Voltammetric behaviour of copper(iii) and its analytical applications

Copper(II) and copper(III) complexes with periodate or tellurate ligands are electroactive at a smooth platinum electrode, giving an anodic, cathodic or cathanodic wave in the presence of alkaline hydroxide solutions containing copper(II), copper(III), or copper(II)-copper(III) species, respectively. The corresponding limiting currents are diffusion-controlled. The following analytical applications are proposed: (a) amperometric titration of copper(III) solutions; (b) voltammetric determination of copper. Results of amperometric titrations of copper(III) were similar to those by an established procedure. Voltammetry of copper(II) allows the metal to be determined down to concentrations of 1·10^-5M, even in the presence of different ions; the procedure can be applied to such heat-transfer media for nuclear reactors as sodium and potassium metals and their hydroxides.     

Determination of iron(II) and iron(III) by flow injection and amperometric detection with a glassy carbon electrode

Flow injection analysis can be used for the determination of both iron(II) and iron(III) with an amperometric detector. The flow-through cell contains a glassy carbon electrode. Selection of the appropriate voltammetric technique, choice of the indication potentials, sample size, composition of the carrier stream, etc., are discussed. The limit of determination is about 10^-6 M; the calibration curves are linear in the concentration ranges 10^-3–10^-5 M for iron(III) and 5 × 10^-4–10^-5 M for iron(II). To illustrate the potentialities of the proposed method, standard rocks have been analysed.     

Electrochemical Behavior of Iron(III)/Iron(II) Couple in Dimethylformamide

The electrochemical behavior of the iron(III)/iron(II) couple was investigated in both complexing (Cl⁻) and noncomplexing (ClO⁻₄) media in dimethylformamide (DMF), and the results were compared with the results obtained in aqueous solutions. The diffusion coefficients for iron(III) and iron(II) in DMF are larger in complexing medium than in noncomplexing medium, contrary to the results obtained in aqueous solutions. The heterogeneous electron transfer rate constants for the iron(III)/iron(II) couple obtained in DMF were found to be smaller in DMF solution as a result of the specific adsorption of DMF. The formal potential of the Fe(III)/Fe(II) couple in DMF is about 0.2 V less positive in noncomplexing medium as a result of the greater stabilization of iron(III) by the strongly cation-solvating DMF. The formal potential of the same couple in complexing medium (Cl⁻) was found to be 0.5 V less positive due to a combination of solvation and complexation effects. Cyclic voltammetric investigations show a quasi-reversible electron transfer without any coupled chemical reaction.     

Influence of cyanide and sulphide ions on the reduction and reoxidation of cobalt(II) in thiocyanate solution at mercury electrodes

The process of reduction and reoxidation of cobalt(II) in thiocyanate solution at hanging mercury drop electrode has been investigated by cyclic voltammetric, chronoamperometric and anodic stripping methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M cobalt(II), the voltammogram on the first cycle at 0.05 V s^?1 gives a cathodic peak at ?1.06 V with hysteresis on reversal, and an anodic wave with a peak potential of ?0.28 V and with two shoulders near ?0.38 and ?0.45 V, respectively. Multicyclic voltammograms under the same conditions give a cathodic peak at ?0.90 V and an anodic peak at ?0.45 V. The reduction and reoxidation of cobalt(II) in thiocyanate solution is accelerated by the reduction products of thiocyanate ion, cyanide and sulphide ions, which are produced during the electroreduction of cobalt(II).A mechanism of reduction and reoxidation of cobalt(II) which involves a chemical reduction of thiocyanate ion by electroreduced metallic cobalt and takes into account cyanide and sulphide ions is proposed. The hysteresis on the cathodic wave is caused by the difference in reduction potentials of cobalt(II)-thiocyanate and-cyanide complexes. Cyclic voltammetric study of cobalt(II) in perchlorate solution containing trace amounts of cyanide and sulphide ions supports these conclusions.     

