Complexation of copper(I) by thiourea in acidic aqueous solution

The interaction of copper(II) and copper(I) with thiourea(Tu) has been investigated by UV and visible spectrophotometry. Over the range of concentrations of copper(I) and Tu(0.1–20)×10^–3 mol-dm^–3 in acid aqueous solutions there are two complexes, CuTu₂ ⁺ (log ₂=11.1) and the other has the ratio Cu/Tu=1/1 with the likely composition Cu₂Tu₂ ²⁺ with log ₂₂=18.5. By the determination of copper(0) solubility in acid thiourea solution and potentiometric measurements it was shown that the potential of the copper electrode is that of a non-equilibrium (corrosive) electrode.     

Étude par spectrographie infrarouge de la structure de l'acide iodique,de l'acide anhydroiodique et des polyiodates alcalins

Résumé L'étude par spectrographie infrarouge entre 2 et 33 des divers produits de déshydratation de l'acide iodique et des nombreux iodates «acides» et «pyroiodates» qu'il donne avec les iodates alcalins montre l'existence de ponts I-O-I analogues à ceux qui existent dans l'anhydride iodique I₂O₅. Ces liaisons se caractérisent dans la région explorée par deux groupes de bandes fortes à 400–460 cm^–1 et à 515–646 cm^–1, c'est-à-dire en dehors des régions d'absorption caractéristiques des groupements IO₂ ou IO₃.

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Summary The infrared spectrographic study between 2 and 33, of various products of dehydration of iodic acid and numerous acid iodates and pyroiodates which it yields with alkaline iodates reveals the existence of I-O-I bridges analogous to those in I₂O₅. In the regions explored, these links are characterized by two groups of strong bands at 400–460 cm^–1 and at 515–646 cm^–1, i. e. beyond the absorption regions characteristic of the IO₂ or IO₃ groups.

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Zusammenfassung Die IR-spektrographische Untersuchung verschiedener durch Wasserabspaltung aus Jodsäure hergestellter Produkte, zahlreicher saurer Salze und mit Alkalijodaten gebildeter Pyrojodate zwischen 2 und 33 zeigt das Vorhandensein von J-O-J-Brücken, wie sie analog im Jodsäureanhydrid J₂O₅ vorliegen. Charakteristisch für diese Bindung sind im untersuchten Bereich zwei starke Bandengruppen bei 400 bis 460 cm^–1 und bei 515 bis 646 cm^–1, das heißt jenseits des Bereiches der charakteristischen Absorption der Atomgruppen JO2 oder JO3.

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En l'honneur du ProfesseurF. Feigl, pour son 70^e anniversaire.     

Metal ion catalysed aquation of carboxylatoamine cobalt(III) complexes. Kinetics of copper(II) catalysed aquation ofcis(diformato)bis(ethylenediamine)cobalt(III) ion

Summary The aquation ofcis-[(en)₂Co(CO₂H)₂]⁺ tocis-[(en)₂Co(OH₂)(CO₂H)]²⁺ is catalysed by Cu²⁺ and the rate equation, –d[complex]_t/dt=(k_Cu[Cu²⁺]+k_H [H⁺]) [complex)_T is valid at [Cu²⁺]_T=0.01–0.1, I=0.5 and [HClO₄]=0.005 mol dm^–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu²⁺ and H⁺-catalysed paths are: k_H(35°C)=(2.44±0.09)×10^–2 dm³ mol^–1 s^–1, H=83±13 kJ mol^–1, S=–8±42 JK^–1 mol^–1, k _Cu (35°C)=(3.30±0.09)×10^–3 dm³ mol^–1 s^–1, H=73.2±6.1 kJ mol^–1, S=–55±20 JK^–1 mol^–1. The formate-bridged innersphere binuclear complex,cis-[(en)₂Co{(O₂CH)₂Cu}]³⁺ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H⁺-bridged species presumed to be present in the acidcatalysed path.     

Method for estimating the largest Lyapunov exponent for the chaotic regime in chemical reactions

Based on the Belousov-Zhabotinskii reaction in CSFR we observe that the mixing rate decrease in the reaction volume of the mixture to the value ₀ leads to a qualitative change in the nature of the chaotic regime, similar to a second order phase transition. We show that the largest Lyapunov exponent for the system is directly proportional to ₀ ².Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 52–56, January–February, 1992.     

