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This review article presents the fundamental and practical aspects of water adsorption in Metal-Organic Frameworks (MOFs). The state of the art of MOF stability in water, a crucial issue to many applications in which MOFs are promising candidates, is discussed here. Stability in both gaseous (such as humid gases) and aqueous media is considered. By considering a non-exhaustive yet representative set of MOFs, the different mechanisms of water adsorption in this class of materials are presented: reversible and continuous pore filling, irreversible and discontinuous pore filling through capillary condensation, and irreversibility arising from the flexibility and possible structural modifications of the host material. Water adsorption properties of more than 60 MOF samples are reported. The applications of MOFs as materials for heat-pumps and adsorbent-based chillers and proton conductors are also reviewed. Some directions for future work are suggested as concluding remarks. [ABSTRACT FROM AUTHOR]

A set of 15 metal–organic frameworks (MIL-53, MIL-68, MIL-125, UiO-66, ZIF) exhibiting different pore size, morphology, and surface chemistry is used to unravel the numerous behaviors of water adsorption at room temperature in this class of materials. Outstanding “S”-shaped (type V) adsorption isotherms are observed for MIL-68 type solids. We show that the underlying mechanism of water adsorption can be rationalized using a simple set of three parameters: the Henry constant (i.e. the slope of the adsorption pressure in the low pressure range), the pressure at which pore filling occurs, and the maximum water adsorption capacity. While the Henry constant and pore filling pressure mostly depend on the affinity of water for the surface chemistry and on pore size, respectively, these two parameters are correlated as they both reflect different aspects of the hydrophobicity–hydrophilicity of the material. For a given type of porous structure, the functionalization of the material by hydrophilic moieties such as hydrogen bonding groups (amine or aldehyde) systematically leads to an increase in the Henry constant concomitantly with a decrease in the pore filling pressure. As for the adsorption mechanism, we show that, for a given temperature, there is a critical diameter (Dc∼ 20 Å for water at room temperature) above which pore filling occurs through irreversible capillary condensation accompanied by capillary hysteresis loops. Below this critical diameter, pore filling is continuous and reversible unless the material exhibits some adsorption-induced flexibility. [ABSTRACT FROM AUTHOR]

of metal-organic frameworks is carried out in a novel fashion for the synthesis of single-site catalysts. Protection-deprotection methodologies open new perspectives to 'unlock' protected functionalities to obtain highly active and/or coordinating moieties on MOFs. This could facilitate the immobilization of organometallic catalysts inside MOF cavities. [ABSTRACT FROM AUTHOR]

Abstract: The mononuclear cations [(η5-C5Me5)RhCl(bpym)]+ (1), [(η5-C5Me5)IrCl(bpym)]+ (2), [(η6-p-Pr i C6H4Me)RuCl(bpym)]+ (3) and [(η6-C6Me6)RuCl(bpym)]+ (4) as well as the dinuclear dications [{(η5-C5Me5)RhCl}2(bpym)]2+ (5), [{(η5-C5Me5)IrCl}2(bpym)]2+ (6), [{(η6-p-Pr i C6H4Me)RuCl}2(bpym)]2+ (7) and [{(η6-C6Me6)RuCl}2(bpym)]2+ (8) have been synthesised from 2,2′-bipyrimidine (bpym) and the corresponding chloro complexes [(η5-C5Me5)RhCl2]2, [(η5-C5Me5)IrCl2]2, [(η6-Pr i C6H4Me)RuCl2]2 and [(η6-C6Me6)RuCl2]2, respectively. The X-ray crystal structure analyses of [3][PF6], [5][PF6]2, [6][CF3SO3]2 and [7][PF6]2 reveal a typical piano-stool geometry around the metal centres; in the dinuclear complexes the chloro ligands attached to the two metal centres are found to be, with respect to each other, cis oriented for 5 and 6 but trans for 7. The electrochemical behaviour of 1–8 has been studied by voltammetric methods. In addition, the catalytic potential of 1–8 for transfer hydrogenation reactions in aqueous solution has been evaluated: All complexes catalyse the reaction of acetophenone with formic acid to give phenylethanol and carbon dioxide. For both the mononuclear and dinuclear series the best results were obtained (50°C, pH 4) with rhodium complexes, giving turnover frequencies of 10.5h−1 for 1 and 19h−1 for 5. [Copyright &y& Elsevier]

