Donor Schiff Base Research Articles

A new linear double phenoxide-bridged trinuclear Cu(II) Schiff base complex: Synthesis, crystallographic elucidation, magneto-structural correlation and DFT Study

The tetradentate (ONNO) donor Schiff base ligand LH2, derived from the condensation of salicylaldehyde and 1,3-diaminopropane, has been synthesized and reacted with CuBr2 to yield a trinuclear complex with the molecular formula [Cu3L2Br2]. Single crystal X-ray diffraction study reveals that the two terminal copper atoms adopt a square pyramidal geometry, whereas the central copper atom, situated at the inversion centre, is surrounded by four phenoxide oxygen atoms in a square planar fashion. Variable temperature magnetic susceptibility measurement study shows strong antiferromagnetic intra-trimer interactions between the copper centers with a J value of −302cm−1. EPR study of the complex depicts that, due to the exchange coupling between the copper ions, the EPR spectra were unresolved, having very broad resonances with g=2.133. A theoretical DFT calculation was also carried out to supplement the experimental results.

Synthesis and Characterization of Four Coordinated Palladium (II) Complex with N<SUB>2</SUB>O Donor Schiff Base: Interaction with Calf Thymus-DNA, Density Functional Theory Study and Antibacterial Activity

Synthesis and Characterization of Four Coordinated Palladium (II) Complex with N<SUB>2</SUB>O Donor Schiff Base: Interaction with Calf Thymus-DNA, Density Functional Theory Study and Antibacterial Activity

Synthesis, structural characterization and biological activity of a trinuclear zinc(II) complex: DNA interaction study and antimicrobial activity

A trinuclear zinc(II) complex [Zn3 L 2(μ-O2CCH3)2(H2O)2]·H2O·2CH3OH (1) was synthesized from an in situ reaction between zinc acetate and a Schiff base ligand (H2 L = 2-((2-hydroxyphenylimino)methyl)-6-methoxyphenol). The ligand was prepared by (1:1) condensation of ortho-vanillin and ortho-aminophenol. The ligand and zinc(II) complex were characterized by elemental analysis, Fourier Transform Infrared (FTIR), 1H-Nuclear Magnetic Resonance (NMR), UV-Vis spectroscopy, Powder X-ray Diffraction (PXRD) and thermogravimetric analysis. 1 crystallizes in P-1 space group with a = 11.9241(3) Å, b = 12.19746 Å, c = 20.47784 Å with unit cell volume is 2674.440 (Å)3. Binding property of the complex with calf thymus DNA (CT-DNA) has been investigated using absorption and emission studies. Thermal melting and viscosity experiments were further performed to determine the mode of binding of 1 with CT-DNA. Spectroscopic and viscosity investigations revealed an intercalative binding mode of 1 with CT-DNA. The ligand and its zinc complex were screened for their biological activity against bacterial species and fungi. Activity data show that the metal complex has more antibacterial and antifungal activity than the parent Schiff base ligand and against those bacterial or fungi species. A trinuclear Zinc(II) complex, [Zn3 L 2(μ-O2CCH3)2(H2O)2]·H2O·2CH3OH (1) of a (N,O)-donor Schiff base ligand has been synthesized and structurally characterized. The Zn(II) complex interacts significantly with CT-DNA and spectroscopic and viscosity investigations revealed an intercalative binding mode of 1 with DNA. The biological activity of the zinc(II) complex against different bacterial and fungal organisms is very promising.

Designed synthesis of copper(II) and nickel(II) complexes with a tridentate N2O donor Schiff base: Modulation of crystalline architectures through C[sbnd]H⋯π and anion⋯π interactions

Two copper(II) complexes, Cu(L1)Cl (1), Cu(L1)NCS (3) and two nickel(II) complexes Ni(L1)Cl (2), Ni(L1)NCS (4), where HL1=1-[(2-diethylamino-ethylimino)-methyl]-naphthalen-2-ol act as tridentate N2O donor ligand, have been prepared and characterized by elemental analysis, IR and UV–Vis spectroscopy and single crystal X-ray diffraction studies. The geometry of the central metal ion in each of the four complexes is square planar. The existence of CH⋯π interactions in 2 gives rise to one dimensional chain structure. Complex 3 shows two CH⋯π interactions and one anion⋯π interactions which leads to a two dimensional layer structure. Each mononuclear unit of 4 has two CH⋯π interactions along b axis to form a double strand one dimensional array of the molecules in crystal packing.

