Heterobimetallic Synergism in Triple-Redox 2D Framework for Largely Boosted Water Oxidation and Flanked Carboxylic-Acid-Triggered Unconventional Tandem Catalysis.

A fish-bone-shaped and thermochemically stable 2D metal-organic framework (MOF) with multimodal active center-decked pore-wall is devised. Redox-active [Co2(COO)4] node and thiazolo[5,4-d]thiazole functionalization benefit this mixed-ligand MOF exhibiting electrochemical water oxidation with 375 mV overpotential at 10 mA cm-2 current density and 78 mV per dec Tafel slope in alkaline medium. Pair of oppositely oriented carboxylic acids aids postmetalation with transition metal ions to engineer heterobimetallic materials. Notably, overpotential of Ni2+ grafted triple-redox composite reduces to 270 mV with twofold declined Tafel slope than the parent MOF, ranking among the best-reported values, and outperforming majority of related catalysts. Significantly, turnover frequency and charge transfer resistance display 35.5 and 1.4-fold upsurge, respectively, with much uplifted chronopotentiometric stability and increase active surface area owing to synergistic Co(II)-Ni(II) coupling. The simultaneous presence of ─COOH and nitrogen-rich moieties renders this hydrogen-bonded MOF as acid-base synergistic catalyst for recyclable deacetalization-Knoevenagel reaction with >99% product yield under solvent-free mild condition. Besides control experiments, unique role of ─COOH as hydrogen-bond donor site in substrate activation is validated from comparing the performances of molecular-shearing approach-derived structurally similar unfunctionalized MOF, and the heterobimetallic composite. To the best of tandem Knoevenagel condensation, larger-sized acetal exhibits poor yield of α,ß-unsaturated dicyanides, and demonstrates pore-fitting-mediated size-selectivity.

Largely Entangled Diamondoid Framework with High-Density Urea and Divergent Metal Nodes for Selective Scavenging of CO2 and Molecular Dimension-Mediated Size-Exclusive H-Bond Donor Catalysis.

Pore environment modulation with high-density polarizing groups in metal-organic frameworks (MOFs) can effectively accomplish selective and multicyclic carbon dioxide (CO2) adsorption, whereas the incorporation of task-specific organic sites inside these porous vessels promise to evade self-quenching, solubility, and recyclability issues in hydrogen-bond donating (HBD) catalysis. However, concurrent amalgamation of both these attributes over a single platform is rare but extremely demanding in view of sustainable applications. We designed a robust diamondoid framework CSMCRI-17 (CSMCRI = Central Salt and Marine Chemicals Research Institute) from the mixed-ligand assembly of azo group-containing dicarboxylate ligand, urea-functionalized pyridyl linker, and Zn(II) nodes with specific divergent coordination. Seven-fold interpenetration to the microporous structure largely augments N-rich functionality that facilitates high CO2 uptake in the activated form (17a) with good CO2 selectivity over N2 and CH4 that outperform many reported materials. The framework displays very strong CO2 affinity and no reduction in adsorption capacity over multiple uptake-release cycles. Benefitting from the pore-wall decoration with urea functionality from the pillaring strut, 17a further demonstrates hydrogen-bond-mediated Friedel-Crafts alkylation of indole with ß-nitrostyrene under mild conditions, with multicyclic usability and excellent reactivity toward wide ranges of substituted nucleophiles and electrophiles. Interestingly, interpenetration-generated optimum-sized pores induce poor conversion to sterically encumbered substrate via molecular dimension-mediated size selectivity that is alternatively ascribed from additional control experiments and support the occurrence of HBD reaction within the MOF cavity. The catalytic path is detailed in light of the change of emission intensity of the framework by the electrophile as well as the judicious choice of the substrate, which authenticates the prime role of urea moiety-governed two-point hydrogen bonding.

Coordination Unsaturation and Basic Site-Immobilized Nanochannel in a Chemorobust MOF for 3-Fold-Increased High-Temperature Selectivity and Fixation of CO2 under Mild Conditions with Nanomolar Recognition of Roxarsone.

