Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium-Sulfur Battery Cathodes.

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

Fluorocarbon-Functionalized Superhydrophobic Metal-Organic Framework: Enhanced CO2 Uptake via Photoinduced Postsynthetic Modification.

The design and synthesis of porous materials for selective capture of CO2 in the presence of water vapor is of paramount importance in the context of practical separation of CO2 from the flue gas stream. Here, we report the synthesis and structural characterization of a photoresponsive fluorinated MOF {[Cd(bpee)(hfbba)]·EtOH}n (1) constructed by using 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (hfbba), Cd(NO3)2, and 1,2-bis(4-pyridyl)ethylene (bpee) as building units. Due to the presence of the fluoroalkyl -CF3 functionality, compound 1 exhibits superhydrophobicity, which is validated by both water vapor adsorption and contact angle measurements (152°). The parallel arrangement of the bpee linkers makes compound 1 a photoresponsive material that transforms to {[Cd2(rctt-tpcb)(hfbba)2]·2EtOH}n (rctt-tpcb = regio cis,trans,trans-tetrakis(4-pyridyl)cyclobutane; 1IR) after a [2 + 2] cycloaddition reaction. The photomodified framework 1IR exhibits increased uptake of CO2 in comparison to 1 under ambient conditions due to alteration of the pore surface that leads to additional weak electron donor-acceptor interactions with the -CF3 groups, as examined through periodic density functional theory calculations. The enhanced uptake is also aided by an expansion of the pore window, which contributes to increasing the rotational entropy of CO2, as demonstrated through force field based free energy calculations.

A Dynamic Chemical Clip in Supramolecular Framework for Sorting Alkylaromatic Isomers using Thermodynamic and Kinetic Preferences.

Adsorptive chemical separation is at the forefront of future technologies, for use in chemical and petrochemical industries. In this process, a porous adsorbent selectively allows a single component from a mixture of three or more chemical components to be adsorbed or permeate. To separate the unsorted chemicals, a different adsorbent is needed. A unique adsorbent which can recognize and separate each of the chemicals from a mixture of three or more components is the necessity for the next generation porous materials. In this regard, we demonstrate a "dynamic chemical clip" in a supramolecular framework capable of thermodynamic and kinetics-based chemical separation. The dynamic space, featuring a strong preference for aromatic guests through π-π and C-H⋅⋅⋅π interactions and adaptability, can recognize the individual chemical isomers from mixtures and separate those based on thermodynamic and kinetic factors. The liquid-phase selectivity and separation of the aromatic isomers are possible by the adaptability of the "chemical clip" and here we elucidate the prime factors in a combinatorial approach involving crystallographic evidence and detailed computational studies.

Guest-Responsive Reversal in Structural Transformation after a [2 + 2] Topochemical Reaction in a 3D Pillared Layer MOF: Uncovering the Role of C-H···O Interaction.

Here, we report the influences of the C-H···O interaction, weaker than other conventional noncovalent interactions, on the guest-responsive structural modification of a photoactive metal-organic framework (MOF) and the impact on gas sorption properties. A photoactive pillared-layer three-dimensional MOF {[Cd(pzdc)(bpee)]2·3H2O}n (1) (where bpee = 1,2-bis(4-pyridyl)ethylene and pzdc = 2,3-pyrazinedicarboxylate) was synthesized and characterized. Compound 1 shows guest-responsive structural contraction by the movement of two-dimensional layers supported by the C-H···O interaction between the pillar (bpee) and layer (pzdc) linkers. Further, 1 was postsynthetically modified using light by exploiting the parallel arrangement of the olefinic double bondsof the bpee pillars based on a [2 + 2] cycloaddition reaction to produce {[Cd2(pzdc)2(rctt-tpcb)]·3H2O}n, (1IR) (rctt-tpcb = regio cis,trans,trans-tetrakis(4-pyridyl)cyclobutane) in a single-crystal-to-single-crystal transformation (SCSC) manner. The C-H···O interaction between the two linkers is not possible in the photomodified framework, and thus guest-responsive structural expansion is realized. Such a reversal of the structural transformation facilitates the enhanced CO2 uptake in 1IR with respect to 1 at their dehydrated states. Further, the photomodified compound 1IR does not uptake N2 and CH4 at 273 K and shows high selectivity as realized by an ideal adsorbed solution theory calculation. The facile diffusion of CO2 in the irradiated framework is also supported by the kinetic measurements based on MeOH adsorption isotherms at 293 K. Here, postsynthetic modification by a [2 + 2] photochemical reaction is the key to control the structural change for enhanced CO2 uptake capacity.

