adsorption mechanism in SCU-1. Dashed lines indicate hydrogen bonding and C–O Lewis acid–base interactions between CO\u003csub\u003e2\u003c/sub\u003e and the frameworks. (D) Schematic illustration of the catalytic sites in SCU-1 for photocatalysis. (E) Schematic representation of the photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction process over SCU-1.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/e10f80b83d1dbd4f2624ffe4.png"},{"id":108494061,"identity":"26025dd2-e355-4cd2-8f3d-d4ea0b47a5fb","added_by":"auto","created_at":"2026-05-05 10:02:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1571551,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic illustration of the formation of the rod-like structure of SCU-1. (B) SEM images of SCU-1. (C) Reciprocal-space projections of the 3D electron diffraction (3DED) data collected from a single crystal of SCU-1. (D) PXRD pattern of SCU-1 refined using the crystal structure of SU-101 as the structural model. (E) Plot for the structure refinement of SCU-1. (F) PXRD of SCU-1 made from reflux synthesis, hydrothermal synthesis, and a simulated PXRD pattern of SCU-1. (G) The structure of the interconnected pore channels. (H) The underlying SVD net. (I) Choice of nodes for the deconstruction of the infinite IBU.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/94dcdd2345a7bd72d2b519d6.png"},{"id":108494060,"identity":"a749abf2-2782-4ccb-9ac5-3b9d265e6940","added_by":"auto","created_at":"2026-05-05 10:02:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":197455,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Structural analysis of the HMT molecule (purple, site A; pink, site B), including the HOMO energy distribution and condensed Fukui functions. The Hess’s law thermodynamic cycle describes ligand (LH) binding to a metal ion (M\u003csup\u003e+\u003c/sup\u003e). ΔG\u003csub\u003eI/LH\u003c/sub\u003e represents the binding strength between the (protonated) ligand and its conjugate base, whereas ΔG\u003csub\u003eI/MLH\u003c/sub\u003e denotes the binding energy of the metal–ligand complex. ΔG\u003csub\u003eI\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e incorporates both the binding and deprotonation processes. (B) Optimized structures of HMT and its corresponding complexes in the solution phase, together with the corrected Gibbs free energy changes for binding (in kJ mol\u003csup\u003e–1\u003c/sup\u003e, calculated at 120 °C).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/95eab506c3fc20040920fffe.png"},{"id":108482207,"identity":"ddc161fe-2d49-428e-a862-fae410f809a1","added_by":"auto","created_at":"2026-05-05 08:17:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":786377,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Thermogravimetric measurement of SCU-1 in air. The dashed lines indicate expected relative mass remaining, assuming an initial formula of Bi\u003csub\u003e2\u003c/sub\u003eO(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e6\u003c/sub\u003e)·H\u003csub\u003e2\u003c/sub\u003eO, which is then converted into Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e when heated beyond 360 °C. (B) Powder X-ray diffraction patterns acquired of SCU-1 after thermal treatment in air and N\u003csub\u003e2\u003c/sub\u003e. (C) The structure of the IBUs. (D) Schematic illustration of the coordination structure between HMT and Bi\u003csup\u003e3+\u003c/sup\u003e. The coordination interactions between Bi\u003csup\u003e3+\u003c/sup\u003e and water molecules are depicted as dashed lines. (E) Intermolecular distance between non-coordinated hydroxyl groups within the SCU-1 frameworks.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/f4d6f96888def76992c3a495.png"},{"id":108482208,"identity":"d7bf6302-5c0d-4aba-b004-3c4e99b4554e","added_by":"auto","created_at":"2026-05-05 08:17:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1562430,"visible":true,"origin":"","legend":"\u003cp\u003e(A) PXRD patterns of SCU-1 after being stirred in a variety of aqueous conditions, including hydrothermal conditions and simulated biological media. (B) PXRD patterns of SCU-1 after being stirred in aqueous solutions at various pH levels, at room temperature. When exposed to 1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, the material is dissolved. (C, D) PXRD patterns of SCU-1 after being immersed in various solvents or solutions for 24 h at 25 °C and 80 °C. (E) Schematic illustration of MOF framework degradation induced by coordinating acids. (F) HOMO energy level distributions and condensed Fukui functions of formic acid and acetic acid calculated by DFT. (G) PXRD patterns of SCU-1 after 24 h under dark and light irradiation in an aqueous system using triethanolamine as the sacrificial agent.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/74d5bec14ea523dd28a5f13c.png"},{"id":108494046,"identity":"8d75d3d8-c40c-4cb3-9758-aa830049095a","added_by":"auto","created_at":"2026-05-05 10:02:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1350845,"visible":true,"origin":"","legend":"\u003cp\u003e(A) The pore size distribution diagram was calculated by Zeo++. (B) N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherm of as-synthesized SCU-1, all recorded at liquid N\u003csub\u003e2\u003c/sub\u003e temperature (77 K). The adsorption points are shown as solid symbols and the desorption points as hollow symbols. BET surface areas 181 m\u003csup\u003e2 \u003c/sup\u003eg\u003csup\u003e–1\u003c/sup\u003e. (C) Pore size distribution as determined for SCU-1, using a N\u003csub\u003e2\u003c/sub\u003e slit pore model. The dashed line is drawn at a pore-size value of 13.5 Å. (D) Pore size distribution as determined for SCU-1, using a CO\u003csub\u003e2\u003c/sub\u003e slit pore model. The dashed line is drawn at a pore-size value of 5.4 Å. (E) Comparative analysis of Bi-MOFs: thermal stability, S\u003csub\u003eBET\u003c/sub\u003e, and ligand cost. The literature data points labeled 1–9 correspond to Refs. 30, 31, 32, 33, 26, 34, 35, 36, and 37, respectively. (F) CO\u003csub\u003e2\u003c/sub\u003e, CH\u003csub\u003e4,\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption isotherms of SCU-1 recorded at 0 °C. (G) Slice through the calculated potential field for CO\u003csub\u003e2\u003c/sub\u003e derived from GCMC simulations. (H) DFT-calculated CO\u003csub\u003e2\u003c/sub\u003e adsorption binding site. Color codes: red, O; gray, C; blue, Bi; light gray, H. Dashed lines represent distances between adsorbed CO\u003csub\u003e2\u003c/sub\u003e molecules and framework atoms.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/1d17347589310a9b1aa8d1c7.png"},{"id":108482210,"identity":"9f477a71-fbd3-4cfd-8f7c-d1dd62f59a06","added_by":"auto","created_at":"2026-05-05 08:17:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":729865,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Yield of carbon dioxide reduction products under different reaction conditions. (B) Product generation after four cycles in stability testing. (C) \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of the product. (D) UV-Vis DRS of SCU-1 and corresponding Tauc plots drawn using the Kubelka–Munk parameter ((αhν)\u003csup\u003e2\u003c/sup\u003e) as a function of photon energy (eV). (E) Electrochemical band edge measurements by Mott-Schottky plot. (F) Electronic band structure diagram of SCU-1.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/770049525a7174acb3e2a792.png"},{"id":108809152,"identity":"40eec572-63df-4ca8-ba9c-d8ec9b78959b","added_by":"auto","created_at":"2026-05-08 15:50:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7982530,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/40f51d7f-5080-4114-88b8-96e6d46508bb.pdf"},{"id":108804264,"identity":"499288bc-d754-4741-914b-3bfe59ba949b","added_by":"auto","created_at":"2026-05-08 15:18:38","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":12089892,"visible":true,"origin":"","legend":"TOC","description":"","filename":"TOC.tif","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/acfb7d470d45b67d9052c3b6.tif"},{"id":108482205,"identity":"efbea7e5-dc5c-401d-b00e-c359739c4880","added_by":"auto","created_at":"2026-05-05 08:17:15","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":7106168,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-9550934/v1/68a682691d5d20da29ae05f4.