Browsing by Author "Brajesh Pathak"

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Complexes of Zn(II) containing (o-)/(p-) carboxylato phenyl azo pentane 2,4-dione and 2,2′ bipyridine as ligands: Synthesis, characterization, colorimetric and fluorometric modulation in the presence of Ag+ ions
(Elsevier Ltd, 2013) Md. Amin Hasan; Niraj Kumari; Pankaj Kumar; Brajesh Pathak; Lallan Mishra
Azo-enol based ligands 2-[N′-(1-acetyl-2-oxo-propylidene) hydrazino]-benzoic acid (L1H2) and 4-[N′-(1 acetyl-2 oxo-propylidene)-hydrazino]-benzoic acid (L2H2) and their complexes [Zn(L1H)2(bpy)] (1) and [Zn(L 2H)2(bpy)] (2) (where bpy = 2, 2′-bipyridine) have been synthesized and characterized using elemental analyses, spectral (FT-IR, 1H NMR, 13C NMR, electronic absorption), emission and single-crystal X-ray diffraction studies. Complexes 1 and 2 display selective chromogenic and fluorogenic responses with Ag+ ions in the presence of several other metal ions. The binding is monitored separately using UV-Vis, fluorescence and 1H NMR spectral titrations. Job's plot supports a 1:2 stoichiometry for 1 and 2 with Ag+ ions. The pH dependent "on-off" switching of fluorescence from complexes 1 and 2 have been studied. The fluorescence intensity quenches (turns-off) upon addition of OH- ions, while it enhances (turns-on) in the presence of H + ions. © 2012 Elsevier Ltd. All rights reserved.
Metal assisted self-assembled nano sized porous 2-D structures incorporating malonic acid dihydrazide and melamine
(2006) Lallan Mishra; Brajesh Pathak; G.V.S. Sastry; S. Umamaheswara Rao
The solids Cu(MADH)2•Cl2•2TAT•9H 2O and Zn(MADH)2•Cl2•2TAT• 2H2O (MADH = malonic acid dihydrazide and TAT = melamine) characterized by spectroscopic and elemental analysis, have been investigated by transmission electron microscope. Microstructure at high magnification revealed the supramolecular assembly of MADH and TAT into a mesh structure in presence of Cu(II) metal ions and tubular structure with intermittent openings on the tube walls and Y- junctions for Zn(II) complex. The mesh structure of the Cu(II) complex has uniformly spaced 40-50 nm long and 20-30 nm wide openings, while the diameter of the tubular structure of the Zn(II) complex is 50-200 nm.The assembly of the supramolecular structure is attributed to H-bonding and the different architectures of the assembly with different metal ions to the difference in waters of crystallization. The potential of the complex for gas adsorption was also investigated. © Springer Science+Business Media, Inc. 2006.
Supramolecular motifs in metal complexes of malonic acid dihydrazide: Copper(II) and zinc(II) assisted assembly of malonic acid dihydrazide with melamine
(2004) Lallan Mishra; Brajesh Pathak; Yadvendra Agrawal
One pot condensation of malonic acid dihydrazide (MADH) in the presence of metal salts (CuCl2 · H2O and ZnCl2) with melamine (TAT) has been achieved. The solids Cu(MADH)2Cl2 · 2TAT · 9H2O and Zn(MADH)2Cl2 · TAT · 1/2H2O thus obtained were characterized by elemental analysis, FAB mass, i.r., n.m.r., u.v.-visible and e.p.r. spectral data together with their powder X-ray diffraction, optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) (Zn complex only). Variable temperature solid slate conductance measurements have also been made.
Synthesis and spectroscopic characterization of cobalt(III) based supramolecular complexes bearing thymine and adenine
(Indian Chemical Society, 2001) Lallan Mishra; Brajesh Pathak
Multifunctional ligand 5-cyano-6-(4-pyridyl)-2-thiouracil (L) possessing hydrogen bonding groups complementary to those found in nucleotide bases has been synthesized and complexed with trans-[Co(en)2Cl2]+Cl- (en = ethylene diamine) resulting into two types of complexes [Co(en)2LCl]2+.2Cl- and [Co(en)2L2]3+.3Cl-. These complexes were allowed to react with thymine (T) and adenine (A) bases separately. Solid complexes thus synthesized have been characterized using elemental analysis, FAB mass, spectral (1R, UV-visible, 1H NMR) and scanning electron microscopic (SEM) studies. Association of ligand (L) and its one representative complex [Co(en)2LCl]2+.2Cl- with thymine base has been studied by UV-visible spectrophotometry.
XRD and optical microscopic studies of Co(III) complexes containing 5-cyano-6-(4-pyridyl)-2-thiouracil, thymine and adenine bases
(2001) Lallan Mishra; Brajesh Pathak; R.K. Mandal
Multifunctional ligand 5-cyano-6-(-4-pyridyl)-2-thiouracil (L) was prepared and allowed to react with trans [Co(en)2Cl2]+Cl- resulting into [Co(en)2LCI]2+·2Cl- which upon further reaction with equimolar ratio of ligand [L] gave the complex [Co(en)2L2]3+·3Cl-. These metal complexes were then separately reacted with thymine and adenine bases. Complexes thus prepared after characterization by their elemental analysis, FAB mass and spectral (IR, 1HNMR, UV-visible) data were studied for their powder X-ray diffraction and optical microscopic characteristics.