Structural reorganization in a hydrogen-bonded organic framework

Self-recognition of 3,3′,5,5′-azobenzenetetracarboxylic acid drives the formation of a grid-like anionic hydrogen-bonded framework with channels occupied by organic cations. This supramolecular solid is capable of reorganizing its connectivity in the presence of specific guests into a different crystalline architecture by sequential dissolution and recrystallization

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4 paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science & Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites

Surface Functionalization of Metal-Organic Framework Crystals with Catechol Coatings for Enhanced Moisture Tolerance

Robust catechol coatings for enhanced moisture tolerance were produced in one step by direct reaction of Hong Kong University of Science and Technology (HKUST) with synthetic catechols. We ascribe the rapid formation of homogeneous coatings around the metal-organic framework particles to the biomimetic catalytic activity of Cu(II) dimers in the external surface of the crystals. Use of fluorinated catechols results in hydrophobic, permeable coatings that protect HKUST from water degradation while retaining close to 100% of its original sorption capacity

Metal Node Control of Brønsted Acidity in Heterobimetallic Titanium–Organic Frameworks

Compared to indirect framework modification, synthetic control of cluster composition can be used to gain direct access to catalytic activities exclusive of specific metal combinations. We demonstrate this concept by testing the aminolysis of epoxides with a family of isostructural mesoporous frameworks featuring five combinations of homometallic and heterobimetallic metal-oxo trimers (Fe3, Ti3, TiFe2, TiCo2, and TiNi2). Only TiFe2 nodes display activities comparable to benchmark catalysts based on grafting of strong acids, which here originate from the combination of Lewis Ti4+ and Brønsted Fe3+–OH acid sites. The applicability of MUV-101(Fe) to the synthesis of β-amino alcohols is demonstrated with a scope that also includes the gram scale synthesis of propranolol, a natural β-blocker listed as an essential medicine by the World Health Organization, with excellent yield and selectivity

Ti-based robust MOFs in the combined photocatalytic degradation of emerging organic contaminants.

Photocatalysis process is a promising technology for environmental remediation. In the continuous search of new heterogeneous photocatalysts, metal-organic frameworks (MOFs) have recently emerged as a new type of photoactive materials for water remediation. Particularly, titanium-based MOFs (Ti-MOFs) are considered one of the most appealing subclass of MOFs due to their promising optoelectronic and photocatalytic properties, high chemical stability, and unique structural features. However, considering the limited information of the reported studies, it is a hard task to determine if real-world water treatment is attainable using Ti-MOF photocatalysts. In this paper, via a screening with several Ti-MOFs, we originally selected and described the potential of a Ti-MOF in the photodegradation of a mixture of relevant Emerging Organic Contaminants (EOCs) in real water. Initially, two challenging drugs (i.e., the β-blocker atenolol (At) and the veterinary antibiotic sulfamethazine (SMT)) and four water stable and photoactive Ti-MOF structures have been rationally selected. From this initial screening, the mesoporous Ti-trimesate MIL-100(Ti) was chosen as the most promising photocatalyst, with higher At or SMT individual photodegradation (100% of At and SMT photodegradation in 2 and 4 h, respectively). Importantly, the safety of the formed by-products from the At and SMT photodegradation was confirmed. Finally, the At and SMT photodegradation capacity of MIL-100(Ti) was confirmed under realistic conditions, by using a mixture of contaminants in tap drinking water (100% of At and SMT photodegradation in 4 h), proven in addition its potential recyclability, which reinforces the potential of MIL-100(Ti) in water remediation

Direct visualization of pyrrole reactivity by confined oxidation in a Cyclodextrin Metal‐Organic Framework

Metal-organic frameworks can be used as porous templates to exert control over polymerization reactions. Shown here are the possibilities offered by these crystalline, porous nanoreactors to capture highly‐reactive intermediates for a better understanding of the mechanism of polymerization reactions. By using a cyclodextrin framework the polymerization of pyrrole is restricted, capturing the formation of terpyrrole cationic intermediates. Single‐crystal X‐ray diffraction is used to provide definite information on the supramolecular interactions that induce the formation and stabilization of a conductive array of cationic complexes

Chemical Engineering of Photoactivity in Heterometallic Titanium-Organic Frameworks by Metal Doping

