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.     

Crystal structure determination of complexes of monomethylammonium chloride and mercury(II) chloride: CH3NH3HgCl3, (CH3NH3)2HgCl4, and CH3NH3Hg2Cl5

The crystal structures have been determined of CH₃NH₃HgCl₃, (CH₃NH₃)₂HgCl₄, and CH₃NH₃Hg₂Cl₅. In (CH₃NH₃)₂HgCl₄ the Hg^II atom is tetrahedrally coordinated by four Cl atoms with Hg? Cl bond lengths of 2.464 to 2.478 Å. In the other two compounds the Hg^II atom is involved in two short covalent Hg? Cl bonds, forming a pseudo HgCl₂ molecule and two much longer bridging Hg? Cl bonds. The methylammonium groups are connected by hydrogen bonds to the chlorine atoms. The nature of the hydrogen bonding scheme probably causes disorder of the methylammonium groups.     

Crystal structure of tris(ethylenediamine)cobalt(III) (aqua)hexachloromercurate(II) chloride [Co(En)3]2[Hg2(H2O)Cl6]Cl4

The compound [Co(En)₃]₂[Hg₂(H₂O)Cl₆]Cl₄ (I, En is ethylenediamine) has been synthesized and studied by X-ray diffraction. The crystals of I (a = 21.8745(14) Å, b = 10.6008(6) Å, c=15.4465(12) Å, space group Pna2₁) consist of tris(ethylenediamine)cobalt(III) complexes (the unit cell contains two [Co(En)₃]³⁺ cations of opposite chirality). [Hg₂(H₂O)Cl₆]^2? anions, and isolated chloride ions. The complex anion consists of the tetrahedral [HgCl₄]^2? group (Hg-Cl, 2.44–2.56 Å) and the hydrated molecule [Hg(H₂O)Cl₂] (Hg-Cl, 2.301 and 2.308 Å; Hg-O, 2.788 Å) combined by weak Hg-Cl interactions (2.915 and 3.220 Å).     

Studies on the differences in the effects of SeO2 and organic Se-compounds on the distribution of Hg,Co, Fe,Zn and Rb in mice by instrumental neutron activation analysis

The interaction of inorganic mercury (as HgCl₂) with SeO₂ and organic Se-compounds is compared. Instrumental neutron activation analysis (INAA) was applied as the analytical method. Organ concentrations of Hg and Se were always significantly higher after simultaneous i. p. injections with HgCl₂ and Se-compounds. Especially high abundances of Se and Hg in mice organs were found after simultaneous injection with Se-methionine and HgCl₂. We suggest that Hg²⁺ ions are bonded by selenohydryl groups of the metabolites of injected Se-compounds. Binding yield of Hg²⁺ ions with metabolites of Se-compounds depends upon the chemical form of injected Se-compounds. Variations in the content of Zn, Co, Fe and Rb were observed in all the investigated organs after a single injection with HgCl₂ or Se-compounds. Simultaneous injection with HgCl₂ and Se-compounds affects the contents of these elements in comparison with single injections.     

Direct Detection of Solid Inorganic Mercury Salts at Ambient Pressure by Electron-Capture and Reaction-Assisted HePI Mass Spectrometry

Solid HgCl₂ is readily detected at ambient conditions by electron capture in a HePI-MS source. The captured electron occupies the empty 6 s orbital of the Hg atom. The resulting radical-anion HgCl₂ ^?? can exist as three “flexomers” of different Cl-Hg-Cl angle. The facile in-source formation of HgCl₂ ^?? and the adduct [HgCl₃]^–- is exploited to detect other solid Hg compounds by exposing them to an external chloride source, such as HCl, NaCl, or vapors emanating from solid TiCl₃. In situ oxidation of Hg₂Cl₂ with H₂O₂ generated signals for HgCl₂ ^?? and [HgCl₃] ^–, suggesting that oxidation makes Hg 6 s orbital available for electron capture.

