Synthesis of phase-pure interpenetrated MOF-5 and its gas sorption properties

For the first time, phase-pure interpenetrated MOF-5 (1) has been synthesized and its gas sorption properties have been investigated. The phase purity of the material was confirmed by both single-crystal and powder X-ray diffraction studies and TGA analysis. A systematic study revealed that controlling the pH of the reaction medium is critical to the synthesis of phase-pure 1, and the optimum apparent pH (pH*) for the formation of 1 is 4.0-4.5. At higher or lower pH*, [Zn(2)(BDC)(2)(DMF)(2)] (2) or [Zn(5)(OH)(4)(BDC)(3)] (3), respectively, was predominantly formed. The pore size distribution obtained from Ar sorption experiments at 87 K showed only one peak, at ~6.7 ?, which is consistent with the average pore size of 1 revealed by single crystal X-ray crystallography. Compared to MOF-5, 1 exhibited higher stability toward heat and moisture. Although its surface area is much smaller than that of MOF-5 due to interpenetration, 1 showed a significantly higher hydrogen capacity (both gravimetric and volumetric) than MOF-5 at 77 K and 1 atm, presumably because of its higher enthalpy of adsorption, which may correlate with its higher volumetric hydrogen uptake compared to MOF-5 at room temperature, up to 100 bar. However, at high pressures and 77 K, where the saturated H(2) uptake mostly depends on the surface area of a porous material, the total hydrogen uptake of 1 is notably lower than that of MOF-5.     

抗肿瘤药物在金属有机骨架中的装载及体外释放

以三乙胺直接加入法制备金属-有机骨架MOF-5, 采用X射线粉末衍射(XRD), 红外光谱(IR)和热重分析(TG)对所得样品进行表征. 分别以辣椒素和5-氟尿嘧啶(5-Fluouourail, 5-FU)为模型药物, 研究了MOF-5对2种药物的载药及体外释药性能. 通过将所得样品的XRD和IR谱图与标准谱图比对确定了样品的结构. TG结果表明, 所制备的MOF-5热稳定性良好. MOF-5对辣椒素的最高载入量达0.592 g/g载体, 对5-FU的最高载入量为0.315 g/g载体, 两种载药体系的体外释药均为明显的两相模式. 体外细胞毒性实验结果表明, MOF-5具有良好的生物相容性.     

离子液体负载的金属框架Py/MOF-199的制备及其吸附脱硫性能

制备了金属框架MOF-199(Cu-BTC),并将[Hnmp][H2PO4]离子液体负载到MOF-199上合成了离子液体负载的金属框架Py/MOF-199。对吸附剂进行了X射线衍射、红外光谱、扫描电镜、比表面积表征。考察了MOF-199预处理条件、离子液体负载方式、负载量、负载温度、负载时间对噻吩吸附脱除性能的影响,通过正交实验优化了吸附剂的制备条件和吸附脱硫条件。结果表明,离子液体改性得到的Py/MOF-199保持了MOF-199的规则的八面体结构。Py/MOF-199的适宜制备条件为:采用二氯甲烷索氏提取并真空干燥法进行预处理MOF-199后,再用溶剂热法负载[Hnmp][H_2PO_4],负载温度为50℃,负载时间为8 h,负载量为7%。各因素对吸附剂脱硫性能影响大小顺序为:负载温度负载时间离子液体负载量。适宜Py/M OF-199吸附脱硫条件为:模拟油为10 mL,吸附剂用量0.2 g,吸附温度70℃,吸附时间1 h。在此条件下,噻吩脱除率可达到96.7%。     

Methyl modified MOF-5: a water stable hydrogen storage material

Water stable methyl modified MOF-5s have been synthesized via a solvothermal route. Methyl- and 2,5-dimethyl-modified MOF-5s show the same topology and hydrogen uptake capability as that of MOF-5. The H(2) uptake capacity of MOF-5, however, drops rapidly when exposed to the ambient air, whereas the H(2) uptake capacities of the methyl modified MOF-5s remain stable for 4 days.     

Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-177, MOF-199, and IRMOF-0

Room temperature synthesis of metal-organic frameworks (MOFs) has been developed for four well-known MOFs: MOF-5, MOF-74, MOF-177, and MOF-199. A new isoreticular metal framework (IRMOF), IRMOF-0, having the same cubic topology as MOF-5, has been synthesized from acetylenedicarboxylic acid using this method to accommodate the thermal sensitivity of the linker. Despite acetylenedicarboxylate being the shortest straight linker that can be made into an IRMOF, IRMOF-0 forms as a doubly interpenetrating structure, owing to the rod-like nature of the linker.     

