Parent Schiff Base Research Articles

Synthesis and characterization of a novel schiff base metal complexes and their application in determination of iron in different types of natural water

A novel, simple approach to the synthesis of macrocyclic Schiff base ligand resulted from the condensation of bisaldehyde and ethylenediamine was prepared (7, 8, 15, 16, 17, 18-hexahydrodibenzo (a, g) (14) annulene) (L) and its complexes were synthesized and characterized using different physicochemical studies as elemental analysis, FT-IR, 1H NMR, conductivity, magnetic properties, thermal analysis, and their biological activities. The spectroscopic data of the complexes suggest their 1:1 complexe structures which are investigated by elemental analysis, FT-IR, 1H NMR, conductivity, magnetic properties, thermal analysis, and their biological activities. The spectroscopic studies suggested the octahedral structure for the all complexes. The spectroscopic data of the complexes suggest their structure in which (N2O2) group act as a tetradentate ligand and two chlorides as monodentate ligands. Also electronic spectra and magnetic susceptibility measurements indicate octahedral structure of these complexes. The synthesized Schiff base and its metal complexes also were screened for their antibacterial and antifungal activity. Here we report the effect of a neutral chelating ligand on the complexation with iron to determine it in different types of natural water using recovery test. The activity data show that the metal complexes to be more potent/ antibacterial than the parent Schiff base ligand against one or more bacterial species.

Synthesis and Characterization of Thermally Stable and Biologically Active Metal-Based Schiff Base Polymer

Schiff base was prepared via condensation of ethanedihydrazide with 2-hydroxy benzaldehyde and further this monomeric Schiff base polymerize with formaldehyde and barbituric acid and form polymeric Schiff base (PLSB) ligand. The ligand and its polymer metal complexes were characterized by using elemental analysis, IR, UV–VIS, 1HNMR, magnetic susceptibility and thermogravimetric studies. On basis of elemental analysis and spectral studies, six coordinated geometry was assigned for Mn(II), Co(II) and Ni(II) complexes and four coordinated for Cu(II) and Zn(II) complexes. PLSB act as a tetradentate and coordinate through the azomethine nitrogen and phenolic oxygen. The thermal behavior of these polymer metal complexes showed that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The (PLSB) ligands and its polymer metal complexes were screened against bacterial species Escherichia coli, Staphylococcus aureus, Bacillus subtilis and fungal species Aspergillus flavus, Candida albicans, A. niger. The activity data show that the metal complexes were more potent than the parent Schiff bases.

Spectroscopic and biological activity studies on tridentate Schiff base ligands and their transition metal complexes

Schiff base ligands are prepared via condensation of pyridine-2,6-dicarboxaldehyde with 2-aminothiophenol (H 2 L 1 ) and 2-aminobenzoic acid (H 2 L 2 ), respectively. The ligands are characterized based on elemental analysis, mass, IR and 1 H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, 1 H NMR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes except Th(IV) H 2 L 2 complex which is 1:1 electrolyte . IR spectra show that H 2 L 1 and H 2 L 2 ligands behave as neutral tridentate ligands and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III)- and Fe(III)-H 2 L 1 and H 2 L 2 , Th(IV)-H 2 L 2 and Mn(II)-H 2 L 1 complexes) and triagonal bipyramidal (Co(II), Ni(II), Cu(II), Cd(II) and UO 2 (II)-H 2 L 1 and H 2 L 2 and Mn(II)-H 2 L 2 complexes). The thermal behaviour of these chelates is studied using TG and DTA techniques and the activation thermodynamic parameters are calculated using Coats-Redfern method. The synthesized ligands and their metal complexes were screened for their biological activity against bacterial species ( Escherichia coli , P. vulgavis , B. subtilis and S. pyogones ) and fungi ( F. solani , A. niger and A. liavus ). The activity data show that the metal complexes have antibacterial and antifungal activity more than the parent Schiff base ligands against one or more bacterial or fungi species.

