[H2en]2{La2M(SO4)6(H2O)2} (M=Co, Ni): First organically templated 3d-4f mixed metal sulfates

The first organically templated 3d-4f mixed metal sulfates, [H₂en]₂{La₂M(SO₄)₆(H₂O)₂} (M=Co 1, Ni 2) have been synthesized and structurally determined from non-merohedrally twinned crystals. The two compounds are isostructural and their structures feature a three-dimensional anionic network formed by the lanthanum(III) and nickel(II) ions bridged by sulfate anions. The La(III) ions in both compounds are 10-coordinated by four sulfate anions in bidentate chelating fashion, and two sulfate anions in a unidentate fashion. The transition metal(II) ion is octahedrally coordinated by six oxygens from four sulfate anions and two aqua ligands. The doubly protonated enthylenediamine cations are located at the tunnels formed by 8-membered rings (four La and four sulfate anions).     

Experimental evidence of consecutive electron transfers for the Sb(III)−Sb(Hg) couple in 4 M H(Cl,ClO4) at low chloride concentrations

A dc polarographic and cyclic voltammetric study has been made of the reduction of Sb(III) ions from 0.01 M HCl+3.99 M HClO₄ and 0.001 M HCl+3.999 M HClO₄ supporting electrolytes in which a quasi-reversible, respectively irreversible behaviour is observed. It is shown that the Sb(III) reduction can be explained on the assumption of a reaction mechanism that consists of three successive one-electron transfers. Along the reduction wave the Sb(III)→Sb(II) and Sb(II)→Sb(I) step are rate determining, respectively at more negative and more positive potentials. Kinetic parameters were determined and the rate constants are shown to increase with chloride ion concentration.     

Canavanine assay of some alfalfa varieties (Medicago sativa) by fluorescence: Practical procedure for canavanine preparation

Canavanine is extracted with 0.3 M H₂SO₄. Protein is removed by adding CHCl₃ and centrifugation. SO₄^t- is removed as BaSO₄. The canavanine is adsorbed to Dowex 50 (NH₄⁺ form) and eluted with 0.16 M NH₄OH. It is isolated by lyophilization and recrystallization from 90% ethanol. It is assayed, when present in high concentration, by weighing after lyophilization, and by the pentacyanoferrate reagent. For low concentrations, an improved fluorometric procedure is described. To 2 ml of an extract, 0.25 ml of 0.2 mM phenanthrenequinone in ethanol is added followed by 0.2 ml 0.5 M NaOH. After incubation at 37 °C for 1 hr, the cooled solution is acidified with 4 M HCl. The blank is minimized by extraction with 1 ml heptane. Excitation is at 305–308 nm, and emission is at 395–400 nm. Canavanine reduces with Pd-BaSO₄ to guanidine and homoserine. In the fluorometric procedure, guanidine has a sensitivity, 4.8 times that of canavanine on a molar basis, and 14.3 times per weight. Increase of fluorescence after reduction ascertains that canavanine is being assayed. The methods were applied to 7 varieties of alfalfa (Medicago sativa) seeds, leaves, and stems, 3 of clover seed (Trifolium repens and pratense), and the jack bean (Canavalia ensiformis). The values found for the seeds in grams/kilogram were 26 for the jack bean, from 8 to 15 for the alfalfa varieties, and from 4.1 to 4.25 for the clover. Alfalfa leaves contained 0.9-1.2 g/kg and stems 0.6-0.9 g/kg.     

