Catalytic Fe-Oxo Clusters Stabilized on the MOF-808 Metal ...

doi.org/10.26434/chemrxiv.12937691.v1

Catalytic Fe-Oxo Clusters Stabilized on the MOF-808 MetalOrganicframework for the Degradation of Water PollutantsCelia Castillo-Blas, Ignacio Romero-Muñiz, Andreas Mavrandonakis, Laura Simonelli, Ana Eva Platero Prats

Submitted date: 10/09/2020 • Posted date: 11/09/2020Licence: CC BY-NC-ND 4.0Citation information: Castillo-Blas, Celia; Romero-Muñiz, Ignacio; Mavrandonakis, Andreas; Simonelli, Laura;Platero Prats, Ana Eva (2020): Catalytic Fe-Oxo Clusters Stabilized on the MOF-808 MetalOrganicframework for the Degradation of Water Pollutants. ChemRxiv. Preprint.https://doi.org/10.26434/chemrxiv.12937691.v1

Stabilizing catalytic iron-oxo-clusters within nanoporous metal-organic frameworks (MOF) is a powerfulstrategy to prepare new active materials for the degradation of toxic chemicals, such as bisphenol A. Herein,we combine pair distribution function analysis of total X-ray scattering data and X-ray absorptionspectroscopy, with computational modelling to understand the local structural nature of added redox-activeiron-oxo clusters bridging neighbouring zirconia-nodes within MOF-808.

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Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

Catalytic Fe-oxo clusters stabilized on the MOF-808 metal organic-framework for the degradation of water pollutants Celia Castillo-Blas,a Ignacio Romero-Muñiz,a Andreas Mavrandonakis,b Laura Simonelli,c and Ana E. Platero-Prats a, d*

Stabilizing catalytic iron-oxo-clusters within nanoporous metal-organic frameworks (MOF) is a powerful strategy to prepare new active materials for the degradation of toxic chemicals, such as bisphenol A. Herein, we combine pair distribution function analysis of total X-ray scattering data and X-ray absorption spectroscopy, with computational modelling to understand the local structural nature of added redox-active iron-oxo clusters bridging neighbouring zirconia-nodes within MOF-808.

The removal of emerging pollutants of chemical complexity from water sources is a global health challenge. Water quality is often compromised by the presence of a variety of toxic compounds produced by human activities − ranging from heavy metals to a wide scope of organic compounds.1 In particular, bisphenol A (BPA) is an abundant endocrine disrupting chemical (EDC) pollutant in water, which is widely used for the manufacture of plastics and epoxy resins. Over the last years, a variety of porous solids, such as zeolites2 and mesoporous carbons,3 have been used to capture BPA. On the other hand, Fenton reactions catalyzed by iron(II) are a powerful methodology to afford the oxidative degradation of this pollutant in water into mainly carbon dioxide and water.4,5 However, acidic conditions are typically required to stabilize iron species in water under catalytic conditions. Therefore, developing porous materials with intrinsic highly acidic surfaces and redox-active iron sites able to capture BPA and subsequently convert it into non-toxic compounds, would represent an elegant strategy to degrade this water pollutant under mild conditions.

Metal-Organic Frameworks (MOFs) are porous and crystalline materials composed of organic ligands linked by metal-oxo nanoclusters, to give open architectures with large surface areas and pores of different shapes and sizes.6 The exceptional textural and chemical properties of these materials, make them excellent candidates for the selectively capture and degradation of many types of hazardous chemicals.7,8 In particular, the family of Zr(IV)-MOF materials present a high thermal and

chemical stability in water,9 allowing the applicability in aqueous-based degradation of pesticides, pharmaceuticals and pollutants processes. The Zr(IV)-MOFs are composed of Zr6O8 clusters, which can be 12-, 8-, or 6-fold connected to carboxylate organic ligands, being UiO-type, NU-1000 and MOF-808 the archetypical ones, respectively.10 MOF-808 is an interesting platform to target liquid-phase applications, including capture and degradation processes.11 Its structure is built from linking unsaturated Zr6O8 clusters by benzene-1,3,5-tricarboxilate (BTC) ligands, to give mesopores of around 20 Å size. Besides its high porosity, MOF-808 has a remarkably highly tunable structure arising from the low saturation of the Zr6O8 clusters. Within the octahedral Zr6O8 clusters, the linking positions around the equatorial plane can serve as scaffold to insert discrete functional groups, including aminacids,12 sulfates,13 and metal complexes.14 Furthermore, the presence of available hydroxyl groups within the Zr6O8 clusters represents an excellent platform to further modifying the MOF-808 chemistry with transition metals.

Solvothermal incorporation in MOF (SIM) materials has been widely explored to decorate Zr6O8 clusters, by soaking the pristine MOF into a solution containing a target transition metal precursor.15 Thus, a variety of MOF chemical modifications with catalytic transition metal sites have been reported using this method.16 In this regard, the SIM method using a redox-active transition metal such as iron, would be a promising approach for tailoring MOF catalytic properties towards the oxidative degradation of organic EDC pollutants.

In this work, we show the chemical modification of MOF-808 with binuclear iron clusters, active for the selective capture and subsequent catalytic degradation of BPA via Fenton reactions. Detailed synchrotron characterization including pair distribution function (PDF) analysis of X-ray total scattering data and Fe K-edge X-ray absorption spectroscopy (XAS) together with density functional theory (DFT) computational modelling are applied to understand the local structural nature of the added redox-active iron clusters within MOF-808.

The SIM synthesis of Fe-MOF-808 was performed by immersion of pristine material, previously activated, in a solution containing FeCl2 in N,N’-dimethylformamide (see ESI). To explore the kinetic aspects of the iron incorporation within MOF-808, different Fe-SIM reaction times were tested using

a. Departamento de Química Inorgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain.

b. Electrochemical Processes Unit, IMDEA Energy, Avenida Ramón de la Sagra 3, 28935 Móstoles, Madrid, Spain.

c. CLAESS beamline, ALBA Synchrotron, 08290 Cerdanyola del Vallès, Spain. d. Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid,

28049, Campus de Cantoblanco, 28049 Madrid, Spain. † Electronic Supplementary Information (ESI) available: [details of any supplementary information available should be included here]. See DOI: 10.1039/x0xx00000x

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two different starting Fe to Zr6 molar ratios, that is 12 and 24 hours. Powder X-ray diffraction (PXRD) data collected on the activated materials showed the presence of the MOF-808 phase for all reaction times tested, with subtle differences in relative peak intensities. Interestingly, scanning electron microscopy and energy dispersive X-rays spectroscopy (SEM-EDS) analyses indicated that the incorporation of iron within MOF-808 strongly depends on the Fe-SIM reaction time. At short reaction times (i.e. 1 h), the amount of iron incorporated in MOF-808 was significantly high (i.e. Fe to Zr6O8 molar ratio ca. 2 using a starting Fe to Zr molar ratio of 12). However, the material obtained showed a heterogeneous distribution of iron within the crystals, as evidenced by SEM-EDS analyses (S3, ESI). When using longer reaction times, the amount of iron incorporated decreased significantly until it reaches a plateau after 16 h, together with the occurrence of an improved homogeneity of the iron distribution within the MOF crystals. The final Fe to Zr6O8 molar ratio determined was of ca. 0.5 (i.e. Fe-0.5-MOF-808). Similar behaviour was observed for the synthesis of the high-content Fe-1.2-MOF-808 (S4, ESI). These results demonstrated that optimal iron MOF modification is obtained at long Fe-SIM reaction times, resulting in materials with enhanced homogeneity in their chemistries and lacking of unwanted iron oxide nanoparticles as by-products.

