Department of Chemistry
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Item N-Glycosylamines of 4,6-O-ethylidene-α-D-glucopyranose: synthesis, characterisation and structure of CO2H, Cl and F ortho-substituted phenyl derivatives and metal ion complexes of the CO2H derivative(RSC, 2000) Sah, Ajay KumarA saccharide based ligand suitable for metal binding (HLCOOH) has been synthesized using 4,6-O-ethylidene-α-D-glucopyranose (4,6-O-EGP) and anthranilic acid. A few analogous glycosylamines with chloro and fluoro ortho substitutions have also been synthesized and characterised. Complexes of HLCOOH with Na+, K+, Mg2+, Ca2+, Ba2+, Cd2+ and Hg2+ have been isolated and characterised fully. The crystal structures of 4,6-O-EGP, the chloro analogue of HLCOOH and the K+ complex of LCOOH are established. The anomeric nature, orientation of the binding core and the co-ordination aspects of K+ have been derived from these structures.Item First Crystallographic Investigation of Complexes of cis-VO2+, cis-MoO22+, and trans-UO22+ Species with Schiff-Base Molecules Derived from 4,6-O-Ethylidene-β-D-glucopyranosylamine(EJIC, 2001-09) Sah, Ajay KumarThe interaction of Schiff-base ligands derived from 4,6-O-ethylidene-β-D-glucopyranosylamine with cis-VO2+, cis-MoO22+, and trans-UO22+ species have been studied by isolating and characterizing the corresponding products. The structures of one complex of each type of species have been established by single-crystal X-ray diffraction analysis. In all the complexes, the saccharide moiety adopts a chair conformation and has a β-anomeric form. A gradual increase in coordination number (5, 6, and 7) and a gradual variation in the geometry (distorted trigonal-bipyramidal, distorted octahedral, and pentagonal-bipyramidal) are observed on going from the complexes of cis-VO2+ (mononuclear) to cis-MoO22+ (mononuclear) to trans-UO22+ (dinuclear). A variation in the binding mode of the ligand towards these dioxometal species is also observed. Intermolecular interactions of the type O−H···O, C−H···O, and N−H···O present in the lattices of these complexes lead to the formation of interesting structures.Item Synthesis, characterization and the first crystal structure of the Zn(II) complex of 4,6-O-ethylidine-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine(Elsiever, 2001-12) Sah, Ajay Kumar4,6-O-Ethylidine-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine (H3L1) and N-(5-bromo-2-hydroxybenzylidene-4,6-O-ethylidine-β-d-glucopyranosylamine (H3L2) molecules possessing a C-1NC(H) moiety for metal-ion binding were synthesized by condensing the 4,6-O-ethylidene-β-d-glucopyranosylamine with salicylaldehyde or 5-bromosalicylaldehyde. Complexes of these ligands with Zn(II) were isolated and characterized using elemental analysis, FTIR, UV–Vis absorption, NMR spectroscopic and FAB mass spectrometric techniques. The structure of the Zn(II) complex derived from H3L1 was established for the first time by a single-crystal X-ray diffraction study. The anomeric nature of the saccharide moiety was established based on 1H NMR studies and was confirmed by the crystal structure. Further, the structure and binding aspects of the ligand, and the coordination features of this in its Zn(II) complex were derived from the corresponding crystal structure.Item Structure of the first tetranuclear Ni(II) complex derived from N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine(Chemical Society of Japan., 2001) Sah, Ajay KumarIn order to understand the binding nature of the glycosylamines possessing imine functionality, a novel tetranuclear Ni(II) complex of N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine having twisted Ni4O4 cubane core was synthesized and structurally characterized.Item Crystal structure of 4,6-O-ethylidene-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine(Elsiever, 2002-01) Sah, Ajay Kumar4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The anomeric nature of the saccharide moiety was proposed based on 1H NMR studies and was confirmed by the crystal structure. The lattice structure of this compound was compared with that of its analoguesItem Dinuclear Copper Complexes of N-(2-Hydroxybenzylidene or 5-Bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine: Coordination Variation and Structural Diversity(CSJ, 2002) Sah, Ajay KumarDinuclear Cu(II) complexes of N-(2-hydroxybenzylidene or 5-bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine with coordination variation and molecular and lattice structural variations are explored.Item A soluble complex of Zn(II) with N2O4 core: a structural study(IAS, 2003) Sah, Ajay KumarA soluble complex of Zn(II) with 1-hydroxy-3-hydroxy-2-hydroxymethyl-2-(5'-formyl-salicylidimino) propane resulting in a distorted octahedral ZnN2O4 core has been synthesized and characterized by analytical and spectralmethods and the structure has been established by single crystal XRD.Item Bis-(μ-saccharide-C-2-oxo) dinuclear Cu(ii) complexes of 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o-hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-d-glucopyranosylamine: structural aspects and data correlations(RSC, 2003) Sah, Ajay KumarA total of five dinuclear copper complexes were synthesized using 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o-hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-D-glucopyranosylamine. Upon recrystallisation from different solvents, viz., dmso/MeOH/pyridine, seven different dinuclear copper complexes were generated, wherein the geometry around one or both of the copper centers changes from square planar to square pyramidal due to the binding of solvent molecule as the fifth ligand. The ligands and their complexes were characterized by elemental analysis, 1H and 13C NMR, FT-IR, FABMS, UV-Vis, optical rotation, CD and magnetic susceptibility measurements. The 3D structures of all the seven complexes were established by single crystal XRD. All the complexes are neutral and dinuclear with the metal to the glycosylamine ratio being 1 ∶ 1. Each glycosylamine acts as tridentate with di-negative charge and bridges between the two copper centers through the C-2-oxo group of the saccharide part and further the coupling between the copper centers is antiferromagnetic. At least four different types of Cu2O22+ core structures were identified depending upon the presence or absence of a fifth ligand at the Cu(II) center. The β-4C1-pyranose form of the glycosylamine is retained even in complexes. The dinuclear complex is stabilized through intra-complex hydrogen bond interaction. The inter-molecular C–H⋯O interactions are manifested in the formation of a helical structure where the water molecules occupy the cavity. The structural diversity observed in the complexes and several data correlations are discussed in detail.Item Trinuclear coordinatively labile Cu(ii) complex of 4,6-O-ethylidene-β-d-glucopyranosylamine derived Schiff baseligand and its reactivity towards primary alcohols and amines(RSC, 2005) Sah, Ajay KumarA novel neutral trinuclear Cu(II) complex of a Schiff base ligand derived from D-glucose has been synthesised and structurally characterised, which exhibits excellent alcohol binding affinity and activates the C–Cl bond of chloroform in the presence of primary amine.Item Crystal-to-crystal transformation from tri- to mononuclear Cu(ii) complex with a sugar-derived ligandvia proton transfer reaction and rearrangement of hydrogen bonding networks†(ACS, 2005) Sah, Ajay KumarTreatment of a glycosylamine derived Cu(II) complex with ethylamine resulted in crystal-to-crystal transformation from trinuclear complex [Cu3(L1)2(EtNH2)2(MeOH)2]x2MeOHxCHCl3 (2x2MeOHxCHCl3) to a dimeric structure of mononuclear complex [Cu(HL1)(EtNH2)] (3) through proton transfer reaction and rearrangement of hydrogen bonding networks.