The inconsistency in adsorption properties and powder XRD data of MOF-5 is rationalized by framework interpenetration and the presence of organic and inorganic species in the nanocavities

MOF-5 is the archetype metal-organic framework and has been subjected to numerous studies the past few years. The focal point of this report is the pitfalls related to the MOF-5 phase identification based on powder XRD data. A broad set of conditions and procedures have been reported for MOF-5 synthesis. These variations have led to materials with substantially different adsorption properties (specific surface areas in the range 700 to 3400 m(2)/g). The relatively low weight loss observed for some as synthesized samples upon solvent removal is also indicative of a low pore volume. Regrettably, these materials have all been described as MOF-5 without any further comments. Furthermore, the reported powder XRD patterns hint at structural differences: The variations in surface area are accompanied by peak splitting phenomena and rather pronounced changes in the relative peak intensities in the powder XRD patterns. In this work, we use single-crystal XRD to investigate structural differences between low and high surface area MOF-5. The low surface area MOF-5 sample had two different classes of crystals. For the dominant phase, Zn(OH)2 species partly occupied the cavities. The presence of Zn species makes the hosting cavity and possibly also adjacent cavities inaccessible and thus efficiently reduces the pore volume of the material. Furthermore, the minor phase consisted of doubly interpenetrated MOF-5 networks, which lowers the adsorption capacity. The presence of Zn species and lattice interpenetration changes the symmetry from cubic to trigonal and explains the peak splitting observed in the powder XRD patterns. Pore-filling effects from the Zn species (and partly the solvent molecules) are also responsible for the pronounced variations in powder XRD peak intensities. This latter conclusion is particularly useful for predicting the adsorption properties of a MOF-5-type material from powder XRD.     

Proton and water activity-controlled structure formation in zinc carboxylate-based metal organic frameworks

The contributions of terephthalic acid and Zn(2+)-coordinated water in N,N-diethylformamide (DEF) to the overall proton activity in the synthesis of MOF-5 (Zn4O(BDC)3, BDC = 1,4-benzenedicarboxylate) were quantitatively determined by combined electrochemical and UV-vis spectroscopic measurements. Structural transformations of zinc carboxylate-based metal organic frameworks due to their exposure to environments with variable water concentrations and the chemical means necessary to revert these transitions have been investigated. It was found that the water-induced structural transition of MOF-5 to the hydroxide structure Zn3(OH)2(BDC)2 x 2 DEF (MOF-69c) can be reverted by a thermal treatment of the obtained compound and its subsequent exposure to anhydrous DEF. MOF-5 syntheses from simple carboxylates as well as a water-free synthesis based on nitrate decomposition are presented. The latter demonstrates that nitrate can serve as the sole source for the oxide ion in MOF-5.     

Reversible interpenetration in a metal-organic framework triggered by ligand removal and addition

Caging cages: Crystals of a metal-organic framework, MOF-123 [Zn(7) O(2) (NBD)(5) (DMF)(2) ] have a three-dimensional porous structure in which DMF ligands (see picture, pink) protrude into small channels. Removal of these ligands triggers the transformation of this MOF to the doubly interpenetrating form, MOF-246 [Zn(7) O(2) (NBD)(5) ]. Moreover, addition of DMF into MOF-246 triggers reverse transformation to give MOF-123. NBD=2-nitrobenzene-1,4-dicarboxylate.     

Precise Control of Molecular Self-Diffusion in Isoreticular and Multivariate Metal-Organic Frameworks

Understanding the factors that affect self-diffusion in isoreticular and multivariate (MTV) MOFs is key to their application in drug delivery, separations, and heterogeneous catalysis. Here, we measure the apparent self-diffusion of solvents saturated within the pores of large single crystals of MOF-5, IRMOF-3 (amino-functionalized MOF-5), and 17 MTV-MOF-5/IRMOF-3 materials at various mole fractions. We find that the apparent self-diffusion coefficient of N,N-dimethylformamide (DMF) may be tuned linearly between the diffusion coefficients of MOF-5 and IRMOF-3 as a function of the linker mole fraction. We compare a series of solvents at saturation in MOF-5 and IRMOF-3 to elucidate the mechanism by which the linker amino groups tune molecular diffusion. The ratio of the self-diffusion coefficients for solvents in MOF-5 to those in IRMOF-3 is similar across all solvents tested, regardless of solvent polarity. We conclude that average pore aperture, not solvent-linker chemical interactions, is the primary factor responsible for the different diffusion dynamics upon introduction of an amino group to the linker.     

Enhanced Hydrostability in Ni-Doped MOF-5

Ni-doped MOF-5s were successfully synthesized for the first time via solvothermal crystallization process to enhance the hydrostability. Several characterization techniques, including X-ray diffraction (XRD), thermogravimetrical analysis (TGA), scanning electron microscopy (SEM), energy-dispersive spectroscopy instrument (EDS), inductively coupled plasma (ICP), infrared spectroscopy (IR), atomic sorption, diffuse-reflectance UV-vis spectroscopy, and gas sorption measurement, strongly support the effective incorporation of Ni(II) ions into the framework. The results demonstrated that the Ni-doped MOF-5s not only exhibit larger Langmuir specific surface areas and larger pores than the undoped MOF-5, but also significantly enhance water resistance of the framework. The H(2) uptake capacity of undoped MOF-5 drops rapidly when exposed to the ambient air, whereas the H(2) adsorptions of the Ni-doped MOF-5s remain stable for 4 days.     

Gaseous species as reaction tracers in the solvothermal synthesis of the zinc oxide terephthalate MOF-5

Gaseous species emitted during the zinc oxide/zinc hydroxide 1,4-benzenedicarboxylate metal organic framework synthesis (MOF-5, MOF-69c) have been used to investigate the reaction scheme that leads to the framework creation. Changes of the gas-phase composition over time indicate that the decomposition of the solvent diethylformamide occurs at least via two competing reaction pathways that can be linked to the reaction's overall water and pH management. From isotope exchange experiments, we deduce that one of the decomposition pathways leads to the removal of water from the reaction mixture, which sets the conditions when the synthesis of an oxide-based (MOF-5) instead of an hydroxide-based MOF (MOF-69c) occurs. A quantitative account of most reactants and byproducts before and after the MOF-5/MOF-69c synthesis is presented. From the investigation of the reaction intermediates and byproducts, we derive a proposal of a basic reaction scheme for the standard synthesis zinc oxide carboxylate MOFs.     

Transformation of a metal-organic framework from the NbO to PtS net

Two metal-organic frameworks (MOFs), MOF-501 and MOF-502, respectively, formulated as Co(2)(BPTC)(H(2)O)(5).G(x) and Co(2)(BPTC)(H(2)O)(DMF)(2).G(x) (BPTC = 3,3',5,5'-biphenyltetracarboxylate; G = guest molecules), have been synthesized and structurally characterized, and their topologies were found to be based on the NbO (MOF-501) and PtS (MOF-502) nets. Heating MOF-501 in solution results in the more thermodynamically favored MOF-502.     

碱性金属修饰金属有机骨架材料MOF-5吸附位点及其常态下分离二氧化碳/甲烷的应用

利用“一步法”合成并表征了4种碱性金属修饰的金属有机骨架材料MOF-5(记作M-MOF-5,M=Li,Na,K,Mg)。 并应用理想溶液吸附理论(IAST)对样品吸附选择性进行计算比较。 结果表明,碱性金属掺入可以降低MOF-5材料骨架结构的“互穿”程度,同时,在常温常压下,M-MOF-5对CO₂/CH₄的吸附选择性相对MOF-5(选择性为3.79)有着显著提高,尤其是Li-MOF-5(选择性为7.39)。 此外,Li-MOF-5的CO₂捕获能力相对MOF-5也有提高。     

金属有机骨架材料MOF-5吸附苯并噻吩性能

苯并噻吩类硫化物的脱除是燃油实现深度脱硫的关键。实验研究了典型的金属有机骨架材料MOF-5吸附苯并噻吩性能。结果表明,MOF-5对模型油中苯并噻吩的吸附动力学过程满足拟二级动力学模型。Langmuir、Freundlich和Dubinin-Radushkevich (D-R) 三种等温吸附模型均可较好地描述MOF-5对苯并噻吩的等温吸附行为 (Freundlich>D-R>Langmuir)。热力学参数表明,MOF-5对苯并噻吩的吸附是自发的吸热吸附过程。     

Facile xenon capture and release at room temperature using a metal-organic framework: a comparison with activated charcoal

Two well-known metal-organic frameworks (MOF-5, NiDOBDC) were synthesized and studied for facile xenon capture and separation. Our results indicate that NiDOBDC adsorbs significantly more xenon than MOF-5, and is more selective for xenon over krypton than activated carbon.     

