A Series of Metal-Organic Frameworks with 2,2'-Bipyridyl Derivatives: Synthesis vs. Structure Relationships, Adsorption, and Magnetic Studies.

Five new metal-organic frameworks based on Mn(II) and 2,2'-bithiophen-5,5'-dicarboxylate (btdc2-) with various chelating N-donor ligands (2,2'-bipyridyl = bpy; 5,5'-dimethyl-2,2'-bipyridyl = 5,5'-dmbpy; 4,4'-dimethyl-2,2'-bipyridyl = 4,4'-dmbpy) [Mn3(btdc)3(bpy)2]·4DMF, 1; [Mn3(btdc)3(5,5'-dmbpy)2]·5DMF, 2; [Mn(btdc)(4,4;-dmbpy)], 3; [Mn2(btdc)2(bpy)(dmf)]·0.5DMF, 4; [Mn2(btdc)2(5,5'-dmbpy)(dmf)]·DMF, 5 (dmf, DMF = N,N-dimethylformamide) have been synthesized, and their crystal structure has been established using single-crystal X-ray diffraction analysis (XRD). The chemical and phase purities of Compounds 1-3 have been confirmed via powder X-ray diffraction, thermogravimetric, and chemical analyses as well as IR spectroscopy. The influence of the bulkiness of the chelating N-donor ligand on the dimensionality and structure of the coordination polymer has been analyzed, and the decrease in the framework dimensionality, as well as the secondary building unit's nuclearity and connectivity, has been observed for bulkier ligands. For three-dimensional (3D) coordination polymer 1, the textural and gas adsorption properties have been studied, revealing noticeable ideal adsorbed solution theory (IAST) CO2/N2 and CO2/CO selectivity factors (31.0 at 273 K and 19.1 at 298 K and 25.7 at 273 K and 17.0 at 298 K, respectively, for the equimolar composition and the total pressure of 1 bar). Moreover, significant adsorption selectivity for binary C2-C1 hydrocarbons mixtures (33.4 and 24.9 for C2H6/CH4, 24.8 and 17.7 for C2H4/CH4, 29.3 and 19.1 for C2H2/CH4 at 273 K and 298 K, respectively, for the equimolar composition and the total pressure of 1 bar) has been observed, making it possible to separate on 1 natural, shale, and associated petroleum gas into valuable individual components. The ability of Compound 1 to separate benzene and cyclohexane in a vapor phase has also been analyzed based on the adsorption isotherms of individual components measured at 298 K. The preferable adsorption of C6H6 over C6H12 by 1 at high vapor pressures (VB/VCH = 1.36) can be explained by the existence of multiple van der Waals interactions between guest benzene molecules and the metal-organic host revealed by the XRD analysis of 1 immersed in pure benzene for several days (1≅2C6H6). Interestingly, at low vapor pressures, an inversed behavior of 1 with preferable adsorption of C6H12 over C6H6 (KCH/KB = 6.33) was observed; this is a very rare phenomenon. Moreover, magnetic properties (the temperature-dependent molar magnetic susceptibility, χp(T) and effective magnetic moments, µeff(T), as well as the field-dependent magnetization, M(H)) have been studied for Compounds 1-3, revealing paramagnetic behavior consistent with their crystal structure.

Highly Luminescent Crystalline Sponge: Sensing Properties and Direct X-ray Visualization of the Substrates.

A phenomenon of crystalline sponge is represented by guest-dependent structural fluidity of the host polymeric lattice in highly crystalline sorbents, such as metal-organic frameworks, driven by multiple weak intermolecular interactions. Such induced fitting in MOFs is a valuable property in selective adsorption, guest determination by single-crystal XRD and in-situ structural analysis under external stimuli. In this work, a porous three-dimensional metal-organic framework [Eu2(DMF)4(ttdc)3]·4.45DMF (1DMF; DMF = N,N-dimethylformamide, ttdc2- = trans-thienothiophenedicarboxylate anion) was applied as a crystalline sponge bearing luminescent functionality to couple its sensing properties with direct structural determination of the adsorbed molecules. As a result, the paper discusses crystal structures and luminescent properties for the successfully obtained new adducts with the crystallographic formulae [Eu2(DMSO)4(ttdc)3]·2.5DMSO·2.2H2O (1DMSO; DMSO = dimethylsulfoxide), [Eu2(DMF)4(ttdc)3]·3phet (1phet; phet = phenylethanal) and [Eu2(DMF)3.5(cin)0.5(ttdc)3]·1.64cin (1cin; cin = trans-cinnamaldehyde). As a result of inclusion of DMSO into 1, a slight increase in the quantum yield and excited state phosphorescence lifetime was observed, while the adsorption of phet leads to a considerable (up to three times) decrease in the corresponding values. The incorporation of cinnamal results in a full quenching of QY, from 20% down to zero, and a more than order of magnitude diminishing of the excited state lifetime compared to the initial 1DMF. The effective sensing of cinnamal was explained from the structural point of view by its direct coordination to the Eu3+ emitter, as well as by multiple weak intermolecular interactions with ttdc antenna ligand, both capable of enhancing the non-radiative energy dissipation.

