This is the accepted version of the article: Broto-Ribas A., Vignatti C., Jimenez-Almarza A., Luis-Barrera J., Dolatkhah Z., Gándara F., Imaz I., Mas-Ballesté R., Alemán J., Maspoch D.. Heterogeneous catalysts with programmable topologies generated by reticulation of organocatalysts into metal-organic frameworks: The case of squaramide. Nano Research, (2020). . : - . 10.1007/s12274-020-2779-8. Available at: https://dx.doi.org/10.1007/s12274-020-2779-8 Heterogeneous Catalysts with Programmable Topologies Generated by Reticulation of Organocatalysts into Metal-Organic Frameworks: the Case of Squaramide Anna Broto-Ribas,†, Claudia Vignatti,,† Alicia Jimenez-Almarza,‡ Javier Luis-Barrera,§ Zahra Dolatkhah,‡ Felipe Gándara, ◊ Inhar Imaz,†,*, Rubén Mas‐Ballesté,§,#*, José Alemán‡,#*, and Daniel Maspoch†,⊥,* † Catalan Institute of Nanoscience and Nanotechnology (ICN2), Spain ‡ Universidad Autónoma de Madrid, Spain § Universidad Autónoma de Madrid, Spain ◊ Instituto de Ciencia de Materiales de Madrid (ICMM), Spain . # Institute for Advanced Research in Chemical Sciences (IAdChem), Spain A series of MOF-based catalysts with programmable topologies are ⊥ Institució Catalana de Recerca i Estudis Avançats generated by incorporating squaramide organocatalysts, using reticular (ICREA), Spain chemistry and exploiting MOF-structural data from Cambridge Structural  A. B.-R. and C. V. contributed equally. Database. Daniel Maspoch, http://www.nanoup.org/daniel-maspoch Heterogeneous Catalysts with Programmable Topologies Generated by Reticulation of Organocatalysts into Metal-Organic Frameworks: the Case of Squaramide Anna Broto-Ribas,†, Claudia Vignatti,,† Alicia Jimenez-Almarza,‡ Javier Luis-Barrera,§ Zahra Dolatkhah,‡ Felipe Gándara, ◊ Inhar Imaz,†,* (), Rubén Mas‐Ballesté,§,#* (), José Alemán‡,#* (), and Daniel Maspoch†,⊥,*() † Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Barcelona, Spain ‡ Inorganic Chemistry Department, Módulo 7, Universidad Autónoma de Madrid, Madrid, Spain § Organic Chemistry Department, Módulo 1, Universidad Autónoma de Madrid, Madrid, Spain ◊ Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Calle Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain # Institute for Advanced Research in Chemical Sciences (IAdChem), Campus Universidad Autónoma de Madrid, Madrid, Spain ⊥ Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain  A. B.-R. and C. V. contributed equally. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018 Received: day month year / Revised: day month year / Accepted: day month year (automatically inserted by the publisher) ABSTRACT A well-established strategy to synthesize heterogeneous, metal-organic framework (MOF) catalysts that exhibit nanoconfinement effects, and specific pores with highly-localized catalytic sites, is to use organic linkers containing organocatalytic centers. Here, we report that by combining this linker approach with reticular chemistry, and exploiting 3D MOF-structural data from the Cambridge Structural Database, we have designed four heterogeneous MOF-based catalysts for standard organic transformations. These programmable MOFs are isoreticular versions of pcu-IRMOF-16, fcu-UiO-68 and pillared-pcu-SNU-8X, the three most common topologies of MOFs built from the organic linker p,p’-terphenyldicarboxylic acid (tpdc). To synthesize the four squaramide-based MOFs, we designed and synthesized a linker, 3,4‐dioxocyclobut‐1‐ene‐1,2‐diyl)bis(azanedyil)‐p‐dibenzoic acid) (Sq_tpdc), which is identical in directionality and length to tpdc but which contains organocatalytic squaramide centers. Here, squaramides were chosen because their immobilization into a framework enhances its reactivity and stability while avoiding any self-quenching phenomena. Therefore, the four MOFs share the same organocatalytic squaramide moiety, but confine it within distinct pore environments. We then evaluated these MOFs as heterogeneous H-bonding catalysts in organic transformations: a Friedel-Crafts alkylation and an epoxide ring-opening. Some of them exhibited good performance