Synthesis and characterization of a thioether Schiff base ligand and its metal complexes and crystal structure determination of the nickel(II) complex

Reactions of 1,2-di(o-aminophenylthio)ethane with 3-ethoxy-2-hydroxybenzaldehyde yield the new hexadentate N₂S₂O₂ donor thioether Schiff base 1,2-bis(2-((2-(thio)phenylimino)methyl)-6-ethoxyphenol)ethane (H₂L). Ni(II), Zn(II), Cd(II), and Hg(II) complexes of this ligand were prepared. Of these complexes, [NiL]·2H₂O has been structurally characterized by X-ray crystallography. The coordination geometry around Ni(II) was described as octahedral. Zn(II), Cd(II), and Hg(II) complexes and the Schiff base ligand have been characterized by CHN analyses, molar conductivity, UV–vis, FT-IR, ¹H, and ¹³C NMR spectroscopy.     

Template synthesis and physicochemical studies of 14-membered hexaazmacrocyclic complexes with Co(II), Ni(II), Cu(II) and Zn(II): a comparative spectroscopic approach on DNA binding with Cu(II) and Ni(II) complexes

A new series of 14-membered pendant arm hexaazamacrocyclic complexes of the type [MLX₂] · [M = Co(II), Ni(II), Cu(II) or Zn(II) for X = Cl; Co(II), Ni(II), Cu(II) or Zn(II) for X = NO₃] has been synthesized by metal template condensation of 1,2-phenylenediamine and 1,4-phenylenediamine with formaldehyde in methanol. The mode of bonding and overall geometry of these complexes have been deduced by elemental analyses, molar conductance values, FT-IR, ¹H-NMR, ¹³C-NMR, EPR, ESI-mass and UV–VIS along with magnetic measurement studies. The fluorescence and UV–VIS studies revealed a significant binding ability to DNA.     

Interaction of Co(II), Ni(II), Cu(II), and Zn(II) with 12- and 14-membered macrocycles containing O2N2 donors

The 12- and 14-membered diazadioxo macrocyclic ligands, 1,2?:?7,8-diphenyl-6,9-diaza-3,12-dioxocyclododecane (L¹) and 1,2?:?8,9-diphenyl-7,10-diaza-3,14-dioxocyclotetradecane (L²), were synthesized by condensation between o-phenylenediamine, 1,2-dibromoethane/1,3-dibromopropane, and catechol. Metal complexes [ML¹Cl₂] and [ML²Cl₂] [M?=?Co(II), Ni(II), Cu(II), and Zn(II)] were prepared by interaction of L¹ or L² with metal(II) chlorides. The ligands and their complexes were characterized by elemental analyses, IR, ¹H, and ¹³C NMR, EPR, UV-Vis spectroscopy, magnetic susceptibility, conductivity measurements, and Electrospray ionization-mass spectral (ESI-MS) studies. The results of elemental analyses, ESI-MS, Job's method, and conductivity measurements confirmed the stoichiometry of ligands and their complexes while absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of ligand framework around the metal ions. Stereochemistry was inferred from the UV-Vis, EPR, and magnetic moment studies.     

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

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

Syntheses,characterization and biological studies of zinc(II), copper(II) and cobalt(II) complexes with Schiff base ligand derived from 2‐hydroxy‐1‐naphthaldehyde and selenomethionine

Novel zinc(II), copper(II), and cobalt(II) complexes of the Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde and D, L ‐selenomethionine were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements and powder XRD. The analytical data showed the composition of the metal complex to be ML(H₂O), where L is the Schiff base ligand and M = Co(II), Cu(II) and Zn(II). IR results confirmed the tridentate binding of the Schiff base ligand involving azomethine nitrogen, naphthol oxygen and carboxylato oxygen atoms. ¹H NMR spectral data of lithium salt of the Schiff base ligand [Li(HL)] and ZnL(H₂O) agreed with the proposed structures. The conductivity values of complexes between 12.50 and 15.45 S cm² mol^?1 in DMF suggested the presence of non‐electrolyte species. The powder XRD studies indicated that Co(II) complex is amorphous, whereas Cu(II) and Zn(II) complexes are crystalline. The results of antibacterial and antifungal screening studies indicated that Li(HL) and its metal complexes are active, but CuL(H₂O) is most active among them. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis,characterization, and anticancer activity of some metal complexes with a new Schiff base ligand