Isomeric Scandium-Organic Frameworks with High Hydrolytic Stability and Selective Adsorption of Acetylene.

Two solvent-controlled topological isomers of scandium-organic frameworks [Sc(Hpzc)(pzc)]·DMF·2H2O (1·DMF·2H2O) and [Sc(Hpzc)(pzc)]·DMA·4H2O (2·DMA·4H2O) were synthesized using 2,5-pyrazinedicarboxylate (pzc2-) (DMF = dimethylformamide; DMA = dimethylacetamide). Despite the isomeric nature of the obtained metal-organic frameworks (MOFs), they possess different structural features and unique adsorption properties toward gases and iodine. The compound 1 has widely spread among MOF structures a dia topology with ultranarrow channels, which together with inner surface functionalization leads to enhanced CO2 adsorption and high selectivity factors in CO2/CH4 and CO2/N2 gas mixtures (25.9 and 35.6, respectively, 1/1 v/v). Moreover, a rare preferable adsorption of CO2 over C2H2 was demonstrated. The biporous isomeric framework 2 has a crb topology inherent in zeolites. A remarkable adsorption affinity to C2H2 with the ideal adsorbed solution theory selectivity factor of 127.1 for a C2H2/C2H4 mixture (1/99 v/v) was achieved for 2. Both compounds have exceptional chemical stability in a wide range of pH from acidic to basic media.

Cinnamal Sensing and Luminescence Color Tuning in a Series of Rare-Earth Metal-Organic Frameworks with Trans-1,4-cyclohexanedicarboxylate.

Three isostructural metal-organic frameworks ([Ln2(phen)2(NO3)2(chdc)2]·2DMF (Ln3+ = Y3+ for 1, Eu3+ for 2 or Tb3+ for 3; phen = 1,10-phenanthroline; H2chdc = trans-1,4-cyclohexanedicarboxylic acid) were synthesized and characterized. The compounds are based on a binuclear block {M2(phen)2(NO3)2(OOCR)4} assembled into a two-dime nsional square-grid network containing tetragonal channels with 26% total solvent-accessible volume. Yttrium (1)-, europium (2)- and terbium (3)-based structures emit in the blue, red and green regions, respectively, representing the basic colors of the standard RGB matrix. A doping of Eu3+ and/or Tb3+ centers into the Y3+-based phase led to mixed-metal compositions with tunable emission color and high quantum yields (QY) up to 84%. The bright luminescence of a suspension of microcrystalline 3 in DMF (QY = 78%) is effectively quenched by diluted cinnamaldehyde (cinnamal) solutions at millimolar concentrations, suggesting a convenient and analytically viable sensing method for this important chemical.

3D Metal-Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis, Crystal Structures, Gas Adsorption, and Magnetic Properties.

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2'-bithiophen-5,5'-dicarboxylate (btdc2-) [Co3(btdc)3(bpy)2]·4DMF, 1; [Co3(btdc)3(pz)(dmf)2]·4DMF·1.5H2O, 2; [Co3(btdc)3(dmf)4]∙2DMF∙2H2O, 3 (bpy = 2,2'-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co3(RCOO)6}, connected either by btdc2- ligands (1, 3) or by both btdc2- and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N2, O2, CO, CO2, CH4 adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m2⋅g-1 and promising gas separation performance with selectivity factors up to 35.7 for CO2/N2, 45.4 for CO2/O2, 20.8 for CO2/CO, and 4.8 for CO2/CH4. The molar magnetic susceptibilities χp(T) were measured for 1 and 2 in the temperature range 1.77-330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are µeff (300 K) ≈ 4.93 µB. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.