in both reactions but all showed distinct catalytic profiles that r eflect their structural differences. KEYWORDS Reticular Chemistry, Metal-Organic Frameworks, H-bond catalysis, Squaramide, Friedel-Crafts, Epoxide ring-opening 1 Introduction can benefit from reticular chemistry, which can facilitate rational Metal-organic frameworks (MOFs) are crystalline porous design of MOF-based catalysts with pre-defined framework compounds based on metal ions or clusters connected by organic topologies and pores. Indeed, as Prof. O. M. Yaghi has affirmed, an ligands, whose topology, pore size and/or chemical composition important feature of reticular chemistry is that “for a given can be modulated to achieve functionalities such as catalysis or framework, the constituents can also be chemically functionalized adsorption. Those MOFs that exhibit confinement effects, and either pre- or post-synthetically, while maintaining the framework’s pores functionalized with specific and highly-localized catalytic connectivity, to produce functionalized pores.” [29], [30] In our sites, are a potentially limitless source of new heterogeneous field, this idea translates to the ability to modify the organic linker catalysts. Most reported MOF-based catalysts have been designed of an existing MOF by inserting an organocatalytic center, without around metallic catalytic sites. In these, coordinatively unsaturated modifying the linker length or topology, thus enabling synthesis of metal sites form the MOF structure itself, or metal the corresponding isoreticular MOF structure containing the ions/complexes/clusters/nanoparticles are encapsulated within the desired center. MOF pores or connected to the MOF organic linkers.[1]–[5] Telfer et al. were among the first to prepare a MOF-based catalyst An alternative, less-explored approach to synthesizing by this organocatalytic-center approach: an isoreticular MOF-5 with heterogeneous MOF catalysts is to incorporate organocatalytic organocatalytic N-Boc-L-proline moieties that, after removing the centers within MOFs.[6],[7] This can be done via post-synthetic thermolabile group, catalyzed aldol reactions.[26] Also, Kapteijn et modifications of the organic linkers in existing MOFs[8]–[12], or al. reported the isoreticular NH2-MIL-101, showing high activity in during MOF synthesis, by using organic linkers that contain these base-catalyzed Knoevenagel condensations.[22] Soon afterwards, organocatalytic centers.[13]–[28]The latter approach in particular Hupp et al. similarly introduced H-bonding organocatalytic centers Address correspondence to First A. Firstauthor, email1; Third C. Thirdauthor, email2 2 (e.g. urea and squaramide) into programmable MOFs.[23],[24],[25] Zinc(II) nitrate hexahydrate, zirconium(IV) oxychloride, 4,4’- For example, they synthesized two isoreticular UiO-67 catalysts bipyridyne and 2,5-bispyridylethane, dimethyl squarate, 4- from biphenyl-4,4’-dicarboxylate linkers functionalized with aminobenzoic acid, trimethylamine, anilines were purchased from pendant urea and squaramide groups.[23], [25] This type of commercial sources and used as received without further strategy has since been extended to many other isoreticular MOF- purification. 4,4'-(3,4-dioxocyclobut-1-ene-1,2- based catalysts containing urea moieties. [19]–[21], [23], [24] diyl)bis(azanediyl))dibenzene used as molecular catalyst (MC) was synthesized following a described procedure in the literature.[27] NMR spectra were acquired on a Bruker Avance 300 MHz spectrometer, running at 300 MHz (1H) or 75 MHz (13C). In some cases (noted), they were acquired on a Bruker Avance 250 MHz spectrometer. Chemical shifts (δ) are reported in ppm relative to residual solvent signals (CDCl3: 7.26 ppm for 1H-NMR and 77.16 ppm for 13C-NMR; DMSO-d6: 2.50 ppm for 1H-NMR and 39.52 ppm for 13C-NMR). Coupling constants are reported in Hertz. The following abbreviations are used to describe peak patterns: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), bs (broad singlet). Different methods were used for measuring the exact