Potentiometric,spectrophotometric, and AM1d studies of the equilibria between silver(I) ion and monoaza-crown ethers with anthraquinone in various solvents

Complex formation and stability constants between silver(I) and monoaza-12-crown, monoaza-15-crown, and monoaza-18-crown ethers with anthraquinone were determined in acetonitrile, methanol, and propylene carbonate by potentiometric and UV-spectrophotometric methods. Complexes of 1?:?1 and 1?:?2 metal-to-ligand stoichiometry were formed. The solvent composition and the size of the macrocyclic ring affect the stability constants of the complexes. The energetically most favorable structures of the 1?:?1 metal-to-ligand complexes were calculated and visualized by the AM1d method at a semiempirical level of theory.     

Complexation of silver(I) with different substituted diaza-18-crown-6 ethers in methanol

A large number of derivatives of the diaza-18-crown-6 ligand have been synthesized and characterized. These derivatives have different alkyl or aryl side arms at the nitrogen donor atoms of the macrocyclic diazacrown ether. In some side chains additional donor atoms are available. These diazacrown ethers are used as ligands for the complexation of Ag^I in MeOH. The complexation reactions have been studied using potentiometric and calorimetric methods. The thermodynamic data show the absence of a lariat effect. The increase of the values of the reaction enthalpies are due only to changes in solvation of the different ligands.     

1D Chain and 3D framework of silver(I) organo-metallic polymers self-assembled with triptycene

For the purpose of investigating the coordination behavior of sterically congested alkenes and exploring the possibility of non-planar complexation in the polycyclic aromatic system for formation of extended polymeric networks, triptycene (tpty) has been studied with regard to its complexation with the silver(I) ion. The crystal structures of [Ag(tpty)(THF)₂](ClO₄) (1) and [Ag₆(tpty)₄(CF₃SO₃)₂(H₂O)₆](CF₃SO₃)₄ (2) have been determined by single-crystal X-ray diffraction. The polycyclic aromatic hydrocarbon triptycene is found to offer a potential site for complexation, which can be utilized to generate an interesting array of organo-metallic polymers with one-dimensional (1D) chain and three-dimensional (3D) porous frameworks.     

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.     

1D coordination polymers of silver(I) and copper(II) based on bis(N-heterocyclic carbene) ligands: Synthesis and structural studies

The alkyl chain-linked diimidazolium (or dibenzimidazolium) salts, 1,1′-diethyl-4,4′-tetramethylene-diimidazolium-diiodide (L¹H₂·I₂) and 1,1′-diethyl-3,3′-trimethylene-dibenzimidazolium-diiodide (L²H₂·I₂), and their silver(I) and copper(II) coordination polymers, [L¹AgI]_n (1) and [L²Cu₂I₄]_n (2), have been prepared and characterized. Complex 1 is a 1D helical polymer generated by bidentated carbene ligands (L¹) and Ag(I) atoms. The 1D polymer of 2 is formed by bidentated carbene ligands (L²) and coplanar quadrilateral Cu₂I₂ units. 3D supramolecular frameworks in the crystal packings of 1 and 2 are formed via intermolecular weak interactions, including C–H···π contacts, π–π interactions and C–H···I hydrogen bonds.     

Syntheses, structures and properties of silver(I) complexes with flexible 1,3,5-tris(pyridylmethoxyl)benzene ligands

Five new silver(I) complexes [Ag₂(L₂)₂](BF₄)₂·CH₃CN·CH₃OH (1), [Ag(L₂)(CF₃SO₃)] (2), [Ag(L₃)]ClO₄·CH₃OH (3), [Ag₂(L₃)₂](CF₃SO₃)₂·CH₃CN·CH₃OH·H₂O (4) and [Ag(L₃)]PF₆·2CH₃CN (5) [L₂=1,3,5-tris(2-pyridylmethoxyl)benzene, L₃=1,3,5-tris(3-pyridylmethoxyl)benzene] were synthesized and characterized by single crystal X-ray diffraction analyses. In complexes 1-5, ligands L₂ and L₃ show different conformations and act as three-connectors, while the Ag(I) atom serves as three-connecting node to result in the formation of 2D and 3D frameworks. Complexes 1 and 2 with different counteranions have similar 2D network structure with the same (4,8²) topology. Complex 3 has a 3D structure with (10,3)-a topology while complexes 4 and 5 have the same 2D (6,3) topological structure. The results showed that the structure of organic ligands and counteranions play subtle but important role in determining the structure of the complexes. In addition, the photoluminescence and anion-exchange properties of the complexes were investigated in the solid state at room temperature.     

