Highly selective acetylene binding over CO 2 and ethylene is observed in the first example of a rigid sorbent that is composed of cis -bridging hexafluorosilicate anions.

Guest transport through discrete voids (closed pores) in crystalline solids is poorly understood. Herein, we report the gas sorption properties of a nonporous coordination network, {[Co(bib) 2 Cl 2 ] ⋅ 2MeOH} n ( sql-bib-Co-Cl-α ), featuring square lattice ( sql ) topology and the bent linker 1,3-bis(1 H -imidazol-1-yl)benzene (bib). The as-synthesized sql-bib-Co-Cl-α has 11.3 % (313 Å 3 ) of its unit cell volume in closed pores occupied by methanol (MeOH). Upon desolvation and air exposure, sql-bib-Co-Cl-α underwent a single-crystal to single-crystal (SC-SC) phase transformation to sql-bib-Co-Cl-β′ , wherein MeOH was replaced by water. Activation (vacuum or N 2 flow) resulted in dehydration and retention of the closed pores, affording sql-bib-Co-Cl-β with 7.7 % (194 Å 3 ) guest-accessible space. sql-bib-Co-Cl-β was found to preferentially adsorb C 2 H 2 (at 265 K) over CO 2 (at 195 K) through gate-opening mechanisms, at gate-opening pressures of 59.8 and 27.7 kPa, respectively, while other C2 gases were excluded. PXRD was used to monitor transformations between the three phases of sql-bib-Co-Cl , while in situ DSC, in situ SCXRD under CO 2 pressure, and computational studies provided insight into the guest transport mechanism, which we attribute to the angular, flexible nature of the bib ligand. Further, the preferential adsorption of C 2 H 2 over CO 2 and other C2 gases suggests that transiently porous sorbents might have utility in separations.

Two series of robust pillared metal–organic frameworks (MOFs) are obtained under solvothermal conditions by combining a metal salt with either H2bpdc, biphenyl‐4,4′‐dicarboxylic acid, or H2pda, 1,4‐phenylenediacrylic acid, forming 2D layers, which are pillared by L, an alloxazine derivative of 1,4‐di(pyridin‐4‐yl)benzene using a one‐pot three‐component strategy. Crystallographic studies reveal the formation of two isomorphous series of compounds, namely 1‐M (from H2bpdc with M = Co, Ni, Cu, and Zn) and 2‐M (from H2pda with M = Co or Cu). The multifunctional compounds have high decomposition temperatures, and their sorption properties were measured, revealing relatively low surface areas. Furthermore, 1‐Zn displays a moderate uptake of CO2 and C2H4 at high pressures. In addition, for 1‐M (M = Co, Cu or Zn), solid‐state electrochemistry reveals redox behavior for the MOF, centered on the ligand. This study provides evidence for the first account of a one‐pot formation of redox‐active pillared MOFs, which exhibit gas sorption abilities before the reduction.

Flexible metal-organic materials (FMOMs) with stepped isotherms can offer enhanced working capacity in storage applications such as adsorbed natural gas (ANG) storage. Unfortunately, whereas >1000 FMOMs are known, only a handful exhibit methane uptake of >150 cm3/cm3 at 65 atm and 298 K, conditions relevant to ANG. Here, we report a double-walled 2-fold interpenetrated diamondoid (dia) network, X-dia-6-Ni, [Ni2L4(μ-H2O)]n, comprising a new azo linker ligand, L- (L- = (E)-3-(pyridin-4-yldiazenyl)benzoate) and 8-connected dinuclear molecular building blocks. X-dia-6-Ni exhibited gas (CO2, N2, CH4) and liquid (C8 hydrocarbons)-induced reversible transformations between its activated narrow-pore β phase and γ, a large-pore phase with ca. 33% increase in unit cell volume. Single-crystal X-ray diffraction (SCXRD) studies of the as-synthesized phase α, β, and γ revealed that structural transformations were enabled by twisting of the azo moiety and/or deformation of the MBB. Further insight into these transformations was gained from variable temperature powder XRD and in situ variable pressure powder XRD. Low-temperature N2 and CO2 sorption revealed stepped Type F-II isotherms with saturation uptakes of 422 and 401 cm3/g, respectively. X-dia-6-Ni exhibited uptake of 200 cm3/cm3 (65 atm, 298 K) and a high CH4 working capacity of 166 cm3/cm3 (5-65 bar, 298 K, 33 cycles), the third highest value yet reported for an FMOM and the highest value for an FMOM with a Type F-II isotherm.