The investigation of the adsorptive behaviour of electroactive species by means of admittance analysis: Part II. Anion-induced adsorption of cadmium(II) from bromide and iodide solutions at the dropping mercury electrode

The adsorption of Cd(II) has been studied by measuring the interfacial admittance spectra at different dc potentials of the dropping mercury electrode (DME) in solutions of: (a) 1 M KBr+0.48 mM Cd(NO₃)₂,(b) 1 M KI+0.105 mM CdI₂ and (c) 0.1 M NaI+0.9 M NaClO₄ +0.116 mM CdI₂ The experimental data were analysed using the procedures described in Part I of this series. The frequency dependence of the admittance corresponds to that of a reversible electrode reaction with reactant adsorption. The potential dependence of the resulting adsorption parameters can be mathematically described by a Langmuir isotherm for adsorption of Cd(II) with the adsorption energy being at least a quadratic function of potential. Detailed checks on the consistency of this model have been applied and were found to be satisfactory.     

Effect of anions on the dissolution of Al in acid solutions

The effect of Cl^?, Br^?, I^?, ClO₄^?, NO₃^?, HSO₄^?, HCrO₄^? and H₂PO₄^? on the of Al in 2 M HCl is studied by the thermometric method. Three sets of experiments are carried out, which allow the variation of the concentration of the various species in a programmed manner. Dissolution promotion is noted in solutions to which HCl, HBr and H₂CrO₄ are added. The way of action of each of these anions is discussed. Additions of HI, HClO₄, H₂SO₄ and H₃PO₄, on the other hand, first retard and later enhance the dissolution of Al in 2 M HCl, as their concentration in solution is increased. This is related to anion adsorption, which is counterbalanced by increase in acidity. HNO₃ differs from the other tested acids in causing only dissolution retardation. Experiments in which LaCl₃ is added to the test solution indicate that the NO₃^? is adsorbed as such on Al₂O₃. The ability of the various anions to retard the dissolution of Al in 2 M HCl decreases in the succession: NO₃^? (strong)>I^?>HSO₄^?>H₂PO₄^?>Br^?, ClO₄^? (weak)     

The electrochemical Peltier effect observed with electrode reactions of Fe(II)/Fe(III) redox couples at a gold electrode

The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Π_c)_I=0, were determined by analyzing the observed temperature change as a function of current. The values of (Π_c)_I=0 were found to be positive for the Fe(H₂O)₆²⁺/Fe(H₂O)₆³⁺ systems in HClO₄ (1 M), HNO₃ (1 M), H₂SO₄ (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Π_c)_I=0 was obtained in the case of a Fe(CN)₆^4?/Fe(CN)₆^3? couple in a H₂SO₄ (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.     

Effect of ammonia on the Zn(Hg)/Zn(II) electrode reactions in aqueous chloride solutions

The title subject has been studied using single pulse and chronopotentiometric polarization measurements on the Zn(Hg)/Zn(II) electrode and equilibrium measurements on the same and the Zn/Zn(II) electrode, mainly in 2 M NH₄Cl with 0–0.3 M NH₃. At low ammonia concentrations, the Zn(Hg)/Zn(II) reactions are found to occur in two consecutive charge-transfer steps with Zn(I) as intermediate, and with little or no participation of ammonia. At higher ammonia concentrations, however, nearly symmetric transfer by divalent zinc ion (α=0.5 and n=2) to and from diammine species appears to be the predominant charge-transfer step.     

Calculation of exchange coupling constants in solid state transition metal compounds using localized atomic orbital basis sets

The application of theoretical methods based on density functional theory using hybrid functionals and localized, atomic orbital type basis sets is shown to provide good estimates for exchange coupling constants in non-metallic, solid state transition metal compounds with relatively complex crystal structures. The accuracy of the calculated exchange coupling constants is similar to that previously obtained for dinuclear and polynuclear molecular compounds. As an application of this procedure, the magnetic properties of the high-temperature phase of CuGeO₃, the recently synthesized silver copper oxide Ag₂Cu₂O₃, and the family of M[N(CN)₂]₂ (M=Cr(II), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II)) compounds are analyzed via the computation of their most relevant exchange coupling constants.     

