Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis

Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis | 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 Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis Omar Farha, Haomiao Xie, Milad Khoshooei, Mukunda Mandal, Simon Vornholt, and 19 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5357011/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Jul, 2025 Read the published version in Nature Chemistry → Version 1 posted You are reading this latest preprint version Abstract Metal sulfide binary compounds, renowned for their exceptional electronic properties, are advantageous in applications such as hydrogenation, dehydrogenation, and photocatalysis. Typically, the majority of active sites in these compounds reside on the surfaces and edges of catalyst particles, leaving the bulk catalyst underutilized. This study introduces a strategy to embed metal-sulfur active sites into metal-organic frameworks (MOFs) via post-synthetic modification, exploiting the MOFs’ accessible internal surfaces. Two MOF systems, including M 2 Cl 2 (BBTA) (H 2 BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole, M = Co, Ni), which features one-dimensional M–Cl chains and hexagonal channels, and M-MFU-4 l -Cl (M = Co, Ni), which contains discrete ZnM 4 metal nodes, were selected as starting materials. The conversion processes, from M 2 Cl 2 (BBTA) to M 2 (SH) 2 (BBTA) and from M-MFU-4 l -Cl to M-MFU-4 l -SH, were executed through a two-step post-synthetic modification protocol and confirmed by single-crystal XRD, PXRD, PDF, SEM, XPS, and N 2 sorption techniques. Catalytic performance was assessed using the reduction of 4-nitrophenol to 4-aminophenol with molecular hydrogen as a model reaction, and significant improvement in performance was observed upon introduction of the SH groups. Density functional theory calculations suggest that the flexibility of the sulfur moiety is crucial in the M–X bond cleavage pathway, enhancing hydrogen activation. This study underscores the efficacy of post-synthetic modification in developing advanced MOF-based catalysts with superior performance for selective hydrogenation reactions, highlighting the strategic advantage of incorporating polarizable sulfur components within MOFs. Physical sciences/Chemistry/Chemical synthesis/Catalyst synthesis Physical sciences/Chemistry/Catalysis/Catalyst synthesis Physical sciences/Chemistry/Materials chemistry/Metal–organic frameworks Introduction Highly polarizable components, such as sulfur-containing groups, in catalytic processes have emerged as a forefront area of research due to their unique ability to modulate chemical reactivity through electronic coupling. In this context, metal-sulfide compounds are of particular interest as they leverage the electronic flexibility of sulfur centers, 1 – 5 resulting in a more covalent nature of M–S bonds compared to their oxygen analogues, enhancing the charge transfer properties that play important roles in catalytic processes. 1 , 6 – 9 Nature’s ingenious use of sulfur-containing species, such as Fe 4 S 4 , Fe-V-S, Fe-Mo-S clusters and Cu-S moieties, in the active sites of enzymes for critical redox reactions has afforded excellent reactivity within biological systems for transformations like hydrogenation and dehydrogenation. 8 , 10 – 15 Despite their efficacy, however, the fragility and complexity of enzyme systems often limit their scalability and industrial application. 16 In contrast to enzymatic sulfur-containing species, transition metal-sulfur compounds, exemplified by MoS 2 17–20 and CoS x 21 – 23 , offer relatively greater stability and have been demonstrated to play a significant role in various catalytic processes, including hydrogen splitting and hydrogenation. 6 , 7 , 21 , 22 The catalytic efficacy of these compounds is intrinsically tied to the local environment of the active sites, where the morphology of particles, particularly at the surfaces and edges, becomes crucial for catalytic performance. This necessitates sophisticated defect engineering to maximize exposure of active sites. It has been demonstrated that increasing the surface areas of these systems improves the catalytic performance as the active sites are more easily accessible, ensuring efficient mass transport. 24 – 27 Beyond these well-known materials, metal-organic frameworks (MOFs) represent a burgeoning class of materials with significant implications for catalysis. The structural robustness and high internal surface areas of MOFs makes them ideal for serving as high-performing catalysts and hosting catalytic substrates. 28 – 30 In fact, encapsulating enzymes within MOF pores can substantially enhance both stability and catalytic efficiency relative to those of the free enzyme. 31 – 34 Furthermore, MOFs featuring open metal sites as reactive centers have been identified as promising candidates in catalysis, offering well-organized and protected reactive centers in a solid-state framework. 30 , 35 – 37 However, the synthesis of MOFs incorporating highly polarizable components, such as sulfide bridges, metal-sulfur based clusters, or thiolate linkers, remains largely underexplored, with only a few known examples. 38 – 45 The primary challenges hindering progress in this area include the instability of metal-sulfur clusters, the comparatively lower crystallinity than metal-oxide based MOFs resulting from the irreversible nature of forming highly polarized bonds, the poorly understood effects of templating agents on sulfur-containing structures, and the overarching need for novel synthetic methodologies to achieve desired topologies. 38 Post-synthetic modification 46 emerges as a promising strategy by leveraging the inherent topology of parent MOFs, the extensive database of known structures, and the simplification of synthetic conditions to modify bridging linkers and/or transform metal clusters, such as metal-oxide clusters, into their sulfur counterparts (Fig. 1 (a)). This approach not only mitigates the challenges associated with direct synthesis but also opens new avenues for the development of advanced catalytic materials. In this study, we selected two families of specific MOFs with potentially redox-active metal centers and accessible open metal sites: M 2 Cl 2 BBTA ( M = Co, Ni; H 2 BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) and M-MFU-4 l -Cl ( [M x Zn 5−x Cl 4 (BTDD) 3 ; x = 4 for M = Co and x = 2.5 for M = Ni; H 2 BTDD = bis(1H-1,2,3-triazolo[4,5-b][4′,5′-i])dibenzo[1,4]dioxin)) (Fig. 1 ) as parent MOFs. We successfully converted them to their hydroxide-bridged versions, M 2 (OH) 2 BBTA and M-MFU-4 l -OH, and then further converted them to their sulfided versions, M 2 (SH) 2 BBTA and M-MFU-4 l -SH. The crystal structures of post-synthetically modified sulfided MOFs were elucidated using a combination of single-crystal X-ray diffraction and electron diffraction techniques. In situ pair distribution function (PDF) analysis provided real-time insights into the sulfidation process, allowing for dynamic tracking of structural transformations during modification. To assess the catalytic performance of the sulfided MOFs, a model reaction was employed, focusing on the chemoselective hydrogenation of nitroarenes—the reduction of aryl –NO₂ to –NH₂. The sulfided MOFs exhibited markedly enhanced hydrogenation reactivity compared to their parent MOFs, which featured terminal or bridging chloride and hydroxyl groups. Computational studies, using density functional theory (DFT), offered deeper mechanistic insights, revealing that the incorporation of sulfide ligands facilitates the homolytic cleavage of metal-ligand (M–X) bonds, enabling more efficient H₂ activation. These integrated experimental and theoretical investigations highlight key reactivity trends and underscore the crucial role sulfur incorporation plays in modulating the catalytic properties of MOFs. Results and discussion For the post-synthetic modification, we selected two types of MOFs: M 2 Cl 2 BBTA and M-MFU-4 l -Cl (M = Co, Ni), to investigate how isolated metal nodes or 1-D chains with adjacent centers affect the properties in hydrogenation reactions. Both MOFs have similar triazolate linkers as supporting ligands and comparable pore sizes. (Fig. 1 ) In enzymes, nitrogen-containing heterocyclic groups like imidazoles have been proposed to extend the conjugation system for electron tunneling with metal-sulfide clusters. 47 Similarly, the triazolate groups in these MOFs can potentially act as π-acceptors to enhance the electronic polarizability of the metal center. 48 – 50 With these two types of parent MOFs in hand, we then performed post-synthetic modifications to install metal-sulfur linkages. In M 2 Cl 2 BBTA (M = Co, Ni), chloride serves as a bridging ligand between adjacent metal centers, providing a well-defined substitutionally labile bridge that can be targeted easily to access other functionalities. During our initial attempts at replacing chloride in the presence of H 2 S, we observed slow and incomplete conversion to the SH variant (e.g., ~ 50% Cl replaced by SH after 48 hours). We presume this limited reactivity is due to the formation of the byproduct HCl, which is a strong acid and drives the reaction backward. To circumvent this issue, we elected to treat the chloride-based MOFs with KOH to transform the bridging chloride anions into bridging hydroxyl groups, with the MOF products denoted as M 2 (OH) 2 BBTA. Replacement of the chloride was confirmed by X-ray photoelectron spectroscopic (XPS) analysis (Figure S9 and S12), while the integrity of the frameworks was confirmed by powder X-ray diffraction (PXRD) analysis (Figure S1 and S2) and N 2 sorption isotherms collected at 77 K (Figure S6). We reasoned that bridging hydroxyl groups would make the subsequent sulfidation reaction more feasible as water would be the leaving group. Indeed, reacting M 2 (OH) 2 BBTA with in situ -generated H 2 S converted the lightly colored MOF powders to dark brown within minutes, signaling the formation of the SH-bridging analogues M 2 (SH) 2 BBTA (Fig. 2 ). XPS (Table S6 and S9) and energy dispersive X-ray spectroscopic (EDS) analyses (Figure S21 and S23) revealed the anticipated 1:1 ratio between metal and sulfur, which suggests complete replacement of the hydroxyls with thiolates. Importantly, scanning electron microscopy (SEM) images confirmed that these post-synthetic modifications did not affect the particle size or morphology (Figure S20 and S22). We note that the ratio between Co and S can exceed 1:1 when excess H 2 S is used (Figure S21), which can be attributed to the formation of polysulfides in the MOF cavities (see below). For the M 2 X 2 BBTA series (M = Co, Ni; X = Cl, OH, SH), single-crystal X-ray diffraction (SCXRD) or electron diffraction (ED) experiments enabled us to determine the solid-state structures of these MOFs. All structures were solved under the R-3m space group with similar unit cell parameters (Table S1 ), indicating that the parent MOFs’ topology was preserved through these transformations. The simulated PXRD patterns closely match those of the experimental data (Fig. 3 . (a) and Figure S1 -2), which confirms the phase purity of the bulk samples. Examination of the coordination sphere revealed that all metal ions are octahedrally coordinated and surrounded by three nitrogen atoms from different triazolate linkers. Two additional sites are occupied by X atoms from bridging groups, and the final site by terminal water molecules, except in the SH version. Notably, in the SH version, we discovered a disordered S 5 chain bridging two cobalt atoms across two distinct 1-D metal chains. This corresponds well with the high Co:S ratios observed when excess H 2 S was used in the synthesis (Figure S21). On the other hand, the Co–N bond distances shortened from approximately 2.1 Å to 2.0 Å and 1.9 Å as the bridging groups changed from –Cl to –OH to –SH, respectively. This indicates that varying the bridging group alters the interactions between the metal centers and the coordinating triazole moiety, affecting the metal-ligand bonding environment. In contrast, the Ni–N bond distances remained relatively consistent, around 2.1 Å across all versions, suggesting less variation in the metal-triazole interactions for the nickel-based structures. Next, we collected N 2 adsorption isotherms of six samples (M 2 X 2 BBTA where M = Co, Ni and X = Cl, OH, SH) at 77 K to analyze the intrinsic porosity of these materials. The total N 2 uptakes of M 2 Cl 2 BBTA are STP 312 and 330 cm 3 /g with calculated BET areas of 1180 m 2 /g and 1190 m 2 /g (Fig. 3 . (c)) for M = Co and Ni, respectively, which corresponds well with the reported values and the theoretical values calculated from crystal structures (Table S3). The total N 2 uptakes of M 2 (SH) 2 BBTA are STP 200 and 228 cm 3 /g with calculated BET surface areas of 650 and 730 m 2 /g for M = Co and Ni, respectively, which correspond well with the theoretical values calculated from crystal structures with one terminal water occupying the open-metal site. Combined, these results demonstrate that the intrinsic porosity of the framework is preserved after this post-synthetic modification protocol. Similarly, the conversion of M-MFU-4 l -Cl to M-MFU-4 l -SH (where M = Co, Ni) utilized the same stepwise methodology as in the BBTA version (i.e., conversion of Cl to OH to SH; Section B in SI). First, the parent MOF Zn-MFU-4 l -Cl was synthesized, followed by partial transmetallation to Co-MFU-4 l -Cl or Ni-MFU-4 l -Cl upon incubation of the Zn analogue in DMF solutions of the corresponding metal chloride salt according to a previously published procedure. 