Synthesis, structure and fluorescence of novel cadmium(II) and silver(I) complexes with in situ ligand formation of 1-(5-tetrazolyl)-4-(imidazol-1-ylmethyl)benzene

Hydrothermal reactions of cadmium(II) or silver(I) salt, NaN₃, 4-(imidazol-1-ylmethyl)benzonitrile (IBN) yield three coordination complexes, [Cd(L)₂(H₂O)₂]·3H₂O (1), [Cd₃(L)₅(OH)] (2) and [Ag₂(L)₂] (3) where HL=1-(5-tetrazolyl)-4-(imidazol-1-ylmethyl)benzene. The crystal structure analysis revealed that 1 has 1D hinged-chain structure containing 24-membered ring with a Cd···Cd intra-chain distance of 13.18 Å, while 2 is 1D ladder-like chain with Cd₃O core. However, the complex 3 is a 3D 4-connected framework with Schläfli symbol of (4²·6³·8)(4³·6²·8). The L⁻ ligand was found to show four different coordination modes in 1-3, as 2-, 3- and 4-connector, respectively. The results indicate that the coordination modes of the ligand and metal centers with different coordination geometry have great influence on the structures of the complexes. In addition, the photoluminescence of the complexes were studied in the solid state at room temperature.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

Two new silver(I) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz): Preparation,characterization, crystal structure and alcohol oxidation activity in the presence of oxone

Two new silver(I) complexes ((tptz)Ag₂(NO₃)₂ and [Ag₅(tptz)₄](NO₃)₅) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, ¹H NMR, IR, fluorescence, UV–Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in organic solvent, using oxone (2KHSO₅·KHSO₄·K₂SO₄) as an oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Ion-solvent interactions of silver(I)-18-crown-6 perchlorate complex in methanol-acetonitrile mixtures

The standard Gibbs transfer energies of the silver(I)-18-crown-6 perchlorate complex salt from methanol to various compositions of methanol-acetonitrile mixtures were determined from solubility measurements at 30°C and these data were separated into the corresponding ionic contributions by employing the negligible liquid junction potential method of Parkeret al. The solvent transport numbers _AN, for the salt were also determined at various solvent compositions using a concentration cell with transference.The Gibbs transfer energy of the silver(I)-18-crown-6 complex cation is negative and decreases with the addition of acetonitrile but the transfer energy of the anion is positive and increases under the same conditions. The solvent transport number, _AN, increases and passes through a maximum value of 5.48 at _AN=0.55. These results indicate that the complex salt is heteroselectively solvated in these mixtures with the cation being preferentially solvated by acetonitrile and the anion by methanol molecules.     

Synthesis,crystal structure and ferromagnetic interactions of a silver(I) complex with imizadolyl-substituted nitroxide radicals

A silver(I) complex with nitronyl nitroxide, [Ag₂(NIT-R)₄(NO₃)₂]?·?CH₃OH [NIT-R?=?2-(5-methylimidazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl-3-oxide], has been prepared and characterized by magnetic and single-crystal X-ray diffraction studies. In the complex, the silver(I) ion is coordinated with two monodentate nitronyl nitroxide radicals by the nitrogen of the imizadole ring. The silver(I) ion is two-coordinate and forms a dimer through Ag?···?Ag weak metal bonding interactions. The magnetic properties for the title complex have been investigated in the temperature range 2?～?300?K showing ferromagnetic interactions between the coordinated nitronyl nitroxides (J?=?3.64?cm^?1) and intermolecular antiferromagnetic interactions.     

Spectroscopic studies on 2,3,4,5-tetraphenylpyrylium salts with and without silver (I)-bridged structures

Two novel phenylated pyrylium compounds, silver (I)-bridged 2,3,4,5-tetraphenylpyrylium perchlorate (P1) and its silver (I)-free pyrylium ligand (P2) were prepared from 1,2,3,4-tetraphenylcyclopentadiene to examine their spectroscopic behaviors. The UV/vis absorption and fluorescent emission spectra of P1 and P2, measured in three solvents (acetonitrile, dichloromethane and toluene), reveal that the photophysical behaviors are closely related to silver (I) fragment, and strongly dependent on solvent polarity. In polar acetonitrile, P1 displays longer absorption wavelength and much lower fluorescent emission intensity than P2, although they exhibit much similarity in shape. In contrast, in nonpolar toluene, while P2 shows an apparent absorption band at 338 nm, P1 displays a tail-like line without absorption band observed. All the spectra obtained indicate a better coplanarity and a stronger intra-molecular charge transfer in P1 due to the effect of silver (I) fragment. Additionally, the 1H NMR spectra of P1 and P2, which were recorded under the same conditions, indicate that the silver (I) fragment reinforces pyrylium ring's capacity to localize the formal positive charge within the heterocyclic ring.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.     