Mixed-ligand ternary complexes of potentially pentadentate but functionally tridentate Schiff base chelates

The potentially pentadentate chelate 2,6-diacetylpyridine-bis(N-methyl-S-methyldithiocarbazate) (Nmedapsme) has been synthesized and structurally characterized by X-ray diffraction. Its reactions with nickel(II) salts did not lead to pentadentate coordinated ligand complexes but ternary complexes of general formula, [Ni(Nmedapsme)(nmesme)L]X·H 2O (L = Br −, I −; X = I −, BF 4 −) where Nmedapsme binds as a tridentate and nmesme = N-methyl-S-methyldithiocarbazate. The related ternary nickel(II) complexes of formula, Ni(Nmedapsme)(nmetsc)Br 2 has also been prepared and characterized. X-ray crystal structures of [Ni(Nmedapsme)(nmesme)I]I·H 2O and [Ni(Nmedapsme)(nmesme)Br]BF 4·H 2O revealed that, in these complexes, the Nmedapsme ligand acts as a tridentate NNN donor while the distal S-donors are not coordinated. The bidentate ( NS) ligand, nmesme coordinates to the nickel(II) ion via the amino nitrogen and the thione sulfur atoms, the sixth coordination site is occupied by an anion. In both complexes, the nickel(II) ion adopts a distorted octahedral configuration. The complex [Cu(nmesme) 2(ONO 2)]NO 3 was obtained from an unsuccessful attempt to complex copper(II) with Nmedapsme. Hydrolysis of the parent Schiff base Nmedapsme occurred during complexation. An X-ray crystallographic structure analysis shows that the complex, [Cu(nmesme) 2(ONO 2)]NO 3 has an approximately square–pyramidal geometry with the two nmesme ligands coordinated to the copper(II) ion as NS bidentate chelating agents via the amino nitrogen and thione sulfur atoms and the fifth coordination position of copper(II) is occupied by a monodentate nitrate ligand.

DNA interaction, enhanced DNA photocleavage, electrochemistry, thermal investigation and biopotencial properties of new mixed-ligand complexes of Cu(II)/VO(IV) based on Schiff bases

Using the Schiff base ligand, dbdppo (4-(3′,4′-dimethoxybenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-one or hnbdppo (4-(3′-hydroxy-4′-nitrobenzaldehydene)2-3-dimethyl-1-phenyl-3-pyrazolin-5-one with polypyridyl ligand(s) as co-ligand(s), Cu(II) and VO(IV) complexes have been synthesized and characterized by the physicochemical properties. The electrochemical properties, DNA binding affinities, as well as photonuclease activities of the complexes, were examined in detail. The DNA binding characteristics of the Cu(II) and VO(IV) complexes was investigated by spectroscopic, electrochemical and viscosity measurements. The UV–Vis, and magnetic moment data revealed an octahedral geometry around Cu(II) ion and square-pyramidal geometry around VO(IV) ion and conductivity data conveyed the electrolytic nature of the complexes. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both of the complexes bound to CT DNA by partial intercalation into the base pairs of DNA. Moreover, these complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. Further, the synthesized ligands, in comparison to their metal complexes were screened for their antimicrobial activity against bacterial and fungal species. The activity data show that the metal complexes have more antimicrobial potent than the parent Schiff base ligands.

Preparation of macrocyclic Schiff-base ligand and antibacterial activities of transition metal complexes thereof

A macrocyclic Schiff-base (H2L) ligand is prepared via condensation of 2,6-pyridine dicarboxaldehyde with triethylene tetramine. The ligand is characterized using elemental analysis, by mass spectrometry, infrared (IR) spectroscopy, and proton nuclear magnetic resonance spectroscopy. The corresponding 1:1 metal complexes with Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Cd(II), UO2(II), and Th(IV) are additionally characterized by determining their magnetic moment, molar conductance, thermal analysis (thermogravimetry and differential thermoanalysis), and solid reflectance measurements. The complexes have the general formulae [M(H2L)(H2O)](X) n · yH2O (X = Cl or AcO, n = 2,3, y = 2–5) except for the Th(IV) complex having the formula [Th(H2L)(Cl)]Cl3. The molar conductance data reveal that all the metal chelates are electrolytes. IR spectra show that H2L is coordinated to the metal ions in a neutral pentadentate manner with 5N donor sites of the two azomethine–N, pyridine–N, and two amino–NH groups. The magnetic and solid reflectance spectra reveal that the complexes are octahedral. Thermal analysis shows that the complexes decompose in four to five steps. The activation thermodynamic parameters are calculated using the Coats–Redfern method. The parent Schiff base and its eight metal complexes were assayed against four bacterial species, two Gram negative, and two Gram positive. The Schiff base and five of its metal complexes showed antibacterial activity at different rates. The complexes Cr(III) and Cu(II) inhibited Gram-positive bacteria, while Co(II) complex inhibited all tested bacteria greater than the parent Schiff base. Three metal complexes (Ni, Cd, and Th) completely missed antibacterial activity.

