Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal-Organic Frameworks

Conductive metal-organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu‐CAT‐1 is described

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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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

Hydroxamate Titanium−Organic Frameworks and the Effect of Siderophore-Type Linkers over Their Photocatalytic Activity

The chemistry of Metal-Organic Frameworks (MOFs) relies on the controlled linking of organic molecules and inorganic secondary building units to assemble an unlimited number of reticular frameworks. However, the design of porous solids with chemical stability remains still limited to carboxylate or azolate groups. There is a timely opportunity to develop new synthetic platforms that make use of unexplored metal binding groups to produce metal-linker joints with hydrolytical stability. Living organisms use siderophores (iron carriers in greek) to effectively assimilate iron in soluble form. These compounds make use of hard oxodonors as hydroxamate or catecholate groups to coordinate metal Lewis acids like iron, aluminium or titanium to form metal complexes very stable in water. Inspired by the chemistry of these microorganisms, we report the first hydroxamate MOF prepared by direct synthesis. MUV-11 (MUV = Materials of Universidad de Valencia) is a crystalline, porous material (close to 800 m2·g-1) that combines photoactivity with good chemical stability in acid conditions. By using a high-throughput approach, we also demonstrate that this new chemistry is compatible with the formation of single crystalline phases for multiple titanium salts, thus expanding the scope of precursors accessible. Titanium frameworks are regarded as promising materials for photocatalytic applications. Our photoelectrochemical and catalytic tests suggests important differences for MUV-11. Compared to other Ti-MOFs, changes in the photoelectrochemical and photocatalytic activity have been rationalized with computational modelling revealing how the chemistry of siderophores can introduce changes to the electronic structure of the frontier orbitals, relevant to the photocatalytic activity of these solids

Bottom‐Up Fabrication of Semiconductive Metal-Organic Framework Ultrathin Films

Though generally considered insulating, recent progress on the discovery of conductive porous metal-organic frameworks (MOFs) offers new opportunities for their integration as electroactive components in electronic devices. Compared to classical semiconductors, these metal-organic hybrids combine the crystallinity of inorganic materials with easier chemical functionalization and processability. Still, future development depends on the ability to produce high-quality films with fine control over their orientation, crystallinity, homogeneity, and thickness. Here self-assembled monolayer substrate modification and bottom-up techniques are used to produce preferentially oriented, ultrathin, conductive films of Cu-CAT-1. The approach permits to fabricate and study the electrical response of MOF-based devices incorporating the thinnest MOF film reported thus far (10 nm thick)

Homochiral Metal-Organic Frameworks for Enantioselective Separations in Liquid Chromatography

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification owing to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here we disclose a porous, robust homochiral metal-organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural L-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale

Structure and Reactivity of Supported Hybrid Platinum Nanoparticles for the Flow Hydrogenation of Functionalized Nitroaromatics

This contribution targets the first comprehensive understanding of the next-generation catalyst for nitroarene hydrogenation, featuring ligand-capped 2 nm platinum nanoparticles (Pt-HHDMA, HHDMA: hexadecyl(2-hydroxyethyl)- dimethylammonium dihydrogen phosphate) deposited on carbon. Fundamental questions related to the structure, properties, and mechanistic fingerprints of the metal−organic interphase of the hybrid system were addressed through a battery of advanced characterization methods and theoretical calculations. Catalytic tests conducted in a flow reactor at variable temperature and pressure revealed the superior activity of Pt-HHDMA in comparison with the archetypal and industrially relevant Lindlar-type Pt−Pb/CaCO3, with outstanding chemoselectivity and leaching resistance. The analysis of the reaction mechanism by Density Functional Theory, which was never addressed systematically, showed that the benefits of the ligand-modified catalyst arise from the facilitated H2 activation and weak nitroarene adsorption on the HHDMA-modified surface. At the same time, the ligand isolates the platinum ensemble, reducing the possibility of unselective routes by controlling the adsorption geometry and extent of the reactant and product intermediates. These results substantially enrich the mechanistic understanding of HHDMA-modified Pt catalyst and are of fundamental relevance for future improvements of this hybrid catalyst and for extrapolating this technology to other challenging reactions