51 , 52 The chemical formulas for these MOFs were determined to be Co 4 ZnCl 4 (BTDD) 3 and Ni 2.5 Zn 2.5 Cl 4 (BTDD) 3 through inductively coupled plasma-optical emission spectroscopy (ICP-OES) and XPS analyses. We were able to substitute the four peripheral Zn 2+ with Co 2+ but only partial substitution with Ni 2+ , which corresponds well with the results in the literature. 52 Next, we converted chlorides to hydroxyl groups through the use of a 1 M aqueous solution of organic base 4-ethylmorpholine instead of KOH as the former prevented the degradation of the Co- and Ni-based MOFs. Finally, treatment of these hydroxyl-based MOFs with in situ -generated H 2 S afforded the anticipated color change of the crystals to dark brown, which is indicative of transformation of the hydroxyls to thiols. SCXRD analysis revealed that the framework structure remained largely intact post-conversion to the thiol analogues with only minor changes observed in the unit cell parameters (Table S1 ). The M sites of M-MFU-4 l -SH are in an octahedral coordination sphere. Three coordination bonds are occupied by nitrogen atoms from the triazolyl groups of the linkers, two by oxygen atoms from coordinating water molecules, and one by a sulfur atom from the –SH group (Fig. 2 (b)). Positional disorders of coordinating oxygen and sulfur atoms are observed due to the threefold axis imposed by the crystallographic symmetry. Additionally, the experimental PXRD patterns (Fig. 3 . (b) and Figure S3-4) closely match those that were simulated from the crystal structures, confirming the phase purity of the bulk samples. The N 2 adsorption isotherms of these six samples at 77 K are shown in Fig. 3 . (d) and confirm the permanent porosity of these samples. The theoretical values of N 2 uptake calculated from single-crystal structures match well with the experimental values (Table S3) for M-MFU-4 l -X where M = Co, Ni and X = Cl, OH and SH, which confirm retainment of the intrinsic porosity of the initial frameworks. Crystallographic analysis for both variants (M = Co, Ni) showed that the post-synthetic functionalization results in the same topology and space group, which suggests that exchanging the bridging ligands is associated with a local rearrangement that leads to the overall same long-range order. To confirm this retainment of long-range order, we further studied Co 2 X 2 BBTA samples using in situ pair distribution function measurements. Specifically, these unique, in situ total scattering experiments followed the local rearrangement during the dechlorination of Co 2 Cl 2 BBTA to Co 2 (OH) 2 BBTA and the subsequent sulfidation of Co 2 (OH) 2 BBTA to Co 2 (SH) 2 BBTA. Initially, a sample of Co 2 Cl 2 BBTA was packed in a glass capillary and assembled in a liquid flow reactor under constant flow of 1 M KOH to initiate the dechlorination. 53 Following this process using fast PDF data acquisition allowed for the direct observation of time-dependent structural changes in the local order of the framework material. We observed that local changes occur almost immediately upon contact with the highly concentrated KOH solution (e.g., within ~ 30 s (Fig. 3 (a))). The delay of about 15 s after the start of the experiment is assigned to dead volume in the sample environment upstream of the sample. The rapid conversion of Co 2 Cl 2 BBTA to Co 2 (OH) 2 BBTA was also confirmed by ex situ PDF studies using a more dilute media, which allowed us to track the rearrangement at a higher time resolution. After 5 exposure cycles to minimal amounts of KOH (0.1 µL of 0.01 M KOH), ligand exchange at the local order of the metal nodes is observed from changes in peak intensities in the PDF data in which the Co-Cl peak decreases in intensity and Co-O peak rises (Fig. 4 (b)). The sulfidation of Co 2 (OH) 2 BBTA was initiated through in situ generation of H 2 S using NaSH and acidified water as precursor, which was directed over the sample using nitrogen as the carrier gas. This unique method of generating H 2 S during an in situ experiment allows for the use of well-defined and limited amounts of H 2 S to be directed over the sample, which ensures safe handling and limits exposure of corrosive gases to the sample. Similar to the transformation from Co-Cl to Co-OH species, the local rearrangement of the metal centers also occurs rapidly, within minutes after the gas flow reached the sample (Fig. 3 (c)). Conversion can be verified by a shift in the peak position around 2 Å (e.g., shift from 2.05 Å to 2.13 Å) due to the difference in Co-O and Co-S bond lengths. In addition to structural verification from PDF analysis, the crystallinity and lattice symmetry was confirmed via PXRD analysis after each conversion step (Figure S5). Following the successful conversion of MOFs to their sulfided versions, confirmed by X-ray techniques, XPS spectroscopy was employed to further identify the oxidation state of the sulfided MOFs in the post-synthetically modified samples. For the M 2 X 2 BBTA series, the results indicate that after the treatments of KOH, there is no chloride left in the samples (Figure S8-9, S11-12, Table S4-5. S7-8). After the H 2 S treatment, a peak of binding energy (B.E.) at ~ 163 eV (162.7 and 162.6 eV for Co 2 (SH) 2 BBTA and Ni 2 (SH) 2 BBTA, respectively) starts appearing on the XPS spectra (Fig. 3 . (e), Figure S10, 13, Table S6 and S9), which falls into the range of -SH functional groups with sulfur in the − 2 oxidation state. On the other hand, the peak corresponding to the 2p 3/2 band of Co only shifts in B.E. from 780.5 to 781.0 to 779.0 eV from X = Cl to OH to SH due to the different coordination environments. The preservation of the satellite feature indicates the oxidation state of Co remains + 2. 54–56 The B.E. of the 2p 3/2 band of Co 2 (SH) 2 BBTA is similar to those of previously reported cobalt sulfide compounds. 57 For the M = Ni case, the 2p 3/2 peaks of Ni shift from 855.7 to 854.6 to 853.0 eV for X = Cl, OH, and SH, respectively. The B.E. value of the Ni 2p 3/2 band for Ni 2 (SH) 2 BBTA is similar to those of the reported nickel sulfide compounds. 57 Furthermore, the XPS results for the M-MFU-4 l -X series showed similar patterns (Fig. 3 . (f)). For instance, the treatment of M-MFU-4 l -Cl (M = Co, Ni) with the organic base to form M-MFU-4 l -OH significantly removed the chloride in the samples (Figure S14-15. S17-18, Table S10-11 and S13-14). Similarly, following treatment of M-MFU-4 l -OH with H 2 S, the peaks that appear in the XPS spectra around 162 eV demonstrate the successful incorporation of –SH group to the framework and the formation of M-MFU-4 l -SH (Fig. 3 . (f), Figure S16,19 and Table S12, 15). To test the catalytic performance of the sulfur-incorporated MOFs towards hydrogenation reactivity, the reduction of 4-nitrophenol to 4-aminophenol was selected as a model reaction. All twelve MOFs (M 2 X 2 BBTA and M-MFU-4 l -X, where M = Co, Ni and X = Cl, OH, SH) were tested under the same conditions at 150 ℃ for 4.25 hours under 13.8 bar (RT) H 2 (Fig. 5 (a)) in a Parr vessel. The results of the reactions are summarized in Table 1 . The M 2 Cl 2 BBTA MOFs showed minimal conversion (i.e., close to that of the background reaction without MOF included, Figure S29, S32), and the conversion rate improved slightly for both M 2 (OH) 2 BBTA samples with ~ 9% and 18% conversion for M = Co and Ni respectively. In contrast, M 2 (SH) 2 BBTA exhibited a significant improvement in the conversion rate to ~ 37% for Ni and ~ 100% for Co. Interestingly, for the M-MFU-4 l -X series, Co-MFU-4 l -X showed relatively low conversion when X = Cl (~ 4%), X = OH (~ 1%), and even when X = SH (~ 23%). In contrast, the Ni-MFU-4 l -X analogues demonstrated relatively higher conversion rates (~ 8% for X = Cl and ~ 20% for X = OH), and Ni-MFU-4 l -SH achieved > 99% conversion under these conditions. Cycling studies revealed that both Co 2 (SH) 2 BBTA and Ni-MFU-4 l -SH showed consistent conversion rates of > 99% under the same conditions. Next, we studied the kinetics of these reactions with lower catalyst loadings. At 1.5 mol% loading, Co 2 (SH) 2 BBTA achieved a turnover frequency (TOF) of 2.4 ± 0.1 h – 1 (Fig. 5 (b)). On the other hand, the turnover frequency for Ni-MFU-4 l -SH at the 5% catalyst loading was measured to be 1.7 ± 0.1 h – 1 (Fig. 5 (c)) under analogous conditions. Table 1 Conversion rates of 4-nitrophenol to 4-aminophenol via hydrogenation using molecular hydrogen and different MOFs. (a) MOFs with 1-D metal chains Co 2 X 2 BBTA % Conversion Ni 2 X 2 BBTA % Conversion X = Cl 2 X = Cl 8 X = OH 9 X = OH 18 X = SH > 99 X = SH 37 (b) MOFs with discrete 3-D metal nodes Co-MFU-4 l -X % Conversion Ni-MFU-4 l -X % Conversion X = Cl 4 X = Cl 8 X = OH 1 X = OH 20 X = SH 23 X = SH > 99 Mechanistic Elucidation with Density Functional Theory (DFT) Calculations. To elucidate the experimentally observed reactivity trends in nitroarene hydrogenation, we performed density functional theory (DFT) calculations, focusing on two key aspects: 1) The consistent ordering of ligand reactivity (X = –SH > –OH > –Cl) observed across both 1D BBTA- and 3D MFU-4 l -based MOFs and 2) the trends for different metal centers (Co and Ni) and particularly the intriguing reversal in catalytic performance between Co and Ni centers depending on the MOF structure. We began by optimizing all systems using periodic boundary conditions with the PBESol-D3(0) density functional employing the projector augmented wave (PAW) method as implemented in Vienna Ab-initio Simulation Package (VASP, version 6.3.1; see Supporting Information for details). 58 – 62 From these optimized periodic structures, we constructed finite-sized cluster models by truncating the framework around a metal node (Fig. 5 ). In all subsequent cluster calculations, the C atoms of the organic linkers were constrained to their coordinates obtained from the optimized periodic framework, thus preserving the geometry of the extended structure. We explored the energetics of various possible spin states using these cluster models (Table S16 and S17). Our findings confirmed that high-spin configurations were energetically favored in all cases. Specifically, for individual metal centers, we found that quartet states were preferred for Co II and triplet states for Ni II . For the 1D BBTA MOFs, cluster models comprising four metal centers and four benzobistriazolate ligands were used (Fig. 5 a). For the 3D MFU-4 l MOFs, we explored “Kuratowski-type” secondary building units, 63 including both 1,2,3-benzotriazolate (Figure S39) and smaller triazolate ligands (Fig. 5 b). Results from the triazolate model are presented in the main text (see Supporting Information, Section H.3 for a comparison with benzotriazolate clusters). Cluster calculations were performed using the Gaussian 16 (Rev. A.03) electronic structure program. 