Synthesis of new tripodal receptors—a ‘PET’ based ‘off-on’ recognition of Ag

A new set of tripodal receptors based upon an aromatic platform have been synthesized in high yields. The compounds have been characterized by spectroscopic techniques and by single crystal X-ray crystallography. These receptors are found to have good extraction ability and high transport rate for Ag(I). The receptor with imine linkages exhibits weak fluorescence emission bands at λ_max=413 and 540 nm, upon excitation at λ_max=365 nm. The fluorescence spectrum of the receptor shows enhancement in the intensity of the signal at 413 nm on binding with the Ag⁺ cation. No such significant changes are observed with other metal ions. An absorption at ∼365 nm is typical of an intraligand (π-π^∗) transition involving the imine chromophore, which produces a weak emission band at 413 nm due to quenching caused by PET from a neighboring -OH group. Participation of OH group in coordination to the metal ion reduces PET and an enhancement of fluorescence intensity is observed, signaling recognition of the metal ion.     

Cyclic and acyclic S2O2 donor-type ionophores. Ion-pair extraction and transport of Ag(I) picrate, and X-ray confirmation of existence of the ion-pair complex

Extraction and transport behaviors of isomeric oxathia macrocycles (L₂, ortho-; L₃, meta- and L₄, para-isomer) and their structure related open-chain compound (L₁) towards Ag(I) picrate have been examined. From the plot of log (D_Ag(I)/[pic⁻]) vs. log [L]₀ for all of the ionophores were linear with slope near unity, thereby confirming the 1:1:1 complex formations of Ag(I)/ligand/picrate ion to be extracted into the dichloromethane phase. The extractability of an acyclic ionophore was superior to those of the corresponding cyclic ones. In membrane transport experiments, the slow rate of release of Ag(I) from the membrane into the receiving phase seems to be responsible for lower transport efficiency. Upon addition of sodium thiosulfate as a stripping reagent in receiving phase, the efficiency of transport is significantly enhanced in the order of L₁ (acyclic)>L₂ (ortho-)>L₃ (meta-)>L₄ (para-) in accordance with those of log K_ex values. It is hypothesized that the ion-pair complexation of L₁ in extraction step would be more favorable in extraction and transport of Ag(I). Its structure have been confirmed by X-ray diffraction analysis of [Ag(L₁)pic], where L₁=1,10-bis(mercaptobenzylyl)-4,7-dioxadecane.     

Liquid — Liquid extraction of silver(I) by diphenyl-2-pyridylmethane in benzene from aqueous mineral acid — Thiocyanate solutions

Liquid — liquid extraction of Ag(I) by diphenyl-2-pyridylmethane (DPPM) in benzene from aqueous nitric and sulfuric acid solutions containing thiocyanate ions has been studied at ambient temperature (24±2 °C). The metal is extracted quantitatively from 0.01M HNO₃+0.02M KSCN; or 0.25M H₂SO₄+0.02M KSCN by 0.1M DPPM (optimum extraction conditions). Slope analysis indicates that two types of ion-pair complexes i.e. [(DPPMH)⁺·Ag(SCN) ₂ ^– ] and [(DPPMH) ₂ ⁺ ·Ag(SCN) ₃ ^2– ] are involved in the extraction process. Separation factors determined at optimum conditions reveal the separation of Ag(I) from Cs(I), Br(I), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Fe(III), Au(III) (from HNO₃ solution only), Cr(III), Hf(IV), Ta(V), Sn(IV) and Cr(VI). With the exception of thiosulfate, other complexing anions like ascorbate, acetate, citrate, oxalate do not hinder the extraction of Ag(I) under optimum conditions.     

Coupled transport of Ag(I) ions through triethanolamine–cyclohexanone-based supported liquid membranes