SEM-EDS mapping elemental analyses showed a highly homogeneous distribution of iron along the MOF crystallites for both 0.5- and 1.2-MOF-808 (Fig. 1C). Additionally, EDS spectra indicated the presence of chlorine in the materials in a Cl to Fe ratio of 3.6 (Fig. S3.3-S3.4). We hypothesize that chloride could be partially replacing hydroxyl groups from the Zr-cluster.17 N2 isotherms revealed an expected decrease in specific surface area associated with the iron incorporation within the MOF-808 structure together with subtle variations in the pore size distribution (Fig. 1A-B and S4). Detailed analysis of the pore volume contributions showed the occurrence of a significant decrease in volume linked to the mesopores of 18 Å (ca. 50%) compared to the minor loss seen for the micropores of 12 Å Fig. 1B and S4). These results would suggest that the iron sites are located pointing towards the MOF-808 hexagonal channels.

PXRD data collected on both the low- and high-content Fe-MOF-808 materials showed the unique presence of the Bragg peaks linked to the MOF-808 phase together with subtle differences in relative peak intensity. Pawley refinements of the diffraction data corroborated that the average MOF architecture is preserved after Fe-SIM, together with the occurrence of a minor cell expansion and peak broadening compared to the pristine system (Fig. 1D and Table S7.1). These results demonstrated that MOF-808 is a robust platform towards the incorporation of iron sites through SIM methods.

To probe the atomic local structure of the iron sites within MOF-808, we applied PDF analysis of X-ray total scattering data (xPDF). xPDF data collected on the Fe-SIM and pristine MOF-808 materials showed two major contributions at short range, that is, Zr-O (ca. 2.2 Å) and Zr···Zr (ca. 3.5 Å) distances characteristic of the Zr6O8 clusters.18,19 With the purpose of highlighting the subtle contributions in this region that are associated to the iron sites, differential analysis of the xPDF data20 were carried out by subtracting the PDF of the pristine material to that of the Fe-MOF-808 systems. d-PDF analysis carried out on the Fe-MOF-808 materials revealed the appearance of new correlations

associated with the iron-clusters at ~1.9-2.0 Å, ~2.3 Å and ~3.0 Å (Fig. 2.A). The Fe–O distance values are sensitive to the oxidation state of iron,21 being shorter for Fe(III) (~1.85 Å) compared to Fe(II) (~2.05 Å). The broad d-PDF signal observed at ~1.9-2.0 Å indicated the presence of mixed oxidation states for iron within the Fe-MOF-808 systems. In addition, the presence of chloride groups bonded to the iron sites is confirmed by the peak centred at ~2.3 Å, associated with Fe–Cl bonds. Interestingly, the correlation centred at ~3.0 Å is characteristic of Fe-O-Fe distances within edge-sharing geometries.22 Additionally, two d-PDF peaks centred at ~3.3 and ~3.7 Å are observed, which could be attributed to Zr…Fe correlations. These results indicated the presence of iron-oxo clusters binding the Zr6-nodes within the Fe-MOF-808 materials, where some of the oxygen positions have been replaced by chloride, as suggested by SEM-EDS.

Fig. 1 A. N2 adsorption/desorption isotherms at 77 K showing the decrease in surface area upon iron incorporation; B. Pore size distribution (PSD) data for pristine and Fe-SIM MOF-808 materials; C. Mapping of Zr (yellow) and Fe (green) for Fe-0.5-MOF-808 (right) and Fe-1.2-MOF-808 (left); D. PXRD data of the synthesized materials and their comparison with the calculated data for MOF-808,23 including Bragg positions.

Quantitative analysis of the relative d-PDF peak intensities is a powerful strategy to estimate the size of metal-oxo clusters deposited in MOF-808.24 Thus, the signals linked to Fe-O, Fe-Cl and Fe-O-Fe were fitted to Gaussian curves and compared to preliminary models of different iron cluster sizes (i.e. bearing two, three or four iron atoms, Fig.2.B). By comparing the experimental d-PDF peak intensities of the Fe-O,Cl and contributions to simulated values, we hypothesized that Fe-0.5-MOF-808 contains clusters of two iron atoms in distorted tetrahedral environments. Furthermore, the results suggest that the iron sites are bonded to both chlorine and oxygen atom (including aquo, hydroxo or oxo group) in a 1 to 2 ratio (Figure S8.3, Table S8.1). For the Fe-1.2-MOF-808 system, quantitative analyses indicated the formation of slightly larger iron clusters compared to Fe-0.5-MOF-808 (Figure S8.4, Table S8.2), suggesting that the use of high concentrations of iron precursor during SIM on MOF-808 would favoured aggregation.

To better understand the chemical nature of the binuclear iron clusters within MOF-808, Fe K-edge extended X-ray absorption fine

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structure (EXAFS) and X-ray absorption near edge spectroscopy (XANES) data were collected on the Fe-MOF-808 materials. XANES data showed the occurrence of rising edge and pre-edge features at ca. 7122 and ca. 7114 eV, characteristic of binuclear iron complexes.25 A slight shift of rising-edge position of ca. 1 to higher values is observed for Fe-1.2-MOF-808 compared to Fe-0.5-MOF-808, in agreement with the oxidation of Fe2+ to Fe3+ (Fig. 3A). The observed pre-edge signal corresponds to the Fe-1s to Fe-3d electronic transition, and its intensity is indicative of the local symmetry of the iron sites. The XANES data collected on both Fe-MOF-808 materials suggested the appearance of tetrahedral iron geometries.26 This experimental evidence is in agreement with the most energetically favoured geometry compatible with both II/III oxidation states found for iron within these materials. Further analyses of the EXAFS data collected on Fe-0.5-MOF-808 indicated the presence of three main signals at ca. 1.35, ca. 1.81 and 2.58 Å (without phase correction), linked to FeII–O, Fe–Cl (2.25 Å) and Fe···Fe distances, respectively (Fig. 3B).27 Interestingly, EXAFS data of Fe-1.2-MOF-808 showed a single contribution at ca. 1.56 Å (without phase correction) linked to FeIII–Cl,O bonds together with a significant increase in intensity of the signal linked to Fe···Fe distances. This evidence corroborates the presence of larger clusters with an oxidized state of iron in Fe-1.2-MOF-808 compared to Fe-0.5-MOF-808, in agreement with the xPDF analyses.

Fig. 2 A. Total PDFs of pristine and Fe-MOF-808 materials (up) and the corresponding d-PDFs for Fe-0.5-MOF-808 and Fe-1.2-MOF-808, obtained from the subtraction of MOF-808 pristine (blue) (down); B. Simulated (up) and experimental (down) d-PDF signals linked to the iron clusters were fitted to Gaussian curves for quantitative analyses.

Fig. 3 A. Fe K-edge XANES data of Fe-MOF-808 materials (left) and first derivate analysis (right) showing the rising-edge shift between both materials; B. The k3-wighted χ(r) Fe K-edge EXAFS spectra of Fe-0.5- and Fe-1.2-MOF-808 systems.

