Organic cage supported metal nanoparticles for applications.

Porous shape-persistent organic cages can anchor metal nanoparticles either inside the cavity or in the external cavity generated through self-assembly. The size of these nanoparticles range from 1-2 nm depending upon the host and can be controlled within a narrow size distribution. The nanoparticles thus formed are quite stable as they are segregated efficiently preventing their association and eventual precipitation. These fine nanoparticles are found to be quite effective in catalyzing a number of organic transformations besides showing interesting emission properties.

Metal-Organic Frameworks of Cu(II) Constructed from Functionalized Ligands for High Capacity H2 and CO2 Gas Adsorption and Catalytic Studies.

Two Cu(II)-based metal-organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1Me and 1ipr, were synthesized solvothermally using two new bent di-isophthalate ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m2/g for 1Me and 1402 m2/g for 1ipr). For 1Me, very high CO2 adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1ipr, it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1Me exhibited H2 uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1ipr, the H2 uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H2 and CO2 for 1Me could be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2 and CS2 into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.

Flexibility Induced Encapsulation of Ultrafine Palladium Nanoparticles into Organic Cages for Tsuji-Trost Allylation.

A series of three positional isomers of organic cages namely o-OC, m-OC, and p-OC, have been self-assembled using dynamic covalent chemistry. Their room temperature controlled fabrication with palladium gives ultrafine diameter (1-2 nm) of palladium nanoparticles (Pd NPs). We observed that the shape-flexibility of cages have great impact on the formation of Pd NPs. Theoretical calculations reveals that theoretically obtainable size of Pd NPs for each cage which was complementary to the experimental results. Theoretical studies indicate that the driving forces for the specific orientational preference may be ascribed to subtle variations on the level of π-π interactions, which ultimately governs the growth of Pd NPs therein. It is the first example of shape-flexible synthesis of organic cages where flexibility governs the nanoparticle growth. Pd NPs have shown excellent catalysis of Tsuji-Trost allylation at room temperature and pressure in water.

Dual Functionalized CuMOF-Based Composite for High-Performance Supercapacitors.

Herein, we utilized our previously reported highly porous CuMOF, {[Cu2(L)(H2O)2]·(5DMF)·(4H2O)}n, decorated with amine and trifluoromethyl functional groups for energy storage application. This robust framework in CuMOF enhances the chemical and thermal stabilities as well as improves the interfacial binding interactions. The poor conductivity of CuMOF usually restricts its practical utility in energy storage systems, due to which rGO was introduced along with CuMOF to form a CuMOF/rGO composite (1) through a facile ultrasonication technique. The synergistic effects between CuMOF and rGO induce a dramatic enhancement in specific capacitance (462 F g-1 at 0.8 A g-1) of 1 with a cycle life of 93.75% up to 1000 cycles. The results highlight 1 as an emerging contestant for next generation supercapacitors.

Benzothiazole integrated into a cryptand for ESIPT-based selective chemosensor for Zn2+ ions.

A novel benzothiazole-based cryptand was designed and synthesized, and it exhibited high fluorescence intensity in the presence of Zn2+ ions based on the metal chelation inhibition of the excited state intramolecular proton transfer (ESIPT) process. The structure of the cryptand was confirmed by NMR, mass spectroscopy and X-ray crystallography. Importantly, this probe showed high selectivity over other biologically relevant metal ions and anions and a detection limit of 0.20 µM, which is acceptable within the EPA (US) limit.

Cost-Effective Realization of Multimode Exciton-Polaritons in Single-Crystalline Microplates of a Layered Metal-Organic Framework.

We report the observation of multimode exciton-polaritons in single-crystalline microplates of a two-dimensional (2D) layered metal-organic framework (MOF), which can be synthesized through a facile solvothermal approach, thereby eliminating all fabrication complexities usually involved in the construction of polariton cavities. With a combination of experiments and theoretical modeling, we have found that the exciton-polaritons are formed at room temperature as a result of a strong coupling between Fabry-Perot cavity modes formed inherently by two parallel surfaces of a microplate and Frenkel excitons provided by the 2D layers of dye molecular linkers in the MOF. Flexibility in rational selection of dye linkers for synthesizing such MOFs renders a large-scale, low-cost production of solid-state, micro-exciton-polaritonic devices operating in the visible and near-infrared range. Our work introduces MOFs as a new class of potential materials to explore polariton-related quantum phenomena in a cost-effective manner.