Facilitated transport of silver(I) ions in acidic medium, across a supported liquid membrane (SLM) by using triethanolamine (TEA) as carrier, dissolved in cyclohexanone, has been investigated. The parameters studied are HNO₃ concentration variation in the feed, pH of the feed solution, carrier concentration in the membrane phase, silver(I) ions concentration in the feed phase and KCN concentration in the stripping phase. Increase in H⁺ concentration by increasing HNO₃ concentration from 0.5 to 1 M results into an increase in silver ions flux but a decrease in flux has been found beyond 1 M HNO₃ concentration in the feed, providing a maximum flux of 3.21 × 10⁻⁷ mol/m² s at 1 M HNO₃. Increase in TEA concentration inside the membrane enhances flux with its maximum value at 2.25 M TEA. Further increase in the concentration of TEA leads to a decreased rate of transport due to the increase in viscosity of membrane liquid. The optimum conditions for Ag(I) ions transport are 1 M HNO₃ (feed), 2.25 M TEA (membrane) and 1.5 M KCN in the stripping phase. It has been observed that Ag(I) flux across the membrane tends to increase with increase in Ag(I) ions concentration in the feed phase. Applying the studied conditions to silver plating waste solutions, Ag ions have been removed up to 99% in a time interval of 5 h.     

N,N-bis-(2-benzimidazolylmethyl)L-methionine: An efficient Ag(I) extractant

A new ligand N,N-bis-(2-benzimidazolylmethyl)L-methionine has been synthesized and well characterized by different analytical techniques. The ligand has a very strong affinity for silver(I) and is used for the selective extraction of silver ions from aqueous solution into 1-butanol. The effect of concentration of Ag(I), pH, diverse ions, and temperature on the extraction is reported. The developed method has success-fully been applied to the determination of silver in different samples. Radiotracer technique, using ^110mAg(I) as a tracer, has been used for monitoring the concentration of silver ion.     

Extraction of Sr(II), Ag(I) and Pb(II) by some oxa-tia- and tia-crown ethers

Liquid-liquid extraction of several cations by some oxa-tia- and tia-crown ethers was studied. Sr(II), Pb(II) and Ag(I) were taken as hard, borderline and soft Lewis acids, respectively. Trace amounts of²¹⁰Sr and^110mAg were used as chemical yield monitors. The results were explained by the Pearson theory. Some of the examined compounds posses high affinity towards Ag(I) and Pb(II) extraction. The distribution coefficent for Ag(I) reached the value of 140.     

A study on the solvent extraction of Ag/I/ with 1,2,3-benzotriazole in chloroform

A rapid and selective method has been developed for the substoichiometric extraction of Ag/I/with 1,2,3-benzotriazole /1,2,3-BT/ in chloroform in the presence of versenate. The effect of various parameters such as pH, time of equilibration, solvent, anions, cations, etc., on the extraction coefficient value has been studied. The stoichiometry of the extracted species of 11 /Ag:1,2, 3-BT/ was obtained by the slope ratio method and substoichiometric extraction. Decontamination factors for most elements in the substoichiometric extraction of Ag/I/ were found to be higher than 10⁴.     

Radiochemical separation of110mAg,210Pb,127Te and131I from aqueous nitric acid solution by bis-2-(butoxyethyl ether)

A bis-2-(butoxyethyl ether) (DBC) solvent extraction method has been developed for the radiochemical separation of^110mAg,²¹⁰Pb,¹²⁷Te and¹³¹I in varying concentrations of aqueous HNO₃. Various factors were examined to determine the optimum conditions of extraction. The effect of various masking agents has been studied. The extraction of¹³¹I is enhanced to 99% at 2.4M HNO₃ in the presence of KSCN.¹³¹I was stripped into aqueous sodium hydroxide from the oxygenated organic extractant. The method was then applied for the recovery of¹³¹I from neutron irradiated tellurium metal. The mechanism and reactivity of DBC with metal ions is described.     

Investigations on equilibria between Ag(I) and tetraazacyclic amines in dimethylsulfoxide

Summary The formation constants of complexes of Ag(I) with 1,4,8,11-tetraazacyclotetradecane (TACT), 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMTACT), and 1,4,8,12-tetraaza-cyclopentadecane (TACP) as well as equilibrium constants of the disproportionation of Ag(TACT)⁺ and Ag(TACP)⁺ in dimethylsulfoxide have been determined by spectrophotometry and potentiometry. Ag(II) complexes of the same amines have also been characterized by spectrophotometry. The mechanism of the electrode processes of the complexes under investigations has been elucidated by voltammetric and coulometric methods; formal potentials of the redox systems have been determined.