Density Functional Theory (DFT) calculations were performed in order to elucidate the possible conformations of the bimetallic core of the Fe-MOF-808. The structural and energetic properties of several binuclear iron-oxo and iron-hydroxo clusters deposited on the nodes of the MOF-808 were

modelled. The approach in this study is similar to previous works, where the deposition of small copper-, cobalt- and nickel-(hydro)oxo clusters was investigated on the nodes of the NU-1000.24,28,29 An exhaustive description of the possible iron-(hy)droxo clusters explored can be found in the ESI S10. Among the possible structures investigated, two possess structural features that agree with the experimental PDF. Moreover, from a thermodynamic point of view, they are the most stable conformations because of the most negative computed free energies of formation. In both of them, the bimetallic core is deposited as -Fe2Cl2(μ-OH)2- on the nodes via the terminal-OH groups. In one case, the iron-hydroxo cluster is bridging two Zr6O8 octahedra (model A), while in the second case (model B) it is deposited on one node and the cluster is terminated by an additional hydroxo group (Fig. 4). The presence of an intense dPDF signal at ca. 3.3 Å, linked to Fe···Fe and Fe···Zr distances within model A, demonstrated the stabilization of the Fe-oxo clusters by bridging two Zr6O8 clusters as main species. Additionally, the occurrence of signals at ca. 3.0 and ca. 3.7 Å, associated with Fe···Fe and Fe···Zr distances within the model B, evidenced the deposition of the Fe-oxo clusters within the Zr6O8 cluster trough terminal hydroxo groups. Remarkably, these results demonstrated that the Fe-oxo clusters are stabilized by bridging two neighbouring Zr6O8 nodes within MOF-808, as previously identified for other zirconia-based MOF systems.24

Fig. 4. DFT computed structures of possible bimetallic iron-hydroxo clusters deposited on the MOF-808. A. Iron cluster acts as bridge between two Zr-nodes. B. Iron cluster is linked to one Zr-node only with a terminal disposition. Their M06-L computed free energies of formation are also given. A more detailed description of the calculations can be found in the ESI.

As a proof of concept, activated Fe-MOF-808 materials were evaluated for the capture and subsequent catalytic degradation of BPA through Fenton reactions. The experiments were performed using solutions containing Milli-Q water and ethanol in a 95 to 5 ratio (see ESI, S11) at room temperature. Under these conditions, Fe-0.5-MOF-808 was able to capture ca. 50% of BPA after 1 h, contrary to the ca. 11% captured by Fe-1.2-MOF-808 (Fig. 5). This result is in accordance with the textural properties of the materials (Fig. 1A-B)- the MOF with a lower iron content (i.e. Fe-0.5-MOF-808) has larger free space to capture molecules than its analogue with higher iron content (i.e. Fe-1.2-MOF-808). To study the performance of the Fe-MOF-808 materials as catalysts, the degradation of BPA was carried out through a Fenton reaction using H2O2 (see details in ESI). The catalytic degradation was compared at 30 and 60 min reaction time (Fig. 5). Interestingly, the structural differences seen for the two MOFs play also a role in their catalytic performance regarding both the kinetic and the thermodynamic aspects. Thus, Fe-0.5-MOF-808 degraded the 26% of the total BPA after 30 minutes, being this value three times better than the activity determined for Fe-1.2-MOF-808. After 1 hour of reaction time, a plateau is reached and ca. 40% of the total BPA is removed by the low Fe-loaded material, being

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this value remarkably larger than the performance observed for Fe-1.2-MOF-808 containing larger iron-oxo clusters.

600

25

50

18%

40%

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ure

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d (%

)

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Fe-0.5-MOF-808 Fe-1.2-MOF-808

30 600

25

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26%

8%11%

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49%

Fig. 5 Removal test of 1 mg / 1 mL 100 ppm BPA after 60 min (left), and catalytic degradation, 0.04 % molar in Fe over 5 mL BPA 100 ppm (right).

In conclusion, we have reported the stabilization of catalytic Fe-oxo clusters within the MOF-808 through SIM methods, active in the degradation of BPA via Fenton reactions. Interestingly, synchrotron XAFS and PDF characterization combined with DFT modelling demonstrated the occurrence of Fe-oxo dimers bridging two neighbouring Zr6O8 nodes as the main species. We hypothesize that the terminal Fe-oxo species (model B) might be formed under kinetic control at short reaction times, and subsequent react with a terminal hydroxo group from a neighbouring zirconia node giving the formation of the most thermodynamically stable bridging species (model A). Further studies are currently under investigation to elucidate the structural mechanism of this Fe-oxo cluster stabilization.

This work was supported by the Spanish Government (RTI2018-096138-A-I00 and RTI2018-101049-BI00) and the Regional Government of Madrid (TALENTO grants 2017-T1/IND5148 and 2017-T1/AMB-5264) for funding. We acknowledge the computing facilities of CSUC for providing computational resources. XAS experiments were performed at BL22 beamline (proposal 2019093796) at ALBA Synchrotron with the collaboration of ALBA staff. We thank DESY and Dr M. Wharmby for assistance in using the beamline P02.1 for the PDF experiments (proposal I-20190239 EC). The research leading to this result has been supported by the project CALIPSOplus (Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020). C. C. B. acknowledges the European Social Funds and the Regional Government of Madrid for a postdoctoral contract (PEJD-2018-POST/IND-7909). I. R. M. acknowledges the Universidad Autónoma de Madrid for predoctoral fellowship.

Conflicts of interest There are no conflicts to declare.

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S1

Catalytic Fe-oxo clusters stabilized on the MOF-808 metal organic-framework for the degradation of water pollutants Celia Castillo-Blas,1 Ignacio Romero-Muñiz,1 Andreas Mavrandonakis,2 Laura Simonelli,3 Ana E. Platero-Prats*1,4 1 Departamento de Química Inorgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain. 2 Electrochemical Processes Unit, IMDEA Energy, Avenida Ramón de la Sagra 3, 28935 Móstoles, Madrid, Spain. 3 CLAESS beamline, ALBA Synchrotron, 08290 Cerdanyola del Vallès, Spain. 4 Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049, Campus de Cantoblanco, 28049 Madrid, Spain.

KEYWORDS. Insert here the keywords of the communication.

Supporting Information

S1 General information .............................................................................................. 2

S2 Synthesis of the materials .................................................................................... 4

S3 Scanning Electron Microscopy. Energy Dispersing X-ray Spectroscopy...... 5

S3.1. Metal incorporation tests .............................................................................. 7

S4 Nitrogen adsorption-desorption analyses ....................................................... 11

S5 Thermal gravimetric analysis ............................................................................ 13

S6 ATR-FTIR analysis ............................................................................................... 15

S7 X-ray powder diffraction ..................................................................................... 17

S8 Pair Distribution Function .................................................................................. 21

S9 X-Ray Absorption Spectroscopy ....................................................................... 31

S10 Computional details .......................................................................................... 32

S10.1 Computational methodology..................................................................... 32

S10.2 Results ......................................................................................................... 34

S11 Capture and catalytic test ................................................................................ 38

References ................................................................................................................. 40

S2

S1 General information All other reagents were used as received from commercial suppliers unless otherwise stated. Powder X-ray diffraction (PXRD) patterns were measured with a Bruker D8 diffractometer with a copper source operated at 1600 W, with step size = 0.02° and exposure time = 0.5 s/step. Samples were placed on a borosilicate sample holder and then the sample surface was levelled with a clean microscope slide. All the samples were grinded prior to analysis unless otherwise stated. Data were measured using a continuous 2θ scan from 3.0-45º θ. For all samples, PXRD patterns are presented from 0–30º θ for visual clarity. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectra (EDS) were collected with an S-3000N microscope, equipped with an ESED and an INCAx-sight of Oxford Instruments, respectively. All samples were prepared for SEM and EDS by dispersing the material onto a double sided adhesive conductive carbon tape that was attached to a flat aluminum sample holder and were metallized with a gold layer of 15 nm with a Quórum Q150T-S sputter. Field emission scanning electron microscopy (FE-SEM) observations were performed on a JSM 6335F microscope operating at 15 kV. All samples were prepared for FE-SEM by dispersing the material onto a double sided adhesive conductive carbon tape that was attached to a flat aluminum sample holder and were coated in C with a Sputter Coater Quorum, Q150T-S. Mapping were performed during 300 s with an INCAx X-Max of Oxford Instruments. Nuclear magnetic resonance (NMR) spectra were acquired on a Bruker AV-300 spectrometer, running at 300 MHz for 1H. Chemical shifts (δ) are reported in ppm relative to residual solvent signal with a value of 2.50 ppm for DMSO-d6. 1H digested solution NMR (300 µL DMSO-d6, 50 µL D2O, 50 µL HF, and 300 µL 5% D2SO4 in DMSO-d6 (v:v) solution) of as-synthesized sample MOF-808.