Theoretical and Experimental Study of Pb2+ and Hg2+ Adsorption on Biopolymers, 1. Theoretical Study

Chitosan and pectic acid have been modeled as disaccharides or oligosaccharides for Hg²⁺ and Pb²⁺ adsorption. Reasonable models of both biopolymers were used. Several adsorption sites of both polysaccharides were considered, mainly NH₂ in chitosan and CO₂^– in pectic acid. Hg²⁺ has several points of anchorage on chitosan. The most important one is NH₂ . The Molecular Mechanic modeling permit us to compare in relative terms the different conformations of models of pectic acid and chitosan and their effect in heavy metal coordination. Using the Parameterized Model version 3 (PM3), we report the formation enthalpy of inter‐ and intramolecular compounds with Hg and Pb. The Extended Huckel method (EHM) results seem to indicate that electrostatic interaction (leading to adsorbed cation on NH₂ and on sites different to NH₂) could be the reason for the high uptake found for Hg²⁺ using chitosan. Besides NH₂, the OH near the amine group is the preferred site for Hg²⁺ adsorption, especially if it is ionized. In the case of Pb²⁺ adsorption, several sites of chitosan present no interaction with this cation. Only the NH₂ group and the ionized OH group mentioned above seem to be the preferred sites, following the EH modified (EHMO) results. The Hg‐ and Pb‐adsorption modeling on pectic acid permit us to conclude that the best site is the same for both metals: the bridge oxygen between monomers of galacturonic acid. the carbonyl group from carboxylate is the best second site for Hg²⁺, whereas the internal oxygen bridge is the best second site for Pb²⁺. Considering the Hg ²⁺ chemistry in aqueous solution, we evaluated the HgOH⁺ and HgCl⁺ or HgCl₃^– adsorption on both copolymers, using EHMO. The energetic of adsorption changed on both biopolymers for these species, comparing them with Hg²⁺.     

Crystal structure of bis(l-arginine)copper(II) hexachlorodimercurate, [Cu(l-Arg)2]Hg2Cl6

By means of X-ray diffraction the chain structure of [Cu(l-Arg)₂]Hg₂Cl₆ (monoclinic, a = 10.2348(9) Å, b = 9.1386(7) Å, c = 14.8521(14) Å, β = 97.455(11)°, space group P2₁) is established. The chains are formed by square-planar [Cu(l-Arg)₂]²⁺ cations of the type trans-[Cu(N)₂(O)₂] (l-Arg is the zwitter-ion of arginine; Cu-N 1.992 Å and 1.938(6) Å, Cu-O 1.953 Å and 1.967(4) Å) that are bonded to two adjacent binuclear [Cl₂Hg(μ-Cl)₂HgCl₂]^2? ions through its clorine atoms Cl (Hg-Cl bonds are within 2.34–2.78 Å). With these two additional Cu…Cl contacts Cu adopts the geometry of an elongated octahedron with two apical Cl (Cu-Cl 2.961 Å and 3.064(3) Å).     

Untersuchungen über das Gleichgewicht des Hg2+-Hg 2 2+ -Hg-Systems in konzentrierten Perchloratlösungen

The formal potentials of the Hg²⁺/Hg ₂ ²⁺ , Hg ₂ ²⁺ /Hg and Hg²⁺/Hg redox couples and the apparent equilibrium constants of the reaction Hg²⁺ + Hg ∝ Hg ₂ ²⁺ in conc. aqueous solutions of Mg(ClO₄)₂ and Ca(ClO₄)₂ have been determined from emf measurements performed using cells with liquid junction. Based on these data, the hydration numbers of the Hg²⁺ and Hg ₂ ²⁺ ions were estimated.     

Oxidation processes at mercury electrodes for tetraphenyllead and related compounds in dichloromethane

Two oxidation waves are observed at mercury electrodes for tetraphenyllead in dichloromethane. The mechanisms of the oxidation processes have been investigated by dc and differential pulse polarography. The first wave is a broad two-electron step and represents the summation of a number of processes related to mercury exchange and halide abstraction. The exchange reactions are as follows: 2 Φ₄Pb + Hg→2Φ₃Pb⁺ + Φ₂Hg+2e^? 2 Φ₃Pb⁺ + Hg→2Φ₂Pb²⁺ + Φ₂Hg+2e^? Dichloroethane and HgCl₂ are identified as products of controlled potential electrolysis experiments as well as Φ₂Hg and Φ₂PbCl₂ implying that the coordinatively unsaturated Φ₃Pb⁺ and/or Φ₂Pb²⁺ react with the solvent dichloromethane and abstract chloride. The second oxidation process is the two electron step. Φ₂Hg+Hg→2 ΦHg⁺ + 2e^?Tetraalkyllead compounds (tetramethyl, tetraethyl, tetrabutyl) also give rise to related electrode processes at mercury electrodes and polarographic techniques may form the basis of a method for their analytical determination if separated chromatographically prior to detection.     

Zur thermischen Zersetzung des Hg2Cl2 und Hg2Br2

Thermical Decomposition of Hg₂Cl₂ and Hg₂Br₂ The thermical decomposition of Hg₂Cl₂ and Hg₂Br₂ was proved by total pressure measurements in a membrane manometer. The decomposition according to Hg₂X_2,s = Hg_,g + HgX_2,g and their thermodynamic data were confirmed.     