A new Schiff base ligand, 2-((E)-((4-(((E)-benzylidene)amino)phenyl)imino)methyl)-naphthalene-1-ol, was prepared by the reflux condensation of p-phenylenediamine with 2-hydroxy-1-naphthaldehyde and benzaldehyde. Metal complexes were prepared by reacting the ligand with metal salts: VCl₃, CrCl₃·6H₂O, MnCl₂·3H₂O, FeCl₃·6H₂O, CoCl₃·6H₂O, NiCl₂·6H₂O, CuCl₂·2H₂O, and ZnCl₂. The ligand and its metallic complexes were characterized by various techniques such as elemental analysis, AAS, NMR, IR, UV–Vis, TGA, DTA, XRD and TEM. The data confirmed that the ligand coordinated with the metal ions in a bidentate nature, bonding through its azomethine nitrogen atom and phenolic oxygen atom; this gave an octahedral geometry. The XRD patterns of the complexes indicated that they were of various structures: the Mn(II), Co(III), and Cu(II) complexes were triclinic, the ligand and Ni(II) complex were orthorhombic, the V(III) and Zn(II) complexes were hexagonal, the Cu(II) complex was monoclinic, and the Fe(II) complex was cubic. TEM analysis confirmed that the complexes were nanoscale in nature. The antibacterial and antifungal activities of the ligand and its complexes against Salmonella enterica serovar typhi and Candida albicans were investigated by the hole plate diffusion method. It was observed that the Co(II) and Zn(II) complexes had intermediate antibacterial activities, while the V(III) complex had the highest activity against C. albicans fungi. The in vitro anticancer activities of the ligand and its metal complexes were tested towards PC-3, SKOV3, and HeLa tumour cell lines, where they exhibited higher antitumour activities against these selected human cell lines than clinically used drugs such as cisplatin, estramustine, and etoposide.     

Synthesis, spectroscopic, antimicrobial, DNA binding and cleavage studies of some metal complexes involving symmetrical bidentate N, N donor Schiff base ligand

The Schiff base ligand, N,N′-bis-(4-isopropylbenzaldimine)-1,2-diaminoethane (L), obtained by the condensation of 4-isopropylbenzaldehyde and 1,2-diaminoethane, has been used to synthesize the complexes of the type [ML₂X₂] [M = Co(II), Ni(II) and Zn(II); X = Cl and OAc]. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analyses, mass, ¹H and ¹³C-NMR, molar conductance, IR, UV–vis, magnetic moment, CV and thermal analyses, powder XRD and SEM. IR spectral data show that the ligand is coordinated to the metal ions in a bidentate manner. The geometrical structures of these complexes are found to be octahedral. Interestingly, reaction with Cu(II) ion with this ligand undergoes hydrolytic cleavage to form ethylenediamine copper(II) complex and the corresponding aldehyde. The antimicrobial results indicate that the chloro complexes exhibit more activity than the acetato complexes. The complexes bind to CT–DNA by intercalation modes. Novel chloroform soluble ZnL₂Cl₂ complex exhibits tremendous antimicrobial, DNA binding and cleaving properties.     

Synthesis,characterization, antifungal,antibacterial and DNA cleavage studies of some heterocyclic Schiff base metal complexes

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, magnetic moment, powder XRD and SEM. The IR results demonstrate the bidentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The electronic spectral and magnetic moment results indicate that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex is square planar. Powder XRD and SEM indicate the crystalline state and surface morphology studies of the complexes. The antimicrobial activity of the synthesized ligand and its complexes were screened by disc diffusion method. The results show that the metal complexes were found to be more active than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence of H₂O₂. The Cu(II) complex showed increased nuclease activity in the presence of an oxidant when compared to the ligand and other complexes.     