A thermometric study of the dissolution of copper in acid solutions

The dissolution of Cu in solutions of HNO₃ of different concentrations has been studied by the thermometric method. Starting from the initial temperature, T_i, the temperature—time curves exhibit an induction period followed by a rapid rise in temperature to a maximum value, T_m, attained t min after the start of the reaction. T_m increases and t decreases with increase of the acid concentration, M. ΔT (i.e.T_m ? T_i) and the reaction number (R.N. = (T_m ? T_i)/t) vary with M according to: ΔT = k(M ? M₀) and R.N. = A₁Mⁿ, where k, M₀, A₁ and n are constants.The effect of varying concentrations of HCl, H₂SO₄ and H₃PO₄ on the R.N. of Cu in 3.5 M HNO₃ was examined. Small amounts of these acids lower the R.N. (inhibition) due to the displacement of an active species on the surface of the metal by the anion of the acid. Larger additions of the acids accelerate dissolution. The concentration at which the added acid changes from corrosion-inhibitor to accelerator varies as HCl < H₂SO₄ < H₃PO₄. This sequence is considered to parallel the strength of adsorption of the respective anions. The results of experiments with salt additions confirm this view; all salts act only as dissolution-retardants. Calculations pertaining to the effect of the various ions on the R.N. support the conclusion that the dissolution of Cu in HNO₃ is autocatalytic in nature, and depends on the [H⁺]/[NO₃^?] ratio.Cu does not dissolve in air-free, cold HCl. Attack takes place, however, in the presence of KNO₃. Under these conditions attack is of the pitting- rather than the general type. The temperature rises suddenly after an incubation period, which decreases in length with increase of the amount of the added salt.Proof of the involvement of HNO₂ in the autocatalytic cycle of Cu dissolution in HNO₃ is obtained from the results of urea additions to the solution.     

Effects of substrate orientation on underpotential monolayers of Pb and Tl deposited on single crystals

The behaviour of some cations was studied qualitatively in a medium of 1 M KOH and 0.25 M inositol and the half-wave potential values were determined. The behaviour of manganese complexes with this reagent (L) was studied in detail. It has been verified polarographically and potentiometrically that an anodic wave with E_1/2=0.65 V (SCE) corresponds to the oxidation of Mn(II)L to Mn(III)L and a cathodic wave with the same E_1/2 corresponds to the reduction of Mn(III)L to Mn(II)L. The conditional stability-constant value was determined for Mn(II)L using the substitution reaction between Mn(II)-EDTA and Mn(II)L. The effect of some anions and cations was studied from the point of view of analytical chemistry.     

Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

Investigation of the surface properties of platinum,rhodium and iridium electrodes in hydrofluoric acid solutions

The charging curves, the potentiodynamic curves and the isoelectric potential shifts have been measured on Pt, Rh and Ir electrodes in HF and HF + KF solutions in a Teflon cell. From the obtained data, the Γ_H⁺?? curves and the Δσ?? curves of the first kind have been calculated by means of the thermodynamic theory of the hydrogen electrode. The Γ_H⁺ values in 0.14 M HF and 0.3 M HF + 0.12 M KF are much less than in 0.005 M H₂SO₄ and 0.005 M H₂SO₄ + 0.5 M K₂SO₄ solutions. In the presence of F^? anions, the potentials ?_ε=0 and ?_Q=0 are by 25–55 mV more anodic than in the presence of SO^2?₄ anions. In an acidified fluoride solution the values of σ are higher than in an acidified sulfate solution. The analysis of the results obtained leads to the conclusion that on platinum metals the fluoride anions in the ?_r region investigated (from ?_r = 0 to ?_r = 900 mV) are the most weakly adsorbed anions.     