A multifaceted metal-organic framework (MOF) with task-specific site-engineered pores can promise high-temperature and moisture-tolerant capture and non-redox fixation of CO2 under mild conditions as well as ultrasensitive detection of carcinogenic contaminants in water. Herein, we report a pillar-bilayered MOF that holds a nanochannel with contrasting functionalities for both these sustainable applications with improved performance characteristics. The twofold entangled robust framework exhibits CO2 adsorption at elevated temperatures with considerable MOF-gas interaction. Interestingly, CO2 selectivity unveils nearly a 3-fold improvement upon the rise of temperature, affording a CO2/N2 value of 820 at 313 K, which outperforms many porous adsorbents. Additionally, breakthrough simulation establishes complete separation and attests the potential of this MOF in the separation of flue gas mixture. Importantly, minor CO2 loss during multiple capture-release cycles and under a relative humidity of 75% promise practical usability of the material. Density functional theory (DFT) not only portrays the atomistic level snapshots of temperature-triggered CO2 inclusion inside this microporous vessel alongside the role of diverse CO2-philic sites but also validates the basis of N2-phobicity of an azo-functionalized linker on such increased selectivity. The guest-free MOF further demonstrates non-redox and recyclable CO2 fixation with wide epoxide tolerance under solvent-free mild conditions and even works at atmospheric pressure and room temperature. The crucial roles of high-density acid-base sites in both adsorption and catalysis are supported by control experiments and by comparing the activity of an unfunctionalized MOF. The hydrolytic stability and strong luminescence signature benefit the framework in aqueous-phase selective and fast responsive detection of detrimental roxarsone (ROX) with high quenching (7.56 × 104 M-1) and very low sensitivity (68 nM). Apart from varying degrees of an energy-transfer mechanism, the fluorosensing of ROX is comprehensively supported by in-depth DFT studies that manifest alteration of MOF energy levels in the presence of organoarsenic compounds and depict MOF-analyte supramolecular interactions.

Selective and Multicyclic CO2 Adsorption with Visible Light-Driven Photodegradation of Organic Dyes in a Robust Metal-Organic Framework Embracing Heteroatom-Affixed Pores.

Pore environment modulation with polarizing groups is one of the essential prerequisites for selective carbon dioxide (CO2) adsorption in metal-organic frameworks (MOFs), wherein judicious installation of the photocatalytic feature can promise visible light-triggered degradation of toxic organic dye molecules. However, astute amalgamation of both these attributes over a single MOF is rather rare, yet much anticipated in view of sustainable applications. Pore engineering is effectively harnessed in a Zn(II)-based three-dimensional (3D) MOF, CSMCRI-16 (CSMCRI = Central Salt and Marine Chemicals Research Institute), through mixed-ligand assembly of a N-rich linker (L), 4,4'-oxybis(benzoic acid) (H2oba) ligand, and [Zn2(CO2)4N2] paddle-wheel secondary building units (SBUs). The noninterpenetrated structure contains unbound nitrogen and accessible oxygen atom-decorated porous channels and exhibits admirable stability in diverse organic solvents, open air, and at elevated temperatures. The heteroatom-decorated porous channels facilitated excellent CO2 uptake in the activated MOF (16a) with high selectivity over N2 (CO2/N2: 155.3) at 273 K. The framework further exhibits reasonable CO2 affinity and multicyclic CO2 sorption recurrence without a significant loss in the uptake capacity. Benefitting from the presence of the [Zn2(CO2)4N2] cluster in conjugation with π-conjugated organic ligands, the extended 3D network revealed an optical band gap energy of 2.55 eV, which makes the MOF an efficient photocatalyst toward the degradation of the cationic dyes crystal violet (CV) and methylene blue (MB) in the presence of a simple 40 W visible light lamp without any assistance of external oxidants. The catalyst exhibits multicyclic performance and short reaction time in addition to the fact that catalytic efficiencies (CV: 97.2%, MB: 97.8%) are comparable to those of contemporary materials.

Pore-Functionalized and Hydrolytically Robust Cd(II)-Metal-Organic Framework for Highly Selective, Multicyclic CO2 Adsorption and Fast-Responsive Luminescent Monitoring of Fe(III) and Cr(VI) Ions with Notable Sensitivity and Reusability.