Textural analyses. Nitrogen adsorption and desorption isotherms were measured at 77 K using a Micromeritics ASAP 2020 system. The samples were outgassed at indicated temperature for 16 h before the measurements. The specific surface areas (BET) were calculated by application of the Brunauer-Emmett-Teller equation taking the area of the nitrogen molecule as 0.162 nm2. The linear range of the BET equation was located between 0.05–0.35 P/P0, however, for all other materials studied due to their microporous natures this linear range was much narrower and displaced to lower relative pressures: P/P0= 0.015–0.1. The micropore volume and external surface area, i.e. the area not associated with the micropores, were calculated using a t-plot analysis. taking the thickness of an adsorbed layer of nitrogen as 0.354 nm and assuming that the arrangement of nitrogen molecules in the film was hexagonal close packed. The mesopore volumes of the materials were calculated from the volume of gas adsorbed at a relative pressure of 0.6 on the desorption branch of the isotherms, equivalent to the filling of all pores below 50 nm, minus the microporosity calculated from the corresponding t-plot. The total pore volume was calculated from the volume of gas adsorbed at a relative pressure of 0.95 on the absorption branch of the isotherms. The pore-size-distribution (PSD) curves were obtained from the adsorption branches using non-local density functional theory (NLDFT) method for a cylinder pore in pillared clays, using a regularization of 0.00316.

S3

Thermogravimetric analyses and differential thermal analyses (TGA-DTA) were performed using a SDT Q600 from TA Instruments equipment in a temperature range between 40 °C and 800 °C in air (100 mL/min flow) atmosphere and heating rate of 10 ºC/min. Infrared spectra (FTIR) were recorded on a PerkinElmer 100 spectrophotometer using a PIKE Technologies MIRacle Single Reflection Horizontal ATR Accessory from 4000-450 cm-1. Elemental analyses were performed with a LECO CHNS-932 analyser, with dry samples. ICP analyses were performed with an Inducted Coupled Plasma Emission Spectrometer ICP PERKIN ELMER mod. OPTIMA 2100 DV. Samples were digested in 5 mL of a 1:1 H2O2:H2SO4 mixture (v:v) and taken to a 15 mL volume with distilled water.

S4

S2 Synthesis of the materials

MOF-808. Trimesic acid (117 mg, 0.55 mmol) was added to a stirred suspension of zirconyl chloride octahydrate (539 mg, 1.6 mmol) in DMF (45 mL) and formic acid (45 mL) in a screwed bottle. The reaction was heated at 130 ºC for 48 h (aprox.) in the oven. The reaction mixture was centrifuged, and the solid was washed with DMF, water and acetone three times each. The solid was dried under ambient pressure yielding MOF 808 as a white powder. The powder was treated with supercritical CO2 (SC-CO2) and dried under dynamic vacuum 4 hours at room temperature and 100 °C overnight. Yield: 405.7 mg, 85% based on Zr). EA of sample: Calcd. For Zr6C24.5H64.5N1.5O47.5 = [Zr6O4(OH)6(C9H3O6)2(COOH)2(C3H7NO)1.5(H2O)20]: C 17.44%, H 3.82%, N 1.25%; Found: C 17.57%, H 4.10%, N 1.31%. 8.56 (s, 3H, 1 × BTC), 8.02 (s, 2H, 2 × HCOOH), 7.84 (s, 1H, 1.5 × DMF), 2.85 (s, 3H, 1.5 × DMF), 2.69 (s, 3H, 1.5 × DMF).

Fe-0.5-MOF-808. A mixture of MOF-808 (100 mg, 0.074 mmol), FeCl2·4H2O (180 mg, 0.905 mmol) and 10 mL of DMF was placed in a sealed vial. The solution was stirred at 60 °C for 24 h. After cooling, the reaction was allowed to cool to room temperature. Light yellow powder was collected by centrifugation (8,000 rpm, 2 min), washed with DMF, water and with acetone three times each. The solid was dried under ambient pressure yielding FeMOF-808 as an orangish powder. The powder was treated with supercritical SC-CO2 and dried under dynamic vacuum 4 hours at room temperature and 60°C overnight. Yield: 97.2 mg, 71% based on Zr. ICP ratio Fe/Zr6: 0.0833. EA of sample: Calcd. For Fe0.5Zr6C24.5H74.5N1.5O52.5Cl1.5 = [Fe0.5Zr6O4Cl1.5(OH)6(C9H3O6)2(COOH)2(C3H7NO)1.5(H2O)25]: C 15.83%, H 4.04%, N 1.13%; Found: C 15.99%, H 4.20%, N 1.40%.

Fe-1.2-MOF-808. A mixture of MOF-808 (100mg, 0.074 mmol), FeCl2·4H2O (360mg, 1.810 mmol) and 10mL of DMF was placed in a sealed vial. The solution was stirred at 60 °C for 24h. After cooling, the reaction was allowed to cool to room temperature. Light yellow powder was collected by centrifugation (8,000 rpm, 2 min), washed with DMF, water and with acetone three times each. The solid was dried under ambient pressure yielding FeMOF-808 as an orange powder. The powder was treated with supercritical SC-CO2 and dried under dynamic vacuum 4 hours at room temperature and 60 °C overnight. Yield: 94.2 mg, 69% based on Zr. ICP ration Fe/Zr6: 0.2. EA of sample: Calcd. For Fe1.2Zr6C23H61NO47Cl3.6 = [Fe1.2Zr6O4Cl3.6(OH)6(C9H3O6)2(COOH)2(C3H7NO)(H2O)20]: C 14.97%, H 3.33%, N 0.76%; Found : C 15.22%, H 3.99%, N 0.58%.

Water molecules are removed from the pores under dynamic vacuum at 150 ºC. However, with the pass of the time these molecules can be re-adsorpted in the pores.

S5

S3 Scanning Electron Microscopy. Energy Dispersing X-ray Spectroscopy

Fig S3.1. Mapping Fe-0.5-MOF-808. Accumulating images (A) and corresponding elemental mappings of (B) Zr, (C) Fe, (D) C, (E) O and (F) Cl.

Fig S3.2. Mapping Fe-1.2-MOF-808. Accumulating images (A) and corresponding elemental mappings of (B) Zr, (C) Fe, (D) C, (E) O and (F) Cl.

Mapping images show the presence of all the elements in the crystallites. Zirconium, chlorine and iron are homogeneously distributed in the octahedral crystals.

S6

Fig S3.3. SEM-EDS analyses of Fe-0.5-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

Fig S3.4. SEM-EDS analyses of Fe-1.2-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

SEM images present crystallites with a size between 0.5-1 µm and homogenous shape of octahedron. The distribution of the iron and the zirconium is homogenous.