Structural Dynamics and Adsorption Properties of the Breathing Microporous Aliphatic Metal-Organic Framework.

A mixed-ligand metal-organic framework [Zn2(chdc)2(dabco)]·2NMP (chdc2- = trans-1,4-cyclohexanedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane; NMP = N-methylpyrrolidone) was synthesized under solvothermal conditions. This coordination compound demonstrates a guest-driven framework breathing due to a conformational change between e,e-chdc and a,a-chdc forms of the linkers with a reversible restoration of crystallinity. Both the local and longer-range coordination environment of the metal centers were extensively studied by electron paramagnetic resonance on a Cu(II)-doped compound. This approach allowed the detailed investigation of the ligand structural conformations and the framework structural dynamics, supported by an X-ray diffraction method. Carbon dioxide and methane adsorption measurements as well as vapor sorption of benzene and cyclohexane at 298 K of the activated compound were studied. While adsorption of small gas molecules, such as CO2, CH4, and N2, is moderate and does not induce the phase transition, the multistepped character of C6H6 and C6H12 adsorption isotherms characterize the breathing nature of [Zn2(chdc)2(dabco)]. The uptake of benzene from the vapor phase reaches 125 mL·g-1 at 298 K, which surpasses most of benzene uptake values reported for microporous metal-organic frameworks.

A Selenophene-Incorporated Metal-Organic Framework for Enhanced CO2 Uptake and Adsorption Selectivity.

A new metal-organic coordination polymer [Zn2(sedc)2(dabco)] (1se; sedc2- = selepophene-2,5-dicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane) was synthesized and characterized by single-crystal X-ray diffraction analysis. This MOF is based on {Zn2(OOCR)4N2} paddle wheels and is isoreticular to the family of [Zn2(bdc)2(dabco)] derivatives (1b; bdc2- = 1,4-benzenedicarboxylate) with pcu topology. The gas adsorption measurements revealed that 1se shows a 15% higher CO2 volumetric uptake at 273 K and 28% higher CO2 uptake at 298 K (both at 1 bar) compared to the prototypic framework 1b. Methane and nitrogen adsorption at 273 K was also investigated, and IAST calculations demonstrated a pronounced increase in CO2/CH4 and CO2/N2 selectivity for 1se, compared with 1b. For example, the selectivity factor for the equimolar CO2/CH4 gas mixture at 1 bar = 15.1 for 1se and 11.9 for 1b. The obtained results show a remarkable effect of the presence of selenium atom on the carbon dioxide affinity in the isoreticular metal-organic frameworks with very similar geometry and porosity.

A Series of Mesoporous Metal-Organic Frameworks with Tunable Windows Sizes and Exceptionally High Ethane over Ethylene Adsorption Selectivity.

The NIIC-20 (NIIC stands for Nikolaev Institute of Inorganic Chemistry) is a family of five isostructural metal-organic frameworks (MOFs) based on dodecanuclear wheel-shaped carboxylate building blocks {Zn12 (RCOO)12 (glycol)6 } (glycol is deprotonated diatomic alcohol: ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol or glycerol), quantitatively crystallized from readily available starting chemicals. The crystal structures contain large mesoporous cages of 25 Šconnected through {Zn12 } rings, of which inner diameter and chemical nature depend solely on the chosen glycol. The NIIC-20 compounds feature high surface area and rarely observed inversed adsorption affinity for saturated hydrocarbon (ethane) over the unsaturated ones (ethylene, acetylene). The corresponding IAST (Ideal Adsorbed Solution Theory) adsorption selectivity factors reach as much as 15.4 for C2 H6 /C2 H4 and 10.9 for C2 H6 /C2 H2 gas mixtures at ambient conditions, exceeding those for any other porous MOF reported so far. The remarkable combination of high adsorption uptakes and high adsorption selectivities makes the NIIC-20 series a new benchmark of porous materials designed for ethylene separation applications.

Tuning the Molecular and Cationic Affinity in a Series of Multifunctional Metal-Organic Frameworks Based on Dodecanuclear Zn(II) Carboxylate Wheels.

