In situ electrochemical microbalance studies of polymerization and redox processes in polymeric complexes of transition metals with Schiff bases

The mechanism and kinetics of polymerization of [M(Schiff)] complexes (M = Ni, Pd, Cu; Schiff is tetradentate N₂O₂ Schiff bases) and also the regularities of redox processes involving poly-[M(Schiff)] polymers are studied by electrochemical quartz crystal microbalance method. The number of electrons involved in the reversible oxidation-reduction of each polymer fragment is calculated and the composition of species that take part in the charge transport at the polymer oxidation-reduction is elucidated.     

The electrocatalytic reactions of adenine, guanine, H2O, H2O2, N2H4, and l -cysteine catalyzed by poly(Ni(4-TMPyP)) film-modified electrodes

Electrochemical preparation of poly(nickel tetrakis(N-methyl-4-pyridyl)porphyrin) tetratosylate (poly-Ni(4-TMPyP)) produces stable and electrochemically active films in strong and weak basic aqueous solutions. These films were produced on glassy carbon and gold electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly(Ni(4-TMPyP)) films. The electrochemical properties of poly(Ni(4-TMPyP)) films indicate that the redox process was confined in to the immobilized film. The electrochemical quartz crystal microbalance results showed an ion exchange reaction for the redox couple. The polymer films showed one new redox couple when transferred to strong and weak basic aqueous solutions and the formal potential was found to be pH dependent. The electrocatalytic oxidation of H₂O by a nickel tetrakis(N-methyl-4-pyridyl)porphyrin film-modified electrode was also performed. The mechanism of oxygen evolution was determined by cyclic voltammetry, chronoamperometry and rotating ring disc electrode methods. The oxygen evolution was determined by a bicatalyst system using hemoglobin, and iron tetrakis (N-methyl-2-pyridyl)porphyrin as catalyst to detect the oxygen by electrocatalytic reduction. The electrocatalytic oxidations of adenine, guanine, H₂O₂, N₂H₄, NH₂OH, and l-cysteine by the film-modified electrode obtained from water-soluble nickel porphyrin were also investigated.     

Synthesis,characterization, electrochemical behaviour and X-ray crystal structures of nickel(II) complexes with a N2O4 donor set macrocyclic Schiff base ligand

Two nickel(II) complexes of [1 + 1] macrocyclic Schiff base ligand (L) have been prepared by cyclocondensation reactions between 1,3-diamino-2-propanol and 2-[3-(2-formylphenoxy)-2-hydroxypropoxy] benzaldehyde, using NiX₂ (X = Br, and I) salts as template agents, and characterized by elemental analyses, IR, molar conductivity and electronic spectra in both solid and solution states. The single-crystal X-ray diffractions of the complexes are also reported that contain nickel(II) ion in a distorted octahedral geometry coordination of N₂O₃X (X = Br, I and NO₃). In all complexes the ligand behaves as a pentadentate ligand. Cyclic voltammetric studies of nickel(II) complexes indicate a quasi-reversible redox wave in the negative potential range.     

Synthesis and characterization of a new Schiff base derived from 2,3-diaminopyridine and 5-methoxysalicylaldehyde and its Ni(II), Cu(II) and Zn(II) complexes. Electrochemical and electrocatalytical studies

We describe the synthesis and characterization of a new tetradentate Schiff base ligand obtained from 2,3-diaminopyridine and 5-methoxysalicylaldehyde. This ligand (H₂L) reacted with nickel(II), copper(II), and zinc(II) acetates to give complexes. The ligand and its metal complexes were characterized using analytical, spectral data (UV–vis, IR, and mass spectroscopy), and cyclic voltammetry (CV). The crystal structure of the copper complex was elucidated by X-ray diffraction studies. The electrochemical behavior of these compounds, using CV, revealed that metal centers were distinguished by their intrinsic redox systems, e.g. Ni(II)/Ni(I), Cu(II)/Cu(I), and Zn(II)/Zn(I). Moreover, the electrocatalytic reactions of Ni(II) and Cu(II) complexes catalyze the oxidation of methanol and benzylic alcohol.     