Syntheses and Crystal Structures of a New Niobium Polysulfide K6Nb4S22 and two New Dimorphic Tantalum Polysulfides K6Ta4S22

The new compounds K₆Nb₄S₂₂ and K₆Ta₄S₂₂ ( I ) have been synthesised by the reaction of NbS₂ or Ta metal in a K₂S₃ flux. Using TaS₂ as educt a second modification of K₆Ta₄S₂₂ ( II ) is obtained. K₆Nb₄S₂₂ and K₆Ta₄S₂₂ (form I ) crystallise in the monoclinic space group C2/c with a = 35.634 (2)Å, b = 7.8448 (4)Å, c = 12.1505 (5)Å, β = 100.853 (5)°, V = 3335.8 (3)ų, and Z = 4 for K₆Nb₄S₂₂ and a = 35.563 (7) Å, b = 7.836 (2)Å, c = 12.139 (2)Å, β = 100.56 (3)°, V = 3325.5 (2)ų, and Z = 4 for K₆Ta₄S₂₂ ( I ). The second modification K₆Ta₄S₂₂ (form II ) crystallises in the monoclinic space group P2₁/c with a = 7.5835 (6)Å, b = 8.7115 (5)Å, c = 24.421 (2)Å, β = 98.733 (9)°, V = 1594.6 (2)ų, and Z = 2. The structures consist of [M₄S₂₂]^6— anions composed of two M₂S₁₁ sub‐units which are linked into M₄S₂₂ units via terminal sulfur ligands. The anions are well separated by the K⁺ cations. Differences between the structures of the title compounds and those with the heavier alkali cations Rb⁺ and Cs⁺ are caused by the different arrangement of the [M₄S₂₂]^6— anions around the cations and the different S^2—/S₂^2— binding modes. The thermal behaviour of both modifications was investigated using differential scanning calorimetry (DSC). From these investigations there is no hint for a polymorphic transition between the two forms. After heating crystals of form II above the melting point and cooling the melt to room temperature a crystalline powder of form I can be isolated.     

Organotin polymers—III: Copolymerization and terpolymerization of tributyltin acrylate with methyl methacrylate,propyl methacrylate,butyl methacrylate and acrylonitrile

Copolymerizations of tri-n-butyltin acrylate (M₁) with (a) methyl methacrylate (M₂), (b) propyl methacrylate (M₃), (c) butyl methacrylate (M₄) and (d) acrylonitrile (M₅) in solution at 70 using AIBN as initiator led to monomer reactivity ratios as follows: (a) r₁ = 0.401 and r₂ = 2.199, (b) 0.323 and 1.713, (c) 0.196 and 1.65, and (d) 0.243 and 1.008. The variation of the average copolymer composition with conversion for two copolymers from M₁ with M₂ and M₄ were calculated and verified experimentally. Four terpolymer compositions involving M₁ and M₅ with M₂ or M₄ were prepared and the terpolymer compositions were calculated on the basis of tin and nitrogen analyses. The variations of instantaneous and average terpolymer composition with conversion fit satisfactorily the experimental results over a wide range of conversion.     

Anion Binding Properties of N-Confused Porphyrins at the Peripheral Nitrogen

Ni(II), Pd(II), and Cu(II) complexes of N-confused porphyrin (NCP) exhibit anion binding properties through a hydrogen bonding interaction at the peripheral NH of confused pyrrole ring. The binding constants of the tetrakis(pentafluorophenyl)-NCP metal complexes (1-M, M= Ni, Pd, Cu) for various halide anions in CH₂C1₂ increase in the order of F^? > Cl^? > Br^? > I^?, respectively. Zwitterionic resonance form of the NCP complexes as well as interactions between halide anions and a pentafluorophenyl group are suggested to be important for efficient anion binding.     

π-Bis(benzene)chromium(0)-catalyzed oligomerization of perfluoropropylene

In the presence of zerovalent π-bis(benzene)chromium(0) (I), perfluoropropylene (II) was found to undergo oligomerization under very mild conditions to dimers (b.p. 46°, M⁺, 300) and trimers (b.p. 100–102°C, M⁺ - 19, 431) in the ratio of 2.5–3.0 to 1. One mol of metal complex could catalyze the conversion of 50 mol of perfluoropropylene. On the basis of ¹⁹F NMR, the structures of the dimers are III and IV in a ratio of ca. 80/20 and the trimers V and VI; VII and VIII also seemed to be present. V/VI/(VII + VIII) is 80/10/4. In benzene solution, perfluoropropylene was shown not to be catalytically oligomerized by fluoride ion (KF, CrF₂ or (CH₃)₄NF) (nor by monovalent π-dibenzenchromium(I). A possible mechanism of the reaction was proposed.     

