Electrochemical measurements demonstrate that magnesium surfaces can be protected by alkyl carboxylate. In a nearly neutral pH solution of sodium decanoate, the reduced corrosion rate and a passivation behaviour are attributed to the formation of Mg(C10H19O2)2(H2O)3 (Mg(C10)2) at the magnesium surface whereas heptanoate Mg(C7H13O2)2(H2O)3 (Mg(C7)2) is not efficient in such media. The crystal structures of the two metal carboxylates Mg(C7)2 and Mg(C10)2 are determined by X-ray diffraction. Single crystal data: Mg(C7)2, P21/a, a = 9.130(5) Å, b = 8.152(5) Å, c = 24.195(5) Å, β = 91.476(5)°, V = 1800.3(15) Å3, Dx = 1.242 g cm−3, Z = 4. Synchrotron powder data: Mg(C10)2, P21/a, a = 9.070(3) Å, b = 8.165(1) Å, c = 32.124(1) Å, β = 98.39(1)°, V = 2353.85(8) Å3, Dx = 1.188 g cm−3, Z = 4. Their layered structures are quite similar and differ mainly by the length of the hydrophobic chains. They consist of two planes of O-octahedra centred by Mg atoms, parallel to (001). The distorted octahedra are constituted by three oxygen atoms from carboxylate groups and by three oxygen atoms coming from water molecules. The layers are connected by hydrogen bonds. The carboxylate chains are located perpendicularly and on both sides of these planes. One carboxylate chain is bridging the Mg atom along [010] while the other is monodendate. The presence of structural water is confirmed by thermal analyses. 相似文献
This perspective article is aimed at providing a comparison of similarities and dissimilarities between the catalytic properties of zeolites and metal organic frameworks (MOFs). In the first part of the paper, we comment the general characteristics of MOFs with relevance to catalysis, making emphasis of how the properties of MOFs can serve to compliment those of zeolites as catalysts. The lower chemical and thermal stability of MOFs compared to zeolites is commented and correlated to the requirements for some liquid-phase reactions conducted under mild conditions. In the second part, we discuss the behaviour of zeolites and MOFs for four types of general organic reactions (acid catalysed, base catalysed, oxidation and hydrogenations). Particular attention is paid to provide critical comments on how MOFs could be adapted by design or can be modified by post-synthetic treatments to give well performing catalysts. 相似文献
Controlled synthesis of hydrogen-bonded organic frameworks (HOFs) remains challenging, because the self-assembly of ligands is not only directed by weak hydrogen bonds, but also affected by other competing van der Waals forces. Herein, we demonstrate the coordination-bond-directed synthesis of HOFs using a preformed metal–organic framework (MOF) as the template. A MOF (CuI-TTFTB) based on two-coordinated CuI centers and tetrathiafulvalene-tetrabenzoate (TTFTB) ligands was initially synthesized. CuI-TTFTB was subsequently oxidized to the intermediate (CuII-TTFTB) and hydrated to the HOF product (TTFTB-HOF). Single-crystal-to-single-crystal (SC-SC) transformation was realized throughout the MOF-to-HOF transformation so that the evolution of structures was directly observed by single-crystal X-ray diffraction. The oxidation and hydration of the CuI center are critical to breaking the Cu–carboxylate bonds, while the synergic corbelled S⋯S and π⋯π interactions in the framework ensured stability of materials during post-synthetic modification. This work not only provided a strategy to guide the design and discovery of new HOFs, but also linked the research of MOFs and HOFs.The MOF-to-HOF transformation was realized in a single-crystal-to-single-crystal manner by the oxidation and hydration of the CuI center in CuI-TTFTB. The corbelled S⋯S and π⋯π interactions ensured the framework stability during transformation. 相似文献
Photoelectrochemical system combines together the merits of both electrocatalysis and photocatalysis and provides an intriguing approach to artificial photosynthesis via solar-to-chemical energy conversion. This article outlines recent developments in the applications of metal–organic frameworks to realize artificial photosynthesis via photoelectrochemical route. 相似文献
Au nanoparticles decorated with mononuclear Ti-oxo units dispersed in silica clusters were formed by activating Au nanoparticles (~2 nm) stabilized with Ti- and amine-functionalized siloxane oligomers. These Au nanoparticles were active catalysts for selective oxidation of propane to acetone, and the activity increased with increasing Ti density. 相似文献