Synthesis, characterization and electrochemical investigation of a novel vic-dioxime ligand and its some transition metal complexes

4-(Chloroacetyl)diphenyl ether was synthesized from chloroacetyl chloride and diphenyl ether in the presence of AlCl₃ as catalyst in a Friedel-Crafts reaction. Then, its keto oxime and dioxime derivatives were prepared. 4-phenoxy-(N-4-chlorophenylamino)phenylglyoxime (H₂L) was synthesized from 4-(phenoxy)chlorophenylglyoxime and 4-chloroaniline. Ni(II), Co(II) and Cu(II) complexes of H₂L were obtained. The mononuclear Ni(II), Co(II) and Cu(II) complexes of H₂L have a metal–ligand ratio of 1:2 and the ligand coordinates through the two N atoms, as do most of the vic-dioximes. The structure of the ligand was identified by FT-IR, ¹H NMR, ¹³C NMR, ¹³C NMR (APT) spectroscopy and elemental analysis data. The structures of the complexes were characterized on the basis of FT-IR, ICP-AES, UV-Vis, elemental analysis, magnetic susceptibility measurements, and cyclic voltammetry. The electrochemical measurements were obtained by using cyclic voltammetry in DMF solution at room temperature. The electrochemical behaviors of H₂L and its complexes showed that the redox process of H₂L has one irreversible oxidation wave, whereas the redox processes of the complexes have both oxidation and reduction waves with metal centered.     

Crystal structure of a new pentadentate symmetrical: di[4-(phenylimino)pentan-2-one] ether. Structural and electrochemical studies of its Co<Superscript>II</Superscript>, Ni<Superscript>II</Superscript>, Cu<Superscript>II</Superscript> and Cd<Superscript>II</Superscript> complexes

The crystal structure of a new symmetrical pentadentate N₂O₃ Schiff base: di[4-(phenylimino)pentan-2-one] ether (H₂L) is described. In the solid state, the ligand appears as a keto-imine tautomer, while in DMSO solution, the eneamine form is observed. This ligand coordinates cobalt(II), nickel(II), copper(II) and cadmium(II). The structures of these new complexes are described using infrared and electronic spectroscopy, ¹H-n.m.r. and d.s.c. The cyclic voltammograms of the ligand and the complexes in DMF are discussed.     

Synthesis,spectroscopic, DNA cleavage and antibacterial activity of binuclear schiff base complexes

The binuclear Schiff base complexes are formed newly using different transition metals at their stable oxidation state as Cu(II), Ni(II), and VO(II). 3,3′,4,4′-tetraminobiphenyl and 2-aminobenzaldehyde were condensed to form a new Schiff base ligand having an two N₄ group responsible for better chelating to the metal centers. The ligand and their complexes have been established by analytical, spectral and electrochemical data. The interaction studies of the complexes with CT-DNA were carried out using cyclic voltammetry, viscosity measurements and fluorescence spectroscopy. The free ligand and their metal complexes were screened for their antimicrobial activities against the following species: Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus. A comparative study of minimum inhibitory concentration (MIC) values of the Schiff base and its complexes indicate that the metal complexes exhibit higher antibacterial activity than the free ligand.     

Variation in coordinative property of two different N<Subscript>2</Subscript>O<Subscript>2</Subscript> donor Schiff base ligands with nickel(II) and cobalt(III) ions: characterisation and single crystal structure elucidation

A nickel(II) and a cobalt(III) complex of two different potentially tetradentate Schiff bases with different binding modes have been synthesised. The nickel(II) complex [NiL¹] · CH₃OH (1) was formed, on reacting the metal salt with a perfectly symmetrical N₂O₂ tetradentate Schiff base ligand H ₂ L ¹ , which is the 1:2 condensation product of 1,3-diamino propane and 2-hydroxyacetophenone. The cobalt(III) complex [Co(HL²)₃] · (ClO₄)₃ · H₂O (2) was synthesised using an asymmetric N₂O₂ tetradentate Schiff base ligand HL ² on condensing N,N-dimethyl-1,3-diamino propane with o-vanillin in 1:1 mmol ratio. Although both Schiff bases are N₂O₂ functionalised, they showed variation in their coordinative property with nickel(II) and cobalt(III) ions. Both the complexes were characterised by IR spectroscopy and cyclic voltammetry and their single crystal structures clearly indicate that 1 is a mononuclear species whereas 2 is a hydrogen-bonded dimer.     

