Iodide‐Selective Electrodes Based on Bis[N(2‐methyl‐phenyl) 4‐Nitro‐thiobenzamidato]mercury(II) and Bis[N‐phenyl 3,5‐Dinitro‐thiobenzamidato]mercury(II) Carriers

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on recently synthesized mercury complexes including Hg(Nmpntb)₂ and Hg(Npdntb)₂ as new carriers for iodide‐selective electrodes by incorporating the membrane ingredients on the surface of graphite electrodes are reported. The effect of various parameters including the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses toward iodide over a wide concentration range of 7×10^?7 to 0.1 M and 1×10^?6 to 0.1 M, with slopes of 59.6±0.8 and 58.9±0.9 mV per decade of iodide concentration and detection limit of 3×10^?7 M and 7×10^?7 for Hg(Npdntb)₂ and Hg(Nmpntb)₂, respectively, over a wide pH range of 3–11. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show good ability to discriminate iodide over several inorganic and organic anions. The electrodes were successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water and as indicator electrodes in precipitation titrations.     

Selective thiocyanate poly(vinyl chloride) membrane based on a 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) perchlorate

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) as a membrane carrier with unique selectivity toward thiocyanate is reported. The influence of membrane composition, pH and foreign anions were investigated. The sensor exhibits a Nernstian response for thiocyanate over a wide concentration range of 3.3×10⁻⁶ to 0.10 M, with a slope 58.4±0.3 mV per decade. The limit of detection is 3.0×10⁻⁶ M SCN⁻. The sensor has a response time of <20 s and can be used for at least 2 months without any considerable divergence in potential. The proposed electrode shows fairly a good discriminating ability towards SCN⁻ ion in comparison to other anions. It was successfully applied to direct determination of thiocyanate in urine and saliva and it was also used as an indicator electrode in titration of thiocyanate with Ag⁺ ions.     

A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone

A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg²⁺] versus EMF response over a wide concentration range of 1.778×10⁻⁶-1.0×10⁻¹ M with Nernstian slope of 29 mV per decade with the detection limit of 1.0×10⁻⁶ M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0-3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg²⁺ ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference (K^Pot_Hg,M values of the order of 10⁻³-10⁻⁴). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg²⁺ions with I⁻ and Cr₂O₇²⁻.     

Mercury(II) ion-selective polymeric membrane sensor based on a recently synthesized Schiff base

A new polyvinyl chloride (PVC) membrane electrode that is highly selective to Hg(II) ions was prepared by using bis[5-((4-nitrophenyl)azo salicylaldehyde)] (BNAS) as a suitable neutral carrier. The sensor exhibits a Nernstian response for mercury ions over a wide concentration range (5.0×10⁻²-7.0×10⁻⁷ M) with a slope of 30±1 mV per decade. It has a response time of <10 s and can be used for at least 3 months without any measurable divergence in potential. The electrode can be used in the pH range from 1.0 to 3.5. The proposed sensor shows fairly good discriminating ability towards Hg²⁺ ion in comparison with some hard and soft metals. The electrode was used in the direct determination of Hg²⁺ in aqueous solution and as an indicator electrode in potentiometric titration of mercury ions.     

3-(Aryl)-2-sulfanylpropenoates of mercury(II) and phenylmercury(II)

Compounds [HQ]₂[Hg(L)₂] and [HQ][PhHg(L)] [where HQ = diisopropylammonium cation; L = pspa, fspa, tspa, where p = 3-(phenyl), f = 3-(2-furyl), t = 3-(2-thienyl), and spa = 2-sulfanylpropenoato] have been prepared by the reaction of mercury(II) acetate or phenylmercury(II) acetate with the corresponding acid in the presence of diisopropylamine in ethanol. The compounds have been characterized by elemental analysis, FAB mass spectrometry and IR and NMR (¹H, ¹³C) spectroscopy. The crystal structures of the [HQ]₂[Hg(L)₂] compounds show the presence of diisopropylammonium cations and [Hg(L)₂]²⁻ anions. In each anion the Hg atom is in an HgO₂S₂ environment and this can be described as nido-tbp. The crystal structures of the [HQ][PhHg(L)] compounds show the presence of diisopropylammonium cations and [PhHg(L)]⁻ anions in which the Hg atom adopts an HgCOS distorted T-environment. The NMR data suggest that the coordination mode of the ligand L²⁻ determined by X-ray diffractometry in the solid remains in solution.     

