Unsymmetrical Tetradentate Schiff Base Research Articles

Ruthenium(III) unsymmetrical Schiff base complex supported on γ-Fe2O3 magnetic nanoparticles: A new heterogeneous nanocatalyst for efficient oxidation of hydrocarbons with tert-butyl hydroperoxide

In the present work, an unsymmetrical salen-type ruthenium(III) complex, Ru(salenac)Cl, where the unsymmetrical tetradentate Schiff base H2salenac = salicylideneiminoethyliminopentane-2-one, was synthesized and anchored on the surface of aminopropyl-functionalized silica-coated γ-Fe2O3 magnetic nanoparticles. The characterization of the resulting γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanoparticles was performed using XRD, FT-IR, VSM, TGA, ICP, TEM, BET, SEM and EDX methods. The prepared γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl magnetic nanoparticle was successfully employed as an efficient heterogeneous nanocatalyst for alkenes epoxidation and alkanes oxidation with tert-butyl hydroperoxide (tert-BuOOH, 70 % aqueous solution) as oxidant in acetonitrile at ambient temperature. In the mentioned catalytic system, the intended products were obtained with good to excellent yields along with high selectivity. The heterogeneous γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst can be recovered easily using an external magnet and recycled six times with no notable decrease in catalytic activity. Moreover, FT-IR, XRD, SEM and EDX techniques were used to characterize the recovered γ-Fe2O3@SiO2@APTES@Ru(salenac)Cl nanocatalyst and it was demonstrated that the catalyst maintained its structure intact following the recovery process.

Synthesis and characterization of Co (II), Ni (II) and Cu (II) complexes with unsymmetrical tetradentate Schiff base ligand

A novel series of cobalt (II), nickel (II) and copper (II) complexes of unsymmetrical Schiff base ligand 1-(2-hydroxynaphthalideneimino)-2-(5 methoxysalicylidene imino)-4 chlorobenzene-1,2-diamine was synthesised by condensation reaction of 1:1:1 molar ratio of 2-hydroxynaphthalene-1-carbaldehyde, 4-chlorobenzene -1,2-diamine and 5-methoxysalicyidehyde in alcoholic medium. The synthesised ligand and its metal complexes were characterised by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, UV-Vis and infrared spectral data. The molar conductance of synthesised metal complexes in DMSO solution indicates their non-electrolytic nature. The analytical data show the general formula for the complexes to be [M(L)2] where L = Schiff base ligand and M = Co (II), Ni (II) and Cu (II). The spectral data and magnetic moment suggested that Schiff base behaves as a tetradentate ligand, coordinating through azomethine nitrogen and phenolic oxygen atoms to the metal ion. Magnetic susceptibility measurements, UV-Vis and infrared spectral data geometry of metal complexes were proposed to be square planar.

Oxovanadium and copper complexes of new unsymmetrically tetradentate ligands: X- ray structure, theoretical and NLO properties, catalytic oxidation and bromoperoxidase activities

A series of mononuclear oxovanadium VOLBz, VOLT and copper CuLBz, CuLT complexes containing unsymmetrical tetradentate Schiff base ligands were synthesized and fully characterized by conventional spectroscopic techniques such as FT-IR, UV–vis, 1HNMR and mass spectrometry (MS). Crystal structure data of CuLT, solved by X-ray diffraction, shows a monoclinic system with Cc space group and Z = 4 molecules per unit cell. The central copper ion adopts a nearly ideal square planar coordination geometry. Cyclic voltammetry of oxovanadium and copper complexes revealed quasi reversible redox couples corresponding to VOIV/VOV and CuI/CuII redox processes, respectively. The quantum calculations, performed by DFT and TD-DFT theory at the M062X/6-311**G/SDD level, agree well with the experimental data. The results show that the copper and the oxovanadium compounds have larger static and dynamic hyperpolarizability values than the urea. For instance, the β0 value of H2LT is about 68 times larger than that of the urea. The results predict that the studied compounds have the ability to be excellent second and third-order NLO materials. The prepared complexes catalyzed effectively homogeneous oxidation reaction of cyclohexene in the presence of H2O2 as oxidant. Higher conversion of 98% is attained using CuLBz as catalyst. The bromoperoxidase activity is explored in the oxidative bromination of phenol red as a trap employing the studied complexes which can be considered as potential functional models of bromoperoxidase, CuLBz catalyst exhibits the better catalytic activity, the reaction rate constant k is equal to 2.203×105 (mol L-1)-2s-1.

