Tetradentate Schiff Base Complexes Research Articles

Homodinuclear tetradentate Schiff base complexes of nickel(II), cadmium(II) and mercury(II): synthesis, photophysical and mesophase investigation

ABSTRACT Dinuclear Ni(II), Cd(II) and Hg(II) complexes have been prepared from photoluminescent salicylaldimine tetra-coordinated [N4O4] donor compartmental Schiff base ligand. The photophysical and mesogenic properties of the compounds are investigated. The compounds are characterized by elemental analyses, mass, 1HNMR, FT-IR and UV–visible spectroscopy. The complexes adopted distorted square planar geometry. The ligand and Ni complex exhibit monotropic thermal transition in DSC thermogram whereas Cd or Hg complexes are non-mesogenic. All the complexes displayed blue emission at ∼450 nm.

A novel Hercynite‐supported tetradentate Schiff base complex of manganese catalyzed one‐pot annulation reactions

The present study is the first report on the synthesis and catalytic performance of Hercynite nanoparticles capped with a novel Schiff base–manganese(II) complex brought from a synthetic procedure. The solid support and the catalyst were characterized using various analytical techniques. The characterization results suggest excellent dispersibility, stability, high Mn content under the catalyst surface, and small size of catalyst, which leads to excellent catalytic activity and selectivity. Moreover, the catalyst proved to be sustainable and recyclable for rapid synthesis of various chromene‐ and pyran‐annulated heterocycles under ambient conditions. The effect of various crucial catalytic parameters was investigated and optimized. The scope of the reaction was extended to various aryl aldehydes and keto–enol tautomeric pairs (2‐hydroxy‐1,4‐naphthoquinone or dimedone), and the corresponding 2‐amino‐3‐cyano‐4H‐chromene and 2‐amino‐3‐cyano‐4H‐pyran products were obtained with excellent yield (82–99%) and at low reaction time (10–115 min). Significantly, the catalyst indicated magnetic, cost‐effective, and nontoxic properties, which result in having high recycling efficiency (5 cycles).

Synthesis and Characterisation of Novel Tetra dentate Schiff base Complexes: Biological Evaluation Exploring Anticancer Activity towards MCF 7 Cell Breast Cancer lines with in vitro Docking Studies

A method to synthesize novel tetra dentate ligand and a new series of metal complexes comprising Co (II), Fe (II), Cu (II) and Zn (II) (1-4) were synthesized using 3,5-dichlorosalicylaldehyde and trans 1,2-di aminocyclohexane is described. The structural features and mode of bonding exhibited by Schiff base have been characterized by spectral methods like UV-Vis, FT-IR and ESI-MS. Schiff base ligand and (1-4) complexes displayed superior antibacterial towards both Gram positive and Gram negative bacteria. As well, the antioxidant studies reveal that significant free radical scavenging activity towards the free radical DPPH. Theoretical molecular docking studies to elucidate the interactions of synthesized compounds with biomolecules, a model illustrating specific DNA-binding of synthesized compounds and groove binding mode of DNA interaction was evolved. Cu(II) complex (3) with more pronounced biological activity (antibacterial and antioxidant) was subjected to Cytotoxicity studies against MCF-7 breast cancer cell lines through MMT assay. Cu (II) complex exhibited stronger anti-cancer activity in comparision to ligand in that way the synergistic effects of signifying Cu Schiff base complexes illustrating the higher inhibiting efficiency of 77.2% at 320µg/mL. The proposed study, therefore discloses potentiality of the synthesized new Schiff base derived complexes as a prodrug for cancer treatment.

Synthesis, spectral characterization and antibacterial activity of transition metal (II) complexes of tetradentate Schiff base ligand

Nickel, zinc and cadmium complexes of a Schiff base derived from 4-nitro-o-phenylenediamine and 5-methoxysalicylaldehyde were synthesized and characterized using infrared, ultra violet, molar conductance measurements and nuclear magnetic resonance spectroscopy. Tetradentate schiff base complexes are widely used for the industrial purpose and also exhibit the wide range of biological activities. Hence the antibacterial activity of the Schiff base ligand and the metal complexes against some clinically important bacteria namely Escherichia coli, Proteus mirabilis, Streptococcus pneumoniae, Bacillus subtilis were investigated and the obtained results have shown that the complexes were possesses more antibacterial activity than the parent Schiff base ligand and hence could be potentially used in the preparation of anti bacterial agents.

Synthesis, Characterization, and In Vitro Cytotoxicity of Unsymmetrical Tetradentate Schiff Base Cu(II) and Fe(III) Complexes.