Photoluminescent columnar zinc(II) bimetallomesogen of tridentate [ONO]-donor Schiff base ligand

A new zinc(II) bimetallomesogenic complex, [Zn2L2], of tridentate [ONO]-donor Schiff base ligand (L = N-(2-hydroxyethyl)-4-hexadecyloxysalicylaldimines) was synthesised and their mesomorphic and photoluminescence properties were investigated. The compounds were characterised by Fourier transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR), ultraviolet-visible spectroscopy (UV-Vis) spectroscopy, elemental analyses and fast atom bombardment (FAB) mass spectrometry. The mesomorphic behaviour of the complex was investigated by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction (XRD) study. A rectangular or oblique columnar mesophase is conjectured on the basis of powder X-ray diffraction (PXRD) study. The complex is found to be blue light emitter in solution, in solid and in condensed states with broad emission maxima at ∼427–464 nm. The density functional theory (DFT) calculations revealed a distorted square planar structure around each zinc(II) centre in the dinuclear framework. Time-dependent DFT spectral correlative study was undertaken to account for the electronic transition.

Counter anion modulated variation of denticity of NNO donor Schiff base in copper(II) complexes: Isolation of a zwitterionic Schiff base as the metal complex

Three copper(II) complexes [Cu(HL)2(ClO4)]ClO4·H2O (1), [Cu(L)DMF]ClO4 (2) and [CuL(NCO)][Cu2L2(NCO)2] (3) [where HL=2-[(2-Diethylamino-ethylimino)-methyl]-4-nitro-phenol, a tridentate Schiff-base] have been synthesized and characterized by elemental analysis, IR and UV–Vis spectroscopy and single-crystal X-ray diffraction studies. In complexes 2 and 3, the Schiff base is acting as a tridentate ligand. However, in complex 1, the Schiff base is present in its zwitterionic form. The denticity of the tridentate Schiff base has been modulated by the acidity of counter anions. Complexes 1 and 2 are monomeric. Copper(II) assumes square pyramidal geometry in 1 (Addison parameter (τ)=0.15) and square planar geometry in 2. The asymmetric unit of complex 3 consists of two crystallographically different double end-on cyanate bridged dimers, containing square pyramidal copper(II) {Addison parameter (τ)=0.157}. Complexes 1 and 3 crystallize in triclinic space group, P1¯ with cell dimensions a=11.3479(10), b=12.5198(9), c=13.6640(12), α=94.299(7)°, β=97.281(7)° and γ=116.007(6)° (for 1) and a=11.6149(8), b=11.8145(9), c=13.8741(13), α=65.524(6)°, β=73.373(6)° and γ=63.857(5)° (for 3), whereas complex 2 crystallizes in monoclinic space group, P21/c with cell dimensions a=7.5765(2), b=19.6005(6), c=14.5861(4) and β=102.679(1)° (for 2). The weak forces like lone pair⋯π/π⋯π/anion⋯π interactions lead to various supramolecular architectures.

Synthesis, structure and catalase activity of three new manganese(III) complexes with a N,N,O donor Schiff-base ligand

Three new Mn(III) complexes [Mn(L)(L′)(N3)] (1), [Mn(L)(L′)(Cl)] (2) and {[Mn(L)(L′)(H2O)](ClO4)}2 (3) (where, HL=2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol and HL′=o-hydroxyacetophenone) have been synthesized and characterized by UV–Vis and IR spectroscopy and single-crystal X-ray diffraction analyses. All of the three monomeric complexes show six-coordinate octahedral geometry around the Mn(III) center and are bonded to the deprotonated tridentate ligand L together with the deprotonated bidentate ligand L′ and a labile monodentate donor i.e. azide in 1, chloride in 2 and water in 3, respectively. All of the complexes catalyze the disproportionation of hydrogen peroxide into water and dioxygen i.e. they possess catalase activity. The turnover numbers of the complexes follow the order: 3>1>2.

Two new twisted helical nickel(II) and cobalt(III) octahedral monomers: Easy-plane anisotropy of nickel(II)

Two mononuclear complexes namely [NiII(L)] (1) and [CoIII(L)](NO3) (2) of a hexacoordinating N4O2 donor Schiff base ligand were synthesized and characterized by single crystal X-ray studies. The two complexes are isostructural with octahedral coordination environment, basal plane being occupied by four nitrogen atoms of the N,N′-bis(3-aminopropyle)ethylenediamine moiety and axial positions are being occupied by the phenolate oxygen atoms from two o-vanilline moieties. In compound 2 the central cobalt is in +3 oxidation state and found to be diamagnetic, while compound 1 with nickel ion in +2 oxidation state is paramagnetic with S=1, g=2.16, D=+6.5cm−1, |E/D|=0.33. Both the complexes display mononuclear single helical topology, may be due to the presence of rigid and bulky terminal o-vanilline to a comparatively flexible central N,N′-bis(3-aminopropyle)ethylenediamine moiety.