Acetylene/Ethylene Separation and Solid-State Structural Transformation via [2 + 2] Cycloaddition Reactions in 3D Microporous ZnII Metal-Organic Frameworks.

Purification of ethylene by removing acetylene from an ethylene/acetylene (99/1 v/v) mixture is a challenging task in the petrochemical industry. Our effort toward finding new porous materials that can selectively uptake acetylene resulted in two 3D metal-organic frameworks. Compound 1, {[Zn(p-pda)(bpee)]} (p-pda = p-phenylenediacetate and bpee = 1,2-bis(4-pyridyl)ethylene) turned out to be a nonporous structure due to the presence of a bulky and rigid aromatic ring in the p-pda ligand. Interestingly, replacement of p-pda with succinic acid yields the microporous framework {[Zn2(µ3-OH)(suc)1.5(bpee)]·CH3OH·2H2O} (2; suc = succinate), which offers a 1D channel along the a direction occupied by guest methanol and water molecules. Remarkably, the desolvated framework of 2 shows selective uptake of C2H2 over other gas molecules such as C2H4, C2H6, CO2 and CH4 at 293 K. An ideal absorbed solution theory (IAST) study predicts a high selectivity value for acetylene adsorption over the other gas molecules mentioned above. The efficiency of removal of acetylene from ethylene/acetylene mixtures containing 1% acetylene was established through a column breakthrough experiment performed at room temperature. The performance of our material in the purification of ethylene by removing acetylene is comparable with those reported in the literature. In the frameworks of both 1 and 2, the ethylenic double bonds of adjacent bpee linkers are aligned parallel and readily undergo [2 + 2] cycloaddition reactions upon UV-light irradiation to yield {[Zn2(p-pda)2(rctt-tpcb)]} (1IR) and {[Zn4(µ3-OH)2(suc)3(rctt-tpcb)]·2CH3OH·4H2O} (2IR), respectively (rctt-tpcb = regio-cis,trans,trans-tetrakis(4-pyridyl)cyclobutane). Photochemical structural transformations of 100% were observed in single-crystal to single-crystal fashions, which were also supported by 1H NMR spectroscopy. The structures of both 2 and 2IR underwent temperature-dependent reversible structural transformations, which was confirmed by SCXRD and DSC analysis. Selective C2H2 uptake of the dehydrated framework of 2IR was also examined, which demonstrates results similar to those of 2.

Guest-Responsive Reversible Electron Transfer in a Crystalline Porous Framework Supported by a Dynamic Building Node.

We demonstrate a redox-active, crystalline donor-acceptor (D-A) assembly in which the electron transfer (ET) process can be reversibly switched. This ET process, induced by a guest-responsive structural transformation at room temperature, is realized in a porous, metal-organic framework (MOF), having anthracene (D)-naphthalenediimide (A) as struts. A control MOF structure obtained by a solvent-assisted linker exchange (SALE) method, replacing an acceptor strut with a neutral one, supported the switchable electronic states in the D-A MOF. Combined investigations with X-ray diffraction, spectroscopy, and theoretical analyses revealed the dynamic metal paddle-wheel node as a critical unit for controlling structural flexibility and the corresponding unprecedented ET process.

Solvent-Modulated Emission Properties in a Superhydrophobic Oligo( p-phenyleneethynylene)-Based 3D Porous Supramolecular Framework.