Nanosized Bispyrazole-Based Cryptand-Stabilized Palladium(0) Nanoparticles: A Reusable Heterogeneous Catalyst for the Suzuki-Miyaura Coupling Reaction in Water.

A macrobicyclic cryptand with a long rigid cavity incorporating a chelating bispyrazole moiety in each of the three bridges was synthesized. The multiple chelating metal binding sites were utilized for the controlled synthesis and stabilization of ultrafine palladium nanoparticles (Pd NPs) of nearly ∼2 nm size. The as-synthesized Pd NPs were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The well-dispersed cryptand-stabilized nanoparticles are found to catalyze the C-C bond-forming Suzuki-Miyaura reaction heterogeneously using water as a green solvent.

Regioisomeric cryptand stabilized gold supraspheres and elongated dodecahedron supraparticles for reversible host-guest chemistry.

Addition of bis-pyrazole based cryptand regioisomers (1 and 2) to citrate stabilized gold nanoparticles (AuNPs) led to gold supraspheres (AuSSL) and elongated dodecahedron (AuEDL) supraparticles, respectively. These supraparticles as heterogenous hosts show a high uptake of a small fluorophore SEA-SC1 in an aqueous medium and reversible release in organic solvents.

A Multifunctional Metal-Organic Framework for Oxidative C-O Coupling Involving Direct C-H Activation and Synthesis of Quinolines.

A robust paddle-wheel Cu(II)-based metal-organic framework (MOF) 1, having dual functionalities, namely, Lewis acid and basic sites, has been explored as a heterogeneous catalyst. This MOF, because of its large void volume (10298 Å3, 67.6%), large surface area (1480 m2/g), and high thermal stability, encouraged us to see its applicability in two catalytic reactions, namely, oxidative C-O coupling (cross-dehydrogentaive coupling reaction) involving direct C-H activation and Friedländer reaction under solvent free and ambient conditions. This study demonstrates the green aspect of MOFs in coupling reactions because of the simplified recovery, shorter reaction time, minimum waste, and smooth activation of the C-H bond, which is very challenging in synthetic chemistry.

A Cu(ii) metal-organic framework with significant H2 and CO2 storage capacity and heterogeneous catalysis for the aerobic oxidative amination of C(sp3)-H bonds and Biginelli reactions.

A Cu(ii) metal-organic framework, {[Cu2(L)(H2O)2]·(5DMF)(4H2O)}n (1), has been synthesized using an angular tetracarboxylic acid ligand (H4L) incorporating both trifluoromethyl (-CF3) and amine (-NH2) groups. Notably, the framework possesses high water and thermal stability. At atmospheric pressure, the activated framework 1' exhibits substantially high amounts of CO2 (35.5 and 20.8 wt% at 273 and 298 K respectively) and H2 (1.72 wt% at 77 K) adsorption. Also, 1' exhibits excellent catalytic activity for the condensation-cyclization reaction between 2-benzoyl pyridine and different benzylamines via oxidative amination of the C(sp3)-H bond to form 1,3-diarylated imidazo[1,5-a]pyridines under mild aerobic conditions. In addition to this, 1' shows excellent heterogeneous catalytic activity in Biginelli reactions. The solid catalyst could be recycled several times without significant loss in the catalytic activities.

A Cu(ii)-MOF capable of fixing CO2 from air and showing high capacity H2 and CO2 adsorption.

A porous Cu(ii)-MOF shows an adsorption of 6.6 wt% of H2 at 77 K and 62 bar and a very high 60 wt% of CO2 at 298 K and 32 bar. When air is bubbled into a suspension of the activated MOF in the presence of different epoxides at room temperature, the CO2 in air is readily converted into the corresponding cyclic carbonates.

Chiral Cadmium(II) Metal-Organic Framework from an Achiral Ligand by Spontaneous Resolution: An Efficient Heterogeneous Catalyst for the Strecker Reaction of Ketones.