Catalytic efficacy of an oxido-peroxido tungsten(VI) complex: synthesis, X-ray structure and oxidation of sulfides and olefins

An oxido-peroxido tungsten(VI) complex [WO(O2)L(CH3OH)] using salicylidene benzoyl hydrazine as a tridentate ONO donor Schiff base (H2L) has been synthesized and characterized by elemental analysis, IR, 1H NMR, molar conductance data, and single-crystal X-ray analysis. The complex was used as a catalyst for epoxidation of olefins and oxidation of sulfides. The results show that epoxides and sulfoxides were produced in high yield, turnover number, and selectivity.

Copper(II) complexes with tridentate N2O donor Schiff base isomers: Modulation of molecular and crystalline architectures through supramolecular interactions

Four copper(II) complexes, [Cu(L1)(μ-Cl)]n (1), [Cu2(L2)2(μ-Cl)2] (2), [Cu(L1)(μ1,5-NCNCN)]n (3) and [Cu(L2)(μ1,5-NCNCN)]n (4), where HL1=1-[(2-dimethylamino-ethylimino)-methyl]-naphthalen-2-ol and HL2=1-[(2-ethylamino-ethylimino)-methyl]-naphthalen-2-ol, acting as tridentate N2O donor ligands, have been prepared and characterized by elemental analysis, IR and UV–Vis spectroscopy and single crystal X-ray diffraction studies. Complexes 1, 3 and 4 show polymeric chain structures, whereas 2 has a double chloride bridged dimeric structure. The existence of C–H⋯π interactions between the dimeric units of 2 gives rise to a 2D supramolecular network. Complex 3 shows a zipper structure through π⋯π interactions between two polymeric chains. Complex 4 shows hydrogen bonding interactions which produces a 2D hydrogen bonded structure and these 2D layers then show interlayer π⋯π interactions.

Encapsulation of copper(I)-Schiff base complex in NaY nanoporosity: An efficient and reusable catalyst in the synthesis of propargylamines via A3-coupling (aldehyde-amine-alkyne) reactions

Nanodimensional microreactor containing bis[2-(phenylthio)benzylidene]-1,2-ethylenediamine copper(I) complexes, [Cu(N2S2)]X-Y (X=CN, Cl, Br, I) was successfully prepared. This nano composite was used as a catalyst in one-pot multicomponent coupling reaction of aldehydes, amines and alkynes toward synthesis of propargylamines. The copper(I) complex with N2S2 donor Schiff base ligand was readily trapped in the nanocavity of zeolite-Y through a template synthetic (TS) method. Two consecutive processes in the liquid phase were carried out: (i) preparation of a solution of [Cu(MeCN)4]X coordinated with 2-(phenylthio)-benzaldehyde in the presence of zeolite-Y. This process caused the inclusion of [Cu(MeCN)2(S2O2)]X complex into the nanopores of zeolite Y via pre-adsorption method; (ii) template synthesis of the [Cu(MeCN)2(N2S2)]X-Y, through Schiff condensation between [Cu(MeCN)2(S2O2)]X and 1,2-ethylenediamine moiety into the nanopores of NaY. The resulting catalysts were fully characterized by spectroscopic techniques such as AAS, FT-IR, BET isotherm, XRD, UV-Vis and TGA. The results confirmed encapsulation of Y-zeolite with copper(I) complex of N2S2 donor ligand. The catalytic activity of this nanocomposite material was investigated for preparation of propargylamines via three-component reaction of aldehydes, amines and alkynes. Also, the effective factors on this condensation reaction were discussed, such as reaction temperature, solvent, catalyst loading, leaching and reusability of the catalyst.