A series of new zinc(II)-thiophene-2,5-dicarboxylate (tdc) MOFs based on novel dodecanuclear wheel-shaped building blocks has been synthesized in almost quantative yields. Single-crystal X-ray diffraction analyses reveal 3D porous frameworks with a complex composition [Zn12(tdc)6(glycolate)6(dabco)3] where glycolate is a deprotonated polyatomic alcohol (ethylene glycol, EgO2, 1; 1,2-propanediol, PrO2, 2; 1,2-butanediol, BuO2, 3; 1,2-pentanediol, PeO2, 4; glycerol, GlO2, 5) and dabco is 1,4-diazo[2.2.2.]bicyclooctane. All compounds 1-5 are isostructural except for pendant groups of the diols decorating the surface of channels. The adsorption of small gases (N2, CO2, CH4, C2H2, C2H4, C2H6) and larger hydrocarbons (benzene, cyclohexane) both in liquid and vapor phases was thoroughly investigated for all compounds. The zero-coverage adsorption enthalpies, Henry constants, and selectivity factors by various models are calculated and discussed. The versatile adsorption functionality of the title series results from the variable nature of the diol and could be tailored for a specific adsorbate system. For example, 1 shows excellent selectivity of benzene over cyclohexane (20:1 for vapors, 92:1 for liquid phase), while 4 demonstrates unprecedented adsorption preference of cyclohexane over benzene (selectivity up to 5:1). The compound 5 demonstrates great adsorption selectivity for CO2/N2 (up to 75.1), CO2/CH4 (up to 7.7), C2H2/CH4 (up to 14.2), and C2H4/CH4 (up to 9.4). Also, due to polar nature of the pores, 5 features size-selective sorption of alkaline metal cations in order Li+ > Na+ > K+ > Cs+ as well as a notable luminescent response for cesium(I) ions and urea.

Understanding Hysteresis in Carbon Dioxide Sorption in Porous Metal-Organic Frameworks.

Two new isostructural microporous coordination frameworks [Mn3(Hpdc)2(pdc)2] (1) and [Mg3(Hpdc)2(pdc)2] (2) (pdc2- = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g-1 for 1 and 102.5 mL·g-1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis.

Enhancement of CO2 Uptake and Selectivity in a Metal-Organic Framework by the Incorporation of Thiophene Functionality.

The complex [Zn2(tdc)2dabco] (H2tdc = thiophene-2,5-dicarboxylic acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase in carbon dioxide (CO2) uptake and CO2/dinitrogen (N2) selectivity compared to the nonthiophene analogue [Zn2(bdc)2dabco] (H2bdc = benzene-1,4-dicarboxylic acid; terephthalic acid). CO2 adsorption at 1 bar for [Zn2(tdc)2dabco] is 67.4 cm3·g-1 (13.2 wt %) at 298 K and 153 cm3·g-1 (30.0 wt %) at 273 K. For [Zn2(bdc)2dabco], the equivalent values are 46 cm3·g-1 (9.0 wt %) and 122 cm3·g-1 (23.9 wt %), respectively. The isosteric heat of adsorption for CO2 in [Zn2(tdc)2dabco] at zero coverage is low (23.65 kJ·mol-1), ensuring facile regeneration of the porous material. Enhancement by the thiophene group on the separation of CO2/N2 gas mixtures has been confirmed by both ideal adsorbate solution theory calculations and dynamic breakthrough experiments. The preferred binding sites of adsorbed CO2 in [Zn2(tdc)2dabco] have been unambiguously determined by in situ single-crystal diffraction studies on CO2-loaded [Zn2(tdc)2dabco], coupled with quantum-chemical calculations. These studies unveil the role of the thiophene moieties in the specific CO2 binding via an induced dipole interaction between CO2 and the sulfur center, confirming that an enhanced CO2 capacity in [Zn2(tdc)2dabco] is achieved without the presence of open metal sites. The experimental data and theoretical insight suggest a viable strategy for improvement of the adsorption properties of already known materials through the incorporation of sulfur-based heterocycles within their porous structures.

A Cryptand Metal-Organic Framework as a Platform for the Selective Uptake and Detection of Group I Metal Cations.