Advances in the Design of Nanostructured Catalysts for Selective Hydrogenation

Selective hydrogenations lay at the heart of many industrial processes. The archetypal catalysts for this class of reactions are generally prepared by ‘metal poisoning’ strategies: the active metal is protected and selectively deactivated with vari- ous compounds. This approach has been applied for decades, with limited understanding. Low product selectivity and pres- ence of toxic elements in the catalyst pose severe constraints in the utilization of these materials in the future. Thus, to de- velop more sustainable catalysts, this field has recently gained momentum. This Review analyzes the concepts and frontiers that have been developed in the last decade: from nanostruc- turing less conventional metals in order to improve their ability to activate H2, to the use of oxides as active phases, from alloy- ing, to the ensemble control in hybrid materials, and site isola- tion approaches in single-site heterogeneous catalysts. Particu- lar attention is given to the hydrogenation of alkynes and ni- troarenes, two reactions at the core of the chemical industry, importantly applied in the manufacture of polymers, pharma- ceuticals, nutraceuticals, and agrochemicals. The strategies here identified can be transposed to other relevant hydrogena- tions and can guide in the design of more advanced materials

Electrochemical Effects at Surfactant–Platinum Nanoparticle Interfaces Boost Catalytic Performance

Nanoparticles are applied in a variety of industrially relevant transformations as heterogeneous catalysts typically with the help of an external force (pressure, temperature, or voltage) to steer the chemistry. The modification of platinum nanoparticles by a phosphate–amino surfactant enables catalysis without external energy supply in the hydrogenation of nitrobenzene to aniline. This can be attributed to the complex surfactant/metal interface which is able to split hydrogen into protons and electrons. The subsequent hydrogenation process mimics the electrochemical reduction described by Haber. The surfactant decorated Pt catalyst is two orders of magnitude more active than the state-of-the-art Pb-poisoned Pt catalyst. Our study provides a new approach to understand the functionality of emerging catalytic systems and can be applied to design new materials with optimal interfaces

Chemical complexity for targeted function in heterometallic titanium-organic frameworks

Research on metal-organic frameworks is shifting from the principles that control the assembly, structure, and porosity of these reticular solids, already established, into more sophisticated concepts that embrace chemical complexity as a tool for encoding their function or accessing new properties by exploiting the combination of different components (organic and inorganic) into these networks. The possibility of combining multiple linkers into a given network for multivariate solids with tunable properties dictated by the nature and distribution of the organic connectors across the solid has been well demonstrated. However, the combination of different metals remains still comparatively underexplored due to the difficulties in controlling the nucleation of heterometallic metal-oxo clusters during the assembly of the framework or the post-synthetic incorporation of metals with distinct chemistry. This possibility is even more challenging for titanium-organic frameworks due to the additional difficulties intrinsic to controlling the chemistry of titanium in solution. In this perspective article we provide an overview of the synthesis and advanced characterization of mixed-metal frameworks and emphasize the particularities of those based in titanium with particular focus on the use of additional metals to modify their function by controlling their reactivity in the solid state, tailoring their electronic structure and photocatalytic activity, enabling synergistic catalysis, directing the grafting of small molecules or even unlocking the formation of mixed oxides with stoichiometries not accessible to conventional routes.This work was supported by the EU (ERC-2021-COG-101043428), the Generalitat Valenciana (PROMETEU/2021/054, SEJIGENT/2021/059 & MFA/2022/026) and the Spanish government (CEX2019-000919-M & PID2020-118117RB-I00). J.C.-G. thanks the GVA for an APOSTD postdoctoral grant (CIAPOS/2021/272). B. L.-B. thanks the Spanish government and Next Generation EU funding for a postdoctoral grant (MS21-127). N. M. P. thanks La Caixa Foundation for a Postdoctoral Junior Leader–Retaining Fellowship (LCF/BQ/PR20/11770014)