A chromophoric oligo( p-phenyleneethynylene) (OPE) bola-amphiphile with dioxyoctyl side chains (H2OPE-C8) has been self-assembled with CdII to form a 1D coordination polymer, {Cd(OPE-C8)(DMF)2(H2O)} (1), which is further interdigitated to form a 2D network. Such 2D networks are further interwoven to form a 3D supramolecular framework with surface-projected alkyl chains. The desolvated framework showed permanent porosity, as realized from the CO2 adsorption profile. 1 showed high water contact angles, portraying its superhydrophobic nature. 1 also showed a linker-based cyan luminescence. Solvent removal led to a bathochromic shift in emission into the green region. Resolvation with N, N-dimethylformamide brought back the original cyan emission, whereas for tetrahydrofuran, ethanol, and methanol, it persisted at an intermediate state. Density functional theory calculations unraveled that, twisting of the OPE phenyl rings generated the red shift in emission.

Host-Guest [2+2] Cycloaddition Reaction: Postsynthetic Modulation of CO2 Selectivity and Magnetic Properties in a Bimodal Metal-Organic Framework.

Simultaneous tuning of permanent porosity and modulation of magnetic properties by postsynthetic modification (PSM) with light in a metal-organic framework is unprecedented. With the aim of achieving such a photoresponsive porous magnetic material, a 3D photoresponsive biporous framework, MOF1, which has 2D channels occupied by the guest 1,2-bis(4-pyridyl)ethylene (bpee), H2 O, and EtOH molecules, has been synthesized. The guest bpee in 1 is aligned parallel to pillared bpee with a distance of 3.9 Šbetween the ethylenic groups; this allows photoinduced PSM of the pore surface through a [2+2] cycloaddition reaction to yield MOF2. Such photoinduced PSM of the framework structure introduces enhanced CO2 selectivity over that of N2 . The higher selectivity in MOF2 than that of MOF1 is studied through theoretical calculations. Moreover, MOF2 unveils reversible changes in Tc with response to dehydration-rehydration. This result demonstrates that photoinduced PSM is a powerful tool for fabricating novel functional materials.

Crystal Dynamics in Multi-stimuli-Responsive Entangled Metal-Organic Frameworks.

An understanding of solid-state crystal dynamics or flexibility in metal-organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single-crystallinity. In this article, detailed experimental studies on a twofold entangled MOF (f-MOF-1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f-MOF-1, by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f-MOF-1 a and f-MOF-1 b, could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO2 adsorption profiles. DFT-based calculations provide an insight into the selective and gated adsorption behavior with CO2 of f-MOF-1 b. The gate-opening threshold pressure of CO2 adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (-CH2 -CH2 -) in f-MOF-1 to an azo (-N=N-) functionality in an analogous MOF, f-MOF-2. The modulation of functionality has an indirect influence on the gate-opening pressure owing to the difference in inter-net interaction. The framework of f-MOF-1 is highly responsive toward CO2 gas molecules, and these results are supported by DFT calculations.

Stoichiometry-controlled two flexible interpenetrated frameworks: higher CO2 uptake in a nanoscale counterpart supported by accelerated adsorption kinetics.