Metal-organic frameworks (MOFs) show a distinctive pre-eminence over other heterogeneous systems for adsorption of carbon dioxide (CO2) gas and fluorescence detection of water contaminating ions, where integration of both these attributes along with enhancement of pore functionality and water stability is crucial for potential applications related to environmental remediation. Pore functionalization has been achieved in a 2-fold interpenetrated, mixed-ligand Cd(II)-framework [Cd1.5(L)2(bpy)(NO3)]·2DMF·2H2O (CSMCRI-5) (HL = 4-(4-carboxyphenyl)-1,2,4-triazole, bpy = 4,4'-bipyridine, DMF = dimethylformamide, CSMCRI = Central Salt & Marine Chemicals Research Institute) by utilizing a bifunctional ligand HL. The bpy-pillared framework, containing diverse Cd(II) nodes, optimum sized voids, and free N-atom affixed one-dimensional porous channels, shows notable structural robustness in diverse organic solvents and water. In spite of a negligible surface area, the activated MOF (5a) exhibits good CO2 uptake and highly selective CO2 adsorption over N2 (259.94) and CH4 (14.34) alongside minor loss during multiple CO2 adsorption-desorption cycles. Luminescence studies demonstrate extremely selective and ultrafast sensing of Fe3+ ions in the aqueous phase with notable quenching (1.13 × 104 M-1) as well as an impressive 98 ppb limit of detection (LOD). Importantly, Fe3+ detection is exclusively retained under simulated physiological conditions. The framework further serves as a quick-responsive scaffold for toxic CrO42- and Cr2O72- anions, where individual quenching constants (CrO42-: 1.73 × 104 M-1; Cr2O72-: 5.42 × 104 M-1) and LOD values (CrO42-: 280 ppb; Cr2O72-: 320 ppb) rank among the best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress vivid monitoring of all these aqueous pollutants by a handy paper-strip method, besides outstanding applicability of 5a toward their recyclable detection. Mechanism of selective quenching is comprehensively investigated in light of the absorption of the excitation/emission energy of the host framework by an individual studied analyte.

Highly Active Ultrasmall Ni Nanoparticle Embedded Inside a Robust Metal-Organic Framework: Remarkably Improved Adsorption, Selectivity, and Solvent-Free Efficient Fixation of CO2.

We report integrating additional functionality in an amine decorated, robust metal-organic framework (MOF) by encapsulating Ni nanoparticles (NPs). In-depth characterization of the postmodified structure confirms well-dispersed and ultrasmall NPs inside the framework pores. Although, the surface area is more reduced than pristine MOF, the CO2 uptake capacity is remarkably increased by 35% with a large 10 kJ/mol rise in adsorption enthalpy that validates favorable interactions between CO2 and NPs. In particular, CO2 adsorption selectivity over N2 and CH4 displays significant improvement (CO2/N2 = 145.7, CO2/CH4 = 12.65), while multicycle CO2 uptake demonstrates outstanding sorption recurrence. Impressively, the embedded NPs act as highly active functional sites toward solvent-free CO2 cycloaddition with epoxides in 98% yield and 99% selectivity under relatively mild conditions. The catalyst shows high recyclability without leaching of any metal-ion/NPs and greater pre-eminent activity than the unmodified analogue or contemporary reports. Of note is that outstanding conversion and selectivity are maintained for a wide range of aliphatic and aromatic epoxides, while larger substrates exhibit insignificant conversion, demonstrating admirable size selectivity. Based on the literature reports and experimental outcome, a rationalized mechanism is proposed for the reaction. This study exclusively demonstrates how strategic encapsulation of Ni NPs influences the inherent electronic properties in a MOF for highly selective CO2 adsorption and represents a step forward to sustainable CO2 valorization in terms of abundant active sites, sufficient stability, and consistent usability.

A Versatile CuII Metal-Organic Framework Exhibiting High Gas Storage Capacity with Selectivity for CO2 : Conversion of CO2 to Cyclic Carbonate and Other Catalytic Abilities.

