Electrochemical studies of bi- and polymetallic complexes featuring acetylide based bridging ligands

Acetylide-based bridging ligands have been widely used in the preparation of complexes that display a degree of electronic interaction between metal-based redox groups located at the ligand termini. The electrochemical response of these systems has been selectively reviewed, with a focus on the variation in properties that accompany changes in the structure of the bridging ligand and the nature of the metal groups.

Argentophilicity and solvent-induced structural diversity in double salts of silver acetylide with silver perfluoroalkyl carboxylates

A series of novel double salts of silver(I) were isolated by dissolving Ag(2)C(2) in a concentrated aqueous solution of R(F)CO(2)Ag (R(F) = CF(3), C(2)F(5)) and AgBF(4). Different ancillary solvento ligands such as H(2)O, CH(3)CN, and C(2)H(5)CN were found to affect the crystallization process that led to the assembly of various silver(I) cages with embedded C(2)(2-) ions. 2Ag(2)C(2) x 12CF(3)CO(2)Ag x 5H(2)O (1) consists of two independent C(2)@Ag(7) cages, each having the shape of a basket with a square base. Ag(2)C(2) x 6CF(3)CO(2)Ag x 3CH(3)CN (2) contains a zigzag chain of edge-sharing triangulated dodecahedra, and 4Ag(2)C(2) x 23CF(3)CO(2)Ag x 7C(2)H(5)CN x 2.5H(2)O (3) features an unusual double-walled silver column constructed from the fusion of four different kinds of irregular polyhedra. Ag(2)C(2) x 10C(2)F(5)CO(2)Ag x 9.5H(2)O (4), Ag(2)C(2) x 9C(2)F(5)CO(2)Ag x 3CH(3)CN x H(2)O (5), and Ag(2)C(2) x 6C(2)F(5)CO(2)Ag x 2C(2)H(5)CN (6) all contain an edge-sharing double cage with each single cage in the shape of a square antiprism, a capped square antiprism, and a triangulated dodecahedron, respectively.     

Structural characteristics of alkylimidazolium-based salts containing fluoroanions

An overview of recent structural studies on alkylimidazolium-based salts containing fluoroanions is presented. Alkylimidazolium cations have been most extensively used for syntheses of ionic liquids (room temperature molten salts) because they usually exhibit low melting points, low viscosities and high conductivities. This review mainly focuses on structures of alkylimidazolium-based salts combined with a fluorocomplex anion ((FH)_nF⁻, BF₄⁻, PF₆⁻, AsF₆⁻, SbF₆⁻, NbF₆⁻, TaF₆⁻), N(SO₂CF₃)₂⁻ (TFSI⁻) and OSO₂CF₃⁻. The first part describes crystal structures of these salts and the second part describes computational, spectroscopic and diffraction studies on their liquid structures. Related studies on ionic liquids of non-alkylimidazolium cation and non-fluoroanion are also briefly summarized.     

Synthesis and crystal structure of three silver indium double phosphates

Three new silver indium double phosphates Ag₃In(PO₄)₂ (I), β-(II) and α-Ag₃In₂(PO₄)₃ (III) were synthesized by solid state method (I and II—700 °C, III—900 °C). Compounds I and II crystallize into a monoclinic system (I—sp. gr. C2/m, Z=2, a=8.7037(1)Å, b=5.4884(1)Å, c=7.3404(1)Å, β=93.897(1)°; II—sp. gr. C2/c, Z=4, a=12.6305(1)Å, b=12.8549(1)Å, c=6.5989(1)Å, β=113.842(1)°), and compound III crystallize into a hexagonal system (sp. gr. R-3c, Z=6, a=8.9943(1)Å, c=22.7134(1)Å). Their crystal structures were determined by the Rietveld analysis (I—R_p=6.47, R_wp=8.54; II—R_p=5.67, R_wp=6.40; III—R_p=7.30, R_wp=9.91). Structure of Ag₃In(PO₄)₂ is related to the sodium chromate structure type and is isotypic to α-Na₃In(PO₄)₂. The polymorphous modifications of β- and α-Ag₃In₂(PO₄)₃ are isostructural to sodium analogs (β- and α-Na₃In₂(PO₄)₃) and are related to alluaudite (II) and NASICON (III) structure types. Compounds I and II are not stable at temperature above 850 °C. Ag₃In(PO₄)₂ is decomposed providing silver orthophosphate Ag₃PO₄ and α-Ag₃In₂(PO₄)₂. β-Ag₃In₂(PO₄)₃ is transformed to α-Ag₃In₂(PO₄)_3.     