64 Geometry optimizations and frequency calculations were performed at the TPSSh-D3(BJ)/basis-I level of theory, 65 , 66 where basis-I denotes def2-SVP for nonmetals and def2-TZVP with SDD effective core potential for Co, Ni, and Zn. 67 , 68 Electronic energies were recomputed at the M06-D3(0)/basis-II/SMD(MeOH) level, 69 , 70 where basis-II is def2-TZVP for all atoms with SDD effective core potential for Co, Ni, and Zn. 67 , 68 Our computational analysis reveals key insights into the catalytic mechanisms for nitroarene hydrogenation. For both MOF systems, we propose a reaction pathway that begins with the coordination of a MeOH molecule to the metal centers, followed by M–X bond cleavage, H 2 chemisorption, and H–H bond dissociation. 71 , 72 To probe the enhancement of reactivity of the MOF catalysts using methanol as the reaction solvent, we systematically explored MeOH coordination in both 3D MFU-4 l and 1D BBTA MOFs. Sections H.4–H.5 of the Supporting Information provide a detailed analysis of progressive MeOH solvation at the metal centers of the MFU-4 l , covering neutral M II species as well as open metal site-generated M I or [M II ] + species. This comprehensive study revealed distinct resting solvated states for key reaction intermediates. For instance, the Co II center in neutral MFU-4 l remained unsolvated, while its Ni II counterpart adopted an octahedrally solvated configuration (Figure S39). Notably, as illustrated in Figs. 7 and 10 , we propose a methanol-assisted pathway for molecular hydrogen dissociation and the generation of the active species E ( vide infra ). This mechanism aligns with analogous hydrogenation catalysis observed in cobalt single-atom catalysts using protic solvents, 72 underscoring the crucial role of MeOH as the solvent. In the 1D BBTA system, the initial MeOH coordination to the square pyramidal metal centers (species A to B , Fig. 7 ) is endergonic for both Co and Ni across all X ligands (X = Cl, OH, SH). The subsequent M–X bond cleavage can occur either homolytically ( C1 ) or heterolytically ( C2 ), generating an open metal site for H 2 chemisorption ( D1 , D2 ). The H–H bond then dissociates, facilitated by a N-atom on the ligand, forming species E1 and E2 . 72 – 75 Since similar species have been proposed in the literature as active in Ar–NO 2 hydrogenation, 71 , 72 we suggest that E1 serves as the active species for this reaction. The reaction pathways computed to be more energetically favored for Co-BBTA are reported in Fig. 6 (for additional data and discussion, please see the Supporting Information). The calculations show that for Co-BBTA, the formation of E1 via the homolytic route is energetically more favorable than the heterolytic route, especially with the SH ligand (Fig. 7 a). A similar trend is also observed for Ni-BBTA (Figure S47). Importantly, comparing M-BBTA-SH (M = Co, Ni), we find that Co requires less energy to generate E1 (Δ G = 62.4 kcal/mol) than Ni (Δ G = 67.6 kcal/mol), which corroborates the larger conversion rates observed for Co over Ni in the 1D BBTA framework. For the 3D MFU-4 l system, we focused on the homolytic M–X bond cleavage pathway leading to species E (Fig. 10 ; See Figure S40 for heterolytic pathway). The subsequent steps involve the transfer of the dissociated H atoms onto the Ar–NO 2 substrate, forming Ar–N(OH)(OH) (species F ), followed by H 2 O release to form Ar–NO (species G ). This nitroso intermediate is then expected to undergo further reduction to –NH 2 via the Haber mechanism. 76 , 77 In the MFU-4 l -X catalyst, the formation of species E is most favorable again with the SH ligand for both Co and Ni (Fig. 8 ). Notably, for Ni–SH, this transformation is less endergonic (Δ G = 50.7 kcal/mol) compared to Co–SH (Δ G = 61.0 kcal/mol), which aligns with nickel’s superior performance in the 3D MFU-4 l framework compared to its Co analogue. To gain deeper insights into the reactivity trends of various ligands X (Cl, OH, SH) bound to metal centers M (Co, Ni), we employed an energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMO). 78 , 79 This approach allowed us to separately analyze the different contributions to the M–X bonding interactions in 3D MFU-4 l -Ni systems (Table 2 ). In the EDA framework, the total electronic contribution (Δ E Tot ) for binding X(•) to a formal M(I) site, forming an M(II)–X site, comprises three fundamental components. 80 The frozen term (Δ E Frz ) represents the energy change when bringing two fragments together without altering their electron distributions. The polarization term (Δ E Pol ) accounts for the energy reduction when the electron distribution of each fragment adjusts to the other’s presence, without electron sharing. Lastly, the charge transfer term (Δ E CT ) quantifies the additional energy lowering from orbital mixing between the two fragments. Table 2 Energy Decomposition Analysis of Ni II –X Homolytic Dissociation in MFU-4 l -Ni-X (X = Cl, OH, SH) at M06-D3(0)/def2-TZVP Level. Energy Contribution (kcal/mol) MFU-4 l -Ni-Cl MFU-4 l -Ni-OH MFU-4 l -Ni-SH Frozen (Δ E Frz ) 13.3 23.7 4.7 Polarization (Δ E Pol ) –15.0 –21.0 –16.4 Charge Transfer (Δ E CT ) –92.7 –85.9 –59.9 Total (Δ E Tot ) –94.4 –83.2 –72.0 The calculated Δ E Tot values show a clear trend (in kcal/mol): − 72.0 (SH) < − 83.2 (OH) < − 94.4 (Cl), indicating that the metal-ligand interaction strength increases from SH to OH to Cl. Among the energy contributions, the charge transfer term (Δ E CT ) emerged as the most significant. Analysis of Δ E CT showed a similar ordering (in kcal/mol): − 59.9 (SH) < − 85.9 (OH) < − 92.7 (Cl). This trend suggests reduced electron density sharing between the metal center and the SH ligand compared to OH or Cl ligands, resulting in a more labile M–SH bond with an enhanced propensity for generating an open metal site. Consequently, our findings indicate that the ease of homolytic M II –X bond cleavage, decreases in the order: SH > OH > Cl. This insight provides valuable information regarding the relative reactivity of these ligands in the context of the MFU-4 l framework. We further explored the differential reactivity of Co II –SH and Ni II –SH active sites in BBTA and MFU-4 l frameworks by analyzing bonding interactions between open metal sites (M I ; M = Co, Ni) and H 2 molecules (Table 3 ). Our focus was on the formation of chemisorbed adduct D and subsequent formation of catalytically active species E . Using the ALMO-EDA scheme, 79 we specifically probed the “frozen” energy between the catalyst (species C ) and approaching H 2 , decomposing this interaction energy term into three components: 81 , 82 the electrostatic term Δ E Elec for interactions between fragment charge distributions, Δ E Pauli accounting for repulsion between overlapping filled orbitals, and the dispersion interaction term Δ E Disp . Table 3 Energy Decomposition Analysis of H 2 Binding at an M I Site in both BBTA and MFU-4l Systems Calculated at the M06-D3(0)/def2-TZVP Level. The individual components comprising Δ E Frz (= Δ E Elec + Δ E Pauli + Δ E Disp ) are also shown. Energy Contribution (kcal/mol) BBTA-M-SH MFU-4 l -M-SH Co Ni Co Ni Frozen (Δ E Frz ) –3.0 17.5 13.6 7.4 Electrostatic (Δ E Elec ) –8.9 –25.6 –20.6 –20.1 Pauli (Δ E Pauli ) 13.5 51.8 39.4 32.0 Dispersion (Δ E Disp ) –7.6 –8.8 –5.1 –4.4 Polarization (Δ E Pol ) –0.9 –11.7 –14.2 –13.0 Charge Transfer (Δ E CT ) –1.9 –9.6 –14.3 –15.2 Total (Δ E Tot ) –5.8 –3.7 –14.9 –20.9 In the pseudo-octahedral environment of BBTA, Co I ( d 8 ) with two singly occupied e g orbitals experiences lower Pauli repulsion (13.5 kcal/mol) compared to Ni I ( d 9 ) (51.8 kcal/mol) with one doubly and one singly occupied e g orbital. This results in a more favorable Δ E Frz for Co (–3.0 kcal/mol vs. +17.5 kcal/mol for Ni), reflected in stronger H 2 adsorption at Co I centers in BBTA (–5.8 kcal/mol) than at Ni I (–3.7 kcal/mol). Conversely, in the pseudo-tetrahedral MFU-4 l framework, the trend in H 2 binding interaction energy is reversed (–20.9 vs − 14.9 kcal/mol for Ni I vs Co I ), which can be attributed to inverted crystal field splitting. Here, Ni I ( d 9 ) showed lower Pauli repulsion (32.0 kcal/mol) than Co I ( d 8 ) (39.4 kcal/mol), leading to a more favorable Δ E Frz for Ni (+ 7.4 kcal/mol vs. +13.6 kcal/mol for Co). These findings provide a qualitative rationale for the observed reactivity trends: Co exhibits enhanced performance in the BBTA framework due to its favorable octahedral crystal field splitting, while Ni demonstrates superior activity in the MFU-4 l framework, benefiting from the inverted tetrahedral crystal field. This analysis highlights the critical role of coordination geometry in determining the electronic structure and, consequently, the catalytic activity of metal centers in these metal-organic frameworks. In conclusion, we have developed a strategy for synthesizing MOFs with highly polarizable SH groups coordinated to metal nodes through the stepwise conversion of M–Cl species to M–OH and subsequently M–SH species (M = Co or Ni). This strategy circumvents challenges associated with the de novo synthesis of MOFs featuring metal-sulfur bonds that have limited the development of this class of MOFs. We demonstrated that this post-synthetic modification method works for the M 2 (SH) 2 BBTA series of MOFs, which contain 1D chains of metal ions, as well as the M-MFU-4 l -SH series, which feature discrete 3D clusters of single metal ions, for both Co and Ni analogues. A combination of SCXRD and PDF analyses elucidated the solid-state structures of all MOFs and confirmed the quantitative conversion to M–SH species in both series. Catalytic studies probing the hydrogenation of 4-nitrophenol to 4-aminophenol as a model reaction indicated that the installation of more labile sulfur-based ligands is critical for this catalytic reaction and significantly improves conversion relative to the chloride- and hydroxide-based analogues. Finally, density functional theory (DFT) calculations revealed that the electronic flexibility of the sulfur moiety plays important role in the M–X bond cleavage pathway for hydrogen activation, providing additional insights that future MOF-based catalyst design strategies may benefit from. Overall, this post-synthetic modification strategy opens up a new methodology in synthesizing porous materials with polarizable sulfur components and presents new avenues for developing high-performance catalysts. Declarations ACKNOWLEDGMENTS This research was supported by the Catalyst Design for Decarbonization Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under grant DE-SC0023383. Additionally, the IMSERC Crystallography facility at Northwestern University was utilized, with support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633) and Northwestern University. The EPIC facility at Northwestern University’s NUANCE Center was also employed, supported by the SHyNE Resource (NSF ECCS-2025633), the International Institute for Nanotechnology (IIN), and Northwestern’s Materials Research Science and Engineering Center (MRSEC) program (NSF DMR-1720139). Lastly, the Keck-II facility at Northwestern University’s NUANCE Center was used, with backing from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern’s MRSEC program (NSF DMR-1720139). This research used beamline 28-ID-1 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory under Contract No. DE-SC0012704. The computing resources were provided by The University of Chicago Research Computing Center (RCC). Corresponding Author Omar K. Farha – Department of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States ; Email: [email protected] Laura Gagliardi – Department of Chemistry, Pritzker School of Molecular Engineering, James Franck Institute, Chicago Center for Theoretical Chemistry, University of Chicago, Chicago, Illinois 60615, United States ; Email: [email protected] Haomiao Xie – Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States ; Email: [email protected] Notes O.K.F. has financial interest in NuMat Technologies, a startup company that is seeking to commercialize MOFs. Supporting Information Materials / General Methods / Instrumentation, Synthetic Protocols, DFT Computations Details can be found in the supporting information. References Omann, L.; Königs, C. D. F.; Klare, H. F. T.; Oestreich, M. Cooperative Catalysis at Metal–Sulfur Bonds. 