Science China Chemistry - Human health is always under global spotlight, but now it suffers from severe environmental issue and various diseases. Developing highly selective and effective... 相似文献
A new urea-containing metal-organic framework (MOF) was synthesized to act as a heterogeneous catalyst. Ureas are well-known for self-recognition and aggregation behavior, resulting in loss of catalytic competency. The catalyst spatial isolation achievable in a porous MOF environment suggests a potentially general solution. The combination of a symmetrical urea tetracarboxylate strut, 4,4'-bipyridine, and Zn(NO(3))(2)·6H(2)O under solvothermal conditions afforded a new microporous MOF (NU-601). This material is indeed an effective hydrogen-bond-donor catalyst for Friedel-Crafts reactions between pyrroles and nitroalkenes, whereas a homogeneous urea is much less competent. The higher rates of reaction of small substrates relative to larger ones with NU-601 strongly suggest that catalysis primarily occurs within the pores of this new material rather than on its exterior. To the best of our knowledge, this approach is the first example of specific engineering of successful hydrogen-bonding catalysis into a MOF material. 相似文献
We report the H2 uptake properties of six covalent organic frameworks (COFs) from first-principles-based grand canonical Monte-Carlo simulations. The predicted H2 adsorption isotherm is in excellent agreement with the only available experimental result (3.3 vs 3.4 wt % at 50 bar and 77 K for COF-5), also reported here, validating the predictions. We predict that COF-105 and COF-108 lead to a reversible excess H2 uptake of 10.0 wt % at 77 K, making them the best known storage materials for molecular hydrogen at 77 K. We predict that the total H2 uptake for COF-108 is 18.9 wt % at 77 K. COF-102 shows the best volumetric performance, storing 40.4 g/L of H2 at 77 K. These results indicate that the COF systems are most promising candidates for practical hydrogen storage. 相似文献
Covalent organic frameworks (COFs) are a class of crystalline porous polymers that allow the atomically precise integration of organic units to create predesigned skeletons and nanopores. They have recently emerged as a new molecular platform for designing promising organic materials for gas storage, catalysis, and optoelectronic applications. The reversibility of dynamic covalent reactions, diversity of building blocks, and geometry retention are three key factors involved in the reticular design and synthesis of COFs. This tutorial review describes the basic design concepts, the recent synthetic advancements and structural studies, and the frontiers of functional exploration. 相似文献
Commensurate adsorption occurs when the number of molecules adsorbed per unit cell relates to the symmetry of the framework
and its topology. While rare in zeolite materials, commensurate adsorption has been observed in several MOF materials. In
some MOF materials, several molecules having dimensions within a limited size range show this effect. This paper describes
the commensurate adsorption properties of three MOF materials and also two MOFs showing unusual combined structure-composition
adsorption features. 相似文献
A mean field model for NO oxidation with H2 over supported catalysts is proposed and solved numerically. The model is composed of a system of PDEs subject to nonclassical conjugate conditions at the catalyst–support interface and includes the bulk diffusion of reactants and reaction products and surface diffusion of all intermediate products. The influence of the particle jumping rate constants via the catalyst–support interface and reaction rate constants on the evolution of the reactivity of the catalyst surface is investigated. It is shown that the conversion rates (turnover frequencies) of NO and H2 into products, N2, H2O, NH3, and N2O, are nonmonotonous functions of time. The conversion rates of NO and H2 into N2 and N2O can have one or two local maxima, while their conversion rates into H2O and NH3 can possess one, two, or three local maxima. The mechanism and conditions for arising of the second maximum are discussed and reaction steps that essentially increase the surface reactivity are indicated.