Spectroscopic investigation, molecular structure, catalytic activity with computational studies of a novel Pd(II) complex incorporating unsymmetrical tetradentate Schiff base ligand

The treatment of an unsymmetrical tetradentate Schiff base ligand with Pd(OAc)2 salt yields novel palladium(II) Schiff base complex. The generated palladium(II) complex was characterized using elemental analysis (CHN) and different spectroscopic methods such as FT-IR and 1H NMR. Single crystal X-ray diffraction (SC-XRD) investigation has also been used to examine the crystal structure of the palladium complex. It is revealed from the SC-XRD study that the palladium ion in the complex is tetra-coordinated, inhabited by ONNO donor sites of the chelated ligand in a distorted square planar manner. The non-covalent interactions were explored by Hirshfeld surface analysis. The theoretical parameters calculated by DFT using the B3LYP/Def2-TZVP level of theory revealed that the theoretical conclusions matched the actual findings. For different aryl halides, the palladium(II) complex has exhibited excellent efficiency in the Suzuki-Miyaura cross-coupling reactions (SMCR), yielding biaryls in good to high yield.

Unsymmetrical Ni(II) Schiff base complex: Synthesis, spectral characterization, crystal structure analysis, Hirshfeld surface investigation, theoretical studies, and antibacterial activity

A new nickel(II) complex (NiLUns) is synthesized by the reaction of unsymmetrical tetradentate salophen-based Schiff base (H2LUns) with Ni(CH3COO)2.4H2O. The different techniques, like elemental analysis (C, H, and N), FT-IR, UV-Vis, and NMR (1H & 13C), were used for structural elucidation of the H2LUns and NiLUns complex. The crystal structure of the nickel complex was studied in detail with the help of the X-ray diffraction technique. It was revealed from the diffraction data that the ligand chelates the Ni(II) ion by using its ONNO set of donor sites and forms a square planar geometry. The different types of strong as well as weak intermolecular interactions were explored with the help of Hirshfeld surface investigation. The theoretical parameters of the optimized structures were calculated by the DFT employing the B3LYP/Def2-TZVP level of theory. Furthermore, the synthesized NiLUns complex was screened against four different bacterial strains to evaluate its biocidal potential, which revealed that metal chelate is slightly more active than the free ligand. The synthesized NiLUns complex is novel concerning its spectroscopic analysis, diffraction studies, theoretical investigation, and antibacterial screening.

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.

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.

Preparation and Characterization of Co(II), Ni(II),Cu(II) and Zn(II) Complexes with Unsymmetrical Tetradentate Schiff Bases Ligands

Preparation and Characterization of Co(II), Ni(II),Cu(II) and Zn(II) Complexes with Unsymmetrical Tetradentate Schiff Bases Ligands

Synthesis, Characterization and Antibacterial Activities of New Metal Complexes of Unsymmetrical Tetradentate Schiff Bases

Synthesis, Characterization and Antibacterial Activities of New Metal Complexes of Unsymmetrical Tetradentate Schiff Bases

Syntheses, structures and electrochemical properties of ruthenium(II/III) complexes with tetradentate Schiff base ligands