Here, we report the synthesis, structural characterizations, and gas storage properties of two new 2-fold interpenetrated 3D frameworks, {[Zn2(bpdc)2(azpy)]·2H2O·2DMF}n (1) and {[Zn3(bpdc)3(azpy)]·4H2O·2DEF}n (2) [bpdc = 4,4'-biphenyldicarboxylate; azpy = 4,4'-azobipyridine], obtained from the same set of organic linkers. Furthermore, 1 has been successfully miniaturized to nanoscale (MOF1N) of spherical morphology to study size dependent adsorption properties through a coordination modulation method. The two different SBUs, dinuclear paddle-wheel {Zn2(COO)4} for 1 and trinuclear {Zn3(µ2-OCO)2(COO)4 }for 2, direct the different network topologies of the frameworks that render different adsorption characteristics into the systems. Both of the frameworks show guest induced structural transformations as supported by PXRD studies. Adsorption studies of 1 and 2 show CO2 selectivity over several other gases (such as N2, H2, O2, and Ar) under identical experimental conditions. Interestingly, MOF1N exhibits significantly higher CO2 storage capacity compared to bulk crystals of 1 and that can be attributed to the smaller diffusion barrier at the nanoscale that is supported by studies of adsorption kinetics in both states. Kinetic measurement based on water vapor adsorption clearly distinguishes between the rate of diffusion of bulk (1) and nanospheres (MOF1N). The respective kinetic rate constant (k, s(-1)) for MOF1N (k = 1.29 × 10(-2) s(-1)) is found to be considerably higher than 1 (k = 7.1 × 10(-3) s(-1)) as obtained from the linear driving force (LDF) model. This is the first account where a new interpenetrated MOF has been scaled down to nanoscale through a coordination modulation method, and their difference in gas uptake properties has been correlated through a higher rate of mass diffusion as obtained from kinetics of adsorption.

Cyclocondensation of arylhydrazines with 1,3-bis(het)arylmonothio-1,3-diketones and 1,3-bis(het)aryl-3-(methylthio)-2-propenones: synthesis of 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity.

Two efficient highly regioselective routes for the synthesis of unsymmetrically substituted 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity starting from active methylene ketones have been reported. In the first protocol, the newly synthesized 1,3-bis(het)aryl-monothio-1,3-diketone precursors (prepared by condensation of active methylene ketones with het(aryl) dithioesters in the presence of sodium hydride) were reacted with arylhydrazines in refluxing ethanol under neutral conditions, furnishing 1-aryl-3,5-bis(het)arylpyrazoles 7, in which the het(aryl) moiety attached to the thiocarbonyl group of monothio-1,3-diketones is installed at the 3-position. In the second method, the corresponding 3-(methylthio)-1,3-bis(het)aryl-2-propenones (prepared in situ by base-induced alkylation of 1,3-monothiodiketones) were condensed with arylhydrazines in the presence of potassium tert-butoxide in refluxing tert-butyl alcohol, yielding 1-aryl-3,5-bis(het)arylpyrazoles 9 with complementary regioselectivity (method A). The efficiency of this protocol was further improved by developing a one-pot, three-component procedure for the synthesis of pyrazoles 9, directly from active methylene ketones, by reacting in situ generated 3-(methylthio)-1,3-bis(het)aryl-2-propenones with arylhydrazines in the presence of sodium hydride (instead of potassium tert-butoxide as base). The structures and regiochemistry of newly synthesized pyrazoles were confirmed from their spectral and analytical data along with X-ray crystallographic data of three pairs of regioisomers.

Effect of pillar modules and their stoichiometry in 3D porous frameworks of Zn(II) with [Fe(CN)6]3-: high CO2/N2 and CO2/CH4 selectivity.

We report the synthesis, single-crystal structural characterization, and selective gas adsorption properties of three new 3D metal-organic frameworks of Zn(II), {[Zn3(bipy)3(H2O)2][Fe(CN)6]2·2(bipy)·3H2O}n (1), {[Zn3(bipy)][Fe(CN)6]2·(C2H5OH)·H2O}n (2), and {[Zn3(azpy)2(H2O)2][Fe(CN)6]2·4H2O}n (3) (bipy = 4,4'-bipyridyl and azpy = 4,4'-azobipyridyl), bridged by [Fe(CN)6](3-) and exobidentate pyridyl-based linkers. Compounds 1-3 have been successfully isolated by varying the organic linkers (bipy and azpy) and their ratios during the synthesis at RT. Frameworks 1 and 3 feature a biporous-type network. At 195 K, compounds 1-3 selectively adsorb CO2 and completely exclude other small molecules, such as N2, Ar, O2, and CH4. Additionally, we have also tested the CO2 uptake capacity of 1 and 3 at ambient temperatures. By using the isotherms measured at 273 and 293 K, we have calculated the isosteric heat of CO2 adsorption, which turned out to be 35.84 and 35.53 kJ mol(-1) for 1 and 3, respectively. Furthermore, a reasonably high heat of H2 adsorption (7.97 kJ mol(-1) for 1 and 7.73 kJ mol(-1) for 3) at low temperatures suggests strong interaction of H2 molecules with the unsaturated Zn(II) metal sites and as well as with the pore surface. Frameworks 1 and 3 show high selectivity to CO2 over N2 and CH4 at 273 K, as calculated based on the IAST model. The high values of ΔH(CO2) and ΔH(H2) stem from the preferential electrostatic interaction of CO2 with the unsaturated metal sites, pendent nitrogen atoms of [Fe(CN)6](3-), and π-electron cloud of bipyridine aromatic rings as understood from first-principles density functional theory based calculations.