Bidentate phosphonate monoesters are analogues of popular dicarboxylate linkers in MOFs, but with an alkoxy tether close to the coordinating site. Herein, we report 3-D MOF materials based upon phosphonate monoester linkers. Cu(1,4-benzenediphosphonate bis(monoalkyl ester), CuBDPR, with an ethyl tether is nonporous; however, the methyl tether generates an isomorphous framework that is porous and captures CO(2) with a high isosteric heat of adsorption of 45 kJ mol(-1). Computational modeling reveals that the CO(2) uptake is extremely sensitive both to the flexing of the structure and to the orientation of the alkyl tether. 相似文献
A bifunctional imidazolium linker was used for the production of highly crosslinked element organic frameworks by Suzuki-coupling with tetrafunctional boronic acids. The resulting porous materials are good heterogeneous organocatalysts in the N-heterocyclic carbene-catalyzed conjugated umpolung of α,β-unsaturated cinnamaldehyde. 相似文献
For the first time, iron oxide on carbon aerogel, amine functionalized carbon nanotube, black carbon and carboxylic acid functionalized carbon nanotube in the presence of H2O2 was reported as an efficient and stable catalyst for the selective oxidation of sulfides and alcohols. The catalysts were characterized by scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy and atomic absorption spectroscopy. In the next step, catalytic reactivity toward sulfide to sulfoxide and alcohol to aldehyde/ketone oxidation in the presence of H2O2 was studied and discussed. 相似文献
The extra-large cavities of zeolite-like metal-organic frameworks (ZMOFs) offer great potential for their exploration in applications pertinent to larger molecules, like porphyrins. The anionic nature of the framework allowed for facile in situ encapsulation of a cationic free-base porphyrin, and the alpha-cage of our (In-imidazoledicarboxylate)-based rho-ZMOF is ideally suited to the isolation of one porphyrin molecule per cage, which prevents the oxidative self-degradation associated with self-dimerization common in homogeneous catalysis and upon aggregation in solid supports like mesoporous silicates or polymers. The encapsulation of a free-base porphyrin [5,10,15,20-tetrakis(1-methyl-4- pyridinio)porphyrin] and the stability of the rho-ZMOF to metalation conditions, allows for the preparation of a variety of metalloporphyrins (i.e., Mn, Cu, Co, Zn ions) with the ZMOF serving as a platform. The Mn-metallated porphyrin encapsulated in rho-ZMOF shows catalytic activity toward the oxidation of cyclohexane, with turn-over numbers, to the best of our knowledge, higher than reported for similar heterogeneous systems, and our system can be recycled up to 11 cycles, which represents a longer lifetime than reported for any other system. 相似文献
Dendritic manganese, iron, and ruthenium porphyrins with dendritic wedges attached to the periphery of meso-tetraphenylporphyrin (TPP) or meso-triarylporphyrin macrocycle were reported to be active catalysts for epoxidation or cyclopropanation of alkenes or oxidation of sulfides. The dendritic manganese and iron porphyrin catalysts exhibit considerably higher regioselectivity and shape selectivity than the respective parent catalyst [M(TPP)Cl] (M = Mn, Fe). Systematic increase in shape selectivity, diastereoselectivity, epoxide/sulfoxide selectivity, or catalyst stability with increasing generation number of the dendritic wedges is observed for the alkene epoxidation or sulfide oxidation reactions catalyzed by these dendritic manganese, iron, and ruthenium porphyrins. To cite this article: C.-M. Che, C. R. Chimie 6 (2003).相似文献
Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity, and the ease of work-up after reaction. In each case, mechanistic information is presented, e.g., on the site of reaction (whether interlayer or surface), rate determining steps, etc. The regiochemical consequences of the restricted reaction space are stressed.Based on material presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986. 相似文献