[EN] We report a new family of titanium-organic frameworks that enlarges the limited number of crystalline, porous materials available for this metal. They are chemically robust and can be prepared as single crystals at multi-gram scale from multiple precursors. Their heterometallic structure enables engineering of their photoactivity by metal doping rather than by linker functionalization. Compared to other methodologies based on the post-synthetic metallation of MOFs, our approach is well-fitted for controlling the positioning of dopants at an atomic level to gain more precise control over the band-gap and electronic properties of the porous solid. Changes in the band-gap are also rationalized with computational modelling and experimentally confirmed by photocatalytic H-2 production.This work was supported by the EU (ERC Stg Chem-fs-MOF 714122) and Spanish MINECO (MDM-2015-0538, MAT2016-75586-C4-4-P & CTQ2017-83486-P). C.M.-G. and J.C.-G. thank the Spanish MINECO for a Ramon y Cajal Fellowship and FPI Scholarship (CTQ2014-59209-P), respectively. N.M.P. thanks the Junta de Andalucia for post-doctoral fellowship (P10-FQM-6050). BSC-RES and UG-Alhambra are acknowledged for the computational resources and F. Lloret for helpful discussions.Castells-Gil, J.; Padial, NM.; Almora-Barrios, N.; Albero-Sancho, J.; Ruiz-Salvador, AR.; Gonzalez-Platas, J.; García Gómez, H.... (2018). Chemical Engineering of Photoactivity in Heterometallic Titanium-Organic Frameworks by Metal Doping. Angewandte Chemie International Edition. 57(28):8453-8457. https://doi.org/10.1002/anie.201802089S845384575728Furukawa, H., Cordova, K. E., O’Keeffe, M., & Yaghi, O. M. (2013). The Chemistry and Applications of Metal-Organic Frameworks. Science, 341(6149), 1230444-1230444. doi:10.1126/science.1230444Adil, K., Belmabkhout, Y., Pillai, R. S., Cadiau, A., Bhatt, P. M., Assen, A. H., … Eddaoudi, M. (2017). 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A New Photoactive Crystalline Highly Porous Titanium(IV) Dicarboxylate. Journal of the American Chemical Society, 131(31), 10857-10859. doi:10.1021/ja903726mGao, J., Miao, J., Li, P.-Z., Teng, W. Y., Yang, L., Zhao, Y., … Zhang, Q. (2014). A p-type Ti(iv)-based metal–organic framework with visible-light photo-response. Chem. Commun., 50(29), 3786-3788. doi:10.1039/c3cc49440cBueken, B., Vermoortele, F., Vanpoucke, D. E. P., Reinsch, H., Tsou, C.-C., Valvekens, P., … De Vos, D. (2015). A Flexible Photoactive Titanium Metal-Organic Framework Based on a [TiIV3(μ3-O)(O)2(COO)6] Cluster. Angewandte Chemie International Edition, 54(47), 13912-13917. doi:10.1002/anie.201505512Bueken, B., Vermoortele, F., Vanpoucke, D. E. P., Reinsch, H., Tsou, C.-C., Valvekens, P., … De Vos, D. (2015). A Flexible Photoactive Titanium Metal-Organic Framework Based on a [TiIV3(μ3-O)(O)2(COO)6] Cluster. Angewandte Chemie, 127(47), 14118-14123. doi:10.1002/ange.201505512Yuan, S., Liu, T.-F., Feng, D., Tian, J., Wang, K., Qin, J., … Zhou, H.-C. (2015). A single crystalline porphyrinic titanium metal–organic framework. Chemical Science, 6(7), 3926-3930. doi:10.1039/c5sc00916bYuan, S., Qin, J.-S., Xu, H.-Q., Su, J., Rossi, D., Chen, Y., … Zhou, H.-C. (2017). [Ti8Zr2O12(COO)16] Cluster: An Ideal Inorganic Building Unit for Photoactive Metal–Organic Frameworks. ACS Central Science, 4(1), 105-111. doi:10.1021/acscentsci.7b00497Dhakshinamoorthy, A., Asiri, A. M., & García, H. (2016). Metal-Organic Framework (MOF) Compounds: Photocatalysts for Redox Reactions and Solar Fuel Production. Angewandte Chemie International Edition, 55(18), 5414-5445. doi:10.1002/anie.201505581Dhakshinamoorthy, A., Asiri, A. M., & Garcia, H. (2016). Metall-organische Gerüstverbindungen: Photokatalysatoren für Redoxreaktion und die Produktion von Solarbrennstoffen. Angewandte Chemie, 128(18), 5504-5535. doi:10.1002/ange.201505581Deng, X., Li, Z., & García, H. (2017). Visible Light Induced Organic Transformations Using Metal-Organic-Frameworks (MOFs). Chemistry - A European Journal, 23(47), 11189-11209. doi:10.1002/chem.201701460Horiuchi, Y., Toyao, T., Saito, M., Mochizuki, K., Iwata, M., Higashimura, H., … Matsuoka, M. (2012). Visible-Light-Promoted Photocatalytic Hydrogen Production by Using an Amino-Functionalized Ti(IV) Metal–Organic Framework. The Journal of Physical Chemistry C, 116(39), 20848-20853. doi:10.1021/jp3046005Hendon, C. H., Tiana, D., Fontecave, M., Sanchez, C., D’arras, L., Sassoye, C., … Walsh, A. (2013). Engineering the Optical Response of the Titanium-MIL-125 Metal–Organic Framework through Ligand Functionalization. Journal of the American Chemical Society, 135(30), 10942-10945. doi:10.1021/ja405350uChambers, M. B., Wang, X., Ellezam, L., Ersen, O., Fontecave, M., Sanchez, C., … Mellot-Draznieks, C. (2017). Maximizing the Photocatalytic Activity of Metal–Organic Frameworks with Aminated-Functionalized Linkers: Substoichiometric Effects in MIL-125-NH2. Journal of the American Chemical Society, 139(24), 8222-8228. doi:10.1021/jacs.7b02186Blatov, V. A., Shevchenko, A. P., & Proserpio, D. M. (2014). Applied Topological Analysis of Crystal Structures with the Program Package ToposPro. Crystal Growth & Design, 14(7), 3576-3586. doi:10.1021/cg500498kDelgado-Friedrichs, O., & O’Keeffe, M. (2003). Identification of and symmetry computation for crystal nets. Acta Crystallographica Section A Foundations of Crystallography, 59(4), 351-360. doi:10.1107/s0108767303012017Dincă, M., Han, W. S., Liu, Y., Dailly, A., Brown, C. M., & Long, J. R. (2007). Observation of Cu2+–H2 Interactions in a Fully Desolvated Sodalite-Type Metal–Organic Framework. Angewandte Chemie International Edition, 46(9), 1419-1422. doi:10.1002/anie.200604362Dincă, M., Han, W. S., Liu, Y., Dailly, A., Brown, C. M., & Long, J. R. (2007). Observation of Cu2+–H2 Interactions in a Fully Desolvated Sodalite-Type Metal–Organic Framework. Angewandte Chemie, 119(9), 1441-1444. doi:10.1002/ange.200604362Liu, T.-F., Vermeulen, N. A., Howarth, A. J., Li, P., Sarjeant, A. A., Hupp, J. T., & Farha, O. K. (2016). Adding to the Arsenal of Zirconium-Based Metal-Organic Frameworks: the Topology as a Platform for Solvent-Assisted Metal Incorporation. European Journal of Inorganic Chemistry, 2016(27), 4349-4352. doi:10.1002/ejic.201600627Wang, B., Lv, X.-L., Feng, D., Xie, L.-H., Zhang, J., Li, M., … Zhou, H.-C. (2016). Highly Stable Zr(IV)-Based Metal–Organic Frameworks for the Detection and Removal of Antibiotics and Organic Explosives in Water. Journal of the American Chemical Society, 138(19), 6204-6216. doi:10.1021/jacs.6b01663Tan, Y.-X., He, Y.-P., & Zhang, J. (2011). Pore partition effect on gas sorption properties of an anionic metal–organic framework with exposed Cu2+ coordination sites. 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Selective Implantation of Diamines for Cooperative Catalysis in Isoreticular Heterometallic Titanium-Organic Frameworks

