Theoretical and electrochemical studies on organometallic symmetrical schiff base complexes of Zn(II), Cu(II), Ni(II) and Co(II)

The electronic communication between two redox centres through a Schiff base complex has been investigated in a series of ethylenediimine-bis(1-ferrocenyl-1,3-butanedionate) complexes of Zn(II) 1, Cu(II) 2, Ni(II) 3 and Co(II) 4. Cyclic voltammetry experiments of 1 and 2 exhibit a unique two-electron reversible oxidation wave, whereas in the case of 3 and 4 two and three one-electron oxidation processes are, respectively, observed. These results suggest some electronic interaction between the iron atoms of the ferrocenyl groups. DFT calculations carried out on model complexes show that for all the studied compounds the removal of the first two electrons corresponds to the oxidation processes of the iron centres in the weakly coupled ferrocenyl termini. The electronic communication between the two iron centres increases on going from 1 to 4. Finally, a re-indexation of the bands observed in the UV-Visible spectra has been carried out using TDDFT calculations.     

Characterization studies of some bi- and tetradentate bifunctionalSchiff base complexes with Co(II), Ni(II), and Cu(II)

Co(II), Ni(II) and Cu(II) complexes of some bifunctional arylidene-o-phenylenediamineSchiff bases have been prepared. Formation, stoichiometry and stability of the complexes have been tested in solution using electronic spectral measurements. Characterization of the complexes has been accomplished primarily by elemental analysis, molar conductance as well as electronic and IR spectral measurements. It is concluded that theo,o-hydroxy derivative (L ₁) acts as a bivalent ONNO tetradentate ligand while the molecules of the other derivatives (L ₂-L ₅) are coordinated to the metal ions as bidentate NN ligands. The Cu(II)-L ₁ complex is suggested to possess a tetrahedral geometry whereas the other complexes are suggested to exhibit a distarted octahedral geometry. The different bands observed in the electronic spectra of the complexes inDMF solutions have been assigned to the -*,L M CT and d-d electronic transitions.

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Untersuchungen zur Charakterisierung einiger zwei- und vierzähniger bifunktionellerSchiffbasen-Komplexe mit Co(II), Ni(II) und Cu(II)

Zusammenfassung Es wurden die Co(II)-, Ni(II)- und Cu(II)-Komplexe einiger bifunktioneller Aryliden-o-phenylendiamin-Schiffbasen hergestellt. Unter Verwendung elektronenspektroskopischer Methoden wurde die Bildung, Stöchiometrie und Stabilität der Komplexe in Lösung untersucht. Die Charakterisierung erfolgte mittels Elementaranalysen, Leitfähigkeitsmessungen und Elektronen- bzw. IR-Spektroskopie. Es wird darauf geschlossen, daß daso,o-HydroxyderivatL ₁ als bivalenter vierzähniger ONNO Ligand wirkt, während die anderen Derivate (L ₂-L ₅) als zweizähnige NN Liganden an die Metallionen koordiniert sind. Für den Cu(II)-L ₁ Komplex wird eine tetraedrische Geometrie vorgeschlagen, währenddessen die anderen Komplexe eine verzerrte octaedrische Geometrie aufweisen. Die in den Elektronenspektren der Komplexe inDMF-Lösung auftretenden Banden werden den -*,L M CT und d-d Elektronenübergängen zugeordnet.

     

Salisaldehyde-2-aminobenzimidazole schiff base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)

New metal complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with salicylidine-2-aminobenzimidazole (SABI) are synthesized and their physicochemical properties are investigated using elemental and thermal analyses, IR, conductometric, solid reflectance and magnetic susceptibility measurements. The base reacts with these metal ions to give 1:1 (Metal:SABI) complexes; in cases of Fe(III), Co(II), Cu(II), Zn(II) and Cd(II) ions; and 1:2 (Metal:SABI) complexes; in case of Ni(II) ion. The conductance data reveal that Fe(III) complex is 2:1 electrolyte, Co(II) is 1:2 electrolyte, Cu(II), Zn(II) and Cd(II) complexes are 1:1 electrolytes while Ni(II) is non-electrolyte. IR spectra showed that the ligand is coordinated to the metal ions in a terdentate mannar with O, N, N donor sites of the phenloic -OH, azomethine -N and benzimidazole -N3. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes. The thermal decomposition of the complexes is studied and indicates that not only the coordinated and/or crystallization water is lost but also that the decomposition of the ligand from the complexes is necessary to interpret the successive mass loss. Different thermodynamic activation parameters are also reported, using Coats-Redfern method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,structures, and property studies on Zn(II), Ni(II), and Cu(II) complexes with a Schiff base ligand containing thiocarbamide group

