Gewinnung und Verhalten der Amalgame der Metalle der IVa- bis VIa-Gruppe

The usual methods for the production of amalgams—dissolving of metals in mercury, or electrolytic deposition on mercury—are not suitable for the preparation of amalgams of transition metals. However amalgams of the transitions elements can be prepared by reduction of their dry halides with sodium amalgam. These amalgams are unstable against aqueous solutions under oxidising conditions and decompose by dewetting of the suspended metal particles. The stability can be improved by addition of components, e.g. oxalic acid or HF to the solution, which prevent the formation of oxide layers on the dewetted metal particles. By using such solutions in processing the reaction products of the halides with sodium amalgam the amalgams of the transition elements can be obtained without decomposition.

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Mit 3 Abbildungen

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Herrn Prof. Dr.H. Hohn zum 70. Geburtstag gewidmet.     

Electroanalytical chemistry of metal complexes with S-containing ligands

Summary The main types of electrochemical reactions of complexes in organic and mixed solvents are considered. Fast electrochemical reactions (k _s=n×10^–2 cm · s^–1) were used to reduce the minimal concentrations (c _min) in a.c. voltammetry. The role of pre- and post-chemical reactions in the formation of the analytical signal in extraction voltammetry is elucidated. The principles of the influence of the special structure of the complexes on their redox properties are determined using complexes of the transition metals with phosphorus dithioacids and bidentate heterocyclic amines. The features of the electrooxidation and electroreduction of inert complexes of the platinum metals with heterocyclic dithioacids and organic sulphides in nonaqueous media are discussed. The products of the electrochemical reaction of these compounds in protic media catalyze the hydrogen evolution on the mercury electrode. Kinetic data of the chelate formation are used for developing highly selective methods for the determination of the platinum metals with c _min=2×10^–9–5×10^–8 mol/l.

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Elektrochemische Reaktionen von Komplexen mit S-haltigen Liganden

     

Diffusion of Cesium Ions in Agar Gel Containing Alkali Metal Bromides

The present paper gives an account of different aspects of the tracer diffusion of Cs⁺ ions in alkali metal bromides. We have measured the diffusion coefficients, D, of cesium ions in 1% agar gel medium at 25 ^∘C using a zone-diffusion technique over a concentration range of 5 × 10⁻⁵ to 0.1 mol,dm⁻³. The values of the diffusion coefficients were found to deviate from theory, which are explained on the basis of different types of interactions occurring in the ion-gel-water system. The study is also focused on the effect of alkali metal bromides on the obstruction effect and activation energy for the tracer-diffusion of cesium ions in agar gel medium. It is observed that both parameters, extent of obstruction, ∝, and activation energy, E, decrease with increasing charge density of the cation of the supporting electrolyte. The influence of these trends is explained on the basis of competitive hydration between the ions and agar molecules, and the relative distortion in the water structure that is brought about by these different ions and agar molecules.     

Total and free charge densities on mercury coated with self-assembled phosphatidylcholine and octadecanethiol monolayers and octadecanethiol/phosphatidylcholine bilayers

The thermodynamic ‘total’ charge density is the charge to be supplied to the electrode to keep the applied potential constant when the electrode surface is increased by unity, while the extrathermodynamic ‘free’ charge density is the charge actually experienced by the diffuse layer ions. The total charge density at dioleoylphosphatidylcholine (DOPC) and octadecanethiol (ODT) monolayers and mixed ODT/DOPC bilayers self-assembled on mercury from aqueous solutions was determined from chronocoulometric single potential steps to a final potential negative enough to cause complete desorption of the film. The effect of different alkali metal ions and of tetramethylammonium on DOPC desorption was examined. The total charge for ODT monolayers and ODT/DOPC bilayers, +56±3 μC cm⁻², agrees with the value obtained by integration of the current under the reductive desorption voltammetric peaks, only provided the scan rate is higher than 100 mV s⁻¹. An approximate model of the interface of the ODT-coated electrode, which accounts for partial charge transfer from sulfur to mercury and for the degree of dissociation of the sulfhydryl group upon self-assembly, was employed to estimate the free charge density.     