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Sophisticated construction of single-atom cobalt catalyst based on microbial hyphae for high-performance hydrogenation. J. Chem. Eng. 2024, 490 , 151678. DOI: https://doi.org/10.1016/j.cej.2024.151678 . Leipzig, B. Über stufenweise Reduktion des Nitrobenzols mit begrenztem Kathodenpotential. Z. Elektrochem. 1898, 4 (22), 506–514. DOI: https://doi.org/10.1002/bbpc.18980042204 . Wang, H.; Zhang, W.; Liu, Y.; Pu, M.; Lei, M. First-Principles Study on the Mechanism of Nitrobenzene Reduction to Aniline Catalyzed by a N-Doped Carbon-Supported Cobalt Single-Atom Catalyst. J. Phys. Chem. C 2021, 125 (35), 19171–19182. DOI: 10.1021/acs.jpcc.1c01877 . Khaliullin, R. Z.; Cobar, E. A.; Lochan, R. C.; Bell, A. T.; Head-Gordon, M. Unravelling the Origin of Intermolecular Interactions Using Absolutely Localized Molecular Orbitals. The Journal of Physical Chemistry A 2007, 111 (36), 8753–8765. DOI: 10.1021/jp073685z . Horn, P. R.; Mao, Y.; Head-Gordon, M. Probing non-covalent interactions with a second generation energy decomposition analysis using absolutely localized molecular orbitals. Phys. Chem. Chem. Phys. 2016, 18 (33), 23067–23079, 10.1039/C6CP03784D . DOI: 10.1039/C6CP03784D. Jaramillo, D. E.; Jiang, H. Z. H.; Evans, H. A.; Chakraborty, R.; Furukawa, H.; Brown, C. M.; Head-Gordon, M.; Long, J. R. Ambient-Temperature Hydrogen Storage via Vanadium(II)-Dihydrogen Complexation in a Metal-Organic Framework. J. Am. Chem. Soc. 2021, 143 (16), 6248–6256. DOI: 10.1021/jacs.1c01883 PubMed . Levine, D. S.; Head-Gordon, M. Energy decomposition analysis of single bonds within Kohn–Sham density functional theory. Proceedings of the National Academy of Sciences 2017, 114 (48), 12649–12656. DOI: doi: 10.1073/pnas.1715763114 . Andrada, D. M.; Foroutan-Nejad, C. Energy components in energy decomposition analysis (EDA) are path functions; why does it matter? Phys. Chem. Chem. Phys. 2020, 22 (39), 22459–22464, 10.1039/D0CP04016A . DOI: 10.1039/D0CP04016A. Additional Declarations Yes there is potential Competing Interest. O.K.F. has a financial interest in NuMat Technologies, a startup company that is seeking to commercialize MOFs. Supplementary Files 20241029SISulfidatedMOFsforHydrogenation.docx Cite Share Download PDF Status: Published Journal Publication published 24 Jul, 2025 Read the published version in Nature Chemistry → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-5357011","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":380959768,"identity":"7241c5d9-7aa8-43a9-b4f3-00b84d0b3466","order_by":0,"name":"Omar 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07:05:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":975214,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5357011/v1/eb2f9f19-12ad-4c2f-bb2b-135dabc30ff3.pdf"},{"id":69782332,"identity":"8c415e71-d165-4b16-9486-5ebb625aeb90","added_by":"auto","created_at":"2024-11-25 08:23:09","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":12848872,"visible":true,"origin":"","legend":"","description":"","filename":"20241029SISulfidatedMOFsforHydrogenation.docx","url":"https://assets-eu.researchsquare.com/files/rs-5357011/v1/045bb7daaa17e4e05767df51.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nO.K.F. has a financial interest in NuMat Technologies, a startup company that is seeking to commercialize MOFs.","formattedTitle":"Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHighly polarizable components, such as sulfur-containing groups, in catalytic processes have emerged as a forefront area of research due to their unique ability to modulate chemical reactivity through electronic coupling. In this context, metal-sulfide compounds are of particular interest as they leverage the electronic flexibility of sulfur centers, \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 resulting in a more covalent nature of M\u0026ndash;S bonds compared to their oxygen analogues, enhancing the charge transfer properties that play important roles in catalytic processes.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e Nature\u0026rsquo;s ingenious use of sulfur-containing species, such as Fe\u003csub\u003e4\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e, Fe-V-S, Fe-Mo-S clusters and Cu-S moieties, in the active sites of enzymes for critical redox reactions has afforded excellent reactivity within biological systems for transformations like hydrogenation and dehydrogenation.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan additionalcitationids=\"CR11 CR12 CR13 CR14\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e Despite their efficacy, however, the fragility and complexity of enzyme systems often limit their scalability and industrial application.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast to enzymatic sulfur-containing species, transition metal-sulfur compounds, exemplified by MoS\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e17\u0026ndash;20\u003c/sup\u003e and CoS\u003csub\u003ex\u003c/sub\u003e\u003csup\u003e\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, offer relatively greater stability and have been demonstrated to play a significant role in various catalytic processes, including hydrogen splitting and hydrogenation.\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e The catalytic efficacy of these compounds is intrinsically tied to the local environment of the active sites, where the morphology of particles, particularly at the surfaces and edges, becomes crucial for catalytic performance. This necessitates sophisticated defect engineering to maximize exposure of active sites. It has been demonstrated that increasing the surface areas of these systems improves the catalytic performance as the active sites are more easily accessible, ensuring efficient mass transport.\u003csup\u003e\u003cspan additionalcitationids=\"CR25 CR26\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eBeyond these well-known materials, metal-organic frameworks (MOFs) represent a burgeoning class of materials with significant implications for catalysis. The structural robustness and high internal surface areas of MOFs makes them ideal for serving as high-performing catalysts and hosting catalytic substrates.\u003csup\u003e\u003cspan additionalcitationids=\"CR29\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e In fact, encapsulating enzymes within MOF pores can substantially enhance both stability and catalytic efficiency relative to those of the free enzyme.\u003csup\u003e\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e Furthermore, MOFs featuring open metal sites as reactive centers have been identified as promising candidates in catalysis, offering well-organized and protected reactive centers in a solid-state framework.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e However, the synthesis of MOFs incorporating highly polarizable components, such as sulfide bridges, metal-sulfur based clusters, or thiolate linkers, remains largely underexplored, with only a few known examples.\u003csup\u003e\u003cspan additionalcitationids=\"CR39 CR40 CR41 CR42 CR43 CR44\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e The primary challenges hindering progress in this area include the instability of metal-sulfur clusters, the comparatively lower crystallinity than metal-oxide based MOFs resulting from the irreversible nature of forming highly polarized bonds, the poorly understood effects of templating agents on sulfur-containing structures, and the overarching need for novel synthetic methodologies to achieve desired topologies.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003ePost-synthetic modification\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e emerges as a promising strategy by leveraging the inherent topology of parent MOFs, the extensive database of known structures, and the simplification of synthetic conditions to modify bridging linkers and/or transform metal clusters, such as metal-oxide clusters, into their sulfur counterparts (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a)). This approach not only mitigates the challenges associated with direct synthesis but also opens new avenues for the development of advanced catalytic materials.\u003c/p\u003e \u003cp\u003eIn this study, we selected two families of specific MOFs with potentially redox-active metal centers and accessible open metal sites: M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA ( M\u0026thinsp;=\u0026thinsp;Co, Ni; H\u003csub\u003e2\u003c/sub\u003eBBTA\u0026thinsp;=\u0026thinsp;1H,5H-benzo(1,2-d:4,5-d')bistriazole) and M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl ( [M\u003csub\u003ex\u003c/sub\u003eZn\u003csub\u003e5\u0026minus;x\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e(BTDD)\u003csub\u003e3\u003c/sub\u003e; x\u0026thinsp;=\u0026thinsp;4 for M\u0026thinsp;=\u0026thinsp;Co and x\u0026thinsp;=\u0026thinsp;2.5 for M\u0026thinsp;=\u0026thinsp;Ni; H\u003csub\u003e2\u003c/sub\u003eBTDD\u0026thinsp;=\u0026thinsp;bis(1H-1,2,3-triazolo[4,5-b][4\u0026prime;,5\u0026prime;-i])dibenzo[1,4]dioxin)) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) as parent MOFs. We successfully converted them to their hydroxide-bridged versions, M\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA and M-MFU-4\u003cem\u003el\u003c/em\u003e-OH, and then further converted them to their sulfided versions, M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA and M-MFU-4\u003cem\u003el\u003c/em\u003e-SH. The crystal structures of post-synthetically modified sulfided MOFs were elucidated using a combination of single-crystal X-ray diffraction and electron diffraction techniques. \u003cem\u003eIn situ\u003c/em\u003e pair distribution function (PDF) analysis provided real-time insights into the sulfidation process, allowing for dynamic tracking of structural transformations during modification. To assess the catalytic performance of the sulfided MOFs, a model reaction was employed, focusing on the chemoselective hydrogenation of nitroarenes\u0026mdash;the reduction of aryl \u0026ndash;NO₂ to \u0026ndash;NH₂. The sulfided MOFs exhibited markedly enhanced hydrogenation reactivity compared to their parent MOFs, which featured terminal or bridging chloride and hydroxyl groups. Computational studies, using density functional theory (DFT), offered deeper mechanistic insights, revealing that the incorporation of sulfide ligands facilitates the homolytic cleavage of metal-ligand (M\u0026ndash;X) bonds, enabling more efficient H₂ activation. These integrated experimental and theoretical investigations highlight key reactivity trends and underscore the crucial role sulfur incorporation plays in modulating the catalytic properties of MOFs.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eFor the post-synthetic modification, we selected two types of MOFs: M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA and M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl (M\u0026thinsp;=\u0026thinsp;Co, Ni), to investigate how isolated metal nodes or 1-D chains with adjacent centers affect the properties in hydrogenation reactions. Both MOFs have similar triazolate linkers as supporting ligands and comparable pore sizes. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) In enzymes, nitrogen-containing heterocyclic groups like imidazoles have been proposed to extend the conjugation system for electron tunneling with metal-sulfide clusters.\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e Similarly, the triazolate groups in these MOFs can potentially act as π-acceptors to enhance the electronic polarizability of the metal center.