Abstract: The monocationic chloro complexes containing chelating 1,10-phenanthroline (phen) ligands [(arene)Ru(N∩N)Cl]+ (1: arene=C6H6, N∩N=phen; 2: arene=C6H6, N∩N=5-NO2-phen; 3: arene= p-MeC6H4Pr i , N∩N=phen; 4: arene= p-MeC6H4Pr i , N∩N=5-NO2-phen; 5: arene=C6Me6, N∩N=phen; 6: arene=C6Me6, N∩N=5-NO2-phen; 7: arene=C6Me6, N∩N=5-NH2-phen) have been prepared and characterised as the chloride salts. Hydrolysis of these chloro complexes in aqueous solution gave, upon precipitation of silver chloride, the corresponding dicationic aqua complexes [(arene)Ru(N∩N)(OH2)]2+ (8: arene=C6H6, N∩N=phen; 9: arene=C6H6, N∩N=5-NO2-phen; 10: arene= p-MeC6H4Pr i , N∩N=phen; 11: arene= p-MeC6H4Pr i , N∩N=5-NO2-phen; 12: arene=C6Me6, N∩N=phen; 13: arene=C6Me6, N∩N=5-NO2-phen; 14: arene=C6Me6, N∩N=5-NH2-phen), which have been isolated and characterised as the tetrafluoroborate salts. The catalytic potential of the aqua complexes 8–14 for transfer hydrogenation reactions in aqueous solution has been studied: complexes 12 and 14 catalyse the reaction of acetophenone with formic acid to give phenylethanol and carbon dioxide with turnover numbers around 200 (80°C, 7h). In the case of 12, it was possible to observe the postulated hydrido complex [(C6Me6)Ru(phen)H]+ (15) in the reaction with sodium borohydride; 15 has been characterised as the tetrafluoroborate salt, the isolated product [15]BF4, however, being impure. The molecular structures of [(C6Me6)Ru(phen)Cl]+ (1) and [(C6Me6)Ru(phen)(OH2)]2+ (12) have been determined by single-crystal X-ray structure analysis of [1]Cl and [12](BF4)2. [Copyright &y& Elsevier]

The last decade has seen a tremendous expansion of the field of heterogenized molecular catalysis, especially with the growing interest in metal–organic frameworks and related porous hybrid solids. With successful achievements in the transfer from molecular homogeneous catalysis to heterogenized processes come the necessary discussions on methodologies used and a critical assessment on the advantages of heterogenizing molecular catalysis. Here we use the example of nickel-catalyzed ethylene oligomerization, a reaction of both fundamental and applied interest, to review heterogenization methodologies of well-defined molecular catalysts within porous solids while addressing the biases in the comparison between original molecular systems and heterogenized counterparts. [ABSTRACT FROM AUTHOR]

The catalytic activity of multifunctional, microporous materials is directly linked to the spatial arrangement of their structural building blocks. Despite great achievements in the design and incorporation of isolated catalytically active metal complexes within such materials, a detailed understanding of their atomic‐level structure and the local environment of the active species remains a fundamental challenge, especially when these latter are hosted in non‐crystalline organic polymers. Here, we show that by combining computational chemistry with pair distribution function analysis, 129Xe NMR, and Dynamic Nuclear Polarization enhanced NMR spectroscopy, a very accurate description of the molecular structure and confining surroundings of a catalytically active Rh‐based organometallic complex incorporated inside the cavity of amorphous bipyridine‐based porous polymers is obtained. Small, but significant, differences in the structural properties of the polymers are highlighted depending on their backbone motifs. [ABSTRACT FROM AUTHOR]

Die katalytische Aktivität multifunktionaler, mikroporöser Materialien hängt direkt von der räumlichen Anordnung ihrer Strukturbausteine ab. Trotz großer Erfolge bei dem Design und der Heterogenisierung isolierter, katalytisch aktiver Metallkomplexe in solchen Materialien bleibt ein detailliertes Verständnis ihrer Struktur auf atomarer Ebene und der lokalen Umgebung der aktiven Spezies eine grundlegende Herausforderung, insbesondere wenn diese in amorphe organische Polymere eingebaut sind. Hier zeigen wir, dass durch die Kombination von Computerchemie mit Paarverteilungsfunktionsanalyse, 129Xe NMR‐ und dynamischer Kernpolarisations NMR‐Spektroskopie eine sehr genaue Beschreibung der Molekülstruktur und der Umgebung eines katalytisch aktiven, Rh‐basierten organometallischen Komplexes möglich ist, der in die Poren eines amorphen Bipyridin‐basierten porösen Polymers eingebaut ist. Kleine, aber signifikante Unterschiede in den strukturellen Eigenschaften der Polymere in Abhängigkeit ihrer Funktionalisierung werden hervorgehoben. [ABSTRACT FROM AUTHOR]