The effect of high pressure on the ion pair equilibrium constant of alkali metal fluorides: A spectrophotometric study

Bromophenol blue indicator was used in UV-visible spectrophotometric measurements to study ion association constants of alkali metal fluorides. The equilibrium constants for the ion pair formation of the alkali metal fluorides were determined as a function of ionic strength at one atmosphere pressure and 25°C. The effect of pressure on these association constants was measured at a constant total ionic strength of 1.0 mol-kg^–1 over a pressure range of 1 to 2000 atmospheres at 25°C. The pressure dependences of the stoichiometric association constants of the alkali metal fluorides are given by: lnK _LiF ^* =0.77–2.47×10^–4P–2.12×10^–8P²; lnK _NaF ^* =0.53–1.08×10^–4P–1.66×10^–8P²; lnK _KF ^* =0.24–4.41×10^–5P–7.15×10^–8P²; lnK _RbF ^* =–0.17–8.65×10^–5P–4.51×10^–8P²; and lnK _CsF ^* = –0.37–1.14×10^–4P–6.82×10^–8P², where P is the pressure in atmospheres. The stoichiometric molar volume and compressibility changes for ion pair formation of the alkali metal fluorides were evaluated from the pressure dependence of K _MF ^* data. The thermodynamic association constants were also calculated making use of activity coefficient data from the Pitzer equations. The partial molal volume and compressibility changes for ion pair formation of each alkali metal fluoride are reported.     

Pulse radiolysis of solutions of alkali metals in liquid amines

Pulse radiolysis of solutions of alkali metals in methylamine and ethylamine shows the formation of three distinct species; the solvated electron e^?_s, the alkali metal anion M^? and a species considered to be a metal—electron pair with stoichiometry M. Hitherto no kinetic or conclusive optical evidence has been obtained for the species M in amine solutions. The three species coexist in equilibrium according to the equation c^?_s + M⁺ ? M + e^? ? M^? with the corresponding rate constants markedly dependent on the solvent and nature of the alkali metal.     

Ion-Selective Electrodes Based on Adamantylcalix[4,8]arenes for the Determination of Alkali Cations

Calix[4,8]arenes bearing adamantyl substituents in the upper rim and ethoxycarbonylmethoxy groups in the lower rim of the macrocycle were proposed as ionophores in membranes of ion-selective electrodes (ISEs) for determining alkali cations. Depending on the number of phenolic fragments (n) in the calixarene molecule, ISEs respond to either sodium (n = 4) or cesium (n = 8) ions. Sensors based on membranes that, along with ionophores, contain tetraphenyl borate ions as a lipophilic additive are selective for Na and Cs ions in the presence of other alkali metals. They exhibit almost theoretical responses over the concentration range from 1 × 10^–4 to 1 × 10^–1 M at pH 5.5–12 for Na-SE and pH 3–11 for Cs-SE, respectively.     

Thermodynamics of Coordination Bonds in Metal closo-Heteroclusters of the Endofullerene Type M@N k B r C s n – (m = k + r + s = 12, 24, or 28; n = 0–4), Where M = Li,Mg, Al,Ti, Zr,Hf, V,Nb, Mo,Ru, Rh,Ir, Ta,Pt, Pd,and Au

The energy of coordination-induced stabilization and the enthalpy of formation of gaseous metal closo-heteroclusters of the M@N _k B _r C _s ^{n –} type (m = k + r + s = 12, 24, or 28; n = 0–4), where M = Li, Mg, Al, Ti, Zr, Hf, V, Nb, Mo, Ru, Rh, Ir, Ta, Pt, Pd, and Au, were estimated in terms of a structural-thermodynamic model. The stabilizing role of metals in clusters was demonstrated. The energies D ₀ of M–N, M–B, and M–C bonds were found to be underestimated by the MO LCAO method at the HF/6-31G* level.     

Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(III), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10^–3. mol·dm^–3. Cations of zinc, manganese and mercury which form much weakerammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions.     

