Phase transitions in a metal–organic coordination polymer: [Zn₂(C₈H₄O₄)₂(C₆H₁₂N₂)] with guest molecules. Thermal effects and molecular mobility

<p>Thermal effects of a series of [Zn₂(C₈H₄O₄)₂(C₆H₁₂N₂)] porous compound with the guest molecules located in the pores were studied using differential scanning calorimetry combined with solid-state ¹H nuclear magnetic resonance spectroscopy. The intercalation of the molecules was shown to produce various thermal anomalies and phase transitions, which were characterized and analyzed.</p

Microporous Manganese Formate: A Simple Metal−Organic Porous Material with High Framework Stability and Highly Selective Gas Sorption Properties

Novel microporous metal−organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 °C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor

Microporous Manganese Formate: A Simple Metal−Organic Porous Material with High Framework Stability and Highly Selective Gas Sorption Properties

Novel microporous metal−organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 °C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor

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*, [Zn2(BDC)2(DMF)2] (2) or [Zn5(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 H2 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

Enantioselective Chromatographic Resolution and One-Pot Synthesis of Enantiomerically Pure Sulfoxides over a Homochiral Zn−Organic Framework

(R)- and (S)- enantiomers of alkyl aryl sulfoxides can be obtained by chromatographic resolution of the racemic mixtures of the sulfoxides on a microporous homochiral Zn-organic polymer or by simultaneous catalytic oxidation of the corresponding sulfides with H2O2 and enantioselective chromatographic resolution of the resulting sulfoxides in a one-pot process

Quantum Rotations and Chiral Polarization of Qubit Prototype Molecules in a Highly Porous Metal–Organic Framework: ¹H NMR <i>T</i>₁ Study

Rotations of bistable diazabicyclooctane (dabco) molecules N2(C2H4)3 in a layered highly porous metal–organic framework [Zn2(C8H4O4)2·N2(C2H4)3] have been studied at 310–8 K by the 1H NMR spin–lattice relaxation method. Above 165 K, the relaxation is characterized by a single longitudinal relaxation time, T1, related to the hindered rotation of the dabco molecules. Below 165 K, the quantum tunneling mechanism was found to be responsible for dabco reorientation and spin relaxation. At 165–25 K, the system is characterized by two different spin–lattice relaxation times, T1_1 and T1_2, related to two separate states of dabco in the ratio of ∼1:2. The first state is related to the conformation of point symmetry D3h, and the second to the sum of right- and left-twisted D3 forms. At 25 K, a transition to a low-temperature phase occurs. The transition is characterized by three different spin–lattice relaxation times, T1_1, T1_2, and T1_3, related to three conformation states of dabco in the ratio of ∼2:3:5. The observed relationship of state populations indicates an inequality of right- and left-twisted forms and a chiral polarization of the system because of the break in its right/left symmetry

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*, [Zn2(BDC)2(DMF)2] (2) or [Zn5(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 H2 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

Phosphorous Acid and Arsenious Acid as Ligands

Phosphorous Acid and Arsenious Acid as Ligand

Metal-Cation-Independent Dynamics of Phenylene Ring in Microporous MOFs: A ²H Solid-State NMR Study

Mobility of the organic linkers in metal–organic frameworks (MOFs) is an established phenomenon. Knowledge of the details of linker motion in MOFs could provide a great deal of information about the linker structure and the way the guest molecules interact with the organic framework. However, the mobility of the organic linkers is poorly characterized. The extent of the influence of the metal cation or guest molecules on linker motion is still unknown for MOFs with identical topologies. In this work, we have analyzed the rotational dynamics of the phenylene ring fragments of terephthalate (1,4-benzenedicarboxylate, bdc) linkers in the series of MOFs [M₂(bdc)₂(dabco)]·G (M = Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺; dabco =1,4-diazabicyclo[2.2.2]­octane; G = none or dimethylformamide, DMF). We have established that the reorientational motion of the phenylene rings is performed by π-flipping of the plane of the ring about its <i>C</i>₂ axis. The dynamics of the phenylene rings is insensitive to the variation of the metal cation, whereas the loading of the guest DMF molecules provides both a significant decrease of the rate of π-flips and an increase of the activation energy for the motion of the phenylene rings

Supramolecular Assemblies Based on Cucurbituril Adducts of Hydrogen-Bonded Molybdenum and Tungsten Incomplete Cuboidal Aqua Complexes

Supramolecular Assemblies Based on Cucurbituril Adducts of Hydrogen-Bonded Molybdenum and Tungsten Incomplete Cuboidal Aqua Complexe