Three unsymmetrical tetradentate Schiff base ligands, H2salipn, H2salipn-Br4 and H2salipn-Cl2, have been synthesized from the typical condensation reactions of treating 1,2-diaminopropane with salicylaldehyde, 3,5-dibromosalicylaldehyde and 5-chlorosalicylaldehyde, respectively. Treatment of [RuCl2(PPh3)3] with one equivalent of H2salipn or H2salipn-Br4 in the presence of triethylamine in tetrahydrofuran (THF) afforded the corresponding ruthenium(III) complexes [RuIIICl(PPh3)(salipn)] (1) and [RuIIICl(PPh3)(salipn-Br4)] (2). Interaction of [RuHCl(CO)(PPh3)3] with one equivalent of H2salipn-Cl2 or H2salipn-Br4 under the same conditions led to isolation of ruthenium(II) complexes [RuII(CO)(PPh3)(salalipn-Cl2)] (3) and [RuII(CO)(PPh3)(salalipn-Br4)] (4), respectively, in which one of the imine bonds was nucleophilically attacked by hydride to result in the formation of a mixed imine-amine ligand. The molecular structures of 1⋅1.5CH2Cl2, 2, 3⋅0.5CH2Cl2 and 4 have been determined by single-crystal X-ray crystallography. The electrochemical properties of 1–4 were also investigated. Their cyclic voltammograms displayed quasi-reversible Ru(IV)/Ru(III) and Ru(III)/Ru(II) couples with Eo ranging from 0.67 to 1.05 V and 0.74 to 0.80 V vs. Ag/AgCl (0.1 M), respectively.

Cobalt (II) complex with novel unsymmetrical tetradentate Schiff base (ON) ligand: in vitro cytotoxicity studies of complex, interaction with DNA/protein, molecular docking studies, and antibacterial activity

[C20H17N3O2] and cobalt (II) complex [Co(L2)(MeOH)2].ClO4, (L2 = 4-((E)-1-((2-(((E)-pyridin-2-ylmethylene) amino) phenyl) imino) ethyl) benzene-1, 3-diol) novel Schiff base has been synthesiszed and chracterized by Fourier transform infrared, UV–vis, 1H-NMR spectroscopy, and elemental analysis techniques. The interaction of Co(II) complex with DNA and BSA was investigated by electronic absorption spectroscopy, fluorescence spectroscopy, circular dichroism, and thermal denaturation studies. Our experiments indicate that this complex could strongly bind to CT-DNA via minor groove mechanism. In addition, fluorescence spectrometry of BSA with the complex showed that the fluorescence quenching mechanism of BSA was of static type. The complex exhibited significant in vitro cytotoxicity against three human cancer cell lines (JURKAT, SKOV3, and U87). The molecular docking experiment effectively proved the binding of complex to DNA and BSA. Finally, antibacterial assay over gram-positive and gram-negative pathogenic bacterial strains was studied.

Synthesis, Characterization, Spectral Studies, Antibacterial Evaluation, Thermodynamics and DFT Calculations of Dimethyltin(IV) Dichloride Schiff Base.

A number of new 1:1 complexes of SnMe(2)Cl(2) with unsymmetrical tetradentate Schiff base ligand with NNOS coordination sphere have been synthesized and fully characterized by a variety of physico-chemical techniques viz. elemental analysis, molar conductivity, (1)H and (119)Sn NMR, IR and mass spectroscopy. IR spectral data show that the fifth coordination position of tin atom is occupied by an oxygen atom of Schiff base ligands. In the light of titled techniques, trigonal bipyramidal geometry around the tin atom is proposed for the synthesized complexes. The in vitro antibacterial activities of the complexes against Staphylococcus aureus and Escherichia Coli have been studied. It was found that they possess significant antibacterial activity. Also, DFT/B3LYP method was used to analyze the electronic structures and study of the geometries. The thermodynamic formation constants of the complexes were determined spectrophotometrically at 25ºC in DMF solvent.