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO₃)₄], has a Nernstian potentiometric response from 2.0×10^–8 to 2.0×10^–2 mol L^–1 with a detection limit of 8.0×10^–9 mol L^–1 and a slope of –59.0±0.5 mV/decade in 0.01 mol L^–1 phosphate buffer solution (pH 3.0, 20°C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV–Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.     

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.     

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).     

The synthesis of bis(benzo-crown ether)s and their incorporation into potassium-selective PVC membrane electrodes

Five bis(benzo-15-crown-5) derivatives connected with different bridge chains were synthesized as neutral carriers in K⁺-selective electrodes. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as plasticizers of the PVC membrane. The selectivity coefficients (K _M ⁿ⁺:K _K+) for various alkali and alkaline-earth metal ions were measured. The electrodes based on the bis(crown ether)s are more selective for K⁺ than those based on monomeric crown ethers. The selectivity of one of the prepared potassium selective electrodes was higher than that of the electrode based on valinomycin and three of them were stable over a wide pH range.     

Preparation and Spectral Investigation of Bis[N(2-methyl-phenyl) 4-Nitro-thiobenzamidato] mercury(II), Bis[N(2-methoxy-phenyl) 4-Nitro-thiobenzamidato]mercury(II), and Bis[N(2-chloro-phenyl) 4-Nitro-thiobenzamidato]mercury(II) Complexes

Several preparative routes to bis[N(substituted-phenyl) 4-nitro-thiobenzamidato] mercury(II) complexes are presented, including the reaction of mercury(II) oxide, fluoride, chloride, bromide, cyanide, acetate, and nitrate with N(substituted-phenyl) 4-nitro-thiobenzamide derivatives. ¹ H-NMR, Raman, and IR measurements confirmed the complexation of mercury to sulphur.     

PVC-based bis(2-nitrophenyl)disulfide sensor for zinc ions

A PVC membrane electrode based on bis(2-nitrophenyl)disulfide carrier exhibits a very good response for Zn²⁺ in a wide concentration range (from 2.9×10⁻⁷ to 3.2×10⁻² mol l⁻¹) with a slope of 29.9±0.4 mV per decade of Zn²⁺ concentration. The response time of the sensor is about 10 s and the membrane can be used for more than 3 months without any observed divergence in potentials. The proposed sensor exhibits very good selectivity for Zn²⁺ over many cations and can be used in a wide pH range (2-9). This assembly served also as an indicator electrode in potentiometric titrations involving zinc ions and direct potentiometric determination of zinc ions in real and synthetic samples.     

Zinc(II) and Cadmium(II) Metal Complexes with Bis(tetrazole) Ligands: Synthesis and Crystal Structures

Two new metal complexes [Zn( L¹ )]_n ( 1 ) and [Cd₃( L² )₂Cl₂(H2O)6]_n ( 2 ) (H₂ L¹ = 1,5‐bis(tetrazol‐5‐yl)‐3‐oxapentane, H₂ L² = bis(tetrazol‐5‐yl)methane) have been synthesized and characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction analysis. Complex 1 was a 2‐D sheet constructed by L¹ and Zn(II) center, further assembled to form a three‐dimensional (3‐D) supramolecular networks through weak hydrogen‐bonding interactions. In the complex 2 , there were two unequivalent Cd(II) centers, and some of ligands L² adopted chelate coordination mode, and others adopted bridge coordination mode linking the Cd1 center and simultaneously bridging the Cd2 center, the Cl^‐ anions adopted μ₂ bridging mode, ligands L² and the Cl^‐ anions linked the Cd(II) centers to form a 3‐D supramolecular networks.     