Substoichiometric Extraction of Mercury by Diethyldithiocarbamic Acid

The substoichiometric extraction of Hg²⁺ using diethyldithiocarbamic acid and ²⁰³Hg tracer was studied. Chloroform was employed to remove the complexes from the aqueous media which were 0.5M H₂SO₄ or 1 M HClO₄ and 0 to 5 M NaCL. - Systems containing Cl^? allowed extraction of Hg²⁺ for all DDC/Hg molar ratios, the extracted complexes being HgCl(DDC) and Hg(DDC)₂. Their exchange constant was determined. - In the absence of Cl^?, no extraction could be effected in either system if the DDC/Hg molar ratio was < 1; the H₂SO₄ system remained clear, whereas a precipitate of HgClO₄(DDC) formed in the HClO₄ system. For molar ratios > 1, the extraction of Hg²⁺ increased linearly with the addition of DDC, the extracted complex being Hg(DDC)₂.     

Photochemistry in van der Waals complexes: Observation of the intermediate state of the Hg*,Cl2 reaction

A novel method designed to observe the collision complex of a photochemical reaction is reported here. The reactants Hg, Cl₂ are frozen in a van der Waals complex (HgCl₂), and then promoted by an optical excitation (250 nm) to the reactive state. The broad complex action spectrum, presumably due to the Hg⁺-Cl₂^? intermediate, is monitored through the HgCl(B ²Σ⁺) fluorescence.     

Reaction of Hg2+ Insertion into Cysteine Pairs Within Bovine Insulin Crystals Followed via Raman Spectroscopy

Chemical modifications of protein crystals may be achieved via soaking of reactants from their precipitating solution, through the solvent channel, into the protein matrix. We describe a Raman microscopy approach to follow mercury insertion into cysteine pairs within protein single crystals, via soaking in an aqueous Hg²⁺ solution. The method has been developed using bovine insulin as the model system. Applying an efficient mercuration protocol, consisting of a first step of disulphide bridge TCEP-induced reduction within the crystal, followed by overnight reaction with a HgCl₂ solution, we obtained Hg-derivative crystals. Raman spectra collected on these derivative crystals, kept in the mother liquor, reveal a characteristic Raman band at 335 cm^?1, which has been assigned to a –S–Hg–S– bridge. The analysis provides Raman-based markers of mercury binding to cysteines, and thus of mercury intoxication.     

X-ray structural analysis of a novel organic metal (BEDT-TTF)4[Hg2Cl6]·PhCl

X-ray structural analysis has revealed that reaction of (BEDT-TTF)[HgCl₃]^– with PhCl leads to the formation of a cation-radical salt (BEDT-TTF)₄[Hg₂Cl₆]· PhCl, which exhibits a laminar crystal structure. The cationic layer is characterized by a grid or lattice network of contracted S...S intermolecular distances (3.396(4)–3.647(5) Å), which unite the BEDT-TTF cations in ribbons or bands, parallel to the [014] direction, and which also bind the ribbons together in a direction close to the [010] axis. The presence of this type of lattice network explains the metallic nature of the conductivity of this salt (BEDT-TTF)₄Hg₂Cl₆]·PhCl in the temperature range 300.0–1.5 K, and is the basis of assigning this salt to a new class of organic, two-dimensional conductors. The [Hg₂Cl₆]^2– anions and PhCl solvent molecules are united via secondary Hg...Cl 3.176(5) Å and Cl...Cl 3.480(6) Å interaction forces to form centrosymmetric tetramers [Hg₂Cl₆PhCl]₂ ^4–, stretched out along the [014] axis direction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2062–2070, September, 1991.The authors wish to acknowledge R. N. Lyubovskaya for supplying the crystals and for helpful discussion of the results.     

Détermination de l'ion chlorhydrique dans de l'eau condensée

The titration of chloride with Hg⁺² according to CLARKE allows the determination of lower concentrations as was possible according to MOHR. The greater sharpness of the endpoint at lower concentrations and the use of a more dilute Hg+2 solution permit a further lowering of the concentration limit down to 0.05 mg Cl^-/l, when using a calibration curve, the remarkable form of which perhaps may be attributed to the formation of HgCl₂.2HgO. This sensibility allows a suitable chloride determination in boiler condensates and the wetness determination of steam.     