A linear tetracarboxylic acid ligand, H4 L, with a pendent amine moiety solvothermally forms two isostructural metal-organic frameworks (MOFs) LM (M=ZnII , CuII ). Framework LCu can also be obtained from LZn by post- synthetic metathesis without losing crystallinity. Compared with LZn , the LCu framework exhibits high thermal stability and allows removal of guest solvent and metal-bound water molecules to afford the highly porous, LCu '. At 77 K, LCu ' absorbs 2.57 wt % of H2 at 1 bar, which increases significantly to 4.67 wt % at 36 bar. The framework absorbs substantially high amounts of methane (238.38 cm3 g-1 , 17.03 wt %) at 303 K and 60 bar. The CH4 absorption at 303 K gives a total volumetric capacity of 166 cm3 (STP) cm-3 at 35 bar (223.25 cm3 g-1 , 15.95 wt %). Interestingly, the NH2 groups in the linker, which decorate the channel surface, allow a remarkable 39.0 wt % of CO2 to be absorbed at 1 bar and 273 K, which comes within the dominion of the most famous MOFs for CO2 absorption. Also, LCu ' shows pronounced selectivity for CO2 absorption over CH4 , N2 , and H2 at 273 K. The absorbed CO2 can be converted to value-added cyclic carbonates under relatively mild reaction conditions (20 bar, 120 °C). Finally, LCu ' is found to be an excellent heterogeneous catalyst in regioselective 1,3-dipolar cycloaddition reactions ("click" reactions) and provides an efficient, economic route for the one-pot synthesis of structurally divergent propargylamines through three-component coupling of alkynes, amines, and aldehydes.

A Partially Fluorinated, Water-Stable Cu(II)-MOF Derived via Transmetalation: Significant Gas Adsorption with High CO2 Selectivity and Catalysis of Biginelli Reactions.

A partially fluorinated, angular tetracarboxylic acid linker (H4L) incorporating a pendant amine moiety forms a three-dimensional Zn(II) framework, 1. The structure consists of paddle-wheel Zn2(CO2)4 secondary building units (SBUs) and Zn12(CO2)24 supramolecular building blocks (SBBs). Thermal stability of 1 is found to be low. However, it undergoes transmetalation reaction with Cu(II) at room temperature without losing crystallinity affording an isostructural framework, 1Cu. Framework 1Cu is thermally robust and allows generation of the solvent-free porous framework 1Cu' upon activation with coordinatively unsaturated metal centers. Framework 1Cu' exhibits water stability and at 77 K, adsorbs 2.56 wt % of H2 up to 1 bar that significantly increases to 4.01 wt % at 13 bar. Also, this framework gives a high adsorption of 164.70 cc/g of CH4 (11.7 wt %) at 303 K and 60 bar. The channel surfaces decorated with -NH2 group and unsaturated metal centers in 1Cu' allow a promising 36.4 wt % of CO2 adsorption at 1 bar and 273 K. Moreover, it exhibits pronounced selectivity of CO2 adsorption over N2 and H2 at 273 K. Finally, the versatility of 1Cu' is shown by its excellent heterogeneous catalytic activity in the Biginelli coupling reactions involving an aldehyde, urea, and ethylacetoacetate to afford dihydroprimidinones.

Single-Crystal to Single-Crystal Linker Substitution, Linker Place Exchange, and Transmetalation Reactions in Interpenetrated Pillared-Bilayer Zinc(II) Metal-Organic Frameworks.

A twofold interpenetrated pillared-bilayer framework, {[Zn3 (L)2 (L2 )(DMF)]⋅(18DMF)(6H2 O)}n (1), has been synthesized from the ligands tris(4'-carboxybiphenyl)amine (H3 L) and 1,2-bis(4-pyridyl)ethylene (L2 ). The structure contains [Zn3 (COO)6 ] secondary building units (SBUs), in which three Zn(II) ions are almost linear with carboxylate bridging. This framework undergoes reversible pillar linker substitution reactions at the terminal Zn(II) centers with three different dipyridyl linkers of different lengths to afford three daughter frameworks, 2-4. Frameworks 2-4 are interconvertible through reversible linker substitution reactions. Also, competitive linker-exchange experiments show preferential incorporation of linker L3 in the parent framework 1. The larger linker L5 does not undergo such substitution reactions and framework 5, which contains this linker, can be synthesized solvothermally as a twofold interpenetrated structure. Interestingly, when framework 5 is dipped in a solution of L3 in DMF, linker substitution takes place as before, but linker L5 now moves and diagonally binds two Zn(II) centers to afford 6 as a nonpenetrated single framework. This linker place exchange reaction is unprecedented. All of these reactions take place in a single-crystal to single-crystal (SC-SC) manner, and have been observed directly through X-ray crystallography. In addition, each 3D framework undergoes complete copper(II) transmetalation.