Synthesis, structural, thermal studies and biological activity of a tridentate Schiff base ligand and their transition metal complexes

Schiff base (L) ligand is prepared via condensation of pyridine-2,6-dicarboxaldehyde with -2-aminopyridine. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes. IR spectra shows that L ligand behaves as neutral tridentate ligand and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Th(IV)) and tetrahedral (Mn(II), Cd(II), Zn(II), and UO 2(II)). The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, Δ H*, Δ S* and Δ G* are calculated from the DTG curves using Coats–Redfern method. The synthesized ligand, in comparison to their metal complexes also was screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi ( Candida). The activity data shows that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.

Metal complexes of a novel Schiff base derived from sulphametrole and varelaldehyde. Synthesis, spectral, thermal characterization and biological activity

Metal complexes of a novel Schiff base (HL = 3-(4′-ethylazomethinobenzene sulphonamide)-4-methoxy-1,2,5-thiadiazole) derived from condensation of sulphametrole and varelaldehyde are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and thermal analysis (TG). From the elemental analyses data, 1:1 metal complexes are formed having the general formulae [MCl 3(HL)(H 2O)]·3H 2O (M = Cr(III), Fe(III)) and [MCl 2(HL)(H 2O) 2]· yH 2O (where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II), y = 0–3). The important infrared (IR) spectral bands corresponding to the active groups in the ligand and the solid complexes under investigation were studied. IR spectra show that HL is coordinated to the metal ions in a neutral bidentate manner with ON donor sites of the enolic sulphonamide- OH and thiodiaza- N. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats–Redfern equation. All the metal chelates are found to be non-electrolytes. From the magnetic and solid reflectance spectra, the complexes have octahedral structures. The antibacterial and antifungal activities of the synthesized ligand and its metal complexes were screened against bacterial species ( Escherichia coli and Staphylococcus aureus) and fungi ( Candida and Aspergillus flavus). The activity data show that the metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species.

The structural and electrochemical consequences of hydrogenating copper N2S2 Schiff base macrocycles

A series of cis and trans tetradentate copper macrocyclic complexes, of ring size fourteen - sixteen, which employ amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane copper(I) (cis-[Cu(H4NbuSen)]+) all of the complexes are obtained in the copper(II) form. Crystallographic analysis shows that the copper(II) complexes all adopt a distorted planar geometry around the copper. In contrast, cis-[Cu(H4NbuSen)]+ is found to adopt a distorted tetrahedral geometry. The complexes were subjected to electrochemical analysis in water and acetonitrile. The effect of the solvent, positions of the donor atoms (cis/trans) on E1/2 is discussed as is the comparison of the electrochemical behaviour of these complexes with their parent Schiff base macrocycles.

Synthesis and Characterization of Transition Metal Complexes with

The Schiff bases namely MIMFMA, MIMTMA and MIPMA have been prepared by reacting 3-amino-5-methyl isoxazole with 5-methyl furan-2-carboxyaldehyde, 5-methyl thiphene-2-carboxaldehyde and pyridine-2-carboxaldehyde. The Cu(II), Ni(II), Co(II), Zn(II) and VO(IV) have been prepared by reacting metal chlorides with those Schiff bases in an alchololic medium. The complexes are electrolytes in DMSO. These have been characterized by using elemental analysis, IR, UV-VIS, 1H, 13C, mass spectra, magnetic susceptibility, conductance measurements and thermo gravimetric studies. The complexes were found to have composition ML2. On basis of elemental and spectral studies, six coordinated geometry is assigned for these complexes. The Schiff bases act as neutral and bidentate and coordinate through the azomethine nitrogen and furfural oxygen, thiophene sulphur and pyridine nitrogen, respectively. The synthesized ligands and their metal complexes were screened against bacteria and fungi. The activity data show that the metal complexes are more potent than the parent Schiff bases. Keywords; Schiff bases; Transition metal complexes; Spectral studies; Antimicrobial studies. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v2i1.2732 J. Sci. Res. 2 (1), 114-126 (2010)