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Untersuchungen der Gleichgewichte zwischen Ag(I) und tetraazacyclischen Aminen in Dimethylsulfoxid

Zusammenfassung Die Bildungskonstanten von Komplexen zwischen Ag(I) und 1,4,8,11-Tetraazacyclotetradecan (TACT), 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecan (TMTACT) und 1,4,8,12-Tetraazacyclopentadecan (TACP) sowie die Gleichgewichtskonstanten der Disproportionierungsreaktion von Ag(TACT)⁺ und Ag(TACP)⁺ wurden in Dimethylsulfoxid spektrophotometrisch und potentiometrisch ermittelt. Ag(II)-Komplexe derselben Amine wurden ebenfalls spektrophotometrisch charakterisiert. Der Mechanismus der Elektrodenprozesse der untersuchten Komplexe wurde mittels voltammetrischer und coulometrischer Methoden aufgeklärt; die formalen Potentiale der Redoxsysteme wurden bestimmt.

     

Synthesis,crystal structures and competitive complexation property of a family of calix-crown hybrid molecules and their application in extraction of potassium from bittern

A family of calix-crown hybrid molecules containing calix[4]arene and crown-5/6, either at lower rim or at both upper and lower rims, have been synthesised, characterised and their competitive complexation property towards alkali and alkaline earth metal ions in aqueous media have been investigated. The competitive metal ion extraction study, carried out with equimolar mixture of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺ in aqueous media, revealed that the amount of K⁺ extracted is remarkably high compared to other metal ions. Complexation with K⁺ has been investigated by ¹H NMR, association constants and thermodynamic parameters have been determined by isothermal calorimetric study. The molecular structures of one of the receptors and two of the K⁺ complexes have been established by single crystal X-ray study. One of the receptors formed bimetallic complex and it exhibited interesting polymeric network structure with bridged picrate anion. These receptors have been applied for extraction of metal ions from bittern.     

Solid phase extraction of trace amounts of silver (I) using dithizone-immobilized alumina-coated magnetite nanoparticles prior to determination by flame atomic absorption spectrometry

A new, simple, fast and reliable solid-phase extraction (SPE) method has been developed to separation/preconcentration of trace amounts of silver ion from environmental water samples using dithizone/sodium dodecyl sulfate immobilized on alumina-coated magnetite nanoparticles (DTZ/SDS-ACMNPs) and its determination by flame atomic absorption spectrometry. The coating of alumina on Fe₃O₄ NPs not only avoids the dissolving of Fe₃O₄ NPs in acidic solution, but also extends their application without sacrificing their unique magnetization characteristics. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of DTZ/SDS-ACMNPs with an adscititious magnet. Optimal experimental conditions including amount of DTZ/SDS, pH value, standing time, sample volume, type, volume and concentration of eluent and co-existing ions have been studied and established. Under the optimal experimental conditions, the detection limit for Ag(I) with enrichment factors of 100 was found to be 0.52?ng?mL^?1 and its relative standard deviations (RSD) was 3.4% (n?=?10, C?=?5.0?µg?mL^?1). The linear range of calibration curve for Ag(I) was 2–5000?ng?mL^?1 with a correlation coefficient of 0.9991. The proposed method was successfully applied to the determination of target analyte in different water and wastewater samples. The validity of the method has been checked by applying it to study the recovery of silver ion in spiked water and wastewater samples.     

Coordination modes of N-2-(4-amino-1-methyl-5-nitroso-6-oxo-1,6-dihydropyrimidinyl) potassium L-alaninate toward Ag(I), Cd(II) and Pd(II). Crystal structure of {Ag((η4-μ3-L)]·3H2O}n,first example of a silver 3D-polymer with a pyrimidine-derivative ligand

The acid-base behaviour of the N-2-(4-amino-1-methyl-5-nitroso-6-oxo-1,6-dihydropyrimidinyl) potassium L-alaninate (KL) and its reactivity with Ag(I), Cd(II) and Pd(II) metal ions have been studied. Three solid species with formulae AgL·3H₂O, CdL₂·6H₂O and PdClL·H₂O have been obtained and characterized by IR, ¹H and ¹³C NMR spectroscopic methods and thermal, conductivity and magnetic measurements. The structure of {Ag((η⁴-μ₃-L)]·3H₂O}_n has been established by single-crystal X-ray diffraction and consists in a 3D-polymer. Within the polymer each Ag(I) ion is tetrahedrally coordinated to three differents L anions, while each ligand is coordinated in a rather unusual η⁴-μ₃ coordination mode. Spectroscopic data show a similar coordination mode for the Cd(II) complex, while for the Pd(II) one a different coordination mode is proposed.     