金属有机骨架复合材料RhB/MOF-5的制备及其发光性质

通过溶剂扩散法成功地将激光染料分子罗丹明B(RhB)组装到了金属有机骨架材料MOF-5中, 从而制备出具有光学活性的主-客体金属有机骨架复合材料RhB/MOF-5. 通过光学显微镜、XRD、FTIR、UV-Vis和PL表征证明RhB存在于MOF-5晶体孔道中, 而且该金属有机骨架复合材料表现出很好的光致发光性质.     

A novel low density metal-organic framework with pcu topology by dendritic ligand

A novel low density two-fold interpenetrated MOF-5 analogue with pcu topology, JUC-100, was designed and prepared successfully. It can be regarded as MOF-5 in which half of the Zn(4)O(CO(2))(6) units are replaced by organic 1,3,5-triphenylbenzene segments. JUC-100 exhibits H(2) uptake ability comparable to interpenetrated MOF-5, but relatively low initial isosteric heat of adsorption.     

Assembly of metal-organic frameworks from large organic and inorganic secondary building units: new examples and simplifying principles for complex structures

The secondary building unit (SBU) has been identified as a useful tool in the analysis of complex metal-organic frameworks (MOFs). We illustrate its applicability to rationalizing MOF crystal structures by analysis of nine new MOFs which have been characterized by single-crystal X-ray diffraction. Tetrahedral SBUs in Zn(ADC)(2).(HTEA)(2) (MOF-31), Cd(ATC).[Cd(H(2)O)(6)](H2O)(5) (MOF-32), and Zn(2)(ATB)(H2O).(H2O)(3)(DMF)(3) (MOF-33) are linked into diamond networks, while those of Ni(2)(ATC)(H(2)O)(4).(H2O)(4) (MOF-34) have the structure of the Al network in SrAl(2). Frameworks constructed from less symmetric tetrahedral SBUs have the Ga network of CaGa(2)O(4) as illustrated by Zn(2)(ATC).(C(2)H(5)OH)(2)(H2O)(2) (MOF-35) structure. Squares and tetrahedral SBUs in Zn(2)(MTB)(H2O)(2).(DMF)(6)(H2O)(5) (MOF-36) are linked into the PtS network, which is the simplest structure type known for the assembly of these shapes. The octahedral SBUs found in Zn(2)(NDC)(3).[(HTEA)(DEF)(ClBz)](2) (MOF-37) form the most common structure for linking octahedral shapes, namely, the boron network in CaB(6). New structure types for linking triangular and trigonal prismatic SBUs are found in Zn(3)O(BTC)(2).(HTEA)(2) (MOF-38) and Zn(3)O(HBTB)(2)(H2O).(DMF)(0.5)(H2O)(3) (MOF-39). The synthesis, crystal structure, and structure analysis using the SBU approach are presented for each MOF.     

Semiconductor behavior of a metal-organic framework (MOF)

Upon light excitation MOF-5 behaves as a semiconductor and undergoes charge separation (electrons and holes) decaying in the microsecond time scale. The actual conduction band energy value was estimated to be 0.2 V versus NHE with a band gap of 3.4 eV. Photoinduced electron transfer processes to viologen generates the corresponding viologen radical cation, while holes of MOF-5 oxidizes N,N,N',N'-tetramethyl-p-phenylenediamine. One application investigated for MOF-5 as a semiconductor has been the shape-selective photocatalyzed degradation of phenol in aqueous solutions.     

Theoretical investigations on the chemical bonding, electronic structure, and optical properties of the metal-organic framework MOF-5

The chemical bonding, electronic structure, and optical properties of metal-organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional leading to a good agreement between the experimental and the theoretical equilibrium structural parameters. The calculated bulk modulus indicates that MOF-5 is a soft material. The estimated band gap from a density of state (DOS) calculation for MOF-5 is about 3.4 eV, indicating a nonmetallic character. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, and electroluminescence cells, the optical properties of this material were investigated. The detailed analysis of chemical bonding in MOF-5 reveals the nature of the Zn-O, O-C, H-C, and C-C bonds, that is, Zn-O having mainly ionic interaction whereas O-C, H-C, and C-C exhibit mainly covalent interactions. The findings in this paper may contribute to a comprehensive understanding about this kind of material and shed insight into the synthesis and application of novel and stable MOFs.