Synthesis, characterization and biological studies of oxovanadium(IV) complexes with triazole‐derived Schiff bases

AbstractA series of triazole‐derived Schiff bases (L1–L5) and their oxovanadium(IV) complexes have been synthesized. The chemical structures of Schiff bases were characterized by their analytical (CHN analysis) and spectral (IR, 1H and 13C NMR and mass spectrometry) data, and oxovanadium(IV) complexes were elucidated by their physical (magnetic susceptibility and conductivity), analytical (CHN analysis), conductance measurements and electronic spectral data. The molar conductivity data indicate the oxovanadium(IV) complexes to be non‐electrolyte. The Schiff bases act as bidentate and coordinate with the oxovanadium(IV)‐forming stoichiometry of a complex as [M (L‐H)2] where M = VO and L = L1–L5 in a square‐pyramidal geometry. The agar well diffusion method was used for in vitro antibacterial screening against E. coli, S. flexenari, P. aeruginosa, S. typhi, S. aureus and B. subtilis and for antifungal activity against T. longifucus, C. albican, A. flavus, M. canis, F. solani and C. glaberata. The biological activity data show the oxovanadium(IV) complexes to be more antibacterial and antifungal than the parent Schiff bases against one or more bacterial and fungal strains. Copyright © 2009 John Wiley & Sons, Ltd.

Preparation, characterization and biological activity of novel metal-NNNN donor Schiff base complexes

Novel Schiff base (H 2L) ligand is prepared via condensation of benzil and triethylenetetraamine. The ligand is characterized based on elemental analysis, mass, IR and 1H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). 1:1 [M]:[H 2L] complexes are found from the elemental analyses data having the formulae [M(H 2L)Cl 2]· yH 2O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)), [Fe(H 2L)Cl 2]Cl·H 2O, [Th(H 2L)Cl 2]Cl 2·3H 2O and [UO 2(H 2L)](CH 3COO) 2·2H 2O. The metal chelates are found to be non-electrolytes except Fe(III), Th(IV) and UO 2(II) complexes are electrolytes. IR spectra show that H 2L is coordinated to the metal ions in a neutral tetradentate manner with 4Ns donor sites of the two azomethine N and two NH groups. The geometrical structures of these complexes are found to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters are calculated using Coats–Redfern method. The ligand (H 2L), in comparison to its metal complexes, is screened for its antibacterial activity. The activity data show that the metal complexes have antibacterial activity more than the parent Schiff base ligand and cefepime standard against one or more bacterial species.

Synthesis, spectroscopic characterization and antibacterial activity of new cobalt(II) complexes of unsymmetrical tetradentate (OSN 2) Schiff base ligands

Cobalt ion complexes with the Schiff bases, (4-X-2-{[2-(2-pyridine-2-yl-ethylsulfanyl)ethylimino]methyl}phenol (X = methoxy (OMe), phenylazo (N 2Ph), bromo (Br), nitro (NO 2)),were synthesized and investigated by several techniques using elemental analysis (C, H, N), FTIR, electronic spectra and molar conductivity. The thermal stability of free ligands and related cobalt complexes were studied by using differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). Cyclic voltammetry indicates that the investigated cobalt complexes, under the experimental conditions, have irreversible redox behavior. The synthesized compounds have antibacterial activity against the four Gram-positive bacteria: Streptococcus pyogenes, Streptococcus agalactiae, Staphylococcus aureus and Bacillus anthracis and also against the two Gram-negative bacteria: Klebsiella pneumoniae and Pseudomonas aeruginosa. The activity data show that the parent Schiff bases are more potent antibacterials than the cobalt complexes.