mass (indicated for each case). MS (ESI) (Electrospray mass spectroscopy) spectra were acquired with an Agilent Technologies 6120 Quadrupole LC/MS. MS (EI) (Electron Ionization Mass Spectroscopy) spectra were acquired with an Agilent Technologies 5977B MSD. For both techniques, MassWorks v. 4.0.0.0 (Cerno Bioscience) was used for the formula identification. MassWorks is MS-calibration software that calibrates for isotope profile as well as for mass accuracy, enabling highly accurate comparisons between calibrated and theoretical spectra. MS (TOF-ESI) (Electrospray Mass Figure 1. The reticular chemistry-based strategy for rational design of MOF- Spectroscopy with Time-of-Flight detector) spectra were acquired based catalysts containing organocatalytic centers. CSD: Cambridge Structural with microTOF-Q Bruker Daltonics spectrometer. Optical rotation Database. was recorded in cells with 10-cm path-length; the solvents and concentrations (in g/100 mL) are indicated in each case. Flash Herein we report the rational synthesis of four heterogeneous, chromatography was performed on silica-gel columns (40 μm to 63 MOF-based catalysts with programmable topologies, based on use μm; pore size: 60 Å). Kinetics were studied by monitored reaction of reticular chemistry and on MOF 3D-structural information from progress by gas chromatography using a 7820A GC System (Agilent the Cambridge Structural Database.[31] Briefly, we confined the Technologies) equipped with a Flame Ionization Detector (FID). same squaramide organocatalytic center into different MOFs that Elemental analyses were obtained on a EA1108 micro-analyzer exhibit distinct nanoscale-pore environments. A squaramide was (CarboErba). Volumetric N2 adsorption–desorption isotherms were chosen as the test case organocatalyst because it is known that its collected at 77 K using an ASAP2020 HD (Micromeritics). immobilization into a framework enhances its reactivity and 2.2. X-Ray Diffraction. stability while avoiding any self-quenching phenomena due to their Composition of all bulk materials was confirmed through X-Ray tendency to self-aggregate in solution.[6],[32] The MOFs are powder diffraction (XRPD) measurements were collected on an isoreticular versions of pcu-IRMOF-16, fcu-UiO-68 and pillared- X’Pert PRO MPD analytical diffractometer (Panalytical) at 45 kV and pcu-SNU-8X, the three most common topologies of MOFs built 40 mA using Cu Kα radiation (λ= 1.5419 Å) and compared with from the organic linker p,p’-terphenyldicarboxylic acid (tpdc). Our single-crystal simulated patterns. Single-Crystal X-Ray Diffraction four-step strategy (Figure 1) entailed the design and synthesis of the (SCXRD) data on Sq_IRMOF-16, Sq_UiO-68, Sq_SNU-8X and linker, 3,4‐dioxocyclobut‐1‐ene‐1,2‐diyl)bis(azanedyil)‐p‐dibenzoic Sq_bptMOF were collected at 100(2) K in the BL13-XALOC acid) (Sq_tpdc),[27] which is identical in directionality and length to beamline[33] at the ALBA synchrotron, on a single-axis goniometer tpdc but which contains organocatalytic squaramide centers. We with a Pilatus 6M detector using a monochromatic X-ray beam (λ = evaluated the four MOF-based catalysts for H-bonding catalysis in a 0.82656 Å). Sq_SNU-8X and Sq_bptMOF were also collected at representative Friedel-Crafts alkylation and a representative 293(2) K. The data frames were integrated and scaled using XDS epoxide ring-opening. Some of these MOFs exhibited good software.[34] Absorption correction was not applied. All structures performance in both reactions but all showed distinct catalytic were solved by direct methods and subsequently refined by profiles that reflect their structural differences. correction of F2 against all reflections, using SHELXT2013 and SHELXL2013 within the WinGX package and OLEX2 software.