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Naturally Asymmetric Plant Polyphenol Linkers Enable Robust Metal-Organic Frameworks with Built-In Structural Heterogeneity","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMetal\u0026ndash;organic frameworks (MOFs) derive their structural diversity from the combination of inorganic nodes and organic linkers. However, the vast majority of crystalline MOFs have been constructed from geometrically regular ligands, because symmetry facilitates predictable network formation, supports long-range order, and simplifies crystallographic analysis\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Although this design logic has been central to the success of reticular chemistry\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, it also narrows the range of accessible molecular building blocks and limits opportunities to introduce local disorder, heterogeneous pore environments, and structurally complex frameworks\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThis limitation is becoming increasingly relevant as MOF research moves beyond defect-free crystals toward framework heterogeneity as a functional design element\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Defect engineering, low-symmetry ligands, and heterogeneous pores have all emerged as effective routes to tune adsorption and catalysist\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Yet most current strategies either modify conventional frameworks or rely on synthetically tailored ligands\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. For example, Dincă and co-workers used a symmetry-reduction strategy to construct an amorphous MOF containing locally ordered MOF-74 domains\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. These studies clearly demonstrate that lowering linker symmetry can generate new structural features and functions. They also highlight a fundamental challenge: asymmetric linkers generally complicate topology prediction, hinder the growth of high-quality single crystals, and make structural determination difficult\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Moreover, most asymmetric linkers explored to date have been derived from synthetic chemistry\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Although effective, such ligands may suffer from limited chemical stability and may not be ideal for applications that demand low cost, environmental compatibility, or biological safety\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. By contrast, intrinsically asymmetric molecules from nature remain largely unexplored in the construction of crystalline MOFs, despite their potential to provide complex coordination environments and diverse pores. Developing asymmetric linkers that combine structural complexity, strong metal-binding ability, and favorable biocompatibility, therefore, remains an important challenge in MOF chemistry.\u003c/p\u003e \u003cp\u003ePlant polyphenols are especially attractive candidates for addressing this challenge. These molecules are renewable, low-cost, and rich in metal-binding and secondary interaction motifs\u003csup\u003e\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Their phenolic hydroxyl groups can strongly chelate metal ions, often producing robust coordination architectures, while their multiple hydrogen-bonding and π-interaction sites can enrich host\u0026ndash;guest interactions within pores\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Nevertheless, plant polyphenols explored in frameworks construction have so far been largely restricted to highly symmetric molecules\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. It remains unclear whether intrinsically asymmetric plant polyphenols can act as framework linkers and introduce local heterogeneity without disrupting long-range order. Such molecules are highly appealing because their non-equivalent coordination sites could create local structural heterogeneity, whereas strong metal-phenolate bonding could preserve framework integrity. This combination suggests a promising route to crystalline MOFs that unite structural complexity with high robustness.\u003c/p\u003e \u003cp\u003eHere, we use haematoxylin (HMT), a naturally occurring plant polyphenol containing two electronically distinct catechol coordination sites, to construct a bismuth-based MOF (SCU-1) synthesized in aqueous acetic acid and accessible at an enlarged scale (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Structural modelling combined with electron diffraction and powder diffraction refinement supports a tetragonal framework with one-dimensional channels and rod-like bismuth oxo subunits. HMT is a typical nonplanar and chiral molecule that provides an intrinsically asymmetric coordination. Quantum-chemical analysis further reveals pronounced site differentiation in HMT, with one catechol unit showing an order-of-magnitude higher reactivity toward Bi\u003csup\u003e3+\u003c/sup\u003e coordination than the other, although both sites are accessible (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). These features indicate that HMT is a naturally low-symmetry linker capable of encoding coordination inequivalence and framework heterogeneity during assembly. The strong Bi\u0026ndash;phenolate chelation enables this heterogeneity to be accommodated without loss of crystallinity or robustness. As a result, SCU-1 combines exceptional stability with ultramicroporosity. This pore enables strong CO\u003csub\u003e2\u003c/sub\u003e binding through confinement-enhanced, multipoint host\u0026ndash;guest interactions and further supports visible-light-driven photocatalytic CO\u003csub\u003e2\u003c/sub\u003e conversion (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC\u0026ndash;E). This work establishes naturally asymmetric plant polyphenols as a viable linker platform for robust MOFs with built-in structural heterogeneity and interaction-rich pore microenvironments, and it provides a new strategy for expanding MOF chemistry beyond conventional symmetry-guided linker design.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and frameworks construction of SCU-1\u003c/h2\u003e \u003cp\u003eSCU-1 was synthesized by hydrothermal treatment of an aqueous suspension of bismuth nitrate and haematoxylin (HMT) for 36 h. The material could also be prepared under ambient-pressure reflux conditions, indicating that framework formation does not depend on a narrow solvothermal window. Phase purity and synthetic reproducibility were markedly improved by the addition of acetic acid as a modulator (6 vol%, pH\u0026thinsp;\u0026asymp;\u0026thinsp;2.3). Notably, this acidity is comparable to that of common household vinegar, highlighting the mild and practical nature of the synthetic conditions. Solvent screening showed that ethanol and acetone did not yield crystalline products, whereas DMF led to a distinct reaction pathway in which Bi\u003csup\u003e3+\u003c/sup\u003e was reduced to Bi nanocrystals dispersed within an HMT-Bi matrix (Figures S1 and S2). Although this material lies beyond the scope of the present study, it further illustrates the rich coordination and redox chemistry of HMT towards bismuth and suggests that this phytochemical may also be useful for constructing uniformly dispersed Bi nanocrystal composites. The frameworks of SCU-1 consist of rod-like inorganic building units (IBUs) aligned along the c-axis and interconnected by HMT linkers to generate a three-dimensional network featuring one-dimensional channels along the same direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The coordination between Bi\u003csup\u003e3+\u003c/sup\u003e ions and the ortho-hydroxy groups of HMT promotes the formation of rod-like metal subunits, which further assemble into nanorod crystals with diameters of approximately 100 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eStructure determination was complicated by the intrinsic asymmetry of the HMT ligand. Despite extensive optimization of the synthetic conditions, crystals large enough for single-crystal X-ray diffraction could not be obtained. Only microcrystals were formed, and their local disorder along the c axis prevented direct structure solution by 3D electron diffraction (3DED). Nevertheless, the combination of 3DED, indexed diffraction patterns, and PXRD refinement provides strong evidence for a well-defined long-range ordered framework. Indexing of the 3DED data yielded unit-cell parameters consistent with those of SU-101 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC, Table S1)\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, and the refined PXRD pattern shows excellent agreement with a structural model derived from SU-101 (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD\u0026ndash;F and Table S2). On this basis, SCU-1 was modelled in the tetragonal space group P4\u003csub\u003e2\u003c/sub\u003e (no. 77) with unit-cell constants a\u0026thinsp;=\u0026thinsp;b = 18.967 \u0026Aring; and c\u0026thinsp;=\u0026thinsp;5.666 \u0026Aring;. Powder X-ray diffraction (PXRD) further confirmed the phase purity of SCU-1 and demonstrated excellent consistency between samples prepared via hydrothermal and reflux methods (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF). High isolated yields were achieved on both small (30 mL, 79%, 0.35 g) and larger scales (600 mL, 72%, 5.66 g), highlighting the scalability of this system using a renewable phytochemical linker. This result is particularly notable given that intrinsically asymmetric natural molecules are typically considered difficult to incorporate into crystalline MOF architectures due to their irregular coordination geometries and reduced predictability in long-range ordering.