Yadagiri Rachuri

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.

Mixed-Ligand LMOF Fluorosensors for Detection of Cr(VI) Oxyanions and Fe3+/Pd2+ Cations in Aqueous Media

Zn(II)/Cd(II)-based dual ligand Luminescent Metal-Organic Frameworks (LMOFs) {[M(ATA)(L)]}n·xH2O (1) and (2) were synthesized by versatile synthetic routes, viz., diffusion of precursor solutions, conventional reflux, and green mechanochemical (grinding) reactions from bipyridyl-based Schiff base, (E)-N-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and amino functionalized 2-aminoterephthalic acid (H2ATA) as linkers. Chemical and thermal stability, phase purity, and characterization of both LMOFs were established by various analytical methods. SXRD analysis revealed the 3D framework is composed of two-dimensional [M(ATA)]n nets doubly pillared by L through the terminal nitrogen atom. Selective and sensitive detection of chromate anions (CrO42-/Cr2O72-) and Fe3+/Pd2+ cations in the aqueous phase by fluorescent quenching of the LMOFs 1 and 2 has been established. Competitive experiments in the presence of interfering anions/cations with 1 and 2 revealed no major change in the quenching efficiency. The observed limits of detection (LOD) values by 1 for CrO42-/Cr2O72- were 0.25 μM (48 ppb)/0.43 μM (126 ppb) and for Fe3+/Pd2+ were 3.76 μM (0.61 ppm)/0.20 μM (35 ppb), whereas LOD values by 2 were 0.18 μM (35 ppb)/0.19 μM (55 ppb) and 1.77 μM (0.29 ppm)/0.10 μM (18 ppb), respectively. Simple fluorescent-based test paper strips have been developed for reliable and visual detection of the mentioned analytes in practical applications. The present investigation clearly demonstrates selective detection of CrO42-/Cr2O72- and Fe3+/Pd2+ in aqueous media, and the probable mechanism for the quenching phenomena based on structural aspects has also been discussed.

Binary co-crystals of the active pharmaceutical ingredient 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and camphoric acid

Co-crystals comprising the active pharmaceutical ingredient 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, C12H10N4, and the chiral co-formers (+)-, (-)- and (rac)-camphoric acid (cam), C10H16O4, have been synthesized. Two different stoichiometries of the API and co-former are obtained, namely 1:1 and 3:2. Crystallization experiments suggest that the 3:2 co-crystal is kinetically favoured over the 1:1 co-crystal. Single-crystal X-ray diffraction analysis of the co-crystals reveals N-H...O hydrogen bonding as the primary driving force for crystallization of the supramolecular structures. The 1:1 co-crystal contains undulating hydrogen-bonded ribbons, in which the chiral cam molecules impart a helical twist. The 3:2 co-crystal contains discrete Z-shaped motifs comprising three molecules of the API and two molecules of cam. The 3:2 co-crystals with (+)-cam, (-)-cam (space group P21) and (rac)-cam (space group P21/n) are isostructural. The enantiomeric co-crystals contain pseudo-symmetry consistent with space group P21/n, and the co-crystal with (rac)-cam represents a solid solution between the co-crystals containing (+)-cam and (-)-cam.

Nanoemulsions with All Ionic Liquid Components as Recyclable Nanoreactors

Nanoemulsions (NEs) comprising ionic liquids (ILs); ethanolammonium formate (HO-EOAF), proliniumisopropylester dioctylsulfosuccinate ([ProC3][AOT]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([Bmim][NTf2]) as insoluble hydrophilic, surface active, and hydrophobic components have been constructed. This novel class of colloidal formulations exhibited several contrasting properties vis-à-vis conventional water-in-oil or water-in-ionic liquid or nonaqueous NEs such as (i) spontaneous formation, (ii) thermodynamic stability and isotropic nature, (iii) decrease of droplet size with increase in polar medium concentration, and (iv) high thermal and kinetic stability. Mechanisms and characteristics for such anomalies have been investigated by physical, spectroscopic, and imaging techniques. NEs have been demonstrated as versatile recyclable nanoreactors for user-friendly synthesis of materials such as metal-organic frameworks/light harvesting hybrid systems. We anticipate that this development will lead to the construction of several other need-based all ionic-liquid nanoemulsions in view of the flexibility provided by the tailoring nature of ILs.

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.