Symmetrical Schiff Base Ligand Research Articles

Effect of remote substituents and coordination anions on the magnetic properties of Co(ii) dimer complexes

Four related dinuclear Co(ii) complexes based on symmetric Schiff base ligands were synthesized and characterized. Magnetic studies indicate that remote substituents of the ligands and the coordination anions have no significant effect.

Heterotrimetallic Cu(II)Ho(III)Co(III) complex based on asymmetric Schiff base Ligand: Synthesis, structures and magnetic properties

Two new complexes, [Ho(DMF)4(H2O)2{Fe(CN)6}]n⋅nH2O (1) and [{CuL(H2O)N3Ho(H2O)3}2{Co(CN)6}]n·n[Co(CN)6]·7nH2O (2) (HL = N,N’-ethylene(3-methoxysalicylaldiimine) were obtained. They were synthesized from the precursors of asymmetric Schiff-base CuII, lanthanide metal ion of HoIII and hexacyanometalates. The single crystal X-ray diffraction measurement revealed their peculiar interesting chain structures: heterobimetallic neutral HoIII-FeIII chain for 1 and heterotrimetallic CuIIHoIIICoIII cationic chain for 2, respectively. Due to the asymmetric Schiff-base, the coordination environment of CuII and HoIII in 2 is quite different from the traditional 3d-4f CuII -LnIII systems prepared from symmetric Schiff base ligands. Magnetic investigation reveals the antiferromagnetic FeIII -HoIII and ferromagnetic CuII -HoIII coupling for 1 and 2, respectively. The complexes provide new evidence of designing heterobimetallic systems using various asymmetric Schiff-base ligands.

Comparison the anticorrosion behavior of three symmetrical Schiff-base ligands: experimental and theoretical studies

Comparison the anticorrosion behavior of three symmetrical Schiff-base ligands: experimental and theoretical studies

Exploring Schiff base ligand inhibitor for cancer and neurological cells, viruses and bacteria receptors by homology modeling and molecular docking

Due to theirinteresting hydrogen-bonding properties, Schiff bases are known for their variety of applications in chemistry and medicinal chemistry. In this work, the interaction between symmetrical Schiff base ligand (L: bis [4-hydroxy-6-methyl-3-{(1E)-N-[2 (ethylamino) ethyl] ethanimidoyl}-2H-pyran-2-one]) and cancer cells, neurological, viruses and bacteria receptors was studied theoretically. Density functional theory (DFT) was used to determine the geometry, reactivity and electronic properties of this ligand. Homology modeling and molecular docking were performed to check their biological and medicinal properties, including anticancer, antiviral, antibacterial and neurological activities. DFT revealed that the mulliken charges, the molecular orbitals (HOMO and LUMO) and MEP results are in a good agreement to the localization of electrophilic and nucleophilic attack sites. The theoretical study showed a high chemical reactivity and a low kinetic stability of the ligand. The docking study results revealed that the ligand exhibits a good biological activity against leukemia, breast cancer, Alzheimer and Covid-19 with binding energy values of −7.36 kcal/mol, −6.35 kcal/mol, −6.19 kcal/mol and −5.58 kcal/mol, respectively. These results are explained by the low values of binding energy and inhibition constant and multiple H-bonds.

Preparation of a novel Mixed-Ligand divalent metal complexes from solvent free Synthesized Schiff base derived from 2,6-Diaminopyridine with cinnamaldehyde and 2,2′‐Bipyridine: Characterization and antibacterial activities

The solvent-free conditions were employed to synthesise symmetrical Schiff base ligand from 2,6-diaminopyridine with cinnamaldehyde in (1 min) with a fair yield utilizing formic acid as a catalyst. Through coordination chemistry, new heteroleptic complexes of Cu(II), Co(II), Ni(II), Pt(II), Pd(II) and Zn(II) were achieved from Schiff base as a primary chelator (L 1 ) and 2,2′‐bipyridine (2,2′-bipy) as a secondary chelator (L 2 ). The prepared compounds have been characterized by elemental analysis, molar conductivity, magnetic susceptibility, FTIR, 1 H NMR, UV–visible, mass spectrometry, and thermal gravimetric analysis, and screened in vitro for their potential as antibacterial activity by the agar well diffusion method. The metal complexes were formulated as [M (L 1 ) (L 2 ) (X)] Y ⋅ nH 2 O, L 1 = Schiff base, L 2 = 2,2′-bipy, (M = Cu(II), Co(II), Zn(II), Y = 2NO 3 , n = 1), (M = Ni(II), X = 2H 2 O, Y = 2NO 3, n = 0) and (M = Pd(II) Pt(II), Y = 2Cl, n = 0). Both L 1 and L 2 act as a neutral bidentate ligand and coordinates via nitrogen atoms of imine and 2,2′-bipy to metal ions. The metal complexes were found to be electrolytic, with square-planar heteroleptic Cu(II), Co(II), Pt(II), and Pd(II) chelates and octahedral Ni(II) complex. As well as tetrahedral geometry, has been proposed for the complex of Zn(II). Furthermore, the biological activity study revealed that some metal chelates have excellent activity than Schiff base when tested against Gram-negative and Gram-positive strains of Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ). Finally, it was found that the Zn(II) and Pd(II) complexes were more effective against both types of bacteria tested than the imine and other metal complexes.