\u003csup\u003e\u003cspan additionalcitationids=\"CR49\" citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e With these two types of parent MOFs in hand, we then performed post-synthetic modifications to install metal-sulfur linkages.\u003c/p\u003e \u003cp\u003eIn M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA (M\u0026thinsp;=\u0026thinsp;Co, Ni), chloride serves as a bridging ligand between adjacent metal centers, providing a well-defined substitutionally labile bridge that can be targeted easily to access other functionalities. During our initial attempts at replacing chloride in the presence of H\u003csub\u003e2\u003c/sub\u003eS, we observed slow and incomplete conversion to the SH variant (e.g., ~\u0026thinsp;50% Cl replaced by SH after 48 hours). We presume this limited reactivity is due to the formation of the byproduct HCl, which is a strong acid and drives the reaction backward. To circumvent this issue, we elected to treat the chloride-based MOFs with KOH to transform the bridging chloride anions into bridging hydroxyl groups, with the MOF products denoted as M\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA. Replacement of the chloride was confirmed by X-ray photoelectron spectroscopic (XPS) analysis (Figure S9 and S12), while the integrity of the frameworks was confirmed by powder X-ray diffraction (PXRD) analysis (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and S2) and N\u003csub\u003e2\u003c/sub\u003e sorption isotherms collected at 77 K (Figure S6). We reasoned that bridging hydroxyl groups would make the subsequent sulfidation reaction more feasible as water would be the leaving group. Indeed, reacting M\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA with \u003cem\u003ein situ\u003c/em\u003e-generated H\u003csub\u003e2\u003c/sub\u003eS converted the lightly colored MOF powders to dark brown within minutes, signaling the formation of the SH-bridging analogues M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). XPS (Table S6 and S9) and energy dispersive X-ray spectroscopic (EDS) analyses (Figure S21 and S23) revealed the anticipated 1:1 ratio between metal and sulfur, which suggests complete replacement of the hydroxyls with thiolates. Importantly, scanning electron microscopy (SEM) images confirmed that these post-synthetic modifications did not affect the particle size or morphology (Figure S20 and S22). We note that the ratio between Co and S can exceed 1:1 when excess H\u003csub\u003e2\u003c/sub\u003eS is used (Figure S21), which can be attributed to the formation of polysulfides in the MOF cavities (see below).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor the M\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA series (M\u0026thinsp;=\u0026thinsp;Co, Ni; X\u0026thinsp;=\u0026thinsp;Cl, OH, SH), single-crystal X-ray diffraction (SCXRD) or electron diffraction (ED) experiments enabled us to determine the solid-state structures of these MOFs. All structures were solved under the R-3m space group with similar unit cell parameters (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), indicating that the parent MOFs\u0026rsquo; topology was preserved through these transformations. The simulated PXRD patterns closely match those of the experimental data (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (a) and Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-2), which confirms the phase purity of the bulk samples. Examination of the coordination sphere revealed that all metal ions are octahedrally coordinated and surrounded by three nitrogen atoms from different triazolate linkers. Two additional sites are occupied by X atoms from bridging groups, and the final site by terminal water molecules, except in the SH version. Notably, in the SH version, we discovered a disordered S\u003csub\u003e5\u003c/sub\u003e chain bridging two cobalt atoms across two distinct 1-D metal chains. This corresponds well with the high Co:S ratios observed when excess H\u003csub\u003e2\u003c/sub\u003eS was used in the synthesis (Figure S21). On the other hand, the Co\u0026ndash;N bond distances shortened from approximately 2.1 \u0026Aring; to 2.0 \u0026Aring; and 1.9 \u0026Aring; as the bridging groups changed from \u0026ndash;Cl to \u0026ndash;OH to \u0026ndash;SH, respectively. This indicates that varying the bridging group alters the interactions between the metal centers and the coordinating triazole moiety, affecting the metal-ligand bonding environment. In contrast, the Ni\u0026ndash;N bond distances remained relatively consistent, around 2.1 \u0026Aring; across all versions, suggesting less variation in the metal-triazole interactions for the nickel-based structures. Next, we collected N\u003csub\u003e2\u003c/sub\u003e adsorption isotherms of six samples (M\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA where M\u0026thinsp;=\u0026thinsp;Co, Ni and X\u0026thinsp;=\u0026thinsp;Cl, OH, SH) at 77 K to analyze the intrinsic porosity of these materials. The total N\u003csub\u003e2\u003c/sub\u003e uptakes of M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA are STP 312 and 330 cm\u003csup\u003e3\u003c/sup\u003e/g with calculated BET areas of 1180 m\u003csup\u003e2\u003c/sup\u003e/g and 1190 m\u003csup\u003e2\u003c/sup\u003e/g (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (c)) for M\u0026thinsp;=\u0026thinsp;Co and Ni, respectively, which corresponds well with the reported values and the theoretical values calculated from crystal structures (Table S3). The total N\u003csub\u003e2\u003c/sub\u003e uptakes of M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA are STP 200 and 228 cm\u003csup\u003e3\u003c/sup\u003e/g with calculated BET surface areas of 650 and 730 m\u003csup\u003e2\u003c/sup\u003e/g for M\u0026thinsp;=\u0026thinsp;Co and Ni, respectively, which correspond well with the theoretical values calculated from crystal structures with one terminal water occupying the open-metal site. Combined, these results demonstrate that the intrinsic porosity of the framework is preserved after this post-synthetic modification protocol.\u003c/p\u003e \u003cp\u003eSimilarly, the conversion of M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl to M-MFU-4\u003cem\u003el\u003c/em\u003e-SH (where M\u0026thinsp;=\u0026thinsp;Co, Ni) utilized the same stepwise methodology as in the BBTA version (i.e., conversion of Cl to OH to SH; Section B in SI). First, the parent MOF Zn-MFU-4\u003cem\u003el\u003c/em\u003e-Cl was synthesized, followed by partial transmetallation to Co-MFU-4\u003cem\u003el\u003c/em\u003e-Cl or Ni-MFU-4\u003cem\u003el\u003c/em\u003e-Cl upon incubation of the Zn analogue in DMF solutions of the corresponding metal chloride salt according to a previously published procedure.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e The chemical formulas for these MOFs were determined to be Co\u003csub\u003e4\u003c/sub\u003eZnCl\u003csub\u003e4\u003c/sub\u003e(BTDD)\u003csub\u003e3\u003c/sub\u003e and Ni\u003csub\u003e2.5\u003c/sub\u003eZn\u003csub\u003e2.5\u003c/sub\u003eCl\u003csub\u003e4\u003c/sub\u003e(BTDD)\u003csub\u003e3\u003c/sub\u003e through inductively coupled plasma-optical emission spectroscopy (ICP-OES) and XPS analyses. We were able to substitute the four peripheral Zn\u003csup\u003e2+\u003c/sup\u003e with Co\u003csup\u003e2+\u003c/sup\u003e but only partial substitution with Ni\u003csup\u003e2+\u003c/sup\u003e, which corresponds well with the results in the literature.\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e Next, we converted chlorides to hydroxyl groups through the use of a 1 M aqueous solution of organic base 4-ethylmorpholine instead of KOH as the former prevented the degradation of the Co- and Ni-based MOFs. Finally, treatment of these hydroxyl-based MOFs with \u003cem\u003ein situ\u003c/em\u003e-generated H\u003csub\u003e2\u003c/sub\u003eS afforded the anticipated color change of the crystals to dark brown, which is indicative of transformation of the hydroxyls to thiols. SCXRD analysis revealed that the framework structure remained largely intact post-conversion to the thiol analogues with only minor changes observed in the unit cell parameters (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The M sites of M-MFU-4\u003cem\u003el\u003c/em\u003e-SH are in an octahedral coordination sphere. Three coordination bonds are occupied by nitrogen atoms from the triazolyl groups of the linkers, two by oxygen atoms from coordinating water molecules, and one by a sulfur atom from the \u0026ndash;SH group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (b)). Positional disorders of coordinating oxygen and sulfur atoms are observed due to the threefold axis imposed by the crystallographic symmetry. Additionally, the experimental PXRD patterns (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (b) and Figure S3-4) closely match those that were simulated from the crystal structures, confirming the phase purity of the bulk samples. The N\u003csub\u003e2\u003c/sub\u003e adsorption isotherms of these six samples at 77 K are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (d) and confirm the permanent porosity of these samples. The theoretical values of N\u003csub\u003e2\u003c/sub\u003e uptake calculated from single-crystal structures match well with the experimental values (Table S3) for M-MFU-4\u003cem\u003el\u003c/em\u003e-X where M\u0026thinsp;=\u0026thinsp;Co, Ni and X\u0026thinsp;=\u0026thinsp;Cl, OH and SH, which confirm retainment of the intrinsic porosity of the initial frameworks.\u003c/p\u003e \u003cp\u003eCrystallographic analysis for both variants (M\u0026thinsp;=\u0026thinsp;Co, Ni) showed that the post-synthetic functionalization results in the same topology and space group, which suggests that exchanging the bridging ligands is associated with a local rearrangement that leads to the overall same long-range order. To confirm this retainment of long-range order, we further studied Co\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA samples using \u003cem\u003ein situ\u003c/em\u003e pair distribution function measurements. Specifically, these unique, \u003cem\u003ein situ\u003c/em\u003e total scattering experiments followed the local rearrangement during the dechlorination of Co\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA to Co\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA and the subsequent sulfidation of Co\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA to Co\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eInitially, a sample of Co\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA was packed in a glass capillary and assembled in a liquid flow reactor under constant flow of 1 M KOH to initiate the dechlorination.\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e Following this process using fast PDF data acquisition allowed for the direct observation of time-dependent structural changes in the local order of the framework material. We observed that local changes occur almost immediately upon contact with the highly concentrated KOH solution (e.g., within ~\u0026thinsp;30 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a))). The delay of about 15 s after the start of the experiment is assigned to dead volume in the sample environment upstream of the sample. The rapid conversion of Co\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA to Co\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA was also confirmed by \u003cem\u003eex situ\u003c/em\u003e PDF studies using a more dilute media, which allowed us to track the rearrangement at a higher time resolution. After 5 exposure cycles to minimal amounts of KOH (0.1 \u0026micro;L of 0.01 M KOH), ligand exchange at the local order of the metal nodes is observed from changes in peak intensities in the PDF data in which the Co-Cl peak decreases in intensity and Co-O peak rises (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (b)).