Determination of Hg on poly(vinylferrocenium) (PVF)-modified platinum electrode

A new surface based on poly(vinylferrocenium) (PVF⁺)-modified platinum electrode was developed for determination of Hg²⁺ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF⁺ClO₄⁻. Cl⁻ ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg²⁺ solution. Hg²⁺ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl⁻. Detection of Hg²⁺ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg²⁺. Mercury ions as low as 5 × 10⁻¹⁰ M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10⁻⁶ M concentration (n = 6). Interferences of Ag⁺, Pb²⁺ and Fe³⁺ ions were also studied at two different concentration ratios with respect to Hg²⁺. The developed electrode was applied to the determination of Hg²⁺ in water samples.     

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.     

Assessment of dispersive liquid–liquid microextraction for the simultaneous extraction,preconcentration, and derivatization of Hg2+ and CH3Hg+ for further determination by GC–MS

This work reports the development of a dispersive liquid – liquid microextraction method for the simultaneous extraction, preconcentration, and derivatization of Hg²⁺ and CH₃Hg⁺ species from water samples for further determination by GC – MS. Some parameters of the proposed method, such as volume and type of disperser and extraction solvent, and Na[B(C₆H₅)₄] concentration were investigated using response surface methodology. Suitable recoveries were obtained using 80 μL C₂Cl₄ (as extraction solvent), 1000 μL ethanol (as disperser solvent), and 300 μL 2.1 mmol/L Na[B(C₆H₅)₄] (as derivatizing agent). Accuracy was evaluated in terms of recovery and ranged from 87 to 99% with RSD values <7%. In addition, a certified reference material of water (NIST 1641d) was analyzed and agreed with the certified value about 107% (for Hg²⁺), with RSD values <8.5%. LODs were 0.3 and 0.2 μg/L, with enrichment factors of 112 and 115 for Hg²⁺ and CH₃Hg⁺, respectively. The optimized method was applied for the determination of Hg²⁺ and CH₃Hg⁺ in tap, well, and lake water samples.     

Einkristallstudien zur Temperaturabhängigkeit der Kristallstruktur von α-Na3Hg

Temperature Dependent Single Crystal Investigations of α-Na₃Hg In contrast to β-Na₃Hg (rhomboedrally distorted Li₃Bi-type) α-Na₃Hg crystallizes in a hitherto poorly understood variant of the Na₃As-type. Based on temperature dependent measurements of poly- and single crystalline samples (?100°C < T < +35°C) we show, that in particular the sodium atoms (Na1) located in the region of the octahedral Hg₆-holes show a pronounced temperature dependent dynamical behaviour. To a lesser extend this is also true for the tetrahedrally coordinated Na-atoms (Na2). With increasing temperature the former ones more and more approach the centers of the opposite triangular faces of mercury atoms, limiting the Hg₆-octahedra along [001]. Occupation of the latter positions by sodium atoms would lead to unusual short interatomic distances d_{Na? Hg}. However before reaching this unreasonable situation α-Na₃Hg decomposes under formation of β-Na₃Hg.     

X-ray study of Hg2Cl2Br2 and HgCl2HgBr2 reactions in solid state

The reactions (I) Hg₂Cl₂(s) + Br₂(g) and (II) HgCl₂(s) + HgBr₂(s) have been investigated by an X-ray method. Both the reactions yield two forms of the mixed halide HgClBr, designated as α-HgClBr and β-HgClBr. The cell parameters of the two are as follows:α-HgClBr: $\text{a = 6.196}\text{A}\text{?}$, $\text{b = 13.12}\text{A}\text{?}$, $\text{c = 4.37}\text{A}\text{?}$, z = 4, ? = 5.91 g/cm³. The powder pattern and cell parameters are similar to that of HgCl₂. Therefore it is probable that the chlorine atoms, in the linear halogenHghalogen molecules of HgCl₂ structure have been replaced by bromines, and since the radius of the bromine atom is larger than that of chlorine, the lattice is larger in this case.β-HgClBr: $\text{a = 6.78}\text{A}\text{?}$, $\text{b = 13.175}\text{A}\text{?}$, $\text{c = 4.17}\text{A}\text{?}$, z = 4, ? = 5.40. These parameters are the same as those reported in the literature for β-Hg(ClBr)₂, and its X-ray powder pattern is similar to HgCl₂. Therefore this phase also has linear halogenHghalogen molecules but the distribution of Cl and Br atoms is perhaps random.Heating the products (I) and (II) up to the melting point increases the amount of α phase and decreases the β phase, whereas crystallization increases the β phase. DTA study has supported the X-ray findings.