We demonstrate that fluorous metal-organic frameworks (FMOFs) are highly hydrophobic porous materials with a high capacity and affinity to C(6)-C(8) hydrocarbons of oil components. FMOF-1 exhibits reversible adsorption with a high capacity for n-hexane, cyclohexane, benzene, toluene, and p-xylene, with no detectable water adsorption even at near 100% relative humidity, drastically outperforming activated carbon and zeolite porous materials. FMOF-2, obtained from annealing FMOF-1, shows enlarged cages and channels with double toluene adsorption vs FMOF-1 based on crystal structures. The results suggest great promise for FMOFs in applications such as removal of organic pollutants from oil spills or ambient humid air, hydrocarbon storage and transportation, water purification, etc. under practical working conditions.
A fluorous metal−organic framework, FMOF-1, is obtained by reaction of Ag(I) with 3,5-bis(trifluoromethyl)-1,2,4-triazolate, giving rise to a neutral, hydrogen-free, extended 3D nanotubular porous framework consisting of tetranuclear clusters [Ag4Tz6] connected by three-coordinate Ag(I) centers. The fluoro-lined channels and cavities of the framework show hysteretic adsorption of H2 with a volumetric capacity of 41 kg/m3 at 77 K and 64 bar. The framework also exhibits very high adsorptions for O2 and N2 with volumetric uptake of ∼550 and 400 kg/m3 at 77 K even at very low pressures (<10-2 bar).
The kinetics of methane hydrate formation was investigated by in-situ time-of-flight neutron powder diffraction. Samples were prepared from deuterated ice particles (< 0.25 mm) and transformed to clathrate hydrate by pressurizing the system with methane gas. The rates of sI methane hydrate formation were measured in-situ under isothermal conditions with a methane pressure of 1000 psi (6.9 MPa). Kinetic data were analyzed in terms of a shrinking core model, including possible contributions of nucleation, methane diffusion, and interface reaction. The data support the hypothesis that methane hydrate formation reaction from ice particles is diffusioncontrolled. The reaction starts quickly at the nucleation stage, which propagates to form a hydrate layer that covers the ice particle. Further reaction is limited by the growth of the hydrate layer and inward diffusion of methane molecules through the hydrate layer to the unreacted ice core. The reaction rate at the interface between hydrate and unreacted ice particle is fast compared to that of methane diffusion. The conversion of ice particle to methane hydrate follows Arrhenius behavior, from which an activation energy of 14.7(5) kcal/ mol was derived. Complete transformation of ice to methane hydrate was achieved through temperature rampingsa nonisothermal procedure that involves slowly increasing the sample temperature through the ice melting point.
Playing accordion: Cooling a single crystal of a microporous fluorous metal-organic framework under ambient atmosphere leads to very large breathing upon gas adsorption, during which multiple N(2) molecules are filled into channels and cages (see picture). While the framework exhibits remarkable positive thermal expansion under vacuum, a gigantic apparent negative thermal expansion takes place when the crystal is exposed to N(2) at ambient pressure.
We report the crystal growth of well-faceted single crystals of methylammonium lead iodide, CH 3 NH 3 PbI 3 , and detailed single crystal neutron diffraction structural studies aimed at elucidating the orientation of the methylammonium (CH 3 NH 3 + ) cation in the tetragonal and cubic phases of the hybrid inorganic−organic perovskite. Room temperature experiments reveal a tetragonal structure where the protonated amine substituent (−NH 3 + ) of the cation is disordered in four positions, each preferentially located near the neighboring iodine of the [PbI 6 ] octahedra, while the methyl substituent (−CH 3 ) is disordered in eight positions located near the body position of the unit cell. High temperature experiments show a cubic structure where the cation aligns along the [011] (edge), the [111] (diagonal), and the [100] (face) directions of the unit cell. The resulting site occupancy ratio suggests the CH 3 NH 3 + cation resides primarily along the [011] direction, in agreement with reported DFT calculations. One important feature that was observed for both tetragonal and cubic structures measured at 295 and 350 K, respectively, is the middle point of the C−N bond being located off-center from the high symmetry sites in the crystal structure, induced by the formation of hydrogen bond-like interactions between the −NH 3 + substituent of the organic cation and the iodine atoms of [PbI 6 ] octahedra.
The linear trinuclear compound Co 3 (dpa) 4 Cl 2 (1; dpa ) di(2-pyridyl)amide anion) crystallizes from CH 2 Cl 2 solution in two forms simultaneously, namely, an orthorhombic form 1‚CH 2 Cl 2 and a tetragonal form 1‚2CH 2 Cl 2 . The three linearly arranged cobalt atoms in 1 are supported by four dpa ligands in a spiral configuration. The chain of cobalt atoms is symmetrical in 1‚CH 2 Cl 2 , but unsymmetrical in 1‚2CH 2 Cl 2 . Both crystal structures have been studied at various temperatures. A reversible second-order phase transition (165 K) from orthorhombic (Pnn2) to monoclinic (Pn) symmetry for the crystal of 1‚CH 2 Cl 2 has been documented by X-ray studies at 296, 168, and 109 K as well as a neutron diffraction study at 20 K. The linear tricobalt unit in 1‚CH 2 Cl 2 becomes slightly unsymmetrical at low temperature although the two Co-Co bonds remain statistically equivalent (Co-Co ≈ 2.32 Å) throughout the experimental temperature range. No phase transition was observed for the tetragonal form 1‚2CH 2 Cl 2 at low temperature, but the Co-Co distances in 1 changed from 2.299(1) and 2.471(1) Å at 298 K to 2.3035(7) and 2.3847(8) Å at 20 K. Magnetic susceptibility measurements indicate that the two compounds are in an S ) 1 / 2 ground state at low temperature and exhibit gradual spin-crossover at higher temperature.
An air- and moisture-stable nanoscale polyhydrido copper cluster [Cu32 (H)20 {S2 P(OiPr)2 }12 ] (1H ) was synthesized and structurally characterized. The molecular structure of 1H exhibits a hexacapped pseudo-rhombohedral core of 14 Cu atoms sandwiched between two nestlike triangular cupola fragments of (2×9) Cu atoms in an elongated triangular gyrobicupola polyhedron. The discrete Cu32 cluster is stabilized by 12 dithiophosphate ligands and a record number of 20 hydride ligands, which were found by high-resolution neutron diffraction to exhibit tri-, tetra-, and pentacoordinated hydrides in capping and interstitial modes. This result was further supported by a density functional theory investigation on the simplified model [Cu32 (H)20 (S2 PH2 )12 ].
A combination of single-crystal X-ray and neutron diffraction experiments are used to determine the electron density distribution in orthorhombic rubrene. The topology of electron density, NCI analysis and energetics of intermolecular interactions clearly demonstrate the presence of π⋯π stacking interactions in the crystalline state.
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