Sol—Gel Derived Carbon Ceramic Electrode Bulk—Modified with Tris（1,10—phenanthroline—5,6—dione） iron （Ⅱ）Hexafluorophosphate and Its Use as an Amperometric Iodate Sensor

A surface‐renewable tris(1, 10‐phenanthroline‐5, 6‐dione) iron (D) hexafluorophosphate (FePD) modified carbon ceramic electrode was constructed by dispersing FePD and graphite powder in methyltrimethoxysilane (MTMOS) based gels. The FePD‐modified electrode presented pH‐dependent voltammetric behavior, and its peak currents were diffusion‐controlled in 0.1 mol/L Na₂SO₄ + H₂SO₄ solution (pH = 0.4). In the presence of iodate, dear electrocatalytic reduction waves were observed and thus the chemically modified electrode was used as an amperometric sensor for iodate in common salt. The linear range, sensitivity, detection limit and response time of the iodate sensor were 5 × 10^?6–1 × 10^?2 mol/L, 7.448 μA·L/ mmol, 1.2 × 10^?6 mol/L and 5 s, respectively. A distinct advantage of this sensor is its good reproducibility of surface‐renewal by simple mechanical polishing.     

The electrochemical determination of ammonium based on the selective inhibition of the low-spin iron(II)/(III) system of Prussian blue

A new method is described for the determination of ammonium in aqueous solutions with electrodes modified by Prussian blue (PB). The specific voltammetric response of PB-modified electrodes to ammonium ions is used for their analytical determination. In the presence of ammonium ions, a concentration-dependent inhibition of the low-spin iron(II/III) system of PB occurs. Only thallium and rubidium ions cause similar inhibition. A useful electrochemical determination method is thus available for detecting ammonium ions in the presence of frequently interfering potassium and sodium ions. Paraffin-impregnated graphite electrodes modified with a mechanically transferred PB layer and bulk-modified PB-composite electrodes are studied. The method is applicable within a concentration range which extends from 4 × 10⁻⁵ mol/l to 10⁻² mol/l NH₄ ⁺. The composite electrode is used in an electrochemical flow-through system in conjunction with the Kjeldahl method. Received: 21 April 1997 / Accepted: 28 May 1997     

Synthesis and characterization of manganese(IV) and ruthenium(III) complexes derived from bis (2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone(naohH₄) interacts with manganese(II) acetate in methanol followed by addition of KOH giving [Mn^IV(naoh)(H₂O)₂]. Activated ruthenium(III) chloride reacts with naohH₄ in methanol yielding [Ru^III(naohH₄)Cl(H₂O)Cl₂]. The replacement of aquo by heterocyclic nitrogen donor in these complexes has been observed when the reaction is carried out in presence of heterocyclic nitrogen donors such as pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF for these complexes suggest non-electrolytic nature. Magnetic moment values suggest +4 oxidation state for manganese in its complexes, however, ruthenium(III) complexes are paramagnetic with one unpaired electron. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that naohH₄ coordinates in enol-form and keto-form to manganese and ruthenium, respectively. ESR and cyclic voltammetric studies of the complexes have also been reported.     

Novel repaglinide complexes with manganese(II), iron(III), copper(II) and zinc(II): Spectroscopic,DFT characterization and electrochemical behaviour

Novel transition metal complexes with the repaglinide ligand [2-ethoxy-4-[N-[1-(2piperidinophenyl)-3-methyl-1-1butyl] aminocarbonylmethyl]benzoic acid] (HL) are prepared from chloride salts of manganese(II), iron(III), copper(II), and zinc(II) ions in water-alcoholic media. The mononuclear and non-electrolyte [M(L)₂(H₂O)₂]?nH₂O (M = Mn²⁺, n = 2, M = Cu²⁺, n = 5 and M = Zn²⁺, n = 1) and [M(L)₂(H₂O)(OH)]?H₂O (M = Fe³⁺) complexes are obtained with the metal:ligand ratio of 1:2 and the L-deprotonated form of repaglinide. They are characterized using the elemental and molar conductance. The infrared, ¹H and ¹³C NMR spectra show the coordination mode of the metal ions to the repaglinide ligand. Magnetic susceptibility measurements and electronic spectra confirm the octahedral geometry around the metal center. The experimental values of FT-IR, ¹H, NMR, and electronic spectra are compared with theoretical data obtained by the density functional theory (DFT) using the B3LYP method with the LANL2DZ basis set. Analytical and spectral results suggest that the HL ligand is coordinated to the metal ions via two oxygen atoms of the ethoxy and carboxyl groups. The structural parameters of the optimized geometries of the ligand and the studied complexes are evaluated by theoretical calculations. The order of complexation energies for the obtained structures is as follows:

$$Fe(III) complex < Cu(II) complex < Zn(II) complex < Mn(II) complex.$$

The redox behavior of repaglinide and metal complexes are studied by cyclic voltammetry revealing irreversible redox processes. The presence of repaglinide in the complexes shifts the reduction potentials of the metal ions towards more negative values.

     

Kinetics of oxidation of iron(II) by vanadium(V) under the conditions where VO2+ and decavanadate coexist

The kinetics of the reaction between iron(II) and vanadium(V) have been investigated in the pH range 2.6–4.2 where decavanadates and VO₂⁺ coexist in equilibrium. Under these conditions, the observed kinetic pattern is radically different from the one reported for the reaction in strong acid medium. In the pH range employed, the reaction rate is not appreciably altered by variation in the stoichiometric vanadium(V) concentration due to the operation of the equilibrium between the reactive species, VO₂⁺, and the unreactive species, decavanadates. The reaction, however, obeys first‐order kinetics with respect to Fe(II). In the presence of salicylic acid, which imparts considerable reactivity to iron(II) by reducing the reduction potential of iron(III)/iron(II) couple by forming a stronger complex with iron(III) than iron(II), the kinetic results provide evidence for the participation of decavanadates in the electron transfer. The mechanism under both conditions is discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 535–541, 2000     

Steric interaction of solvation and sterically enhanced halogeno complexation of manganese(II), cobalt(II) and nickel(II) ions inN,N-dimethylacetamide

The complexation of manganese(II), cobalt(II) and nikel(II) with bromide ions has been studied in N,N-dimethylacetamide(DMA) by calorimetry and spectrophotometry. The formation of [MBr]⁺, [MBr₂] and [MBr₃]^– (M=Mn, Co, Ni) was revealed in all the metal systems. Interestingly, the complexation is significantly enhanced in DMA over N,N-dimethylformamide (DMF). This is unusual because physicochemical properties of DMA and DMF as solvent are similar. Furthermore, extracted electronic spectra of individual complexes of Ni^II suggested the presence of a geometry equilibrium, [NiBr(DMA)₅]⁺=[NiBr(DMA)₄]⁺+ DMA, in DMA. A similar geometry equilibrium is also suggested, [NiBr₂(DMA)₃]=[NiBr₂(DMA)₂]+DMA. Such geometry equilibria were not observed in DMF. With regard to cobalt(II), electronic spectra show the presence of the four-coordinated [CoBr(DMA)₃]⁺ complex in DMA, unlike the six-coordinated [CoBr(DMF)₅]⁺ one in DMF. These facts suggest that a specific strong steric interaction operates between coordinating solvent molecules, which plays a key role in the complexation behavior of the divalent transition metal ions in DMA.     

Determination of components of the Cd(II)-Pb(II)-Cu(II) system in aqueous solutions of (polyethylene imine)methylthiourea by stripping voltammetry

Conditions were studied for the stripping voltammetric determination of components of the Cd(II)-Pb(II)-Cu(II) system in aqueous solutions of (polyethylene imine)methylthiourea (PMT), the most efficient polymer complexant for the membrane preconcentration of heavy metal ions. It was shown that PMT significantly enhances the selectivity of determining Pb(II) and Cd(II) in solutions of Cu(II) by stripping voltammetry. Pb(II) and Cd(II) can be determined in the presence of up to 200- and 50-fold amounts of Cu(II), respectively. The limits of detection for Pb(II) and Cd(II) after a 40-s accumulation were 6.9 x 10^-8 and 6.8 x 10^-7 M, respectively.     

