New acyclic Schiff-base copper(II) complexes and their electrochemical,catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) 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 copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800?nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around ?1.10 to ?1.60?V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ _eff?=?1.72–1.76?BM, close to the spin-only value of 1.73?BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.     

Synthesis, characterization, crystal structure and antimicrobial activities of new transN,N-substituted macrocyclic dioxocyclam and their copper(II) and nickel(II) complexes

New trans-disubstituted macrocyclic ligands, 1,8-[N,N-bis(3-formyl-12-hydroxy-5-methyl)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L¹), 1,8-[N,N-bis(3-formyl-12-hydroxy-5-bromo)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L²), N,N-bis[1,8-dibenzoyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L³), N,N-bis[1,8-(2-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L⁴), and N,N-bis[1,8-(4-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L⁵) were synthesized. The ligands were characterized by elemental analysis, FT IR, ¹H NMR and mass spectrometry studies. The crystal structure of L¹ is also reported. The copper(II) and nickel(II) complexes of these ligands were prepared and characterized by elemental analysis, FT IR, UV-Vis and mass spectral studies. The cyclic voltammogram of the complexes of ligand L^1-3 show one-electron quasi-reversible reduction wave in the region −0.65 to −1.13 V, whereas that of L⁴ and L⁵ show two quasi-reversible reduction peaks. Nickel(II) complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.95 to +1.06 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μ_eff 1.70-1.73 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.     

Synthesis,characterization, and antioxidant activities of three Cu(II) complexes with Schiff-base ligands

Cu(II) complexes of three bis(pyrrol-2-yl-methyleneamine) ligands were synthesized and characterized by elemental analyses, mass spectra, and IR spectra. X-ray diffraction analysis shows that [CuL³]₂ is a dinuclear complex with an extremely distorted square-planar geometry. Furthermore, the antioxidant activities of the compounds have been investigated. The electrochemical properties of the Cu(II) complexes have also been studied by cyclic voltammetry. The Cu(II) complexes show similar superoxide dismutase (SOD) activity compared with that of the native Cu, Zn-SOD.     

Synthesis,crystal structures and properties of five-coordinate Schiff-base Zn(II) complexes

Five-coordinate Schiff-base Zn complexes (1,2-cyclohexanediamino-N,N′-bis(salicylidene)) zinc-pyridine 1 and (1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)) zinc-pyridine 2 were synthesized and the structures of 1 and 2 have been determined by single-crystal X-ray analysis. All Zn atoms are five-coordinate in both structures. Both complexes exhibit interesting structures based on intermolecular π–π stacking and hydrogen bond interactions. Complex 1 has a one-dimensional molecular chain structure via π–π stacking interaction, while complex 2 has an interesting lattice structure (with cavities with dimensions 10.9?×?6.9?Å) formed through intermolecular π–π stacking and hydrogen bond interactions. 1 and 2 are compared and characterized by MS, elemental analysis, IR, UV-Vis and Photoluminescence (PL). Fluorescence spectra show that the maximal emission wavelength of 1 and 2 are 454?nm, and 480?nm, respectively, upon radiation by UV light. Cyclic voltammetry performed on 1 and 2 indicate a dependence of the cathodic potentials upon conformational and electronic effects. Electronic spectral properties of 1 and 2 were studied by TD-DFT methods. The fluorescent emission of these complexes originates from ligand-centred π–π? transitions. The Zn (II) centres play a key role in enhancing the fluorescent emission of the ligands.     

Synthesis,spectral characterization and antimicrobial activity of macrocyclic Schiff-base copper(II) complexes containing polycrystalline nanosized grains

Schiff-base copper(II) complexes were prepared using macrocyclic ligands, synthesized by condensation of diethylmalonate with Schiff bases derived from o-phenylenediamine and Knoevenagel condensed β-ketoanilides (obtained by the condensation of acetoacetanilide and substituted benzaldehydes). The ligands and their copper complexes were characterized by microanalytical, mass, UV–Vis, IR, ¹H-NMR, ESR and CV studies, as well as conductivity data. Microanalytical, mass and magnetic moment analyses are consistent with formation of monomeric [CuL]Cl₂. Spectral studies indicate square-planar geometry around copper. The smaller grain sizes found from XRD data suggest that these complexes are polycrystalline with nanosized grains. The SEM images of [CuL¹]Cl₂ have leaf-like morphology. The in vitro biological screening of the investigated compounds against the bacteria Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aeruginosa and Staphylococcus aureus and fungi Aspergillus niger, Rhizopus stolonifer, Aspergillus flavus, Rhizoctonia bataicola and Candida albicans were tested by the well diffusion method to assess growth inhibition. A comparative study of MIC values of the Schiff-base ligands and their complexes indicate that the complexes exhibit higher antimicrobial activity than the free ligands.     