Investigation of 3-amino-1,2,4-triazole azodye derivatives as reagents for determination of mercury(II)

The reaction of mercury(II) with 3-(2,4-dihydroxyphen-1-ylazo)-1,2,4-triazole (HL¹), 3-(2-hydroxy-5-methylphen-1-ylazo)-1,2,4-triazole (HL²), 3-(2-hydroxy-5-ethoxycarbonylphen-1-ylazo)-1,2,4-triazole (HL³), 3-(2-hydroxy-5-acetylphen-1-ylazo)-1,2,4-triazole (HL⁴), 3-(2-hydroxy-5-formylphen-1-ylazo)-1,2,4-triazole (HL⁵), and 3-(2-hydroxy-5-bromophen-1-ylazo)-1,2,4-triazole (HL⁶) was studied. A new, direct, and simple procedure was suggested for the spectrophotometric determination of mercury(II) based on its complexation reaction with HL¹-HL⁶. The best reagent was found to be HL³ due to its high sensitivity and selectivity. In aqueous media of pH 9.0 containing 40 vol. % of methanol, Hg(II) reacts with HL³ to form a 1:2 (Hg(II) · HL³) complex having a sensitive absorption peak at 490 nm with the molar extinction coefficient of 3.31 × 10⁴ L mol⁻¹ cm⁻¹ using 4 × 10⁻⁴ M of the reagent. Beer’s law is obeyed over the range from 0.00 μg mL⁻¹ to 12.04 μg mL⁻¹ of mercury(II). The proposed method was applied in the determination of mercury(II) in tap water, seawater and synthetic seawater samples, without the need of prior treatment, with satisfactory results.     

Thermodynamics,a suitable reporter in the design of mercury (II) ion selective electrodes

A fully functionalised calix[4]pyrrole derivative, namely, meso-tetramethyl-tetrakis[(diethylthiocarbamoyl)phenoxy] calix[4]-pyrrole, 1 has been synthesised and structurally characterised. Its complexing properties with metal cations in acetonitrile were investigated with particular emphasis on the thermodynamics of these systems. These data and those previously reported for a partially functionalised calix[4]arene based receptor, 5,11,17,23-tetra-tert-butyl[25,27 bis(diethylthiocarbamoyl)oxy]calix[4]arene, 2 were used to, i) further corroborate their use to predict the selectivity coefficients of carrier mediated mercury (II) ion selective electrodes (ISEs) and ii) to obtain approximate stability constant data from selectivity coefficients. The optimum working conditions of both electrodes were determined. It is shown that while the ISE based on 1 is characterised by a wider linear range and a lower mercury (II) detection than the one based on 2, the latter has the advantage of lower interference of other metal cations due to the much lower stability constants of bivalent cations relative to Hg(II). The response characteristics of these electrodes are compared with those found in the literature. SEM micrographs along with EDX spectra of the PVC membranes containing ionophore 1 or 2 unloaded and loaded with Hg(II) are reported.     

Thiocyanate-selective electrode based on N-salicylidene-benzylamineato copper(II) complex

Highly selective poly(vinyl chloride) (PVC) membrane electrode based on N-salicylidene-benzylamineato copper(II) complexes [Cu(SBA)₂] as new carriers towards thiocyanate-selective electrode was reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The resulting electrode exhibits anti-Hofmeister selectivity sequence: SCN⁻ > ClO₄⁻ > Sal⁻ > I⁻ > Br⁻ > NO₃⁻ > NO₂⁻ > SO₃²⁻ > H₂PO₄⁻ > Cl⁻ > SO₄²⁻, and a near-Nernstian potential linear range for thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ M with a detection limit of 7.0 10⁻⁷ M and a slope of , over a wide pH range of 3.0–9.0 in phosphate buffer solution at 20°C. The proposed electrode has a fast response time of about 5–10 s and can be used for at least 3 months without any considerable divergence in potential. The electrode was successfully applied to the determination of thiocyanate in waste water and human urine and saliva samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 3, pp. 293–299. The text was submitted by the authors in English.     