[35][36] The framework atoms were located and refined. For both Sq_IRMOF-16 and Sq_UiO-68, the atoms belonging to the squaramide units were refined using rigid body constrains, and with partial occupancies, due to the disorder that they exhibit. Residual electron density was found inside the pores, likely corresponding to 2. Experimental presence of disorder molecules. In all structures, attempts to 2.1 Materials and methods adequately model the disordered molecules were unsatisfactory; 3 therefore, the PLATON/SQUEEZE routine was applied to mask out dissolved in 4.8 mL DMF. The mixture was placed in a 10-mL the disordered electron density.[37] Erlenmeyer flask, which was covered with a septum, and then 2.3. Synthesis of 4-((2-methoxy-3,4-dioxocyclobut-1-en-1- heated to 85 ºC for 5 days. This afforded orange crystals (0.013 g; yl)amino)benzoic acid. 0.013 mmol, 45% yield). FT-IR (ATR; cm-1, selected bands): 3200 A white suspension of dimethyl squarate (1.00 g, 7.00 mmol) and 4- (OH), 1787, 1703, 1644 (C=O from carboxylate), 1602, 1543, 1493, aminobenzoic acid (0.960 g, 7.00 mmol) in 20 mL of dry MeOH was 1440, 1241, 1177, 1102, 775. Anal. Calcd for Zn2C54H54N8O18: C, stirred 24 hours at room temperature. The resulting yellow 52.57; H, 4.41; N, 9.08, found: C, 52.00; H, 4.16; N, 9.20. suspension was filtered, washed with MeOH and Et2O, and then 2.9. Catalysis experiments. dried under vacuum to afford the desired pure compound 4-((2- A 0.005 mmol-(squaramide equivalent) aliquot of a single, dried methoxy-3,4-dioxocyclobut-1-en-1-yl)amino)benzoic acid (1.30 g, MOF-based catalyst (2.8 mg of Sq_IRMOF-16; 2.9 mg of Sq_SNU- 5.26 mmol, 75% yield). 1H-NMR (300 MHz, DMSO-d6): δ 12.71 (bs, 8X; 2.9 mg of Sq_BptMOF; or 2.4 mg of Sq_UiO-68), 0.1 mmol (12.3 1H), 10.96 (s, 1H), 7.94 – 7.86 (m, 2H), 7.50 – 7.40 (m, 2H), 4.40 (s, mg) of p-methoxyaniline and a stirring bar were transferred to a 3H). 13C-NMR (75 MHz, DMSO-d6): δ 187.6, 184.4, 179.5, 169.1, septum-sealed vial, which was flushed with N2 for 15 minutes. Note 166.8, 142.0, 130.6, 125.7, 118.7, 60.7. that Sq_SNU-8X, Sq_BptMOF, and Sq_UiO-68 were incubated in 2.4. Synthesis of 4,4'-((3,4-dioxocyclobut-1-ene-1,2- methanol for 72 hours before use. Then, 200 μL of ethyl epoxide diyl)bis(azanediyl))dibenzoic acid (Sq_tpdc). was added to the mixture. The mixture was heated to 60 °C and A mixture of 4-((2-methoxy-3,4-dioxocyclobut-1-en-1- stirred for 8 hours. At different time-points (1h, 2h, 4h, 6h and 8h), yl)amino)benzoic acid (0.90 g, 3.60 mmol), 4-aminobenzoic acid b a 20-μL aliquot of the reaction mixture was removed, and then (0.497 g, 3.60 mmol) and Et3N (0.503 mL, 3.60 mmol) in 18 mL of diluted with 500 μL of a 0.005 M solution of 2-methylnaphthalene dry CH3CN in a sealed tube was heated at 80 ºC for 24 hours. The (gas chromatography standard) in toluene. The resulting sample resulting suspension was concentrated down to ca. 9 mL. Then, H2O was then analyzed by gas chromatography with FID. (20 mL) was added, and the pH was adjusted to 1 (conc. HCl). The For the Friedel-Craft reaction, a 0.01 mmol-aliquot of a single, solid was filtered and washed thoroughly with H2O until neutral pH, dried MOF-based catalyst (5.6 mg of Sq_IRMOF-16; 4.9 mg of Sq- washed with Et2O and finally, and dried under vacuum to afford UiO-68; 5.7 mg of Sq_SNU-8X; or 5.8 mg of Sq_bptMOF), 0.15 pure squaramide Sq_tpdc (1.01 g, 2.87 mmol, 80% yield). 1H-NMR mmol of indole, 0.10 mmol of -nitrostyrene and a stirring bar were (250 MHz, DMSO-d6): δ 12.72 (bs, 2H), 10.31 (bs, 2H), 7.94 (d, J = transferred to a septum-sealed vial. Then, 1 mL of toluene was 8.4 Hz, 4H), 7.57 (d, J = 8.4 Hz, 4H). 13CNMR (63 MHz, DMSO-d6): δ added to the mixture. The mixture was heated to 60˚C and stirred 182.0, 166.8, 165.9, 142.4, 130.9, 125.1, 118.0. MS (TOF-ESI-): for 3 days. At different time-points (4h, 7h, 24h, 48h and 72h), a Calculated for C18H11N2O6 - [M-H] -: 351.0623. Found: 351.0614. 