Kamal Kumar Bisht

Spontaneous Resolution to Absolute Chiral Induction: Pseudo-Kagomé Type Homochiral Zn(II)/Co(II) Coordination Polymers with Achiral Precursors

It is observed that conglomerate crystallization of achiral precursors yielding racemate metal organic frameworks/coordination polymers (MOFs/CPs) can be driven to absolute homochiral crystallization of the desired enantiomorph by utilizing a suitable chiral induction agent. In a series of crystallization experiments isostructural Zn and Co homochiral CPs (1P, 1M and 2P, 2M) are prepared using the achiral precursors. In the presence of enantiopure camphoric acid, the crystallization process prefers absolute chiral induction over conglomerate formation which is established by single crystal X-ray diffraction and CD spectroscopy.

Spontaneous Resolution of a Mixed-Ligand Nickel(II) Coordination Polymer with Achiral Precursors

Metal-center-driven spontaneous resolution of a chiral coordination polymer, [Ni(SDB)(BIX)](n) (1), from achiral precursors has been probed by single-crystal X-ray diffraction and circular dichroism spectroscopy. Enantiomorphs 1P and 1M showed a parallel interpenetrated 2D → 3D chiral framework with (8(2).10) topology. Switching of the metal center under the same reaction parameters resulted in isostructural achiral and noninterpenetrating (4,4) grid-type sql networks [M(SDB)(BIX)](n), where M = Co(II), Zn(II), and Cd(II) for 2-4, respectively.

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.

Structure modulation, argentophilic interactions and photoluminescence properties of silver(I) coordination polymers with isomeric N-donor ligands

Synthesis, crystal structure, and photoluminescence studies of a one dimensional silver coordination polymer {[Ag(L1)(CH3CN)][Ag(L1)(OTf)](OTf)}n (1) comprising of Ag(I) and a new flexible organic linker bis(pyridine-3-ylmethyl)terephthalate (L1) exhibiting closed-shell d10⋯d10 argentophilic interaction, is reported. The compound 1 consists of two kinds of (double and single stranded) 1D coordination polymeric chains running parallel and displaying short Ag(I)⋯Ag(I) distances. Notably, the coordinated triflate anion, μ2-bridging mode of acetonitrile and stacking interactions play an important role in the realization of 1D quadruple metal–organic chain in compound 1. Treatment of silver triflate with isomeric ligand, bis(pyridine-2-ylmethyl)terephthalate (L2) resulted in a polymorph of previously reported 1D zigzag coordination polymer {[Ag(L2)](OTf)(H2O)}n (2). Both organic ligands and Ag coordination polymers are characterized by various analytical techniques. Crystal and molecular structures of the isomeric ligands (L1, L2) and their Ag(I) coordination polymeric architectures (1, 2) are correlated with their photoluminescence 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.

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.