SYNTHESIS OF NOVEL BIDENTATE (Te,N) LIGANDS-2-ARYLTELLUROETHYLAMINES AND THEIR COMPLEXATION WITH MERCURY (II)

Abstract

Sodium aryltellurolate (ArTe^?Na⁺, where Ar = 4-MeOC₆H₄ or 4-EtOC₆H₄) reacts with 2- bromoethylamine resulting in the (Te, N) ligands 2-aryltelluroethylamine (ArTeCH₂CH₂NH₂, 1) which have been characterized by elemental analyses, molecular weight, IR, ¹H and ¹³C NMR spectra. With HgCI₂, they form HgC1₂·1 type of complexes. IR, ¹H and ¹³C NMR spectra of the complexes suggest that 1 ligates as a bidentate ligand with respect to Hg(II). Osmometric molecular weight measurements suggest that on heating the mercury complex HgCl₂·lb (Ar = 4-EtOC₆H₄) in solution, relatively less soluble species result. It seems to have two Hg atoms bridged by two (Te, N) ligands. The HgC₂·la (Ar = 4-MeOC₆H₄) has very low solubility in organic solvents and. therefore, seems to be dimerized or polymerized during the synthesis. Analysis of CH₂ rocking bands in IR spectra suggests that two CH₂ groups of the ligands are most probably in a gauche conformation in the mercury complexes.     

Neutral carriers based polymeric membrane electrodes for selective determination of mercury (II)

The potentiometric response characteristics of mercury ion-selective membrane electrodes based on 2-amino-6-purinethiol (I₁) and 5-amino-1, 3, 4-thiadiazole-2-thiol (I₂) were described. Ion selectivities were tested for various plasticizers, which were used as solvent mediators to incorporate the ionophores into the membrane. Effects of experimental parameters such as membrane composition, nature and amount of plasticizers and additives, pH and concentration of internal solution on the potential response of Hg²⁺ electrodes were investigated. The best performance was obtained with the electrode having a membrane composition (w/w) of (I₁) (3.17%): PVC (31.7%): DOP (dioctylpthalate) (63.4%): NaTPB (sodium tetraphenylborate) (1.58%). The proposed electrode reveals a Nernstian response over Hg²⁺ ion in the concentration range of 7.0 × 10⁻⁸-1.0 × 10⁻¹ M with limit of detection 4.4 × 10⁻⁸ M. The electrode shows good discrimination toward Hg²⁺ ion with respect to most common cations. It shows a short response time (10 s) for whole concentration range and can be used for 2 months without any considerable divergence in potentials. For evaluation of the analytical applicability, the electrode was used in the determination of Hg²⁺ ion in different environmental and biological samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

Summary The solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm^–3 (NaClO₄). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (_max=325nm, =0.8·10⁴lmol^–1cm^–1). The system obeyed Beer's law up to 36.1 µg ml^–1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml^–1. Interference caused by a number of ions was masked by the addition of fluoride ions.

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Lösungsgleichgewichte und Stabilitätskonstanten von Komplexen der Pyridincarbonsäuren: Die Komplexierungsreaktion von Quecksilber(II) mit 2-Hydroxynikotinsäure

Zusammenfassung Die Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm^–3 (NaClO₄) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (_max=325nm, =0.8·10⁴lmol^–1cm^–1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml^–1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml^–1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

     

Two new zinc(II) and mercury(II) complexes based on N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide): synthesis,crystal structures and antibacterial activities

Reaction of N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide), C₂₀H₁₈F₂N₄O₂, ( L^F ), with zinc chloride and mercury(II) chloride produced different types and shapes of neutral coordination complexes, namely, dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ²N,O]zinc(II), [ZnCl₂(C₂₀H₁₈F₂N₄O₂)], ( 1 ), and dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ⁴O,N,N′,O′]mercury(II), [HgCl₂(C₂₀H₁₈F₂N₄O₂)], ( 2 ). The organic ligand and its metal complexes are characterized using various techniques: IR, UV–Vis and nuclear magnetic resonance (NMR) spectroscopies, in addition to powder X‐ray diffraction (PXRD), single‐crystal X‐ray crystallography and microelemental analysis. Depending upon the data from these analyses and measurements, a typical tetrahedral geometry was confirmed for zinc complex ( 1 ), in which the Zn^II atom is located outside the bis(benzhydrazone) core. The Hg^II atom in ( 2 ) is found within the core and has a common octahedral structure. The in vitro antibacterial activities of the prepared compounds were evaluated against two different bacterial strains, i.e. gram positive Bacillus subtilis and gram negative Pseudomonas aeruginosa bacteria. The prepared compounds exhibited differentiated growth‐inhibitory activities against these two bacterial strains based on the difference in their lipophilic nature and structural features.