\u003c/p\u003e \u003cp\u003eStructurally, each repeating unit contains one HMT anion and two Bi\u003csup\u003e3+\u003c/sup\u003e cations. Each Bi\u003csup\u003e3+\u003c/sup\u003e adopts an octahedral coordination geometry defined by six oxygen donors originating from coordinated water molecules, \u0026micro;\u003csub\u003e4\u003c/sub\u003e-oxygen atoms, and the ortho-hydroxy groups of HMT, resulting in a charge-neutral framework with the composition Bi\u003csub\u003e2\u003c/sub\u003eO(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e6\u003c/sub\u003e) (Figure S3). Within the coordination environment, one phenolate group of HMT binds to a single Bi\u003csup\u003e3+\u003c/sup\u003e center, while the other bridges two Bi\u003csup\u003e3+\u003c/sup\u003e ions along the rod-like IBU (Figure S4). In addition, non-coordinated water molecules located within the one-dimensional channels, along with neighboring coordinated water molecules, phenolic hydroxyl oxygen, hydroxyl oxygen, and pyran oxygen atoms, form multiple hydrogen-bonding interactions with distances ranging from 2.8 to 3.4 \u0026Aring;, indicating that SCU-1 possesses multiple host\u0026ndash;guest interaction sites (Figure S5). The nonplanar geometry of the HMT ligand imposes significant steric confinement in the ab plane, leading to relatively narrow pore apertures. Although this geometric constraint reduces the accessible surface area, it is expected to enhance size-selective adsorption and separation through spatial confinement effects (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG, \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eTo simplify the structural description, a topological analysis was conducted using the node-deconstruction approach proposed by Michael O'Keeffe and Omar Yaghi\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The nodes are linked to neighboring vertices along the rod, giving a 6-connected node. When the connections between adjacent rods through HMT anions are considered, the overall frameworks can be described as a uninodal 7-connected svd net (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH, I).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEffect of linker asymmetry on framework formation\u003c/h3\u003e\n\u003cp\u003eUnderstanding how linker asymmetry affects periodic framework formation is a central aim of this study. To examine the site selectivity of HMT coordination, high-level quantum chemical calculations were first performed to evaluate the Gibbs free energies (ΔG) of binding between Bi\u003csup\u003e3+\u003c/sup\u003e and the two catechol coordination sites of HMT. The HMT molecule contains two catechol groups in distinct local environments: one attached to a fused five-membered ring (A ring) and the other to a pyran ring (B ring). HOMO analysis shows a clear difference in electron density between the two catechol units, with the A ring displaying a higher electron density and therefore a stronger coordination tendency (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). This trend is supported by condensed Fukui function and dual descriptor analyses, which show that the electron density on the phenolic oxygen atoms of the A ring is approximately one order of magnitude higher than that of the B ring (Table S3). The corresponding binding thermodynamics further support this site selectivity. We next evaluated site selectivity using ΔG\u003csub\u003eI\u003c/sub\u003e*, which describes ligand binding strength. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, site selectivity is predicted for Bi\u003csup\u003e3+\u003c/sup\u003e\u0026ndash;HMT complexes, with coordination at the A ring favored by approximately 4.7 kJ mol\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e relative to the B ring. This energy difference corresponds to a selectivity of about 4.2:1 at 120\u0026deg;C between the two sites. Importantly, the Gibbs free energy changes associated with chelating coordination at both sites are negative, indicating that chelation between Bi\u003csup\u003e3+\u003c/sup\u003e and either catechol group is thermodynamically favorable. As a result, both coordination modes can lead to the formation of the S3 motif, which subsequently self-assembles into the infinite periodic frameworks of SCU-1. These results demonstrate that differences in local chemical environments do not prevent the formation of periodic frameworks, provided that the linker structure is compatible with the coordination geometry of the node, highlighting the potential of such asymmetric linkers for Bio-MOF design. In addition, previous studies have shown that MOFs constructed from catechol- or pyrogallol-based linkers often display high structural stability\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e (Figure S9), further supporting the potential of polyphenols with chelating phenolate motifs as robust MOF linkers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003ePhysicochemical characterization and frameworks robustness\u003c/h3\u003e\n\u003cp\u003eThe thermal stability of MOF materials is a key consideration for their practical applications. To evaluate the thermal stability of SCU-1, thermogravimetric analysis (TGA) was performed under air and revealed three distinct stages of degradation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The initial mass loss in the 35\u0026ndash;95\u0026deg;C range corresponds to the evacuation of free guest H\u003csub\u003e2\u003c/sub\u003eO trapped in the pores. The subsequent mass loss up to approximately 190\u0026deg;C is assigned to the removal of two Bi-coordinated water molecules. The final stage, below 360\u0026deg;C, corresponds to decomposition of the organic linker and oxidation of the organic component, consistent with the known thermal behavior of phenolic MOFs. Additionally, TGA of SCU-1 agrees with the proposed sum formula. The stepwise weight loss and complete combustion of the organic content in the final stage allowed us to estimate the contents of guest molecules, coordinated H\u003csub\u003e2\u003c/sub\u003eO, HMT ligands, and residual Bi. Notably, in an ideal defect-free framework, the Bi:HMT ratio should be 2:1, whereas the TGA-derived value is 1.87:1. This deviation suggests a degree of node loss in the framework. Consistent with this interpretation, low-angle PXRD shows a broad diffraction feature, indicating the presence of nanoregions with missing metal nodes (Figure S10).\u003c/p\u003e \u003cp\u003eVariable-temperature PXRD further confirms the high thermal stability of SCU-1. In air, structural changes become evident above 190\u0026deg;C, consistent with oxidation of the phenolic groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). Under N\u003csub\u003e2\u003c/sub\u003e, however, SCU-1 retains its framework structure up to 450\u0026deg;C, demonstrating excellent thermal robustness (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). This stability can be understood from several structural features. First, Bi\u003csup\u003e3+\u003c/sup\u003e in this system assembles into compact rod-like IBUs, which are known to impart high structural robustness (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). Second, the ortho-hydroxy groups of HMT form five-membered chelate rings with Bi\u003csup\u003e3+\u003c/sup\u003e ions, with Bi\u0026ndash;O bond lengths of approximately 2.1\u0026ndash;2.2 \u0026Aring;, indicating deprotonation of the phenolic hydroxyls before coordination. These shorter bond lengths suggest stronger bonding compared to carboxylate-Bi coordination (typically 2.4\u0026ndash;2.8 \u0026Aring;), contributing to the enhanced stability of the MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). In addition, the distance between the phenolic hydroxyl groups on the pyran rings of two adjacent HMT molecules in the ab plane is 2.8 \u0026Aring;, indicating hydrogen bonding between the HMT linkers and further stabilizing the structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eChemical stability is equally important for practical applications, especially under aqueous conditions. SCU-1 retains its crystallinity after 24 h in water, phosphate-buffered saline (PBS), and cell culture medium (RPMI 1640), indicating strong resistance to common coordinating species and biologically relevant media (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). The acid\u0026ndash;base tolerance of SCU-1 was further examined by exposure to aqueous H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and NaOH solutions over a wide pH range. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB, the frameworks remain intact from pH 1 to 13. In concentrated sulfuric acid (pH\u0026thinsp;=\u0026thinsp;0), SCU-1 undergoes complete decomposition. At pH\u0026thinsp;\u0026ge;\u0026thinsp;14, framework collapse is likely caused by the oxidation of phenolic hydroxyl groups under strongly alkaline conditions. The stability of SCU-1 was further examined in fourteen commonly used catalytic solvents and reagents, including aromatic and aliphatic hydrocarbons, halogenated hydrocarbons, alcohols, ethers, esters, and ketones. Stability tests were carried out at room temperature and at 80\u0026deg;C for 24 h. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD, SCU-1 remains stable in all of these media except formic acid and acetic acid.\u003c/p\u003e \u003cp\u003eThe HOMO energy distributions and condensed Fukui functions indicate that the carbonyl oxygen atoms of formic acid and acetic acid have strong coordination ability and can compete with the phenolic oxygen atoms of HMT for Bi\u003csup\u003e3+\u003c/sup\u003e centers, thereby destabilizing the framework (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE, F). Formic acid shows nearly twice the coordination activity of acetic acid, consistent with its stronger destabilizing effect. After immersion in formic acid at 80\u0026deg;C for 24 h, both SCU-1 and bismuth nitrate were converted into the same bismuth triformate phase, which strongly supports this interpretation (Figure S11). Since bismuth-based materials have attracted growing interest in CO\u003csub\u003e2\u003c/sub\u003e reduction catalysis, we also evaluated the stability of SCU-1 under photocatalytic conditions. Triethanolamine (TEA), a common CO\u003csub\u003e2\u003c/sub\u003e-reduction additive, often decomposes MOFs because of its strong coordinating amino and hydroxyl groups. In contrast, SCU-1 remains crystalline after 24 h in 0.5% TEA and under xenon lamp irradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eG). Overall, the chemical stability of SCU-1 appears to be superior to that of benchmark BioMOFs such as CD-MOFs\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e and Bio-MOF-1\u003csup\u003e29\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further evaluate the intrinsic properties of this material, we examined its biocompatibility, sulfur tolerance, and colloidal behavior. In vitro cytotoxicity tests using the B16 melanoma cell line showed that neither SCU-1 nor its constituent components inhibited cell growth even at concentrations up to 1000 \u0026micro;g mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Figure S12). Because sulfur-containing molecules often destabilize MOFs by competing with linkers for metal coordination, the stability of SCU-1 was also tested in aqueous solutions of L-cysteine and L-cystine. As shown in Figure S13, SCU-1 retains its structural integrity after 24 h, demonstrating its robustness under sulfur-rich conditions. In addition to chemical stability, surface charge and colloidal stability can significantly affect interactions between materials and various biological structures or drug molecules. We further investigated the surface chemistry of SCU-1 in both complete cell culture medium (RPMI) and water. As shown in Figure S14, SCU-1 exhibited a negative surface charge, suggesting its potential for electrostatic interactions with positively charged molecules. The reduced absolute value of the zeta potential in RPMI is attributed to protein adsorption from the culture medium. These results further demonstrate the unusual robustness of SCU-1 under biologically relevant conditions.\u003c/p\u003e\n\u003ch3\u003ePorosity and CO-binding microenvironment\u003c/h3\u003e\n\u003cp\u003eThe porosity of SCU-1 was investigated by combining theoretical and experimental analyses. The ideal framework was analyzed using the Zeo\u0026thinsp;+\u0026thinsp;+\u0026thinsp;program with N\u003csub\u003e2\u003c/sub\u003e as the probe sorbate. The pore-size distribution indicates that the ideal structure contains a dominant pore size of approximately 5 \u0026Aring; (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). The theoretical surface area was calculated to be 231 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which reflects the narrow channel aperture (~\u0026thinsp;2.8 \u0026Aring;) that limits diffusion of N\u003csub\u003e2\u003c/sub\u003e molecules. Experimental N\u003csub\u003e2\u003c/sub\u003e sorption at 77 K, after activation at 150\u0026deg;C under vacuum for 10 h, confirmed the presence of permanent porosity in SCU-1. The adsorption isotherm displays a type IV profile according to the IUPAC classification, indicating the coexistence of micropores and mesopores (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB). The Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) surface area is 181 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, slightly lower than the theoretical value. This difference is consistent with the presence of structural defects, which may partially merge micropores into mesopores and thereby reduce the accessible surface area. The pore-size distribution derived from N\u003csub\u003e2\u003c/sub\u003e sorption is consistent with this interpretation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC).\u003c/p\u003e \u003cp\u003eTo exclude possible interference from the quadrupole moment of N\u003csub\u003e2\u003c/sub\u003e, additional adsorption experiments were performed with Ar at 87 K. As shown in Figures S15 and S16, the adsorption behavior and pore-size distribution were similar to those obtained with N\u003csub\u003e2\u003c/sub\u003e, supporting the same structural interpretation. However, because of the kinetic diameter limitations of both N\u003csub\u003e2\u003c/sub\u003e and Ar, ultramicropores of about 5 \u0026Aring; cannot be fully resolved using these gases. We therefore carried out CO\u003csub\u003e2\u003c/sub\u003e sorption measurements at 273 K (Figure S17). The resulting pore-size distribution shows a clear microporous feature centered at 5.4 \u0026Aring; (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eD), in excellent agreement with the crystallographic model and thus providing independent support for the proposed pore structure. Given that only a limited number of porous Bi-based MOFs have been reported, we further compared SCU-1 with representative Bi-MOFs in terms of thermal stability, BET surface area, and ligand cost (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eE)\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan additionalcitationids=\"CR31 CR32 CR33 CR34 CR35 CR36\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. SCU-1 combines high thermal stability, appreciable surface area, and low linker cost, which together support its potential practical value.\u003c/p\u003e \u003cp\u003eThe selective adsorption of CO\u003csub\u003e2\u003c/sub\u003e by SCU-1 was then examined under conditions relevant to gas separation. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eF, SCU-1 displays a stronger affinity for CO\u003csub\u003e2\u003c/sub\u003e than for N\u003csub\u003e2\u003c/sub\u003e or CH\u003csub\u003e4\u003c/sub\u003e. This result indicates that the framework provides not only geometric confinement but also a favorable chemical environment for CO\u003csub\u003e2\u003c/sub\u003e. To understand this, grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations were used to identify the preferred adsorption sites and the corresponding host\u0026ndash;guest interactions. At low loading, CO\u003csub\u003e2\u003c/sub\u003e preferentially accumulates at the center of the small pores of SCU-1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eG). DFT optimization of the adsorption configurations shows that all tested starting positions converge to the same host\u0026ndash;guest structure (Figure S18), indicating a well-defined preferred adsorption configuration. Notably, the diameter of the small pores in SCU-1 is approximately 5 \u0026Aring;, only slightly larger than the kinetic diameter of CO\u003csub\u003e2\u003c/sub\u003e (3.3 \u0026Aring;). This close size match creates a strong confinement effect, allowing each CO\u003csub\u003e2\u003c/sub\u003e molecule to be surrounded by multiple non-covalent interactions within the pore. Specifically, the oxygen atoms of CO\u003csub\u003e2\u003c/sub\u003e participate in O\u0026ndash;H\u0026middot;\u0026middot;\u0026middot;O and C\u0026ndash;H\u0026middot;\u0026middot;\u0026middot;O hydrogen bonds with framework hydroxyl groups, with intermolecular distances of 2.4, 2.7, and 3.3 \u0026Aring;. In addition, the electropositive carbon atom of CO\u003csub\u003e2\u003c/sub\u003e forms close contacts with framework oxygen atoms at distances of 2.7 and 3.7 \u0026Aring;, consistent with Lewis acid\u0026ndash;base interactions (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eH). In agreement with these structural features, the calculated adsorption energy reaches approximately\u0026thinsp;\u0026minus;\u0026thinsp;87.5 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These results show that the strong affinity of SCU-1 for CO\u003csub\u003e2\u003c/sub\u003e arises from the combined effects of pore confinement and multiple host\u0026ndash;guest interactions within the phenolic pore environment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eVisible-light-driven CO conversion\u003c/h3\u003e\n\u003cp\u003eGiven the known photocatalytic and electrocatalytic activity of Bi-based materials towards CO\u003csub\u003e2\u003c/sub\u003e reduction, we next investigated whether SCU-1 could function as a photocatalyst under visible light. Photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction was conducted in water under 50 kPa CO\u003csub\u003e2\u003c/sub\u003e and simulated solar irradiation (AM 1.5 G, 100 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), without any added sacrificial agents or photosensitizers. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA, SCU-1 produced C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH, CH\u003csub\u003e3\u003c/sub\u003eOH, and HCOOH, with ethanol as the major product at a rate of 50.13 \u0026micro;mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. HPLC analysis indicated that formic acid, methanol, and ethanol were the only detectable liquid products (Figure S19), and the \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR spectrum further confirmed the presence of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH, CH\u003csub\u003e3\u003c/sub\u003eOH, and HCOOH in the liquid-phase products (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eC). No products were detected under Ar, confirming that CO\u003csub\u003e2\u003c/sub\u003e is the sole carbon source under the reaction conditions. Compared with representative Bi-based catalysts reported to date, SCU-1 shows a competitive ethanol production rate under visible light even without post-synthetic modification (Table S4). It is also notable that this activity is observed in pure water, without sacrificial agents or carbonate-containing media. The photocatalytic activity of SCU-1 can be understood in light of the adsorption results discussed above. The pore surface provides multiple interaction sites for CO\u003csub\u003e2\u003c/sub\u003e, and the resulting strong adsorption energy promotes local enrichment of CO\u003csub\u003e2\u003c/sub\u003e near the catalytic sites. At the same time, the porous framework ensures that these sites remain accessible, thereby facilitating contact between the substrate and the active centers. To assess durability, SCU-1 was subjected to four consecutive photocatalytic cycles. No obvious loss of activity was observed after the fourth cycle (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB), and both PXRD and SEM confirmed that the framework structure and morphology were retained after the reaction (Figures S20A and S20B). These results demonstrate that SCU-1 combines photocatalytic activity with good operational stability.\u003c/p\u003e \u003cp\u003eTo evaluate the thermodynamic feasibility of this process, the optical and electronic properties of SCU-1 were examined. UV-vis diffuse reflectance spectra show broad absorption across the visible region, with a maximum near 570 nm, indicating effective light harvesting by the plant polyphenol-Bi coordination (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eD). Based on Tauc plot analysis derived from the UV-vis spectra, the energy gap (E\u003csub\u003eg\u003c/sub\u003e) of SCU-1 was determined to be 1.87 eV. Mott-Schottky measurements conducted at different frequencies show positive slopes for the sample, confirming its n-type semiconductor behavior (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eE). On this basis, the conduction band minimum (E\u003csub\u003eCB\u003c/sub\u003e) and valence band maximum (E\u003csub\u003eVB\u003c/sub\u003e) of SCU-1 were calculated to be \u0026minus;\u0026thinsp;0.62 V and 1.25 V versus the NHE, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eF). These band-edge positions indicate that SCU-1 is thermodynamically capable of driving CO\u003csub\u003e2\u003c/sub\u003e reduction coupled with H\u003csub\u003e2\u003c/sub\u003eO oxidation under light irradiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, we show that haematoxylin, a natural asymmetric plant polyphenol, can serve as a linker for the construction of a crystalline bismuth-based MOF. Despite the low symmetry of the linker, SCU-1 retains long-range order and can be synthesized under aqueous acidic conditions with good scalability. Structural analysis and theoretical calculations show that the intrinsic coordination asymmetry of haematoxylin creates framework heterogeneity without disrupting long-range order. These findings also reveal the potential of intrinsically asymmetric plant polyphenols to serve as linkers for robust MOFs with intrinsic structural heterogeneity. In SCU-1, linker asymmetry is not merely a structural feature but also contributes to the properties of the material. Strong Bi-phenolate chelation, rod-like inorganic building units, and hydrogen-bonding interactions confer exceptional thermal and chemical robustness, while the resulting ultramicroporous phenolic environment enables strong CO\u003csub\u003e2\u003c/sub\u003e binding through combined confinement and multipoint host\u0026ndash;guest interactions, and supports visible-light-driven CO\u003csub\u003e2\u003c/sub\u003e conversion in water. More broadly, this work expands the linker space of MOF chemistry beyond symmetry-compatible molecules and shows that intrinsically asymmetric plant polyphenols can be used to construct robust porous frameworks with built-in structural heterogeneity and interaction-rich pore microenvironments.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eChemicals\u003c/h2\u003e \u003cp\u003eAll chemicals and reagents were used as obtained without further purification unless otherwise mentioned. Bismuth(III) nitrate pentahydrate (Bi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO, 99.995% metals basis), HMT (99%, HPLC), acetic acid, L-cysteine, L-cystine, triethanolamine, formic acid, N,N-dimethylformamide, dimethyl sulfoxide, acetone, acetonitrile, cyclohexanone, dichloromethane, 1,4-dioxane, ethyl acetate, methanol, N-methylpyrrolidone, tetrahydrofuran, toluene were purchased from Titan (China). MTT Cell Proliferation and Cytotoxicity Assay Kit (MTT) was purchased from Beyotime (China). Roswell Park Memorial Institute (RPMI), phosphate-buffered saline (PBS), and normal saline were purchased from Gibco (USA). High-purity Milli-Q (MQ) water with a resistivity of 18.2 MΩ cm was obtained from an inline Millipore RiOs/Origin water purification system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis\u003c/h2\u003e \u003cp\u003eIn a typical synthesis, 45.3 mg of reagent-grade HMT (0.15 mmol) and 145.5 mg of bismuth(III) nitrate pentahydrate (0.3 mmol) were separately dissolved in 7.5 mL of acetic acid aqueous solution (6 vol.% acetic acid, made from glacial acetic acid), then mixed in a Teflon autoclave reactor (25 mL) for hydrothermal treatment at 120\u0026deg;C. After 36 h, the obtained product was collected by centrifugation (8000 rpm for 8 min) and washed with water and ethanol. Yield (after washing with water and ethanol, then drying overnight at 60\u0026deg;C): 0.175 g (79% of theoretical yield).\u003c/p\u003e \u003cp\u003eLarger batches of SCU-1 were synthesized using 1.71 g of HMT (6 mmol) and 5.82 g bismuth(III) nitrate pentahydrate (12 mmol), which was added to a Teflon autoclave reactor (1 L) containing 600 mL of a water and acetic acid mixture (6 vol.% acetic acid) for hydrothermal treatment at 120\u0026deg;C. After 36 h, it was placed in an oven at 60\u0026deg;C overnight. Yield after washing with water and ethanol, then drying overnight at 60\u0026deg;C: 5.66 g (72% of theoretical yield). The phase purity of both materials was confirmed by PXRD and elemental analysis.\u003c/p\u003e \u003cp\u003eAtmospheric reflux method:​​ 90.6 mg of reagent-grade HMT (0.3 mmol) and 291 mg of bismuth(III) nitrate pentahydrate (0.6 mmol) were separately dissolved in 15 mL of an acetic acid aqueous solution (6 vol.% acetic acid, prepared from glacial acetic acid). The mixtures were then combined in a 50 mL round-bottom flask and refluxed at 100\u0026deg;C for 36 h. The contents were then washed and left to dry at ambient conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eStructure determination and characterization\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003eScanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eSEM images and energy dispersive spectroscopy (EDS) mapping were conducted on a scanning electron microscope (ZEISS Gemini 300).