Crown ethers as ancillary ligands in the assembly of silver(i) aggregates containing embedded acetylenediide

Five silver(I) double salts containing embedded acetylenediide, [Ag([12]crown-4)(2)][Ag(10)(C(2))(CF(3)CO(2))(9)([12]crown-4)(2)(H(2)O)(3)] x H(2)O (2), [Ag(2)C(2) x 5 AgCF(3)CO(2) x (benzo[15]crown-5) x 2 H(2)O] x 0.5 H(2)O (3), [Ag(4)([18]crown-6)(4)(H(2)O)(3)][Ag(18)(C(2))(3)(CF(3)CO(2))(16)(H(2)O)(2.5)] x 2.5 H(2)O (4), [Ag(2)C(2) x 6 AgC(2)F(5)CO(2) x 2([15]crown-5)](2) (5), and [(Ag(2)C(2))(2) x (AgC(2)F(5)CO(2))(9) x ([18]crown-6)(2) x (H(2)O)(3.5)] x H(2)O (6), have been isolated by varying the types of crown ethers and anions employed. Single-crystal X-ray analysis has shown that complex 2 is composed of winding anionic chains with sandwiched [Ag([12]crown-4)(2)](+) ions accommodated in the concave cavities between them. In 3, silver(I) double cages each sandwiched by a couple of benzo[15]crown-5 ligands are linked by [Ag(2)(CF(3)CO(2))(2)] bridges to form a one-dimensional structure. For 4, an anionic silver column is generated through fusion of two kinds of silver polyhedra (triangulated dodecahedron and bicapped trigonal antiprism), and the charge balance is provided by aqua-ligated [Ag([18]crown-6)](+) ions. Complex 5 is a centrosymmetric hexadecanuclear supermolecule composed of two [(eta(5)-[15]crown-5)(2)(C(2)@Ag(7))(mu-C(2)F(5)CO(2))(5)] moieties connected through a [Ag(2)(C(2)F(5)CO(2))(2)] bridge. Compound 6 is a discrete supermolecule containing an asymmetric (C(2))(2)@Ag(13) cluster core capped by two [18]crown-6 ligands in mu(3)-eta(5) and mu(4)-eta(6) ligation modes.     

Role of anions for the reduction behavior of silver ions in polymer/silver salt complex membranes

The reduction of silver ions to silver nanoparticles is an essential issue in polymer/silver salt complex membranes for facilitated olefin transport, because it has a critical influence on the long-term stability of membrane performance. In this study, the role of anions for the formation of silver nanoparticles in polymer/silver salt complexes was investigated. This role was assessed for the complexes of poly(N-vinyl pyrrolidone) (PVP) with three silver salts including AgBF₄, AgCF₃SO₃, and AgNO₃. Especially, UV irradiation to the membranes was used to clearly investigate the reduction behavior of silver ions. Separation performance test, UV–vis spectroscopy and transmission electron microscopy (TEM) clearly show that the reduction rate of silver ions strongly depends on the counteranions of salt, and has the following order: AgBF₄ > AgCF₃SO₃ > AgNO₃. This behavior of the formation of silver nanoparticles in polymer/silver salt complex membranes is explained in terms of the interaction strength of silver ions with the carbonyl oxygens of polymer, and that of silver ions with counteranions. It is concluded that when the former interaction is strong and the latter one is weak, the reduction rate of silver ions to silver nanoparticles is fast, and vice versa. These interactions were characterized using FT-IR, FT-Raman spectroscopy, and theoretical ab initio calculation.     