Unsymmetrical tetradentate Schiff base Fe(III) and Cu(II) complexes were prepared by the coordination of some unsymmetrical tetradentate Schiff base ligands with CuCl2·2H2O or FeCl3·6H2O. The obtained complexes were characterized by ESI-MS, IR, and UV-Vis. The spectroscopic data with typical signals are in agreement with the suggested molecular formulae of the complexes. Their cyclic voltammetric studies in acetonitrile solutions showed that the Cu(II)/Cu(I) and Fe(III)/Fe(II) reduction processes are at (−)1.882–(−) 1.782 V and at (−) 1.317–(−) 1.164 V, respectively. The in vitro cytotoxicity of obtained complexes was screened for KB and Hep-G2 human cancer cell lines. The results showed that almost unsymmetrical tetradentate Schiff base complexes have good cytotoxicity. The synthetic complexes bearing the unsymmetrical tetradentate Schiff base ligands with different substituted groups in the salicyl ring indicate different cytotoxicity. The obtained Fe(III) complexes are more cytotoxic than Cu(II) complexes and relative unsymmetric Schiff base ligands.

Synthesis, characterization, thermal stability, electrochemical behavior, and antioxidant activity of new oxovanadium(iv) and iron(ii) tetradentate Schiff base complexes

Two new tetradentate oxovanadium(IV) and iron(II) Schiff base complexes have been prepared by the interaction of vanadyl(IV) and iron(III) acetylacetonate with the ligand obtained from the reaction of ethylenediamine and 5′-(N-methyl-N-phenylaminomethyl)-2′-hydroxyacetophenone in methanol. These complexes have been characterized by means of different spectroscopic techniques such as UV–visible, FT-IR, mass spectrometry, and elemental analysis. In addition, thermogravimetric (TG) and differential thermogavemetric analysis (DTG) have been utilized to investigate the thermal stability of these complexes. Results showed that both Schiff base complexes decompose in five consecutive stages, and a mechanism has been proposed for each stage of thermal decomposition. Thermogravimetric analysis has been carried out using four different heating rates of 5, 10, 15, and 20 °C min−1, and the kinetic parameters of these complexes have been calculated using the Kissinger method. Cyclic voltammetry has been employed to examine the electrochemical behavior of the two synthesized complexes in dimethyl sulfoxide (DMSO) at a glassy carbon electrode. Each of these complexes displayed one quasi-reversible single electron transfer peak near 0.255 V vs. saturated calomel electrode (SCE) for the V(V)–V(IV) couple and near −0.690 V vs. SCE for the Fe(III)–Fe(II) redox couples, respectively. Finally, the antioxidant activity of the newly prepared complexes has been investigated using the 2,2-diphenyl-1-picrylhydrazyle (DPPH) free radical scavenging assay. Results revealed that the oxovanadium Schiff base complex exhibits good antioxidant activity.

Spectral characterization of tetradentate Schiff base complexes of N2O2 donor groups

Copper(II) complexes of tetra dentate Schiff bases N, N’ – disalicylidene – 1, 2 – phenylenediamine(H2dsp), N, N’ – disalicylidene – 3, 4 – diaminotoluene(H2dst), 4 – nitro - N, N’ – disalicylidene – 1, 2 – phenylenediamine(H2ndsp), N, N’ – disalicylideneethylenediamine(H2salen) have been synthesized and characterized by elemental analysis, electronic spectra, IR spectra, magnetic susceptibility measurement, EPR, CV and thermal studies. TG studies show that Cu(dsp) and Cu(ndsp) complexes thermally degrade in two steps and Cu(dst) and Cu(salen) in one step. Kinetic and thermodynamic parameters were computed from thermal decomposition data. The activation energies of both the thermal degradation step lie in between 52 – 74 kJ/mol .

Tetradentate Schiff Base Complexes of Transition Metals for Antimicrobial Activity

Synthesis of tetradentate Schiff base (SB) complexes of Cu(II), Co(II), and Ni(II) was done by the condensation of 2-aminophenol/o-phenylenediamine and terepthaldehyde in an alcohol medium, and the complexes were characterized by utilizing FTIR, LCMS, and UV–visible analysis. From the analytical, electronic, and magnetic data, octahedral geometry has been proposed for all the complexes. The antibacterial studies were studied for the SB ligands and their complexes against Bacillus subtilis 2393, Proteus vulgaris 426, Klebsiella sp., S. aureus 3160, and Escherichia coli 4604. Their antifungal activities were studied against Aspergilus flavus, Aspergillus niger, Cryptococcus neoformans, and Penicillium chrysogenum. The outcomes revealed that the transition metal complexes revealed good antibacterial and antifungal activities.