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eTransmission electron microscopy (TEM)\u003c/h2\u003e \u003cp\u003eTEM images were acquired by Tecnai G2 F20 S-TWIN with an operation voltage of 200 kV.\u003c/p\u003e \u003cp\u003e \u003cb\u003e3D electron diffraction (3DED)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe crystal powder was drop-casted onto a copper grid (R1.2/1.3, QUANTIFOIL), and the grid was plunged into liquid nitrogen rapidly. The grid was then transferred to the Fischione 2550 cryo holder and TEM at liquid nitrogen temperature (77 K). The cRED data were collected on a JEOL 2100-plus TEM equipped with a MerelinEM detector under 200 kV acceleration voltage and installed with DiffProAcquire data collection software (software developed by the ReadCrystal Tech Co.). The tilting range depends on the location of the crystals on the grid. For the sample, 85 electron diffraction patterns were collected with the tilting angle ranging from \u0026minus;\u0026thinsp;54.98\u0026deg; to 18.50\u0026deg;. Each frame was collected with an exposure time of 1 s, resulting in a 1.07\u0026deg; wedge per frame. According to the 3DED data, the indexed unit cell parameters indicate that SCU-1 has an identical unit cell to SU-101 along all three crystallographic axes\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003ePowder X-ray diffraction (PXRD)\u003c/h2\u003e \u003cp\u003eThe powder diffraction data of SCU-1 were measured at room temperature on a Rigaku Ultima IV, in the 2θ range 1\u0026ndash;40\u0026deg;. The system is equipped with a Ge(111) monochromator producing Cu Kα1 radiation (λ\u0026thinsp;=\u0026thinsp;1.54060 \u0026Aring;) and a LynxEye detector. The refinement of the electron-diffraction model against high-resolution PXRD data was carried out in GSAS II\u003csup\u003e38\u003c/sup\u003e. Topological analysis of the SCU-1 framework was carried out using the software package ToposPro\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eModel building\u003c/h2\u003e \u003cp\u003eThe structural model of the SCU-1 was developed using the Materials Studio software suite. Initially, the lattice was constructed based on the P1 space group, with the a and b lattice parameters set to 19.110 \u0026Aring;. These parameters were determined by measuring the center-to-center distances between the vertices of SU-101\u003csup\u003e26\u003c/sup\u003e. The model underwent geometry optimization using the Forcite module, which employs Universal force fields and Ewald summations to ensure accurate structural refinement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eComputational details\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003eCoordination structure of the SCU-1\u003c/h2\u003e \u003cp\u003eAll complexes were optimized using the Perdew-Burke-Ernzerhof hybrid functional (PBE0) method and Def2-SVP basis set with Grimme\u0026rsquo;s DFT-D3(BJ) empirical dispersion correction by the Gaussian 16 package\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. The single-point energy calculations were performed using the Def2-TZVP basis set. Harmonic vibrational frequency calculations were carried out at the same level to confirm that imaginary frequency is absent in the molecules, i.e., they are located at the minima of the potential energy surface. Moreover, water has been introduced as an implicit solvent by the SMD (Solvation model density) solvation model. The HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of these complexes were obtained by combining Multiwfn 3.8\u003csup\u003e40\u003c/sup\u003e and VMD 1.9.3\u003csup\u003e41\u003c/sup\u003e software, whose input files were extracted from a Gaussian checkpoint file. The condensed Fukui function and condensed dual descriptor were computed via Multiwfn, employing Hirshfeld charges for assessment\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eSolution-phase Gibbs free energies were then calculated using the \u0026ldquo;direct method\u0026rdquo;\u003csup\u003e44\u003c/sup\u003e. For systems that undergo large geometry changes upon solvation, the direct method affords energetics that are superior to those obtained using (gas phase to solution) thermocycles\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Given the high partial charges on atoms within these metal complexes, significant geometry changes upon solvation (in water) would be anticipated. The default standard state used within the Gaussian 16 package for entropic components (even in a SMD solvent field) is based on the statistical mechanics for an ideal gas (evaluated at 1 atm of pressure and 25\u0026deg;C). Thus, appropriate standard state corrections were applied to ensure all binding energies were calculated at a standard state for solutes in solution (of 1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 120\u0026deg;C). This correction takes the following form.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{\\text{\u0026Delta;G}}^{\\text{1atm\u0026rarr;1M}}\\text{=\u0026Delta;mRTln[}\\frac{\\text{RT}}{\\text{P}}]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHere, Δm is the change in moles upon reaction, R is the ideal gas constant (8.3145 J mol\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e K\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e), T is the temperature of interest at which the Gibbs free energy is also evaluated (typically 393.15 K), and P is pressure (101.325 kPa\u0026thinsp;=\u0026thinsp;1 atm).\u003c/p\u003e \u003cp\u003eFor reactions that either generate or consume water (i.e., reactions where water is a product or reagent), a further state correction is required. The standard state for any liquid is the pure substance at 1 atm of pressure, so the standard state of liquid water should be [H\u003csub\u003e2\u003c/sub\u003eO]\u0026thinsp;=\u0026thinsp;55.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (rather than 1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for an aqueous solute). Gibbs free energies for reactions involving water as a reagent must be further corrected by adding the following additional term:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{{\\Delta\\:}\\text{G}}^{1\\text{M}\\to\\:55.5\\text{M}}=-\\text{n}\\text{R}\\text{T}\\text{l}\\text{n}\\left[{\\text{H}}_{2}\\text{O}\\right]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHere, n is the number of moles of water acting as a reagent. Conversely, for reactions that generate water as a product, Gibbs free energies are corrected by the following term:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{{\\Delta\\:}\\text{G}}^{1\\text{M}\\to\\:55.5\\text{M}}=+\\text{n}\\text{R}\\text{T}\\text{l}\\text{n}\\left[{\\text{H}}_{2}\\text{O}\\right]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWithin standard continuum solvation models, solvation energies are profoundly influenced by the overall charge of the metal‒ligand (ML) complex as well as the coordination number (CN) and oxidation/spin state of the metal ion\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThese issues can be resolved by constructing isodesmic proton-transfer reactions, taking the A-ring reaction as an example:\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003cp\u003eI: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{6}\\right]}^{3+}+\\text{H}\\text{M}\\text{T}={\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{4}\\right(\\text{H}\\text{M}\\text{T}-\\text{A}\\left)\\right]}^{3+}+2{\\text{H}}_{2}\\text{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003cp\u003eII:\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{4}\\right(\\text{H}\\text{M}\\text{T}-\\text{A}\\left)\\right]}^{3+}+{\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{4}{\\left(\\text{O}\\text{H}\\right)}_{2}\\right]}^{+}={\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{4}{(\\text{H}\\text{M}\\text{T}-\\text{A})}^{2-}\\right]}^{+}+{\\left[\\text{B}\\text{i}{\\left({\\text{H}}_{2}\\text{O}\\right)}_{6}\\right]}^{3+}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cdiv id=\"Sec21\" class=\"Section4\"\u003e \u003cp\u003eΔG* = ΔG\u003csub\u003eI\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;ΔG\u003csub\u003eII\u003c/sub\u003e\u003c/p\u003e \u003cp\u003eΔG*\u003csup\u003ecorr\u003c/sup\u003e = ΔG* + Δ\u0026#119866;\u003csup\u003e1atm\u0026rarr;1M\u003c/sup\u003e + 2Δ\u0026#119866;\u003csup\u003e1M\u0026rarr;55.5M\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eGrand Canonical Monte Carlo (GCMC)\u003c/h2\u003e \u003cp\u003eClassical GCMC simulations are performed using the RASPA\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e software to calculate the adsorption uptake of