The metal-organic framework (MOF) complex (H3 O)2 [Zn4 (ur)(Hfdc)2 (fdc)4 ] (1, ur=urotropine, H2 fdc=furan-2,5-dicarboxylic acid) incorporates cryptand-like cavities, which can be used to separate and detect Rb+ and Cs+ optically. This is the first example of the effective employment of a MOF material for optical detection of these cations.

Rational Synthesis and Investigation of Porous Metal-Organic Framework Materials from a Preorganized Heterometallic Carboxylate Building Block.

The tetranuclear heterometallic complex [Li2Zn2(piv)6(py)2] (1, where piv- = pivalate and py = pyridine) has been successfully employed as a presynthesized node for the construction of four porous metal-organic frameworks (MOFs) [Li2Zn2(R-bdc)3(bpy)]·solv (2-R, R-bdc2-; R = H, Br, NH2, NO2) by reaction with 4,4'-bipyridine (bpy) and terephthalate anionic linkers. The [Li2Zn2] node is retained in the products, representing a rare example of the rational step-by-step design of isoreticular MOFs based on complex heterometallic building units. The permanent porosity of the activated frameworks was confirmed by gas adsorption isotherm measurements (N2, CO2, CH4). Three compounds, 2-H, 2-Br, and 2-NH2 (but not 2-NO2), feature extensive hysteresis between the adsorption and desorption curves in the N2 isotherms at low pressures. The substituents R decorate the inner surface and also control the aperture of the channels, the volume of the micropores, and the overall surface area, thus affecting both the gas uptake and adsorption selectivity. The highest CO2 absorption at ambient conditions (105 cm3·g-1 or 21 wt % at 273 K and 1 bar for 2-NO2) is above the average values for microporous MOFs. The photoluminescent properties of the prototypic 2-H as well as the corresponding host-guest compounds with various aromatic molecules (benzene, toluene, anisole, and nitrobenzene) were systematically investigated. We discovered a rather complex pattern in the emission response of this material depending on the wavelength of excitation as well as the nature of the guest molecules. On the basis of the crystal structure of 2-H, a mechanism for these luminescent properties is proposed and discussed.

Hierarchical guest exchange and step-by-step activation of a biporous coordination framework.

A unique step-by-step activation of the biporous material via formation of the intermediate host-guest complex with a labile ligand has been presented on the example of the metal-organic framework [Zn4(ur)2(ndc)4]. The difference in the chemical environment of channels allows highly selective separation of the mixture of S4N4 and benzene.

Diastereoselective guest-shape dependent [2+2]-photodimerization of 2-cyclopenten-1-one trapped within a metal-organic framework.

UV-induced [2+2] dimerization of 2-cyclopenten-1-one and 2-methyl-2-cyclopenten-1-one was successfully carried out in a single-crystal-to-single-crystal manner within a porous metal-organic framework. Intermolecular contacts direct the orientation of the α,ß-enone molecules within the host channels, which drives the subsequent photoaddition reaction in a facile and diastereoselective fashion, yielding head-to-tail anti dimers only.

Synthesis, Structural Versatility, Magnetic Properties, and I- Adsorption in a Series of Cobalt(II) Metal-Organic Frameworks with a Charge-Neutral Aliphatic (O,O)-Donor Bridge.

Four new metal-organic frameworks based on cobalt(II) salts and 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide (odabco) were obtained. Their crystallographic formulae are [Co3(odabco)2(OAc)6] (1, OAc- = acetate), [Co(H2O)2(HCOO)2]·odabco (2), [Co2(H2O)(NO3)(odabco)5](NO3)3·3.65H2O (3), and [Co2(DMF)2(odabco)4](NO3)4·3H2O (4; DMF = N,N-dimethylformamide). Crystal structures of 1-4 were determined by single-crystal X-ray crystallography. Coordination polymer 1 comprises binuclear and mononuclear metal-acetate blocks alternating within uncharged one-dimensional chains, in which odabco acts as a bridging ligand. A layered Co(II) formate 2 contains odabco only as guest molecules located in the interlayer space. Layered compound 3 and three-dimensional 4 have cationic coordination frameworks with 26% and 34% specific void volumes, respectively, unveiling high structural diversity of Co(II)-odabco MOFs based on quite a rare aliphatic moiety. Magnetization measurements were performed for 1, 3, and 4 and the obtained data were interpreted on the basis of their crystal structures. A strong (J/kB~100 K) antiferromagnetic coupling was found within binuclear metal blocks in 1. Ion exchange experiments revealed a considerable iodide uptake by 3 resulting in an up to 75% guest nitrate substitution within the voids of a coordination framework, found by capillary zone electrophoresis data and confirmed by single-crystal XRD. A preservation of 3 crystallinity during the exchange allowed for the guest I- positions within a new adduct with the formula [Co2(H2O)(NO3)(odabco)5]I2(NO3)·1.85H2O (3-I) to be successfully determined and the odabco aliphatic core to be revealed as a main adsorption center for quite large and easily polarizable iodide anions. In summary, this work presents a comprehensive study for a series of 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide-based MOFs of cobalt(II) within the framework of magnetic properties and reports the first example of anion exchange in odabco-based coordination networks, supported by direct X-ray structural data. The reported results unveil promising applications of such frameworks bearing ligands with an aliphatic core in the diverse structural design of selective adsorbents and other types of functional materials.