Co(II), Ni(II), Cu(II), and Zn(II) complexes of 4-aminoantipyrine-derived Schiff base. Synthesis,structural elucidation,thermal, biological studies,and photocatalytic activity

The Schiff base ligand was prepared from 4-aminoantipyrine, acetamide, and m-phenylenediamine. Metal salts used for the synthesis of these complexes are Co(II), Ni(II), Cu(II), and Zn(II) acetates. The elemental analysis results are in accordance with proposed formula assigned to these complexes. In the IR spectra, the imine band is shifted to a lower wave number in the complexes. UV spectra and magnetic susceptibility measurements proposed square planar geometry for Co(II), Ni(II), and Cu(II) complexes and tetrahedral geometry for Zn(II) complex. The grain size of the metal complexes was estimated by the Scherrer formula using powder XRD. In the present study, the ligand and its metal complexes are found to be nanocrystalline. Thermal decomposition pattern is in agreement with the proposed formula of the complexes. Irreversible redox behavior of the complex was identified by cyclic voltammetric analysis. The photocatalytic activity of the synthesized complexes are high under UV-spectra using methylene blue dye. DNA studies reveal that the synthesized complexes exhibit both DNA cleavage and DNA binding properties. Antibacterial and antifungal activities were done by the minimum inhibitory concentration (MIC) method. Anticancer activity shows that Cu(II) complex has the highest cytotoxic effect in SK-MEL-28 cell line.     

A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: synthesis,characterization, and antibacterial properties

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L)₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal–ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.     

Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of tridentate Schiff base derived from vanillin and DL-alpha-aminobutyric acid

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from vanillin and dl-alpha-aminobutyric acid were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The analytical data show the composition of the metal complex to be [ML(H(2)O)], where L is the Schiff base ligand. The conductance data indicate that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen, phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex. The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that the metal complexes are more active than the ligand.     

Synthesis and photoluminescent properties of a Schiff-base ligand and its mononuclear Zn(II), Cd(II), Cu(II), Ni(II) and Pd(II) metal complexes

Mononuclear Zn(II), Cd(II), Cu(II), Ni(II) and Pd(II) metal complexes of Schiff-base ligand(HL₁) derived from 8-acetyl-7-hydroxycoumarin and P-phenylenediamine were prepared and characterized by microanalytical, mass, UV–Vis, IR, ¹H NMR, ¹³C NMR, ESR, conductance and fluorescence studies. The measured low molar conductance values in DMSO indicate that the complexes are non-electrolytes. The structures of the solid complexes under study are established by using IR, electronic and ESR spectroscopy suggesting that Zn(II) and Ni(II) complexes are octahedral, Cd(II) complex is tetrahedral, Cu(II) and Pd(II) complexes are square planar. The ESR spectrum of the Cu(II) complex in DMSO at 298 and 150 K was recorded and its salient features are reported, it supports the mononuclear structure. The Schiff base exhibited photoluminescence originating from intraligand (π–π*) transitions. Metal-mediated enhancement is observed on complexation of HL with Zn(II) and Cd(II), whereas metal-mediated fluorescence quenching occurs in Cu(II), Ni(II) and Pd(II).     

Spectral,thermal, electrochemical,biological and DFT studies on nanocrystalline Co(II), Ni(II), Cu(II) and Zn(II) complexes with a tridentate ONO donor Schiff base ligand

