Luminescent multifunctional lanthanides-based metal-organic frameworks

Metal-organic frameworks based on trivalent lanthanides (LnMOFs) are a very promising class of materials for addressing the challenges in engineering of luminescent centres. Lanthanide-bearing phosphors find numerous applications in lighting, optical communications, photonics and biomedical devices. In this critical review we discuss the potential of LnMOFs as multifunctional systems, which combine light emission with properties such as microporosity, magnetism, chirality, molecule and ion sensing, catalysis and activity as multimodal imaging contrast agents. We argue that these materials present a unique chance of observing synergy between several of these properties, such as the coupling between photoluminescence and magnetism. Moreover, an integrated approach towards the design of efficient, stable, cheap, environmentally-friendly and multifunctional luminescent LnMOFs is still missing. Although research into LnMOFs is at its early stage and much basic knowledge is still needed, the field is ripe for new ideas, which will enable sensor devices and photonic prototypes to become a commercial reality (81 references).     

Conjugated ligands modulated sandwich structures and luminescence properties of lanthanide metal-organic frameworks

A conjugated ligand, 2-(carboxylic acid)-6-(2-benzimidazolyl) pyridine (Hcbmp), and a series of Lanthanide metal-organic frameworks (MOFs) [Ln(2)(cbmp)(ox)(3)(H(2)O)(2)](2)·2H(3)O(+)·7H(2)O (Ln = Sm (3), Eu (4), and Gd (5), H(2)ox = oxalic acid) have been designed and assembled. To elucidate how the conjugated ligands modulate the structures and luminescence properties, we carried out the structural characterizations and luminescence studies of complexes 3 and 4, and their corresponding oxalate complexes [Ln(ox)(1.5)(H(2)O)(3)]·2H(2)O (Ln = Sm (1) and Eu (2)) were also investigated for comparison. The changes of luminescence behaviors upon dehydration and D(2)O-rehydration processes are presented and discussed in detail. The results indicated that, the cbmp(-) ligands distribute on both sides of the ox(-)-Ln bilayer network to construct a sandwich structure. Moreover, the lowest triplet state of cbmp(-) ligands can match well the energy levels of the Sm(3+) and Eu(3+) cations which allow the preparation of new Ln-MOF materials with enhanced luminescence properties. Meanwhile, the crystallinity of solid states produces more substantial change in the luminescence behaviors than removal or replacement of effective nonradiative relaxers.     

Microwave-assisted synthesis of a series of lanthanide metal-organic frameworks and gas sorption properties

A series of isostructural microporous lanthanide metal-organic frameworks (MOFs) formulated as [Ln(2)(TPO)(2)(HCOO)]·(Me(2)NH(2))·(DMF)(4)·(H(2)O)(6) {Ln = Y (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Tm (9), Yb (10), and Lu (11); H(3)TPO = tris-(4-carboxylphenyl)phosphineoxide; DMF = N,N-dimethylformamide} has been synthesized under microwave-assisted solvothermal reaction for 30 min. Alternatively, if a conventional solvothermal reaction is carried out under the same temperature, a much longer time (3 days) is needed for the same phase in similar yield. Structure analysis reveals that the framework is a 4,8-connected network with point symbol (4(10)·6(16)·8(2)) (4(5)·6)(2), which is the subnet of alb net. Thermal gravimetric analyses performed on as-synthesized MOFs reveal that the frameworks have high thermal stability. The luminescent properties of 2, 3, 5, and 6 were investigated and show characteristic emissions for Sm(III), Eu(III), Tb(III), and Dy(III) at room temperature, respectively. Gas sorption properties of 1 and 3 were studied by experimentally measuring nitrogen, argon, carbon dioxide, methane, and hydrogen sorption isotherms. The resulting materials show high and preferential CO(2) adsorption over N(2) gas at ambient temperature, indicating that the present materials can be applied in a CO(2) capture process.     

Luminescent nanoscale metal–organic frameworks for chemical sensing

Metal–organic frameworks(MOFs) are a fascinating class of crystalline materials constructed from selfassembly of metal cations/clusters and organic ligands. Both metal and organic components can be used to generate luminescence, and can further interact via antenna effect to increase the quantum yield,providing a versatile platform for chemical sensing based on luminescence emission. Moreover, MOFs can be miniaturized to nanometer scale to form nano-MOF(NMOF) materials, which exhibit many advantages over conventional bulk MOFs in terms of the facile tailorability of compositions, sizes and morphologies, the high dispersity in a wide variety of medium, and the intrinsic biocompatibility. This review will detail the development of NMOF materials as chemical sensors, including the synthetic methodologies for designing NMOF sensory materials, their luminescent properties and potential sensing applications.     