Determination of lutetium by fluorimetry, using BPMPHD and CTMAB

Lutetium(III) forms an association compound with a new synthetic reagent, 1,6-bi(1-phenyl-3-methyl-5-pyrazolone-4)hexandione (BPMPHD), and cetyltrimethylammonium bromide (CTMAB). The compound enhances the natural fluorescence of BPMPHD remarkably, upon which a new fluorescence method was developed for determining lutetium in rare earth (RE) samples. The determination range was 1.80 × 10^–7–8.8 × 10^–6 g/ml. The determination limit was 29 ng/ml. The composition of the ion associate was [Lu(BPMPHD)₂]–CTMAB⁺.     

Photometrische Bestimmung von Sulfid mit Jodnitrotetrazoliumchlorid

Zusammenfassung S^2– kann mit Jodnitrotetrazoliumchlorid (INT) innerhalb von 30 min photometrisch bestimmt werden. PO₄ ^3–, Cl^– und SO₄ ^2– in Konzentrationen bis zu 5 · 10^–2 mol/l, S₂O₃ ^2– bis zu 10^–4 mol/l und S₃O₆ ^2– bis zu 2 · 10^– mol/l stören nicht. Die untere Bestimmungsgrenze beträgt 3,4 · 10^–5 mol/l, entsprechend 1 g S^2–. Als relative Standardabweichung ergibt sich bei der Bestimmung von 3,2 g S²}±6,4 Rel.%.Die Untersuchungen wurden mit Hilfe eines Stipendiums der Alexander von Humboldt-Stiftung durchgeführt, der an dieser Stelle herzlich gedankt sei.     

Cobalt-Selective Electrode Based on Titanium Ditelluride Intercalated with Cobalt

A cobalt-selective solid-contact electrode was prepared on the basis of titanium ditelluride. The electrode exhibits the slope of the electrode function –(29 ± 1) mV/pC and provides the determination of 1 × 10^–5–1 × 10^–1 M cobalt(II) in the pH range 4.5–6.5. The electrode was used for the potentiometric indication of the titration end point in the determination of cobalt(II) in lanthanum–strontium cobaltite La_0.5Sr_0.5CoO₃. The intercalant concentration range providing optimal ion-selective properties was determined.     

Spectrophotometric and derivative spectrophotometric determination of nickel with hydroxynaphthol blue

The reaction of nickel(II) cation with hydroxynaphthol blue (HNB) in aqueous media at pH 5.2–6.0 results in a red complex that is stable for at least 2h. Beer's Law is obeyed up to 3.2 g/ml of nickel(II) with an apparent molar absorptivity of 1.38 × 10⁴l/mol/cm at 563 nm. This paper proposes procedures for nickel determination by ordinary and first-derivative spectrophotometry. The results demonstrate that the linear dynamic range is 0.08–3.20 g/ml with a limit of detection of 23 ng/ml for ordinary spectrophotometry, compared with 21–800 ng/ml and 6 ng/ml, respectively, for first-derivative spectrophotometry. Calcium(II), magnesium(II), barium(II), strontium(II), cadmium(II), lead(II), manganese(II), bismuth(III) and molybdenum(VI) ions do not interfere for at least 1001 mass ratios. The main interferents are cobalt(II), titanium(IV), aluminium(III), mercury(II) and copper(II). The interferences of titanium(IV), aluminium(III), zirconium(IV) and iron(III) can be masked by fluoride and mercury(II) and copper(II) with thiosulfate or thiourea. The derivative method is applied to nickel determination in standard brasses and the results demonstrate that there is no significant difference between the results and certified values at the 95% confidence level.     

Equilibrium constants of some protonated,nonprotonated and hydroxo complexes of uranium(VI) with xylenol orange

Summary The species, UO₂H₃L^–, UO₂H₂L^2–, UO₂HL^3–, UO₂L^4–, UO₂(OH)L^5– and UO₂(OH)₂L^6– are found in the equilibria between uranyl ions and 3,3-bis[N,N-di(carboxymethyl)-aminomethyl]-o-cresolsulphonphthalein (H₆L; xylenol orange; dcac) in aqueous solution. The equilibria have been studied by the potentiometric method at 25° and at an ionic strength of 0.1M (KNO₃). New algebraic equations have been employed to evaluate the equilibrium constants.     