Symmetrical Pd(II) and Ni(II) Schiff base complexes: Synthesis, crystal structure determination, spectral characterization, and theoretical studies

Schiff base complexes of new palladium(II) and nickel(II) are prepared through the treatment of symmetrical Schiff base ligand which are derivative of 4,5-dimethyl-o-phenylenediamine with Ni(OAc)2.4H2O and Pd(OAc)2 salts. Elemental analysis, as well as spectroscopic methods like FT-IR and 1H NMR, were employed to investigate the molecular structure of the produced ligand and its associated metal complexes. The crystal structure investigation confirms that the coordination environment of the nickel in the NiL complex is tetra-coordinate occupied by ONNO sets of the coordinated ligand in slightly distorted square planar geometry. A Hirshfeld surface investigation is carried out for further exploration and understanding of the intermolecular interactions and a comparative study with some relevant crystal structures. The DFT's theoretical calculations, which used the B3LYP/Def2-TZVP level of theory, showed that the theoretical conclusions corresponded to the actual findings.

Spectroscopic characteristic (FT-IR, 1H, 13C NMR and UV–Vis) and theoretical calculations (MEP, DOS, HOMO-LUMO, PES, NBO analysis and keto–enol tautomerism) of new tetradentate N,N′-bis(4-hydroxysalicylidene)-1,4-phenylenediamine ligand as chelating agent for the synthesis of dinuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes

The synthesis and characterization of a novel symmetrical Schiff base ligand N,Nʹ-bis(4-hydroxysalicylidene)-1,4-phenylenediamine (BHSP) was presented in this study and characterized by FT-IR, NMR (1H and 13C) and UV–Vis spectroscopy experimentally and theoretically. Also a series of binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes of BHSP ligand have been synthesized by conventional sequential route in 1:1 equivalent of L:M ratio and characterized by routine physicochemical characterizations. The molecular geometry and vibrational frequencies of the BHSP in the ground state were calculated by using density functional theory (DFT) B3LYP method invoking 6-31G(d,p) and 6–31++G(d,p) basis sets. To study different conformations of the molecule, potential energy surface (PES) scan investigations were performed. The energetic behavior of the ligand compound (BHSP) in solvent media has been examined using B3LYP method with the 6-31G(d,p) and 6–31++G(d,p) basis sets by applying the polarized continuum model (PCM). In addition, DFT calculations of the BHSP ligand, molecular electrostatic potential (MEP), contour map, natural bond orbital (NBO) analysis, frontier molecular orbitals (FMO) analysis, NMR analysis and TD-DFT calculations were conducted. The calculated properties are in agreement with the available experimental data and closely related molecule BSP. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters.

Elucidation of the two-step relaxation processes of a tetranuclear dysprosium molecular nanomagnet through magnetic dilution.

A new centrosymmetric tetranuclear aggregate [Dy4(L)2(OAc)8(CH3OH)2] (1) was assembled using a unique symmetrical Schiff base ligand 1,5-bis(salicylidene)-carbohydrazide (H2L). Magnetic studies reveal ferromagnetic interactions between dysprosium ions and two obvious relaxation processes under zero dc field with effective energy barriers Ueff of 38 K and 223 K, the highest among the reported tetranuclear dysprosium molecular nanomagnets. To obtain further evidence on the origination of the slow magnetic relaxation, a diamagnetic yttrium analogue [Y4(L)2(OAc)8(CH3OH)2] (2) and a diluted sample [(Dy0.06Y0.94)4(L)2(OAc)8(CH3OH)2] (3) were synthesized. Further magnetic studies on the diluted sample combined with theoretical calculations indicate that the two-step magnetic relaxation processes in complex 1 originate from the single-ion magnetic behaviors of dysprosium ions with different coordination environments.

