Bhavesh Parmar

Mechanochemical and Conventional Synthesis of Zn(II)/Cd(II) Luminescent Coordination Polymers: Dual Sensing Probe for Selective Detection of Chromate Anions and TNP in Aqueous Phase

Isostructural Zn(II)/Cd(II) mixed ligand coordination polymers (CPs) {[M(IPA)(L)]}n (CP1 and CP2) built from isophthalic acid (H2IPA) and 3-pyridylcarboxaldehyde nicotinoylhydrazone (L) were prepared using versatile synthetic routes: viz., diffusion of precursor solutions, conventional reflux methods, and green mechanochemical (grinding) reactions. Both robust CPs synthesized by different routes were characterized by various analytical methods, and their thermal and chemical stability as well as the phase purity was established. Crystallographic studies revealed that CP1 and CP2 are isostructural frameworks and feature a double-lined two-dimensional network composed of Zn2+/Cd2+ nodes connected through IPA and pillared by the Schiff base ligand L with a double-walled edge. The photoluminescent (PL) properties of CP1 and CP2 have been exploited as dual detection fluorosensors for hexavalent chromate anions (CrO42-/Cr2O72-) and 2,4,6-trinitrophenol (TNP) because it was observed that the emission intensity of aqueous suspensions of CPs selectively quenches by chromate anions or TNP among large pools of different anions or nitro compounds, respectively. Competitive experiments in the presence of interfering anions/other nitro compounds also revealed no major effect in the quenching efficiency, suggesting the selective detection of hexavalent chromate anions as well as TNP by the LCPs. The limits of detection by CP1 for CrO42-/Cr2O72- and TNP are 4 ppm/4 ppm and 28 ppb, respectively, whereas the limits of detection by CP2 for the same analytes are 1 ppm/1 ppm and 14 ppb, respectively. A probable mechanism for the quenching phenomena is also discussed.

Progress in the synthetic and functional aspects of chiral metal–organic frameworks

In this highlight, two aspects of chiral metal–organic frameworks, in particular synthetic approaches to achieve chiral MOFs and their applications, have been discussed. There has been considerable research advancement towards the synthesis of chiral MOFs by direct or indirect methods. More recently, homochiral MOFs have been exploited for valued applications such as asymmetric catalysis, enantioselective separation and recognition processes. Each part is subdivided with regard to the issues focused on and provides seminal as well as recent reports from the literature.

Structural studies and detection of nitroaromatics by luminescent 2D coordination polymers with angular dicarboxylate ligands

Luminescent two dimensional coordination polymers (CPs) {[Cd(SDB)(H2O)]·3H2O}n1 and {[Zn3(μ-OH)2(SDB)2]·(PPZ)}n2, (where SDB = 4,4′-sulfonyldibenzoate; PPZ = piperazine) have been synthesized by solvothermal methods. The crystal structure of 1 revealed that the carboxylate moieties of the SDB ligands are involved in “paddle wheel” type coordination with the metal nodes to engender a double chain loop which is further connected by μ-2 type coordination from one of the carboxylate oxygens, generating a two dimensional coordination polymer. In the case of 2, the two dimensional framework is constructed by bridging the one dimensional tri-metallic (Zn3μ3-OH) strands with the SDB ligand with a cylindrical cavity occupied by a piperazine moiety. Comprehensive characterization of both pristine compounds 1 and 2 by various physico-chemical methods, structural analysis and photoluminescence properties of activated CPs 1′ and 2′ towards the detection of nitroaromatics have been investigated. Both activated compounds 1′ and 2′ showed sensing of nitro explosive TNP (2,4,6-trinitrophenol) compared to other nitro analytes by fluorescence quenching properties.

Structural and functional studies on ternary coordination polymers from 5-bromoisophthalate and imidazole based flexible linker

Three ternary coordination polymers (CPs), namely, {[Cd2(BrIP)2(BITMB)(H2O)2]·(THF)2·H2O}n (CP1), [Cu(BrIP)(BITMB)(H2O)]n (CP2), {[Ni(BrIP)(BITMB)(H2O)]·(THF)(H2O)2}n (CP3) were synthesized by solvothermal reactions between H2BrIP (5-bromoisophthalate), BITMB (1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene) and respective metal nitrates. Single crystal X-ray diffraction studies reveal a variety of supramolecular interactions such as inter/intra molecular hydrogen bonding, C–H⋯π, and π⋯π stacking in the 1D interwoven metal organic triple helical motifs of CP1 and sql networks of CP2 and CP3. Solvents employed for the synthesis of these CPs may be acting as structure directing agents. The photocatalytic properties of all three CPs, for the decomposition of Metanil Yellow by dilute hydrogen peroxide in the presence of visible light, have been evaluated and up to 89% dye removal from aqueous solution was achieved in the case of CP2. Solid state fluorescence studies disclose the promising luminescence properties of synthesized CPs.