Alkyl Ammonium Ion Selectivity of Hexahomotrioxacalix[3]arene Triamide Derivative having the Intramolecular Hydrogen-Bonding Group

The lower rim functionalized hexahomotrioxacalix[3]arene triamide 4 with cone-conformation was synthesized from triol 1 by a stepwise reaction. The different extractability for alkali metal ions, transition metal ions, and alkyl ammonium ions from water into dichloromethane is discussed. Due to the strong intramolecular hydrogen bonding between the neighboring NH and CO groups in triamide 4, its affinity to metal cations was weakened. Triamide 4 shows a single selectivity to n-BuNH₃⁺. The anion complexation of triamide 4 was also studied by ¹H NMR titration experiments. Triamide 4 binds halides through the intermolecular hydrogen bonding among the NH hydrogens of amide in a 1:1 fashion in CDCl₃. The association constants calculated from these changes in chemical shifts of the amide protons are K_a = 223 M⁻¹ for Cl⁻ and K_a = 71.7 M⁻¹ for Br⁻. Triamide 4 shows a preference for Cl⁻ complexation than Br⁻ complexation.     

Soluble,crystalline, and thermally stable alkali CO2− and carbonite (CO22−) clusters supported by cyclic(alkyl)(amino) carbenes

The mono- and dianions of CO₂ (i.e., CO₂⁻ and CO₂²⁻) have been studied for decades as both fundamentally important oxycarbanions (anions containing only C and O atoms) and as critical species in CO₂ reduction and fixation chemistry. However, CO₂ anions are highly unstable and difficult to study. As such, examples of stable compounds containing these ions are extremely limited; the unadulterated alkali salts of CO₂ (i.e., MCO₂, M₂CO₂, M = alkali metal) decompose rapidly above 15 K, for example. Herein we report the chemical reduction of a cyclic (alkyl)(amino) carbene (CAAC) adduct of CO₂ at room temperature by alkali metals, which results in the formation of CAAC-stabilized alkali CO₂⁻ and CO₂²⁻ clusters. One-electron reduction of CAAC–CO₂ adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals [M(CAAC–CO₂)]_n (M = Li, Na, K, 2–4) analogous to the alkali CO₂⁻ radical, and two-electron alkali metal reduction affords dianionic clusters of the general formula [M₂(CAAC–CO₂)]_n (5–8) with reduced CO₂ units which are structurally analogous to the carbonite anion CO₂²⁻. It is notable that crystalline clusters of these alkali–CO₂ salts may also be isolated via the “one-pot” reaction of free CO₂ with free CAAC followed by the addition of alkali metals – a process which does not occur in the absence of carbene. Each of the products 2–8 was investigated using a combination of experimental and theoretical methods.

The direct chemical reduction of CAACCO2 adducts by alkali metals to yield multinuclear clusters is reported. The mono- and dianions of CO₂ have been studied for decades and are fundamentally important oxycarbanions and critical species in CO₂ fixation chemistry.     

Synthesis and Complexing Properties of <Emphasis Type="Italic">N,N</Emphasis>′-Bis(2-hydroxyethyl) Diaza Crown Ethers

The stability constants of complexes of 12-, 15-, and 18-membered diaza crown ethers, N,N′-dimethyl diaza crown ethers, and N,N′-bis(2-hydroxyethyl) diaza crown ethers with alkali and alkaline-earth metal ions in 95% aqueous methanol at 25°C were determined. The stability of the complexes of unsubstituted diaza crown ethers with alkali metal cations is low, probably because of stabilization of the exo,exo conformation of the ligands due to interaction of the nitrogen lone electron pairs with the solvent. The complexes with the double-charged cations are appreciably more stable. N,N′-Dimethyl diaza crown ethers form stable complexes with all the ions studied. As compared to the dimethyl derivatives, N,N′-bis(2-hydroxyethyl) diaza crown ethers form more stable complexes with the Na⁺, K⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions, which is due to participation of the side hydroxyethyl groups in the coordination.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 665–669.Original Russian Text Copyright © 2005 by Kulygina, Vetrogon, Basok, Luk’yanenko.     

