On Mn(Hg)/Mn(II) equilibria and reactions in aqueous solution

The title subject has been studied through galvanostatic single-pulse and chronopotentiometric measurements on the Mn(Hg)/Mn(II) electrode and equilibrium measurements on the same and the Ag/AgCl electrode, all in x MMnCl₂+(0.5?x)M MgCl₂ solutions of pH 4.3–4.9 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps, an unsymmetric (α_c near 0.8) ion-transfer step Mn(Hg)/Mn(I) and an essentially symmetric (α_c near 0.5) electron-transfer step Mn(I)/Mn(II). Besides charge transfer, no sluggishness other than diffusion is observed, but the dispersed precipitate Mn₂Hg₅ of saturated amalgam serves as an ageing-dependent source of anodic reactant Mn(Hg). Quantitative kinetic and thermodynamic data are presented and discussed. Comparisons are made to corresponding reactions for the succeeding elements iron, cobalt, nickel, copper, and zinc.     

Effect of halides and alkali cations on the Zn(Hg)/Zn(II) electrode reactions

The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Zn(Hg)/Zn(II) electrode in x M KI+(1?x) M KCl (x from 0 to 1), 1 M KBr and 1 M MeCl (Me=Li, Na, K and Cs) solutions of pH 3 at 25°C. Quantitative information about the effect of specifically adsorbed halides on the rates of the Zn(II)/Zn(I) and the Zn(I)/Zn(Hg) steps is obtained separately (for the latter step mainly at potentials near ?1.0 V(SCE)), and the latter step seems to be more influenced than the former by the adsorption. An attempt is made to correlate the adsorption effect on the rate of the Zn(II)/Zn(I) step to double-layer parameters according to recent models for such effects. The extra current observed at potentials where the halides are adsorbed, seems to vary with the surface activity of the specifically adsorbed ion. The lack of any observed kinetic effect of Cs⁺, which is specifically adsorbed at these potentials, is possibly due to the Cs⁺ specific adsorption enhancing the Cl^? specific adsorption and vice versa, so that the decelerating and accelerating effects by these ions may cancel each other.     

Single-ion activities and Mn(Hg)/Mn(II) reactions in aqueous solutions of alkaline-earth chlorides

Combined thermodynamic and kinetic studies have yielded convenient single-ion activity coefficients for manganese(II), alkaline-earth, and chloride ions and standard exchange currents for the two steps of the Mn(Hg)/Mn(II) electrode in 0.005 M MnCl₂+0.495 M MeCl₂ (for Me=Mg, Ca, Sr, Ba, and Mn) at 25°C. The results indicate that the fall in mean ionic activity coefficient for the alkaline-earth chlorides along the sequence from magnesium to barium is carried to a larger extent by the cation than by the anion, that also the activity coefficient for the minority cation Mn(II) falls along this sequence, and that other than activity-coefficient effects on the Mn(Hg)/Mn(II) reactions appear only with barium ions, which retard the reactions additionally. The results are discussed with emphasis on ionic interactions and double-layer effects.     

Kinetics and mechanism of the Cu(I)/Cu(Hg) electrode reactions in DMSO solutions of halide ions

The electrode reaction Cu(I)/Cu(Hg) in complex chloride, bromide and iodide solutions with DMSO as solvent has been studied at the equilibrium potential by the faradiac impedance method and a cyclic current-step method. The kinetic data refer to the ionic strength 1 M with ammonium perchlorate as supporting electrolyte and to the temperature 25°C. Double-layer data have been obtained from electrocapillary measurements. From the results for the chloride system at [Cl^?]>15 mM it is concluded that the charge transfer is catalysed by ligand bridging at the amalgam and the following parallel reactions predominate: Cl_ads^?-Cu⁺+e^?(am)Cl_ads^?+Cu(am) Cl_ads^?-Cu₂Cl_j^2?j+e^?(am)Cl_ads^?+Cu(am)+CuCl_j^1?j At lower [Cl^?] and in the whole ligand concentration range available in the bromide and iodide systems the impedance measurements indicate a rate-controlling adsorption step. It is suggested that uncharged complex CuL (L^?=halide ion) then forms an adsorbed two-dimensional network on the amalgam surface.     