This is the peer reviewed version of the following article: Selective Implantation of Diamines for Cooperative Catalysis in Isoreticular Heterometallic Titanium-Organic Frameworks, which has been published in final form at https://doi.org/10.1002/anie.202100176. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] We introduce the first example of isoreticular titanium-organic frameworks, MUV-10 and MUV-12, to show how the different affinity of hard Ti(IV) and soft Ca(II) metal sites can be used to direct selective grafting of amines. This enables the combination of Lewis acid titanium centers and available -NH, sites in two sizeable pores for cooperative cycloaddition of CO2 to epoxides at room temperature and atmospheric pressure. The selective grafting of molecules to heterometallic clusters adds up to the pool of methodologies available for controlling the positioning and distribution of chemical functions in precise positions of the framework required for definitive control of pore chemistry.This work was supported by the EU (ERC Stg Chem-fs-MOF 714122) and Spanish Government (CTQ2017-83486-P, RTI2018-098568-A-I00 & CEX2019-000919-M). E.L.-M. and S.T. thanks the Spanish Government for their Juan de la Cierva Fellowship (FJCI-2017-32956) and Ramon y Cajal contract (RYC-2016-1981), respectively. A.R.G. acknowledges funding from Generalitat Valencia (ACIF/2020/090)and Fondo Social Europeo. N.M.P. thanks the European Union for a Marie Sklodowska-Curie Global Fellowship (H2020MSCA-IF-2016-GF-749359-EnanSET) and to the "2020 Postdoctoral Junior Leader-Retaining Fellowship, la Caixa Foundation (ID 100010434 and fellowship code LCF/BQ/PR20/11770014)". F.G.C. acknowledges the support of a fellowship from "la Caixa" Foundation (ID 100010434 and the fellowship code LCF/BQ/PI19/11690011). S.N. thanks financial support by the Ministerio de Ciencia, Innovacion y Universidades (RTI 2018-099482-A-I00 project), Fundacion Ramon Areces (XVIII Concurso Nacional para la Adjudicacion de Ayudas a la Investigacion en Ciencias de la Vida y de la Materia, 2016) and Agencia Valenciana de la Innovacion (AVI-GVA, Carboagua project, INNEST/2020/111).López-Maya, E.; Padial, NM.; Castells-Gil, J.; Ganivet, CR.; Rubio-Gaspar, A.; García Cirujano, F.; Almora-Barrios, N.... (2021). Selective Implantation of Diamines for Cooperative Catalysis in Isoreticular Heterometallic Titanium-Organic Frameworks. Angewandte Chemie International Edition. 60(21):11868-11873. https://doi.org/10.1002/anie.2021001761186811873602

