Novel electrorheological properties of a metal-organic framework Cu3(BTC)2

A metal-organic framework, Cu(3)(BTC)(2), was synthesized and applied as an electro-responsive electrorheological material dispersed in insulating oil. Powder of crystalline Cu(3)(BTC)(2) exhibited excellent chain-like structures and controllable rheological properties in an applied electric field.     

Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate)

An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. [Cu3(btc)2] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in [Cu3(btc)2] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed.     

Stability improvement of Cu3(BTC)2 metal-organic frameworks under steaming conditions by encapsulation of a Keggin polyoxometalate

Cu(3)(BTC)(2) with an incorporated Keggin polyoxometalate was demonstrated to be stable under steaming conditions up to 483 K, while the isostructural HKUST-1 degrades and transforms into [Cu(2)OH(BTC)(H(2)O)](n)·2nH(2)O from 343 K onwards.     

Effects of varying water adsorption on a Cu3(BTC)2 metal-organic framework (MOF) as studied by 1H and 13C solid-state NMR spectroscopy

The process of water adsorption on a dehydrated Cu(3)(BTC)(2) (copper (II) benzene 1,3,5-tricarboxylate) metal-organic framework (MOF) was studied with (1)H and (13)C solid-state NMR. Different relative amounts of water (0.5, 0.75, 1, 1.5, 2, and 5 mole equivalents with respect to copper) were adsorbed via the gas phase. (1)H and (13)C MAS NMR spectra of dehydrated and water-loaded Cu(3)(BTC)(2) samples gave evidence on the structural changes due to water adsorption within the MOF material as well as information on water dynamics. The analysis of (1)H spinning sideband intensities reveals differences in the (1)H-(63/65)Cu hyperfine coupling between dehydrated and water-loaded samples. The investigation was continued for 60 days to follow the stability of the Cu(3)(BTC)(2) network under humid conditions. NMR data reveal that Cu(3)(BTC)(2) decomposes quite fast with the decomposition being different for different water contents.     

Argon adsorption on Cu3(benzene-1,3,5-tricarboxylate)2(H2O)3 metal-organic framework

Using volumetric adsorption techniques, we have measured the adsorption of argon on Cu3(BTC)2(H2O)3, (BTC = benzene-1,3,5-tricarboxylate), a microporous metal-organic framework structure, at temperatures between 66 and 143 K. In addition to the experiments, we have used Grand Canonical Monte Carlo simulations to calculate the adsorption isotherm of argon at 87 K. Our experimental and theoretical results are compared to those of previous studies. The experiments were performed using a high density of points, allowing us to obtain, in detail, the isosteric heat's coverage dependence. Our values from the simulations are in reasonable agreement with those obtained in the experiments.     

Adsorptive separation of isobutene and isobutane on Cu3(BTC)2

The metal organic framework material Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) has been synthesized using different routes: under solvothermal conditions in an autoclave, under atmospheric pressure and reflux, and by electrochemical reaction. Although the compounds display similar structural properties as evident from the powder X-ray diffraction (XRD) patterns, they differ largely in specific surface area and total pore volume. Thermogravimetric and chemical analysis support the assumption that pore blocking due to trimesic acid and/or methyltributylammoniummethylsulfate (MTBS) which has been captured in the pore system during reaction is a major problem for the electrochemically synthesized samples. Isobutane and isobutene adsorption has been studied for all samples at different temperatures in order to check the potential of Cu3(BTC)2 for the separation of small hydrocarbons. While the isobutene adsorption isotherms are of type I according to the IUPAC classification, the shape of the isobutane isotherm is markedly different and closer to type V. Adsorption experiments at different temperatures show that a somewhat higher amount of isobutene is adsorbed as compared to isobutane. Nevertheless, the differential enthalpies of adsorption are only different by about 5 kJ/mol, indicating that a strong interaction between the copper centers and isobutene does not drive the observed differences in adsorption capacity. The calculated breakthrough curves of isobutene and isobutane reveal that a low pressure separation is preferred due to the peculiar shape of the isobutane adsorption isotherms. This has been confirmed by preliminary breakthrough experiments using an equimolar mixture of isobutane and isobutene.     

Cu3(BTC)2: CO oxidation over MOF based catalysts

Crystalline and amorphized MOFs (Cu(3)(BTC)(2)) have been demonstrated to be excellent catalysts for CO oxidation. The catalytic activity can be further improved by loading PdO(2) nanoparticles onto the amorphized Cu(3)(BTC)(2).     

Distorted five-fold coordination of Cu2+(aq) from a Car-Parrinello molecular dynamics simulation

The solvation shell structure and dynamics of a single Cu2+ ion in a periodic box with 32 water molecules under ambient conditions has been investigated using Car-Parrinello molecular dynamics simulations in a time-window of 18 ps. Five-fold coordination with four equidistant equatorial water molecules at 2.00 A and one axial water molecule at 2.45 A from the Cu2+ ion is found. A "hole" without water molecules is found on the opposite side of the axial water. The ion-water bonding character for the equatorial water molecules is different from that of the axial water molecules, as shown by a localized orbital analysis of the electronic structure. Moreover, the calculated OD stretching vibrational band for the equatorial water molecules lies ca. 175 cm-1 below the axial-water band, in good agreement with experimental data. The equatorial-water band lies below, and the axial-water band above, the pure liquid D2O band, also in agreement with experimental data.     

Porous homo- and heterochiral cobalt(II) aspartates with high thermal stability of the metal-organic framework

Metal-organic coordination polymers with the compositions [Co₂(L-asp) ₂-(bpy)] · MeOH · H₂O (1), [Co₂(L-asp)₂(bpe)] · 0.28(bpe) · H₂O (2), and [Co₂(d-asp)(l-asp)-(bpa)] · 0.25(bpa) · 1.5H₂O (3) (H₂asp is aspartic acid, bpy is 4,4′-bipyridine, bpe is trans-bis(4- pyridyl)ethylene, and bpa is 1,2-bis(4-pyridyl)ethane) were synthesized on heating cobalt(II) as-partate and N-donor ligands (bpy, bpe, or bpa) in an aqueous-methanol mixture. The structures of compounds 1⁗ash;3 were established by X-ray diffraction analysis and confirmed by X-ray powder crystallography, IR spectroscopy, thermogravimetry, and elemental analysis. The stability of the synthesized coordination polymers was studied. It was shown that they retain the framework structure on heating to 300 °C.     

A novel (3,36)-connected and self-interpenetrated metal-organic framework with high thermal stability and gas-sorption capabilities

By using a ligand containing pyridyl and carboxylate groups as units, a novel (3,36)-connected and self-interpenetrated metal-organic framework was constructed, which exhibited high thermal stability and gas sorption capabilities.     

Hydrothermal synthesis,structure,fluorescence property of a novel 3D metal-organic framework with high thermal stability

A novel 3D metal-organic framework(MOF) with remarkable thermal stability,Ni(BIC)2.2·5H2O(JUC-86)(HBIC = 1-H-benzimidazole-5-carboxylic acid and JUC = Jilin University China),has been synthesized under hydrothermal conditions.It crystallizes in tetragonal symmetry with P43212 space group.The 3D structure consists of channels assembled from triple helices with a 4.5 × 4.52 aperture,which are formed by the parallel alignment of three infinite helical chains.The thermogravimetric analysis(TGA) and powder X-ra...     

Mixed-valence Cu(II)Cu(I)15I17 cluster builds up a 3D metal-organic framework with paramagnetic and thermochromic characteristics

Four cubane-like Cu4I4 units are assembled around an iodine atom to form the giant, mixed-valent Cu(II)Cu(I)15I17 cluster. The Cu(II)Cu(I)15I17 cluster and a bipyrazole linker form a 3D open framework with paramagnetic and thermochromic properties. This paper also touches on the resemblance of this cluster to the self-similar object of a Sierpinski tetrahedron.     

A (3,6)-connected metal-organic framework consisting of chair-like {Fe6} clusters and BTC linkers

A 2-D framework composed of a chair-like {Fe₆} cluster and BTC linkers, [Fe₆(BTC)₂(HCOO)₆(DMF)₆] (1, BTC?=?1,3,5-benzenetricarboxylate), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction analysis. The {Fe₆} cluster contains six iron ions and six formate ligands, with each formate coordinating with three iron ions to construct the hexa-nuclear iron wheel. The {Fe₆} wheels are further connected via BTC ligands resulting in the first example of a 2-D framework based on {Fe₆} clusters and BTC linkers. A magnetic study indicates that intramolecular antiferromagnetic interactions exist in the hexa-nuclear iron cluster.     

Car-Parrinello molecular dynamics simulation of Fe 3+ (aq)

The optimized geometry and energetic properties of Fe(D2O)n 3+ clusters, with n = 4 and 6, have been studied with density-functional theory calculations and the BLYP functional, and the hydration of a single Fe 3+ ion in a periodic box with 32 water molecules at room temperature has been studied with Car-Parrinello molecular dynamics and the same functional. We have compared the results from the CPMD simulation with classical MD simulations, using a flexible SPC-based water model and the same number of water molecules, to evaluate the relative strengths and weaknesses of the two MD methods. The classical MD simulations and the CPMD simulations both give Fe-water distances in good agreement with experiment, but for the intramolecular vibrations, the classical MD yields considerably better absolute frequencies and ion-induced frequency shifts. On the other hand, the CPMD method performs considerably better than the classical MD in describing the intramolecular geometry of the water molecule in the first hydration shell and the average first shell...second shell hydrogen-bond distance. Differences between the two methods are also found with respect to the second-shell water orientations. The effect of the small box size (32 vs 512 water molecules) was evaluated by comparing results from classical simulations using different box sizes; non-negligible effects are found for the ion-water distance and the tilt angles of the water molecules in the second hydration shell and for the O-D stretching vibrational frequencies of the water molecules in the first hydration shell.     

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.     

A lanthanide metal-organic framework with high thermal stability and available Lewis-acid metal sites

A lanthanide metal-organic framework, Dy(BTC)(H2O).DMF, with excellent thermal stability shows a high surface area, 655 m(2) g(-1), high hydrogen and carbon dioxide storage capability, and available Lewis-acid metal sites which could be anticipated to use in catalysis and metal-site specific chemical sensor.     

Novel (3,4,6)-connected metal-organic framework with high stability and gas-uptake capability

A microporous and noninterpenetrated metal-organic framework [Cu(3)(L)(2)(DABCO)(H(2)O)]·15H(2)O·9DMF (1) has been synthesized using two different ligands, [1,1':3',1″-terphenyl]-4,4″,5'-tricarboxylic acid (H(3)L) and 1,4-diazabicyclo[2.2.2]octane (DABCO). As revealed by variable-temperature powder X-ray diffraction (VT-PXRD) measurements, N,N'-ditopic DABCO plays an important role for stabilization of the Cu-L framework. The three-dimensional framework of 1 exhibits high stability and excellent adsorption capacity for H(2) (54.3 mg g(-1) at 77 K and 20 bar), CO(2) (871 mg g(-1) at 298 K and 20 bar), CH(4) (116.7 mg g(-1), 99 cm(3) (STP) cm(-3) at 298 K and 20 bar), and n-pentane (686 mg g(-1) at 298 K and 1 bar). Interestingly, the excellent selectivity toward CO(2) over N(2) at ambient temperature (273 and 298 K) and 1 bar makes complex 1 possess practical application in gas separation and purification.