Thermal decomposition of silver(I) and mercury(I) anthranilates and salicyloaldoximates

The processes of thermal decomposition of silver(I) and mercury(I) anthranilates and salicyloaldoximates were studied. Thermal, chemical and X-ray analyses and infrared spectroscopy were used to determine the mechanisms of decomposition of these complexes. The factor determining the decomposition is the character of the Ag⁺ and Hg ₂ ²⁺ ions, which are easily reduced to free metals. The final reaction product of the compounds of silver is the pure metal; the compounds of mercury are volatilized completely when heated.     

Kinetics of the oxidation of nitrous acid by tetrachloroaurate(III) inHCl

Summary The kinetics of the reaction between nitrous acid and gold(III) in an HCl medium was studied. The reaction was first order with respect to [Au^III] and [HNO₂]·H⁺ and Cl^- ions inhibit the rate and alkali metal ions have specific effects on the rate. The reaction appears to involve different gold(III) species, viz. AuCl _inf4 ^sup– , AuCl₃(OH₂) and AuCl₃(OH)^–, which undergo a two-equivalent reduction to gold(I) leading to the formation of NO _inf2 ^sup&#x002B; which under-goes rapid hydrolysis to give nitric acid.     

Separation radiochimique rapide des ions argent par reduction sur le mercure

A rapid separation .of silver on mercury is proposed in order to utilize shortlived isotopes for the determination of silver by activation. The conditions allowing quantitative reduction of silver were studied; a. kinetic study showed that after 90 sec, 97% of silver could be transferred to the mercury. The spectrometric analysis of ¹¹⁰Ag was also examined. Only metals with a redox potential greater than that of mercury form amalgams, and under the irradiation conditions these metals produce virtually no activity.     

Surface Tension Calculations for Liquid Metals

Abstract

We present a class of models for the surface of a liquid metal, which may be part of an electrochemical interface. The particles of the system, for the purpose of derivation of thermodynamic properties, are the charged ion cores, while the energy of the electrons is evaluated using the electron density functional formalism, previously principally applied to solids. An expression for the surface energy U^s , defined as the energy required to create unit area of surface by separation of a volume of homogeneous metal into two parts, is derived (Eqs. 18–20). The surface tension γ is obtained by differentiating the Helmholtz free energy with respect to the area of the system, keeping volume and particle number constant (Eqs. 27–37). The surface tension is also equal to the difference between the free energy of the system containing a surface and the free energy of a reference system. It thus defines a surface energy through the Gibbs-Helmholtz equation, and this surface energy is shown to be identical to U^s .

The expressions for U^s and γ are made explicit (Eqs. 45–57) by insertion of particular assumptions for the ion-density profile, the electron-density profile, the interionic interaction and pair distribution function, and the electronic energy. Only information about bulk liquid metal is used. The parameter in the electron-density profile is obtained by minimizing the surface energy. The simplest assumption for the interionic interaction, hard-sphere and Coulombic repulsions, requires a choice for the hard-sphere diameter, which is made such that the pressure of bulk metals is given correctly (52–55). For the alkali metals, the surface tension calculated from this model is about half the experimental value in each case, while calculated surface energies are too high (1/5 too high for Cs, but three times too high for Li). For the electrical potential difference between the inside and the outside of a metal, and for the electrochemical potential, agreement with experiment is good. The main reason for the disagreements in the other properties is traced to the simple form used for the ion pair distribution function.     

2,3-Dihydroxypyridine-loaded cellulose: a new macromolecular chelator for metal enrichment prior to their determination by atomic absorption spectrometry