\u003c/p\u003e \u003cp\u003eThe sulfidation of Co\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA was initiated through \u003cem\u003ein situ\u003c/em\u003e generation of H\u003csub\u003e2\u003c/sub\u003eS using NaSH and acidified water as precursor, which was directed over the sample using nitrogen as the carrier gas. This unique method of generating H\u003csub\u003e2\u003c/sub\u003eS during an \u003cem\u003ein situ\u003c/em\u003e experiment allows for the use of well-defined and limited amounts of H\u003csub\u003e2\u003c/sub\u003eS to be directed over the sample, which ensures safe handling and limits exposure of corrosive gases to the sample. Similar to the transformation from Co-Cl to Co-OH species, the local rearrangement of the metal centers also occurs rapidly, within minutes after the gas flow reached the sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (c)). Conversion can be verified by a shift in the peak position around 2 \u0026Aring; (e.g., shift from 2.05 \u0026Aring; to 2.13 \u0026Aring;) due to the difference in Co-O and Co-S bond lengths. In addition to structural verification from PDF analysis, the crystallinity and lattice symmetry was confirmed \u003cem\u003evia\u003c/em\u003e PXRD analysis after each conversion step (Figure S5).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFollowing the successful conversion of MOFs to their sulfided versions, confirmed by X-ray techniques, XPS spectroscopy was employed to further identify the oxidation state of the sulfided MOFs in the post-synthetically modified samples. For the M\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA series, the results indicate that after the treatments of KOH, there is no chloride left in the samples (Figure S8-9, S11-12, Table S4-5. S7-8). After the H\u003csub\u003e2\u003c/sub\u003eS treatment, a peak of binding energy (B.E.) at ~\u0026thinsp;163 eV (162.7 and 162.6 eV for Co\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA and Ni\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA, respectively) starts appearing on the XPS spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (e), Figure S10, 13, Table S6 and S9), which falls into the range of -SH functional groups with sulfur in the \u0026minus;\u0026thinsp;2 oxidation state. On the other hand, the peak corresponding to the 2p\u003csub\u003e3/2\u003c/sub\u003e band of Co only shifts in B.E. from 780.5 to 781.0 to 779.0 eV from X\u0026thinsp;=\u0026thinsp;Cl to OH to SH due to the different coordination environments. The preservation of the satellite feature indicates the oxidation state of Co remains\u0026thinsp;+\u0026thinsp;2.\u003csup\u003e54\u0026ndash;56\u003c/sup\u003e The B.E. of the 2p\u003csub\u003e3/2\u003c/sub\u003e band of Co\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA is similar to those of previously reported cobalt sulfide compounds.\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e For the M\u0026thinsp;=\u0026thinsp;Ni case, the 2p\u003csub\u003e3/2\u003c/sub\u003e peaks of Ni shift from 855.7 to 854.6 to 853.0 eV for X\u0026thinsp;=\u0026thinsp;Cl, OH, and SH, respectively. The B.E. value of the Ni 2p\u003csub\u003e3/2\u003c/sub\u003e band for Ni\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA is similar to those of the reported nickel sulfide compounds.\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e Furthermore, the XPS results for the M-MFU-4\u003cem\u003el\u003c/em\u003e-X series showed similar patterns (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (f)). For instance, the treatment of M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl (M\u0026thinsp;=\u0026thinsp;Co, Ni) with the organic base to form M-MFU-4\u003cem\u003el\u003c/em\u003e-OH significantly removed the chloride in the samples (Figure S14-15. S17-18, Table S10-11 and S13-14). Similarly, following treatment of M-MFU-4\u003cem\u003el\u003c/em\u003e-OH with H\u003csub\u003e2\u003c/sub\u003eS, the peaks that appear in the XPS spectra around 162 eV demonstrate the successful incorporation of \u0026ndash;SH group to the framework and the formation of M-MFU-4\u003cem\u003el\u003c/em\u003e-SH (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. (f), Figure S16,19 and Table S12, 15).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo test the catalytic performance of the sulfur-incorporated MOFs towards hydrogenation reactivity, the reduction of 4-nitrophenol to 4-aminophenol was selected as a model reaction. All twelve MOFs (M\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA and M-MFU-4\u003cem\u003el\u003c/em\u003e-X, where M\u0026thinsp;=\u0026thinsp;Co, Ni and X\u0026thinsp;=\u0026thinsp;Cl, OH, SH) were tested under the same conditions at 150 ℃ for 4.25 hours under 13.8 bar (RT) H\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (a)) in a Parr vessel. The results of the reactions are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eBBTA MOFs showed minimal conversion (i.e., close to that of the background reaction without MOF included, Figure S29, S32), and the conversion rate improved slightly for both M\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003eBBTA samples with ~\u0026thinsp;9% and 18% conversion for M\u0026thinsp;=\u0026thinsp;Co and Ni respectively. In contrast, M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA exhibited a significant improvement in the conversion rate to ~\u0026thinsp;37% for Ni and ~\u0026thinsp;100% for Co. Interestingly, for the M-MFU-4\u003cem\u003el\u003c/em\u003e-X series, Co-MFU-4\u003cem\u003el\u003c/em\u003e-X showed relatively low conversion when X\u0026thinsp;=\u0026thinsp;Cl (~\u0026thinsp;4%), X\u0026thinsp;=\u0026thinsp;OH (~\u0026thinsp;1%), and even when X\u0026thinsp;=\u0026thinsp;SH (~\u0026thinsp;23%). In contrast, the Ni-MFU-4\u003cem\u003el\u003c/em\u003e-X analogues demonstrated relatively higher conversion rates (~\u0026thinsp;8% for X\u0026thinsp;=\u0026thinsp;Cl and ~\u0026thinsp;20% for X\u0026thinsp;=\u0026thinsp;OH), and Ni-MFU-4\u003cem\u003el\u003c/em\u003e-SH achieved\u0026thinsp;\u0026gt;\u0026thinsp;99% conversion under these conditions. Cycling studies revealed that both Co\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA and Ni-MFU-4\u003cem\u003el\u003c/em\u003e-SH showed consistent conversion rates of \u0026gt;\u0026thinsp;99% under the same conditions. Next, we studied the kinetics of these reactions with lower catalyst loadings. At 1.5 mol% loading, Co\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA achieved a turnover frequency (TOF) of 2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 h\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (b)). On the other hand, the turnover frequency for Ni-MFU-4\u003cem\u003el\u003c/em\u003e-SH at the 5% catalyst loading was measured to be 1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 h\u003csup\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (c)) under analogous conditions.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eConversion rates of 4-nitrophenol to 4-aminophenol via hydrogenation using molecular hydrogen and different MOFs.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003e(a) MOFs with 1-D metal chains\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCo\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e% Conversion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNi\u003csub\u003e2\u003c/sub\u003eX\u003csub\u003e2\u003c/sub\u003eBBTA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e% Conversion\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;Cl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;Cl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;OH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;OH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;SH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e\u0026gt;\u0026thinsp;99\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;SH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003e(b) MOFs with discrete 3-D metal nodes\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCo-MFU-4\u003cem\u003el\u003c/em\u003e-X\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e% Conversion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNi-MFU-4\u003cem\u003el\u003c/em\u003e-X\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e% Conversion\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;Cl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;Cl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;OH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;OH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;SH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eX\u0026thinsp;=\u0026thinsp;SH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026gt;\u0026thinsp;99\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eMechanistic Elucidation with Density Functional Theory (DFT) Calculations.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the experimentally observed reactivity trends in nitroarene hydrogenation, we performed density functional theory (DFT) calculations, focusing on two key aspects: 1) The consistent ordering of ligand reactivity (X = \u0026ndash;SH \u0026gt; \u0026ndash;OH \u0026gt; \u0026ndash;Cl) observed across both 1D BBTA- and 3D MFU-4\u003cem\u003el\u003c/em\u003e-based MOFs and 2) the trends for different metal centers (Co and Ni) and particularly the intriguing reversal in catalytic performance between Co and Ni centers depending on the MOF structure.\u003c/p\u003e \u003cp\u003eWe began by optimizing all systems using periodic boundary conditions with the PBESol-D3(0) density functional employing the projector augmented wave (PAW) method as implemented in Vienna Ab-initio Simulation Package (VASP, version 6.3.1; see Supporting Information for details).\u003csup\u003e\u003cspan additionalcitationids=\"CR59 CR60 CR61\" citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e From these optimized periodic structures, we constructed finite-sized cluster models by truncating the framework around a metal node (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In all subsequent cluster calculations, the C atoms of the organic linkers were constrained to their coordinates obtained from the optimized periodic framework, thus preserving the geometry of the extended structure. We explored the energetics of various possible spin states using these cluster models (Table S16 and S17). Our findings confirmed that high-spin configurations were energetically favored in all cases. Specifically, for individual metal centers, we found that quartet states were preferred for Co\u003csup\u003eII\u003c/sup\u003e and triplet states for Ni\u003csup\u003eII\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFor the 1D BBTA MOFs, cluster models comprising four metal centers and four benzobistriazolate ligands were used (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). For the 3D MFU-4\u003cem\u003el\u003c/em\u003e MOFs, we explored \u0026ldquo;Kuratowski-type\u0026rdquo; secondary building units,\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e including both 1,2,3-benzotriazolate (Figure S39) and smaller triazolate ligands (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). Results from the triazolate model are presented in the main text (see Supporting Information, Section H.3 for a comparison with benzotriazolate clusters).\u003c/p\u003e \u003cp\u003eCluster calculations were performed using the \u003cem\u003eGaussian 16\u003c/em\u003e (Rev. A.03) electronic structure program.\u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e Geometry optimizations and frequency calculations were performed at the TPSSh-D3(BJ)/basis-I level of theory,\u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e where basis-I denotes def2-SVP for nonmetals and def2-TZVP with SDD effective core potential for Co, Ni, and Zn.\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e Electronic energies were recomputed at the M06-D3(0)/basis-II/SMD(MeOH) level,\u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e\u003c/sup\u003e where basis-II is def2-TZVP for all atoms with SDD effective core potential for Co, Ni, and Zn. \u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOur computational analysis reveals key insights into the catalytic mechanisms for nitroarene hydrogenation. For both MOF systems, we propose a reaction pathway that begins with the coordination of a MeOH molecule to the metal centers, followed by M\u0026ndash;X bond cleavage, H\u003csub\u003e2\u003c/sub\u003e chemisorption, and H\u0026ndash;H bond dissociation.