CO\u003csub\u003e2\u003c/sub\u003e within SCU-1 structures at 50 kPa, 298 K. The structures of the SCU-1 were treated as rigid frameworks during the simulations. The Monte Carlo moves in the GCMC simulations, including translational, rotational, addition/deletion, reinsertion, and identity change moves, were tried with equal probability. A total of 1 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e steps was set for the initialization run, followed by a production run of another 1 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e steps. To describe adsorbate-adsorbate interactions, the UFF\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e force field was used for SCU-1\u003csup\u003e49\u003c/sup\u003e. CO\u003csub\u003e2\u003c/sub\u003e molecules, including charges and LJ parameters, are modeled using the EPM2 model\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. In the calculations for each structure, a supercell comprising 2 \u0026times; 2 \u0026times; 5 unit cells for SCU-1 was used, ensuring the simulation box was at least twice the cutoff radius along each crystal direction. Nonbonded interactions are represented by the Lennard-Jones (LJ) potential with a cutoff radius of 12.9 \u0026Aring;. The partial atomic charges of the structures are calculated using the PACMOF package\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. The long-range electrostatic interactions were processed by the Ewald summation method, while the Van Der Waals interactions were handled using the atom-based summation method.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eDFT of the CO\u003csub\u003e2\u003c/sub\u003e adsorption structure within the framework\u003c/h2\u003e \u003cp\u003eDFT calculations were performed using the Vienna Ab Initio Simulation Package (VASP)\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, employing plane-wave basis sets and the projector augmented-wave (PAW) method. The exchange-correlation functional was approximated using the Perdew-Burke-Ernzerhof (PBE) parametrization within the generalized gradient approximation (GGA). Van der Waals interactions were accounted for using the DFT-D3 correction by Grimme. The energy cutoff was set to 450 eV, and Brillouin-zone integration was performed using a Monkhorst-Pack grid with a k-point mesh of 1\u0026times;1\u0026times;3. Structural optimizations were carried out until the maximum force on each atom was less than 0.02 eV \u0026Aring;\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, and energy convergence was set to 10\u003csup\u003e\u0026ndash;5\u003c/sup\u003e eV. All structures were fully relaxed to the minimum energy configuration. Computational efficiency was further enhanced by enabling the automatic optimization of real-space projectors with an additional support grid.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eStability\u003c/h2\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eTGA\u003c/h2\u003e \u003cp\u003eThermogravimetric analysis data were gathered on a sample of SCU-1 using a TA Instruments Discovery TGA. The sample was put into a platinum crucible and heated in air from 35\u0026deg;C to 600\u0026deg;C with a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The empirical formula best matching the observed data was determined as Bi\u003csub\u003e2\u003c/sub\u003eO(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e(C\u003csub\u003e16\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e6\u003c/sub\u003e)\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eThermal stability\u003c/h2\u003e \u003cp\u003eThe SCU-1 was calcined in a muffle furnace under air or in a tube furnace under nitrogen atmosphere for 10 hours, respectively, and then characterized by powder X-ray diffraction (PXRD).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section3\"\u003e \u003ch2\u003eStability in solvents and solutions\u003c/h2\u003e \u003cp\u003eFor the stability tests, 30 mg of SCU-1 was added to a 10 mL glass vial fitted with a screw-cap. For every trial, 5 mL of each respective solvent or solution was added, and the resulting dispersion was stirred at room temperature or 80\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003eStability in the presence of triethanolamine\u003c/h2\u003e \u003cp\u003eTo assess the structural integrity of SCU-1 in the presence of triethanolamine, 30 mg of SCU-1 was dispersed in an aqueous triethanolamine solution (0.5% v/v) and maintained at 37\u0026deg;C with continuous stirring for 24 hours. The MOF was then recovered by centrifugation at 8000 rpm for 10 minutes. PXRD patterns were acquired after the powders were allowed to dry under ambient conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec29\" class=\"Section2\"\u003e \u003ch2\u003eStability in the presence of L-cysteine and L-cystine\u003c/h2\u003e \u003cp\u003eThe integrity of SCU-1 in the presence of L-cysteine and L-cystine at 37\u0026deg;C was evaluated by preparing solutions with 5 mg mL\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e of the material and each respective compound in water. The SCU-1 dispersions were then allowed to stir at 37\u0026deg;C for 24 h before the MOF was retrieved by centrifugation (8000 rpm, 10 min). PXRD patterns were acquired after the powders were allowed to dry under ambient conditions. Residual crystalline L-cystine can be observed in the sample previously immersed in a solution of L-cystine.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003epH-dependent stability\u003c/h3\u003e\n\u003cp\u003eFor the pH-dependent stability tests, 20 mg of SCU-1 was immersed in 5 mL of stock solution, prepared from either NaOH or concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, to obtain the desired pH.\u003c/p\u003e \u003cdiv id=\"Sec31\" class=\"Section2\"\u003e \u003ch2\u003eStability in biorelevant media\u003c/h2\u003e \u003cp\u003eSCU-1 in PBS was prepared by dispersing the material in PBS solution (30 mg mL\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e of SCU-1 in 0.01 M phosphate buffer, 0.0027 M KCl, 0.137 M NaCl, pH\u0026thinsp;=\u0026thinsp;7.4) or cell culture medium (30 mg mL\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e of SCU-1 in RPMI). Powder X-ray diffraction was collected on the pellet. The evolution of the SCU-1 ζ-potential was evaluated over time in the presence of diverse physiological media (aqueous solution (Milli-Q water) and cell culture media RPMI).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec32\" class=\"Section2\"\u003e \u003ch2\u003eDegradation mechanisms of SCU-1 by formic and acetic acids\u003c/h2\u003e \u003cp\u003eTo probe the degradation mechanism, SCU-1 was initially treated with sulfuric acid at the same pH (0.5) as pure formic acid. The framework remained intact under these conditions, suggesting that structural collapse in formic/acetic acid likely arises from competition between the carboxylate groups of these acids and the phenolic hydroxyl groups of HMT for the Bi(III) nodes. Furthermore, exposure of SCU-1 to formic acid at 80\u0026deg;C yielded bismuth(III) triformate crystals, a common phase formed from the interaction of Bi(III) ions with formic acid. This phase was also obtained by dispersing bismuth nitrate directly in formic acid at 80\u0026deg;C, confirming that formic acid displaces HMT and coordinates with Bi(III), leading to the formation of the bismuth triformate salt.\u003c/p\u003e \u003cdiv id=\"Sec33\" class=\"Section3\"\u003e \u003ch2\u003ePorosity and sorption properties\u003c/h2\u003e \u003c/div\u003e \u003cdiv id=\"Sec34\" class=\"Section3\"\u003e \u003ch2\u003eSimulated data\u003c/h2\u003e \u003cp\u003eZeo\u0026thinsp;+\u0026thinsp;+\u0026thinsp;Version 0.3 was used to determine cavity localization, connectivity, and volume in the crystal structure of SCU-1\u003csup\u003e52\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003ch3\u003eExperimental adsorption-desorption data\u003c/h3\u003e\n\u003cp\u003eGas adsorption/desorption isotherms were recorded on a Micromeritics Tristar Ⅱ Plus 3030. Prior to the experiments, the samples were pretreated at 150\u0026deg;C under vacuum for 10 h. Nitrogen adsorption/desorption isotherms were recorded at liquid nitrogen temperature (\u0026ndash;196\u0026deg;C). Argon adsorption/desorption isotherms were measured at liquid argon temperature (\u0026ndash;186\u0026deg;C), using a liquid argon bath for temperature control. Nitrogen (N\u003csub\u003e2\u003c/sub\u003e), carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e), and methane (CH\u003csub\u003e4\u003c/sub\u003e) adsorption-desorption isotherms were recorded at 0\u0026deg;C. An ice slurry bath was used as the temperature control for these experiments.