A Schiff base ligand containing thiocarbamide group of 4-phenyl-1-(4-methoxyl-1-phenylethylidene)thiosemicarbazide (HL) and its three mononuclear metal complexes of ZnL₂ (1), NiL₂ (2), and CuL₂ (3) have been synthesized. Elemental analysis, IR, and X-ray single crystal diffraction characterizations for the ligand and the three complexes have been carried out. In the three complexes, the central metallic ions of Zn²⁺, Ni²⁺, and Cu²⁺ coordinate with two deprotonated ligands of L⁻, respectively. In 1, Zn²⁺ ion adopts a distorted tetrahedral geometry, while in 2 and 3, both the Ni²⁺ and Cu²⁺ ions possess distorted square planar configurations. For the four compounds, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of HL and 1 are corresponding with electronic transitions of n → π* and π → π* in the ligand itself and the electronic spectra of 2 and 3 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Electrochemical investigations reveal that the different metal–ligand interactions have changed the peak shapes and peak locations, which are corresponding with the DFT-B3LYP/LANL2DZ calculational results. Fluorescence spectra measurements indicate that the ligand emits purple fluorescence and the complex 1 emits stronger blue fluorescence, while the complexes 2 and 3 quench fluorescence. The thermal analyses result show that the three complexes undergo two similar decomposition processes because of their similar geometric configurations.     

Preparation of Schiff’s base complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) and their spectroscopic, magnetic, thermal, and antifungal studies

The potassium salt of salicylidene-DL-alanine (KHL), bis(benzylidene)ethylenediamine (A¹), thiophene-o-carboxaldene-p-toluidine (A²), and its metal complexes of the formula [(M^II(L)(A)(H₂O)] (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); A = A¹ or A²) are prepared. They are characterized by elemental analysis, magnetic susceptibility measurements, thermogravimetric analysis, and infrared and electronic spectral studies. The electronic spectral and magnetic moment data suggest an octahedral geometry for the complexes. All of these complexes, metal nitrates, fungicides (bavistin and emcarb), and ligands are screened for their antifungal activity against Aspergillus niger, Fusarium oxysporum, and Aspergillus flavus using a plate poison technique. The complexes show higher activity than those of the free ligands, metal nitrate, and the control (DMSO) and moderate activity against bavistin and emcarb. The text was submitted by the authors in English.     

Phenoxide bridged tetranuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes: electrochemical, magnetic and antimicrobial studies

Phenoxide bridged later first row transition metal(II) complexes have been prepared by the interaction of later 3d transition metal(II) chlorides with tetranucleating compartmental Schiff base ligand system derived from 2,6-diformyl-4-methylphenol, p-phenylenediamine and 2-hydrazinobenzothiazole. Ligand and complexes were characterized by analytical, spectral (IR, UV-visible, ESR, FAB-mass and fluorescence), magnetic and thermal studies. All complexes are found to have octahedral geometry. The mutual influence of metal centres in terms of cooperative effect on the electronic, magnetic, electrochemical and structural properties was investigated. The Schiff base and its complexes have been screened for their antibacterial (against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa) and antifungal activities (against Aspergillus niger, and Candida albicans).     