Imparting high proton conductivity to a metal-organic framework material by controlled acid impregnation.

The extensive implementation of hydrogen-powered technology today is limited by a number of fundamental problems related to materials research. Fuel-cell hydrogen conversion technology requires proton-conducting materials with high conductivity at intermediate temperatures up to 120 °C. The development of such materials remains challenging because the proton transport of many promising candidates is based on extended microstructures of water molecules, which deteriorate at temperatures above the boiling point. Here we show the impregnation of the mesoporous metal-organic framework (MOF) MIL-101 by nonvolatile acids H(2)SO(4) and H(3)PO(4). Such a simple approach affords solid materials with potent proton-conducting properties at moderate temperatures, which is critically important for the proper function of on-board automobile fuel cells. The proton conductivities of the H(2)SO(4)@MIL-101 and H(3)PO(4)@MIL-101 at T = 150 °C and low humidity outperform those of any other MOF-based materials and could be compared with the best proton conductors, such as Nafion.

Enhanced Adsorption Selectivity of Carbon Dioxide and Ethane on Porous Metal-Organic Framework Functionalized by a Sulfur-Rich Heterocycle.

Porous metal-organic framework [Zn2(ttdc)2(bpy)] (1) based on thieno [3,2-b]thiophenedicarboxylate (ttdc) was synthesized and characterized. The structure contains intersected zig-zag channels with an average aperture of 4 × 6 Å and a 49% (v/v) guest-accessible pore volume. Gas adsorption studies confirmed the microporous nature of 1 with a specific surface area (BET model) of 952 m2·g-1 and a pore volume of 0.37 cm3·g-1. Extensive CO2, N2, O2, CO, CH4, C2H2, C2H4 and C2H6 gas adsorption experiments at 273 K and 298 K were carried out, which revealed the great adsorption selectivity of C2H6 over CH4 (IAST selectivity factor 14.8 at 298 K). The sulfur-rich ligands and double framework interpenetration in 1 result in a dense decoration of the inner surface by thiophene heterocyclic moieties, which are known to be effective secondary adsorption sites for carbon dioxide. As a result, remarkable CO2 adsorption selectivities were obtained for CO2/CH4 (11.7) and CO2/N2 (27.2 for CO2:N2 = 1:1, 56.4 for CO2:N2 = 15:85 gas mixtures). The computational DFT calculations revealed the decisive role of the sulfur-containing heterocycle moieties in the adsorption of CO2 and C2H6. High CO2 adsorption selectivity values and a relatively low isosteric heat of CO2 adsorption (31.4 kJ·mol-1) make the porous material 1 a promising candidate for practical separation of biogas as well as for CO2 sequestration from flue gas or natural gas.

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 Å, 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.

Metal-Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest-Host Inclusion Compounds.

Separation of hydrocarbon molecules, such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chemical feedstock but challenging because of their similar boiling points and close molecular sizes. Physisorption separation could offer an energy-efficient solution to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with aromatic sorption sites [Li2Zn2(bpy)(ndc)3] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liquid separation. For an equimolar benzene/cyclohexane mixture, it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene separation. In addition, NIIC-30(Ph) is stable enough to carry out at least three separation cycles of benzene/cyclohexane mixtures or ternary o-xylene/m-xylene/p-xylene mixtures both in the liquid and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each aromatic guest inclusion compound.