Synthesis, characterization, electrical and catalytic studies of some coordination compounds derived from unsymmetrical Schiff base ligand

New unsymmetrical tetradentate Schiff base ligand derived from 5-chloro-2-hydroxyacetophenone, 2-hydroxy-5-methyl-3-nitro acetophenone and carbohydrazide and its complexes with VO(IV), Cr(III), Mn(III), Fe(III), MoO2(VI), WO2(VI), Zr(IV) and UO2(VI) have been prepared. They were characterized by elemental analysis, IR and electronic spectra, magnetic susceptibility measurements and thermal analyses. The Schiff base ligand has also been characterised by 1H-NMR spectroscopy. The thermal behaviour of metal complexes shows that the hydrated complexes lose water molecules of hydration in the first and then is immediately followed by decomposition of ligand molecule in the subsequent steps. The IR spectra suggest that ligand acts as dibasic tetradentate nature and coordination takes place through azomethine nitrogen and phenolate oxygen. The crystalline nature of the VO(IV) complex was conformed through the powder XRD analysis. The catalytic activity of the VO(IV) and Mn(III) complexes have been tested in the epoxidation reaction of styrene and conversion of styrene were 11.14-24.35% and 9.64-23.42%, respectively. The solid state electrical conductivity of ligand and its complexes were measured, which could obeyed the relation s = s0 exp (Ea/KT) over the temperature range 313-413 K. KEY WORDS: Schiff base, Metal complexes, TGA, Electrical conductivity, XRD, Oxidation of styrene Bull. Chem. Soc. Ethiop. 2015, 29(3), 387-397. DOI: http://dx.doi.org/10.4314/bcse.v29i3.6

Template synthesis, and X-ray crystal structures of copper(II) and nickel(II) complexes of new unsymmetrical tetradentate Schiff base ligands. Electrochemistry, antibacterial properties, and metal ion effect on hydrolysis–recondensation of the ligand

Two metal complexes, [CuII(naphsal)] (1), and [NiII(salnaph)] (2), of two new unsymmetrical tetradentate Schiff base ligands, H2naphsal {H2naphsal=N-naphthylidene-N′-salicylidene-2-aminobenzylamine} and H2salnaph {H2salnaph=N-salicylidene-N′-naphthylidene-2-aminobenzylamine} have been synthesized by metal template reaction of a tridentate Schiff base, Hnaphtabza {Hnaphtabza=N-(naphthylidene)-2-aminobenzylamine} and salicylaldehyde in the presence of the corresponding metal acetate. The dianionic naphsal2− ligand, produced in the presence of Cu(II), is a simple template condensation product, while the dianionic salnaph2− ligand, produced in the presence of Ni(II), is the hydrolytically rearranged isomer of naphsal2−. The copper(II) and nickel(II) complexes have been fully characterized and their crystal structures have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry. The cyclic voltammetric studies of 1 and 2 in acetonitrile solution showed that the CuII/CuI and NiII/NiI reduction processes are electrochemically reversible. The metal complexes were also screened for their in vitro antimicrobial activity.

Synthetic, Characterization, Biological, Electrical and Catalytic Studies of Some Transition Metal Complexes of Unsymmetrical Quadridentate Schiff Base Ligand

Unsymmetrical tetradentate Schiff base N-(2-hydroxy-5-methylacetophenone)-N'-(2-hydroxy acetophenone) ethylene diamine (H₂L) and its complexes with Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, IR, electronic spectra and thermogravimetric analyses. ¹H, ¹³C-NMR and FAB Mass spectra of ligand clearly indicate the presence of OH and azomethine groups. Elemental analyses of the complexes indicate that the metal to ligand ratio is 1:1 in all complexes. Infrared spectra of complexes indicate a dibasic quadridentate nature of the ligand and its coordination to metal ions through phenolic oxygen and azomethine nitrogen atoms. The thermal behavior of these complexes showed the loss of lattice water in the first step followed by decomposition of the ligand in subsequent steps. The thermal data have also been analyzed for the kinetic parameters by using Horowitz-Metzger method. The dependence of the electrical conductivity on the temperature has been studied over the temperature range 313-403 K and the complexes are found to show semiconducting behavior. XRD and SEM images of some representative complexes have been recorded. The antimicrobial activity of the ligand and its complexes has been screened against various microorganisms and all of them were found to be active against the test organisms. The Fe(III) and Ni(II) complex have been tested for the catalytic oxidation of styrene.