A thermally stable cadmium-based chiral metal-organic framework (MOF), {[Cd2(L)(H2O)(DMF)]·3DMF·2H2O}n (1; DMF = N,N-dimethylformamide), has been synthesized from an achiral ligand by spontaneous resolution. The MOF features 1D open channels with a large density of active metal sites and has a 3,6-c binodal net with a rare sit 3,6-conn topology. The metal-bound water and DMF solvents could be easily removed along with the guest molecules in the lattice upon activation to afford the desolvated framework 1'. It exhibits microporous nature, as confirmed by the gas-sorption measurements with carbon dioxide uptake of 43.2 cm3 g-1 at 273 K. The open metal sites in the framework make it an outstanding heterogeneous catalyst in the Strecker reaction for the synthesis of α-aminonitriles in a solvent-free state at room temperature with excellent conversion yields.

From Zn(II)-Carboxylate to Double-Walled Zn(II)-Carboxylato Phosphate MOF: Change in the Framework Topology, Capture and Conversion of CO2, and Catalysis of Strecker Reaction.

The ligand H2L has been built by linking an imidazole moiety to the 5-position of isophthalic acid. It forms two types of porous frameworks, {[Zn(L)]·2DMF·2H2O}n (1) and {[(CH3)2NH2][Zn2(L)(H2O)PO4]·2DMF}n (2). 1 is a porous neutral framework and has rtl rutile 3,6-conn topology, while 2 is an organo-metallophosphate anionic porous framework with double-walled hexagonal channels. Framework 1' (desolvated) exhibits moderate CO2 adsorption (58 cc g-1 at 273 K, 1 bar), whereas 2' (desolvated) shows a microporous nature with a high adsorption of CO2 (111.7 cc g-1 or 22 wt % at 273 K, 1 bar). Interestingly, this adsorbed CO2 could be converted very efficiently to cyclic carbonates under mild conditions using 2' as the catalyst in the presence of tetrabutylammonium bromide as the cocatalyst. The presence of open metal sites in 2' makes it an efficient heterogeneous catalyst for solvent-free three-component Strecker reaction using various aldehydes/ketones together with amines and trimethylsilyl cyanide in high yields at room temperature. The straightforward experimental and product isolation procedure along with easy recovery and reusability of the catalyst provided an attractive route for the synthesis of α-amino nitriles.

Enantioselective Aldol Reactions in Water by a Proline-Derived Cryptand and Fixation of CO2 by Its Exocyclic Co(II) Complex.

The secondary amine donors present in the bridges of a laterally nonsymmetric oxa-aza cryptand have been derivatized with l-proline to obtain the chiral cryptand L. The cryptand L efficiently catalyzed aldol reactions in water with up to 75% ee. On reacting with Co(II) perchlorate in the presence of KSCN, L readily formed the trinuclear complex {[Co3(L)2(NCS)6]·(15CH3CN)(5acetone)(6H2O)} (1). The complex 1 in combination with the cocatalyst tetrabutylammonium bromide (TBAB) formed an efficient catalytic system in the synthesis of cyclic carbonates from CO2 and epoxides at room temperature and atmospheric pressure.

An Amine Functionalized Metal-Organic Framework as an Effective Catalyst for Conversion of CO2 and Biginelli Reactions.

A highly porous and thermally stable anionic Zn(II)-framework, {[(CH3)2NH2+]2[Zn3((µ3-O))(L)2(H2O)]·4DMF·2H2O}n (1), having exposed metal sites and pendant amine groups has been synthesized adopting the solvothermal technique. This anionic 3D framework showed two-fold interpenetration with 45.1% void volume. It has a 3,6-c binodal net with rare sit 3,6-conn topology. The metal bound aqua ligand could be easily removed along with the guest molecules in the lattice upon activation to afford the desolvated framework 1'. This produced exposed metal sites that, along with the pendant amine groups incorporated in the ligand, generated a coordination space in the framework to make it an outstanding heterogeneous catalyst for the chemical fixation of CO2 with various epoxides under atmospheric pressure and in the three-component Biginelli reaction with different aldehydes, ethyl acetoacetate, and urea to afford dihydropyrimidinones.

A 2D Coordination Network That Detects Nitro Explosives in Water, Catalyzes Baylis-Hillman Reactions, and Undergoes Unusual 2D→3D Single-Crystal to Single-Crystal Transformation.