Iron(II), cobalt(III), nickel(II) and copper(II) chelates of furan and thiophene azo-oximes

Summary Complexes of furan and thiophene azo-oximes with iron(II), cobalt(III), nickel(II) and copper(II) have been prepared and characterised. Iron(II), cobalt(III) and copper(II) complexes are diamagnetic in the solid state. The diamagnetism of the copper(II) chelates is suggestive of antiferromagnetic interaction between two copper centres.¹H n.m.r. spectral data suggest atrans-octahedral geometry for the tris-chelates of cobalt(III). Nickel(II) complexes are paramagnetic, in contrast to the diamagnetism of the analogous complexes of arylazooximes. The electronic spectra are suggestive of octahedral geometry for the iron(II), cobalt(III) and nickel(II) complexes, andD _4h -symmetry for copper(II). Infrared data indicate N-bonding of the oximino-group to the metal ions.     

Complexes of Co(II), Ni(II), Cu(II), and Pd(II) with Sulfametrole-Cyclodiphosph(V)azane Derivatives

Novel [1,3-di-[N ₁ -4-methoxy-1,2,5-thiadiazole-3-yl-sulfanilamide(sulfametrole)]-2″4-bis-[1,3-dithiole-2-thione-4,5-dithiolate]-2′,4′-dichl-orocyclodiphosph(V)azane] (III) , was prepared and their coordinating behavior towards the metal ions Co(II), Ni(II), Cu(II), and Pd(II) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV, ¹ H, and ³¹ P NMR, ESR, magnetic susceptibility, molar ratio, conductometric titration and electrical conductivity measurements. The prepared complexes showed high to moderate bactericidal activity compared with the ligand.     

Voltammetric study of the interaction of lomefloxacin (LMF)–Mg(II) complex with DNA and its analytical application

The voltammetric behavior of the LMF-Mg(II) complex with DNA at a mercury electrode is reported for the first time. In NH₃–NH₄Cl buffer (pH=9.10), the adsorption phenomena of the LMF–Mg(II) complex were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be a reduction of LMF in the complex, and the composition of the LMF–Mg(II) complex is 2:1. In the presence of calf thymus DNA (ctDNA), the peak current of LMF–Mg(II) complex decreased considerably, and a new well-defined adsorptive reduction peak appeared at −1.63 V (vs. SCE). The electrochemical kinetic parameters and the binding number of LMF–Mg(II) with ctDNA were also obtained. Moreover, the new peak currents of LMF–Mg(II)–DNA system increased linearly correlated to the concentration of DNA in the 4.00×10⁻⁷–2.60×10⁻⁶ g ml⁻¹ range when the concentrations of LMF–Mg(II) complex was fixed at 5.00×10⁻⁶ mol l⁻¹, with the detection limits of 2.33×10⁻⁷ g ml⁻¹. An electrostatic interaction was suggested by electrochemical method.     

Anodic Stripping Voltammetric Determination of Iron(II) at a Carbon Paste Electrode Modified with Dithiodianiline (DTDA) and Gold Nanoparticles (GNP)

A differential pulse anodic stripping voltammetric procedure was developed for the determination of trace amounts of iron(II) in the presence of iron(III) at a carbon paste electrode (CPE) modified with dithiodianiline and gold nanoparticle. At the pH working of 3.0, a wide concentration range from 0.1 nM to 100 nM was observed with the detection limit of 0.05 nM. The relative standard deviation for a solution containing 50 nM of iron(II) was found to be 3.11 % (n=9). Possible interferences from the coexisting ions were also investigated. The validity of the method and applicability of the sensor were successfully tested by determining of iron(II) in lentil, wheat seed and barley seed samples.     