Noncovalent interaction guided selectivity of haloaromatic isomers in a flexible porous coordination polymer.

Porous, supramolecular structures exhibit preferential encapsulation of guest molecules, primarily by means of differences in the order of (noncovalent) interactions. The encapsulation preferences can be for geometry (dimension and shape) and the chemical nature of the guest. While geometry-based sorting is relatively straightforward using advanced porous materials, designing a "chemical nature" specific host is not. To introduce "chemical specificity", the host must retain an accessible and complementary recognition site. In the case of a supramolecular, porous coordination polymer (PCP) [Zn(o-phen)(ndc)] (o-phen: 1,10-phenanthroline, ndc: 2,6-naphthalenedicarboxylate) host, equipped with an adaptable recognition pocket, we have discovered that the preferential encapsulation of a haloaromatic isomer is not only for dimension and shape, but also for the "chemical nature" of the guest. This selectivity, i.e., preference for the dimension, shape and chemical nature, is not guided by any complementary recognition site, which is commonly required for "chemical specificity". Insights from crystal structures and computational studies unveil that the differences in the different types of noncovalent host-guest interaction strengths, acting in a concerted fashion, yield the unique selectivity.

Sulfide-Bridged Covalent Quinoxaline Frameworks for Lithium-Organosulfide Batteries.

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing Li-storage mechanism, which can be considered as a lithium-organosulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox-mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organosulfide interactions. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery.

Three-dimensional metal-organic framework with highly polar pore surface: H2 and CO2 storage characteristics.

A three-dimensional (3D) pillared-layer metal-organic framework, [Cd(bipy)(0.5)(Himdc)](DMF)](n) (1), (bipy =4,4'-bipyridine and Himdc = 4,5-imidazoledicarboxylate) has been synthesized and structurally characterized. The highly rigid and stable framework contains a 3D channel structure with highly polar pore surfaces decorated with pendant oxygen atoms of the Himdc linkers. The desolvated framework [Cd(bipy)(0.5)(Himdc)](n) (1') is found to exhibit permanent porosity with high H(2) and CO(2) storage capacities. Two H(2) molecules occluded per unit formula of 1' and the corresponding heat of H(2) adsorption (ΔH(H2)) is about ∼9.0 kJ/mol. The high value of ΔH(H2) stems from the preferential electrostatic interaction of H(2) with the pendent oxygen atoms of Himdc and aromatic bipy linkers as determined from first-principles density functional theory (DFT) based calculations. Similarly, DFT studies indicate CO(2) to preferentially interact electrostatically (C(δ+)···O(δ-)) with the uncoordinated pendent oxygen of Himdc. It also interacts with bipy through C-H···O bonding, thus rationalizing the high heat (ΔH(CO2) ∼ 35.4 kJ/mol) of CO(2) uptake. Our work unveiled that better H(2) or CO(2) storage materials can be developed through the immobilization of reactive hetero atoms (O, N) at the pore surfaces in a metal-organic framework.

Open metal site (OMS)-inspired investigation of adsorption and catalytic functions in a porous metal-organic framework (MOF).