Synthesis,spectral characterization,and antimicrobial activity of copper(II), cobalt(II), and nickel(II) complexes of 3-formylchromoniminopropylsilatrane

A new series of Cu(II), Ni(II), and Co(II) complexes have been synthesized from 3-formylchromoniminopropylsilatrane (C₁₉H₂₄O₅N₂Si) (2) and 3-formylchromoniminopropyltriethoxysilane (1). Silatrane ligand (C₁₉H₂₄O₅N₂Si) (2) has been synthesized by the reaction between 3-aminopropyltriethoxysilane and 3-formylchromone followed by a treatment with triethanolamine. The nature of bonding and the geometry of the complexes have been deduced from elemental analyses, magnetic susceptibility, infrared, electronic, ¹H NMR, ¹³C NMR, and ESR spectral studies. The electronic absorption spectra and magnetic susceptibility measurements of the complexes indicate square planar geometry for Cu(II) and Ni(II) and tetrahedral geometry for Co(II). The redox behavior of copper complexes was studied by cyclic voltammetry. The biological activity of the ligand and metal complexes has been studied on Klebsiella pneumoniae, Staphylococcus aureus, Escherichia Coli, and Bacillus subtilis by the well diffusion method using acetonitrile as solvent. The zone of inhibition values were measured at 37°C for 24 h. Antimicrobial screening tests show better results for the metal complexes than the ligand.     

Synthesis and characterization of manganese(II), nickel(II), copper(II) and zinc(II) Schiff-base complexes derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-mercaptoethylamine leads to 2,9-bis(2-ethanthiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with manganese, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptoethyl)-2-azaethene]-1,10-phenanthroline (L). The [M(L)Cl₂] complexes [where M = Mn(II), Ni(II), Cu(II) and Zn(II) ions] were characterized by physical and spectroscopic measurements which indicated that the ligand is a tetradentate N₄ chelating agent.     

Electrochemical, catalytic and antimicrobial activities of N-functionalized cyclam based unsymmetrical dicompartmental binuclear nickel(II) complexes

Five binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show red shift in the d–d transition. Electrochemical studies of the complexes show two irreversible one electron reduction processes in the range of 0 to −1.4 V. The reduction potential of the complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves in the range 0.4–1.6 V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 1.36 × 10⁻²–9.14 × 10⁻² min⁻¹. The rate constant values for the complexes containing aliphatic diimines are found to be higher than the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes show higher antimicrobial activity than the ligand and metal salt.     

Synthesis,spectral and antimicrobial studies of rare earth metal complexes with Schiff-base hydrazone containing quinoline moiety

The synthesis and characterization of lanthanide(III) complexes with the Schiff-base hydrazone, o-hydroxyacetophenone-7-chloro-4-quinoline, (HL) are reported. The complexes were characterized by different physicochemical methods: mass spectrometry, ¹H NMR, ¹³C NMR, and IR, UV-visible, molar conductance and magnetic studies. They have the stoichiometry [Ln(L)₂(NO₃)]·nH₂O where Ln = La(III), Pr(III), Nd(II), Sm(III), Eu(III) and n = 1–3. The spectra of the complexes were interpreted by comparison with the spectrum of the free ligand. The Schiff-base ligand and its metal complexes were tested against one stain Gram +ve bacteria (Staphylococcus aureus), Gram ?ve bacteria (Escherichia coli), and Fungi (Candida albicans). The tested compounds exhibited high antimicrobial activities     

Synthesis,Characterization and reactivities of Schiff-base complexes of Ruthenium(III)

Schiff-base complexes of ruthenium (1–5) have been synthesized using Schiff-base ligands derived by condensation of either 1,2-phenylenediamine with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) or acetylacetone with amines (2-aminophenol, 2-aminomethylpyridine). All complexes were characterized by analytical, spectroscopic, conductance, magnetic moment and electrochemical studies. At room temperature, complexes 1–5 catalyze the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive high valency Ru(V)-oxo species as the catalytic intermediate is proposed for the processes.     

Synthesis,spectroscopic, thermal,and antimicrobial studies of tetradentate 12 and 14 member Schiff bases and their complexes with Fe(III), Co(II), and Cu(II)

Two Schiff bases, L¹ (5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene) and L² (6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene), bearing functionalized pendant arms have been synthesized by cyclocondensation of 3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentanedione, respectively. Mononuclear macrocyclic complexes [FeL¹Cl₂]Cl, [FeL²Cl₂]Cl, [ML¹Cl₂], and [ML²Cl₂] (where M?=?Co(II) and Cu(II)) have been prepared by reacting iron(III), cobalt(II), and copper(II) with the preformed Schiff base. The ligands and their corresponding metal complexes were characterized by elemental analyses, ESI-mass spectra, conductivity, magnetic moments, UV-Vis, EPR, IR, ¹H-, and ¹³C-NMR spectral studies, and TGA-DTA/DSC data. The TGA profiles exhibit a two-step pyrolysis, although the iron complexes decompose in three steps, leaving behind metal oxides as the final product. The ligands and complexes were screened in vitro against Gram-positive bacteria, Gram-negative bacteria, and fungi.     