The solvothermal reaction of Zn(NO3)2·6H2O and a linear dicarboxylate ligand H2L, in the presence of urotropine in N,N'-dimethylformamide (DMF), gives rise to a new porous two-dimensional (2D) coordination network, {[Zn3(L)3(urotropine)2]·2DMF·3H2O}n (1), with hxl topology. Interestingly, framework 1 exhibits excellent emission properties owing to the presence of naphthalene moiety in the linker H2L, that can be efficiently suppressed by subtle quantity of nitro explosives in aqueous medium. Furthermore, presence of urotropine molecules bound to the metal centers, 1 is found to be an excellent heterogeneous catalyst meant for atom-economical C-C bond-forming Baylis-Hillman reactions. Additionally, crystals of 1 undergo complete transmetalation with Cu(II) to afford isostructural 1Cu. Moreover, the 2D framework of 1 allows replacement of urotropine molecules by 4,4'-azopyridine (azp) linker resulting in a three-dimensional (3D) metal-organic framework, {[Zn(L)(azp)]·4DMF 2H2O}n (2). The 1→2 transformation takes place in single-crystal-to-single crystal manner supported by powder X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy, and morphological studies. Remarkably, during this 2D→3D transformation, the original trinuclear [Zn3(COO)6] secondary building unit changes to a mononuclear node, which is unprecedented.

A NbO type Cu(ii) metal-organic framework showing efficient catalytic activity in the Friedländer and Henry reactions.

A three-dimensional NbO type porous metal-organic framework 1 containing both tertiary amine groups and paddle wheel dinuclear Cu2(COO)4 secondary building units as the active centre was synthesized at room temperature. The activated framework 1' can be used as an efficient heterogeneous catalyst for the synthesis of quinoline derivatives by the Friedländer reaction and for the synthesis of ß-nitroalcohols by the Henry (nitroaldol) reaction. This MOF-based heterogeneous catalyst is easily recycled and reused further without losing its structural integrity and catalytic activity.

Metal ion binding by laterally non-symmetric macrobicyclic oxa-aza cryptands.

Macrobicyclic cryptands incorporating amine groups along with oxygen donors that are laterally non-symmetric constitute an important class of organic compounds. These molecules can form inclusion complexes with different transition and main group metal ions. It is also possible to modify the binding characteristics of these compounds through attachment of different groups. Some of these metal complexes can be useful homogeneous catalysts in different organic transformations. If there are chiral centers present in the cryptands, they can be useful in asymmetric syntheses. The three secondary amine groups present in the bridges can be partially or completely derivatized with different fluorophores for fluorescence signaling of transition, inner-transition and heavy metal ions. It is also possible to sequentially attach different fluorophores to study single- as well as multi-step Förster resonance energy transfer. Different donor/acceptor groups can be attached to study second and third order optical nonlinearity. The present article describes several aspects of the chemistry of laterally non-symmetric cryptands and provides future directions for research in this area.

Synthesis of a NbO Type Homochiral Cu(II) Metal-Organic Framework: Ferroelectric Behavior and Heterogeneous Catalysis of Three-Component Coupling and Pechmann Reactions.

A chiral tetracarboxylic acid ligand, H4L, incorporating the (S)-(+)-2-methylpiperazine moiety in its middle, solvothermally forms a homochiral Cu(II) framework, {[Cu2(L)(H2O)2]·(4DMF)(4H2O)}n (LCu). It forms a non-interpenetrated structure consisting of [Cu2(COO)4] paddle-wheel secondary bonding units (SBUs) with NbO topology. Interestingly, the framework LCu exhibits excellent ferroelectric properties. It shows a remnant polarization (Pr) of ∼3.5 µC cm-2 and a coercive field (Ec) of ∼12 kV cm-1 with a distinct electric hysteresis loop. Dielectric studies of LCu reveal almost frequency-independent behavior with a dielectric constant (εr) of ∼42 and a low dielectric loss (tan δ) of ∼0.04 up to 106 Hz, for potential use in high-frequency applications. In addition, activated framework LCu' having uncoordinated metal sites acts as an efficient heterogeneous catalyst in the three-component coupling of amines, aldehydes, and alkynes, as well as in Pechmann reactions of phenols with ß-ketoesters.

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.