Luminescent zinc and cadmium metal-organic frameworks based on tetrazole ligands

Three metal-organic frameworks with 1D zigzag chain [Zn(dte)(H₂O)₃]·2H₂O (1), 2D double layer [Cd(dtb)(H₂O)(phen)] (2), 3D network [Zn(dte)(phen)] (3) based on tetrazole-based ligands (H₂dtb = 1,3-dis(2H-tetrazol-5-yl)benzene, H₂dte = 1,4-ditetrazolylethylene, phen = 1,10-phenanthroline), have been synthesized and characterized. All the compounds exhibit unusual strong luminescence at room temperature in the solid state and can be potentially used as luminescent materials.     

Synthesis, structure, and luminescent and magnetic properties of novel lanthanide metal-organic frameworks with zeolite-like topology

A series of microporous lanthanide metal-organic frameworks [Ln(BTC)(DMF)(2) x H(2)O, Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5), Yb (6); DMF = N,N'-dimethylformamide] with 4 x 4 x 4 x 6 x 6 x 8 topology, which is very common in the zeolite topologies, have been synthesized under mild conditions. The single-crystal X-ray diffraction analysis reveals that they exhibit the same three-dimensional (3D) architecture and crystallize in monoclinic symmetry space group C2/c. Organic and inorganic four-connected nodes link each other to form a 3D open framework. The framework contains approximate 13 Angstrom x 7 Angstrom rectangle channels along the [1,1,0] and [1,-1,0] directions, respectively. The luminescent properties of these complexes have been studied, and complex 1 shows a Tb(3+) characteristic emission in the range of 450-650 nm at room temperature. Complexes 1-5 exhibit antiferromagnetic interaction between Ln(3+) ions. The water sorption isotherm shows that about 15 water molecules per unit cell can be adsorbed into the micropores of dehydrated complex 4.     

Synthesis, structure, and luminescent properties of microporous lanthanide metal-organic frameworks with inorganic rod-shaped building units

A series of microporous lanthanide metal-organic frameworks, Tb3(BDC)(4.5)(DMF)2(H2O)3.(DMF)(H2O) (1) and Ln3(BDC)(4.5)(DMF)2(H2O)3.(DMF)(C2H5OH)(0.5)(H2O)(0.5) [Ln = Dy (2), Ho (3), Er (4)], have been synthesized by the reaction of the lanthanide metal ion (Ln3+) with 1,4-benzenedicarboxylic acid and triethylenetetramine in a mixed solution of N,N'-dimethylformamide (DMF), water, and C(2)H(5)OH. X-ray diffraction analyses reveal that they are extremely similar in structure and crystallized in triclinic space group P. An edge-sharing metallic dimer and 4 metallic monomers assemble with 18 carboxylate groups to form discrete inorganic rod-shaped building units [Ln6(CO2)18], which link to each other through phenyl groups to lead to three-dimensional open frameworks with approximately 4 x 6 A rhombic channels along the [0,-1,1] direction. A water sorption isotherm proves that guest molecules in the framework of complex 1 can be removed to create permanent microporosity and about four water molecules per formula unit can be adsorbed into the micropores. These complexes exhibit blue fluorescence, and complex 1 shows a Tb3+ characteristic emission in the range of 450-650 nm.     

基于2,5-二溴对苯二羧酸配体的镧系金属有机骨架的合成、结构及性质

采用溶剂热法, 以2, 5-二溴对苯二甲酸(H₂L)为配体, 分别与六水合硝酸钕、六水合硝酸钆反应合成了 2种镧系金属有机骨架(MOFs):{[Nd₂(L)₃(DMF)₂(H₂O)₂]·2DMF}_n (1)和{[Gd₂(L)₃(DMF)₂(H₂O)₂]·2DMF}_n (2)。通过单晶X射线衍射、粉末X射线衍射、红外光谱、元素分析、荧光光谱、热重分析等测试方法对其进行了结构表征与性质研究。结果表明, 2个配合物均是以稀土离子为金属节点, 与配体相互连接, 形成无限延伸的三维网状结构。     

Pillaring of CdCl2-like layers in lanthanide metal-organic frameworks: synthesis, structure, and photophysical properties

A hydrothermal reaction of lanthanide salts, pyridine-2,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, and water gave rise to a new series of three-dimensional mixed carboxylates (homocyclic and heterocyclic) of lanthanides with the general formula [M2(H2O)4][{C5H3N(COO)2}2{C6H4(COO)2}], M=La (I), Pr (II), and Nd (III). The structure consists of M2O14N2 dimeric units connected by pyridine-2,3-dicarboxylate moieties to form two-dimensional layers that are pillared by terephthalate units. The structures also possess two co-ordinated water molecules, which are arranged to form one-dimensional helical chains and can be reversibly adsorbed. The connectivity within the layers closely resembles that of the CdCl2 layered structure with 3(6) topology. To the best of our knowledge, this is the first observation of CdCl2 topology in lanthanide metal-organic framework compounds. Partial substitution of La3+ in I by Eu3+ and Tb3+ (2 and 4 %) gives rise to characteristic red/pink or green emission, which suggests a ligand-sensitized metal-centered emission. The Nd compound III shows interesting UV and blue emission through an up-conversion process.     