The novel pyridine based symmetrical Schiff base ligand and its transition metal complexes: synthesis, spectral definitions and application in dye sensitized solar cells (DSSCs)

The pyridine based azo-linked symmetrical Schiff base ligand, (E)-2,2′-((1E,1′E)-(pyridine-2,6-diylbis(azanylylidene))bis(methanylylidene))bis(4-((E)-phenyldiazenyl)phenol) (H2L), and its Co(II), Ni(II) and Pd(II) transition metal complexes were prepared, and defined by using elemental analysis, Fourier transform infrared, UV–visible, mass, nuclear magnetic resonance spectra, molar conductance, magnetic susceptibility and thermal analysis techniques. The conductivity results pointed out the non-electrolytic nature of all metal complexes. Elemental composition, ultraviolet spectra and magnetic susceptibility data showed that the synthesized complexes are in the binuclear structure and square plane geometry. When compared to the characteristic infrared bands for the functional groups of the ligand structure with complex molecules are reached, the ligand binds to the metal atom via phenolic OH and azomethine-nitrogen. Furthermore, the dye-sensitized solar cells (DSSCs) based on H2L and its metal complexes were fabricated, and photovoltaic properties of these devices were also investigated. The power conversion efficiency of fabricated devices based on ligand H2L can be improved with the incorporation of the transition metal complex.

A new end-on (μ1,1) azido bridged [Zn2(L)2(Na)N3]n 1D chain derived from a trinuclear zinc complex: syntheses, crystal structures, photoluminescence properties and DFT study

A bicompartmental N2O4 donor symmetric Schiff base ligand has been deployed to synthesize a trinuclear zinc complex [Zn3(L)2Cl2], which upon treatment with sodium azide produces a new μ1,1-azido-bridged 1-D polymer [Zn2(L)2(Na)N3]n. Both complexes have been characterized using IR, NMR, UV–vis, and X-ray diffraction techniques. In order to have better understanding of electronic transitions of the complexes, a time-dependent DFT study has been performed. Lifetime measurements have also been performed to learn about the stability of excited states of both complexes. The average fluorescence decay lifetime has been found to be 1.42 and 0.59 ns for 1 and 2, respectively. In Hirshfeld surface mapping, X⋯H/H⋯X (X = O, Cl) contacts are found to be only 2.7% of the total surface, which indicates that no significant X⋯H/H⋯X contacts are present in either of the complexes. Unconventional interactions such as C–H⋯π and π⋯π stacking interactions are found in supramolecular architectures of both complexes.

Synthesis and characterization of some metal complexes of isonitroso-2-acetylnaphthalene derivative

Nickel(II), copper(II), and zinc(II) complexes with the Schiff base obtained from isonitroso-2-acetylnaphthalene and 1,2-phenylenediamine were synthesized. The compounds were characterized by elemental analyses, FT-IR, UV-Vis, and 1H and 13C NMR spectra, conductance measurements, magnetic susceptibility measurements, and thermal analysis. The results suggest tetradentate coordination of the symmetrical Schiff base ligand through the two oxime oxygen atoms and two azomethine nitrogen atoms. The molar conductance data showed that the synthesized complexes are non-electrolytes.

Synthesis, structure and SOD activity of Mn complexes with symmetric Schiff base ligands derived from pyridoxal

This study describes the synthesis, crystal structure and antioxidant activity of manganese(III) complexes with Schiff-base ligands obtained from condensation of pyridoxal with alkyl diamines: [Mn(pyr2en)(H2O)2]Cl·4H2O, [Mn(pyr2en)(H2O)(CH3OH)]Cl, [Mn(pyr2pn)(H2O)2]ClO4 and [Mn2(pyr2bn)3]·4H2O, where H2pyr2en=1,2-bis(pyridoxylidenamino)ethane, H2pyr2pn=1,3-bis(pyridoxylidenamino)propane and H2pyr2bn=1,4-bis(pyridoxylidenamino)butane. The four complexes catalyze the dismutation of superoxide efficiently with IC50 values in the range of 1.22–2.15μM, evaluated through the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, in aqueous solution of pH 7.8. The length of the alkyl spacer in the diamine fragment plays a key role in the antioxidant activity of these complexes, with [Mn(pyr2pn)(H2O)2]ClO4 showing the lowest IC50 value.