\u003csup\u003e\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTo probe the enhancement of reactivity of the MOF catalysts using methanol as the reaction solvent, we systematically explored MeOH coordination in both 3D MFU-4\u003cem\u003el\u003c/em\u003e and 1D BBTA MOFs. Sections H.4\u0026ndash;H.5 of the Supporting Information provide a detailed analysis of progressive MeOH solvation at the metal centers of the MFU-4\u003cem\u003el\u003c/em\u003e, covering neutral M\u003csup\u003eII\u003c/sup\u003e species as well as open metal site-generated M\u003csup\u003eI\u003c/sup\u003e or [M\u003csup\u003eII\u003c/sup\u003e]\u003csup\u003e+\u003c/sup\u003e species. This comprehensive study revealed distinct resting solvated states for key reaction intermediates. For instance, the Co\u003csup\u003eII\u003c/sup\u003e center in neutral MFU-4\u003cem\u003el\u003c/em\u003e remained unsolvated, while its Ni\u003csup\u003eII\u003c/sup\u003e counterpart adopted an octahedrally solvated configuration (Figure S39). Notably, as illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, we propose a methanol-assisted pathway for molecular hydrogen dissociation and the generation of the active species \u003cb\u003eE\u003c/b\u003e (\u003cem\u003evide infra\u003c/em\u003e). This mechanism aligns with analogous hydrogenation catalysis observed in cobalt single-atom catalysts using protic solvents,\u003csup\u003e\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e underscoring the crucial role of MeOH as the solvent.\u003c/p\u003e \u003cp\u003eIn the 1D BBTA system, the initial MeOH coordination to the square pyramidal metal centers (species \u003cb\u003eA\u003c/b\u003e to \u003cb\u003eB\u003c/b\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) is endergonic for both Co and Ni across all X ligands (X\u0026thinsp;=\u0026thinsp;Cl, OH, SH). The subsequent M\u0026ndash;X bond cleavage can occur either homolytically (\u003cb\u003eC1\u003c/b\u003e) or heterolytically (\u003cb\u003eC2\u003c/b\u003e), generating an open metal site for H\u003csub\u003e2\u003c/sub\u003e chemisorption (\u003cb\u003eD1\u003c/b\u003e, \u003cb\u003eD2\u003c/b\u003e). The H\u0026ndash;H bond then dissociates, facilitated by a N-atom on the ligand, forming species \u003cb\u003eE1\u003c/b\u003e and \u003cb\u003eE2\u003c/b\u003e. \u003csup\u003e\u003cspan additionalcitationids=\"CR73 CR74\" citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e\u003c/sup\u003e Since similar species have been proposed in the literature as active in Ar\u0026ndash;NO\u003csub\u003e2\u003c/sub\u003e hydrogenation, \u003csup\u003e\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e we suggest that \u003cb\u003eE1\u003c/b\u003e serves as the active species for this reaction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe reaction pathways computed to be more energetically favored for Co-BBTA are reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (for additional data and discussion, please see the Supporting Information). The calculations show that for Co-BBTA, the formation of \u003cb\u003eE1\u003c/b\u003e via the homolytic route is energetically more favorable than the heterolytic route, especially with the SH ligand (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). A similar trend is also observed for Ni-BBTA (Figure S47). Importantly, comparing M-BBTA-SH (M\u0026thinsp;=\u0026thinsp;Co, Ni), we find that Co requires less energy to generate \u003cb\u003eE1\u003c/b\u003e (Δ\u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;62.4 kcal/mol) than Ni (Δ\u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;67.6 kcal/mol), which corroborates the larger conversion rates observed for Co over Ni in the 1D BBTA framework.\u003c/p\u003e \u003cp\u003eFor the 3D MFU-4\u003cem\u003el\u003c/em\u003e system, we focused on the homolytic M\u0026ndash;X bond cleavage pathway leading to species \u003cb\u003eE\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e; See Figure S40 for heterolytic pathway). The subsequent steps involve the transfer of the dissociated H atoms onto the Ar\u0026ndash;NO\u003csub\u003e2\u003c/sub\u003e substrate, forming Ar\u0026ndash;N(OH)(OH) (species \u003cb\u003eF\u003c/b\u003e), followed by H\u003csub\u003e2\u003c/sub\u003eO release to form Ar\u0026ndash;NO (species \u003cb\u003eG\u003c/b\u003e). This nitroso intermediate is then expected to undergo further reduction to \u0026ndash;NH\u003csub\u003e2\u003c/sub\u003e via the Haber mechanism.\u003csup\u003e\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the MFU-4\u003cem\u003el\u003c/em\u003e-X catalyst, the formation of species \u003cb\u003eE\u003c/b\u003e is most favorable again with the SH ligand for both Co and Ni (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Notably, for Ni\u0026ndash;SH, this transformation is less endergonic (Δ\u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;50.7 kcal/mol) compared to Co\u0026ndash;SH (Δ\u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;61.0 kcal/mol), which aligns with nickel\u0026rsquo;s superior performance in the 3D MFU-4\u003cem\u003el\u003c/em\u003e framework compared to its Co analogue. To gain deeper insights into the reactivity trends of various ligands X (Cl, OH, SH) bound to metal centers M (Co, Ni), we employed an energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMO).\u003csup\u003e\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e\u003c/sup\u003e This approach allowed us to separately analyze the different contributions to the M\u0026ndash;X bonding interactions in 3D MFU-4\u003cem\u003el\u003c/em\u003e-Ni systems (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the EDA framework, the total electronic contribution (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eTot\u003c/em\u003e\u003c/sub\u003e) for binding X(\u0026bull;) to a formal M(I) site, forming an M(II)\u0026ndash;X site, comprises three fundamental components.\u003csup\u003e\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e\u003c/sup\u003e The frozen term (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e) represents the energy change when bringing two fragments together without altering their electron distributions. The polarization term (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePol\u003c/em\u003e\u003c/sub\u003e) accounts for the energy reduction when the electron distribution of each fragment adjusts to the other\u0026rsquo;s presence, without electron sharing. Lastly, the charge transfer term (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e) quantifies the additional energy lowering from orbital mixing between the two fragments.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEnergy Decomposition Analysis of Ni\u003csup\u003eII\u003c/sup\u003e\u0026ndash;X Homolytic Dissociation in MFU-4\u003cem\u003el\u003c/em\u003e-Ni-X (X\u0026thinsp;=\u0026thinsp;Cl, OH, SH) at M06-D3(0)/def2-TZVP Level.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnergy Contribution (kcal/mol)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMFU-4\u003cem\u003el\u003c/em\u003e-Ni-Cl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMFU-4\u003cem\u003el\u003c/em\u003e-Ni-OH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMFU-4\u003cem\u003el\u003c/em\u003e-Ni-SH\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFrozen (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolarization (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePol\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;21.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;16.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCharge Transfer (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;92.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;85.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;59.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eTot\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;94.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;83.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;72.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe calculated Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eTot\u003c/em\u003e\u003c/sub\u003e values show a clear trend (in kcal/mol): \u0026minus;\u0026thinsp;72.0 (SH) \u0026lt; \u0026minus;\u0026thinsp;83.2 (OH) \u0026lt; \u0026minus;\u0026thinsp;94.4 (Cl), indicating that the metal-ligand interaction strength increases from SH to OH to Cl. Among the energy contributions, the charge transfer term (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e) emerged as the most significant. Analysis of Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e showed a similar ordering (in kcal/mol): \u0026minus;\u0026thinsp;59.9 (SH) \u0026lt; \u0026minus;\u0026thinsp;85.9 (OH) \u0026lt; \u0026minus;\u0026thinsp;92.7 (Cl). This trend suggests reduced electron density sharing between the metal center and the SH ligand compared to OH or Cl ligands, resulting in a more labile M\u0026ndash;SH bond with an enhanced propensity for generating an open metal site. Consequently, our findings indicate that the ease of homolytic M\u003csup\u003eII\u003c/sup\u003e\u0026ndash;X bond cleavage, decreases in the order: SH\u0026thinsp;\u0026gt;\u0026thinsp;OH\u0026thinsp;\u0026gt;\u0026thinsp;Cl. This insight provides valuable information regarding the relative reactivity of these ligands in the context of the MFU-4\u003cem\u003el\u003c/em\u003e framework.\u003c/p\u003e \u003cp\u003eWe further explored the differential reactivity of Co\u003csup\u003eII\u003c/sup\u003e\u0026ndash;SH and Ni\u003csup\u003eII\u003c/sup\u003e\u0026ndash;SH active sites in BBTA and MFU-4\u003cem\u003el\u003c/em\u003e frameworks by analyzing bonding interactions between open metal sites (M\u003csup\u003eI\u003c/sup\u003e; M\u0026thinsp;=\u0026thinsp;Co, Ni) and H\u003csub\u003e2\u003c/sub\u003e molecules (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Our focus was on the formation of chemisorbed adduct \u003cb\u003eD\u003c/b\u003e and subsequent formation of catalytically active species \u003cb\u003eE\u003c/b\u003e. Using the ALMO-EDA scheme, \u003csup\u003e\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e\u003c/sup\u003e we specifically probed the \u0026ldquo;frozen\u0026rdquo; energy between the catalyst (species \u003cb\u003eC\u003c/b\u003e) and approaching H\u003csub\u003e2\u003c/sub\u003e, decomposing this interaction energy term into three components: \u003csup\u003e\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e\u003c/sup\u003e the electrostatic term Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eElec\u003c/em\u003e\u003c/sub\u003e for interactions between fragment charge distributions, Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePauli\u003c/em\u003e\u003c/sub\u003e accounting for repulsion between overlapping filled orbitals, and the dispersion interaction term Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eDisp\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEnergy Decomposition Analysis of H\u003csub\u003e2\u003c/sub\u003e Binding at an M\u003csup\u003eI\u003c/sup\u003e Site in both BBTA and MFU-4l Systems Calculated at the M06-D3(0)/def2-TZVP Level. The individual components comprising Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e (= Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eElec\u003c/em\u003e +\u003c/sub\u003e Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePauli\u003c/em\u003e +\u003c/sub\u003e Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eDisp\u003c/em\u003e\u003c/sub\u003e) are also shown.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEnergy Contribution (kcal/mol)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eBBTA-M-SH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eMFU-4\u003cem\u003el\u003c/em\u003e-M-SH\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFrozen (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e13.