Co(II), Ni(II), Cu(II) and Zn(II) Schiff base complexes derived from 3-hydrazinoquionoxaline-2-one and 1,2-diphenylethane-1,2-dione were synthesized. The compounds were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, FTIR, UV–vis, ¹H NMR, ¹³C NMR, ESR, and mass spectral studies. Thermal studies of the ligand and its metal complexes were also carried out to determine their thermal stability. Octahedral geometry has been assigned for Co(II), Ni(II), and Zn(II) complexes, while Cu(II) complex has distorted octahedral geometry. Powder XRD study was carried out to determine the grain size of ligand and its metal complexes. The electrochemical behavior of the synthesized compounds was investigated by cyclic voltammetry. For all complexes, a 2 : 1 ligand-to-metal ratio is observed. The ligand and its metal complexes were screened for their activity against bacterial species such as E. coli, P. aeruginosa, and S. aureus and fungal species such as A. niger, C. albicans, and A. flavus by disk diffusion method. The DNA-binding of the ligand and its metal complexes were investigated by electronic absorption titration and viscosity measurement studies. Agarose gel electrophoresis was employed to determine the DNA-cleavage activity of the synthesized compounds. Density functional theory was used to optimize the structure of the ligand and its Zn(II) complex.     

Tetranuclear Zn(II) and Mononuclear Nickel(II) Complexes Based on Asymmetric Salamo-Type Ligands: Syntheses,Crystal Structures,and Fluorescent Properties

Two new complexes [{Zn(L¹)(μ-OAc)Zn(CH₃CHOHCH₃)}₂] and [Ni(L₂)(H₂O)(CH₃OH)] with asymmetric Salamo-type ligands (H₃L¹ and H₂L²) are synthesized and structurally characterized. In the Zn(II) and Ni(II) complexes, the terminal and central Zn(II) atoms are found to have slightly distorted square pyramidal and trigonal bipyramidal symmetries respectively, while the Ni(II) atom is hexa-coordinated and has a slightly distorted octahedral symmetry. Interestingly, a self-assembling continual zigzag 1D chain is formed by intermolecular hydrogen bonds in the Ni(II) complex. Furthermore, the Zn(II) and Ni(II) complexes in the ethanol solution show intense photoluminescence.     

Synthesis,spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

New metal based triazoles (1–12) have been synthesized by the interaction of novel Schiff base ligands (L¹–L³) with the Co(II), Ni(II), Cu(II) and Zn(II) metal ions. The Schiff base ligands and their all metal(II) complexes have been thoroughly characterized using various physical, analytical and spectroscopic techniques. In vitro bacterial and fungal inhibition studies were carried out to examine the antibacterial and antifungal profile of the Schiff bases in comparison to their metal(II) complexes against two Gram‐positive, four Gram‐negative and six fungal strains. The bioactivity data showed the metal(II) complexes to have more potent antibacterial and antifungal activity than their uncomplexed parent Schiff bases against one or more bacterial and fungal species. Copyright © 2012 John Wiley & Sons, Ltd.     

Dissociation constants of some Schiff bases and stability constants of their copper,cobalt, nickel and zinc complexes

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (H₂L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt (H₂L¹) were studied by potentiometric titration. The stability constants of H₂L and H₂L¹ Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 °C and 0.1 m KCl ionic strength. The dissociation constants for H₂L were obtained as 3.007, 7.620 and 9.564 and for H₂L¹, 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L)₂] for M = Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II) < Ni(II). The high stability of H₂L¹ towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest. Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry, deprotonation and stability constants via the SUPERQUAD computer program.     

Bi-, TRI- and Penta-Nuclear Complexes of Chelating Schiff Bases Derived from o-Acetoacetylphenol and Amine Complexes, [Ni(1,2-pn)2Cl2]·3H2O and [Cu(1,2-pn)2]SO4·2H2O