Tailored synthesis of unsymmetrical tetradentate ONNO schiff base complexes of Fe(IIl), Co(II) and Ni(II): Spectroscopic characterization, DFT optimization, oxygen-binding study, antibacterial and anticorrosion activity

Abstract Two Schiff base ligands namely bis-2-((1E)-((Z)-2-(1,2-diphenylethylideneamino) phenylimino)methyl)phenol (L1) and bis-2-((1E)-((E)-2-(1-phenylethylideneamino)phenylimino) methyl)phenol (L2) were synthesized by tailored reaction of o-phenylenediamine with o-hydroxybenzaldehyde and 2-hydroxy-1,2-diphenylethanone/o-hydroxyacetophenone. The reaction of these ligands with Fe(III), Co(II), and Ni(II) salts yielded six complexes. Ligands and their metal derivatives have been characterized by elemental analysis, molar conductance, magnetic susceptibility, FT-IR, UV–Vis, ESI-mass, 1H NMR, 13C NMR and EPR analysis. Using Gaussian 09 molecular modelling, bond lengths, bond angles and Mulliken charge were also evaluated. In addition to this study of HOMO and LUMO molecular orbital have been performed. The FT-IR spectra have suggested that ligand is coordinated with metal through azomethine-N and phenolic-O. Experimental and theoretical IR and NMR spectrum of ligand L1 and complex 2 exhibits quite good correlation. ESR spectrum of complex 2 at LNT suggests octahedral geometry around Co(II). Complexes were studied for their oxygen-binding activity and displayed significant oxygenation reaction. The thermodynamic parameters such were also calculated. The compounds were screened for antibacterial activity against gram-negative bacteria Escherichia coli and compared with Amoxicillin. Complexes have exhibited significant antibacterial activity. The corrosion inhibition effect of ligands and complexes on mild steel in acidic medium was studied for 24, 48 and 72 h using weight loss measurement.

Schiff base complexes of Mo(VI) immobilized on functionalized graphene oxide nano-sheets for the catalytic epoxidation of alkenes

Mo(VI) tetradentate Schiff base complexes were covalently immobilized onto chemically functionalized graphene oxide (GO) using 3-(tri-methoxysilyl) propylamine as a coupler. The resulting heterogeneous catalysts have been characterized by FTIR, DRS, XRD, SEM, TGA, and atomic absorption spectroscopy (AAS). These catalysts were applied in epoxidation of cyclooctene and other olefins. The catalytic procedures with all catalysts were optimized for different parameters such as oxidant, solvent and temperature. Recycling results indicated that the catalysts were highly stable and maintained activity and selectivity even after being used for five cycles.

Polyethyleneimine Nanofibers Functionalized with Tetradentate Schiff Base Complexes of Dioxomolybdenum(VI) as Efficient Catalysts for Epoxidation of Alkenes

AbstractThree tetradentate Schiff base ligands (H2L1‐3) were prepared from the reaction of 5‐sustituted‐2‐hydroxybenzaldehydes and 3,4‐diaminobenzoic acid. The obtained ligands were reacted with molybdenyl acetylacetonate in ethanol to prepare the corresponding dioxomolybdenum(VI) complexes (MoO2L1‐3) in good yields (80‐82%). Immobilization of the abovementioned complexes on polyethyleneimine (PEI) was achieved via condensation of carboxylic functional groups of the complex with amine functional groups of the polymer in presence of dicyclohexylcarbodiimide (DCC) and 4‐dimethylaminopyridine (DMAP). The obtained hybrid materials were then converted to electrospun nanofibers and used as recyclable catalysts for the epoxidation of alkenes.

Spectrochemical Properties and Solvatochromism of Tetradentate Schiff Base Complex with Nickel: Calculations and Experiments.

Invited for this month's cover picture is Dr. Agnieszka Gonciarz and her team. The team′s cooperation began recently when they met at the Military University of Land Forces (MULF) in Wrocław (Poland). Previously, each team member had various experience, in which chemistry played a major role. Dr. A. Gonciarz conducted spectroscopic research on coordination compounds, Prof. J. Zwoździak is a well‐known expert in the field of environmental protection, and Prof. M. Żuber is an expert in the application of chemistry in security sciences. When they met at MULF, the idea of cooperation arose and their research interest was directed toward the possibility of practical application of Schiff bases and their complexes in various areas. Read the full text of their Full Paper at https://doi.org/10.1002/open.201800100.