Ni(II), Cu(II), and Zn(II) dinuclear metal complexes with an aza-phenolic ligand: crystal structures,magnetic properties,and solution studies

The basicity behavior and ligational properties of the ligand 2-((bis(aminoethyl)amino)methyl)phenol (L) toward Ni(II), Cu(II), and Zn(II) ions were studied by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, l = 0.15 mol dm-3). The anionic L-H- species can be obtained in strong alkaline solution; this species behaves as tetraprotic base (log K1 = 11.06, log K2 = 9.85, log K3 = 8.46, log K4 = 2.38). L forms mono- and dinuclear complexes in aqueous solution with all the transition metal ions examined; the dinuclear species show a [M2(L-H)2]2+ stoichiometry in which the ligand/metal ratio is 2:2. The studies revealed that two mononuclear [ML-H]+ species self-assemble, giving the dinuclear complexes, which can be easily isolated from the aqueous solution due to their low solubility. This behavior is ascribed to the fact that L does not fulfill the coordination requirement of the ion in the mononuclear species and to the capacity of the phenolic oxygen, as phenolate, to bridge two metal ions. All three dinuclear species were characterized by determining their crystal structures, which showed similar coordination patterns, where all the single metal ions are substantially coordinated by three amine functions and two oxygen atoms of the phenolate moieties. The two metals in the dinuclear complexes are at short distance interacting together as shown by magnetic measurements performed with Ni(II) and Cu(II) complexes, which revealed an antiferromagnetic coupling between the two metal ions. The [Cu2(L-H)2]2+ cation shows a phase transition occurring by the temperature between 100 and 90 K; the characterization of the compounds existing at different temperatures was investigated using X-ray single-crystal diffraction, EPR, and magnetic measurements.     

Cu(II), Ni(II), and Hg(II) thiocyanate complexes incorporating 4,5-diazafluoren-9-one: synthesis,spectroscopic characterization,X-ray studies,and magnetic properties

This article presents a combined experimental and computational study of the complexes [Cu(dafone)₂(SCN)₂] (1), [Ni(dafone)₂(SCN)₂] (2) and [Hg(dafone)(SCN)₂] (3), where dafone stands for 4,5-diazafluoren-9-one. The compounds have been studied by IR, UV–Vis spectroscopy, and single crystal X-ray diffraction. The electronic structures of these complexes have been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of 1, 2, and 3 have been calculated with the time-dependent DFT method, and their UV–Vis spectra have been discussed on this basis.     

Synthesis, spectroscopic and cyclic voltammetry studies of novel azacrown ether containing vic-dioxime ligand and its Ni(II), Cu(II), Co(II), Cd(II) and Zn(II) complexes

In this study, the novel vic-dioxime ligand (3) and its Ni(II), Cu(II), Co(II), Cd(II) and Zn(II) complexes (4–8) were synthesized for the first time by condensation reactions of N-(4-aminophenyl)aza-15-crown-5 (1) and anti-chlorophenylchloroglyoxime (2). All of these new compounds were characterized by the elemental analysis, Fourier transform infrared, ultraviolet–visible, mass spectrometry, ¹H NMR, ¹³C NMR and magnetic susceptibility measurements. The electrochemical properties of the ligand and its complexes have been investigated by cyclic voltammetry at the glassy carbon electrode in 0.1 M TBATFB in DMSO.     

DNA interaction studies of Cu(II), Co(II), and Ni(II) chelates derived from schiff base ligand

Chelates of the type M(L)₂ {where, M ?= ?Co(II), Ni(II) and Cu(II), and L ?= ?3-{(E)-[(2-hydroxy-3-methoxyphenyl)methylidene]amino}pyridin-4(1H)-one)} were synthesized by using the Schiff base ligand in the stochiometric ratio 2:1 (L:M) and Schiff base ligand (L) was synthesized by simple condensation between 2-hydroxy-3-methoxybenzaldehyde with 3-aminopyridin-4-ol. The structure and formation of synthesized compounds were established by different analytical and spectroscopic methods like, elemental analysis, UV- spectroscopy, FT-IR, Proton and Carbon NMR, mass spectrometry and Powder XRD. Further, the synthesized chelates screened for the DNA binding studies of Calf Thymus (CT)-DNA by exploiting electronic absorption spectra, relative viscosity measurements and thermal denaturation methods. The proposed DNA binding mode supports the enhancement in the binding activity of the complexes in presence of newly synthesized ligand. The cleavage activities of the PUC-18 DNA in the presence and the absence of the complexes were recorded with the help of gel-electrophoresis. The cleavage experiment results reveals that all the synthesized chelates can cleave pUC-18 DNA effectively.     