Efficient Solvent-Free Carbon Dioxide Fixation Reactions with Epoxides Under Mild Conditions by Mixed-Ligand Zinc(II) Metal-Organic Frameworks

Mixed‐ligand 3 D/2 D Zn metal–organic frameworks (MOFs) {[Zn(bdc)(L1)]⋅x G}n (ZnMOF‐1) and {[Zn(ipa)(L2)]}n (ZnMOF‐2; in which H2BDC=benzene‐1,4‐dicarboxylic acid, L1=4‐pyridyl carboxaldehyde isonicotinoylhydrazone, H2IPA=isophthalic acid, L2=3‐pyridyl carboxaldehyde nicotinoyl hydrazone, and G=lattice guests) were synthesized using versatile synthetic routes that include a green mechanochemical (grinding) reaction. Chemical and thermal stability, phase purity, and characterization of the ZnMOFs synthesized by different approaches were established by using various analytical methods. Both ZnMOFs can be used as a highly active, solvent‐free, binary catalyst for CO2 cycloaddition with epoxides under ambient reaction conditions of 1 atm pressure and room temperature/40 °C, in the presence of the cocatalyst nBu4NBr. The yield, recyclability, and stability of ZnMOF‐1 as a potential catalyst towards epoxide to cyclic carbonate conversion are excellent under ambient conditions. From literature and experimental inferences, a rationalized mechanism mediated by the Zn center of ZnMOFs for the CO2‐epoxide cycloaddition reaction has been proposed. To the best of our knowledge, very few MOF‐based catalysts have been reported to realize the conversion of CO2 to useful products under similar mild conditions. In the present investigation, that is, catalyst preparation by green mechanochemical synthesis and catalysis under ambient, solvent‐free conditions were performed with minimum energy utilization.

Efficient Heterogeneous Catalysis by Dual Ligand Zn(II)/Cd(II) MOFs for Knoevenagel Condensation Reaction: Adaptable Synthetic Routes, Characterization, Crystal Structure and Luminescence Studies

Dual ligand MOFs {[Zn(ADA)(L)]·2H2O}n (1) and {[Cd(ADA)(L)]·2H2O}n (2) involving Zn(II)/Cd(II) metal centres and flexible 1,3-adamantanediacetic acid (H2ADA)/pyridyl based Schiff base ligand, 4-pyridylcarboxaldehydeisonicotinoylhydrazone (L) as linkers have been efficiently synthesized including green mechanochemical methods and characterised using various analytical methods. Crystal structures of both MOFs, and luminescence and semiconducting properties have also been investigated. Both materials were exploited for efficient catalytic activity in the Knoevenagel condensation reaction for a variety of substrates with good yields and recyclability under ambient reaction conditions in aqueous media. Probably the Lewis acidic metal centre and the presence of amide functionality in the L of the MOFs are cooperatively involved in the efficient condensation reaction by these catalytic materials.

Sustainable Heterogeneous Catalysts for CO2 Utilization by Using Dual Ligand ZnII/CdII Metal-Organic Frameworks

Two-dimensional ZnII /CdII -based dual ligand metal-organic frameworks (MOFs) {[M(CHDC)(L)]⋅H2 O}n involving 4-pyridyl carboxaldehyde isonicotinoylhydrazone (L) in combination with flexible 1,4-cyclohexanedicarboxylic acid (H2 CHDC) as linkers have been synthesized by adaptable synthetic protocols including a green mechanochemical (grinding) method. Characterization, chemical/thermal stability, phase purity, and solid-state luminescent properties of both MOFs have been established by various analytical methods. Structural analysis revealed dimeric metal clusters composed of [M2 (CHDC)2 ]n loops doubly pillared with L, generating a 2D framework. Both MOFs can be used as highly active solvent-free binary catalysts for CO2 cycloaddition with epoxides in the presence of the co-catalyst tetrabutylammonium bromide (TBAB) with good catalytic conversion in up to six catalytic cycles without significant loss of activity. The present investigation demonstrates the application of MOFs as efficient heterogeneous catalysts for CO2 utilization under moderate reaction conditions. Based on the single-crystal X-ray data, a probable mechanism for the cycloaddition reaction has also been proposed.