Subhadeep Saha

Selective CO2 and H2 adsorption in a chiral magnesium-based metal organic framework (Mg-MOF) with open metal sites

A rare porous magnesium-based metal–organic framework, Mg-MOF-1 [Mg(3,5-PDC)(H2O)], was synthesized solvothermally in DMF. Structural determination by X-ray single-crystal diffraction technique reveals that this chiral MOF (space group P6122) is constructed by helical assembly of Mg2+ ions with achiral 3,5-pyridine dicarboxylates and coordinating water molecules, to form a three-dimensional framework with parallel hexagonal channels. The structural detail of its 0D analogue Mg-MOF-2 [Mg(2,4-PDC)(H2O)3] has been discussed to show how subtle variation in the ligand architecture changes the resulting structure from 0D to 3D. Mg-MOF-1 remains robust and porous upon evacuation of the coordinating water molecules. This is the first report of a chiral hexagonal Mg-MOF synthesized from an achiral organic building unit. Open Mg metal sites show selective hydrogen (H2) adsorption (ca. 0.8 wt% at 77 K) and carbon dioxide (CO2) uptake (ca. 0.7 mmol g−1 at 298 K) over nitrogen at 1 atm. Ab initio quantum chemical calculation of adsorption energies and possible adsorption sites of hydrogen molecules are also reported.

Photocatalytic Metal–Organic Framework from CdS Quantum Dot Incubated Luminescent Metallohydrogel

Cadmium sulfide (CdS) quantum dots (<10 nm in size) have been successfully synthesized in situ without any capping agent in a Zn(II)-based low-molecular-weight metallohydrogel (ZAVA). Pristine ZAVA hydrogel shows blue luminescence, but the emission can be tuned upon encapsulation of the CdS quantum dots. Time-dependent tunable emission (white to yellow to orange) of the CdS incubated gel (CdS@ZAVA gel) can be attributed to sluggish growth of the quantum dots inside the gel matrix. Once CdS quantum dots are entrapped, their augmentation can be stopped by converting the gel into xerogel, wherein the quantum dots remains embedded in the solid xerogel matrix. Similar size stabilization of CdS quantum dots can be achieved by means of a unique room-temperature conversion of the CdS incubated ZAVA gel to CdS incubated MOF (CdS@ZAVCl) crystals. This in turn arrests the tunability in emission owing to the restriction in the growth of CdS quantum dots inside xerogel and MOF. These CdS embedded MOFs have been utilized as a catalyst for water splitting under visible light.

Proton-conducting supramolecular metallogels from the lowest molecular weight assembler ligand: a quote for simplicity.

Oxalic acid has been proven to be the lowest molecular weight organic ligand able to form robust supramolecular metallogel networks in the presence of metal salts. In particular, two novel multifunctional metallogels were readily prepared at room temperature by simple mixing of stock solutions of Cu(II) acetate monohydrate or Cu(II) perchlorate hexahydrate and oxalic acid dihydrate. Formation of different polymorphs and unprecedented proton conduction under anhydrous conditions were also demonstrated with some of these materials.

Fe( iii ) phytate metallogel as a prototype anhydrous, intermediate temperature proton conductor

A proton conducting metallogel [FNPA; ferric nitrate (FN)–phytic acid (PA)] is synthesized by immobilizing a protogenic ligand (phytic acid) using iron(III) nitrate in DMF. The xerogel shows high proton conductivity of 2.4 × 10−2 S cm−1 at 120 °C, the best value known among all metal organic materials (MOMs). Marking the first such attempt in MOMs, an electrode made using the xerogel showed a power density of 0.94 mW cm−2 at 0.6 V under dry fuel cell conditions.

Structure and Gas Sorption Behavior of a New Three Dimensional Porous Magnesium Formate

A new three-dimensional magnesium formate polymorph, namely, γ-[Mg(3)(O(2)CH)(6)] has been synthesized via in situ formate anion generation method. γ-Mg-formate crystallizes in space group Pbcn, and structural determination by X-ray single crystal diffraction reveals a three-dimensional network of Mg(2+) linked by formate anions. All formate anions possess similar binding mode to the metal center with one oxygen of a particular formate anion binds to one metal center (μ(1) oxygen) and other oxygen binds to two metal centers (μ(2) oxygen). N(2) adsorption studies indicate that the framework displays permanent porosity. The specific surface area of γ-Mg-formate (BET, 120 m(2) gm(-1)) is lower than the α- polymorph (BET, 150 m(2) gm(-1)). However, the initial hydrogen uptake of γ-Mg-formate reached almost 1.0 wt % when the adsorbate pressure approached 760 Torr at 77 K. This is higher than the hydrogen uptake of α-Mg-formate (0.6 wt %). γ-Mg-formate, shows a moderate affinity and capacity for CO(2) (3.4 Å kinetic diameter) at 298 K. The CO(2) uptake at 760 Torr is 2.01 mmol gm(-1) (47.0 cc gm(-1)). Although this CO(2) uptake is somewhat modest, it compares well with the CO(2) uptake of several Mg-MOFs and ZIFs reported in the literature.

Competition between gelation and crystallisation of a peculiar multicomponent liquid system based on ammonium salts

An exemplar competition between gelation and crystallisation phenomena was examined with an unusual synergistic multicomponent (organo)gelator solution (MGS), which consists of a well-defined methanolic solution of (1R,2R)-1,2-diaminocyclohexane L-tartrate containing 2.4 equiv. of concentrated hydrochloric acid. The optimal composition of the MGS was determined through meticulous solubility, gelation and structural studies, which support a transient gelation mechanism based on the kinetic self-assembly of the tartrate salt driven by hydrogen-bonding interactions, involving ammonium nitrogen donors and hydroxyl oxygen acceptors, and electrostatic interactions. The hydrochloric acid is involved in the solubilisation of the salt through an ionic dissociation-exchange process, which ends up with the formation–precipitation of (1R,2R)-1,2-diaminocyclohexane dihydrochloride. As a consequence, an irreversible destruction of the gel takes place, which indicates the metastable nature of this phase that cannot be accessed from the thermodynamically equilibrated state. Gelation of a variety of oxygenated and nitrogenated solvents with moderate polarity occurred efficiently using extremely low MGS concentrations at low temperatures, and the gel phase was confirmed by dynamic rheological measurements. Several features make the described MGS unique: (1) it is a multicomponent solution where each component and its stoichiometry play a key role in the reproducible formation and stabilization of the gels; (2) it is formed by simple, small, and commercially available chiral building blocks (dissolved in a well-defined solvent system), which are easily amenable for further modifications; (3) the gelation phenomenon takes place efficiently at low temperature upon warming up the isotropic solution, conversely to the typical gel preparation protocol; and (4) the formed organogels are not thermoreversible despite the non-covalent interactions that characterize the 3D-network.

CCDC 1578181: Experimental Crystal Structure Determination

Related Article: Saibal Bera, Amit Chakraborty, Suvendu Karak, Arjun Halder, Soumyajyoti Chatterjee, Subhadeep Saha, and Rahul Banerjee|2018|Chem.Mater.|30|4755|doi:10.1021/acs.chemmater.8b01698