Spectrochemical Properties and Solvatochromism of Tetradentate Schiff Base Complex with Nickel: Calculations and Experiments.

The nickel(II) complex with a tetradentate Schiff base ligand obtained by condensation of 1,3‐propanediamine with salicylaldehyde (H2salpn) was studied in a variety of solvents at room temperature. The product, that is, the N′,N′′‐propylenebis(salicylaldiminato)nickel(II) ([Ni(salpn)]) complex, is brown in color in the solid state. The properties of the ligand and complex were characterized by elemental analysis, solubility in common solvents, molar conductivities, and ultraviolet (UV) and visible (Vis) spectroscopy. The [Ni(salpn)] complex is easily soluble in common solvents such as chloroform, methanol, ethanol, dimethyl formamide, dimethyl sulfoxide, acetonitrile, dioxane, acetone, 2‐propanol, and toluene—a necessary condition for observing solvatochromism. The molar conductivity values, equal to 0.0 S mol‐1 cm2 in these solvents, point to a typical non‐electrolyte behavior for this complex. Spectroscopic measurements were used to confirm the square‐planar geometry of the species in solution and to determine the coordination properties of the donor atoms and their bonding abilities (CFM/AOM parameters), as well as trichromaticity coordinate calculations. The results obtained show that the interactions of the metal with the donors depend on the polarity of the solvent.

Synthesis of tetradentate metal Schiff base complexes towards the synthesis of novel antimicrobials

Schiff bases are molecules that carry a characteristic imine bond that are derived from carbonyl compounds and are widely studied due to the versatility of their steric and electronic properties. Schiff bases are significant because of their biologically active properties that can improve and develop agrochemicals, anti‐inflammatories, antivirals, and even radiopharmaceuticals for cancer targeting. This study is focused on synthesizing a family of novel metal Schiff base complexes that have potential to act as antimicrobials over a wide range of pathogenic species.In a previous study, a family of metal Schiff base complexes with an NN'NN coordination sphere was synthesized. This study found that antimicrobial activity using Schiff base complexes with chromium, iron, or manganese as their center showed greater inhibition of Aspergillus sp. growth than a variety of known antimicrobial drugs (Kumar et al., 2012). In an attempt to expand the antimicrobial potential of these compounds, we changed the structure of these Schiff base ligands to utilize an NN'OS coordination sphere with the same set of metal centers. We hypothesized that the chemical activity of the sulfur atom would provide an improved range of antimicrobial function.Our synthesis of NN'OS coordination sphere‐based antimicrobials began with the compound cyclopentanone. Cyclopentanone was condensed with carbon disulfide, recrystallized, protonated, and methylated with dimethyl sulfate. The resultant methylated product was aminated with two different diamines to form a set of novel primary amines. These primary amines were reacted with salicylaldehydes with different substitutions to form a family of Schiff base ligands. The last step in the synthesis process was to add a transition metal to the Schiff base ligands (chromium, iron, or manganese) through a reflux reaction. After synthesis, each metal Schiff base complex was characterized through 1H and 13C nuclear magnetic resonance, infrared, and gas chromatography‐mass spectroscopy.With synthesis complete, current work focuses on the examination of these compounds as effective antimicrobials. The compounds are being tested for these properties against Aspergillus furmigatus as a representative of a broad range of Aspergillus species. Characterized Schiff base complexes are being compared for their level of antimicrobial activity against that shown by Miconazole, an established antimicrobial used to treat an array of fungal infections. The results of these tests may establish Schiff base ligands with NN'OS coordination spheres as a novel effective means of treating an array of dangerous microbial infections.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

X-ray crystallography, electrochemistry, spectral and thermal analysis of some tetradentate schiff base complexes and formation constant measurements

ABSTRACTA series of new transition metal Schiff base complexes was synthesized via the reaction of H2L (N,N′-bis(naphthylidene)-2-aminobenzylamine) with the transition metals (Cu2+, Co2+, Ni2+, Zn2+ and Mn2+) and characterized by elemental analysis, 1HNMR, FT-IR, UV-Vis spectroscopy, thermogravimetric analysis(TG) and in selected cases by X-ray crystallography. Thermodynamics of complex formation, electrochemistry of the metal Schiff base complexes and kinetic aspects of thermal decomposition of the complexes were also studied. The obtained formation constants change according to the following trend due to the electronegativity and Jahn-Teller effects of the central transition metals: Cu > Co > Ni > Zn >Mn. Cyclic voltammogram of the complexes in acetonitrile was done to evaluate the redox behavior of the complexes. Electrochemistry of these complexes showed a redox reaction without any successive reactions. Furthermore, kinetic parameters which calculated by Coats–Redfern equation revealed a first-order kinetics of thermal decomposition in all stages.

