Heats of formation of iodo-complexes of zinc(II), cadmium(II) and mercury(II) in aqueous solutions

Heats of formation of MeI⁺, MeI₂, MeI₃^? and MeI₄^2? where Me²⁺, Cd²⁺ or Hg²⁺ were determined in acidic solutions by flow microcalorimetry. Some gaps in the literature data were filled. In particular, ΔH₃ for the mercury(II) complex was determined and the ΔH₁, ΔH₂ + ΔH₃, ΔH₄ for zinc(II) complexes were measured in sodium free solutions to avoid ionic couple formation. For cadmium(II) complexes, existing data were confirmed. Thermodynamic functions are discussed in term of hard/soft interactions.     

Indirect ultraviolet determination of cyanide with mercury complexes

Cyanide ion can be determined in the range of 0.50 to 10 parts per million by the decrease in ultraviolet absorption of the mercury complexes HgBr₄^2?, HgCl₄^2?, HgI₄^2?, Hg(SCN)₄^2?, and Hg(SO₃)₂^2?. The decrease in absorbance is linear with cyanide concentration. Reaction of cyanide with the complexes is rapid in pH 6.86 and 9.01 buffers and in water. Solutions of the complexes are reasonably stable.     

Mechanism of electroreduction of cobalt(II) in thiocyanate solutions at mercury electrodes

The process of electroreduction of cobalt(II) in thiocyanate solutions at mercury electrodes has been investigated by cyclic voltammetric, chronoamperometric and polarographic methods. The influences of pH, the concentrations of Co(II) and SCN^?, and the reduction products of SCN^?, CN^? and S^2? on the reduction waves are described. The polarographic pre-wave is an autocatalytic in nature. A mechanism involving an initial reduction of Co(II)—SCN^? at a mercury electrode followed by the chemical reduction of thiocyanate ion with the electroreduced metallic cobalt, and taking into account cyanide, sulfide, and hydroxide ions, the latter being produced by the hydrolysis of cyanide ion, is presented. Cobalt sulfide adsorbed at the electrode surface stimulates further reduction of Co(II)—CN^? and —SCN^? complexes, and depresses the interfering influence of Co(OH)₂, which is reductively desorbed from the electrode surface with giving rise to an additional peak near ?1.08 V vs. SCE.     

Photocurrent kinetics at electron emission from metal to electrolyte solution: Part V. Ionization rate constants of hydrogen and deuterium atoms adsorbed on mercury

Absolute ionization rate constant values of hydrogen and deuterium atoms adsorbed on mercury were measured using the method of pulse photoelectronic emission from metal into solution. In accordance with the Tafel law, these constants decrease from 2.5×10⁷s^?1 to 9×10⁵s^?1 (Table 1) in a 1 M solution of KCl in the range ?0.25 to ?0.5 V SCE. The transfer coefficient is 0.33±0.03 and the isotope ratio about 2.5. Owing to specific anion adsorption, rate constants increase as their concentration increases and KBr is added to the solution. In 0.05 M solutions of HCl and H₂SO₄, transfer coefficients are 0.30±0.05. From a comparison of measured values, with the hydrogen ion discharge rate constants found by extrapolation of experimental values into the potential range mentioned (taking into account the transfer coefficient change), the change of the Gibbs free energy in the reaction H₃O⁺+e_Me^?→H_ads+H₂O was calculated and found to be 0.87–0.99 eV at the potential of the normal hydrogen electrode. Adsorption energy of the hydrogen atom from the gas phase on a mercury electrode is 1.55±0.10 eV.The volt-ampere dependence of the hydrogen ion discharge current in the range ?0.25 to ?2.25 V corresponding to the current change by 18 orders of magnitude, agrees with the theoretically determined values (maximum deviation in the current is less than a factor of 3) for the medium reorganization energy E_r=1.75 eV. Despite constancy of the transfer coefficients of the elementary stages, in the range ?0.5 V (SCE), the effective transfer coefficient of the total hydrogen evolution processes increases from 0.5 to 1.0, as the ionization rate of the adsorbed hydrogen atoms becomes greater than their electrochemical desorption rate.     

Bis(N,N′‐dimethylimidazol‐2‐yl­idene)mercury chlorotriiodo­mercury dimethyl sulfoxide solvate

The double mercury salt [Hg(C₅H₈N₂)₂][HgClI₃]·C₂H₆OS was prepared and its structure characterized. The [Hg(C₅H₈N₂)₂]²⁺ cation lies about an inversion centre and the [HgClI₃]^2? anion lies on a mirror plane. Cations and anions are linked to form a one‐dimensional polymer by weak Hg?Cl interactions [Hg?Cl 3.3744 (3) Å]. The mercury–carbene bond distance [2.076 (7) Å] is typical of a dicationic mercury–carbene species.     