Influence of water activity on the Ni(II)/Ni(Hg) electrode reaction in concentrated Ca(ClO4)2 solutions in the temperature range 20–185°C

The electrode reaction of the Ni(II)/Ni(Hg) system occurring in 4–13.7 mol kg^?1 solutions of Ca(ClO₄)₂ in the temperature range 20–185°C was studied by means of pulse polarography and cyclic voltammetry. From analysis of the formal potentials with respect to the ferricinium ionferrocene electrode as a function of the logarithm of the water activity, the hydration numbers of Ni(II) were found. They decrease as both the molality of Ca(ClO₄)₂ and the temperature increase. Limiting values of hydration numbers at both high temperature and concentration of Ca(ClO₄)₂ were near to 6. The electrode reaction proceeds in a step-wise manner with the Ni(I)/Ni(Hg) system controlling the rate of the overall process.The rate constants at formal potentials under different conditions are presented.The electrode reaction orders are determined with respect to the water point to the participation of Ni(H₂O)₄⁺ in the rate-determining step.     

Cathodic and anodic stripping determination of traces of adenine and adenosine based on accumulation of copper(I) compounds at mercury or amalgam electrodes

In the presence of adenine and adenosine, the copper(II)/copper(Hg) couple splits to the copper(II)/copper(I) and copper(I)/copper(Hg) couples. Sparingly soluble complexes of copper(I) with adenine and adenosine can be accumulated on the electrode surface either by reduction of Cu(II) ions or by oxidation of the copper amalgam electrode. The copper(I)/adenine deposit can be stripped either cathodically or anodically with detection limits of 5×10^?9 and 2×10^?8 mol dm^?3, respectively. The copper(I)/ adenosine complex yields only the cathodic stripping peak with a detection limit of 9×10^?6 mol dm^?3. The stripping peaks obtained for the copper(I)/adenine and copper(I)/ adenosine complexes are better defined and appear over a wider range of pH than the peaks related to the corresponding mercury compounds. Adenosine cannot be determined in the presence of adenine bur adenine can be determined in the presence of moderate amounts of adenosine.     

Voltammetric Measurement of [Cu(II)]/[Cu(I)] at a Platinum Rotating Disc Electrode and Control by Electrolysis at a Platinum Net Electrode in Chloride Solutions

ABSTRACT

A method has been described to measure and control the [Cu(II)]/[Cu(I)] bulk concentration ratio in aqueous chloride solutions. A variation of the ratio is achieved by controlled potential electrolysis at appropriate reducing or oxidizing potentials. The concentration ratio can be monitored by a repetitive double potential step amperometric method at a platinum rotating disc electrode. The amperometric signal can be used to control the electrolytic process in order to obtain and maintain a predetermined bulk concentration ratio. Diffusion coefficients of respectively 6.2 10^?6 and 5.6 10^?6 cm² s^?1 have been determined for Cu(II) and Cu(I). Potential applications of the method are the control of polymerisation reactions, of the reduction of textile dyes with the aid of a mediator system and of the colour characteristics of different kinds of glass.     

THE INTERACTION OF 2-AMINO-2-HYDROXYMETHYL-1,3-PROPANEDIOL WITH COBALT(II) AND MANGANESE(II) IONS

Abstract

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO₄) and T = (25.0 ± 0.1)°C, from pH measurements. Data of average ligand number (Bjerrum's function) were obtained from such measurements followed by integration to obtain Leden's function, F ₀(L). Graphical treatment and matrix solution of simultaneous equations have shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (β₁ = (5.04 ± 0.02) M^?1 and β₂ = (5.4 ± 0.5) M^?2) and three for the Co(II)/TRIS system (β₁ = (1.67 ± 0.02) × 10² M^?1, β₂ = (7.01 ± 0.05) × 10³ M^?2 and β₃ = (2.4 ± 0.4) × 10⁴ M^?3). Slow spontaneous oxidation of Co(II) solutions by dissolved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS⁺ 0.010/0.030 M, with a synergistic effect of Mn(II).     