High-pressure experiments on the aperiodic material TRUMOF-1 reveal that linkage disorder thwarts collapse mechanisms, thus enhancing mechanical stability.

The increase in atmospheric carbon dioxide concentration linked to climate change has created a need for new sorbents capable of separating CO2 from exhaust gases. Recently, an easily produced metal-organic framework, CALF-20, was shown to withstand over 450,000 adsorption/desorption cycles in steam and wet acid gases. Further development and industrial application of such materials require an understanding of the observed processes. Herein, we demonstrate that conditioning as-synthesized CALF-20 single crystal transforms it into a different phase, gamma-CALF-20. The transformation resulted in significant structural changes, including the binding of water molecules to Zn(II), accompanied by a reduction of 9% in the unit cell volume. Our experimental findings were supported by the energy-volume dependence of CALF-20 in the presence and absence of water molecules calculated from density functional theory. We have also monitored the sorption process of the dominant greenhouse gas, CO2, on the initial phase of CALF-20 at atomic resolution using in situ single-crystal X-ray diffraction under specific pressure. The new understanding of CALF-20 chemistry from these studies should facilitate development of novel sorbents for gas adsorption technologies.

A novel 0D Cu(II) dinuclear imidazolyl-based metallocycledesolvates in the presence of mother liquor and transforms into a1D coordination polymer in a single-crystal to single-crystal fashion.The mechanism of this transformation has been elucidated, and structuralfeatures responsible for this transformation have been identified. A novel Cu(II) imidazolyl-based metallocycle, [Cu(2)L1(2)(NO3)(4)]& BULL;2MeCN, undergoesa single-crystalto single-crystal transformation to form a 1D coordination polymer,[CuL1(NO3)(2)]( n ). Thistransformation is triggered by the loss of solvent in the presenceof the same solvent, which is counterintuitive. Expulsion of interstitialsolvent molecules occurs with concomitant rearrangement of the ligands,which concertedly recoordinate to nearby metal centers to achievea lower energy state. This is the first imidazolyl-based metallacyclereported to undergo such a phase transformation.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Shape-memory polymers and alloys are adaptable materials capable of reversing from a deformed, metastable phase to an energetically favored original phase in response to external stimuli. In the context of metal-organic frameworks, the term shape-memory is defined as the property of a switchable framework to stabilize the reopened pore phase after the first switching transition. Herein we describe a novel flexible terpyridine MOF which, upon desolvation, transforms into a nonporous structure that reopens into a shape-memory phase when exposed to CO2 at 195 K. Based on comprehensive in situ experimental studies (SC-XRD and PXRD) and DFT energetic considerations combined with literature reports, we recommend dividing shape-memory MOFs into two categories, viz responsive and nonresponsive, depending on the transformability of the gas-free reopened pore phase into the collapsed phase. Furthermore, considering the methodological gap in discovering and understanding shape-memory porous materials, we emphasize the importance of multicycle physisorption experiments for dynamic open framework materials, including metal-organic and covalent organic frameworks.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Compared to rigid physisorbents, switching coordination networks that reversibly transform between closed (non-porous) and open (porous) phases offer promise for gas/vapour storage and separation owing to their improved working capacity and desirable thermal management properties. We recently introduced a coordination network, X-dmp-1-Co, which exhibits switching enabled by transient porosity. The resulting "open" phases are generated at threshold pressures even though they are conventionally non-porous. Herein, we report that X-dmp-1-Co is the parent member of a family of transiently porous coordination networks [X-dmp-1-M] (M = Co, Zn and Cd) and that each exhibits transient porosity but switching events occur at different threshold pressures for CO2 (0.8, 2.1 and 15 mbar, for Co, Zn and Cd, respectively, at 195 K), H2O (10, 70 and 75% RH, for Co, Zn and Cd, respectively, at 300 K) and CH4 (<2, 10 and 25 bar, for Co, Zn and Cd, respectively, at 298 K). Insight into the phase changes is provided through in situ SCXRD and in situ PXRD. We attribute the tuning of gate-opening pressure to differences and changes in the metal coordination spheres and how they impact dpt ligand rotation. X-dmp-1-Zn and X-dmp-1-Cd join a small number of coordination networks (<10) that exhibit reversible switching for CH4 between 5 and 35 bar, a key requirement for adsorbed natural gas storage.