Use of solid-phase extraction to eliminate interferences in the determination of mercury by flow-injection CV AAS

Solid-phase extraction with two-step elution has been developed for effective elimination of copper and iron interference with mercury determination by flow-injection cold vapour atomic absorption spectrometry (CV AAS). Sodium tetrahydroborate(III) was used as reducing agent. Cation-exchanger Dowex 50Wx4 was applied for the sorption of mercury and both interfering ions. In the first step elution of Cu(II) and Fe(III) was performed using 0.5 mol L^–1 KF solution. Then mercury was eluted with 0.1% thiourea in 8% HCl. The detection limit (3) for Hg(II) was 27 ng L^–1. The expanded uncertainty estimated for the whole procedure was about 6%. The accuracy of the proposed method was evaluated by determination of the recovery of known amount of mercury added to mineral, spring, and tap waters, and by analysis of a certified reference material BCR-144R (sewage sludge).     

Determination of microamounts of iron by hydroxamate resin colorimetry

Summary A new, sensitive chelating ion-exchanger colorimetric method has been developed for the determination of iron at the g/l level in water, based on the direct measurement of light absorption of iron hydroxamate resin complex. In 0.2 N perchloric acid solution, iron could be rapidly, selectively and quantitatively absorbed on the hydroxamate resin. The calibration curve for iron(III) of a 25 ml solution was linear in the concentration range 8.00×10^–6 to 5.00×10^–5 M. For iron(III) with larger sample volumes, the relative detection limit was increased. Most of the metals interfered negligibly, such as Ca(II), Co(II), Cu(II), Ni(II) and Zn(II), except for higher concentration of lead(II) and mercury(II) when present at up to 400 times the concentration of iron(III). The effects of EDTA, glycine, thiourea, phosphate, nitrate and chloride on the retention of iron(III) were also examined. Only thiourea significantly influenced the retention of iron(III). The presence of sodium chloride even at a concentration of 3.5×10⁴ times that of iron(III) did not interfere at all.

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Bestimmung von Mikromengen Eisen durch Hydroxamatharz-Colorimetrie

     

Spectrophotometric determination of mercury with 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine by flow injection analysis

5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine (m-Cl-TPPS₄) was synthesized and used for the Spectrophotometric determination of mercury by flow injection analysis. A pseudo-first-order reaction kinetic mechanism was proposed with a rate constant of 0.8 min^–1 for Hg(II) withm-Cl-TPPS₄ in the presence of 8-hydroxyquinoline in a medium of 1.0M acetic acid and sodium acetate buffer solution (pH 6.22). In the optimum conditions of reaction temperature (85 ° C), stopped-flow time (60 s) and sampling volume (100 l), the method's relative standard deviation was 0.82% (n = 12) at 5.0 g ml^–1 mercury, with a linear range of 0–12.0 g ml^–1 and an analytical frequency of 60h^–1. The detection limit (3) was 0.025 g ml^–1. Interference studies showed that most metal ions co-existing with Hg²⁺ could be tolerated at 100-fold excess levels, but Zn²⁺, Cu²⁺ and Mn²⁺ needed to be masked. The method has been applied to the analysis of water samples with satisfactory results.     

Diffusion Impedance of Electrodes of Different Size in Isothermal and Nonisothermal Natural Convection Conditions

The impedance for a reversible K₃[Fe(CN)₆]/K₄[Fe(CN)₆] system is measured at vertical platinum disk electrodes of different diameter in isothermic natural convection conditions and during nonisothermal heating of the electrode. The frequency dependence of the diffusion impedance is described by a classic formula for a finite Warburg impedance. The dimensionless frequency ²/D in the extreme point of the impedance spectrum approached 2.5, in accordance with the theory. Under isothermic conditions near equilibrium, for large-diameter (d > 1 mm) electrodes, the characteristic frequency that corresponds to the extreme point, *, is proportional to the square root of the redox-component concentration, overvoltage, and d ^–1/2. In nonisothermal systems, this frequency is proportional to the square root of the temperature gradient at the electrode/solution interface. These regularities agree with the theory of natural convection. For microelectrodes, the impedance frequency spectrum conforms to the Fleischmann–Pons theory and * is proportional to d ^–2.     

Kinetic and equilibrium study of substitution reactions oftrans-tetracyanodioxorhenate(V) ions with monodentate nucleophiles

Summary The kinetics of the substitution reactions of the protonated froms oftrans-tetracyanodioxorthenate(V) with thiourea (TU),N-methylthiourea (NMTU),N, N-dimethylthiourea (NNDMTU) and hydrazoic acid (HN₃) were studied. The results were compared with those obtained for similar reactions of [WO₂(CN)₄]^4–. This study showed that the diprotonated form [ReO(H₂O)(CN)₄]^– is the only species reactive towards substitution reactions (and not the [ReO(OH)(CN)₄]^2– ion) and that only the aqua ligand in [ReO(H₂O)(CN)₄]^– is substituted by the incoming group. A dissociative mechanism is proposed for the substitution reactions between [ReO(H₂O)(CN)₄]^– and the monodentate nucleophiles. The i.r. data for these Re^v complexes are reported and discussed in terms of the relativetrans influence of the various monodentate ligands.     