In the centrosymmetric dinuclear title complex, [RuCl2(η6-C6H6)]2·2CHCl3 or [Ru2Cl4(C6H6)2]·2CHCl3, accessible from RuCl3. nH2O and 1,3-cyclo­hexa­diene, the benzene ligands are involved in slipped-parallel π–π stacking interactions with neighbouring mol­ecules, thus forming one-dimensional polymeric chains. [ABSTRACT FROM AUTHOR]

The ability to molecularly engineer materials is a powerful tool toward increasingly performing heterogeneous catalysts. Porous organic polymers stand out as photocatalysts due to their high chemical stability, outstanding optoelectronic properties and their easy and tunable syntheses. In photocatalysis, the insertion of photosensitizing π‐extended molecules into molecularly well‐defined donor‐acceptor junctions is supposed to increase the catalytic activity, but yet remain experimentally underdeveloped. This study presents a pyrene‐based Covalent Triazine Framework (CTF) synthesized through a polycondensation approach, which was designed to contain a molecularly‐defined pyrene‐triazine‐bipyridine donor‐acceptor‐acceptor triad as the repetition unit of the CTF. The CTF is an efficient photocatalyst for hydrogen evolution from water reaching a significant production rate of 61.5 mmolH2/h/gcat. Moreover, the same CTF can easily be used as porous macroligand for an organometallic Rh complex to efficiently catalyze the carbon dioxide photoreduction into formic acid under visible light. [ABSTRACT FROM AUTHOR]

An earth‐abundant nickel(II) bipyridine catalyst, combined with lithium hexamethyldisilazide as base, demonstrates its wide applicability in the direct arylation polymerization of di‐ and tri‐thiophene heteroaryls with poly(hetero)aryl halides. With a nickel catalyst loading of 2.5 mol%, a series of twenty highly cross‐linked organic polymers is obtained in 34 to 99 % yields. Using mixed polytopic coupling partners allows obtaining alternating and optically active thiophene‐based solids with intrinsic porosity. [ABSTRACT FROM AUTHOR]

The enanti­omerically pure iridium title complex, [Ir(C13H19N2O2S)(C10H15)Cl]·CHCl3, has the Ir atom in the S configuration, with a distorted octa­hedral geometry. [ABSTRACT FROM AUTHOR]

New catechol‐based porous polymers were synthesized and used as platforms for the heterogenization of molecular Cu complexes. The resulting Cu@CatMP‐1 materials proved to be highly stable and performing catalysts for the oxidation of secondary alcohols with turnover numbers up to 6000, about 1 to 2 orders of magnitude higher than the current relevant state of the art, using catalyst loadings as low as 25 ppm of Cu. The solid catalyst proved to be recyclable for over 10 runs without detectable metal leaching and has been scaled to the gram scale. The coordination of Cu to catechol within the polymer has been evidenced by X‐ray absorption spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical properties of cationic complexes [(η6-arene)Ru(N∩N)Cl]Cl (arene/N∩N=C6H6/1,10-phenanthroline (1), p-MeC6H4Pr i /1,10-phenanthroline (2), C6Me6/1,10-phenanthroline (3), C6Me6/5-NO2-1,10-phenanthroline (4), and C6Me6/5-NH2-1,10-phenanthroline (5)) were studied by cyclic voltammetry in order to rationalize catalytic activity in transfer hydrogenation of the respective aqua complexes [(η6-arene)Ru(N∩N)(OH2)](BF4)2 (6–10). Complexes 1–5 were chosen because the ‘true’ catalysts 6–10 are unstable under the conditions of the measurement. The electrochemical behaviour of 1–5 in acetonitrile solution is rather complicated due to consecutive and parallel chemical reactions that accompany electron transfer processes. Nonetheless, interpretation of the electrochemical data allowed to assess the influence of the structure and substitution on the redox and catalytic properties: the catalytic ability correlates with the reduction potentials, indicating the decisive role of the η6-arene ring directly bonded to the catalytic centre (Ru). [Copyright &y& Elsevier]

A nickel-based catalytic system for the regiospecific C2–H arylation of benzothiophene has been established. NiCl2(bpy) is used as a catalyst in combination with LiHMDS as a base in dioxane. The catalytic system is applicable to a variety of functionalized benzothiophenes, as well as other heteroarenes including thiophene, benzodithiophene, benzofuran and selenophene in combination with iodo aryl electrophiles. The role of LiHMDS as a uniquely potent base and a postulated mechanism are discussed. The applicability of this system is finally demonstrated for the synthesis of an intermediate of an active pharmaceutical ingredient. [ABSTRACT FROM AUTHOR]