Reduction mechanism of cobalt(II)-ammonia complexes on a dropping mercury electrode

The mechanism of the polarographic reduction of cobalt(II) complexes with ammonia at a dropping mercury electrode over a wide ligand concentration range was investigated. It was shown that the Co(II) aquo ion and the Co(NH₃)²⁺ and Co(NH₃²⁺₂ complexes participate in the electrode process. Transfer coefficients, α, for these species and the electrode reaction rates were evaluated. Stability constants of Co(II) complexes with ammonia in 0.5 M ammonium perchlorate were determined on the basis of the polarographic wave equation of totally irreversible reduction of complex specie.     

Investigation of a mercury(II) carbene complex: bis(1,3-dimethylimidazol-2-ylidene) mercury chloride

The reaction of 1,3-dimethylimidazolium chloride with Hg(O₂CCH₃)₂ afforded a bis(carbene)mercury(II) complex (2), which is characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁵N, and ¹⁹⁹Hg) and by single-crystal X-ray analysis. As a consequence of chloride-ion interaction with the mercury center, the C₂-Hg-C₂ angle in 2 is reduced to 161.4 (3)° compared to its near-linear value in complex 4 that contains perchlorate counterions. The C₂ resonance in the mercury complex 2 moves upfield by 36.96 ppm relative to the parent carbene (2), with a large ¹J_HgC = 2741.18 Hz. © 1996 John Wiley & Sons, Inc.     

Sulfite-sensitive solvent/polymeric-membrane electrode based on bis(diethyldithiocarbamato)mercury(II)

A new solvent/polymeric-membrane electrode which exhibits significant potentiometric response toward sulfite ion in the 1 × 10_?6?1 × 10^?3 M range is described. The membrane is prepared by incorporation of neutral bis(diethyldithiocarbamato)mercury (II) in a thin film of plasticized poly (vinyl chloride). In sharp contrast to classical Hofmeister behavior, the resulting membrane displays little or no response to a wide range of anions (log K^pot_i,j ? ?4, i being sulfite) including sulfate, nitrate, nitrite, chloride, perchlorate, salicylate, and alkylsulfonates. Bromide and thiocyanate are moderate interferents, while significant response to iodide, thiosulfate, and sulfide is observed. These selectivity data, along with other response characteristics of the membrane, are used to postulate the mechanism by which the electrode responds to sulfite. Preliminary studies demonstrate that the electrode can be used in conjunction with an outer gas-permeable membrane for highly selective detection of total sulfite species in the form of sulfur dioxide.     

Neutron activation analysis of biological materials for sub ppm amount of mercury without determining the chemical yield

A simple method for the determination of sub ppm amounts of mercury in various biological materials by neutron activation analysis is described. Irradiated samples were decomposed with H₂SO₄-fuming HNO₃ mixture and mercury selectively isolated by ion exchange chromatography using Dowex 50WX2 [H⁺] and Dowex 1X4 [Br⁻] columns in HBr medium. Finally the activity of¹⁹⁷Hg fixed on an anion exchange resin was measured either with a Ge(Li) or a NaI (Tl) detector. Both the high radiochemical purity of mercury and the practically quantitative recovery were achieved thus eliminating the necessity of determining the chemical yield. The method was used for the determination of mercury in flour, milk, butter, margarine, fish, etc.     

Spectroscopic,thermal and structural studies of a new mercury(II) one-dimensional coordination polymer, [Hg(3-bpo)2(SCN)2], 3-bpo = 2,5- bis (3-pyridyl)-1,3,4-oxadiazole

A new mercury(II)-organic polymeric complex generated from 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo) as an angular dipyridyl derivative ligand, [Hg(3-bpo)₂(SCN)₂], was prepared from reactions of ligand 3-bpo with mercury(II) thiocyanate. The compound was characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR-spectroscopy and structurally determined by X-ray single crystal diffraction. The thermal stability of [Hg(3-bpo)₂(SCN)₂] was studied by thermal gravimetric (TG) and differential thermal analyses (DTA).     