Versatile Tailoring of Paddle-Wheel Zn(II) Metal-Organic Frameworks through Single-Crystal-to-Single-Crystal Transformations.

A new tetracarboxylate ligand having short and long arms formed 2D layer Zn(II) coordination polymer 1 with paddle-wheel secondary building units under solvothermal conditions. The framework undergoes solvent-specific single crystal-to-single crystal (SC-SC) transmetalation to produce 1Cu . With a sterically encumbered dipyridyl linker, the same ligand forms non-interpenetrated, 3D, pillared-layer Zn(II) metal-organic framework (MOF) 2, which takes part in SC-SC linker-exchange reactions to produce three daughter frameworks. The parent MOF 2 shows preferential incorporation of the longest linker in competitive linker-exchange experiments. All the 3D MOFs undergo complete SC-SC transmetalation with Cu(II) , whereby metal exchange in different solvents and monitoring of X-ray structures revealed that bulky solvated metal ions lead to ordering of the shortest linker in the framework, which confirms that the solvated metal ions enter through the pores along the linker axis.

Significant Gas Adsorption and Catalytic Performance by a Robust Cu(II) -MOF Derived through Single-Crystal to Single-Crystal Transmetalation of a Thermally Less-Stable Zn(II) -MOF.

By using a bent tetracarboxylic acid ligand that incorporates a pendent-NH2 functional group, a 3D Zn(II)-framework (1) based on Zn2 (CO2)4 secondary building units and Zn12 (CO2)24 supramolecular building blocks has been synthesized. Framework 1 is thermally less stable, which precludes its application as a porous framework for gas adsorption or catalytic studies. This framework undergoes single-crystal to single-crystal transmetalation to give isostructural 1Cu. Unlike 1, the Cu(II) analogue is very stable and can be activated by removing metal-bound lattice solvent molecules by heating to afford 1Cu'. The activated 1Cu' exhibits excellent H2 storage (2.29 wt%) at 77 K and a high 32.1 wt% CO2 uptake at 273 K. Additionally, it displays significant selectivity for CO2 adsorption over N2 and H2 and can catalyse size-selective Knoevenagel condensation reactions.

Construction of non-interpenetrated charged metal-organic frameworks with doubly pillared layers: pore modification and selective gas adsorption.

The rigid and angular tetracarboxylic acid 1,3-bis(3,5-dicarboxyphenyl)imidazolium (H4L(+)), incorporating an imidazolium group, has been used with different pyridine-based linkers to construct a series of non-interpenetrated cationic frameworks, {[Zn2(L)(bpy)2]·(NO3)·(DMF)6·(H2O)9}n (1), {[Zn2(L)(dpe)2]·(NO3)·(DMF)3·(H2O)2}n (2), and {[Zn2(L)(bpb)2]·(NO3)·(DMF)3·(H2O)4}n (3) [L = L(3-), DMF = N,N'-dimethylformamide, bpy = 4,4'-bipyridine, dpe = 1,2-di(4-pyridyl) ethylene, bpb = 1,4-bis(4-pyridyl)benzene]. The frameworks consist of {[Zn2(L)](+)}n two-dimensional layers that are further pillared by the linker ligands to form three-dimensional bipillared-layer porous structures. While the choice of the bent carboxylic acid ligand and formation of double pillars are major factors in achieving charged non-interpenetrated frameworks, lengths of the pillar linkers direct the pore modulation. Accordingly, the N2 gas adsorption capacity of the activated frameworks (1a-3a) increases with increasing pillar length. Moreover, variation in the electronic environment and marked difference in the pore sizes of frameworks permit selective CO2 adsorption over N2, where 3a exhibits the highest selectivity. In contrast, the selectivity of CO2 over CH4 is reversed and follows the order 1a > 2a > 3a. These results demonstrate that even though the pore sizes of the frameworks are large enough compared to the kinetic diameters of the excluded gas molecules, the electronic environment is crucial for the selective sorption of CO2.