An X-ray diffraction study of anion and ratio dependence in the formation of discrete molecules versus polymeric arrays involving silver salts and bipyridine ligands

Described are the reaction of the silver(I) salts of trifluoroacetate (tfa⁻) and trifluoromethanesulfonate (Otf⁻) with the bidentate ligands 4,4′-dimethyl-2,2′-bipyridine (L1), 5,5′-dimethyl-2,2′-bipyridine (L2) and 2,2′-bipyridine (L3), to afford the formation of five structures. A systematic study was conducted to obtain the different coordination moieties possible by changing the ligand to metal ratio and the solvent of crystallization. In total, six discrete molecules (Agtfa)(L1), 1, (Agtfa)(L2), 2A and 2B, (AgOtf)₂(L2)₃, 3A and 3B, (AgOtf)₂(L3)₃, 5, and one polymeric structure (AgOtf)(L3)_n, 4 were obtained. Compounds 2 and 3 form two crystal structures each, where differences in connectivity of the corresponding anion to the metal center are observed, as directed by solvent of crystallization. The varying degree of interaction of the two anions, combined with the functionality of the ligand used in the reaction, gave rise to coordination numbers from 4 to 6, representing capped-trigonal, distorted tetrahedral, trigonal bipyramidal and distorted octahedral environments, which illustrate the range of coordination moieties that can be adopted in silver(I) complexes, and the possibility of systematic control of the coordination framework topology of a compound. This study complements the already reported silver coordinated structures associated with the bipyridine ligands mentioned herein.     

New structural motifs of silver and gold complexes of pyridine-functionalized benzimidazolylidene ligands

Reaction of 1,3-bis(picolyl)benzimidazolium chloride ([HL1]Cl) with Ag₂O yields mononuclear complex [Ag(L1)Cl] (2), further reaction of 2 with Au(Et₂S)Cl afforded [Au(L1)Cl] (3). Treatment of 2 with AgBF₄ gave the trinuclear silver cluster [Ag₃(L1)₃](BF₄)₃ (4), whereas the digold complex [Au₂(L1)₂](BF₄)₂ (5) can be easily obtained from the carbene transfer reaction of 4 with Au(Et₂S)Cl. A one-dimensional coordination polymer {[Ag(L2)](BF₄) · CH₃CN}_n (8) was isolated from the reaction of [Ag(L2)Cl] (7, L2 = 1-benzyl-3-picolylbenzimidazolylidene) with additional Ag⁺ in good yield. The dinuclear [Ag₂(L3)₂](PF₆)₂ (12, L3 = 1,4-di(N-benzylbenzimidazolylidene)but-2-yne) is a 18-membered macrocycle. All these complexes have been structurally characterized. Complex 2 shows a dimeric structure because of intermolecular Ag?Cl interactions. Complex 4 consists of a triangular Ag₃ ring with very short Ag-Ag contacts 2.777(1) Å, the Au-Au distance in 5 is 3.206(2) Å showing very weak Au-Au interaction and the macrocyclic cations in 12 are aligned one above another to form channels filled with hexafluorophosphate anions. The complexes 2-5, 8, and 12 are intensely luminescent upon irradiation of uv light, and their emission properties are briefly described.     

Ditopic binding of cyclodextrin-included ligands in trigonal silver(I) complexes

The X-ray crystal structures of trigonal silver(I) cyclodextrin complexes of introverted bidentate sulfur (1) and phosphorus (2) ligands give a clear indication on how a cyclodextrin-included ligand may bind in a ditopic fashion both the encapsulated metal ion and the cyclodextrin inner wall. In the solid state, the silver-coordinated water molecule of complex [Ag(H₂O)(1)]BF₄ induces a major distortion of the macrocyclic structure, along with dramatic conformational changes in the two opposite glucose units with which it is hydrogen bonded. In complex [AgBr(2)], the included bulky bromide anion, which lacks hydrogen bonding capability, does not affect the overall circular shape of the cyclodextrin receptor. A ¹H-¹⁹F HOESY experiment conducted on the silver(I) complex of 1 in CDCl₃ showed that in this solvent, the water molecule is displaced by the BF₄ counterion at the metal coordination site, the cavity being here no longer distorted.     

Synthesis and characterization of nickel(II) maltolate complexes containing ancillary bisphosphine ligands

Cationic nickel(II) complexes containing chelating O,O′-donor maltolate or ethyl maltolate ligands in conjunction with bidentate bisphosphine ligands Ph₂P(CH₂) _n PPh₂ were prepared by a one-pot reaction starting from nickel(II) acetate, bisphosphine, maltol (or ethyl maltol), and trimethylamine, and isolated as their tetraphenylborate salts. An X-ray structure determination of [Ni(maltolate)(Ph₂PCH₂CH₂PPh₂)]BPh₄ shows that the maltolate ligand binds asymmetrically to the (slightly distorted) square-planar nickel(II) center. The simplicity of the synthetic method was extended to the synthesis of the known platinum(II) maltolate complex [Pt(maltolate)(PPh₃)₂]BPh₄ which was obtained in high purity.     