Metal incorporation of Fe on the Zr6O8H4 SBUs was tested by anion and time condition screening. The experiments was monitored by FE-SEM-EDS (Table S3.1 ans Table S3.2) based on the Fe/Zr ration of each sample. The objetive of the tests were to see a global picture on the incorporation of Fe in a second shell of the Zr-oxo cluster:

S7

S3.1. Metal incorporation tests Metal incorporation of Fe on the Zr6O8H4 SBUs was tested by anion and time condition screening. The counterion test was developed with following the same conditions in all cases. A mixture of MOF-808 pristine (10 mg, 7 mmol), iron salt (70 mmol) and 5 mL of DMF was placed in a sealed vial. The solution was stirred at 60 °C for 16 h, in a general way. After cooling, the reaction was allowed to cool to room temperature. Light yellow powder was collected by centrifugation (8,000 rpm, 2 min), washed with DMF, water and with acetone three times each. The resultant solids were dried under dynamic vacuum. The experiments was monitored by FE-SEM-EDS (Table S3.1) based on the Fe/Zr ration of each sample. The objetive of the tests were to see a global picture on the incorporation of Fe in a second shell of the Zr-oxo cluster:

Table S3.1: optimization parameters of the Zr-oxo metallation:

Metal precursor Time / h Zr6:Fe ratio %Fe Error / % FeCl

3 16 0 0 0.0

Fe(NO3)3 16 0 0 0.0

Fe(acac)3 16 0.79 11.6 3.5

Fe(ox)2 16 2.29 27.5 13.9

Fe(AcO)2 16 0.66 9.9 13.1

FeCl2 0.03 0.92 13.35 0.66

FeCl2 0.15 0.94 13.57 6.47

FeCl2 0.5 1.48 19.81 1.93

FeCl2 1 1.96 24.58 1.64

FeCl2 2 0.45 6.93 0.61

FeCl2 16 0.84 12.3 1.0

FeCl2 160 0.52 8.03 0.96

a Referred to SEM-EDS values

Fig S3.5. SEM-EDS analyses of FeCl2-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

S8

Fig S3.6. SEM-EDS analyses of FeCl3-MOF-808. Red line in A delimits the area where EDS where performed. Spectrum is depicted in B.

Fig S3.7. SEM-EDS analyses of Fe(NO3)3-MOF-808. Red line in A delimits the area where EDS where performed. Spectrum is depicted in B.

Fig S3.8. SEM-EDS analyses of Fe(acac)3-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

S9

Fig S3.9. SEM-EDS analyses of Fe(ox)2-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

Fig S3.10. SEM-EDS analyses of Fe(Ac)2-MOF-808. Red spots in A and B indicate the areas where EDS where performed. Spectrum is depicted in C and the inset plot shows the Metals % (%Fe (orange), %Zr (blue).) by EDS analyses, where each column corresponds to the area indicated by a number in the SEM pictures A and B.

S10

Fig S3.11. Summary of the study of the counterion with their corresponding error bars in the EDS analyses.

We can observe different influence of the counterion employed in the synthesis and the iron amount incorporated in the MOF-808. The use of FeCl3 and Fe(NO3)3 suggest the incorporation of iron is not effective, while with Fe(acac)3, Fe(Ac)2 and Fe(ox)2 is more effective. However, the distribution of Fe amount in the different crystallites is heterogeneous. Thus, the FeCl2 is selected as iron precursor in these impregnation experiments.

S11

S4 Nitrogen adsorption-desorption analyses The BET analysis of the materials show a disminution of the specific surface area of metalated materials. Regarding to the NLDFT pore size distribution calculation, the Fe-loaded MOFs seems to maintain the micropore windown (ca. 12 Å and ca.18 Å) but the micropore contribution (take as the pore width under 22 Å) to the total pore volume rapidly decrease with the metal lodaing. Data collected from the t-plot analysis show an increment in the external surface area of the Fe-1.2-MOF-808 (34 m2g-1 in the presitine and 175 m2g-1 in the high concentrated sample)

Table S4.1. Data collected from N2 isotherms at 77K, BET and t-plot analysis

Sample Heat treatment

Surface area (BET)

/ m2g-1

External area / m2g-1

Micropore volume / cm3g-1

Mesopore volume / cm3g-1

Total pore volume / cm3g-1

MOF808-P 100ºC 1548 34 0.62 0.03 0.72 Fe-0.5-MOF808 60ºC 896 21 0.31 0.02 0.37 Fe-1.2-MOF808 60ºC 619 175 0.17 0.13 0.37

Fig. S4.1. N2 isotherm, BET analysis and DFT pore size distribution of MOF-808 pristine.

S12

Fig. S4.2. N2 isotherm, BET analysis and NLDFT pore size distribution of Fe-0.5-MOF-808.

Fig. S4.3. N2 isotherm, BET analysis and NLDFT pore size distribution of Fe-1.2-MOF-808.

S13

S5 Thermal gravimetric analysis TGA data collected on all the materials showed a mass loss associated with loss of water molecules with values of 31.9%, 34.3% and 14.3% for MOF-808, Fe-0.5-MOF-808 and Fe-1.2-MOF-808, respectively. This first curve is more pronounced in the Fe-0.5-MOF-808, than pristine MOF due to the amount of water which this material possesses, according to EA. Additionally, we can observe that the pristine MOF-808 and Fe-1.2-MOF-808 have two steps in their TGA curves.

The residues of these materials correspond to 43.5, 40.4 and 34.8% for MOF-808, Fe-0.5-MOF-808 and Fe-1.2-MOF-808, respectively. These residues are identified as ZrO2 in all the cases.

Fig. S5.1. Thermogravimetric analyses of materials.

Fig. S5.2. Thermogravimetric analysis and differential thermal analysis of MOF-808.

0 200 400 600 800 10000

20

40

60

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100

Wei

ghtlo

ss (%

)

Temperature (oC)

MOF-808 Fe-0.5-MOF-808 Fe-1.2-MOF-808

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ghtlo

ss (%

)

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TGA

0,0

0,1

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0,3

0,4

DTA

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Fig. S5.3. Thermogravimetric analysis and differential thermal analysis of Fe-0.5-MOF-808.

Fig. S5.4. Thermogravimetric analysis and differential thermal analysis of Fe-1.2-MOF-808.

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ghtlo

ss (%

)

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0,00,10,20,30,40,50,60,7

DTA

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S15

S6 ATR-FTIR analysis

Fig. S6.1. ATR-FTIR of MOF-808 before (solid) and after catalysis (dashed).

Fig. S6.2. ATR-FTIR of Fe-0.5-MOF-808 before (solid) and after catalysis (dashed).

S16

Fig. S6.3. ATR-FTIR of Fe-1.2-MOF-808 before (solid) and after catalysis (dashed).

S17

S7 X-ray powder diffraction X-ray diffraction patterns of the materials show a high crystallinity and pure phases compared with the calculated pattern from single crystal data.1 According to Pawley refinements, impregnated materials present a small 0.425 and 0.899-shift, with the corresponding expansion of the unit cell until 34.73928 and 35.21372 Å for Fe-0.5-MOF-808 and Fe-1.2-MOF-808, respectively (Table S7.1 and Fig S7.2-S7.4). This is consistent with other examples of impregnation of metals in MOFs,2 due to this new metal clusters are located in the pores, expanding the crystalline structure.

A loss of crystallinity is observed in Fe-0.5-MOF-808 after catalysts. This is expected, as the high oxidant conditions (see section S11) employed during catalysis (Fig S7.5).3

Fig S7.1. X-ray powder diffraction patterns of materials and their comparison with the calculated MOF-808 reported by Yaghi et al.1 Bragg positions are depicted as green vertical lines.

Table S7.1. Pawley refinement values for synthetized samples.