\u003c/p\u003e\n\u003ch3\u003ePhotocatalytic CO reduction test\u003c/h3\u003e\n\u003cp\u003eThe CO\u003csub\u003e2\u003c/sub\u003e reduction experiments were conducted in a sealed Pyrex bottle, where a 20 mL glass dish was placed as the reactor. The reactor contained 3 mL of water and 20 mg of photocatalyst. Before irradiation, the reaction system was degassed to remove air and then refilled with high-purity CO\u003csub\u003e2\u003c/sub\u003e to a pressure of 50 kPa. The reaction was carried out under simulated solar irradiation using a 300 W Xe lamp equipped with an AM 1.5 G filter. The light intensity at the reactor position was calibrated to 100 mW cm\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e (Perfectlight Labsolar6A). The gaseous product was detected by an online gas chromatograph (GC 2014, Shimadzu) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) in series, which was used to quantify the produced gases during the photocatalytic reaction. Upon completion of the reaction, the liquid phase was collected, filtered, and analyzed by high-performance liquid chromatography (HPLC).\u003c/p\u003e \u003cdiv id=\"Sec37\" class=\"Section2\"\u003e \u003ch2\u003ePhotoelectrochemical test\u003c/h2\u003e \u003cp\u003eAn electrochemical workstation (PGSTAT30, Autolab) was equipped to perform photoelectrochemical studies. The three-electrode configuration was adopted, where the prepared electrode (SCU-1) served as the working electrode, the Pt sheet as the counter electrode, and the Ag/AgCl as the reference electrode. The electrolyte solution was prepared by dissolving Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in water (0.1 mol L\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e). Mott-Schottky plots were conducted at frequencies of 500, 1500, and 2500 Hz.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cdiv id=\"Sec38\" class=\"Section3\"\u003e \u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eData supporting the findings of this investigation are available from the Article and its Supplementary Information.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\u003cp\u003e \u003ch2\u003eAuthor information\u003c/h2\u003e \u003cp\u003eAuthors and Affiliations\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e \u003csup\u003e1\u003c/sup\u003e College of Biomass Science and Engineering, Sichuan University, Chengdu, Sichuan 610065, China\u003c/strong\u003e \u003cp\u003eZijun Zhu, Tong Shao, Lantao He, Shaojian Lin, Jianwu Lan, Jiaojiao Shang\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e \u003csup\u003e2\u003c/sup\u003e School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China\u003c/strong\u003e \u003cp\u003eJun Deng, Yang Chu, Xuemei Zhou\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e \u003csup\u003e3\u003c/sup\u003e National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, Chengdu, Sichuan 610065, China\u003c/strong\u003e \u003cp\u003eJiajing Zhou, Jiaojiao Shang\u003c/p\u003e \u003cp\u003eContributions\u003c/p\u003e \u003cp\u003eThe original idea was conceived by Z.Z.; the choice of organic linkers was made by Z.Z.; the synthesis of SCU-1 was performed by Z.Z.; MOF structure elucidation, performance investigation, and related data analysis were carried out by Z.Z., L.H., T.S., and J.S.; photocatalytic CO\u003csub\u003e2\u003c/sub\u003e reduction experiments were conducted by Z.Z., J.D., and Y.C.; X.Z., J.S., S.L., J.Z., and J.L. provided critical guidance throughout the project; J.S. supervised the overall research; all authors have reviewed and approved the final manuscript.\u003c/p\u003e \u003cp\u003eCorresponding authors\u003c/p\u003e \u003cp\u003eCorrespondence to Jiaojiao Shang.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003e \u003cb\u003eEthics declarations\u003c/b\u003e \u003c/h2\u003e \u003cp\u003e \u003cstrong\u003eCompeting interests\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the Institutional Research Fund from Sichuan University (Grant No. 2024SCUQJTX020) and the Science and Technology Project of Tibet Autonomous Region (Grant No. XZ202301YD0027C). The authors extend their gratitude to Dr. Zheng (from ReadCrystal Biotechnology) for providing invaluable assistance with the 3DED analysis. We thank A. Ken Inge (Stockholm University) for scientific discussions and encouragement. We thank the Theoretical and Computational Chemistry Team (from Scientific Compass \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ewww.shiyanjia.com\u003c/span\u003e\u003cspan address=\"http://www.shiyanjia.com\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e) for providing invaluable assistance.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMarsh C, Shearer GC, Knight BT, Paul-Taylor J, Burrows AD (2021) Supramolecular aspects of biomolecule interactions in metal-organic frameworks. 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Chem Mater 36:9806\u0026ndash;9821\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKancharlapalli S, Gopalan A, Haranczyk M, Snurr RQ (2021) Fast and accurate machine learning strategy for calculating partial atomic charges in metal-organic frameworks. J Chem Theory Comput 17:3052\u0026ndash;3064\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKohn W, Sham LJ (1965) Self-consistent equations including exchange and correlation effects. Phys Rev 140:A1133\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Asymmetric linker, Plant polyphenol, Bismuth-based MOF, Structural heterogeneity, CO2 photoreduction","lastPublishedDoi":"10.21203/rs.3.rs-9550934/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9550934/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMetal\u0026ndash;organic frameworks (MOFs) have been built largely on geometrically regular linkers, whereas asymmetric molecules have received far less attention. Such asymmetric linkers offer a unique opportunity to encode structural heterogeneity, coordinatively unsaturated sites, and chemically differentiated pores directly at the molecular design stage. However, their structural complexity often makes periodic frameworks assembly and structure determination more challenging. Here, we show that haematoxylin, a naturally occurring plant polyphenol with two chemically inequivalent catechol coordination sites, can serve as an intrinsically asymmetric linker for constructing a crystalline bismuth framework, SCU-1. Despite the low symmetry of the linker, SCU-1 can be synthesized in water with good scalability and retains long-range order. Structural modelling, electron diffraction, powder diffraction refinement, thermogravimetric compositional analysis, and low-angle diffraction collectively support a structurally heterogeneous framework associated with asymmetric coordination behavior. At the same time, strong Bi-phenolate chelation, rod-like inorganic building units, and hydrogen-bond reinforcement endow SCU-1 with exceptional robustness, allowing it to remain crystalline from pH 1 to 13, in diverse aqueous and organic media, and up to 450\u0026deg;C under N\u003csub\u003e2\u003c/sub\u003e. The resulting ultramicroporous phenolic framework exhibits strong CO\u003csub\u003e2\u003c/sub\u003e affinity, with a dominant pore feature of ~\u0026thinsp;5 \u0026Aring; and a calculated binding energy of \u0026minus;\u0026thinsp;87.5 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, arising from cooperative confinement and multipoint host\u0026ndash;guest interactions. Under visible light, SCU-1 further enables additive-free photocatalytic CO\u003csub\u003e2\u003c/sub\u003e conversion in water, favoring ethanol formation at 50.13 \u0026micro;mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These findings establish naturally asymmetric phytochemicals as an underexplored linker platform for creating robust MOFs with structural heterogeneity and functional CO\u003csub\u003e2\u003c/sub\u003e-binding microenvironments.\u003c/p\u003e","manuscriptTitle":"Naturally Asymmetric Plant Polyphenol Linkers Enable Robust Metal-Organic Frameworks with Built-In Structural Heterogeneity","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-05 08:17:10","doi":"10.21203/rs.3.rs-9550934/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"46a9d51e-46c5-4587-bba8-2f24423eafe8","owner":[],"postedDate":"May 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":67388232,"name":"Physical sciences/Chemistry/Supramolecular chemistry/Self-assembly"},{"id":67388233,"name":"Physical sciences/Materials science/Nanoscale materials/Organic\u0026#x2013;inorganic nanostructures"},{"id":67388234,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"},{"id":67388235,"name":"Physical sciences/Chemistry/Coordination chemistry/Organometallic chemistry/Ligands"}],"tags":[],"updatedAt":"2026-05-12T02:20:23+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-05 08:17:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9550934","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9550934","identity":"rs-9550934","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}