Extraction of metals by neutral sulfur-containing extractants: Part I. o-isopropyl-n-ethylthiocarbamate

The formation of neutral mixed complexes of the MX_mS_p type (where M is a metal ion with m⁺ charge, X the inorganic anion, and S the sulfur-containing extractant) allows a selective extraction of various elements. The extraction of many metals from mineral acid solutions or from halide-sulfuric acid mixtures by 0.05 M O-isopropyl-N-ethylthiocarbamate(IPETC) solution in chloroform has been studied. (IPETC) possesses very high selectivity for silver and mercury ions in extractions from HNO₃, H_{2)SO4, HClO4 and HCl solutions. In addition to silver and mercury, Cu, Au, Tl and Se are readily extracted from solutions containing bromide. From iodide solutions, copper, gold and thallium ions may be selectively extracted because silver and mercury cannot be extracted at concentrations of iodide above 0.1 M.(IPETC} extracts metals as mixed complexes, containing the halide and apparently the extractant in the molecular form.     

Anwendung von ionenaustauschverfahren zur bestimmung von spurenelementen in natürlichen wässern—IV: Uran,kobalt und kadmium

A method is described for separating and determining. by spectrofluorimetric or spectrophotometric measurement, traces of uranium. cobalt and cadmium at ppM levels in natural waters. The sample is acidified with HCl. filtered. and after addition of ascorbic acid and potassium thiocyanate, passed through a column of Dowex 1.- × 8 anion-exchange resin in the thiocyanate form. The three ions are concentrated on the resin as thiocyanate complexes, being at the same time separated from most of the other ions present in the sample. Elution with a tetrahydrofuranmethylglycol-HCl mixture removes other interfering ions. then 6M HCl strips the cobalt. 1M HCl the uranium, and 2M HNO₃ the cadmium. Data are presented for concentrations of uranium (0·01–5 ppM) cobalt (0·04–1·9 ppM) and cadmium (0·04–0·6 ppM) in a large number of water sources in Austria.     

Experimental and theoretical studies of media effects on copper corrosion in acidic environments containing 2-amino-5-mercapto-1,3,4-thiadiazole

Corrosion behaviour of copper metal in acid solutions (HCl, H₂SO₄ and H₃PO₄) containing 2-amino-5-mercapto-1,3,4- thiadiazole (AMT) was investigated experimentally and theoretically via gravimetric, potentio-dynamic and quantum electrochemical approaches. Similar behavior was observed for H₂SO₄ and H₃PO₄ media, and related to the nature of anions at metal/solution interface. With regard to HCl, however, the rate of corrosion was determined to be low at initial stages, but high later on using an auto-catalyzing mechanism. In the presence of AMT, the experimental studies revealed that this molecule was a good anodic-type inhibitor causing substantial changes in corrosion potential. Moreover, its adsorption obeys the Langmuir isotherm. The values of ΔG _ads were determined and correlated to the inhibitor powers. Finally, the influence of media (anions) on metal corrosion was also investigated from molecular point of view by calculations of the copper-anions interaction using density functional theory.     

Spectrometric evidence ford-orbital participation in the lowest excited singlet states of naphthalenethiols

Tellurium can be determined polarographically in the range 10^?5–10^?8M by means of the Te⁰_ads→Te^2- reduction in 1M perchloric acid as supporting electrolyte. Pulse polarography, a.c. polarography and linear sweep cyclic voltammetry can be used to determine tellurium in the p.p.b. range. Copper(II), arsenic(III) and selenium(IV) interfere, but the interferences can be overcome by a standard addition method.