Sample a Rwp Rp Zero U V W MOF-808 Pristine 34.3145 (3) 1.10% 0.77% 0.0491 (3) -0.0090 (2) -0.0247 (4) 0.0204 (3) Fe-0.5-MOF-808 34.7392 (2) 0.52% 0.36% 0.0524 (2) -0.0014 (3) -0.0345 (3) 0.0157 (3) Fe-1.2-MOF-808 35.2137 (2) 0.53% 0.34% 0.0518 (5) -0.0010 (2) -0.0292 (2) 0.0132 (2)

S18

5 10 15 20 25 30 35 40 45

Experimental Calculated Difference Bragg positions Systematic absences

Inte

nsity

(a.u

.)

2θ (o)

Fig S7.2. Pawley refinement for MOF-808 pristine.

5 10 15 20 25 30 35 40 45

Experimental Calculated Differential Bragg positions Systematic absences

Inte

nsity

(a.u

.)

2θ (o) Fig S7.3. Pawley refinement for Fe-0.5-MOF-808.

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5 10 15 20 25 30 35 40 45

Experimental Calculated Differential Bragg positions Systematic absences

Inte

nsity

(a.u

.)

2θ (o) Fig S7.4. Pawley refinement for Fe-1.2-MOF-808.

Fig S7.5. X-ray powder diffraction patterns of materials and their comparison with the calculated MOF-808. Bragg positions are depicted as green vertical lines.

5 10 15 20 25 30 35 40 45

Inte

nsity

(a.u

.)

2θ (o)

Fe-0.5-MOF-808 postcatalysis Fe-0.5-MOF-808 precatalysis MOF-808 calculated Bragg positions

S20

Fig S7.6. X-ray powder diffraction patterns of prepared materials at different reaction time of Fe-impregnation.

Fig S7.7. X-ray powder diffraction patterns of prepared materials with different iron-precursors of Fe-impregnation.

5 10 15 20 25 30 35 40

Fe-0.5-MOF-808-16h

Fe-0.5-MOF-808-2h

Fe-0.5-MOF-808-1h

Fe-0.5-MOF-808-30min

Fe-0.5-MOF-808-10min

Inte

nsity

(a.u

.)

2θ (o)

Fe-0.5-MOF-808-2min

5 10 15 20 25 30 35 40

MOF-808 Simulated

Fe(NO3)3-MOF-808

Fe(acac)3-MOF-808

Fe(ox)2-MOF-808

FeCl3-MOF-808

Fe(Ac)2-MOF-808

Inte

nsity

(a.u

.)

2θ (o)

FeCl2-MOF-808

S21

S8 Pair Distribution Function Synchrotron X‐ray total scattering data suitable for PDF analyses were collected at the P02.1 beamline at PETRA IIII (Deutsches Elektronen-Synchrotron) using 60 keV (0.207 Å) X‐rays. Samples were loaded in polyamide (kapton) capillaries (0.8 mm Ø) and sealed using epoxy. Data were collected using an amorphous silicon–based PerkinElmer area detector. Geometric corrections and reduction to 1D data used DAWN Science software.4 PDFs were obtained from the data within PDFgetX3 within xPDFsuite to a Qmax = 22 Å−1.5 Differential PDFs were obtained by subtraction of a reference PDF (MOF-808 pristine) from Fe-MOF-808 in real space using Microsoft Excel. The control was multiplied by an appropriate constant to ensure that the scale of each PDF was the same. Interatomic distances were quantified by fitting Gaussian functions using Fityk software.6 Preliminary models of iron clusters were performed in Materials Studio 2017.7 PDFs for structural models of iron clusters were simulated within PDFgui.8

Fig. S8.1. (Up) PDF patterns for the different materials Fe-1.2-MOF-808, Fe-0.5-MOF-808 and MOF-808 pristine. (Down) Differential patterns for Fe-1.2-MOF-808 and Fe-0.5-MOF-808.

S22

Fig. S8.2. Zoom of figure S8.1. (Up) PDF patterns for the different materials Fe-1.2-MOF-808, Fe-0.5-MOF-808 and MOF-808 pristine. (Down) Differential patterns for Fe-1.2-MOF-808 and Fe-0.5-MOF-808.

S23

Deconvolution of experimental d-PDF data:

Multipeak Fit report for Fe-0.5-MOF-808

Total fitted points: 344

Baseline Type: Constant

Table S8.1. Fit report summarize for differential PDF of Fe-1.2-MOF-808.

Peak 1 2 3 4 5 6 Type Gaussian Gaussian Gaussian Gaussian Gaussian Gaussian Center 1.8 2.01 2.36 2.98 3.33 3.69 Height 0.086642 0.198713 0.169732 0.207713 0.374096 0.128259 Area 0.0212123 0.0655723 0.0289079 0.0442207 0.103535 0.0354971 FWHM 0.23 0.31 0.16 0.22 0.26 0.26 Assignment Fe-O Fe-O Fe-Cl Fe···Fe Fe···Fe Fe···Zr

Fig. S8.3. Representative curve fitting for the d-PDF of Fe-0.5-MOF-808. Experimental data (black circles), fit trace (red). Peaks were fit as Gaussian functions (blue).

S24

Multipeak Fit report for dPDF Fe-1.2-MOF-808



Table S8.2. Fit report summarize for differential PDF of Fe-1.2-MOF-808.

Peak 1 2 3 4 5 Type Gaussian Gaussian Gaussian Gaussian Gaussian Center 1.97 2.37 3.00 3.33 3.73 Height 0.13994 0.0896762 0.159035 0.286742 0.102805 Area 0.0327715 0.0152732 0.0423219 0.0702023 0.0207922 FWHM 0.22 0.16 0.25 0.23 0.19 Assignment Fe-O Fe-Cl Fe···Fe Fe···Fe Fe···Zr

Fig. S8.4. Representative curve fitting for the d-PDF of Fe-1.2-MOF-808. Experimental data (black circles), fit trace (red). Peaks were fit as Gaussian functions (blue).

Peak located at 2.7 Å is a remain of the Fourier Transform.

S25

Deconvolution of simulated iron-oxo clusters data:

Multipeak Fit report for an iron cluster composed by two metallic centers with tetrahedral coordination environmental.



Table S8.3. Fit report summarize for model 1.

Peak 1 2 3 4 5 Type Gaussian Gaussian Gaussian Gaussian Gaussian Center 2.02 2.34 3.04 3.37 3.94 Height 2.48084 1.82894 1.4545 0.526697 0.457954 Area 0.58097 0.564585 0.402549 0.1602589 0.1316 FWHM 0.22 0.29 0.26 0.29 0.27 Assignment Fe-O Fe-Cl Fe···Fe - -

Fig. S8.5. Representative curve fitting for the calculated PDF of od the iron-oxo cluster depicted in the figure inset (red-oxygen, green-chlorine and orange-iron). Calculated data (black circles), fit trace (red). Peaks were fit as Gaussian functions (blue).

S26

Multipeak Fit report for an iron cluster composed by two metallic centers with octahedral coordination environmental.




Peak 1 2 3 4 5 Type Gaussian Gaussian Gaussian Gaussian Gaussian Center 2.09 2.34 3.01 3.75 4.20 Height 4.21831 1.57732 3.32179 1.18367 0.446187 Area 1.05478 0.37878 1.10596 0.39272 0.153259 FWHM 0.23 0.22 0.31 0.31 0.32 Assignment Fe-O Fe-Cl Fe···Fe - -


S27

Multipeak Fit report for an iron cluster composed by three metallic centers with tetrahedral coordination environmental.