Electrocatalytic oxidation of 2-mercaptoethanol using modified glassy carbon electrode by MWCNT in combination with unsymmetrical manganese (II) Schiff base complexes

The performance of modified hybrid glassy carbon electrode with composite of carbon nanotubes and manganese complexes for the electrocatalytic oxidation of 2-mercaptoethanol is developed. GC electrode was modified using MWCNT and new N2O2 unsymmetrical tetradentate Schiff base complexes of manganese namely Manganese Saloph complexes 1-5, with general formula Mn[(5-x-4-y-Sal)(5-x′-4-y′-Sal) Ph], where x, x′=H, Br, NO2 and y, y′=H, MeO. Direct immobilization of CNT on the surface of GCE is performed by abrasive immobilization, and then modified by manganese(II) complexes via direct deposition method. These novel modified electrodes clearly demonstrate the necessity of modifying bare carbon electrodes to endow them with the desired behavior and were identified by HRTEM. Also complexes were characterized by elemental analyses, MS, UV–vis and IR spectroscopy. Modified hybrid GC/MWCNT/MnSaloph electrode exhibits strong and stable electrocatalytic activity towards the electrooxidation of 2-mercaptoethanol molecules in comparison with bare glassy carbon electrode with advantages of very low over potential and high catalytic current. Such ability promotes the thiol’s electron transfer reaction. Also, electron withdrawing substituent on the Saloph was enhanced electrocatalytic oxidation activity.

Detection of trace amounts of Hg2+ in different real samples based on immobilization of novel unsymmetrical tetradentate Schiff base within PVC membrane

A novel fluorescence optical sensor for sensitive and selective determination of Hg2+ ions in aqueous solution has been prepared. The sensing system is made of a novel unsymmetrical tetradentate Schiff base namely N-(2-hydroxyphenyl)-N′-(2-mercaptophenyl)-o-phthalylidene (HMP), as a neutral Hg2+-selective fluoroionophore immobilized in a plasticized PVC membrane containing potassium tetrakis-(4-chlorophenyl) borate (KTpClPB) as a lipophilic anionic additive. The response of the optode is based on the strong fluorescence enhancement of HMP upon exposure to Hg2+ ions. Under the optimum conditions, the proposed sensor displays a linear response in concentration range of 2.27×10−11 to 1.13×10−3mol/L, with a detection limit of 9.57×10−12mol/L. Furthermore, the proposed optode displays a good selectivity toward Hg2+ ions in comparison with common coexisting cations. The sensor was applied successfully for determination of mercury ions in different real samples.

Synthesis, crystal structure, and electrochemical properties of Ni(II) and Cu(II) complexes with two unsymmetrical N2O2 Schiff base ligands

Nickel(II) and copper(II) complexes of two unsymmetrical tetradentate Schiff base ligands [Ni(Me-salabza)] (1), [Cu(Me-salabza)] (2) and [Ni(salabza)] (3), {H2salabza = N,N′-bis[(salicylidene)-2-aminobenzylamine] and H2Me-salabza = N,N′-bis[(methylsalicylidene)-2-aminobenzylamine]}, have been synthesized and characterized by elemental analysis and spectroscopic methods. The crystal structures of 2 and 3 complexes have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry in [Cu(Me-salabza)] and [Ni(salabza)] complexes. The cyclic voltammetric studies of these complexes in dichloromethane indicate the electronic effects of the methyl groups on redox potential.

Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies

An unsymmetrical tetradentate Schiff base (H2L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H2L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance.

Synthetic, characterization and catalytic studies of some coordination compounds derived from unsymmetrical quadridentate Schiff base ligand

The stable complexes of VO(IV), Cr(III), Mn(III), Fe(III), MoO2(VI), and WO2(VI), with an unsymmetrical tetradentate Schiff base ligand derived from 2-hydroxy-5-methylacetophenone, 2-hydroxy-5-chloroacetophenone and carbohydrazide were synthesized and characterized by the elemental analysis, UV-Vis and IR spectroscopy, magnetic measurements and thermal analysis. The VO(IV) and Mn(III) complexes were tested for the catalytic oxidation of styrene. The conversion of styrene increases with use of VO(IV) catalyst and decreases with use of Mn(III) catalyst.