Ni(II) and Cu(II) complexes with ONNO asymmetric tetradentate Schiff base ligand: synthesis,spectroscopic characterization,theoretical calculations,DNA interaction and antimicrobial studies

A novel Schiff base, namely Z ‐3‐((2‐((E )‐(2‐hydroxynaphthyl)methylene)amino)‐5‐nitrophenylimino)‐1,3‐dihydroindin‐2‐one, was synthesized from the condensation of 2‐hydroxy‐1‐naphthaldehyde and isatin with 4‐nitro‐o ‐phenylenediamine. It was structurally characterized on the basis of ¹H NMR, ¹³C NMR and infrared spectra and elemental analyses. In addition, Ni(II) and Cu(II) complexes of the Schiff base ligand were prepared. The nature of bonding and the stereochemistry of the investigated complexes were elucidated using several techniques, including elemental analysis (C, H, N), Fourier transform infrared and electronic spectroscopies and molar conductivity. The thermal behaviours of the complexes were studied and kinetic–thermodynamic parameters were determined using the Coats–Redfern method. Density functional theory calculations at the B3LYP/6‐311G++ (d, p) level of theory were carried out to explain the equilibrium geometry of the ligand. The optimized geometry parameters of the complexes were evaluated using LANL2DZ basis set. The total energy of highest occupied and lowest unoccupied molecular orbitals, Mullikan atomic charges, dipole moment and orientation are discussed. Moreover, the interaction of the metal complexes with calf thymus DNA (CT‐DNA) was explored using electronic spectra, viscosity measurements and gel electrophoresis. The experimental evidence indicated that the two complexes could strongly bind to CT‐DNA via an intercalation mechanism. The intrinsic binding constants of the investigated Ni(II) and Cu(II) complexes with CT‐DNA were 1.02 × 10⁶ and 2.15 × 10⁶ M⁻¹, respectively, which are higher than that of the standard ethidium bromide. Furthermore, the bio‐efficacy of the ligand and its complexes was examined in vitro against the growth of bacteria and fungi to evaluate the antimicrobial potential. Based on the obtained results, the prepared complexes have promise for use as drugs. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and spectroscopic studies of novel Cu(II), Co(II), Ni(II) and Zn(II) mixed ligand complexes with saccharin and nicotinamide

Four novel mixed ligand complexes of Cu(II), Co(II), Ni(II) and Zn(II) with saccharin and nicotinamide were synthesised and characterised on the basis of elemental analysis, FT-IR spectroscopic study, UV–Vis spectrometric and magnetic susceptibility data. The structure of the Cu (II) complex is completely different from those of the Co(II), Ni(II) and Zn(II) complexes. From the frequencies of the saccharinato CO and SO₂ modes, it has been proven that the saccharinato ligands in the structure of the Cu complex are coordinated to the metal ion ([Cu(NA)₂(Sac)₂(H₂O)], where NA — nicotinamide, Sac — saccharinato ligand or ion), whilst in the Co(II), Ni(II) and Zn(II) complexes are uncoordinated and exist as ions ([M(NA)₂(H₂O)₄](Sac)₂).     

Synthesis and spectral studies of new macrocyclic Schiff base Cu(II), Ni(II), Cd(II), Zn(II), Pb(II), and La(III) complexes containing pyridine head unit

1,6-Bis(2-formylphenyl) hexane (I) was derived from 1,6-dibromohexane with salicylaldehyde and K₂CO₃ and the ligand (L) was derived from compound I and 2,6-diaminopyridine. Then, the Cu(II), Ni(II), Pb(II), Zn(II), Cd(II), and La(III) complexes with L were synthesized by the reaction of this ligand and Cu(NO₃)₂ · 3H₂O, Ni(NO₃)₂ · 6H₂O, Pb(NO₃)₂, Zn(NO₃)₂ · 6H₂O, Cd(NO₃)₂ · 6H₂O, and La(NO₃)₃ · 6H₂O, respectively. The ligand and its metal complexes were characterized by elemental analysis, IR, ¹H and ¹³C NMR, UV-Vis spectra, magnetic susceptibility, conductivity measurements, and mass spectra. All complexes are diamagnetic and the Cu(II) complex is binuclear. The article is published in the original.     