Peak 1 2 3 4 5 6 Type Gaussian Gaussian Gaussian Gaussian Gaussian Gaussian Center 1.99 2.22 3.02 3.66 3.97 4.41 Height 3.37455 1.70968 2.49822 0.352431 0.94250 0.34268 Area 0.79026 0.054597 0.71800 0.071279 0.371206 0.11308 FWHM 0.22 0.30 0.27 0.19 0.37 0.31 Assignment Fe-O Fe-Cl Fe···Fe - - -


S28

Fig. S8.8. Representative calculated curve for the model A (iron cluster as a bridge between two Zr-nodes). Only the first coordination sphere around the Fe-oxo dimer is calculated.

Fig. S8.9. Representative calculated curve for the model B (iron cluster is linked in a terminal position to a Zr-node). Only the first coordination sphere around the Fe-oxo dimer is calculated.

S29

The Fe-oxo dimers bridging two neighnouring Zr-nodes is the main specie according to the simulated PDF of the model in comparison with the dPDF of Fe-0.5-MOF-808 (Figure S8.10). Due to the possible presence of both models, the mixture of both was also calculated.

Fig. S8.10. Representative calculated curve for the mixture of both models (A = Bridge, B = Term). The mixtures were depicted as lines with: 90% A, 10% B (cyan); 80% A, 20% B (turquoise); 70% A, 30% B (dark blue); 60% A, 40% B (violet); 50% A, 50%B (pink). dPDF of Fe-0.5-MOF-808 is depicted down (blue).

S30

Fig. S8.7. PDF patterns for pre-catalytic and post-catalytic Fe-0.5-MOF-808. Catalytic conditions are detailed in section S11.

S31

S9 X-Ray Absorption Spectroscopy Transmission and fluorescence geometry XAS measurements were performed at CLAESS (BL22) at the ALBA synchrotron. Fe K-edge XAS spectra were acquired from 7100 to 8100 eV, resulting in a k-range up to 10 Å–1. The data analysis and background removal were performed within ATHENA and ARTEMIS.9 Fe3O4, Fe(acac)3 and FeCp2 were employed as references.

Fig. S9.1. XANES of Fe loaded materials and first derivate analysis (right). Fe-0.5-MOF-808 (black), Fe-1.2-MOF-808 (red).

S32

S10 Computional details S10.1 Computational methodology Density Functional Theory (DFT) calculations were performed in order to elucidate the possible conformations of low-loading Fe-MOF-808. We modelled the structural and energetic properties of several binuclear iron-oxo & iron-hydroxo clusters deposited on the nodes of the MOF-808. As a starting model for the pristine MOF-808, we choose a molecular cluster that is composed by two Zr6O8 octahedra bridged by 2 ligands. The coordinates of the starting model are carved from the experimentally determined crystal structure. The benzene-tricarboxylate ligands, which are bridging the two Zr6O8 octahedra, are cropped to benzene-dicarboxylate. The remaining four ligands are also cropped to formate. Based on the experimental observations, six (6) formate molecules are further added as capping ligands. For charge balancing, four (4) protons have to be added to the μ3-O atoms of each Zr6O8 octahedron. The model is shown in Figure S10.1.

Figure S10.1: Models used in the calculations. (Top) MOF-808 model, where the frozen atoms during the geometry optimizations are shown in dark grey spheres. M1F, M2F and M4F are the MOF models after removing 1, 2 and 4 formate ligands respectively and adding a hydroxo and a water ligand. M2Fs is the MOF model after removing 2 formate ligands from the same Zr6O8 node.

During all geometry optimizations, some restrictions have to be applied in order to mimic the crystal environment. Two (2) of the zirconium atoms at the edges of the molecular cluster, and the twenty-four (24) oxygen atoms that belong to the ligands are kept frozen. These atoms are shown in dark grey colour in Figure S10.1.

As a next step, one, two or four formate capping ligands are removed, with each one being replaced by a hydroxo and a water molecule, giving rise to the models denoted as M1F, M2F, and M4F, respectively. In the case of replacing two formate capping ligands,

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two possibilities exist: i) replacement of two ligands in the same octahedron (M2Fs), or ii) replacement of one ligand in each octahedron (M2F). These models are also shown in Figure S10.1.

Subsequently, we investigated the structural and energetic characteristics of the deposition of a Fe2Cl2(μ2-O)x(OH)y(H2O)z cluster on the nodes of the MOF-808 model. We chose to study the Fe2Cl2(μ2-O)x(OH)y(H2O)z cluster based on the experimental observations for the low-loading Fe-MOF-808. To reduce the complexity of the system, due to many possible combinations of Fe(II,III)/Fe(II,III) pairs and the different ways to couple the unpaired electrons of the Fe(II)/Fe(III) atoms, we decided to study only the deposition of the high-spin ferromagnetically coupled Fe(III)-Fe(III) pair with a spin multiplicity of 11. The M06-L10 method is employed in combination with the 6-31G(d,p) basis set for the C, H, O, Cl and Fe atoms and the SDD for the Zr atoms (along with the appropriate ECPs). Harmonic frequency analysis confirmed structures as minima or saddle points on the potential energy surface. Free energies are calculated based on the harmonic approximation assuming temperatures of 298 K and gas pressures of 1 Atm. All frequencies below 50 cm–1 were replaced by 50 cm–1 when computing the free energy contribution from the vibrational partition functions. All calculations are performed with the Gaussian 16 software package.11

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S10.2 Results Due to the rich proton topology of the MOF-808, several possibilities exist, how a Fe2Cl2(μ2-O)x(OH)y(H2O)z cluster can be deposited on the nodes of the MOF after reaction of the iron-precursor with the available protons from the μ3-ΟΗ, terminal-OH and terminal-Aqua ligands. For example, the iron-precursors may react with: i) the terminal-OH and terminal-Aqua protons giving rise to the conformation A (or Bridging site), ii) a terminal-Aqua proton giving rise to conformation B (or Terminal site), and iii) the μ3-ΟΗ and terminal-Aqua protons creating conformation C (or μ3 site). The lowest energy conformers are presented in Figure SX. For all three conformation, we investigated the deposition of the Fe2Cl2(μ2-O)x(OH)y(H2O)z cluster on all possible models: M1F, M2F, M2Fs , and M4F. Furthermore, we have also calculated the free energies of formation of the different conformations by considering a reaction between the MOF-808 model with the FeCl3 (as iron-precursor) and water molecules, which generate the various Fe-MOF-808 conformers and liberate HCl. Detailed information of the computed structures, including formation free energies and Fe-Fe distances, are listed in Table S10.1.

Conformation A: In the conformation A, the binuclear iron cluster can be deposited either as Fe2Cl2(μ2-O)2 or as Fe2Cl2(μ2-OH)2. Depending on the proton topology of the node, several more possibilities exist. They have been calculated and are shown in Figure S10.2.

Figure S10.2: Most stable structures of binuclear iron clusters deposited on the Bridging site (Conformation A) of models M2F and M4F. Their relative free energies in kJ/mole are also shown.

In all calculations, the deposition of a Fe2Cl2(μ2-OH)2 cluster is more stable than the Fe2Cl2(μ2-O)2. Among all possible configurations, the A2F-1 and A2F-3 corresponding to the model M2F and the A4F-1 and A4F-3 from the model M4F are the most stable structures with the most negative formation free energies. They possess Fe…Fe distances between 3.12 and 3.24 Å.

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Conformation B: Deposition on the Terminal position is possible after reaction of the iron precursor with the protons from the Aqua ligands. The most negative formation free energies have been calculated for the B1F models at ~-165 kJ/mol, whereas they are slightly higher for the B2Fs models with values between -92 and -147 kJ/mol. The results show that the binuclear iron cluster prefers to get the conformation -Fe2Cl2(μ-OH)2(t-OH) for the B1F models with Fe…Fe distances at 3.07 Å.