Preparation of CdS by thermal decomposition of double salts and saturated solutions of the systems Cd(HCOO)2-CS(NH2)2-CH3OH and Cd(CH3COO)2-CS(NH2)2-CH3OH

Summary The solubility isotherms of the systems Cd(HCOO)₂-CS(NH₂)₂-CH₃OH and Cd-(CH₃COO)₂-CS(NH₂)₂-CH₃OH have been investigated at 25°C. Reagents for the equilibrium existence of the salts Cd(HCOO)₂, Cd(HCOO)₂·2CS(NH₂)₂, CS(NH₂)₂, Cd(CH₃COO)₂, Cd(CH₃COO)₂·CS(NH₂)₂, and Cd(CH₃COO)₂·2CS(NH₂)₂ are found. The preparation of CdS by thermal decomposition of double salts and from saturated solutions by the dip technique are discussed.

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Herstellung von CdS durch thermische Zersetzung von Doppelsalzen und gesättigten Lösungen der Systeme Cd(HCOO)₂-CS(NH₂)₂-CH₃OH und Cd(CH₃COO)₂-CS(NH₂)₂-CH₃OH

Zusammenfassung Untersucht werden die Löslichkeitsisothermen der Systeme Cd(HCOO)₂-Cs(NH₂)₂-CH₃OH und Cd(CH₃COO)₂-CS(NH₂)₂-CH₃OH bei 25 °C. Die Kristallisationsfelder der Salze Cd(HCOO)₂, Cd(HCOO)₂·2CS(NH₂)₂, CS(NH₂)₂, Cd(CH₃COO)₂, Cd(CH₃COO)₂·CS(NH₂)₂ und Cd(CH₃COO)₂·2CS(NH₂)₂ werden bestimmt. Die Herstellung von CdS durch thermische Zersetzung von Doppelsalzen und gesättigten Lösungen anhand des Tauchverfahrens wird diskutiert.

     

Reduction of chloride matrix effect using silver oxide as a precipitating reagent for the determination of trace anions in chloride-rich samples via ion chromatography

A new method was developed for the determination of trace anions in chloride-rich samples via ion chromatography by reducing the concentration of chloride ions using silver oxide as a precipitating reagent. In this method the sample pretreatment was started with the addition of silver oxide powder followed by 8 min of stirring and 2 min of centrifugation at a speed of 1500 rpm. The supernatant was diluted with a 1:10 ratio using deionized water and filtered with a 0.22 microm NC filter. All the samples were analyzed in a Dionex ICS-2500 system with an ED50 electrochemical detector in conductivity mode. On the basis of Dionex IonPac AG18 (50 mm x 2 mm) and AS18 (250 mm x 2 mm) columns, 25 AL sample filtrate was eluted isocratically with a mobile phase of 32 mmol/L NaOH at a flow rate of 0.25 mL/ min and each eluted analyte was detected after postcolumn suppression via a Dionex anion suppressor ULTRA II (2 mm). With this method most of the common anions at mg/kg level in chloride-rich samples can be accurately quantified. By controlling the equivalent weight ratio of silver oxide to chloride in sample solutions and the time of pretreatment, the free silver and chloride ions in the sample solution are optimized such that most coexisting common anions can be determined simultaneously.     

Synthesis and anion exchange properties of a Zn/Ni double hydroxide salt with a guarinoite structure