Nitrogen-Rich Covalent Organic Polymer for Metal-Free Tandem Catalysis and Postmetalation-Actuated High-Performance Water Oxidation.

Development of high-performing catalytic materials for selective and mild chemical transformations through adhering to the principles of sustainability remains a central focus in modern chemistry. Herein, we report the template-free assembly of a thermochemically robust covalent organic polymer (COP: 1) from 2,2'-bipyridine-5,5'-dicarbonyl dichloride and 2,4,6-tris(4-aminophenyl)triazine as [2 + 3] structural motifs. The two-dimensional (2D) layered architecture contains carboxamide functionality, delocalized π-cloud, and free pyridyl-N site-decked pores. Such trifunctionalization benefits this polymeric network exhibiting tandem alcohol oxidation-Knoevenagel condensation. In contrast to common metal-based catalysts, 1 represents a one of a kind metal-free alcohol oxidation reaction via extended π-cloud delocalization-mediated free radical pathway, as comprehensively supported from diverse control experiments. In addition to reasonable recyclability and broad substrate scope, the mild reaction condition underscores its applicability in benign synthesis of valuable product benzylidene malononitrile. Integration of 2,2'-bipyridyl units in this 2D COP favors anchoring non-noble metal ions to devise 1-M (M: Ni2+/ Co2+) that demonstrate outstanding electrochemical oxygen evolution reaction in alkaline media with high chronoamperometric stability. Electrochemical parameters of both 1-Co and 1-Ni outperform some benchmark, commercial, as well as a majority of contemporary OER catalysts. Specifically, the overpotential and Tafel slope (280 mV, 58 mV/dec) for 1-Ni is better than 1-Co (360 mV, 78 mV/dec) because of increased charge accumulation as well as a higher number of active sites compared to the former. In addition, the turnover frequency of 1-Ni is found to be 6 times higher than that of 1-Co and ranks among top-tier water oxidation catalysts. The results provide valuable insights in the field of metal-free tandem catalysis as well as promising electrochemical water splitting at the interface of task-specific functionality fuelling in polymeric organic networks.

Control of intermolecular bonds by deposition rates at room temperature: hydrogen bonds versus metal coordination in trinitrile monolayers.

Self-assembled monolayers of 1,3,5-tris(4'-biphenyl-4"-carbonitrile)benzene, a large functional trinitrile molecule, on the (111) surfaces of copper and silver under ultrahigh vacuum conditions were studied by scanning tunneling microscopy and low-energy electron diffraction. A densely packed hydrogen-bonded polymorph was equally observed on both surfaces. Additionally, deposition onto Cu(111) yielded a well-ordered metal-coordinated porous polymorph that coexisted with the hydrogen-bonded structure. The required coordination centers were supplied by the adatom gas of the Cu(111) surface. On Ag(111), however, the well-ordered metal-coordinated network was not observed. Differences between the adatom reactivities on copper and silver and the resulting bond strengths of the respective coordination bonds are held responsible for this substrate dependence. By utilizing ultralow deposition rates, we demonstrate that on Cu(111) the adatom kinetics plays a decisive role in the expression of intermolecular bonds and hence structure selection.

Heteroleptic metallosupramolecular racks, rectangles, and trigonal prisms: stoichiometry-controlled reversible interconversion.

A simple approach toward preparation of heteroleptic two-dimensional (2D) rectangles and three-dimensional (3D) triangular prisms is described utilizing the HETPYP (HETeroleptic PYridyl and Phenanthroline metal complexes) concept. By mixing metal-loaded linear bisphenanthrolines of varying lengths with diverse (multi)pyridine (py) ligands in a proper ratio, six different self-assembled architectures arise cleanly and spontaneously in the absence of any template. They are characterized by (1)H and DOSY NMR, ESI-FT-ICR mass spectrometry as well as by Job plots and UV-vis titrations. Density functional theory (DFT) computations provide information about each structure. A stoichiometry-controlled supramolecule-to-supramolecule interconversion based on the relative amounts of metal bisphenanthroline and bipyridine forces the rectangular assembly to reorganize to a rack architecture and back to the rectangle, as clearly supported by variable temperature and DOSY NMR as well as dynamic light scattering data. The highly dynamic nature of the assemblies represents a promising starting point for constitutional dynamic materials.