In silico screening of metal-organic frameworks in separation applications

Porous materials such as metal-organic frameworks (MOFs) and zeolitic imidazolate frameworks (ZIFs) offer considerable potential for separating a variety of mixtures such as those relevant for CO(2) capture (CO(2)/H(2), CO(2)/CH(4), CO(2)/N(2)), CH(4)/H(2), alkanes/alkenes, and hydrocarbon isomers. There are basically two different separation technologies that can be employed: (1) a pressure swing adsorption (PSA) unit with a fixed bed of adsorbent particles, and (2) a membrane device, wherein the mixture is allowed to permeate through a micro-porous crystalline layer. In view of the vast number of MOFs, and ZIFs that have been synthesized there is a need for a systematic screening of potential candidates for any given separation task. Also of importance is to investigate how MOFs and ZIFs stack up against the more traditional zeolites such as NaX and NaY with regard to their separation characteristics. This perspective highlights the potency of molecular simulations in determining the choice of the best MOF or ZIF for a given separation task. A variety of metrics that quantify the separation performance, such as adsorption selectivity, working capacity, diffusion selectivity, and membrane permeability, are determined from a combination of Configurational-Bias Monte Carlo (CBMC) and Molecular Dynamics (MD) simulations. The practical utility of the suggested screening methodology is demonstrated by comparison with available experimental data.     

Functional porphyrinic metal-organic frameworks: crystal engineering and applications

Metal-organic frameworks (MOFs) are a kind of material which are able to integrate functional groups on their framework backbones. The tunable functionalities let MOFs be applied in various fields of luminescence, gas storage, sensing, magnetics, catalysis and biomedical imaging. Because of their interesting properties of structural robustness, catalysis, charge and energy transformations, using porphyrins and metalloporphyrins as synthons for the fabrication of functional MOFs has attracted considerable interest. Many efficient strategies have been established for the construction of functional porphyrinic MOFs, and some of them present interesting properties for potential applications. This perspective is aimed to summarize recent progress on porphyrinic MOFs, including new synthesis strategies and applications.     

A review on metal-organic frameworks for photoelectrocatalytic applications

Semiconductor-based photoelectrocatalytic processes have attracted considerable research interest for solar energy collection and storage. Photoelectrocatalysis is a heterogeneous photocatalytic process in which a bias potential is applied to a photoelectrode, and thus the photoelectrocatalytic performance is closely related to the photoelectrode prepared by semiconductors. Among various semiconductors, metal-organic frameworks (MOFs) have attracted more and more attention because of their unique properties such as optical properties and adjustable structure. Herein, a comprehensive review on different MOFs (Ti-based, Zn-based, Co-based, Fe-based, Cu-based, and mixed metal-based MOFs) for heterogeneous photoelectrocatalysis is carried out and, in particular, the application of this technique for CO₂ conversion and water splitting is discussed. In addition, the challenges and development prospects of MOFs in photoelectrocatalysis are also presented.     

Porous metal-organic frameworks as platforms for functional applications

Metal-organic frameworks (MOFs), also known as coordination polymers, have emerged as a new class of crystalline porous materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers. MOFs have tunable pores and functionalities, and usually exhibit very high surface areas. The potential applications of porous MOFs cover a broad range of fields and most of their applications are related to pore sizes, shapes and structures/environments. In this feature article, we provide an overview of the recent developments of porous MOFs as platforms in the functional applications of sorption and separation, heterogeneous catalysis, as supports/host matrices for metal nanoparticles, and as templates/nanoreactors for new material preparation.     

基于2，5-二溴对苯二羧酸配体的镧系金属有机骨架的合成、结构及性质

采用溶剂热法,以2,5-二溴对苯二甲酸(H₂L)为配体,分别与六水合硝酸钕、六水合硝酸钆反应合成了2种镧系金属有机骨架(MOFs)：{[Nd₂(L)₃(DMF)₂(H₂O)₂]·2DMF}_n (1)和{[Gd₂(L)₃(DMF)₂(H₂O)₂]·2DMF}_n (2)。通过单晶X射线衍射、粉末X射线衍射、红外光谱、元素分析、荧光光谱、热重分析等测试方法对其进行了结构表征与性质研究。结果表明,2个配合物均是以稀土离子为金属节点,与配体相互连接,形成无限延伸的三维网状结构。     

Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris(β -diketonato)lanthanide(III) complexes were prepared, where the β -diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β -diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.     