Crystal structure, theoretical and experimental electronic structure and DNA/BSA protein interactions of nickel(II) N2O2 tetradentate Schiff base complexes

Nickel(II) allyl arm Schiff base complexes ([NiL1] and [NiL2]) were synthesized and characterized by elemental analysis and ESI-MS, FT-IR, UV–Vis and 1H NMR spectral techniques. The structure of [NiL1] and [NiL2] were analyzed by single crystal X-ray crystallography reveal nickel complexes have slightly distorted square planar geometry around the metal ions. DFT calculations for [NiL1] and [NiL2] in gas phase were performed using SDD basis set for nickel atom and 6-311G(d,p) basis set for the remaining atoms and also at PW91/TZ2P/ZORA level. The electronic transitions of the complexes in acetonitrile were studied by TD-DFT calculations. The energy decomposition analysis was performed to understand the nature of bonding between Ni(II) and Schiff bases (H2L1 and H2L2) suggests that more covalent nature of bonding is in metal complexes. Hypochromism in absorption spectra, emission intensity decrease in EB-DNA complex and DNA viscosity increase by the addition of increasing concentration of the metal complex indicate intercalative mode of binding of the complex with DNA. The binding constants calculated are of the order of 105M−1. The BSA protein binding behavior with [NiL1] and [NiL2] were investigated using absorption and fluorescence titration experiments show alteration in protein’s microenvironment. Also, molecular docking studies were performed to understand the DNA-complex interactions.

Cis-dioxo-Mo(VI) salophen complex supported on Fe3O4@SiO2 nanoparticles as an efficient magnetically separable and reusable nanocatalyst for selective epoxidation of olefins

In this work, paramagnetic Fe3O4/SiO2 nanoparticles were synthesized, characterized and functionalized with dioxo-Mo(VI) tetradentate Schiff base complex and characterized using IR spectroscopy, X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, diffuse reflectance spectroscopy and atomic absorption spectroscopy. Catalyst was used for the selective epoxidation of cyclooctene, cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilbene using tert-butyl hydroperoxide as oxidant in 1,2-dichloroethane. This catalyst is efficient for oxidation of cyclooctene with a 100% selectivity for epoxidation with 100% conversion in 1 h. After the reaction, the magnetic nanocatalyst was easily separated by simply applying an external magnetic field and was used at least five successive times without significant decrease in conversion.

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe3O4 nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans‐1,2‐diphenylethene) and terminal alkenes (n‐heptene, n‐octene, n‐dodecene and styrene) using tert‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h−1 in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.

Epoxidation of alkenes by an oxidovanadium(IV) tetradentate Schiff base complex as an efficient catalyst with tert-butyl hydroperoxide

A new asymmetrical tetradentate N2O2 Schiff base ligand was synthesized from 2-hydroxyacetophenon, 2-hydroxynaphthaldehyde and 1,2 phenylenediimine. The new oxidovanadium(IV) Schiff base complex, VIVOL (L=N-2-hydroxyacetophenon-N′-2-hydroxynaphthaldehyde-1,2 phenylenediimine), was prepared by reaction of Schiff base ligand with vanadyl acetylacetonate. The Schiff base ligand (L) and the oxidovanadium(IV) complex were characterized by spectroscopic methods. The crystal structure of the complex was determined by the single crystal X-ray analysis. The complex crystallized in the orthorhombic system, having one V4+ ion coordinating in an approximately square pyramidal N2O3 geometry by two azomethine N atoms and phenolic oxygens from Schiff base ligand in a square plane and one oxygen atom in an apical position. Electrochemical properties of the complex were examined by means of cyclic voltammetry. The catalytic activity of the oxidovanadium(IV) Schiff base complex was tested in the epoxidation of cyclooctene.

Development of the catalytic reactivity of an oxo–peroxo Mo(vi) Schiff base complex supported on supermagnetic nanoparticles as a reusable green nanocatalyst for selective epoxidation of olefins

A novel ancillary branch coated oxo–peroxo Mo(vi)tetradentate Schiff base complex on superparamagnetic nanoparticles as an epoxidation catalyst.