• Journal of the Korean Chemical Society
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• v.55 no.6
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• pp.912-918
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• 2011

Tetraaza Schiff base macrocyclic ligands, $L^1$,$L^2$ and their transition metal chelates have been synthesized and characterized by elemental analyses, IR, electronic, EPR and $^1H$ NMR spectra, TGA and magnetic measurements. The molar conductance of one milli-molar solution of the complexes measured in DMF indicates that the divalent metal complexes are nonelectrolyte while those of trivalent metal ion, are 1:1 electrolytic in the same solvent. The reduction of Racah parameter from the free ion value confirms the presence of considerable covalence of metal ligand sigma bond in the Co(II) and Mn(II) complexes. The EPR spectra of Cu(II) complexes at room temperature shows axial symmetry indicating a $d_x{^2}_{-y}{^2}$ ground state with significant covalent character. The thermal analysis suggests that the complexes do not contain water molecules because only the metal is left as residue.

• Analytical Science and Technology
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• v.11 no.5
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• pp.366-373
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• 1998

Polydentate Schiff base ligands, BSDT(1,9-bis(2-hydroxyphenyl)-2,5,8-triaza-1,8-nonadiene) having $N_3O_2$ atoms, BSTT(1,12-bis(2-hydroxyphenyl)-2,5,8,11-tetraaza-1,11-dodecadiene) having $N_4O_2$ atoms, BSTP(1,15-bis(2-hydroxyphenyl)-2,5,8,11,14-pentaaza-1,14-pentadodecadiene) having $N_5O_2$ atoms were synthesized. Protonation constants of these polydentate ligands were measured by potentiometry. Stability constants of the complexes between these ligands and the metal ions such as Cu(II), Ni(II) and Zn(II) were measured in DMSO by a polarographic method. It was observed that all metal(II) ions employed in this study formed 1:1 complexes with Schiff base ligands. Stability constants for the complex formation were in the order of Cu(II)>Ni(II)>Zn(II), and for the ligands were in the order of BSTP>BSTT>BSDT. There are due to the increase in the number of donor atoms. Both enthalpy and entropy changes were obtained in negative values. Exothermicity for the complex formation indicated tight binding between the ligands and metal ions. The negative entropy change would be related to the fact that solvent molecules are strongly interacting with the metal complexes.

• Analytical Science and Technology
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• v.37 no.4
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• pp.239-250
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• 2024

This study reports the synthesis of a bi-dentate Schiff base ligand (L), 7-(2-((2-formylbenzylidene) amino)-2-phenylacetamido)-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid, prepared from phthalaldehyde and cephalexin antibiotic. The synthesized Schiff base ligand (L) and the secondary ligand alizarin (Az) are used to prepare the new complexes [M(Az)₂(L)] and [Cr(Az)₂(L)]Cl, where M = Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The mode of bonding of the Schiff base has been characterized by UV-Visible, FT-IR, Mass, ¹H-, and ¹³C-NMR spectroscopic techniques, and micro elemental analysis (CHNS). The complexes were characterized using UV-Vis, FT-IR, molar conductance, magnetic moment, and thermal analysis (TG/DTG). The molar conductance data revealed that the complexes are non-electrolytes except for [Cr(L)(Az)₂]Cl, which is an electrolytic type 1:1. The Schiff base and its complexes have been tested for their biological activity against two strains of bacteria and one fungus. When screened against gram-positive and gram-negative pathogens, the Az and L ligands and their complexes showed potential antimicrobial activity.