Complexes of Mn(II), Co(II), Ni(II) and Cu(II) with 4,4'-bipyridine and dichloroacetates

New mixed-ligand complexes with empirical formulae M(4-bpy)L₂·1.5H₂O (M(II)=Mn, Co), Ni(4-bpy)₂L₂ and Cu(4-bpy) L₂·H₂O (where: 4-bpy=4,4'-bipyridine, L=CC L2HCOO^-) have been isolated in pure state. The complexes have been characterized by elemental analysis, ir spectroscopy, conductivity (in methanol, dimethylformamide and dimethylsulfoxide solutions) and magnetic and x-ray diffraction measurements. The Mn(II) and Co(II) complexes are isostructural. The way of metal-ligand coordinations discussed. the ir spectra suggest that the carboxylate groups are bonded with metal(II) in the same way (Ni, Cu) or in different way (Mn, Co). The solubility in water is in the order of 19.40·10^-3÷1.88·10^-3ł mol dm^-3ł. During heating the hydrate complexes lose all water in one step. The anhydrous complexes decompose to oxides via several intermediate compounds. A coupled TG-MS system was used to analyse the principal volatile products of obtained complexes. The principal volatile products of thermal decomposition of complexes in air are: H₂O₂ ⁺, CO₂ ⁺, HCl⁺, Cl₂ ⁺, NO⁺ and other. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Crystal Structure of Cesium Nitratometalates(II), Cs2[M(NO3)4] (M = Mn,Co, Ni,Zn)

Crystalline cesium nitratometalates(II), Cs₂[M(NO₃)₄] (M = Mn ( I ), Co ( II ), Ni ( III ), and Zn ( IV )) were synthesized from M(NO₃)₂ · n H₂O and CsNO₃ by heating at 80–120 °C over 10–12 h. According to X-ray crystal structure analysis, the compounds are built from Cs⁺ cations and [M(NO₃)₄]^2– anions. The latter differ by the type of metal coordination: a dodecahedron for Mn in I (CN = 8, r_Mn–O 2.24–2.37 Å), a seven coordination for Co in II (CN = 4 + 3, r_Co–O 2.03–2.16 Å and 2.21–2.35 Å) and a tetrahedral distorted dodecahedron for Zn in IV (CN = 4 + 4, r_Zn–O 1.98–2.15 Å and 2.38–2.72 Å). Ni atom in III has a distorted octahedral NiO₆ environment provided by two unidentate and two bidentate NO₃ groups with Ni–O distances of 2.01–2.14 Å. The differences in metal coordination are discussed in terms of valence electron configurations, ionic radii, and the packing effects.     

Triazine based Mn (II) and Mn (II)/Ln (III) complexes: Synthesis,characterization and catecholase activities

In the current work, two triazine‐based multidentate ligands (H₂L¹ and H₂L²) and their homo‐dinuclear Mn (II), mononuclear Ln (III) and hetero‐dinuclear Mn (II)/Ln (III) (Where Ln: Eu or La) complexes were synthesized and characterized by spectroscopic and analytical methods. Single crystals of a homo‐dinuclear Mn (II) complex {[Mn (HL¹)(CH₃OH)](ClO₄·CH₃OH}₂ ( 1 ) were obtained and the molecular structure was determined by X‐ray diffraction method. In the structure of the complex, each Mn (II) ion is seven‐coordinate and one of the phenolic oxygen bridges two Mn (II) centre forming a dimeric structure. The UV–Vis. and photoluminescence properties of synthesized ligands and their metal complexes were investigated in DMF solution and the compounds showed emission bands in the UV–Vis. region. The catecholase enzyme‐like activity of the complexes were studied for 3,5‐DTBC → 3,5‐DTBQ conversion in the presence of air oxygen. Homo‐dinuclear Mn (II) complexes ( 1 and 4 ) were found to efficiently catalyse 3,5‐DTBC → 3,5‐DTBQ conversion with the turnover numbers of 37.25 and 35.78 h^?1 (k_cat), respectively. Mononuclear Eu (III) and La (III) complexes did not show catecholase activity.     