Synthesis and characterization of some metal complexes of cystine: [Mn(C6H10N2O4S2)]; where MII = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II)

Cystine forms metal complexes of general formula [M^II(C₆H₁₀N₂O₄S₂)]; where M^II = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in the aqueous medium. Before reacting with metal salts the ligand solution was neutralized by NaHCO₃ solution. The complexes were formulated by comparing the C, H, N, S and metal analysis data. The prepared complexes were characterized by different physicochemical methods. The UV-vis, FTIR spectral analysis, magnetic susceptibility of these complexes are discussed. Cyclic voltammetric studies of some of the complexes are also reported.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Some synthesized polymeric composite resins for the removal of Co(II) and Eu(III) from aqueous solutions

Summary The ion-exchange and sorption characteristics of new polymeric composite resins, prepared by gamma radiation were experimentally studied. The composite resins show high uptake for Co(II) and Eu(III) ions in aqueous solutions in a wide range of pH. The selectivity of the resins for Co(II) or Eu(III) species in presence of some competing ions and complexing agents (as Na⁺, Fe³⁺, EDTANa₂, etc.) was compared. Various factors that could affect the sorption behavior of metal ions (Co(II) and Eu(III)) on the prepared polymeric composite resins were studied such as ionic strength, contact time, volume mass ratio.     

INTERACTIONS OF COBALT(II) TETRASULFOPHTHALOCYANINE WITH NITRITE IN THE PRESENCE OF NITRATE AND PERCHLORATE IONS

Abstract

Spectroscopic changes observed on addition of nitrite to solutions of cobalt(II) tetra-sulfophthalocyanine ([Co(II)TSPc]^4-) in the presence of N^? ₃ or ClO^? ₄ are reported. There is spectroscopic evidence for the oxidation of [Co(II)TSPc]^4- to a [Co(III)TSPc]^3- species in the presence of nitrite ions. Equilibrium and kinetic studies for the interaction between [Co(II)TSPc]^4- and NO^? ₂ are reported. The rate was found to be first order in both [Co(II)TSPc]^4- and NO^? ₂. The rate constant for the forward reaction, k _f=1.6 × 10^?4 dm³mol^?1s^?1 was determined at 20°C for the interaction between nitrite ions and [Co(II)TSPc]^4- in the presence of NO₃ ^? or ClO₄ ^? ions.     

Extended NMR Study of Spin-Crossover Compounds [Fe(1-alkyl-1H-tetrazole)6](BF4)2 and Their ZnII Analogs

A systematic NMR study was performed on several alkyl–tetrazole complexes of iron(II) and zinc(II) in the 10–300 K temperature range. The experiments were designed to separate the electronic and reorientational phase transitions caused by the spin crossover of the iron compounds from those independent of unpaired electrons. The ¹⁹F spectral data on the propyl-tetrazole compounds show that the electronic spin-transition has a strong effect on the spectra, and their behavior can be explained as a combined response to molecular reorientations and the spin transition. For these complexes, second-moment calculations revealed the strength of the interaction between resonant and nonresonant nuclei. Both of the applied NMR methods show irregularities at the temperature region between 70 and 120 K, suggesting the presence of a phase transition. The data also suggest two kinds of reorientational behavior for the BF₄ ^– counter ions. In the iron–ethyl–tetrazole compound, unlike in the propyl–tetrazole complex, a significant amount of unpaired electrons remains in their original high-temperature HS state. Above their effect, the behavior of the nuclear spins of the iron compound is basically governed by the same structural factors as in its zinc analog. The two-exponential behavior of the ¹H-T ₁ in case of the zinc–methyl–tetrazole compound can be explained on the basis of cross relaxation with the ¹⁹F nuclei due to the low ¹H/¹⁹F ratio. The presence of the two types of methyl reorientation is assumed to be the sign of the two different lattice sites known to be present in the Fe^II compound. The single-exponential T ₁ above T _c in the case of [Fe(mtz)₆](BF₄)₂ is consistently the sign of the strength of the paramagnetic relaxation observed in the ethyl and propyl compounds.