Highly Diastereo- and Enantioselective Michael Addition of Nitroalkanes to 2-Enoyl-Pyridine N-Oxides Catalyzed by Scandium(III)/Copper(II) Complexes.

A C2 -symmetric Schiff-base ligand, derived from tridentate-Schiff-base, was developed and successfully applied to the asymmetric Michael addition of nitroalkanes to 2-enoyl-pyridine N-oxides. With this newly catalytic system, an unprecedented diastereoselectivity was obtained in the asymmetric Michael addition of nitroalkanes to 2-enoyl-pyridine N-oxides. In addition, a switch in enantioselectivity was achieved by using this newly catalytic system and our previous catalyst. After a facile reduction, the optically active adduct was converted to a biologically active dihydro-2H-pyrrol 4 a. Furthermore, a connection of two tridentate-Schiff-base subunits proved to be an effective strategy in ligand design.

Synthesis and Spectral Characterization of Bis(3(4-dimethylaminophenyl)-2-prop-1-enylydene)-1,2-diaminoethane and Some New Mercury Complexes: An Antibacterial and Antifungal Investigation

Synthesis, physical and spectral characterization of a symmetric N2-donor Schiff base ligand of bis(3(4-dimethylaminophenyl)-2-prop-1-enylydene)-1,2-diaminoethane and its new mercury(II) halide/thiocyanate complexes are reported. The entire compounds were studied by elemental analyses, FT-IR, UV-Visible, 1H and 13NMR spectra, melting point, and molar conductivity measurements. The reasonable red and blue shifts in FT-IR, electronic, and NMR spectroscopic signals of the complexes as compared with ligand proved good coordination of ligand so that a pseudotetrahedral geometry around metal center in the complexes is proposed. At last, in vitro antibacterial and antifungal properties of all compounds were screened against four bacterial strains (gram positive and negative bacteria) and two fungi that the results exhibited more antimicrobial activity of all complexes with respect to free ligand.

DNA interaction and efficient antimicrobial activities of 4N chelating metal complexes

A new series of metal(II) complexes using a symmetric Schiff base ligand, obtained by the condensation reaction of 4-formyl-N,N-dimethylaniline with benzene-1,2-diamine were synthesized and characterized. The various physico-chemical data indicate that the complexes have octahedral geometry. The intrinsic binding constant of the complexes with DNA is explored. The UV–Vis., circular dichorism, fluorescence emission spectral data and the viscosity measurements indicate that the complexes bind to calf thymus DNA (CT DNA) by intercalative mode. The intrinsic binding constants of Cu(II), Ni(II), Co(II) and Zn(II) complexes are found to be 7.1×104, 5.2×104, 1.8×105 and 6.3×104M−1, respectively. The cleavage studies of these complexes are investigated by gel electrophoresis method in the presence of peroxide. The complexes exhibit enhanced biological activities compared to the free ligand.

Synthesis, spectral characterization, molecular modeling and antimicrobial activity of new potentially N2O2 Schiff base complexes

Metal complexes of a new potentially tetradentate symmetrical Schiff base ligand (H2L) with Cu(II), Ni(II), Co(II), VO(IV), Zn(II), Cd(II), Ce(III), Fe(III) and UO2(VI) metal ions have been synthesized and characterized based on their elemental analyses, spectral (IR, UV–Vis, 1H NMR and mass spectra), magnetic and molar conductance studies as well as thermal gravimetric analysis (TGA). The synthesized complexes have the general formula [MHxL(H2O)yXn]: x=0–1, y=0–4 and n=0–1; where: L=dianion of 6-hydroxy-5-[N-(2-{[(1E)-1-(6-hydroxy-2,4-dioxo-3,4-dihydro-2H-1,3-thiazin-5-yl)ethylidene]amino}ethyl) ethanimidoyl]-2H-1,3-thiazine-2,4(3H)-dione and X=nitrate or sulphate anion. The ligand behaves as diabasic tetradentate N2O2 sites, except in cases of Co(II), VO(IV) and UO2(VI) metal ions, it behaves as monobasic tetradentate Schiff base ligand. The metal complexes exhibited square planar, square-pyramidal and octahedral geometrical arrangements except for Ce(III) and UO2(VI) complexes, they are octa-coordinated. The Coats-Redfern equation was used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition stages of some complexes. Structural parameters of the ligand and its metal complexes have been theoretically computed on the basis of semiemperical PM3 level, and the results were correlated with their experimental data. The antimicrobial activities of the ligand and its metal complexes were tested against some Gram-positive and Gram-negative bacteria; and fungus strain and the results were discussed.