Polarographic studies on bipyridine complexes: III. Polarography of tris(2,2′-bipyridine) complexes of chromium(I), chromium(0), vanadium(0), titanium(0) and molybdenum(0)

Polarograms and cyclic voltammograms for tris(2,2′-bipyridine) complexes of V(0), Cr(0), Cr(I), Ti(0) and Mo(0) in N,N-dimethylformamide are reported. The reversible half-wave potentials for the following redox systems in lower oxidation states are determined: Cr(?I)/Cr(?II), Cr(?II)/Cr(?III), V(I)/V(0), V(0)/V(?I), V(?I)/V(?II), V(?II)/V(?III), Ti(0)/Ti(?I), Ti(?I)/Ti(?II), Mo(?I)/Mo(?II) and Mo(?II)/Mo-(?III). On the basis of the half-wave-potential shift caused by the methyl substitution of ligands, it is concluded that each excess electron of the reductant species of the redox systems, V(bipy)₃^?/V(bipy)₃^2?, Cr(bipy)₃/Cr(bipy)₃^?, Cr(bipy)₃^?/Cr(bipy)₃^2? and Cr(bipy)₃^2?/Cr(bipy)₃^3? (bipy=2,2′-bipyridine), occupies a ligand π^*-orbital and that of the V(bipy)₃²⁺/V(bipy)₃⁺ and V(bipy)₃⁺/V(bipy)₃ systems a metal t_2g-orbital. The apparent π-character of the excess electron of the redox systems Cr(bipy)₃⁺/Cr(bipy)₃ and V(bipy)₃/V(bipy)₃^? is discussed. It is pointed out that the relative electron affinities of trisbipyridine complexes can be determined from the half-wave potential data. The lowest π^*-orbitals of V(bipy)₃^?, Cr(bipy)₃ and Fe(bidy)₃²⁺ become higher in this order. This suggests that the electrostatic interaction between a π^*-electron and the residual charge on the central metal ion predominantly accounts for the observed π^*-level shift.     

Organic acid solutions in the chromatography of inorganic ions. VII. Cation exchange of Mg(II), Ca(II), Sr(II), Ba(II), Mn(II), Cd(II), Co(II), Ni(II), Zn(II), Cu(II) and Fe(III) in succinate media

Summary The cation-exchange behaviour of Mg(II), Ca(II), Sr(II), Ba(II), Mn(II), Cd(II), Co(II), Ni(II), Zn(II), Cu(II) and Fe(III) in succinate media at various concentrations and pH, was studied with Dowex 50 WX8 resin (200–400 mesh) in the NH ₄ ⁺ form. As examples separations of Cd(II)/Co(II), Cd (II)/Ni(II), Fe(III)/Cu(II)/Ni(II) and Mg(II)/Ca(II)/Sr(II)/Ba(II) have been achieved.This work was supported by C.N.R. of Italy.     

Determination of traces of purine by cathodic stripping voltammetry at the hanging copper amalgam drop electrode

In the presence of purine, the copper(II)/copper(Hg) couple splits into copper(II)/copper(I) and copper(I)/copper(Hg) couples, which form two well-separated systems of peaks under voltammetric conditions. The copper(I)/purine complex adsorbs on the electrode surfacer and can be deposited on the electrode surface by electroreduction of copper(II) ions at the HMDE or by electro-oxidation of the hanging copper amalgam drop electrode (HCADE). The deposit can be stripped either cathodically or anodically over the pH range 2–9. The cathodic stripping variant at the HCADE, in solution with pH 2, offers the best results, with linear response for the range 5 × 10^?9–1.5 × 10^?7 mol dm^?3 purine after an accumulation time of 3 min. The detection limit found with the HMDE in the presence of copper(II) ions is higher.     