A new tridentate Schiff base Cu(II) complex: Synthesis, experimental and theoretical studies on its crystal structure, FT-IR and UV–Visible spectra

A new Cu(II) complex [Cu(L)(NCS)] has been synthesized, using 1-(N-salicylideneimino)-2-(N,N-methyl)-aminoethane as tridentate ONN donor Schiff base ligand (HL). The dark green crystals of the compound are used for single-crystal X-ray analysis and measuring Fourier Transform Infrared (FT-IR) and UV–Visible spectra. Electronic structure calculations at the B3LYP and MP2 levels of theory are performed to optimize the molecular geometry and to calculate the UV–Visible and FT-IR spectra of the compound. Vibrational assignments and analysis of the fundamental modes of the compound are performed. Time-dependent density functional theory (TD-DFT) method is used to calculate the electronic transitions of the complex. A scaling factor of 1.015 is obtained for vibrational frequencies computed at the B3LYP level using basis sets 6-311G(d,p). It is found that solvent has a profound effect on the electronic absorption spectrum. The UV–Visible spectrum of the complex recorded in DMSO and DMF solution can be correctly predicted by a model in which DMSO and DMF molecules are coordinated to the central Cu atom via their oxygen atoms.

Mononuclear and tetranuclear Fe(III) complexes with two different types of N, O donor Schiff base ligands

A mononuclear Fe(III) complex of a tetradentate N2O2 donor Schiff base ligand derived from 3-ethoxysalicaldehyde and ethylenediamine has been reported. In addition two tetranuclear Fe(III) complexes with discrete Fe4III(μ4-O) cores have been synthesized and characterized using two Schiff base ligands (H2L1–2) derived from two different aromatic acid hydrazides and diacetyl monoxime. The mononuclear Fe(III) and one of the tetranuclear Fe(III) complexes have been structurally characterized by single-crystal X-ray crystallography. The mononuclear complex has a highly distorted octahedral geometry. The tetranuclear Fe(III) complexes are found to be rare examples with discrete neutral alkoxido–oxido clusters with Fe4III(μ4-O) cores.

Synthesis, characterization and crystal structures of copper(II) and nickel(II) complexes of propargyl arm containing N2O2 ligands: Antimicrobial activity and DNA binding

Ni(II) and Cu(II) complexes of propargyl arm containing N2O2 Schiff base donor ligands (L1–L3) were prepared and characterised by elemental analysis, IR, NMR and UV–Vis spectroscopy. The crystal structures of CuL3 and NiL3 were determined by single crystal X-ray diffraction measurements. The coordination geometry around the copper and nickel centres is square planar, with the plane formed by the N2O2 donors of the Schiff base ligand. The crystal packing is stabilized by C–H⋯O intermolecular hydrogen bonding and further influenced by C–H⋯π interactions. The electrochemical behaviour of the synthesized copper complexes was studied and the results obtained evidenced their irreversible oxidation. Antibacterial activity was assayed against selective Gram(+ve) and Gram(−ve) microorganisms. The DNA binding behaviour of the complexes was investigated using absorption and fluorescence titration measurements.

Synthesis and physicochemical studies of nitrogen-oxygen and sulphur donor Schiff base complexes of cobalt(II), nickel(II) and copper(II)

Synthesis and physicochemical studies of nitrogen-oxygen and sulphur donor Schiff base complexes of cobalt(II), nickel(II) and copper(II)

A New Family of Trinuclear Nickel(II) Complexes as Single‐Molecule Magnets

Three new trinuclear nickel (II) complexes with the general composition [Ni3 L3 (OH)(X)](ClO4 ) have been prepared in which X=Cl(-) (1), OCN(-) (2), or N3(-) (3) and HL is the tridentate N,N,O donor Schiff base ligand 2-[(3-dimethylaminopropylimino)methyl]phenol. Single-crystal structural analyses revealed that all three complexes have a similar Ni3 core motif with three different types of bridging, namely phenoxido (μ2 and μ3 ), hydroxido (μ3 ), and μ2 -Cl (1), μ1,1 -NCO (2), or μ1,1 -N3 (3). The nickel(II) ions adopt a compressed octahedron geometry. Single-crystal magnetization measurements on complex 1 revealed that the pseudo-three-fold axis of Ni3 corresponds to a magnetic easy axis, being consistent with the magnetic anisotropy expected from the coordination structure of each nickel ion. Temperature-dependent magnetic measurements indicated ferromagnetic coupling leading to an S=3 ground state with 2J/k=17, 17, and 28 K for 1, 2, and 3, respectively, with the nickel atoms in an approximate equilateral triangle. The high-frequency EPR spectra in combination with spin Hamiltonian simulations that include zero-field splitting parameters DNi /k=-5, -4, and -4 K for 1, 2, and 3, respectively, reproduced the EPR spectra well after a anisotropic exchange term was introduced. Anisotropic exchange was identified as Di,j /k=-0.9, -0.8, and -0.8 K for 1, 2, and 3, respectively, whereas no evidence of single-ion rhombic anisotropy was observed spectroscopically. Slow relaxation of the magnetization at low temperatures is evident from the frequency-dependence of the out-of-phase ac susceptibilities. Pulsed-field magnetization recorded at 0.5 K shows clear steps in the hysteresis loop at 0.5-1 T, which has been assigned to quantum tunneling, and is characteristic of single-molecule magnets.

