Browsing by Author "Pawan Raj Shakya"

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A zinc (II) complex comprising an aminoethyl-nitropyridine-derived N,N,O-donor Schiff base ligand serves as an efficient ON–OFF probe for Cu(II)
(John Wiley and Sons Ltd, 2023) Himani Sharma; Arpna Tamrakar; Tarkeshwar Maddeshiya; Pawan Raj Shakya; Kamal Kant Tiwari; Mrituanjay D. Pandey; Rampal Pandey
A new fluorescent zinc (II) complex-based probe 1 encompassing a Schiff's base (E)-2-methoxy-6-((2-[5-nitropyridin-2-ylamino]ethylimino)methyl)phenol (HL) was designed, synthesized, and used for the highly selective detection of Cu2+. Ligand HL and complex 1 were characterized using various spectroscopic techniques such as 1H, 13C-NMR, and FTIR spectroscopy, high-resolution mass spectronomy (HRMS), UV/visible light spectroscopy, and fluorescence studies. Ligand HL did not exhibit any considerable change in fluorescence in the presence of various cations. Notably, its Zn(II) complex 1 exhibited highly selective ‘TURN-OFF’ fluorescence signalling towards Cu2+ that remained uninterrupted with competing analytes. Probe 1 interacted with Cu2+ in 1:2 (1:Cu2+) stoichiometry as estimated through a Job's plot. Moreover, the selectivity of 1 was further confirmed through the interaction of the 1 + Cu2+ complex with some possible interfering metal ions inducing an insignificant response. Additionally, the association and quenching constant were determined to be 3.30 × 104 M−1 and 0.21 × 105 M−1 through the Benesi–Hildebrand method and Stern–Volmer plot, respectively. © 2022 John Wiley & Sons Ltd.
Complexes of some 3d metal ions of the Schiff's base, N,N′-di-4- (4′-pentyloxybenzoate) salicylidene-1″, 3″-diamino-2″- propanol: Synthesis and spectral studies
(2011) Angad Kumar Singh; Sanyucta Kumari; Pawan Raj Shakya; T.R. Rao
A nematogenic Schiff's base, N,N′-di-4-(4′-pentyloxybenzoate) salicylidene-l″, 3″-diamino-2″-propanol, (abbreviated as H2L6), was synthesized and its structure studied by elemental analyses, mass, NMR and IR spectra. The Schiff's base behaves as a dinegative hexa/tetradentate species in its metal complexes of the general formula, [ML6]n where MII, Co, Ni, Cu and Zn. Their structural characterizations were made by various spectroscopic techniques. © 2011 Elsevier B.V. All rights reserved.
Complexes of some 4f metal ions of the mesogenic Schiff-base, N,N -di-(4-decyloxysalicylidene)-1,3-diaminobenzene: Synthesis and spectral studies
(2012) Pawan Raj Shakya; Angad Kumar Singh; T.R. Rao
A mesogenic Schiff-base, N,N-di-(4-decyloxysalicylidene)-1,3- diaminobenzene, H2ddsdbz (abbreviated as H2L), that exhibits a nematic mesophase was synthesized and its structure was studied by elemental analysis, mass spectrometry, NMR, and IR spectral techniques. The Schiff-base, H2L, upon condensation with hydrated lanthanide(III) nitrates yields Ln III complexes, [Ln2(LH2)3(NO3)4](NO3)2, where Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho. Analyses of the IR and NMR spectral data imply bidentate Schiff-base through two phenolate oxygen atoms in its zwitterionic form to Ln III, rendering the overall geometry of the complexes as a seven-coordinate polyhedron -possibly distorted mono-capped octahedron. Polarizing optical microscope and differential scanning calorimetry studies reveal that despite H2L being mesogenic, none of the Ln III complexes synthesized under this study exhibits mesomorphism. © 2012 Copyright Taylor and Francis Group, LLC.
Homo dinuclear lanthanide(III) complexes of a mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′,6′-diaminohexane: Synthesis and characterization
(2011) Pawan Raj Shakya; Angad Kumar Singh; T.R. Rao
A mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′, 6′-diaminohexane, H 2ddsdh (abbreviated as H 2L 2) that exhibits smectic-B (SmB) mesophase, was synthesized and its structure studied by elemental analysis, mass spectrometry, NMR & IR spectral techniques. The Schiff-base, H 2L 2, upon condensation with hydrated lanthanide(III) nitrates, yields Ln III complexes of the general composition [Ln 2(L 2H 2) 3(NO 3) 4](NO 3) 2, where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho. IR and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as L 2H 2) to the Ln III ions through two phenolate oxygens. The POM and DSC studies reveal that none of the Ln III complexes exhibits mesomorphism. Fluorescence studies show that the Tb III complex displays characteristic metal-centered fluorescence (solution state). © 2011 Elsevier B.V. All rights reserved.
Rare earth metal complexes of a mesogenic schiff-base, N,N′-di-(4- decyloxysalicylidene)-1′, 4′-diaminobutane: Synthesis and characterization
(Taylor and Francis Inc., 2014) Pawan Raj Shakya; Angad Kumar Singh; T.R. Rao
A mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′, 4′-diaminobutane, (H2L) that exhibits smectic-B and nematic mesophases, was synthesized and its structure studied by elemental analysis, mass spectrometry, NMR & IR techniques. H2L, upon condensation with hydrated lanthanide(III) nitrates yields LnIII complexes of the composition [Ln2(LH2)3(NO3)4](NO3)2, where LnIII = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho. The PrIII complex shows smectic-A and nematic phases. The IR and NMR spectral data imply a bidentate bonding of H2L in zwitterionic form (as LH2) to the LnIII ions through two phenolate oxygen atoms, rendering the overall geometry of the complexes possibly to distorted mono-capped octahedra. © 2014 Copyright Taylor and Francis Group, LLC.
Synthesis and characterization of lanthanide(III) complexes with a mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-2′,6′- diaminopyridine
(2012) Pawan Raj Shakya; Angad Kumar Singh; T.R. Rao
A mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-2′, 6′-diaminopyridine, H 2ddsdp (abbreviated as H 2L 3) that exhibits nematic mesophase, was synthesized and its structure studied by elemental analysis, mass spectrometry, NMR & IR spectral techniques. The Schiff-base, H 2L 3, upon condensation with hydrated lanthanide(III) nitrates, yields Ln III complexes of the general composition [Ln 2(L 3H 2) 3(NO 3) 4](NO 3) 2, where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho. Among the metal complexes, only that of Ho III is found to be mesogenic with smectic-X and nematic phases. The IR and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as L 3H 2) to the Ln III ions through two phenolate oxygens, rendering the overall geometry of the complexes to seven-coordinated polyhedron, possibly distorted mono-capped octahedron. © 2012 Elsevier B.V. All rights reserved.