Spectroscopic study of molecular structures of novel Schiff base derived from o-phthaldehyde and 2-aminophenol and its coordination compounds together with their biological activity

New Schiff base (H 2L) ligand is prepared via condensation of o-phthaldehyde and 2-aminophenol. The metal complexes of Cr(III), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with the ligand are prepared in good yield from the reaction of the ligand with the corresponding metal salts. They are characterized based on elemental analyses, IR, solid reflectance, magnetic moment, electron spin resonance (ESR), molar conductance, 1H NMR and thermal analysis (TGA). From the elemental analyses data, the complexes are proposed to have the general formulae [M(L)(H 2O) n]· yH 2O (where M = Mn(II) ( n = 0, y = 1), Fe(II) ( n = y = 0), Co(II) ( n = 2, y = 0), Ni(II) ( n = y = 2), Cu(II) ( n = 0, y = 2) and Zn(II) ( n = y = 0), and [MCl(L)(H 2O)]· yH 2O (where M = Cr(III) and Fe(III), y = 1–2). The molar conductance data reveal that all the metal chelates are non-electrolytes. IR spectra show that H 2L is coordinated to the metal ions in a bi-negatively tetradentate manner with ONNO donor sites of the azomethine N and deprotonated phenolic-OH. This is supported by the 1H NMR and ESR data. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II) complexes), tetrahedral (Mn(II), Fe(II) and Zn(II) complexes) and square planar (Cu(II) complex). The thermal behaviour of these chelates is studied and the activation thermodynamic parameters, such as, E*, Δ H*, Δ S* and Δ G* are calculated from the DrTGA curves using Coats-Redfern method. The parent Schiff base and its eight metal complexes are assayed against two fungal and two bacterial species. With respect to antifungal activity, the parent Schiff base and four metal complexes inhibited the growth of the tested fungi at different rates. Ni(II) complex is the most inhibitory metal complex, followed by Cr(III) complex, parent Schiff base then Co(II) complex. With regard to bacteria, only two of the tested metal complexes (Mn(II) and Fe(II)) weakly inhibit the growth of the two tested bacteria.

A DFT study on the mono lithium and sodium salts of N-(2-hydroxyphenyl)salicylaldimine

This computational organic chemistry study presents results based on density functional theory at the B3LYP/6-31G(d) and B3LYP/cc-PVTZ//B3LYP/6-31G(d) levels of theory. Other computational procedures (HF and MP2) are presented for model structures. Three main points were investigated: some of the electronic structure aspects, the relative stability of isomers, and aromaticity. The results suggest that the title salts are the first Schiff base systems in the literature to exist only in the N–H form, which is characterized as the zwitterion form. Also, the estimated delocalization of the π-electron density in the middle ring indicates that these compounds are the first examples of metalla-hetero[10]annulenes. Analysis of the electron density delocalization indicates that the title compounds are better conductors at the molecular level than the parent Schiff base, and therefore, can be considered as new building blocks for organic materials.

Synthesis and anti-fungicidal activity of some transition metal complexes with benzimidazole dithiocarbamate ligand

Seven transition metal complexes of benzimidazole ligand (HL) are reported and characterized based on elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analyses (TGA and DTA). From the obtained data, the complexes were proposed to have the general formulae [MX 2(HL)(H 2O)]· yH 2O, where M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cr(III); X = Cl −, SO 4 2− and y = 0–4. The molar conductance data revealed that all the metal chelates were non-electrolytes. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes is octahedral. The thermal behaviour of these chelates showed that the hydrated complexes loss water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. Fungicidal activity of the prepared complexes and free ligand was evaluated against three soil borne fungi. Data obtained showed the higher biological activity of the prepared complexes than the parent Schiff base ligand. Formulation of the most potent complex was carried out in the form of 25% WP. Fungicidal activity of the new formulation was evaluated and compared with the standard fungicide Pencycuron (Monceren 25% WP). In most cases, the new formulation possessed higher fungicidal activity than the standard fungicide under the laboratory conditions.