Dangling carboxylic-acid functionality in a fish-bone-shaped 2D framework as a hydrogen-bond-donating catalyst in Friedel-Crafts alkylation.

A two-dimensional, layer-stacked metal-organic framework (MOF) with a dangling acid functionality was developed as the first-ever example of carboxylic-acid-catalysed Friedel-Crafts alkylation with high reusability. Contrary to conventional hydrogen-bond-donating catalysis, a pair of oppositely oriented -COOH moieties acted as potential hydrogen-bonding sites, and efficiently worked for electronically assorted substrates. Control experiments including juxtaposing the performances of a post-metalated MOF and an unfunctionalized analogue explicitly authenticated the carboxylic-acid-mediated catalytic route.

Carboxamide functionality grafted entangled Co(II) framework as a unique hydrogen-bond-donor catalyst in solvent-free tandem deacetalization-Knoevenagel condensation with pore-fitting-mediated size-selectivity.

Concerning environmentally benign catalysis with reduced chemical usage, less energy consumption, and waste minimization, metal-organic frameworks (MOFs) with spatially isolated task-specific functionalities not only execute atom-economic important reactions but also enable size-exclusive catalysis at the interface of structure-function synergy. Herein, we synthesized a bipillar-layer Co(II) MOF from the dicarboxylate ligand and carboxamide moiety grafted pyridyl linker. The framework contains a [Co2(COO)4N4] secondary building unit (SBU) and shows excellent hydrolytic stability due to ample non-covalent interactions among the highly conjugated aromatic struts. Notably, the carboxamide functionalities remain free and are perfectly positioned throughout the one-dimensional channels of the framework, wherein three-fold interpenetration of the structure largely increases their density along the pore wall. Benefiting from these structural features, the activated MOF acts as an unprecedented organocatalyst in tandem deacetalization-Knoevenagel condensation towards electronically assorted substrates that were additionally characterized using single-crystal X-ray diffraction. Importantly, the reaction occurs under solvent-free mild conditions, and high catalyst reusability is recorded. In this one-pot cascade reaction, substrates with molecular dimensions larger than that of the three-fold interpenetration generated optimized pore-aperture undergo insignificant conversion, and therefore a rare molecular-dimension-induced size-selectivity is demonstrated. The catalytic route is detailed based on a battery of control experiments, including juxtaposing the performance of an isostructural MOF without any linker functionalization. Compared to the common Lewis acid mediated route, the results explicitly corroborate the first-ever substrate activation via hydrogen bonding to prepare coumarin derivatives via a tandem pathway, and shed light on this futuristic unconventional catalysis using contemporary materials and avoiding major operative glitches.

Redox-Active and Urea-Engineered-Entangled MOFs for High-Efficiency Water Oxidation and Elevated Temperature Advanced CO2 Separation Cum Organic-Site-Driven Mild-Condition Cycloaddition.

Development of the multifaceted metal-organic framework (MOF) with in situ engineered task-specific sites can promise proficient oxygen evolution reaction (OER) and high-temperature adsorption cum mild-condition fixation of CO2. In fact, effective assimilation of these attributes onto a single material with advance performance characteristics is practically imperative in view of renewable energy application and carbon-footprint reduction. Herein, we developed a three-fold interpenetrated robust Co(II) framework that embraces both redox-active and hydrogen-bond donor moieties inside the microporous channel. The activated MOF demonstrates notable OER catalysis in alkaline medium via quasi-reversible Co2+/Co3+ couple and unveils low overpotential with impressive 53.5 mV/dec Tafel slope that overpowers some benchmark, commercial, as well as contemporary materials. In particular, significantly increased turnover frequency (3.313 s-1 at 400 mV) and fairly low charge-transfer resistance (3.02 Ω) compared to Co3O4, NiO, and majority of redox-active MOFs together with 91% Faradaic efficiency and notable framework durability after multiple OER cycles endorse high-performance water oxidation. Pore-wall decked urea groups benefit appreciable CO2 adsorption even at elevated temperatures with considerable MOF-CO2 interactions and exhibit recurrent capture-release cycles at diverse temperatures. Interestingly, CO2 selectivity displays radical upsurge with temperature rise, affording 40% improved CO2/N2 value of 200 at 313 K, which outperforms many porous adsorbents and delineates real-time CO2 scavenging potential. The guest-free MOF effectively catalyzes solvent-free CO2 cycloaddition with broad substrate tolerance and satisfactory reusability under relatively mild condition. Opposed to the common Lewis acid-mediated reaction, two-point hydrogen-bonding activates the substrate, as supported from controlled experiments, juxtaposing the performance of an un-functionalized MOF and fluorescence modification-derived framework-epoxide interaction, providing valuable insights on unconventional cycloaddition route in the MOF.