Synthesis and characterization of a copper(II) complex of a ONN donor Schiff base ligand derived from pyridoxal and 2-(pyrid-2-yl)ethylamine – A novel pyridoxal based fluorescent probe

The title complex, Cu(LH)Cl2 is the first copper(II) complex with a Schiff base derived from pyridoxal and 2-(pyrid-2-yl)ethylamine. The central metal lies in a distorted square pyramidal environment with basal plane occupied by the tridentate ONN donor ligand and a Cl atom. The apical position is occupied by another Cl atom. The existence of two different kinds of H-bonds stabilize the network that propagates as parallel layers along crystallographic b axis. The compound exhibits an irreversible CuII/CuI couple in DMF. As pyridoxal containing moieties are fluorescent in nature, its potential as a fluorescent probe is cultivated. Copper(II) ion effectively quenches the fluorescence of HL and the association constant for Cu(II) was estimated to be 10.8×104M−1 in methanol by the linear Benesi–Hildebrand equation.

Microwave assisted synthesis, spectroscopic characterization and biological aspects of some new chromium(iii) complexes derived from N⁁O donor Schiff bases

The present study is structured to address the development of green microwave processes in the manufacture of a new series of biologically potent (N⁁O) donor Schiff bases and their Cr(III) complexes. These have been characterized by elemental analysis, melting point and molecular weight determinations, IR, UV-vis and EPR spectral analysis, and X-ray powder diffraction studies. The bioefficient compounds have been synthesized by thermal as well as microwave assisted methods. The azomethine ligands 1-(2-pyridyl) ethanone isonicotinoyl hydrazone (L1H) and 1-(2-naphthyl) ethanone isonicotinoyl hydrazone (L2H) have been synthesized by the condensation of 1-(2-pyridyl) ethanone and 1-(2-naphthyl) ethanone with isonicotinic acid hydrazide in a 1 : 1 molar ratio, using ethanol as a solvent. The Cr(III) complexes have been prepared by mixing CrCl3·6H2O in 1 : 1 and 1 : 2 molar ratios with ligands L1H and L2H in methanol. The synthesized ligands and their new metal complexes have been screened in vitro for antimicrobial activity and in vivo for antifertility activity on male albino rats. The spectral data suggested a hexa-coordinated environment around the central metal ion. Physicochemical studies of the ligands and their Cr(III) complexes aided the construction of their proposed structures.

Synthesis, Characterization and Biological Applications of Transition Metal Complexes of [no] Donor Schiff Bases

Ten novel transition metal complexes of N,O donor ligands have been synthesized by the reaction of ligands with metal acetates in 2:1 molar ratio. These reactions were carried out under reflux in methanol for 3-6 hours. The ligands and their transition metal complexes were characterized on the basis of physical properties, elemental analysis, Infrared spectroscopy, Magnetic susceptibility, Ultraviolet and Atomic absorption spectroscopy and 1H-13C NMR spectroscopy. The FT- IR spectra of the complexes indicated that ligands behaved in bidentate manner coordinating via the nitrogen and oxygen. 1H-NMR and 13C-NMR data of the ligands in pure and complex form confirmed the formation of the complexes. Other analytical techniques demonstrated that transition metal complexes of Cu, Ni, Co and Zn are four coordinated and those of Mn are six coordinated. Furthermore, antibacterial activities have been discussed.

Synthesis, Characterization and Biological Activity of Cis- Dioxomolybdenum(VI) Schiff base Complex [MoO2(L)2

A new dioxo-molybdenum(VI) complex [MoO2(L)2] was synthesized using 2,4-dihydroxy–benzalmethylene-o,o’- diethylphosphorohydrazonothionate (HL) as bidentate ON donor Schiff base ligand and MoO2(acac)2. This new compound was characterized by elemental analysis, IR, 1HNMR, MS, UV/vis, and molar conductivity, and the six- coordinate structure with [cis-MoO2]2+ group in the complex was proposed on the basis of spectroscopic characterization. The insecticidal activity of the Mo(VI) complex to bollworm was investigated, and its effect on the cell survial rate of mung bean sprouts was also discussed. The results showed that the activities of the complex in killing aphid were more effective than that of methamidophos and lower in killing red spider than that of methamidophos. Moreover, the complex could promote the cell survial rate of mung bean sprouts.