New macromolecular chelators have been synthesized, by loading 2,3-dihydroxypyridine (DHP) on cellulose via linkers -NH-CH₂-CH₂-NH-SO₂-C₆H₄-N=N- and -SO₂-C₆H₄-N=N-, and characterized by elemental analysis, TGA, IR, and CPMAS ¹³C NMR spectra. The cellulose with DHP anchored by the shorter linker had better sorption capacity (between 69.7 and 431.1 mol g^–1) for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III)) than the other (51.9–378.1 mol g^–1); the former was therefore studied in detail as a solid extractant for these metal ions. The optimum pH ranges for quantitative sorption (recovery 97.6–99.8%) on this matrix were: 7.0–9.0, 6.0–9.0, 3.0–8.0, 6.0–8.0, 6.0–9.0, 6.0–7.0, and 2.0–6.0 respectively. Desorption was quantitative with 0.5 mol L^–1 HCl and 0.5 mol L^–1 HNO₃ (for Pb). Simultaneous sorption (at pH 7.0) of all metal ions other than Fe(III) was possible if their total concentration did not exceed the sorption capacity (lowest value). The recovery of seven metal ions from their mixture at pH 6.0 was nearly quantitative when the concentration level of each metal ion was 0.2 g mL^–1. The optimum flow rate of metal ion solutions for quantitative sorption of metal onto a column packed with DHP-modified cellulose was 2–7 mL min^–1, whereas for desorption the optimum flow rate for the acid solution was 2–4 mL min^–1. The time needed to reach 50% of the total loading capacity (t_1/2) was <5 min for all the metal ions except Ni and Pb. The limit of detection (blank+3s) was from 0.70 to 4.75 g L^–1 and the limit of quantification (blank+10s) was between 0.79 and 4.86 g L^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, Ca(II), and Mg(II) for sorption of all metal ions are reported. The column packed with DHP-anchored cellulose can be reused at least 20 times for enrichment of metal ions in water sample. It has been used to enrich all the metal ions in pharmaceutical and water samples before their determination by flame AAS. RSD for these determinations was between 1.1 and 6.9%.     

Influence of alkaline earth metals on molecular structure of 3-nitrobenzoic acid in comparison with alkali metals effect

The influence of beryllium, magnesium, calcium, strontium and barium cations on the electronic system of 3-nitrobenzoic acid was studied in comparison with studied earlier alkali metal ions [1]. The vibrational FT-IR (in KBr and ATR techniques) and ¹H and ¹³C NMR spectra were recorded for 3-nitrobenzoic acid and its salts. Characteristic shifts in IR and NMR spectra along 3-nitrobenzoates of divalent metal series Mg → Ba were compared with series of univalent metal Li → Cs salts. Good correlations between the wavenumbers of the vibrational bands in the IR spectra for 3-nitrobenzoates and ionic potential, electronegativity, inverse of atomic mass, atomic radius and ionization energy of metals were found for alkaline earth metals as well as for alkali metals. The density functional (DFT) hybrid method B3LYP with two basis sets: 6-311++G** and LANL2DZ were used to calculate optimized geometrical structures of studied compounds. The theoretical wavenumbers and intensities of IR spectra as well as chemical shifts in NMR spectra were obtained. Geometric aromaticity indices, atomic charges, dipole moments and energies were also calculated. The calculated parameters were compared to experimental characteristic of studied compounds.     

A novel lariat crown compound as ionophore for construction of a mercury(II)-selective electrode

Abstract  

The construction, performance, and application of a new PVC membrane electrode for determination of the mercury(II) ion, based on 8,17-bis(pyren-1-ylmethyl)-6,7,8,9,15,16,17,18-octahydrodibenzo[f,m][1,8,4,11]dithiadiazacyclotetradecine as an ionophore, is described. The effects of factors such as membrane composition, the nature and amount of the plasticizers and additives, and pH for the improved sensitivity of the electrode were studied. The electrode had a Nernstian response for mercury(II) ions over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ mol dm⁻³ with a slope of 27.6 ± 0.6 mV/pHg. The detection limit for mercury(II) was 7.9 × 10⁻⁷ mol dm⁻³. The response time of the electrode was between 5 and 15 s, depending on the concentration of mercury, and it can be used in a pH range 4.0–4.5 for approximately 4 months without any substantial divergence of the response characteristics. It showed higher selectivity for mercury(II) ions than for several common alkali, alkaline earth, and transition metal ions except silver(I). The proposed electrode was successfully applied to direct determination of mercury in a dental filling amalgam alloy as a real sample with a complex matrix and as an indicator electrode in complexation titrations.