100-μL aliquot of the reaction mixture was removed, and then 2.5. Synthesis of Sq_IRMOF-16. diluted with 500 μL of a 0.005 M solution of 2-methylnaphthalene Zn(NO3)2·6H2O (0.017 g, 0.057 mmol) and Sq_tpdc (0.020 g, 0.057 (gas chromatography standard) in toluene. The resulting sample mmol) were dissolved in 4.8 mL DMF and heated to 85 ºC for 7 days. was then analyzed by gas chromatography with FID. This afforded yellow cubic crystals (0.010 g; 0.0075 mmol, 53% yield), which were stored in DMF. FT-IR (ATR; cm-1): 1650 (C=O from 3. Results and Discussion. carboxylate) selected band. Anal. Calcd. for 3.1. Design, synthesis and analysis of the squaramide-based linker ([Zn4O(L1)3]·6H2O·4DMF; Zn4C66H70N10O29): C, 45.85; H, 4.08; N, We designed the linker Sq_tpdc by attaching two benzoic acid 8.10, found: C, 45.23; H, 3,97; N, 8.34 moieties to the NH groups of the squaramide (Figure 1), which we 2.6. Synthesis of the Sq_UiO-68. justified based on two factors. Firstly, we reasoned that the phenyl To a DMF solution (4 mL) of Sq_tpdc (20 mg, 0.057 mmol), rings would favor structural planarity and rigidity in the linker, while ZrOCl2·8H2O (18.31 mg, 0.057 mmol) were added 5 mL of a the two opposing carboxyl groups would enable construction of DMF/formic acid mixture (4:1 w/w). The mixture was heated at extended structures via metal ion coordination. Secondly, we 120 °C for 1 week. This afforded yellow crystals, which were filtered, sought to exploit the para position of squaramide groups relative washed with DMF and MeOH, and then, air-dried to give Sq_UiO- to the carboxyl groups, to maximize the acidity of the squaramide- 68 (22.3 mg; 0.008 mmol, 84 %). FT-IR (ATR; cm-1, selected bands): NH protons. Specifically, the electron-withdrawing nature of the 3167 (OH); 2927 (NH); 1793, 1647 (C=O from DMF); 1597 (C=O from carboxylic groups acts by resonance in the ortho and para positions, carboxylate). Anal. Calcd. for ([Zr6O4(OH)4(L1)6]; Zr6C108H64N12O44): C, thereby diminishing the electron density of the NH groups and 46.64; H, 2.32; N, 6.04, found: C, 47.12; H, 2,58; N, 7,00. increasing their acidity and, consequently, their ability to form 2.7. Synthesis of Sq_SNU-8X. hydrogen bonds (i.e. to catalyze H-bonding reactions). We further Zn(NO3)2·6H2O (0.017 g, 0.057 mmol), Sq_tpdc (0.020 g, 0.057 reasoned that since the squaramide ring is roughly equivalent in mmol) and 4,4’-bipyridine (0.009 g, 0.057 mmol) were dissolved in size to a phenyl ring, then the carboxylic groups of Sq_tpdc would 4.8 mL DMF. The mixture was placed in a 10-mL Erlenmeyer flask, be separated by a distance very close (14.6 Å) to that corresponding which was covered with a septum, and then heated to 85 ºC for 5 to three phenyl rings (14.4 Å). Accordingly, we considered that days. This afforded yellow crystals (0.016 g; 0.015 mmol, 53% yield). Sq_tpdc is roughly equivalent in both directionality (topology) and FT-IR (ATR; cm-1, selected bands): 3200 (OH), 1788, 1639, 1598 (C=O length to tpdc (Figure 1), a well-known dicarboxylate linker in MOF from carboxylate), 1558, 1488, 1367, 1240, 1180, 1100, 777, 636, synthesis.[38]–[40] Once we had designed Sq_tpdc, we synthesized 475. Anal. Calcd for Zn2C55H49N9O15: C, 54.74; H, 4.09; N, 10.45, it by a previously-reported, two-step method.[27] found: C, 54.30; H, 3.94; N, 10.60. 2.8. Synthesis of Sq_BptMOF. Zn(NO3)2·6H2O (0.017 g, 0.057 mmol), Sq_tpdc (0.020 g, 0.057 mmol) and 1,2-Bis(4-pyridyl)ethane (0.010 g, 0.057 mmol) were 4 are bridged by four tpdc linkers that form 2D square grids, which are linked by pillared N-based linkers that form 3D structures with bidirectional 1D pores. These pores are delimited by four tpdc linkers and by two tpdc and two pillared linkers. In some cases, the pillared linkers are not truly perpendicular to the cluster-carboxylic layers and the pores are distorted prisms with rhombic windows. The fourteen remaining structures pertain to four MOF topology groups: eight (15%) of them comprise planes or chains of metal oxides [M = Co(II), Ni(II), Mn(II), Pb(II), Mg(II), Eu(III) and Cd(II)] linked by tpdc linkers; three (6%) of them exhibit a diamond topology;[60][61] two (4%) of them, acs topology;[62], [63] and one (2%) of them, bcu topology.