A nickel(II) coordination polymer derived from a tridentate Schiff base ligand with N,O-donor groups: synthesis,crystal structure,spectroscopy, electrochemical behavior and electrocatalytic activity for H<Subscript>2</Subscript>O<Subscript>2</Subscript> electroreduction in alkaline medium

A Ni(II) coordination polymer [C₄₂H₄₂K₂N₄Ni₄O₂₇] has been synthesized under open-air mild reaction conditions and characterized by physicochemical and spectroscopic methods. The X-ray crystal structure of the complex has been obtained. The crystallographic data revealed that each metal center is in a distorted octahedral geometry where the ligand coordinates to the metal centers by a nitrogen from the imine group, an oxygen from the carboxylic acid and a phenoxide group as an endogenous bridge to the metal centers. The coordination sphere is completed by an acetate, coordinated as an exogenous bridging ligand to both nickel centers, plus one terminal water ligand on each nickel. The polymeric structure is an infinite chain involving the binuclear nickel structure and K⁺ ions. Carbon paste electrodes modified with the Ni(II) coordination polymer were prepared, and the electrochemical behavior and electrocatalytic activity toward H₂O₂ reduction were investigated. The electrochemical results suggest that this Ni(II) coordination polymer has good catalytic activity with respect to H₂O₂ reduction.     

Binuclear metal(II) complexes of a 30-membered hexa-aza macro-cyclic ligand

Summary Schiff base [2 + 2] condensation of p-phthalaldehyde with the triamine 1,7-diamino-4-azaheptane followed by reduction with NaBH₄ gives a 30-membered hexa-aza macrocyclic ligand. A series of binuclear copper(II), nickel(II) and zinc(II) complexes have been prepared and characterized, ¹H-n.m.r., u.v.-vis. and i.r. measurements are reported with associated magnetic and electrochemical studies.Author to whom all correspondence should be directed.     

Synthesis,spectral characterization,X-ray crystal structure,electrochemical studies,and DNA interactions of a Schiff base pro-ligand and its homobimetallic complexes containing the cysteamine moiety

A Schiff base, N,N′-(3,4-dithiahexane-1,6-diyl)bis(5-methylsalicylideneimine), was synthesized and characterized by X-ray crystallography. Dimeric complexes of nickel(II), palladium(II), and vanadium(IV) were synthesized by the reactions of the Schiff base with nickel(II) acetate, palladium(II) acetate, and vanadyl acetylacetonate in 1:1 molar ratio. In all three complexes, the thiol group was deprotonated and coordinated to the metal. The X-ray structure of the Schiff base showed that in the crystalline form, the SH groups were oxidized to the corresponding disulfide. In the dimeric complexes, coordination took place through the azomethine nitrogen, enolic oxygen, and sulfur atoms. The metal-to-ligand ratio was 1:1, and molar conductance data revealed that the metal complexes were nonelectrolytes. The free Schiff base and its complexes showed photoluminescence in methanol at room temperature. The redox behavior of the compounds was studied by cyclic voltammetry in DMF, which showed both quasi-reversible and irreversible processes. The interaction of the complexes with DNA was investigated by electronic absorption spectroscopy.     

Studies on DNA cleavage and antimicrobial screening of transition metal complexes of 4-aminoantipyrine derivatives of N2O2 type

A new series of transition metal complexes of Cu(II), Ni(II), Zn(II) and VO(IV), were synthesized from the Schiff base (L) derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and acetylacetone. The structural features were arrived from their elemental analyses, magnetic susceptibility, molar conductance, Mass, IR, UV-Vis., ¹H NMR and ESR spectral studies. The data show that the complexes have composition of [ML]X type. The UV-Vis., magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except for VO(IV) complex which has square-pyramidal geometry. The redox behavior of copper and vanadyl complexes were studied by cyclic voltammetry. The antimicrobial screening tests were also recorded and gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that the copper and nickel complexes cleave DNA through redox chemistry, whereas other complexes are not effective.     

Preparation,characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN]·H2O complex

Nickel(II) complexes of general empirical formula, NiLX·nH₂O (L = deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxybenzaldehyde; X = Cl^–, Br^–, NCS^–, AcO^– or CN^–; n = 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN]·H₂O complex (ONMeS = anionic form of the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands.     

Syntheses and characterization of new tetraazamacrocyclic copper(II) complexes as a dual functional mimic enzyme (catalase and superoxide dismutase)

A series of macrocyclic complexes, [Cu(TAAP)]X₂, X?=?ClO₄ and CH₃COO; [Cu(TAAP)X]X, X?=?NO₃, Cl, and Br, have been synthesized by self-condensation of 5-amino-3-methyl-l-phenylpyrazole-4-carbaldehyde (AMPC) in the presence of copper(II). Elemental analyses and conductivity measurements confirm the stoichiometry of the ligand and complexes, while the characteristic absorption bands in IR spectra confirmed the formation of ligand framework around copper. Square-pyramidal and square-planar stereochemistries have been proposed for the five-coordinate (nitrato and halogeno) and four-coordinate (perchlorate and acetate) complexes. The electrochemical properties and thermal behaviors have been studied by cyclic voltammetry and TGA. Mimetics of antioxidant enzymes such as superoxide dismutase (SOD) and catalase demonstrated that there is a correlation between the observed redox properties and the SOD and catalase biomimetic catalytic activities of the copper(II) complexes.     