In this article, we report the adsorption and catalytic study of the three-dimensional (3D) metal-organic framework (MOF) {Mn2(1,4-bdc)2(DMF)2} (1) (1,4-bdcH2, 1,4-benzene dicarboxylic acid; DMF, N,N-dimethylformamide) together with the synthesis and structure of two new Mn(II)-MOFs {Mn3(Br-bdc)3(DMF)4} (2) and {Mn3(NO2-bdc)3(DMF)4} (3) (Br-bdcH2, 2-bromo-1,4-benzene dicarboxylic acid; NO2-bdcH2, 2-nitro-1,4-benzene dicarboxylic acid) under solvothermal conditions. Compounds 2 and 3 have two-dimensional (2D) extended structures and feature trimeric {Mn3(CO2)6} units that serve as secondary building units for the frameworks. The desolvated compound of 1, denoted as 1', having potential Mn(II) open metal sites (OMSs) lined in a one-dimensional (1D) Mn-chain interconnected by carboxylate groups, exhibits guest-selective adsorption of solvent vapours wherein the compound shows a stepwise profile with H2O vapour, while a gated isotherm was recorded with MeOH. After realizing the favourable interaction of 1' with polar solvent molecules, we have used Mn(II) OMSs in 1' for efficient cyanosilylation reactions of aromatic aldehydes. We have recorded 100% conversion for eight aromatic aldehydes, while several other aldehydes showed appreciable conversion. Notably, the recorded conversions in the case of many substrates are higher than those for many other reported MOF catalysts.

Probing time dependent phase transformation in a flexible metal-organic framework with nanoindentation.

Phase transformation in a flexible metal-organic framework, {[Zn4(1,4-NDC)4(1,2-BPE)2]·xSolvent}n, which loses guest molecules rapidly at room temperature, leading to several phase transitions, is examined using the nanoindentation technique. Nanoindentation results revealed that the time dependent transformation of an open to a closed phase happens gradually, through multiple intermediate phases, with the mechanical properties (elastic modulus and hardness) increasing as the transformation progresses from an open to a closed phase.

Accordion and layer-sliding motion to produce anomalous thermal expansion behaviour in 2D-coordination polymers.

Solvent-free (1) and solvated (2) 2D-coordination polymers have been synthesised by varying the amount of solvent during crystallisation. 1 undergoes a unique accordion motion of 2D zig-zag interwoven layers whereas 2 experiences layer-sliding within 2D layers to produce anomalous thermal expansion behaviour.

Polar functional groups anchored to a 2D MOF template for the stabilization of Pd(0) nps for the catalytic C-C coupling reaction.

A 2D porous MOF, {[Cu(1,2,3-btc)(bpe)(H2O)]·H2O}n (1), has been synthesized using a mixed linker system. The structural determination showed non-coordinated carboxylate groups decorating the pore surface. The desolvated MOF (1a) with pendant carboxylate groups was used as a template for the stabilization of Pd nps (2-3 nm) and the resulting composite Pd(0)@1a showed efficient catalytic activity for the Suzuki-Miyaura C-C coupling reaction.

CO2-induced single-crystal to single-crystal transformations of an interpenetrated flexible MOF explained by in situ crystallographic analysis and molecular modeling.

A molecular-level investigation is reported on breathing behaviour of a metal-organic framework (1) in response to CO2 gas pressure. High-pressure gas adsorption shows a pronounced step corresponding to a gate-opening phase transformation from a closed (1cp ) to a large-pore (1lp ) form. A plateau is observed upon desorption corresponding to narrow-pore intermediate form 1np which does not occur during adsorption. These events are corroborated by pressure-gradient differential scanning calorimetry and in situ single-crystal X-ray diffraction analysis under controlled CO2 gas pressure. Complete crystallographic characterisation facilitated a rationalisation of each phase transformation in the series 1cp → 1lp → 1np → 1cp during adsorption and subsequent desorption. Metropolis grand-canonical Monte Carlo simulations and DFT-PBE-D3 interaction energy calculations strongly underpin this first detailed structural investigation of an intermediate phase encountered upon desorption.