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrostatic (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eElec\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;8.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;25.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;20.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;20.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePauli (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePauli\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e51.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e39.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDispersion (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eDisp\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;4.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolarization (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ePol\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;11.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;14.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;13.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCharge Transfer (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCT\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;9.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;14.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;15.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal (Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eTot\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;14.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;20.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the pseudo-octahedral environment of BBTA, Co\u003csup\u003eI\u003c/sup\u003e (\u003cem\u003ed\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e) with two singly occupied \u003cem\u003ee\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e orbitals experiences lower Pauli repulsion (13.5 kcal/mol) compared to Ni\u003csup\u003eI\u003c/sup\u003e (\u003cem\u003ed\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e) (51.8 kcal/mol) with one doubly and one singly occupied \u003cem\u003ee\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e orbital. This results in a more favorable Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e for Co (\u0026ndash;3.0 kcal/mol vs. +17.5 kcal/mol for Ni), reflected in stronger H\u003csub\u003e2\u003c/sub\u003e adsorption at Co\u003csup\u003eI\u003c/sup\u003e centers in BBTA (\u0026ndash;5.8 kcal/mol) than at Ni\u003csup\u003eI\u003c/sup\u003e (\u0026ndash;3.7 kcal/mol). Conversely, in the pseudo-tetrahedral MFU-4\u003cem\u003el\u003c/em\u003e framework, the trend in H\u003csub\u003e2\u003c/sub\u003e binding interaction energy is reversed (\u0026ndash;20.9 vs \u0026minus;\u0026thinsp;14.9 kcal/mol for Ni\u003csup\u003eI\u003c/sup\u003e vs Co\u003csup\u003eI\u003c/sup\u003e), which can be attributed to inverted crystal field splitting. Here, Ni\u003csup\u003eI\u003c/sup\u003e (\u003cem\u003ed\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e) showed lower Pauli repulsion (32.0 kcal/mol) than Co\u003csup\u003eI\u003c/sup\u003e (\u003cem\u003ed\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e) (39.4 kcal/mol), leading to a more favorable Δ\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eFrz\u003c/em\u003e\u003c/sub\u003e for Ni (+\u0026thinsp;7.4 kcal/mol vs. +13.6 kcal/mol for Co).\u003c/p\u003e \u003cp\u003eThese findings provide a qualitative rationale for the observed reactivity trends: Co exhibits enhanced performance in the BBTA framework due to its favorable octahedral crystal field splitting, while Ni demonstrates superior activity in the MFU-4\u003cem\u003el\u003c/em\u003e framework, benefiting from the inverted tetrahedral crystal field. This analysis highlights the critical role of coordination geometry in determining the electronic structure and, consequently, the catalytic activity of metal centers in these metal-organic frameworks.\u003c/p\u003e \u003cp\u003eIn conclusion, we have developed a strategy for synthesizing MOFs with highly polarizable SH groups coordinated to metal nodes through the stepwise conversion of M\u0026ndash;Cl species to M\u0026ndash;OH and subsequently M\u0026ndash;SH species (M\u0026thinsp;=\u0026thinsp;Co or Ni). This strategy circumvents challenges associated with the \u003cem\u003ede novo\u003c/em\u003e synthesis of MOFs featuring metal-sulfur bonds that have limited the development of this class of MOFs. We demonstrated that this post-synthetic modification method works for the M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003eBBTA series of MOFs, which contain 1D chains of metal ions, as well as the M-MFU-4\u003cem\u003el\u003c/em\u003e-SH series, which feature discrete 3D clusters of single metal ions, for both Co and Ni analogues. A combination of SCXRD and PDF analyses elucidated the solid-state structures of all MOFs and confirmed the quantitative conversion to M\u0026ndash;SH species in both series. Catalytic studies probing the hydrogenation of 4-nitrophenol to 4-aminophenol as a model reaction indicated that the installation of more labile sulfur-based ligands is critical for this catalytic reaction and significantly improves conversion relative to the chloride- and hydroxide-based analogues. Finally, density functional theory (DFT) calculations revealed that the electronic flexibility of the sulfur moiety plays important role in the M\u0026ndash;X bond cleavage pathway for hydrogen activation, providing additional insights that future MOF-based catalyst design strategies may benefit from. Overall, this post-synthetic modification strategy opens up a new methodology in synthesizing porous materials with polarizable sulfur components and presents new avenues for developing high-performance catalysts.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eACKNOWLEDGMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Catalyst Design for Decarbonization Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under grant DE-SC0023383. Additionally, the IMSERC Crystallography facility at Northwestern University was utilized, with support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633) and Northwestern University. The EPIC facility at Northwestern University\u0026rsquo;s NUANCE Center was also employed, supported by the SHyNE Resource (NSF ECCS-2025633), the International Institute for Nanotechnology (IIN), and Northwestern\u0026rsquo;s Materials Research Science and Engineering Center (MRSEC) program (NSF DMR-1720139). Lastly, the Keck-II facility at Northwestern University\u0026rsquo;s NUANCE Center was used, with backing from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern\u0026rsquo;s MRSEC program (NSF DMR-1720139). This research used beamline 28-ID-1 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory under Contract No. DE-SC0012704. The computing resources were provided by The University of Chicago Research Computing Center (RCC).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOmar K. Farha\u003c/strong\u003e \u0026ndash; \u003cem\u003eDepartment of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States\u003c/em\u003e; Email: [email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLaura Gagliardi\u003c/strong\u003e \u0026ndash; \u003cem\u003eDepartment of Chemistry, Pritzker School of Molecular Engineering, James Franck Institute, Chicago Center for Theoretical Chemistry, University of Chicago, Chicago, Illinois 60615, United States\u003c/em\u003e; Email:\u0026nbsp;\u003ca href=\"mailto:[email protected]\"\[email protected]\u003c/a\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHaomiao Xie\u003c/strong\u003e \u0026ndash; \u003cem\u003eDepartment of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States\u003c/em\u003e; Email: [email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eO.K.F. has financial interest in NuMat Technologies, a startup company that is seeking to commercialize MOFs.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupporting Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterials / General Methods / Instrumentation, Synthetic Protocols, DFT Computations Details can be found in the supporting information.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eOmann, L.; K\u0026ouml;nigs, C. 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DOI: 10.1039/D0CP04016A.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5357011/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5357011/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMetal sulfide binary compounds, renowned for their exceptional electronic properties, are advantageous in applications such as hydrogenation, dehydrogenation, and photocatalysis. Typically, the majority of active sites in these compounds reside on the surfaces and edges of catalyst particles, leaving the bulk catalyst underutilized. This study introduces a strategy to embed metal-sulfur active sites into metal-organic frameworks (MOFs) via post-synthetic modification, exploiting the MOFs\u0026rsquo; accessible internal surfaces. Two MOF systems, including M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e(BBTA) (H\u003csub\u003e2\u003c/sub\u003eBBTA\u0026thinsp;=\u0026thinsp;1H,5H-benzo(1,2-d:4,5-d')bistriazole, M\u0026thinsp;=\u0026thinsp;Co, Ni), which features one-dimensional M\u0026ndash;Cl chains and hexagonal channels, and M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl (M\u0026thinsp;=\u0026thinsp;Co, Ni), which contains discrete ZnM\u003csub\u003e4\u003c/sub\u003e metal nodes, were selected as starting materials. The conversion processes, from M\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e(BBTA) to M\u003csub\u003e2\u003c/sub\u003e(SH)\u003csub\u003e2\u003c/sub\u003e(BBTA) and from M-MFU-4\u003cem\u003el\u003c/em\u003e-Cl to M-MFU-4\u003cem\u003el\u003c/em\u003e-SH, were executed through a two-step post-synthetic modification protocol and confirmed by single-crystal XRD, PXRD, PDF, SEM, XPS, and N\u003csub\u003e2\u003c/sub\u003e sorption techniques. Catalytic performance was assessed using the reduction of 4-nitrophenol to 4-aminophenol with molecular hydrogen as a model reaction, and significant improvement in performance was observed upon introduction of the SH groups. Density functional theory calculations suggest that the flexibility of the sulfur moiety is crucial in the M\u0026ndash;X bond cleavage pathway, enhancing hydrogen activation. This study underscores the efficacy of post-synthetic modification in developing advanced MOF-based catalysts with superior performance for selective hydrogenation reactions, highlighting the strategic advantage of incorporating polarizable sulfur components within MOFs.\u003c/p\u003e","manuscriptTitle":"Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-25 08:23:04","doi":"10.21203/rs.3.rs-5357011/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-chemistry","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nchem","sideBox":"Learn more about [Nature Chemistry](http://www.nature.com/nchem/)","snPcode":"","submissionUrl":"","title":"Nature Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"62d98b0b-24af-49ff-8d07-9f5141f40fad","owner":[],"postedDate":"November 25th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":40574098,"name":"Physical sciences/Chemistry/Chemical synthesis/Catalyst synthesis"},{"id":40574099,"name":"Physical sciences/Chemistry/Catalysis/Catalyst synthesis"},{"id":40574100,"name":"Physical sciences/Chemistry/Materials chemistry/Metal\u0026#x2013;organic frameworks"}],"tags":[],"updatedAt":"2025-07-25T07:05:19+00:00","versionOfRecord":{"articleIdentity":"rs-5357011","link":"https://doi.org/10.1038/s41557-025-01876-y","journal":{"identity":"nature-chemistry","isVorOnly":false,"title":"Nature Chemistry"},"publishedOn":"2025-07-24 04:00:00","publishedOnDateReadable":"July 24th, 2025"},"versionCreatedAt":"2024-11-25 08:23:04","video":"","vorDoi":"10.1038/s41557-025-01876-y","vorDoiUrl":"https://doi.org/10.1038/s41557-025-01876-y","workflowStages":[]},"version":"v1","identity":"rs-5357011","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5357011","identity":"rs-5357011","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}