Effect of Linker Distribution in the Photocatalytic Activity of Multivariate Mesoporous Crystals

The use of Metal-Organic Frameworks as crystalline matrices for the synthesis of multiple component or multivariate solids by the combination of different linkers into a single material has emerged as a versatile route to tailor the properties of single-component phases or even access new functions. This approach is particularly relevant for Zr6-MOFs due to the synthetic flexibility of this inorganic node. However, the majority of materials are isolated as polycrystalline solids, which are not ideal to decipher the spatial arrangement of parent and exchanged linkers for the formation of homogeneous structures or heterogeneous domains across the solid. Here we use high-throughput methodologies to optimize the synthesis of single crystals of UiO-68 and UiO-68-TZDC, a photoactive analogue based on a tetrazine dicarboxylic derivative. The analysis of the single linker phases reveals the necessity of combining both linkers to produce multivariate frameworks that combine efficient light sensitization, chemical stability, and porosity, all relevant to photocatalysis. We use solvent-assisted linker exchange reactions to produce a family of UiO-68-TZDC% binary frameworks, which respect the integrity and morphology of the original crystals. Our results suggest that the concentration of TZDC in solution and the reaction time control the distribution of this linker in the sibling crystals for a uniform mixture or the formation of core-shell domains. We also demonstrate how the possibility of generating an asymmetric distribution of both linkers has a negligible effect on the electronic structure and optical band gap of the solids but controls their performance for drastic changes in the photocatalytic activity toward proton or methyl viologen reduction.This work was supported by the EU (ERC Stg Chem-fs-MOF 714122) and Spanish government (CTQ2017-83486-P, RTI2018-098568-A-I00, RYC-2016-1981, CEX2019-000919-M, PID2019-106383GB-C44/AEI/10.13039/501100011033 and RTI2018-098568-A-I00). B.L.-B. thanks the Spanish government for a FPU (FPU16/04162). S.T. thanks the Spanish government for a Ramón y Cajal Fellowship (RYC-2016-60719817). N.M.P. thanks the European Union for a Marie Skłodowska-Curie Global Fellowship (H2020-MSCA-IF-2016-GF-749359-EnanSET). J.G.P. thanks to the SIDIX at Servicios Generales de Apoyo a la Investigación (SEGAI) at La Laguna University. We also thank BSC-RES for computational resources (QS-2020-2-0024) and the University of Valencia for research facilities (Tirant and NANBIOSIS).Peer reviewe

Ti-Catalyzed Straightforward Synthesis of Exocyclic Allenes

Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier-type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five-, six-, and seven-membered carbocycles and nitrogen-containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide