Broadly hysteretic H2 adsorption in the microporous metal-organic framework Co(1,4-benzenedipyrazolate)

Reaction of Co(CF3SO3)2 with the new molecule 1,4-benzenedi(4'-pyrazolyl) (H2BDP) in N,N'-diethylformamide (DEF) at 130 degrees C generates the metal-organic framework Co(BDP).2DEF.H2O (1). X-ray analysis reveals the structure of 1 to contain chains of tetrahedrally ligated Co2+ ions linked through BDP2- ligands to generate a three-dimensional framework with 10 x 10 A2 channels. Thermogravimetric data shows the framework to have a high thermal stability, and complete desolvation occurs upon heating at 170 degrees C under dynamic vacuum for two days to afford 1d. X-ray powder diffraction data indicates that 1d possesses a substantially different structure, but converts back to 1 upon exposure to DEF, consistent with the presence of a flexible framework. Nitrogen adsorption isotherms measured for 1d at 77 and 87 K reveal an unprecedented five-step adsorption process and a Langmuir surface area of 2670 m2/g. In addition, high-pressure H2 adsorption data reveal hysteretic uptake and release, with hysteresis loops of width 1.1, 3.8, 13, and 27 bar that shift to higher pressures as the temperature increases from 50 to 65, 77, and 87 K, respectively. The high H2 uptake capacity of 5.5 excess wt % at 50 K suggests that such materials could potentially find utility for hydrogen storage via a kinetic trapping mechanism. Variable-temperature kinetics measurements have also allowed the first study of H2 diffusion within a metal-organic framework, revealing an energy barrier of 0.62 kJ/mol for H2 diffusing within the pores.     

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.     

Design, synthesis, structure, and gas (N2, Ar, CO2, CH4, and H2) sorption properties of porous metal-organic tetrahedral and heterocuboidal polyhedra

A strategy based on assembling metal ions and organic carboxylate links has been applied for the design and synthesis of a new class of porous, truncated tetrahedral and heterocuboidal polyhedra, whose pore size and functionality can be systematically varied. The synthesis of this series of metal-organic polyhedra (MOPs) employs sulfate-capped oxygen-centered iron-carboxylate trimers, Fe3O(CO2)3(-)(SO4)3, as rigid nodes separated by linear (phenyl, biphenyl, terphenyl, and tetrahydropyrene) or trigonal (benzenetriphenyl) links to yield five highly crystalline polyhedra of general formula [NH2(CH3)2]8[Fe12O4(-)(SO4)12(link)x(py)12].G (x = 6 for linear or 4 for trigonal, py = pyridine, G = guests). In this series, the size of each polyhedron has been varied from 20.0 to 28.5 A (on edge), and the corresponding pore diameter from 7.3 to 13.3 A. Gas sorption isotherms were measured for three members of this series to reveal significant uptake of gases (N2, Ar, CO2, H2, CH4) and benzene and exhibit Type I sorption behavior that is indicative of permanent porosity. The apparent surface areas for these compounds range from 387 to 480 m(2)/g.     

Cd(II)(bpdc).H(2)O](n): a robust, thermally stable porous framework through a combination of a 2-D grid and a cadmium dicarboxylate cluster chain (H(2)bpdc = 2,2'-Bipyridyl-4,4'-dicarboxylic acid)

The synthesis and characterization of a cadmium(II) coordination polymer, [Cd(C(12)H(6)N(2)O(4)) x H(2)O](n)() (1), is reported. A single-crystal X-ray analysis shows that compound 1 presents a non-interpenetrating three-dimensional porous host containing one-dimensional hydrophilic channels, where guest water molecules reside. The strategy in designing the 3-D framework architecture is based on a combination of two building subunits: a porous two-dimensional grid of (4,4) topology and a metal dicarboxylate cluster chain. Both subunits are assembled from the coordination of a cadmium ion with a three-connecting organic modular ligand, 2,2'-bipyridyl-4,4'-dicarboxylic acid (H(2)bpdc). The results of thermogravimetric analysis and powder X-ray diffraction study show that the framework rigidity of compound 1 remains intact upon the removal of guest molecules, and maintains the thermal stability up to 440 degrees C. The second-row transition-metal ions are capable of engaging higher coordination modes (e.g., hepta- and octacoordination) because of their atomic sizes and intrinsic electron configurations. Our results show that the heptacoordinated cadmium center plays an important role in the overall framework rigidity and high thermal stability of compound 1. Crystal data for 1: Cd(C(12)H(6)N(2)O(4)) x H(2)O, triclinic, space group P1 macro, a = 6.7843(5) A, b = 9.3299(7) A, c = 9.4439(7) A, alpha = 104.629(1) degrees, beta = 92.324(1) degrees, gamma = 100.416(1) degrees, Z = 2.     

Multifunctionality and crystal dynamics of a highly stable, porous metal-organic framework [Zn4O(NTB)2

A porous metal-organic framework [Zn(4)O(NTB)(2)].3DEF.EtOH (1), in which (3,6)-connected nets are doubly interpenetrated to generate curved three-dimensional channels, has been prepared. Framework 1 exhibits high permanent porosity (Langmuir surface area, 1121 m(2)/g; pore volume, 0.51 cm(3)/cm(3)), high thermal stability (up to 430 degrees C), high hydrogen adsorption capacity (1.9 wt % at 77 K and 1 atm), selective organic guest binding ability (K(f)()( )(): MeOH > pyridine > benzene > dodecane), and guest-dependent blue luminescence (lambda(max) depending on guest identity). Most interestingly, the framework sustains single crystallinity even at 400 degrees C and 10(-)(5) Torr, and the framework components undergo reversible dynamics, mainly rotational motion, in response to removal and rebinding of the guest molecules.     

Matrix isolation chemistry in a porous metal-organic framework: photochemical substitutions of N2 and H2 in Zn4O[(eta6-1,4-benzenedicarboxylate)Cr(CO)3]3

Reaction of the microporous metal-organic framework Zn4O(BDC)3 (BDC2- = 1,4-benzenedicarboxylate) with Cr(CO)6 at 140 degrees C in a 6:1 mixture of dibutylether and THF affords Zn4O[(BDC)Cr(CO)3]3 (1). This compound retains the porous cubic structure of the parent framework, but features Cr(CO)3 groups attached in an eta6 fashion to all of the benzene rings. Compound 1 is also microporous, exhibiting a BET surface area of 2130 m2/g. It can be fully decarbonylated by heating at 200 degrees C, but the resulting gray solid (2) shows little affinity for N2 or H2 at 298 K, suggesting aggregation of the chromium atoms. In contrast, photolysis of 1 using 450-nm light in an atmosphere of N2 or H2 produces solids with infrared spectra indicative of Zn4O[(BDC)Cr(CO)2(N2)]3 (3) and Zn4O[(BDC)Cr(CO)2(H2)]3 (4). Under an N2 atmosphere, compound 4 completely converts into compound 3 over the course of 12 h, demonstrating the lability of the Cr0-H2 bond. Owing to isolation of the metal centers within the rigid, evacuable framework structures, the N2- and H2-substituted compounds show greatly enhanced stability relative to molecular analogues generated in frozen gas matrices or supercritical fluid solutions.     

Effect of the guest solvent molecules on preparation of different morphologies of ZnO nanomaterials from the [Zn2(1,4-bdc)2(dabco)] metal-organic framework

The host and the apohost framework of [Zn₂(1,4-bdc)₂(dabco)]?·?4DMF?·?½H₂O (1?·?4DMF?·?½H₂O) (1,4-bdc?=?1,4-benzenedicarboxylate and dabco?=?1,4-diazabicyclo[2.2.2]octane) were used for the preparation of ZnO nanomaterials. With calcination of the host framework of 1?·?4DMF?·?½H₂O, ZnO nanoparticles could be fabricated. By the same process on fully desolvated framework of 1, ZnO microrods composed of ZnO nanoparticles were formed. These results indicate with removal of the guest solvent from the pores of this metal-organic framework (MOF), nanoparticle agglomeration increases and the role of this MOF in preparation of ZnO nanoparticles was reduced.     

Thermodynamics of adsorption (as a function of temperature and pressure) of N2, C02, Ar,CH4 and C2H4 on charcoals

Summary A quantitative treatment pertaining to the evaluation of the Gibbs function for the adsorption study of Ar, N₂, CO₂, CH₄ and C₂H₄ on wood-charcoal and charcoal is given. The specific surface areas were determined from the Langmuir adsorption equation; Gibbs function,, was estimated from the areas under them-lnP curves (from data from literature). Related thermodynamic functions are calculated in order to validate a correlation between the quantitatively deduced results with the known qualitative surface aspects in relation to a transition from mobile to a partly localized state for N₂ arid CH₄.

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Zusammenfassung Es wird eine quantitative Ermittlung der Gibbsschen Funktion für die Adsorption von Ar, N₂, CO₂, CH₄ und C₂H₄ an Holzkohle und Kohle gegeben. Die spezifischen Oberflächen wurden aus der Langmuir-Adsorptionsgleichung ermittelt, und die Gibbssche Funktion wurde aus den Flächen unter denm-InP Kurven entnommen (nach Literaturdaten). Um Zusammenhänge zwischen den quantitativ abgeleiteten Ergebnissen und Oberflächenaspekten in Bezug auf einen Übergang von einem mobilen in einen weniger mobilen Zustand von adsorbiertem Stickstoff und Methan zu erlangen, wurden weitere thermodynamische Funktionen berechnet.

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With 11 figures and 6 tables     

On the kinetics of the reaction of Zn(1S) with N2O

The rate constant for the reaction of ground state zinc atoms with nitrous oxide at 303 K was determined to be (1.8 ± 0.5)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ at pressures of ≈ 10 Torr. In contrast to a previous experiment, no chemiluminescent products were observed. The result, discussed in terms of an ionic intermediate mechanism and recent ZnO electronic structure calculations, is shown to be consistent with the surface crossing model even though the rate constant is orders of magnitude less than those typically used to invoke the model.     

A Novel Coordination Polymer, [Ag_4~I (bpdc)(H_2bpdc)(Hbpdc)_2]_n (bpdc=2,2''''-bipyridyl-3,3''''-dicarboxylate): Coordination Models of bpdc Ligands

Introduction Transition metal coordination polymers of one-, twoand three-dimensional infinite frameworks have been aattractive research area because of their diverse structures and useful properties.1,2 Polydentate ligands, whicare used as bridges in constructing the coordinatiopolymers are quite important in the crystal engineerinof supramolecular architecture organized by coordinatcovalent or hydrogen bonding.3 2,2'-Bipyridyl-3,3dicarboxylate (bpdc) is a potential bridging ligand ivariou…     

Shock tube studies of the N2O/Ar and N2O/H2/Ar systems

N₂O decay has been monitored via infrared emission for a series of mixtures containing N₂O/Ar and N₂O/H₂/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 10¹⁸ molec/cm³. In all cases the N₂O decayed exponentially, and a rate constant k_obs was obtained. Runs without added H₂ could be described by the following Arrhenius parameters: log A = ?9.72 ± 0.08 (in units of cm³/molec · sec) and E_A = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H₂ was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H₂, where k_obs doubled. Mixtures with no added H₂ were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k₂ and k₃. The additional reactions were included in the analysis of the mixtures containing H₂. Here agreement was obtained only when low values were assigned to k₂ and k₃. The combinations of k₁ ← k₃ which agreed with all the data were k₁ = 3.25 × 10^?10 exp (?215 kJ/RT) and k₂ = k₃ = 1.91 × 10^?11 exp (-105 kJ/RT).     

A new series of three-dimensional metal-organic framework, [M2(H2O)][C5N1H3(COO)2]3.2H2O, M = La, Pr, and Nd: synthesis, structure, and properties

A new series of lanthanide pyridine dicarboxylates of the general formula, [M2(H2O)][C5N1H3(COO)2]3.2H2O, M = La (1), Pr (2), and Nd (3), has been prepared by the reaction of trivalent lanthanide salts and pyridine dicarboxylic acids employing a mild condition hydrothermal reaction. The structures are built up from MO8N and MO7N2 (M = lanthanide) polyhedra connected to the dicarboxylate anions forming the three-dimensional structure with one-dimensional channels. A striking feature of this structure is the presence of an unusual Z-shaped tetramer of the formula M4O24N6. Extraframework water molecules, located within the open channels, are reversibly adsorbed. Detailed in situ and ex situ investigations using FTIR and PXRD studies clearly show that the removal of the water molecules is reversible and accompanied by changes in the size of the channel. Partial substitution at the La sites by Eu gives rise to characteristic red-pink luminescence, indicating a ligand-sensitized metal-centered emission.     

Effect of the framework flexibility on the centricities in centrosymmetric In2Zn(SeO3)4 and noncentrosymmetric Ga2Zn(TeO3)4

The solid-state syntheses, crystal structures, and characterization of two stoichiometrically similar quaternary mixed metal selenite and tellurite, In(2)Zn(SeO(3))(4) and Ga(2)Zn(TeO(3))(4), respectively, are reported. While In(2)Zn(SeO(3))(4) crystallizes in the centrosymmetric monoclinic space group P2(1)/n (No. 14) with a = 8.4331(7) ?, b = 4.7819(4) ?, c = 14.6583(13) ?, and β = 101.684(6)°, Ga(2)Zn(TeO(3))(4) crystallizes in the non-centrosymmetric space group I-43d (No. 220) with a = b = c = 10.5794(8) ?. In(2)Zn(SeO(3))(4) exhibits a two-dimensional crystal structure consisting of distorted InO(6) octahedra, ZnO(6) octahedra, and SeO(3) polyhedra. Ga(2)Zn(TeO(3))(4) shows a three-dimensional framework structure that is composed of GaO(4) or ZnO(4) and TeO(3) polyhedra. An effect of the framework flexibility on the space group centricity is discussed. The SHG (second harmonic generation) efficiency of noncentrosymmetric Ga(2)Zn(TeO(3))(4), using 1064 nm radiation, is similar to that of KH(2)PO(4) (KDP) and is not phase-matchable (Type 1). Complete characterizations including infrared spectroscopy and thermal analyses for the reported materials are also presented, as are dipole moment calculations.     

Ground- and excited-state properties of Zn(II) tetrakis(4-tetramethylpyridyl) pophyrin specifically encapsulated within a Zn(II) HKUST metal-organic framework

We have examined the photophysical properties of Zn(II) tetramethylpyridyl porphyrin (ZnT4MPyP) specifically encapsulated within the cubioctahedral cavities of a ZnHKUST metal- organic framework. The encapsulated ZnT4MPyP exhibits a Soret maxima at ～458 nm that is bathochromically shifted relative to ZnT4PyP in ethanol solution (Soret maxima centered at 440 nm). The corresponding emission spectra of the encapsulated porphyrin exhibit resolvable bands centered at 636 and 677 nm relative to a single broad emission band of the ZnT4MPyP in ethanol solution centered at 636 nm with a shoulder situated near ～660 nm. The fluorescence lifetime of the encapsulated porphyrin is also perturbed relative to that of the free porphyrin in solution (1.88 ns for the encapsulated porphyrin relative to 1.2 ns in solution). These results are consistent with the ZnT4MPyP being in a more constrained environment in which the peripheral pyridyl groups have restricted rotational motion. The ZnT4MPyP triplet lifetime is also affected by encapsulation, giving rise to a longer lifetime (τ ≈ 3.3 ms) relative to that for the free porphyrin in solution (τ ≈ 1 ms). The triplet-state results indicate that nonplanar vibrational modes of the porphyrin leading to intersystem crossing are retained by encapsulation of the porphyrin but that either the density of vibrational states or the specific nonplanar modes coupling the singlet and triplet states may be perturbed, resulting in the longer observed lifetime.     

Vibrational and thermodynamic properties of Ar, N2, O2, H2 and CO adsorbed and condensed into (H,Na)-Y zeolite cages as studied by variable temperature IR spectroscopy

The adsorption of Ar, H2, O2, N2 and CO on (H,Na)-Y zeolite (Si/Al = 2.9, H+/Na+ approximately 5) has been studied at variable-temperature (90-20 K) and sub-atmospheric pressure (0-40 mbar) by FTIR spectroscopy. Unprecedented filling conditions of the zeolite cavities were attained, which allowed the investigation of very weakly adsorbed species and of condensed, liquid-like or solid-like, phases. Two pressure regimes were singled out, characterized by: (i) specific interaction at low pressure of the probe molecules (P) with the internal Br?nsted and Lewis sites, and (ii) multilayer adsorption at higher pressure. In the case of CO the perturbation of the protonic sites located inside the sodalite cages was also observed. As the molecule is too large to penetrate the sodalite cage, the perturbation is thought to involve a proton jump tunneling mechanism. The adsorption energy for the (HF)OH...P (P = Ar, H2, O2, N2 and CO) specific interaction involving the high frequency Br?nsted acid sites exposed in the supercages was derived following the VTIR (variable temperature infrared spectroscopy) method described by E. Garrone and C. Otero Areán (Chem. Soc. Rev., 2005, 34, 846).     

A three‐dimensional open‐framework zinc arsenate, (C4H12N2)2[Zn7(AsO4)6­(H2O)2]

The title compound, dipiperazinium heptazinc hexakis(arsen­ate) dihydrate, is built from vertex‐sharing AsO₄ tetrahedra, ZnO₄ tetrahedra and ZnO₅ trigonal bipyramids. The connectivity between these polyhedra give rise to an open framework with eight‐ring channels along the crystallographic [001] and [011] directions. The piperazinium cations are located within these channels.     

三维无机-有机杂化骨架微孔材料Zn3(bpdc)3(4,4'-bpy)·DMF·2H2O的合成与结构

合成了一个具有三维骨架结构的无机-有机杂化微孔材料Zn3(bpdc)3(4,4'-bpy)@DMF@2H2O,并通过ICP和X射线单晶衍射分析等手段对其结构进行了表征.晶体属于正交晶系,Pbcn空间群,晶胞参数a=1.4532(3)nm,b=2.50327(5)nm,c=1.8184(4)nm,V=6.616(2)nm3,Z=8,Dc=1.296g/cm3,Mr=645.58,μ=1.145mm-1,F(000)=2656.最后的一致性因子为R=0.0705,Rw=0.2056.     

Understanding the preferential adsorption of CO2 over N2 in a flexible metal-organic framework

The unusual uptake behavior and preferential adsorption of CO(2) over N(2) are investigated in a flexible metal-organic framework system, Zn(2)(bdc)(2)(bpee), where bpdc = 4,4'-biphenyl dicarboxylate and bpee = 1,2-bis(4-pyridyl)ethylene, using Raman and IR spectroscopy. The results indicate that the interaction of CO(2) with the framework induces a twisting of one of its ligands, which is possible because of the type of connectivity of the carboxylate end group of the ligand to the metal center and the specific interaction of CO(2) with the framework. The flexibility of the bpee pillars allows the structure to respond to the twisting, fostering the adsorption of more CO(2). DFT calculations support the qualitative picture derived from the experimental analysis. The adsorption sites at higher loading have been identified using a modified van der Waals-Density Functional Theory method, showing that the more energetically favorable positions for the CO(2) molecules are closer to the C═C bond of the bpee and the C-C bond of the bpdc ligands instead of the benzene and pyridine rings of these ligands. These findings are consistent with changes observed using Raman spectroscopy, which is useful for detecting both specific guest-host interactions and structural changes in the framework.