[41] The diamond MOFs are formed by linkage of tetrahedral Zn(II) or Cd(II) ions through two tpdc and two N,N’-based linkers. The acs MOFs are formed through linkage of trigonal M3O (M= Fe(III) and In(III)] clusters by six tpdc linkers (two linkers per edge). Both structures show pores with the shape of a bipyramidal trigonal base (or a slightly distorted tetrahedron) delimited by six tpdc ligands with (slightly distorted) hexagonal windows of ca. 19 Å. The bcu MOF is formed by octahedral [Zr6O8(OH2)8] clusters coordinated by eight tpdc linkers that generate octahedral pores, which are delimited by eight tpdc linkers and exhibit rhombic windows of ca. 13 Å. 3.3. Selection, synthesis and structural analysis of isoreticular MOFs After the Cambridge Structural Database search, we selected the three most common MOF topologies and investigated the synthesis of the corresponding isoreticular MOFs incorporating the squaramide moieties. Here, we chose both pcu IRMOF-16 and fcu Figure 2. Representation of the crystal structures and cavities/pores of the MOFs UiO-68 frameworks (Figure 2a,b), as they are the only two and their corresponding isoreticular analogs (containing the squaramide rings): topologies reported using the non-functionalized tpdc linker and IRMOF-16 and Sq_IRMOF-16 (a); UiO-68 and Sq_UiO-68 (b); SNU-8X and are highly abundant, together corresponding to 41% of all reported Sq_SNU-8X (c); and OZASUF and Sq-bptMOF (d). 3D structures. We also chose pillared-pcu MOFs (Figure 2c,d), given their rich potential for obtaining myriad compositions by simply 3.2. Cambridge Structural Database search exchanging the pillared linker, and because they, too, are highly We searched the Cambridge Crystallographic Data Centre (CCDC) abundant (32% of all reported 3D structures). Here, we used bipy database (ConQuest v. 2.0.0, CCDC, Cambridge, UK) for 3D MOF and bpt linkers as the pillars, aiming to synthesize isoreticular structures built from tpdc. We found three structures, which we versions of SNU-8X (hereafter, Sq_SNU-8X) and OZASUF (hereafter, classified into two framework topologies: two of the structures Sq_bptMOF).[57] corresponded to IRMOF-16 MOF (pcu topology; one non- Characterization of the synthesized Sq_IRMOF-16 crystals by interpenetrated framework and one double-interpenetrated SCXRD confirmed that they retain the characteristic IRMOF-16 pcu framework (this latter also known as IRMOF-15); Figure 2a); and the topology (Figure 2a, Table S1). Thus, Sq_IRMOF-16 exhibits a 3D third one, to UiO-68 MOF (fcu topology; Figure 2b). The pcu- structure built from the connection of Zn4O clusters through six IRMOF-16 comprises Zn4O clusters linked to six tpdc linkers in an Sq_tpdc linkers to form the expected cubic cavities delimited by octahedral coordination. The non-interpenetrated IRMOF-16 twelve Sq_tpdc linkers and showing a pore opening of 14 Å (Figure contains cubic cavities delimited by twelve tpdc linkers, with a pore 1a; Brunauer-Emmett-Teller surface area SBET measured by N2 opening of ca. 15 Å.[40] The fcu-UiO-68 comprises octahedral sorption at 77 K of 784 m2/g; Figure S6). However, in this structure, [Zr6O4(OH)4] clusters linked by twelve tpdc linkers that create two the squaramide rings of the Sq_tdpc linkers exhibit high mobility types of spaces between them: octahedral cavities delimited by and positional disorder: they could only be partly positioned during twelve tpdc linkers, and tetrahedral cavities delimited by six tpdc the SCXRD refinement, even when it was performed at 100 K. linkers, both showing trigonal pore openings of ca. 10 Å. [38][39] Accordingly, their position and orientation were refined by To extend the number of potential 3D MOF structures that could employing rigid-body restraints, which revealed that Sq_IRMOF-16 be synthesized using Sq_tpdc, we also searched for 3D MOF has cubic cavities containing zero, four or eight squaramide rings structures built from tpdc functionalized at any of the four aromatic pointing towards them (Figure 2a). However, given the high positions of the central phenyl ring by groups that cannot mobility of the squaramide rings, each cubic cavity could also be coordinate to metal ions (i.e. to maintain the directionality of the statistically considered to contain three rings pointing towards it. parent tpdc). This revealed 53 additional 3D structures: fifteen Characterization of the synthesized Sq_UiO-68 crystals by SCXRD (28%) of which exhibit fcu topology and six (11%) of which, pcu confirmed formation of the desired analogous fcu UiO-68 structure topology.