• Journal of the Korean Chemical Society
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• v.56 no.4
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• pp.440-447
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• 2012

Heteroleptic complexes of zirconium (IV) derived from bulky Schiff base ligands containing a sulphur atom and oximes of heterocyclic ${\beta}$-diketones of the general formula ZrLL' (where $LH_2=RCNH(C_6H_4)SC:C(OH)N(C_6H_5)N:CCH_3$, $R=-C_6H_5$, $-C_6H_4Cl(p)$ and $L^{\prime}H_2=R^{\prime}C:(NOH)C:C(OH)N(C_6H_5)N:CCH_3$, $R^{\prime}=-CH_2CH_3$, $-C_6H_5$, $-C_6H_4Cl(p)$ were prepared by the reactions of zirconium tetrachloride with disodium salts of Schiff bases ($L\;Na_2$) and oximes of heterocyclic ${\beta}$-diketones ($L^{\prime}\;Na_2$) in 1:1:1 molar ratio in dry refluxing THF. The structures of these monomeric zirconium (IV) complexes were elucidated with the help of elemental analysis, molecular weight measurements, spectroscopic (IR, NMR and mass) studies. A distorted trigonal bipyramidal geometry may be suggested for these heteroleptic zirconium (IV) complexes. The ligands (bulky Schiff base ligands containing a sulphur atom and oximes of heterocyclic ${\beta}$-diketones) and their heteroleptic complexes of zirconium (IV) were screened against A. flavus, P. aeruginesa and E. coli.

• Journal of the Korean Chemical Society
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• v.52 no.4
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• pp.439-444
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• 2008

• Bulletin of the Korean Chemical Society
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• v.19 no.5
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• pp.587-590
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• 1998

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3581-3588
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• 2012

A new series of acyclic mononuclear gadolinium(III) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and gadolinium nitrate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show azomethine (CH=N) within the range of 410-420 nm. The fluorescence efficiency of Gd(III) ion in the cavity was completely quenched by the higher chain length ligands. Electrochemical studies of the complexes show irreversible one electron reduction process around -2.15 to -1.60 V The reduction potential of gadolinium(III) complexes shifts towards anodic directions respectively upon increasing the chain length. The catalytic activity of the gadolinium(III) complexes on the hydrolysis of 4-nitrophenylphosphate was determined. All gadolinium(III) complexes were screened for antibacterial activity.

• Bulletin of the Korean Chemical Society
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• v.25 no.10
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• pp.1455-1456
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• 2004

• Journal of the Korean Chemical Society
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• v.38 no.4
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• pp.319-327
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• 1994

The novel Schiff base hexadentate ligand, bis-(salicylaldehyde)-triethylentetramine (BSTT) and heptadentate ligand, bis-(salicylaldehyde)-tetraethylenpentamine(BSTP) were synthesized by the reaction of salicylaldehydes with triethylenetetramine and tetraethylenepentamine, having four and five nitrogen atoms, respectively. These liquid Schiff base ligands were become in form of the pale-yellow crystals in the specific pH 4.0 by adding acetic acid concentrated hydrochloric acid. The Cu(Ⅱ) complexes of the Schiff bases were synthesized by reaction of the Schiff base with Cu(Ⅱ) ion and their possible structures were proposed by several analytical data, and physical and chemical properties.

• Analytical Science and Technology
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• v.13 no.5
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• pp.558-564
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• 2000

Mononuclear schiff base ligand N,N'-bissalicylidene-1,2-phenylenediamine(BSPD) and binuclear schiff base ligands N,N',N',N'''-tetrasalicylidene-3,3',4,4'-tetraaminodiphenyl-methane (TSTM), N,N',N'',N'''-tetrasalicylidene-3,3'-diaminobenzidine (TSDB) have been synthesized. Proton dissociation constants of the ligands were determined by potentiometric method. The synthesized ligands and complexes formed with Cu(II) ion. These complexes were investigated by cyclic voltammetry and differential pulse voltammetry. The results revealed two step diffusion controlled redox process. The mononuclear complex Cu(II)-BSPD and binuclear complexes $Cu(II)_2$-TSDB and $Cu(II)_2$-TSTM were used in the oxidation reaction of ascorbic acid. The reaction rates were in the order of $Cu(II)_2$-TSTM>$Cu(II)_2$-TSDB>Cu(II)-BSPD, indicating that the binuclear $Cu(II)_2$-TSTM complex had the fastest values.