Rapid Determination of Mercury in Water by Stripping Voltammetry at a Gold-Modified Carbon Electrode

A procedure was developed for determining mercury in natural water by stripping voltammetry on a gold-modified carbon electrode. The concentration dependence of the anodic stripping current of mercury is linear in the range 0.02–5 g/L Hg(II). The interference of Fe(III), Cu(II), Cl^–, Br^–, I^–, and F^– ions with the determination of mercury was studied. Ozonation was used for rapid sample preparation. The detection limit for mercury was 0.02 g/L at an electrolysis time of 5 min.     

The substitution kinetics of the aqua ligand by cyanide ions in [Ru(TPPS)(CO)(H2O)]4−

Summary The reaction between the title compound, ,,,-tetra(p-sulphonatophenyl)porphynatoaquacarbonylruthenate(II), [Ru(TPPS)(CO)(H₂O)]^4–, and CN^- revealed that only the aqua ligand is substituted even in the presence of a large excess of the nucleophile. The pK _a1 was spectrophotometrically determined as 13.4(5) (at 33.2 °C) and kinetically as 13.44(5) (at 33.6 °C). The rate of aqua substitution was determined as 89(4)m ^–1 s ^–1 at 35.1 °C and the activation enthalpy and entropy as 55.44(1) kJ mol^–1 and-27.90(4) J K^–1 mol^–1, respectively.     

Structural studies of diamine complexes of cobalt(II) and nickel(II) thiocyanates and selenocyanates

Summary Complexes of the types ML₂X₂ [M = cobalt(II) or nickel(II); L = hydrazine, ethylenediamine (en) or o-phenylenediamine (opd) and X = SCN^– or SeCN^–] and NiL₂(NCS)₂MCl₂ [M = cadmium(II) or mercury(II)] have been prepared and characterised by elemental analysis, molar conductance, molecular weight determination, magnetic susceptibility, electronic and i.r. spectral measurements.     

Unsymmetrical dinuclear cobalt and nickel trimethylacetate complexes

The reaction of the dinuclear complex Co₂(-OOCCMe₃)₂(²-OOCCMe₃)₂bpy₂ (1) with the polymer [Co(OH) _n (OOCCMe₃)_2–n ] _x afforded the unsymmetrical dinuclear complex bpyCo₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (2). The reaction of 2,2"-dipyridylamine with [Co(OH) _n (OOCCMe₃)_2–n ] _x gave rise to the analogous complex [(C₅H₄N)₂NH]Co₂(₂-O,²-OOCCMe₃)(-OOCCMe₃)₂(²-OOCCMe₃) (3). The reaction of complex 1 with Ni₄(₃-OH)₂(-OOCCMe₃)₄(OOCCMe₃)₂(MeCN)₂[²-o-C₆H₄(NH₂)(NHPh)]₂ (4) produced an isostructural heterometallic analog of complex 2 with composition bpyM₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (5) (M = Co, Ni; Co : Ni = 1 : 1) and the dinuclear heterometallic complex bpy(HOOCCMe₃)M(-OH₂)(-OOCCMe₃)₂M(OOCCMe₃)₂[o-C₆H₄(NH₂)(NHPh)] (6) (M = Co, Ni; Co : Ni = 0.15 : 1.85). Compounds 2 and 5 exhibit ferromagnetic spin-spin exchange interactions.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Kinetics and mechanism of the interaction of thiourea with cis-diaquaethylene-diamineplatinum(II) perchlorate in aqueous medium

The kinetics of the interaction of thiourea with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [thiourea] and temperature at a particular pH(4.0), where the substrate complex exists predominantly as the diaqua species and the thiourea ligand as a neutral molecule. The reaction proceeds via a rapid outer sphere association followed by two slow consecutive steps, the second step exhibiting first order dependence on the aqua ion and thiourea concentrations. The activation parameters for both the steps have been evaluated: (H ₁ = 54.8 ± 1.2 kJ mol^–1, S ₁ = –96 ± 4 J K^–1 mol^–1, H ₂ = 27.9 ± 0.8 kJ mol^–1 and, S ₂ = –183 ± 2.6 J K^–1 mol^–1). The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both consecutive steps.