Stability and nature of complexes of the type MCl+ in aqueous solution (M=Mn,Co, Ni,and Zn)

Equilibrium constants have been determined both potentiometrically and spectrophotometrically for reactions of the type M²⁺+Cl^??MCl⁺ using aqueous solutions of the corresponding metal perchlorates as the reaction media (M=Mn, Co, Ni, and Zn). The variation in the quotient of the activity coefficients of these reactions with increasing molality of the reaction medium has been found to be approximately the same for the CuCl⁺ (previously studied), MnCl⁺, and ZnCl⁺ complexes, while a different dependence is observed for the CoCl⁺ and NiCl⁺ complexes. The results are interpreted as indicating equilibrium coexistence of the [MCl(OH₂)₅]⁺ and {[M(OH₂)₆]Cl}⁺ species in the latter two cases. Approximate values of the corresponding equilibrium constants are estimated in addition to the derived overall thermodynamic stability constants of the MCl⁺ formal complexes. The latter are found to follow a partly inverted Irving-Williams series, the fact being accountable in terms of the ligand field stabilization energy.     

Mass spectrometric studies of dithiophosphinato metal complexes

Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L₂ (L=Et₂PS₂^?; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L₃ (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)_n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]^+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal-metal interaction is observed even under electron impact.     

1,4,7,10-Tetraoxacyclododecane(12-Crown-4) as Neutral Carrier for Lithium Ion in Lithium Ion Selective Electrode

Abstract

1,4,7,10-Tetraoxacyclododecane (12-crown-4) (I) and its lithium complex (II) are used as neutral carriers for lithium ion in polyvinylchloride membrane ion selective electrodes. The lithium response varies with concentration, being near Mernstian at low (10^?5-10^?4 M) concentrations and sub-Nernstian (24-28 aV) at higher concentrations (10^?3 M). The selectivity coefficients K_Li ^Pot _M for II are: Na⁺ (0.12), K⁺ (0.66), Cs⁺ (0.15), Mg²⁺ (1.6 × 10^?4), Ca²⁺ (3.1 × 10^?4), Ba²⁺ (9.5 × 10^?7), NH⁺ ₄ (9.0 × 10^?2), H⁺ (2.2).     

Use of Cyclic Voltammetry to Evaluate Sorption Properties of Cork Residues Towards Mn(II) in Waters

Cyclic voltammetry is proposed for evaluating the ability of cork wastes to remove Mn(II) ions by sorption from waters to be used for public supply. As the first stage, the concentration of several naturally occurring cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) were analyzed in the acid washings that were performed to remove them from the cork. The obtained results were then related to the total concentrations of cations released, as measured by flame atomic absorption spectroscopy of solutions made by dissolving ashed samples. Cyclic voltammetry is proposed to measure the manganese concentration in the uptake solutions because it allows the metal oxidation state to be controlled, and was determined to be suitable for use with standard addition methods. Contact time and particle size effects on Mn(II) sorption were evaluated.     

Liquid-state mercury(II) ion-selective electrode based on N-(O,O-diisopropylthiophosphoryl)thiobenzamide

A liquid ion-exchange electrode containing a complex of mercury(II) with N-(O,O-diisopropylthiophosphoryl)thiobenzamide in carbon tetrachloride is described. The electrode shows excellent sensitivity and good selectivity. The slope of the calibration graph is 29.0 mV/pHg²⁺ in the pHg²⁺ in the pHg²⁺ range 2–15.2 in mercury(II) ion buffers. The electrode can be used for determination of 5 × 10^?5–10^?2 M Hg(II) in the presence of 10^?2 M Cu(II), Ni(II), Co(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(III), Cr(III), Bi(III) or Al(III) ions and in the presence of 10^?3 M Ag(I) ions. It can bealso used for end-point detection in titrations with EDTA of 10^?3–10^?4 M mercury(II) at pH 2.     

Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins: synthesis and properties

Abstract

Mono-, tetra-, and octa-bromo substituted Mn(II)- and Mn(III)-tetraarylporphyrins were synthesized by reactions of manganese(II) chloride with corresponding porphyrin ligands or their Cd(II)-complexes in DMF. With the use of the metal exchange reaction, the time of the Mn-porphyrins formation is significantly reduced with increase in yield of final products in comparison with the complexation reaction. Mn(III)-tetraarylporphyrins reduce to the Mn(II)-porphyrins in DMF in the presence of NaOH and in pure DMF. The obtained compounds were identified using UV–vis and ¹H NMR spectroscopy, mass-spectrometry, and elemental analysis.