Site-Memory-Triggered Reversible Acronym Encryption in a Nitrogen-Rich Pore-Partitioned MOF for Ultrasensitive Monitoring of Roxarsone and Dichloran over Multiple Platform.

Stimuli-responsive emission color modulation in fluorescent metal-organic frameworks (MOFs) promises luminescence-ink-based security application, while task-specific functionality-engineered pores can aid fast-responsive, discriminative, and ultralow detection of harmful organo-aromatics in the aqueous phase. Considering practical applicability, a self-calibrated fluoro-switch between encrypted and decrypted states is best suited for antiforgery measures, whereas image-based monitoring of organo-toxins by repetitive and handy methods over multiple platforms endorses in-field sensory potential. Herein, we constructed a mixed-ligand based chemically stable and bilayered-pillar MOF from -NH2-hooked pyridyl linker and tricarboxylate ligand that embraces negatively charged [Cd3(µ2-OH)(COO)6] node and shows pore-space-partitioning by nitrogen-rich flanked organic struts. Owing to the presence of a self-calibrating triazolylamine moiety-grafted auxiliary linker, this anionic MOF delineates reversible and multicyclic fluoro-swapping between protonated-encrypted and deprotonated-decrypted domains in the alternative presence of acid and base. Such pH-triggered, site-specific luminescence variation is utilized to construct highly regenerative anticounterfeiting labels for vivid acronym encryption. The intense fluorescence signature of the material is further harnessed in extremely selective and quick responsive sensing of harmful feed additive roxarsone (ROX) and dichloran (DCNA) pesticide in highly recyclable fashion with significant quenching and nanomolar limits of detection (ROX: 52 ppb; DCNA: 26.8 ppb). Notably, the ultrasensitive fluoro-detection of both these organo-toxins is successfully demonstrated via a handy paper-strip method as well as on the vegetable surface for real-time monitoring. Comprehensive density functional theory studies validate the electron transfer mechanism through redistribution of molecular orbital energy levels by each of the targeted analytes in this electron-rich framework besides evidencing MOF-analyte supramolecular interactions.

Implications of stoichiometry-controlled structural changeover between heteroleptic trigonal [Cu(phenAr2)(py)]+ and tetragonal [Cu(phenAr2)(py)2]+ motifs for solution and solid-state supramolecular self-assembly.

A stoichiometric variant of the HETPYP concept (HETeroleptic PYridine and Phenanthroline metal complexes) opens the venue to heteroleptic metallosupramolecular HETPYP-I assemblies both in solution and the solid state, involving the trigonal [Cu(phenAr(2))(py)](+) coordination motif (phenAr(2) = 2,9-diarylphenanthroline; py = various oligopyridines). Combining the same building blocks at another stoichiometric ratio furnished metallosupramolecular HETPYP-II aggregates in the solid state, now based on the tetrahedral [Cu(phenAr(2))(py)(2)](+) coordination motif. Thus, a stoichiometry-controlled structural changeover based on the relative amounts of oligopyridines leads from a discrete assembly with trigonally coordinated copper(I) centers to a coordination polymer with tetrahedrally coordinated copper(I) ions, as shown by solid state studies. In solution, the analysis of both stoichiometric variants indicates that the HETPYP-I structure is congruent with that in the solid state, while the HETPYP-II assembly, as established through DOSY NMR and dynamic light scattering measurements, is only oligomeric at low temperature. At room temperature, i.e. due to entropic costs, the latter assembly prefers to keep "unsaturated" coordination sites that are in rapid exchange, making it an interesting system as a dynamic protecting group and for constitutional dynamic materials through the exchange and reshuffling of components.