[41]–[54] Of the remaining 32 structures, eighteen (24%) (Figure 2b, Table S2).[14] According to the SCXRD refinement, the correspond to pillared-pcu MOFs (Figure 2c,d).[55]–[59] In these Sq_tpdc linker exhibits positional disorder, as evidenced by the latter MOFs, paddle-wheel M2 [M = Zn(II), Cu(II) and Cd(II)] clusters splitting in the position of some of the carbon atoms in the phenyl 5 rings. This implies different possible orientations of the squaramide of crystallinity after both catalytic reactions. The stability of units. Thus, the atoms in the squaramide moieties of the Sq_tpdc squaramide-based MOF was further corroborated by discarding the linkers were refined with the use of rigid body constrains and partial leaching of catalytic species into the reaction media. Such feature occupancies after being located in the density maps. Overall, was assessed by means of experiments consisting on filtering off Sq_UiO-68 exhibits a fcu topology in which [Zr6O4(OH)4] nodes are the catalytic material at intermediate stages of each reaction connected via 12 Sq_tpdc ligands forming a porous network (SBET = observing that product content did not evolve further after MOF 637 m2/g; Figure S8). This network shows octahedral cavities and removal. Crucially, when the molecular squaramide 4,4'-(3,4- tetrahedral cavities delimited by twelve and six Sq_tpdc linkers, dioxocyclobut-1-ene-1,2-diyl)bis(azanediyl))dibenzene was used respectively, and connected by windows of 7 Å. In these cavities, six alone as catalyst, both reactions barely progressed, likely due to its squaramide rings are pointing towards the octahedron cavities self‐aggregation and poor solubility. This result supported our (Figure 2b). original strategy of designing heterogeneous catalysts in which the Similarly to the previous examples, SCXRD of the synthesized squaramide rings are immobilized within MOFs. Sq_SNU-8X crystals revealed formation of the expected pillared We then studied the kinetics of a representative Friedel- MOF with pcu topology (Figure 2c, Table S3). The basic Sq_SNU-8X Crafts alkylation: reaction of indole (0.15 mmol) and β-nitrostyrene units are paddle-wheel Zn2 clusters, in which each Zn(II) ion exhibits (0.10 mmol) in the presence of the corresponding squaramide- square-pyramidal coordination geometry. The equatorial sites of based MOFs (0.005 mmol = 5 mol% [catalytic centers] relative to β- the pyramid are occupied by four oxygen atoms of the carboxylate nitrostyrene) at 60 ºC. Figure 3 is a plot of the kinetics for each groups of four Sq_tpdc linkers, whereas the last axial coordination squaramide-based MOF catalyst over 72 hours. The most active position is occupied by a nitrogen atom of the N-donor bipy linker. catalyst for this reaction was Sq_SNU-8X (yield: 85%) followed by The resulting paddle-wheel Zn2 clusters are connected through four Sq_UiO-68 and Sq-IRMOF-16 (yield for each: ca. 70%), and finally, Sq_tpdc linkers that form 2D square grids, which in turn are Sq_bptMOF (yield: 18%). We attributed the low performance of connected by bipy linkers that form 3D pcu nets, which are doubly Sq_bptMOF to the structural flexibility already observed by SCRXD interpenetrated. Note that the parent SNU-8X is also a doubly- at 293 K and XRPD (Figure S18). Note that structural flexibility is interpenetrated MOF. Interpenetrated Sq_SNU-8X possesses 1D commonly observed when flexible pillar ligands such as bpt, which channels of two sizes: 12 Å x 12 Å, delimited by four Sq_tpdc and have a high degree of rotation freedom due to the –CH2-CH2- chain running along the a-axis; and 8 Å x 12 Å, delimited by two Sq_tpdc between the pyridine fragments, are used to synthesize pillared pcu and two bipy linkers and running along the c-axis (Figure 2c). The MOFs.