The Oxidation of Aliphatic Hydrocarbons in the Presence of Higher Oxidation States of Silver

Abstract

The compound silver “peroxide”? has been known for some time and its preparation is described in the literature.¹ The structure of this compound has been in dispute; however it appears to have been resolved using neutron diffraction techniques. Scatturin, Bellon and Salkind² have shown that silver “peroxide” is a rather complex material in which silver is present in two different oxidation states, namely Ag(I) and Ag(III). In the crystal, Ag(III) atoms are coordinated to oxygen in a square planar array and the Ag(I) atoms are linearly coordinated. There are no peroxide oxygens. Hence the formula for silver “peroxide” is more properly written Ag(I)Ag(III)02.     

Ion-exchange studies of <Superscript>110m</Superscript>Ag(I) using synthetic inorganic ion-exchanger

In the present investigation, the selective adsorption of silver on synthetic inorganic ion exchanger, zinc(II) ferrocyanide, has been established by batch method, under specific conditions, using ^110mAg as a tracer. The efficiency of adsorption has been determined by γ-ray spectrometry and was found to be greater than 96%. The Ag(I) uptake by the exchanger has also been evaluated. The selectivity of the method was checked by studying the adsorption of Ag(I) in the presence of a number of foreign ions using their corresponding tracers. The interfering ions were removed by washing the ion-exchanger with appropriate reagents, so that it could be applied for the determination of trace amount of Ag(I) in complex matrices, containing trace amount of other metal ions.     

Synthesis of calix[4]arene-based dipodal receptors: Competitive solvent extraction and liquid bulk membrane transport for selective recovery of Cu2+

A series of new p-tert-butylcalix[4]arene-based dipodal receptors are synthesised in high yields. The calix[4]arene units of all the receptors have been found to be present in cone conformation. To optimise the good extraction ability and high transport rate, we synthesised the receptors that differ from each other in their end groups. These receptors extract Cu²⁺  ion selectively from the buffered aqueous medium containing a mixture of metal ions. The receptor bearing four sp³ nitrogens has by far the greater ability to extract Cu²⁺  than the other receptors. All these receptors were effectively used for Cu²⁺  ion transport from the aqueous buffered source phase to the aqueous receiving phase.

     

Development of a cloud point extraction and preconcentration method for silver prior to flame atomic absorption spectrometry

The possibility was investigated of using 2-mercaptobenzothiazole (MBT) for Ag(I) concentration by micellar extraction at cloud point (CP) temperature and subsequent determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Ag(I) with 2-mercaptobenzothiazole (MBT) in the presence of non-ionic micelles of Triton X-114. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction was studied. Under the optimum conditions, the preconcentration of 10 mL of water sample in the presence of 0.1% Triton X-114 and 2 × 10⁻⁴ mol L⁻¹ 2-mercaptobenzothiazole permitted the detection of 2.2 ng mL⁻¹ silver. The calibration graph was linear in the range of 10–200 ng mL⁻¹, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Ag(I) in water samples.     

Complexing ability of the substituted oxathiacrown ethers with vicinal arrangement of the sulfur atoms

Complexing ability of crown ethers opens new ways of designing selective extragents and sensitive receptors to various metal cations. The structure of the oxathiacrown ether complexes with Ag(I), Pb(II), Hg(II), Cd(II), Ni(II), Pd(II) ions was investigated using the methods of mass spectrometry and ¹H NMR spectroscopy. Formation of 1:1 and 2:1 ligand-metal complexes was established.     

Solvent extraction of metals with macrocyclic compounds. I

Summary The extractants studied in this work are 5,6; 14,15-dibenzo-l,4-dioxa-8,12-diazacyclopentadeca-7,12-diene (I) and 5,6; 14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane (II). Radioactive nuclides were used to investigate the extraction of Ag(I), Hg(II), Cu(II), Cd, Co(II), Zn, Fe(III), Mn(II), and Pd with chloroform solutions of I and II. It is shown that compound I extracts only silver. The composition of the extracted compound has been established: silver is extracted as an AgLX complexe (L being macrocycle I and X being the counterion). The counterions involved in the experiment were perchlorate, picrate (Pi), and dipicrylaminate (DPA); the extraction of silver is intensified in the series: ClO₄ ^–––. The solvents used include nitrobenzene, 1,2-dichloroethane, chloroform, ando-xylene, the best being nitrobenzene and dichloroethane. Macrocycle II was found to exhibit poorer selectivity; in addition to Ag(I), it also extracts Hg(II), Cu(II) and Pd. The lower selectivity of macrocycle II, as compared to that of I, must be due to the graeter comformational mobility of molecule II.

