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Giant Hysteretic Sorption of CO2: In Situ Crystallographic Visualization of Guest Binding within a Breathing Framework at 298 K

A dynamic ZnII -MOF has been shown to exhibit extreme breathing behavior under gas pressure. The very narrow pore form of the activated framework opens up in the presence of carbon dioxide, thus making it a suitable material for CO2 capture. Sorption of CO2 at 298 K and relatively high pressure clearly shows a two-step isotherm with giant hysteresis for the second step. In-situ single-crystal diffraction analysis was carried out under CO2 gas pressure at 298 K using an environmental gas cell in order to visualize the interaction between CO2 and the host framework. The results are well supported by pressure-gradient differential scanning calorimetry (P-DSC) and variable-pressure powder X-ray analysis. Theoretical calculations have been carried out in order to further back up the crystallographic data.

Reversible Switching between Highly Porous and Nonporous Phases of an Interpenetrated Diamondoid Coordination Network that Exhibits Gate‐Opening at Methane Storage Pressures

Herein, we report that a new flexible coordination network, NiL2 (L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), with diamondoid topology switches between non-porous (closed) and several porous (open) phases at specific CO2 and CH4 pressures. These phases are manifested by multi-step low-pressure isotherms for CO2 or a single-step high-pressure isotherm for CH4 . The potential methane working capacity of NiL2 approaches that of compressed natural gas but at much lower pressures. The guest-induced phase transitions of NiL2 were studied by single-crystal XRD, in situ variable pressure powder XRD, synchrotron powder XRD, pressure-gradient differential scanning calorimetry (P-DSC), and molecular modeling. The detailed structural information provides insight into the extreme flexibility of NiL2 . Specifically, the extended linker ligand, L, undergoes ligand contortion and interactions between interpenetrated networks or sorbate-sorbent interactions enable the observed switching.

Large volumetric thermal expansion of a novel organic cocrystal over a wide temperature range

An organic cocrystal consisting of 4-aminobenzonitrile and 4-(dimethylamino) benzonitrile (ABN·2DMABN) undergoes positive linear thermal expansion along its three principal axes over the temperature range 100–300 K. The associated volumetric thermal expansion coefficient is the largest reported to date for a cocrystal in the wide temperature range investigated.

Distinctive Three-Step Hysteretic Sorption of Ethane with In Situ Crystallographic Visualization of the Pore Forms in a Soft Porous Crystal

A soft porous Zn(II)-MOF (1) displays distinctive three-step hysteretic breathing behavior under ethane gas pressure at ambient temperatures. In situ single-crystal X-ray diffraction analysis was carried out at 298 K using an environmental gas cell in order to elucidate the different porous forms of the breathing framework under ethane gas. The three different phases were further characterized by pressure-gradient differential scanning calorimetry and variable pressure powder X-ray diffraction analysis.

First Orotic Acid and Isonicotinic Acid Based Zn Complex: Hydrothermal Synthesis, Crystal Structure, and Thermogravimetric Analysis

New supramolecular synthon induced complex [Zn(Hor)(Hiso)·3H2O]·H2O (1) is obtained in a selfassembly reaction of zinc nitrate with orotic (H3Or, 1,2,3,6-tetrahydro-2,6-dioxo-4-pyrimidinecarboxylic) acid and isonicotinamide. The isonicotinamide molecule is hydrolyzed in-situ into isonicotinic (Hiso, pyridine-4-carboxylic) acid. A detailed structural analysis and the role of hydrogen bonding synthons in deciding the overall structural diversity is discussed. The {…H–N–C=O…}2 and {…H–O–C=O…}2 dimers play an important role in the metal-organic architecture of 1. Complex 1 is insoluble in almost all organic solvents as well as in water. The complete decomposition of the compound is achieved above 445°C.

Visualizing Structural Transformation and Guest Binding in a Flexible Metal–Organic Framework under High Pressure and Room Temperature

Understanding the effect of gas molecules on the framework structures upon gas sorption in porous materials is highly desirable for the development of gas storage and separation technologies. However, this remains challenging for flexible metal–organic frameworks (MOFs) which feature “gate-opening/gate-closing” or “breathing” sorption behaviors under external stimuli. Herein, we report such a flexible Cd-MOF that exhibits “gating effect” upon CO2 sorption. The ability of the desolvated flexible Cd-MOF to retain crystal singularity under high pressure enables the direct visualization of the reversible closed-/open-pore states before and after the structural transformation as induced by CO2 adsorption/desorption through in situ single-crystal X-ray diffraction experiments. The binding sites of CO2 molecules within the flexible MOF under high pressure and room temperature have also been identified via combined in situ single-crystal X-ray diffraction and powder X-ray diffraction studies, facilitating the elucidation of the states observed during gate-opening/gate-closing behaviors. Our work therefore lays a foundation to understand the high-pressure gas sorption within flexible MOFs at ambient temperature, which will help to improve the design efforts of new flexible MOFs for applications in responsive gas sorption and separation.

A blue luminescent binuclear cadmium-orotate coordination polymer: synthesis, crystal structure, and thermogravimetric analysis

Abstract Assembly of orotic acid (H3Or, 1,2,3,6-tetrahydro-2,6-dioxo-4-pyrimidinecarboxylic) and Cd(NO3)·6H2O yielded a coordination polymer, [(Cd(Hor)·2.5H2O)2]n (1), which has been characterized by X-ray single-crystal diffraction, TGA, and fluorescence spectra. Single-crystal X-ray structural analyses reveal that 1 is a hydrogen-bonded binuclear Cd-orotate coordination polymer in which both Cd2+ ions have different coordination environments with identical distorted octahedral geometry. Crystal data for 1: monoclinic, space group P21/n, a = 7.0209(10) Å, b = 13.974(2) Å, c = 17.541(3) Å, β = 98.842(2)°, V = 1700.5(4) Å, Z = 4, R1 = 0.0269, wR2 = 0.0612, θmax = 25.960. The emission spectrum of the Cd-complex recorded with 265 nm excitation wavelength reveals the complex has strong blue luminescence with the peak maximum 420 nm (2.95 eV) as a result of the n–π* and π–π* transitions on the H3Or ligand.