Two novel macroacylic Schiff base ligands were prepared by condensation of two diamine metal complexes, [Ni(1,2-pn)₂Cl₂]·3H₂O and [Cu(1,2-pn)₂]SO₄·2H₂O with o-acetoacetylphenol. The ligands MH₆L(M = Ni or Cu) are hexabasic and contain two O₄ coordination sites. They act as ligands towards transition metal ions yielding homo- and heteronuclear complexes of the type [NiH₄ LCu(H₂O)₂]·4H₂O, [MH₂LM' ₂(H₂O)₆], [MLM' ₄(H₂O)₈], [MH₂ LCe₂(NO>₃)₂(H₂O)₂] and [NiLTh₂(NO₃)₂(H₂O)₂] (M = Ni or Cu; M' = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ce(III), Th(IV) and UO₂ (VI)). The complexes were characterized by elemental analysis, thermogravimetric analysis (TGA), IR, visible and ESR spectra, magnetic susceptibility measurements and mass spectrometry. Magnetic moments were altered by the introduction of metal cations besides the one already present in the complex ligands. The M' cations were linked to two ketonic oxygen atoms and two phenyl oxygen atoms in [NiH₆ L(H₂O)₂] and [CuH₆ L] complex ligands. All homo- and hetero-, bi- and tri-nuclear complexes show antiferromagnetic interactions which are attributed to inter- or intramolecular interactions of the metal cations. Mass spectra of the complex ligands and selected homo- and heteronuclear complexes support the formula weights of these complexes. Visible and ESR spectra as well as magnetic moments indicated that the parent mononuclear complex ligands [MH₆ L] have an octahedral geometry for Ni(II) and a square-planar geometry distorted towards tetrahedral for Cu(II). The metal cations in bi-, tri- and pentanuclear complexes are octahedral or square-planar. The octahedral configuration is completed by chloride anions and/or solvent molecules.     

Studies on the complexing behavior of a potentially tetradentate Schiff-base ligand with some transition metal ions

The Schiff base furfural-histidine with Co(II), Ni(II), Cu(II), and Zn(II) in solution gives M(AB), M(AB)B, or M(AB)₂. The Schiff base is tetradentate in M(AB)₂ and M(AB)B and tridentate in M(AB)₂; [M(AB)₂] · 2H₂O (M = Co, Ni and Zn) and [Cu(AB)]NO₃ were synthesized and characterized by elemental analysis, molecular weight determination, conductance, IR, UV–Vis, and CV. The electronic spectral measurements indicate that M(AB)₂ (M = Co(II) and Ni(II)) are octahedral and Cu(AB) is square planar geometry. The donor groups in the complexes have been identified by IR. The complexes undergo irreversible one step, two-electron reduction. Antibacterial activity of the complexes was screened for Escherichia coli and Staphylococcus aureus. Cu(II) complex was found to be more active than the Co(II), Ni(II), and Zn(II) complexes.     

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 (L¹) and 2,2′‐bipyridine (2,2′-bipy) as a secondary chelator (L²). The prepared compounds have been characterized by elemental analysis, molar conductivity, magnetic susceptibility, FTIR, ¹H 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 (L¹) (L²) (X)] Y⋅nH₂O, L¹ = Schiff base, L² = 2,2′-bipy, (M = Cu(II), Co(II), Zn(II), Y = 2NO₃, n = 1), (M = Ni(II), X = 2H₂O, Y = 2NO_3, n = 0) and (M = Pd(II) Pt(II), Y = 2Cl, n = 0). Both L¹ and L² 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.     

Synthesis and characterization of nickel(II) complexes with three potentially hexadentate Schiff-base ligands and polyamines: X-ray crystal structure determination of one nickel(II) complex

Three new potentially hexadentate N₄O₂ Schiff-base ligands (H₂L¹, H₂L² and H₂L³) were prepared from the reaction of the polyamines N,N′-bis(2-aminophenyl)-1,2-ethanediamine (L¹), N,N′-bis(2-aminophenyl)-1,3-propanediamine (L²) and N,N′-bis(2-aminophenyl)-1,4-butanediamine (L³), respectively with salicylaldehyde. Reaction of the Schiff bases with Ni(II) salts in the presence of N(Et)₃ gave the neutral complexes [NiL⁴], [NiL⁵] and [NiL⁶]. Ni(II) complexes of the polyamines were also prepared. One of complexes [Ni(L¹)(MeCN)₂](ClO₄)₂·MeCN has been characterized through X-ray diffraction methods.