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Metallextraktion durch makrocykliscbe Verbindungen. I

Zusammenfassung 5,6; 14,15-Dibenzo-1,4-dioxa-8,12-diazacyklopentadeka-7,12-dien (i) und 5,6; 14,15-Dibenzo-1,4-dioxa-8,12-diazacyklopentadekan (II) wurden als Extraktionsmittel verwendet. Radioaktive Nuklide dienten zur Untersuchung der Extraktion von Ag(I), Hg(II), Cu(II), Cd, Co(II), Zn, Fe(III), Mn(II) und Pd durch Chloroformlösungen von I und II. Die Verbindung I extrahiert nur Silber. Die Zusammensetzung der extrahierten Verbindungen wurde ermittelt: Silber wird als AgLX (L=Makrocyklus I, X=Gegenion) extrahiert. Als Gegenionen wurden Perchlorat, Pikrat (Pi) und Dipikrylaminat (DPA) verwendet. Die Extraktion von Silber wächst in der Reihenfolge ClO₄     

The unique liquid chromatographic properties of Group 11 transition metals for the separation of unsaturated organic compounds

Silver(I) and copper(I) are known to form reversible complexes with π bonds, which have been exploited in LC for separating unsaturated organic compounds. Prominent examples include the use of AgNO₃‐impregnated silica gel in LC, and the use of copper(I) salts for selective extraction of alkenes from hydrocarbon mixtures. The Dewar–Chatt–Duncanson model is often invoked to explain the interaction between Ag(I) and Cu(I) and π bonds. However, it is unclear if such a reversible interaction is directly related to their d¹⁰ outer electronic configurations. Particularly, Au(I) has not been reported to separate olefins with different numbers of double bonds in LC. Also, there has not been a systematic comparison of the liquid chromatographic properties of other d¹⁰ transition metal salts (e.g., Zn(II), Cd(II)), making it difficult to fully understand the observed reversible interactions of Ag(I) and Cu(I) with π bonds. We demonstrate for the first time that silica gel impregnated with all three Group 11 transition metals with 1+ oxidation state strongly and similarly retain olefin compounds in LC, while transition metals from Groups 10 and 12 do not. We also tested a range of functionalized silica gels to improve the stability of Cu(I) and Au(I) ions on the surface of the silica.     

Stability of AgIII towards Halides in Organosilver(III) Complexes

The involvement of silver in two-electron Ag^I/Ag^III processes is currently emerging. However, the range of stability of the required and uncommon Ag^III species is virtually unknown. Here, the stability of Ag^III towards the whole set of halide ligands in the organosilver(III) complex frame [(CF₃)₃AgX]⁻ (X=F, Cl, Br, I, At) is theoretically analyzed. The results obtained depend on a single factor: the nature of X. Even the softest and least electronegative halides (I and At) are found to form reasonably stable Ag^III−X bonds. Our estimates were confirmed by experiment. The whole series of nonradiative halide complexes [PPh₄][(CF₃)₃AgX] (X=F, Cl, Br, I) has been experimentally prepared and all its constituents have been isolated in pure form. The pseudohalides [PPh₄][(CF₃)₃AgCN] and [PPh₄][(CF₃)₃Ag(N₃)] have also been isolated, the latter being the first silver(III) azido complex. Except for the iodo compound, all the crystal and molecular structures have been established by single-crystal X-ray diffraction methods. The decomposition paths of the [(CF₃)₃AgX]⁻ entities at the unimolecular level have been examined in the gas phase by multistage mass spectrometry (MSⁿ). The experimental detection of the two series of mixed complexes [CF₃AgX]⁻ and [FAgX]⁻ arising from the corresponding parent species [(CF₃)₃AgX]⁻ demonstrate that the Ag−X bond is particularly robust. Our experimental observations are rationalized with the aid of theoretical methods. Smooth variation with the electronegativity of X is also observed in the thermolyses of bulk samples. The thermal stability in the solid state gradually decreases from X=F (145 °C, dec.) to X=I (78 °C, dec.) The experimentally established compatibility of Ag^III with the heaviest halides is of particular relevance to silver-mediated or silver-catalyzed processes.