Figure S10.3: Most stable structures of binuclear iron clusters deposited on the Terminal site of the Zr6O8 node (Conformation B) of models M1F and M2Fs. Their relative free energies in kJ/mole are also shown.

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Conformation C: Deposition on the μ3-O position is possible after reaction of the μ3-OH, the t-OH and t-OH2 protons with the iron precursor. Several structures have been considered and are presented in Figure SX4. In this case, the conformers have the least negative formation free energies among the conformers A and B. The reaction free energies range between -24 and -73 kJ/mol, while the Fe-Fe distances are shorter especially for the C1F models. One of the iron atoms is always bonded to the μ3-O and is in close proximity to one zirconium atom. One of the chlorine ligands gets a μ2 configuration between the iron and the zirconium atom from the node. For the C2Fs models, slightly more negative formation free energies are calculated. The models C2Fs-1 and C2Fs-2 possess Fe…Fe distances at ~2.95 Å.

Figure S10.4: Most stable structures of binuclear iron clusters deposited on the μ3-O site of the Zr6O8 node (Conformation C) of models M1F and M2Fs. Their relative free energies in kJ/mole are also shown.

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Table S10.1: Summary of results for the different possible conformations of the Fe2Cl2(μ2-O)x(OH)y(H2O)z cluster on the various models of the MOF-808 nodes. The iron-topology is also given along with the proton topology of the nodes. The relative free energies (ΔGrel in kJ/mol) are given for the different conformers for the same stoichiometry. The formation free energies (ΔGform in kJ/mol) calculated from the reaction: MOF-808 + 2FeCl3 +xH2O Fe-MOF-808 + 4HCl, are also given along with the Fe-Fe distance (in Å)

MOF-model Name Iron-topology Proton-topology

on the node ΔGrel

(kJ/mol) ΔGform

(kJ/mol) d(Fe-Fe)

(Å) A - Bridging M2F A2F-1 -Fe2Cl2(μ-OH)2- (μ3-ΟΗ), (t-OH)2 +32.9 -159.0 3.14 A2F-2 -Fe2Cl2(μ-O)2- (μ3-ΟΗ), (t-OH),

(t-OH2) +107.5 -84.4 2.7

A2F-3 -Fe2Cl2(μ-OH)2- (μ3-ΟΗ), (t-O), (t-OH2)

0.0 -191.9 3.12

A2F-4 -Fe2Cl2(μ-O)2- (μ3-ΟΗ), (t-OH), (t-OH2)

+184.7 -7.1 2.67

M4F A4F-1 -Fe2Cl2(μ-OH)2- (μ3-ΟΗ), (t-OH)3, (t-OH2)

0.0 -221.9 3.20

A4F-2 -Fe2Cl2(μ-O)2- (μ3-ΟΗ), (t-OH)2, (t-OH2)2

+146.7 -75.1 2.74

A4F-3 -Fe2Cl2(μ-OH)2- (μ3-ΟΗ), (t-O), (t-OH), (t-OH2)2

+32.4 -189.5 3.24

B - Terminal M1F B1F-1 -Fe2Cl2(μ-OH)2(t-OH) (μ3-ΟΗ), (t-OH)2 0.0 -165.7 3.07 B1F-2 -Fe2Cl2(μ-OH)2(t-OH) (μ3-ΟΗ), (t-OH)2 +0.4 -165.2 3.08 M2Fs B2Fs-1 -Fe2Cl2(μ-OH)2 (μ3-ΟΗ), (t-OH)4 0.0 -146.8 2.87 B2Fs-2 -Fe2Cl2(μ-OH)(μ-O) (μ3-ΟΗ), (t-OH)3,

(t-OH2) +46.7 -100.1 2.71

B2Fs-3 -Fe2Cl2(μ-O)2 (μ3-ΟΗ), (t-OH)2, (t-OH2)2

+55.2 -91.6 2.74

C – μ3 M1F C1F-1 -Fe2Cl2(μ-OH)(t-OH) (μ3-Ο), (t-O) +3.4 -51.4 2.86 C1F-2 -Fe2Cl2(μ-O)2 (μ3-Ο), (t-O) +30.5 -24.3 2.84 C1F-3 -Fe2Cl2(μ-O)2(t-H2O) (μ3-Ο), (t-O) 0.0 -54.7 2.73 M2Fs C2Fs-1 -Fe2Cl(μ-Cl)(μ-OH)(t-OH) (μ3-Ο), (t-OH)3 +8.8 -64.0 3.00 C2Fs-2 -Fe2Cl(μ-Cl)(μ-OH)(t-OH) (μ3-Ο), (t-O), (t-

OH), (t-OH2) 0.0 -72.8 2.95

C2Fs-3 -Fe2Cl(μ-Cl)(μ-OH)(t-H2O) μ3-Ο), (t-O), (t-OH), (t-OH2)

+2.5 -70.3 2.74

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S11 Capture and catalytic test BPA remediation experiments were carried out at natural pH (pH ∼5.75) in a 10 mL glass sealed vial at 30 °C.

BPA uptake model. MOF-808 (5 mg) was added to a stirred solution of BPA (5 mL, 0.00219 mmol, 100 ppm water:ethanol 95:5). The suspension was stirred at RT for 1h. The suspension was filtered through a 0.22 µm syringe filter. The supernatant was analyzed by HPLC-UV, to calculate the sorption of BPA. The solid was washed twice with 2.5 mL of EtOH, and the filtered through a 0.22 µm syringe filter. The supernatant was analyzed using an Agilent HP1260 Infinity HPLC equipped with a C18 column and a UV absorbance detector. A mobile phase of methanol-water (595) at a flow rate of 1 mL/min and an injection volume of 20 μL was used for this experiment and the analysis wavelengths were 254, 250 and 210 nm, and the detection limit of BPA in this study was about 0.01 ppm, according to calibration curve (Figure S11.X).

BPA degradation in water. Fe-MOF-808 (0.04% Fe mmol) was added to a stirred solution of BPA (5 mL, 0.44 mM, 100 ppm water:ethanol 95:5) and hydrogen peroxide (5.55 mg, 0.033 mmol, 30% in water). The beginning of the reaction (t = 0) is determined to be when the catalyst and H2O2 are added. The suspension was filtered through a 0.22 µm syringe filter and quenched with sodium thiosulfate. The solid was washed twice with 2.5 mL of EtOH, and the filtered through a 0.22 µm syringe filter and quenched with sodium thiosulfate. The supernatant was analyzed using an Agilent HP1260 Infinity HPLC equipped with a C18 column and a UV absorbance detector. A mobile phase of methanol-water (595) at a flow rate of 1 mL/min and an injection volume of 20 μL was used for this experiment and the analysis wavelengths were 254, 250 and 210 nm, and the detection limit of BPA in this study was about 0.1 ppm, according to calibration line (Figure S11.2).

The difference between the BPA removal, and the BPA released is the BPA degraded.

Blanks experiments for the study of degradation were performed in presence of H2O2 and MOF-808 pristine. The amount of BPA degraded was depreciable.

60

0

25

50

18%

40%

Degradation Yield (%)

Capt

ure

Yiel

d (%

)

Reaction time (min)

Fe-0.5-MOF-808 Fe-1.2-MOF-808

30 600

25

50

26%

8%11%

Reaction time (min)

49%

Fig. S11.1. Removal test of 1 mg / 1 mL 100 ppm BPA after 1 h (left), and catalytic degradation, 0.04% molar in Fe over 5 mL BPA 100 ppm (right)

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Fig. S11.2. Calibration line for bisphenol-A in methanol as solvent.

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