Synthesis and characterization of 7-deoxycholic amide backbone-based silver(I) ionophores

Four ionophores containing bipyridyl groups on a 7-deoxycholic amide derivative scaffold were designed and synthesized. Potentiometric evaluation of the Poly(vinyl chloride) (PVC) membranes containing those deoxycholic amides bearing bipyridyl moieties with a short linkage showed good affinity to silver(I) ion over alkali, alkaline earth and other transition metal cations. However, two bipyridyl groups flexibly linked to the deoxycholic frame through a long linkage do not result in appreciable potentiometric responses.     

Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents

The reactions between five ferrocenyl derivatives containing both a CO and at least an imidazole or pyridine nitrogen atom and AgPF₆, AgOTf, or [Cu(NCCH₃)₄]PF₆ precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag⁺ (with two ligands) and of Cu⁺ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors.When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag?Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)₂]OTf (L1 = ferrocenyl imidazole) and in the presence of peaks corresponding to {Ag₂(L2)₃(OTf)}⁺ and {Ag₂(L2)₄(OTf)}⁺ in the mass spectra of [Ag(L2)₂]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF₆, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L2)₂]PF₆, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.     

Role of inorganic and organic anions in the formation of metallosupramolecular assemblies of silver(I) coordination polymers with the twisted ligand bis(4-pyridylthio)methane

Reaction of the twisted pyridyl dithioether ligand bis(4-pyridylthio)methane (4bpytm) with silver(I) salts afforded four complexes with 1:1 stoichiometries, namely [Ag(4bpytm)](NO₃) (1), [Ag(4bpytm)](ClO₄) (2) and [Ag(4bpytm)](ClO₄) ½CH₂Cl₂ ½dmf (2·Solv), [Ag(CH₃COO)(4bpytm)]·H₂O (3) and [Ag(CF₃COO)(4bpytm)] (4). X-ray structural analysis of these complexes showed that one-dimensional structures are obtained for 1, 2·Solv and 4 whereas a two-dimensional network is formed in 3. The ligand 4bpytm acts as an N,N′-bis(monodentate) bridging system in all cases except in 3, where an unprecedented coordination mode is obtained with the ligand acting in a tridentate manner using its two pyridine nitrogen atoms and a sulfur atom. The coordination polymers are assembled through secondary contacts: Ag···Ag in 4, Ag···S in 1, 2·Solv and 4, Ag···O in 2·Solv, and hydrogen bonding interactions between crystallization water that join the polymeric layers in 3. All of these weak interactions link the low-dimensional complexes to give high-dimensional supramolecular structures and further stabilize the crystal structures in the solid state.     

Redox equilibria in the In(III)-In(I)-In system in aqueous KBr solutions,I. Potentiometric and coulometric study

Summary The reproportionation of In(I) ions in acidic potassium bromide solutions was studied by means of the coulometric and potentiometric method. The formal potentials of the In(III)/In(I), In(III)/In and In(I)/In redox couples as well as the equilibrium constants of the reaction In(III)+2 In=3 In(I) were determined at a background electrolyte concentration ranging from 1 to 4 mol dm^–3. Based on the experimental results, a scheme of the reproportionation reaction was proposed with regard to the participation of bromide ions. In addition, the diffusion coefficient of In(I) ions was determined using the chronopotentiometric technique.

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Das Redox-Gleichgewicht im In(III)-In(I)-In-System in wäßrigen KBr-Lösungen, I. Potentiometrische und coulometrische Untersuchungen

Zusammenfassung Die Reproportionierung von In(I)-Ionen in sauren Kalium-bromid-Lösungen wurde mittels der coulometrischen und potentiometrischen Meßmethode untersucht. Die Formal-Standardpotentiale der In(III)/In(I)-, In(III)/In- und In(I)/In-Redoxpaare sowie die Gleichgewichts-konstanten der Reaktion In(III)+2 In=3 In(I) wurden im Konzentrationsbereich von 1–4 mol dm^–3 ermittelt. Mit der Steigerung der KBr-Konzentration verschiebt sich das untersuchte Gleichgewicht erheblich zugunsten Indium(I). Aufgrund der potentiometrischen Meßergebnisse wurde ein Schema der Reproportionierung-Reaktion unter Berücksichtigung der Teilnahme von Bromidionen aufgestellt. Zusätzlich wurde der Diffusionskoeffizient von In(I)-Ionen mit Hife chronopotentiometrischer Messungen bestimmt.