[57] This highly dynamic behavior impedes catalytic squaramide rings are parallel to the pores along the a-axis but point performance, as it decreases the pore size and therefore towards those along the c-axis. Based on these apparent voids and accessibility of the substrates to the active sites. free channels, the porosity of Sq_SNU-8X was evaluated by measuring its N2 sorption at 77 K, which gave an SBET value of 634 m2/g (Figure S10). We also prepared Sq_bptMOF by using the same conditions as for Sq_SNU-8X, except that instead of bipy, we used bpt. Interestingly, SCXRD revealed formation of a double- interpenetrated pillared pcu MOF (SBET = 789 m2/g, Table S4 and Figure S13) much like that in Sq_SNU-8X, as it similarly contained 1D channels of two sizes: 8 Å x 11 Å, delimited by two Sq_tpdc and two bipy linkers and running along the a-axis; and 12 Å x 11 Å, delimited by four Sq_tpdc linkers and running along the c-axis (Figure 2d). In this case, the squaramide rings point towards the pores along the a-axis but are parallel to those along the c-axis. Finally, as these type of pillared pcu MOFs (including the isoreticular SNU-8X and OZASUF)[57] tend to show structural flexibility upon solvent removal, we also solved the crystal structures of both Sq_SNU-8X and Sq_bptMOF at 293 K (Tables S5 and S6 and Figures S11 and S14). As expected, both frameworks showed to be flexible, with Sq_bptMOF exhibiting a decrease of its pore sizes (6.5 Å x 11 Å and 11.5 Å x 11 Å) at 293 K. Figure 3. Kinetic plots for the Friedel-Crafts reaction of indole and β-nitrostyrene 3.4. Evaluation of catalytic performance at 60 ºC, forming the alkylated product, in the presence of Sq_IRMOF-16 We hypothesized that synthesis of diverse heterogeneous catalysts (yellow), Sq_SNU-8X (orange), Sq_UiO-68 (blue) or Sq_bptMOF (grey). using our reticular approach, followed by catalytic screening of them in test reactions, would greatly augment the probability of finding high-performing catalysts for any desired chemistry. Thus, we evaluated our MOF-based catalysts in two archetypical, squaramide-catalyzed reactions: a representative Friedel-Crafts alkylation and a representative epoxide ring-opening. Importantly, XRPD performed during and after these two catalytic reactions confirmed the crystallinity and stability of squaramide-based MOFs (see S.I., Figure S15-S18); albeit Sq_bptMOF showed a certain loss 6 We next studied the kinetics of a representative epoxide ring- which is similar in length and directionality to Sq_tpdc. Sq_SNU-8X opening: reaction of 4-methoxy aniline (0.1 mmol) and ethyl was the best catalyst in a representative Friedel-Crafts alkylation, epoxide (molar excess) at 60 °C in the presence of the whereas Sq_IRMOF-16 and Sq_SNU-8X were the best in a corresponding squaramide-based MOF (0.005 mmol = 5 mol% representative epoxide ring-opening (formation of the bis-addition [catalytic centers] relative to 4-methoxy aniline) for 8 hours. Figure product). Using an approach like ours, researchers could ultimately 4 shows the kinetics of the ring-opening reaction. This reaction can design an entire catalog of MOF-based catalysts, thereby greatly consecutively generate two products: the mono‐addition and bis- increasing the chances of finding high-performance catalysts for addition products. The best catalysts for the formation of the bis- targeted chemistries. addition product were Sq_IRMOF-16 and Sq_SNU-8X, which gave nearly quantitative transformation after 8 hours. In contrast, Acknowledgements Sq_UiO-68 and Sq_bptMOF gave roughly 50/50 mixtures of the This work was supported by the Spanish MINECO (projects RTI2018- mono- addition and bis-addition products after 8 hours 095622-B-I00 and CTQ2015‐64561‐R), the Catalan AGAUR (project 2017 SGR 238), the ERC under the EU FP7 (ERC−Co 615954), and European Union's Horizon 2020 research and innovation program, under grant agreement No 685727, and European Structural Funds (S2018/NMT-4367). It was also funded by the CERCA Program/Generalitat de Catalunya. 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