Although diphosphene transition metal complexes are known to undergo E to Z isomerization upon irradiation with UV light, their potential for photoswitching has remained poorly explored. In this study, we present diphosphene complexes capable of reversible photoisomerizations through haptotropic rearrangements. The compounds [( 2 -κ 2 P, κ 6 C)Mo(CO) 2 ][OTf] ( 3 a [OTf]), [( 2 -κ 2 P, κ 6 C)Fe(CO)][OTf] ( 3 b [OTf]), and [( 2 -κ 2 P)Fe(CO) 4 ][OTf] ( 4 [OTf]) were prepared using the triflate salt [(L C )P=P(Dipp)][OTf] ( 2 [OTf) as a precursor (L C =4,5-dichloro-1,3-bis(2,6-diisiopropylphenyl)-imidazolin-2-yl; Dipp=2,6-diisiopropylphenyl, OTf=triflate). Upon exposure to blue or UV light (λ=400 nm, 470 nm), the initially red-colored η 2 -diphosphene complexes 3 a , b [OTf] readily undergo isomerization to form blue-colored η 1 -complexes [( 2 -κ 1 P, κ 6 C)M(CO) n ][OTf] ( 5 a , b [OTf]; a : M=Mo, n=2; b : M=Fe, n=1). This haptotropic rearrangement is reversible, and the ( κ 2 P, κ 6 C)-coordination mode gradually reverts back upon dissolution in coordinating solvents or more rapidly upon exposure to yellow or red irradiation (λ=590 nm, 630 nm). The electronic reasons for the reversible visible-light-induced photoswitching observed for 3 a , b [OTf] are elucidated by DFT calculations. These calculations indicate that the photochromic isomerization originates from the S 1 excited state and proceeds through a conical intersection.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]n (X-dia-4-Co) and [Co(bimbz)(bdc)]n (X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P0≈ 0.008 or P≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry.

Water is one of the most important substances on our planet 1 . It is ubiquitous in its solid, liquid and vaporous states and all known biological systems depend on its unique chemical and physical properties. Moreover, many materials exist as water adducts, chief among which are crystal hydrates (a specific class of inclusion compound), which usually retain water indefinitely at subambient temperatures 2 . We describe a porous organic crystal that readily and reversibly adsorbs water into 1-nm-wide channels at more than 55% relative humidity. The water uptake/release is chromogenic, thus providing a convenient visual indication of the hydration state of the crystal over a wide temperature range. The complementary techniques of X-ray diffraction, optical microscopy, differential scanning calorimetry and molecular simulations were used to establish that the nanoconfined water is in a state of flux above −70 °C, thus allowing low-temperature dehydration to occur. We were able to determine the kinetics of dehydration over a wide temperature range, including well below 0 °C which, owing to the presence of atmospheric moisture, is usually challenging to accomplish. This discovery unlocks opportunities for designing materials that capture/release water over a range of temperatures that extend well below the freezing point of bulk water.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.