Oxoacidity reactions in molten LiCl+KCl eutectic (at 470°C): Potentiometric study of the equilibria of exchange of O2− between Al(III) systems and carbonate and water systems

The reactions between aluminium chloride and oxide anion were studied in molten LiCl+KCl eutectic at 470°C. For that purpose, a pO^2? indicator electrode made with a membrane in yttria-stabilized zirconia has been used and tested by means of a carbonate ion whose dissociation constant, 10^?2.15 atm, was determined. Then, the electrode has allowed us to obtain the formation constant of AlO⁺ (solvated by Cl^?) and the solubility product of Al₂O₃ (S): 10^10.7 and 10^?27.4, respectively (molality scale). The equilibrium constant of the following system: 2HCl (g)+O^2? agH₂O (g)+2Cl^? has also been determined: 10^?9.93 atm mol kg^?1. The conditional solubility of alumina in LiCl+KCl melt is discussed.     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations.     

Thermochemical study of the complex formation of mercury(II) with nitrilotriacetic acid in an aqueous solution

The formation constant of the Hg(Nta) ₂ ^4? complex, where Nta^3? is the nitrilotriacetate ion, is determined by pH-metric titration at 298.15 K and ionic strength I = 0.5 (KNO₃) (logβ = 21.49 ± 0.10). The thermal effects for the formation of the Hg(NTa) _i2?3i complexes (i = 1, 2) are determined by a direct calorimetric method (?56.69 ± 1.04 and ?85.88 ± 1.32 kJ/mol for i = 1 and 2, respectively).     

Homoligand and mixed-ligand complexes of mercury(II) with aspartic acid and iminodiacetic acid and its derivatives

The formation of homoligand mercury(II) complexes with aspartic acid (H₂Asp) and aspartate-chelant mixed-ligand mercury(II) complexes with iminodiacetic acid (H₂Ida, IDA), 2-hydroxyethyliminodiacetic acid (H₂Heida, HEIDA), and nitrilotriacetic acid (H₃Nta, NTA) in an aqueous perchlorate medium was studied by spectrophotometry and pH-potentiometric titration. The following complexes were identified: [Hg(OH)Asp]^?, [HgAsp₂]^2?, [Hg(Asp)Ida]^2?, [Hg(Asp)Heida]^2?, and [Hg(Asp)Nta]^3?. The logarithms of their stability constants are, respectively, 11.74 ± 0.12, 20.18 ± 0.17, 20.11 ± 0.10, 19.82 ± 0.09, 19.48 ± 0.11, and 20.58 ± 0.07 (μ = 0.1 (NaClO₄), t = (20 ± 2)°C). The hydrogen and hydroxyl competition regions were located in the systems, and relationships between the molar yields of complex species and the reactant concentrations were established. The protonation and dissociation constants of aspartic acid were derived from pH-potentiometric titrations. Experimental data were analyzed using mathematical models allowing one to judge the existence of various complex species in the solution and to identify the species that are sufficient to reproduce the observed data.     

Syntheses and spectroscopic studies on zinc(II) and mercury(II) complexes of isatin-3-thiosemicarbazone

Zinc(II) and mercury(II) complexes were prepared by reacting isatin-3-thiosemicarbazone (ISTSCH) with zinc(II) acetate or mercury(II) bromide. The complexes were characterized by IR, Raman, diffuse reflectance, ¹H and ¹³C NMR spectra and elemental analysis. Tetrahedral structures for Zn(ISTSC)₂ and Hg(ISTSCH)Br₂ are suggested.     

Selective detection of mercury(II) and methylmercury(II) via coordination-induced emission of a small-molecule probe

Mercury is one of the major toxic pollutants and has many adverse effects on human health. The main mercury species in the environment or in living organisms are inorganic mercuric ion (Hg²⁺) and organic methylmercury (CH3Hg+). Detection of the two mercury ions is a particularly active topic in the molecular sensing field during the past decade. However, efficient sensors that can sensitively detect and discriminate the two species are rare. In this work, we adopt the concept of restriction of intramolecular rotations which is the basis of aggregation induced emission, and design a molecular probe with pyridyl group as the chelating unit and 1,8-naphthalimide as the fluorescent unit for the detection of both Hg²⁺ and CH₃Hg⁺. When the probe is free in solution, it exhibits weak fluorescence because free intramolecular rotations of the 1,8-naphthalimide moieties non-radiatively annihilate its excited state. However, upon coordination with Hg²⁺ or CH₃Hg⁺, the rotation of 1,8-naphthalimide moieties would be restricted due to the chelation between 1,8-naphthalimide and Hg²⁺ or CH₃Hg⁺, leading to significantly enhanced fluorescent emission. The response induced by Hg²⁺ is much stronger than CH₃Hg⁺; but for specific detection of CH₃Hg⁺, we introduced a T-rich DNA fragment which could completely mask Hg²⁺ in solution. Furthermore, we have employed the sensor for confocal imaging of Hg²⁺ and CH₃Hg⁺in immobilized cells. We expect the probe design tactics can be generally useful for sensing many other analytes.     