Synthesis, characterization and computational studies of zinc(II)-halide complexes with a bidentate schiff base ligand (2,5-MeO-ba)2En: The crystal structure of (2,5-MeO-ba)2En

In this study four coordinated complexes of zinc(II) halides with a new symmetrical bidentate Schiff base ligand (2,5-MeO-ba)2En are synthesized and characterized. The metal to ligand ratio of the complexes is found to be 1:1 with the formula of Zn((2,5-MeO-ba)2En)X2 (X = Cl (1), Br (2), I (3)). The crystal structure of the Schiff base ligand (2,5-MeO-ba)2En is determined by X-ray crystallography from single crystal data. Also, the optimized geometries of the Schiff base ligand (2,5-MeO-ba)2En and its zinc(II) complexes are calculated using the density functional theory method (B3LYP/6-31G). The obtained structural parameters of (2,5-MeO-ba)2En are in agreement with the experimental data.

Synthesis, characterization, electrochemical behavior, thermal study and antibacterial/antifungal properties of some new zinc(II) coordination compounds

A novel symmetrical Schiff base ligand was prepared by condensation reaction of 2,2-dimethyl-1.3-diaminopropane and (E)3-(2nitrophenyl)acrylaldehyde. The ligand and its Zn(II) coordination compounds were well characterized by the elemental analysis, FTIR, 1H, 13C NMR, UV–vis spectra and molar conductance. Thermal behaviors of all compounds were investigated from the room temperature to 600°C with a heating rate of 10°C/min. Furthermore some decomposition thermo-kinetic parameters were evaluated by Coats–Redfern equation at each decomposition step. Electrochemical properties of ligand and its complexes were studied by cyclic voltammetry technique. Also antibacterial/antifungal activities of the ligand and its complexes were tested against three Gram-negative bacteria Escherichia coli (ATCC 25922), Salmonella spp. and Pseudomonas aeruginosa (ATCC 9027) and two Gram-positive bacteria Staphylococcus aureus (ATCC 6538) and Corynebacterium renale and also three fungi (Aspergillus niger, Penicillium chrysogenum and Candida albicans). The results exhibited suitable antibacterial/antifungal properties for ligand and Zn(II) complexes. The study has shown that the complexation of ligand to zinc center lead to enhancement of antibacterial/antifungal activity.

Syntheses, studies and crystal structures of coordination polymers and dinuclear complexes of mercury(II) halides and thiocyanate with a symmetrical Schiff base ligand

A series of mercury(II) compounds, [Hg2(μ-L)(SCN)4]n (1), [Hg2(μ-L)(μ-Cl)2Cl2]n (2), [Hg2(μ-L)Br4].[Hg2(μ-L)(μ-Br)2Br2]n (3) and [Hg2(μ-L)I4] (4) {L=N,N′-(bis-(pyridin-2-yl)benzylidene)-1,2-ethanediamine} have been prepared and characterized by using microanalytical, spectroscopic, thermal and X-ray crystallographic results. In solid states 1 and 2 have 2D and 1D coordination polymer structure, respectively. Solid state 3 consists of both 1D coordination polymers and dinuclear units. Solid state 4 is only composed of dinuclear units. In the polymeric structures, each mercury(II) center is five coordinated with trigonal bipyramidal geometry in 1D and square pyramidal environment in 2D coordination polymers. Coordination geometry around Hg centers in dinuclear units is tetrahedral. HOMO and LUMO of the title compounds and also the energy gap among them have been studied by using the density functional theory (DFT/B3LYP) method with the LANL2DZ pseudo-potential.

Synthesis, Characterization, and Spectroscopic Properties of a Symmetrical Schiff Base Ligand and its Bimetallic Complexes

This article presents the synthesis of new Schiff base ligand and preparation of its transition metal complexes with copper (II), nickel (II), zinc (II), and cobalt (II). Furthermore, absorption and fluorescence properties of ligand and its metal complexes are investigated. The effect of the solvents, such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, methanol, 1,4-dioxane on fluorescence properties of metal complexes, are performed and obtained results are summarized. All of the structures were characterized by using spectroscopic techniques.