Synthesis and characterization of manganese(II), nickel(II), copper(II) and zinc(II) Schiff-base complexes derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-mercaptoethylamine leads to 2,9-bis(2-ethanthiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with manganese, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptoethyl)-2-azaethene]-1,10-phenanthroline (L). The [M(L)Cl₂] complexes [where M = Mn(II), Ni(II), Cu(II) and Zn(II) ions] were characterized by physical and spectroscopic measurements which indicated that the ligand is a tetradentate N₄ chelating agent.     

Synthesis and study of catalysts of electrochemical oxygen reduction reaction based on polymer complexes of nickel and cobalt with Schiff bases

The article presents the results of studies of new nanosize catalysts of electrochemical oxygen reduction reaction (ORR) obtained using the method of thermal decomposition of polymer complexes of nickel and cobalt with tetradentate (N₂O₂) Schiff bases. The catalysts are characterized using the methods of thermogravimetry, electrochemical quartz microgravimetry, scanning electron microscopy with X-ray microanalysis, XPS. The ORR process on electrodes modified by the above catalysts was studied using the voltammetry and rotating disk electrode techniques. The obtained catalysts manifested high specific activity per initial polymer mass (more than 600 mA/mg).     

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

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

Electrochemical and spectroscopic characterization of anodically formed nickel salen polymer films on glassy carbon, platinum, and optically transparent tin oxide electrodes in acetonitrile containing tetramethylammonium tetrafluoroborate

Anodically polymerized films of nickel salen formed on glassy carbon, optically transparent tin oxide, and platinum electrodes in acetonitrile containing tetramethylammonium tetrafluoroborate have been examined by means of cyclic voltammetry, thin-layer voltammetry, spectroelectrochemistry, and scanning electron microscopy. With the aid of thin-layer voltammetry, it has been confirmed that the global oxidative polymerization of nickel(II) salen involves three electrons per monomer. Polymerization proceeds through two distinct phases, the formation of which depend on the potential. Once the polymer film has been formed, the anodic process consists of the reversible one-electron nickel(III)/nickel(II) redox couple. Cyclic voltammetry along with spectroelectrochemistry has been employed to probe the roles of the nickel(III)/nickel(II) and nickel(II)/nickel(I) redox couples in the electrochemical response of the polymer film as well as the interconversion of the different oxidation states of nickel.     

One‐Electron Reduction of Acenaphthene‐1,2‐Diimine Nickel(II) Complexes

New nickel‐based complexes of 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene (dpp‐bian) with BF₄^? counterion or halide co‐ligands were synthesized in THF and MeCN. The nickel(I) complexes were obtained by using two approaches: 1) electrochemical reduction of the corresponding nickel(II) precursors; and 2) a chemical comproportionation reaction. The structural features and redox properties of these complexes were investigated by using single‐crystal X‐ray diffraction (XRD), cyclic voltammetry (CV), and electron paramagnetic resonance (EPR) and UV/Vis spectroscopy. The influence of temperature and solvent on the structure of the nickel(I) complexes was studied in detail, and an uncommon reversible solvent‐induced monomer/dimer transformation was observed. In the case of the fluoride complex, the unpaired electron was found to be localized on the dpp‐bian ligand, whereas all of the other nickel complexes contained neutral dpp‐bian moieties.     

Synthesis,electrochemical properties and electro-oxidative polymerization of copper(II) and nickel(II) complexes with N′-benzoylthiourea ligands containing pyrrole groups

The synthesis of four N-benzoylthioureas containing pyrrole groups are described. The electrochemical behaviour of their copper(II) and nickel(II) complexes has been investigated in aprotic solvents by coulometry and by cyclic voltammetry which indicates that the electrochemical oxidation of copper complexes leads to the formation of Cu^II-benzylureate complexes. The oxidative polymerization of nickel complexes on platinum and a glassy carbon electrode, has been carried out in MeCN.The redox properties of the polymeric films formed have been examined by cyclic voltammetry. The films are catalytically active in the electroreduction of oxygen.