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.     

Synthesis, characterization and antioxidant activity of naringenin Schiff base and its Cu(II), Ni(II), Zn(II) complexes

A new ligand, naringenin-2-hydroxy benzoyl hydrazone (H(5)L), was prepared by condensation of naringenin with 2-hydroxy benzoyl hydrazine. Its Cu(II), Ni(II), Zn(II) complexes have also been synthesized and characterized on the basis of (1)H-NMR, IR, UV-Vis spectra, elemental analyses, molar conductivity and thermal analyses. The general formula of these complexes was M(H(3)L) [M=Cu(II), Ni(II) and Zn(II)]. In addition, the antioxidant activities (superoxide and hydroxyl radical) of the free ligand and its complexes were determined in vitro. These compounds were found to possess potent antioxidant activity and be better than standard antioxidants like vitamin C and mannitol. In particular, the Cu(II) complex displayed excellent activity on the superoxide radical.     

A new molecular building blocks: Synthesis,crystal structure,magnetic and spectroscopic properties of Cu(II) and Ni(II) macrocyclic complexes

New higly unsaturated macrocyclic building blocks [CuLSCN]·ClO₄ (1) (L = N-dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) and [NiL(SCN)₂] (2) (L = N-dl-5,12-dimethyl-7,14-diisopropyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) were synthesized and the crystal structures of both compounds were determined. Both complexes crystallizes in monoclinic, space group P2₁/n (1) and P2₁/c (2). Their magnetic properties were studied over the temperature range 1.8–300 K using a Quantum Design SQUID magnetometer (MPMSXL-5-type). The results indicate that both compounds behave as weakly interacting paramagnetic centers in the crystal lattice. The effects of hydrogen bond mediating the magnetic exchange interactions on the spin density have been evidenced by DFT calculations. The NIR–Vis–UV diffuse-reflectance electronic spectra confirm the square pyramidal and octahedral geometry around Cu²⁺ and Ni²⁺ metal ions.     

Spectroscopic studies of bridged binuclear complexes of Co(II), Ni(II), Cu(II) and Zn(II)

Binuclear cobalt(II), nickel(II), copper(II) and zinc(II) complexes of general composition [M₂L^1-2(μ-Cl)Cl₂] · nH₂O with the Schiff-base ligands (where L¹H and L²H are the potential pentadentate ligands derived by condensing 2,6-diformyl-4-methylphenol with 4-amino-3-antipyrine and 2-hydroxy-3-hydrazinoquinoxiline, respectively) have been synthesized and characterized. Analytical and spectral studies support the above formulation. ¹H-NMR and IR spectra of the complexes suggest they have an endogenous phenoxide bridge, with chloride as the exogenous bridge atom. The electronic spectra of all the complexes are well characterized by broad d–d and a high intensity charge-transfer transitions. The complexes are chloro-bridged as evidenced by two intense far-IR bands centered around 270–280 cm⁻¹. Magnetic susceptibility measurements show that complexes are antiferromagnetic in nature. The compounds show significant growth inhibitory activity against fungi Aspergillus niger and Candida albicans and moderate activity against bacteria Bacillus cirroflagellosus and Pseudomonas auresenosa.     

Synthesis, spectroscopic, and thermal properties of some azomethine complexes of Cu(II), Ni(II), and Pt(II)

Four polydentate azomehines and their mono- and binuclear Pt(II), Cu(II), and Ni(II) complexes were synthesized and characterized. The resulting complexes were characterized by FTIR, magnetic measurements, elemental analysis, conductivity measurements, and thermal analysis. Electronic spectra and magnetic susceptibility measurements sustain the proposed distorted square-planar structures for the copper complexes. The electronic spectra display the characteristic pattern of square-planar stereochemistry for the other complexes. The thermal analyses have evidenced the thermal intervals of stability and also the thermodynamic effects that accompany them. Azomethine complexes have a similar thermal behavior for the selected metal ions. The decomposition processes as water elimination, chloride anion removal as well as degradation of the organic ligands were observed.