Mercury-cycling in surface waters and in the atmosphere — Species analysis for the investigation of transformation and transport properties of mercury

The river Elbe has been one of the most contaminated rivers with regard to mercury for many years. In 1991 a length-profile has been measured for mercury and methylmercury (CH₃Hg⁺) from Obristvi, Czech Republic, to the German bight. Total mercury has been measured by cold vapor atomic absorption spectrometry (CVAAS). The organo mercury compounds have been separated by high performance liquid chromatography (HPLC) connected on-line to an atomic fluorescence spectrometer (AFS) by a continuous flow-system. Total mercury up to 120 mg Hg⁺/kg and CH₃Hg⁺ concentrations up to 130 μg CH₃ Hg⁺/kg could be detected in special sites. The formation of CH₃Hg⁺ in sediments can be caused besides the methylation of mercury, by sulphate reducing or methanogenic bacteria and transmethylation reactions with organometals. Atmospheric mercury concentrations have been measured at three different European sites. Samples have been collected on goldcoated glass balls or on quartz wool, respectively. After thermal desorption mercury has been determined using the two step amalgamation technique with AFS detection. Compared to natural background concentrations of total gaseous mercury (TGM), slightly increased levels could be detected at a rural site in Germany. This increase can probably be explained by long-range transport processes. Within the vicinity of a inactivated mercury production plant high concentrations of up to 13.5 ng/m³ particle associated mercury (Hg_part) have been detected. Consequently, dry deposition of mercury in the particulate form can intensify the total deposition flux close to Hg-emitting sources.     

Spectrophotometric determination of sulfite with soluble mercury(II) compounds

Sulfite ion reacts with mercury(II) ion in acid solution to form the mercury(I) ion. The reaction is rapid and quantitative. The mercury(I) ion absorbs at 237 nm with a molar

5. Beer's law Data for Sulfite Complexes of Covalent Mercury(II) Compounds

SO2 (ppm)	?HgCl2a	?HgBr2	?Hg(Ac)2b	?Hg(SCN)2
2.0	12,500	10,000	10,000	9,200
4.0	12,500	11,500	10,000	9,000
6.0	12,500	11,500	10,000	9,200
8.0	12,000	11,000	10,500	9,800

a

Molar absorptivity based on sulfite ion at 230 nm. Solution was 6.86 buffer.

b

Mercuric acetate solutions seemed to be somewhat unstable. absorptivity of about 25,000. The absorbance is linear over a range of approximately 0.5–5.0 ppm as SO₂. Covalent mercury(II) compounds form a complex with sulfite, Hg(SO₃)₂^2?, which absorbs at 230 nm and shows a linear response over a range of 1–8 ppm as SO₂.

     

Crystal structure of naturally occurring mercury(II) amidonitrate

A naturally-occurring mercuroammonium compound from Pitkin County, Colorado, is shown to be the natural analog of synthetic HgNH₂NO₃. The crystals are isometric, P4₁32 or P4₃32, with a = 10.254(1)Å and twelve formula weights per cell. Using 437 symmetry-independent reflections, the crystal structure was partially determined and refined to a residual of 0.090. The positions of the Hg atoms and the N and O atoms of the nitrate group were determined, but the amide ion could not be located, probably due to positional disorder. The structure contains mercury atoms arranged in equilateral triangles 3.421(1) Å on a side. These triangles are linked through shared vertices into helical chains wound around the fourfold screw axes. Similar triangular units occur in other inorganic Hg(II) compounds. The distortion of the nitrate ion from trigonal planar symmetry is also discussed.     

Crystal chemistry of mercury(I) and mercury(I, II) minerals

The crystal structures of 16 mercury(I)- and mercury(I, II)-containing minerals having (Hg-Hg)²⁺ groups are considered. The Hg-Hg and Hg-X bond lengths and the HgHgX angles (X = Cl, Br, I, O, S) are analyzed. A comparative crystal chemical analysis of the environment of Hg atoms is carried out. The Hg-Hg and Hg-X distances vary within 2.43-2.60 and 1.93-2.43 å, respectively; the angles defining the deviation of the X-Hg-Hg-X groups from linearity are from 146 to 177?. In most cases, the coordination environment of the mercury atoms involves the metal atom of the (Hg-Hg)²⁺ dumbbell and the X atom, but in several compounds the coordination number of the mercury atoms increases due to the additional atoms lying 2.5–3.5 å away. In terlinguaite and kuznetsovite, the Hg₃ triangle is rather unusual; in the latter mineral, the Hg-Hg bonds are lengthened to 2.64-2.70 å. The review covers structural data up to May 1997.