The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy. [ABSTRACT FROM AUTHOR]

The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy. [ABSTRACT FROM AUTHOR]

The integration of catalytically active centers into a solid support without any loss of performance compared to the homogeneous analogue remains a major challenge. In this context, solid macroligands can be regarded as the key element to combine the advantages of homogeneous and heterogeneous catalysis. Porous materials such as periodic mesoporous organosilica, metal‐organic frameworks, porous organic polymers or covalent‐organic frameworks fulfill all requirements of a macroligand acting as a solid ligand of a molecular complex. They all can be tuned at the molecular scale to adapt the properties of the catalyst for a given application. This important feature also allows to directly compare different macroligands, regardless of their nature, and to choose the most appropriate for a target application. [ABSTRACT FROM AUTHOR]

In their Research Article, R. Palkovits, J. Canivet, F. M. Wisser and co-workers demonstrate the crucial role of molecularly defined donor-acceptor-acceptor triad in CTF photocatalysts to enable efficient solar fuel production. Condensation, covalent triazine framework, molecular control, photocatalysis, pyrene Keywords: condensation; covalent triazine framework; molecular control; photocatalysis; pyrene EN condensation covalent triazine framework molecular control photocatalysis pyrene 1 1 1 07/25/23 20230721 NES 230721 B The Front Cover b illustrates a pyrene- and bipyridine-based covalent triazine framework (CTF) as versatile photocatalyst for the production of different renewable energy vectors. [Extracted from the article]

Abstract: Herein, we report the synthesis of two bipyridine‐based porous polymers and their use as platforms for the heterogenization of pentamethylcyclopentadienylrhodium catalytic species. These highly stable heterogeneous catalysts demonstrate their efficiency in the transfer hydrogenation of α‐aryl ketones. Moreover, we show that their catalytic activity is similar to that of homogeneous analogues, highlighting the absence of diffusion limitations in the solids. We rationalize the differences in the measured activities by using the Hammett parameter as a descriptor of the electronic environment of the catalytic site in both homogeneous and heterogeneous systems. [ABSTRACT FROM AUTHOR]

We use density functional theory, newly parameterized molecular dynamics simulations, and last generation 15N dynamic nuclear polarization surface enhanced solid-state NMR spectroscopy (DNP SENS) to understand graft-host interactions and effects imposed by the metal-organic framework (MOF) host on peptide conformations in a peptide-functionalized MOF. Focusing on two grafts typified by MIL-68-proline ( -Pro) and MIL-68-glycine-proline ( -Gly-Pro), we identified the most likely peptide conformations adopted in the functionalized hybrid frameworks. We found that hydrogen bond interactions between the graft and the surface hydroxyl groups of the MOF are essential in determining the peptides conformation(s). DNP SENS methodology shows unprecedented signal enhancements when applied to these peptide-functionalized MOFs. The calculated chemical shifts of selected MIL-68-NH- Pro and MIL-68-NH- Gly-Pro conformations are in a good agreement with the experimentally obtained 15N NMR signals. The study shows that the conformations of peptides when grafted in a MOF host are unlikely to be freely distributed, and conformational selection is directed by strong host-guest interactions. [ABSTRACT FROM AUTHOR]

We present herein the first example of metal-organic frameworks postfunctionalized with peptides. Our microwave-assisted postsynthetic modification method yields enantiopure peptides anchored inside MOF cavities. Al-MIL-101-NH2, In-MIL-68-NH2, and Zr-UiO-66-NH2 were chosen as starting platforms. A single amino acid and various oligopeptides are grafted with yields up to 60% after a 30 min microwave-assisted coupling-deprotection sequence. This allows efficient preparation of a library of functional hybrid solids for molecular recognition applications such as sensing, separation, or asymmetric catalysis, as demonstrated here for the chiral aldol reaction. [ABSTRACT FROM AUTHOR]

We report two new microporous mixed-metal triazolate based MOFs made from zinc and nickel salts combined with either 1,2,4-triazole or 3,5-diamino-1,2,4-triazole. Their structures, refined from X-ray powder diffraction, their CO2 adsorption and photoluminescent properties show a direct correlation with the structure of their parent organic ligand. [ABSTRACT FROM AUTHOR]