Luminescent lanthanide complexes with liquid crystalline properties

Lewis-base adducts of tris( β-diketonato)lanthanide(III) complexes were prepared, where the β-diketone is para -alkoxy-substituted 1,3-diphenyl-1,3-propanedione. These compounds are the first examples of liquid crystalline lanthanide complexes in which the mesomorphism is introduced via a β-diketonate ligand. Depending on the type of the Lewis base, the metallomesogens exhibit a monotropic smectic A or a monotropic highly ordered smectic phase. Intense photoluminescence was observed for the europium(III) complexes at room temperature.     

金属有机框架材料的研究进展

金属有机框架(metal-organic frameworks,MOFs)材料是一类由有机配体与金属中心经过自组装形成的具有可调节孔径的材料。与传统无机多孔材料相比,MOFs材料具有更大的比表面积,更高的孔隙率,结构及功能更加多样,因而已经被广泛应用于气体吸附与分离、传感器、药物缓释、催化反应等领域中。新兴材料的出现极大地促进了各个学科间的相互发展,本文综述了近年来MOFs材料的研究发展,包括MOFs材料自身的特点、国内外发展现状、应用领域以及复合MOFs材料的研究热点,并对今后的发展进行了展望。     

Syntheses, structures and properties of cadmium benzenedicarboxylate metal-organic frameworks

The products isolated from the reaction between Cd(NO3)2 x 4H2O and 1,4-benzenedicarboxylic acid (H2bdc) in DMF are very dependent on the conditions. At 115 degrees C, the reaction gives [Cd(bdc)(DMF)]infinity, which has a three-dimensional network structure, whereas at 95 degrees C, 1 is formed alongside [Cd3(bdc)3(DMF)4]infinity 2, which has a two-dimensional network structure. When the reaction is carried out under pressure, it yields [Cd3(bdc)3(DMF)4]infinity 3, which is a supramolecular isomer of 2. The structure of 3 differs from that of 2 regarding the way the Cd3(O2CR)6 units are interlinked to form layers. When the reaction was carried out in DMF that had undergone partial hydrolysis, the only isolated product was [(NMe2H2)2[Cd(bdc)2] x 2DMF]infinity 4. Compound 4 has a three-dimensional triply-interpenetrated diamondoid structure, with dimethylammonium cations and DMF molecules included within the pores. The reaction between Cd(NO3)2 x 4H2O and H2bdc in DEF gave [Cd(bdc)(DEF)]infinity 5, regardless of the solvent quality. Compound 5 has a three-dimensional network structure. The reaction of Cd(NO3)2 x 4H2O and 1,3-benzenedicarboxylic acid (H2mbdc) in DMF gave [Cd(mbdc)(DMF)]infinity 6 which has a bilayer structure. The thermal properties of the new materials have been investigated, and the coordinated DEF molecules from 5 can be removed on heating to 400 degrees C without any change in the powder X-ray diffraction pattern. The H2 sorption isotherm for the desolvated material shows marked hysteresis between adsorption and desorption, and less adsorption than predicted by simulations. Kinetic data indicate that the hysteresis is not due to mass transfer limitations, and the most likely explanation for this behaviour lies in partial collapse of the framework to an amorphous phase under the conditions of activation.     

高灵敏、多响应的镧系金属有机骨架的设计、合成和荧光传感性能

基于5-(3,4-二羧基苯氧基)间苯二甲酸(H₄dppa)配体,通过水热法设计并合成了2种镧系金属有机骨架(Ln-MOFs)：{(dima)[Dy (dppa)(H₂O)₂]·2.5H₂O}_n(Dy-MOF)和{(dima)[Eu (dppa)(H₂O)₂]·1.5H₂O}_n(Eu-MOF)(dima=二甲胺阳离子)。并用元素分析、红外光谱、单晶X射线衍射等对其进行了结构表征。2种Ln-MOFs为异质同构的二维网状结构,相邻的二维网络通过氢键作用进一步形成三维超分子网络结构。荧光分析表明Dy-MOF和Eu-MOF在室温下具有优良的荧光性能,而且Dy-MOF还具有优异的荧光传感性能,可高效、高灵敏检测多种水中污染物：苯胺(ANI)、硝基苯(NB)、四环素(TC)、嘧霉胺(PTH)以及色氨酸(Trp)。此外还探究了Dy-MOF检测污染物时的荧光淬灭机理。