Synthesis,characterization, antimicrobial,and nuclease activity studies of some metal Schiff-base complexes

A Schiff base (L) is prepared by condensation of cuminaldehyde and L-histidine, and characterized by elemental analysis, IR, UV-Vis, ¹H-NMR, ¹³C-NMR, and mass spectra. Co(II), Ni(II), Cu(II), and Zn(II) complexes of this Schiff-base ligand are synthesized and characterized by elemental analysis, molar conductance, mass, IR, electronic spectra, magnetic moment, electron spin resonance (ESR), CV, TG/DTA, powder XRD, and SEM. The conductance data indicate that all the complexes are 1 : 1 electrolytes. IR data reveal that the Schiff base is a tridentate monobasic donor, coordinating through azomethine nitrogen, imidazole nitrogen, and carboxylato oxygen. The electronic spectral data and magnetic measurements suggest that Co(II) and Ni(II) complexes are tetrahedral, while Cu(II) complex has distorted square planar geometry. XRD and SEM show that Co(II), Cu(II), and Zn(II) complexes have crystalline nature, while the Ni(II) complex is amorphous and the particles are in nanocrystalline phase. The in vitro biological activities of the synthesized compounds were tested against the bacterial species, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus; and fungal species, Aspergillus niger, Aspergillus flavus, and Candida albicans by the disc diffusion method. The biological study indicates that complexes exhibit more activity than the ligand. The nuclease activity of the ligand and its complexes are assayed on CT DNA using gel electrophoresis in the presence and the absence of H₂O₂. The Cu(II) complex shows increased nuclease activity in the presence of an oxidant when compared to the ligand, Co(II) and Ni(II) complexes.     

Synthesis and structure of mononuclear copper(II) complexes with acyclic Schiff-base ligands containing organotellurium substituents: a comparative study with selenium analogs

Tellurium-bearing acyclic Schiff bases, 2,6-bis({N-[2-(phenyltellurato)ethyl]}benzimidoyl)-4-methylphenol (HL³ ) and 2,6-bis({N-[3-(phenyltellurato)propyl]}benzimidoyl)-4-methylphenol (HL⁴ ) of the Te₂N₂O type have been prepared by condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate phenyltellurato(alkyl)amine. HL³ and HL⁴ have been characterized by mass spectrometry, IR, electronic and ¹H-NMR spectroscopies and cyclic voltammetry. Their reactions with Cu(II) acetate monohydrate in a 2?:?1 molar ratio in methanol yield [(C₆H₂(O)(Me){(C₆H₅)C=N(CH₂)_nTe(C₆H₅)}{(C₆H₅)C=O})₂Cu] (3 (n?=?2), 4 (n?=?3)) as suggested by analytical and spectroscopic data and single crystal X-ray crystallography of 3. In both complexes, one arm of the ligand undergoes hydrolysis at the C=N position and two molecules of the partially hydrolyzed ligand coordinate to Cu(II) through imido nitrogen and the phenolic oxygen. The telluriums do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN₂O₂ core. Electrochemical studies of 3 and 4 indicate quasi-reversible reductions (E°′?=??1.113?V (3) and ?1.149?V (4)) corresponding to the reduction of copper(II) to copper(I). The interactions of 3 and 4 with calf thymus DNA, investigated by spectrophotometry and cyclic voltammetry, indicate that 3 and 4 bind to DNA via intercalation, and the binding affinity of 3 is lower than that of its selenium analog.     

Synthesis,characterization and biological activities of mononuclear and binuclear Fe(III) complexes with some symmetric and unsymmetric Schiff-base ligands

A series of mononuclear and binuclear Fe(III) complexes of some new symmetrical and unsymmetrical Schiff bases containing quinoline derivatives were synthesized and characterized by elemental and thermal analysis, conductance measurements and IR spectra. In mononuclear complexes, the unsymmetric Schiff bases are monobasic tetradentate towards the Fe(III) ion. However, in binuclear complexes, the symmetric Schiff-base ligands behave as monobasic bidentate towards each Fe(III) ion. The structure of the solid complexes are discussed and based on magnetic susceptibility measurements, electronic and ESR spectral studies. The biological activities of the ligands and their complexes are reported.     

Synthesis,structures, and characterization of copper(II), nickel(II), and cobalt(III) metal complexes derived from an asymmetric bidentate Schiff-base ligand

An asymmetric bidentate Schiff-base ligand (2-hydroxybenzyl-2-furylmethyl)imine (L–OH) was prepared. Three complexes derived from L–OH were synthesized by treating an ethanolic solution of the appropriate ligand with an equimolar amount of metallic salt. Three complexes, Cu₂(L–O^?)₂Cl₂ (1), Ni(L–O^?)₂ (2) and Co(L–O^?)₃ (3), have been structurally characterized through elemental analysis, IR, UV spectra and thermogravimetric analysis. Single crystal X-ray diffraction shows metal ions and ligands reacted with different proportions 1?:?1, 1?:?2 and 1?:?3, respectively, so copper(II), nickel(II), and cobalt(III) have different geometries.