Synthesis, characterization and biological activity of some platinum(II) complexes with Schiff bases derived from salicylaldehyde, 2-furaldehyde and phenylenediamine

Four platinum(II) complexes of Schiff bases derived from salicylaldehyde and 2-furaldehyde with o- and p-phenylenediamine were reported and characterized based on their elemental analyses, IR and UV–vis spectroscopy and thermal analyses (TGA). The complexes were found to have the general formula [Pt(L)(H 2O) 2]Cl 2· nH 2O (where n = 0 for complexes 1, 3, 4; n = 1 for complex 2. The data obtained show that Schiff bases were interacted with Pt(II) ions in the neutral form as a bidentate ligand and the oxygens rather than the nitrogens are the most probable coordination sites. Square planar geometrical structure with two coordinated water molecules were proposed for all complexes The free ligands, and their metal complexes were screened for their antimicrobial activities against the following bacterial species: E. coli, B. subtilis, P. aereuguinosa, S. aureus; fungus A. niger, A. fluves; and the yeasts C. albican, S. cervisiea. The activity data show that the platinum(II) complexes are more potent antimicrobials than the parent Schiff base ligands against one or more microorganisms.

Synthesis, characterization and biological activity of some transition metals with Schiff base derived from 2-thiophene carboxaldehyde and aminobenzoic acid

Metal complexes of Schiff base derived from 2-thiophene carboxaldehyde and 2-aminobenzoic acid (HL) are reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance and thermal analysis (TGA). The ligand dissociation as well as the metal–ligand stability constants were calculated pH metrically at 25 °C and ionic strength μ = 0.1 (1 M NaCl). The complexes are found to have the formulae [M(HL) 2](X) n · yH 2O (where M = Fe(III) (X = Cl, n = 3, y = 3), Co(II) (X = Cl, n = 2, y = 1.5), Ni(II) (X = Cl, n = 2, y = 1) and UO 2(II) (X = NO 3, n = 2, y = 0)) and [M(L) 2] (where M = Cu(II) (X = Cl) and Zn(II) (X = AcO)). The molar conductance data reveal that Fe(III) and Co(II), Ni(II) and UO 2(II) chelates are ionic in nature and are of the type 3:1 and 2:1 electrolytes, respectively, while Cu(II) and Zn(II) complexes are non-electrolytes. IR spectra show that HL is coordinated to the metal ions in a terdentate manner with ONS donor sites of the carboxylate O, azomethine N and thiophene S. From the magnetic and solid reflectance spectra, it is found that the geometrical structure of these complexes are octahedral. The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E *, Δ H *, Δ S * and Δ G * are calculated from the DrTG curves using Coats–Redfern method. The synthesized ligands, in comparison to their metal complexes also were screened for their antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data show that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.

Cobalt(II) salen complex with two aza‐crown pendants and its analogues as synthetic oxygen carriers

AbstractSalen with two aza‐crown ether pendants H2L1 and its analogues H2L2‐H2L4 were successfully synthesized starting from benzo‐10‐aza‐15crown‐5 (BN15C5) or morpholine. Their structures were characterized by IR, MS, 1H NMR and elemental analysis, and were confirmed by X‐ray diffraction analysis of H2L1. Moreover, the saturated oxygen uptake of their cobalt(II) complexes CoL1‐CoL4 in diethyleneglycol dimethyl ether was determined at different temperature. The oxygenation contants (KO2 ) and thermodynamic parameters (ΔH° and ΔS°) were calculated. The modulation of O2‐binding capabilities by pendant substituents were investigated as compared with the parent Schiff base complex CoL5 (CoSalen). The results indicate that the dioxygen affinities of CoL have been much more enhanced by aza‐crown pendants than that by morpholino pendants, and the O2‐binding capabilities of CoL1 and CoL2 with aza‐crown pendants would also be enhanced by adding alkali metal cations.

Deuterium isotope effects on 13C NMR chemical shifts of some α‐(2‐hydroxyaryl)‐N‐phenylnitrones (Schiff base N‐oxides)

AbstractThe deuterium isotope effect on the 13C NMR chemical shifts of some α‐2‐hydroxyaryl‐N‐phenylnitrones (Schiff base N‐oxides) was studied. The existence of an intramolecular hydrogen bond with the proton localized on the phenolic oxygen atom was evidenced. Exceptionally large isotope effects ΔC‐2(D) and ΔC‐α(D) suggest that the substitution of the proton of the OH group by deuterium leads to a weakening of the hydrogen bond and some conformational changes in the molecule. This conclusion was drawn on the basis of a comparison of the deuterium isotope effects of Schiff base N‐oxides and parent Schiff bases. Copyright © 2001 John Wiley & Sons, Ltd.