In this study, the first route to synthesize a compound with the guarinoite structure (Zn,Co,Ni)₆(SO₄)(OH,Cl)₁₀·5H₂O is reported. Zn/Ni guarinoite is obtained from the reaction of NiSO₄·7H₂O with solid ZnO in aqueous solution. The resulting green Zn/Ni guarinoite ((Zn_3.52Ni_1.63)(SO₄)_1.33(OH_7.64)·4.67H₂O) was characterized by X-ray diffraction, infrared spectrometry, UV–Visible spectrometry and thermal analysis. It is shown that its structure is similar to the one described for the layered Zn sulfate hydroxide hydrate, i.e. brucite layers with empty octahedra presenting tetrahedrally coordinated divalent atoms above and below the empty octahedra. Ni atoms are located in the octahedra and zinc atoms in tetrahedra and octahedra. In this structure the exchangeable anions are located at the apex of tetrahedra. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the Zn/Ni guarinoite is composed of aggregates of hexagonal plates of several hundreds of nanometers. Due to its interest for industrial or environmental applications, the exchange of sulfate groups by carbonates has been investigated. Results show a limited exchange and a higher affinity of the Zn/Ni guarinoite for sulfates compared to carbonates.     

甘草酸银在几种溶剂中的溶解行为及银量测定

研究了甘草酸银在乙醇、乙醚、丙酮、三氯甲烷、磷酸三丁酯，H2O、HCl、HNO3、H2SO4、氨水、NaOH、Na2CO3等溶剂中的溶解行为，建立了在氨性介质中直接用碘化钾电位滴定测定甘草酸银中银含量的方法。该方法已用于过程控制分析。     

Direct determination of gold and silver in rat plasma by graphite furnace atomic absorption spectrometry with Zeeman effect background correction and its application to the pharmacological properties of a mixture of copper,gold and silver salts

Methods for determining gold and silver in rat plasma without prior mineralization are presented. They permit concentrations above 1 μg 1^?1 to be measured. They were applied to 96 rat plasma samples with gold and silver contents up to 3 μg 1^?1. In addition, the anti-inflammatory properties of a solution containing gold, silver and copper at the mg 1^?1 level were tested and demonstrated.     

Synthesis,crystal structure,and reactivity of alkali and silver salts of sulfonated imidazoles

Both 2-methylimidazole and 2-ethyl-4-methylimidazole were monosulfonated with oleum in the five position. In crystals of the monohydrate of 2-methylimidazole-5-sulfonic acid, hydrogen bonds link the molecules into a 3-dimensional network, while in crystals of 2-ethyl-4-methylimidazole-5-sulfonic acid, corrugated 2-dimensional layers are present. The Li and Ag salts and the bis(trimethylsilyl) derivatives of 2-ethyl-4-methylimidazole-5-sulfonic acid were prepared, and there is evidence for doubly deprotonated imidazolesulfonate in aqueous solution. The monohydrate of the Li salt and the Ag salt also form a 3-dimensional, H-bonded network. Only in the Ag salt does the asymmetric unit consist of more than one basic formula unit. One Ag atom is 2-coordinate and links two nitrogen atoms, while the other Ag atom has distorted tetrahedral coordination and links the sulfonate groups into an infinite chain. Reactions of the silver salt with 1,4-dibromobutane in non-protic solvents such as 1-methyl-2-pyrrolidone were used to link two of the imidazolesulfonic acid units with a 4-carbon chain at the nitrogens.     

XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

Anion-selective properties of alkali metal-free lead phosphate glasses containing silver chloride and their application in an ion-selective electrode

Alkali-free lead phosphate glasses containing silver chloride have been developed for anion responsive sensors. From measurements of the final glass compositions by electron probe microanalysis, it became clear that some of chloride ions in the glass bulk were not volatilized during the glass melting process. Compared with phosphate glasses containing silver oxide, the new glass electrodes containing silver chloride could respond more rapidly, although the response behaviour for anionic species were similar. From the electrode potential vs. time curve for the anionic species, the potential rapidly reached equilibrium when these concentrations varied from 10^?5 to 10^?2 M. The response times, t₉₅, to thiocyanate of the new glass electrode and the phosphate glass electrode containing silver oxide were 30 and 110 s, respectively. Moreover, the response time required for an initial potential change with a concentration jump of thiocyanate with the new glass electrode was found to be independent of the membrane thickness within about 2 mm and of the measuring temperature between 15 and 40°C. It is concluded that the diffusion process of species such as silver ion in the glass bulk does not take part in the initial part of the response behaviour.     

Linker effect of ferrocenylnaphthalene diimide ligands in the interaction with double stranded DNA

Ferrocenylnaphthalene diimide ligands 1-7 were synthesized by joining a piperazino or N-methylamino linker of the naphthalene diimide skeleton with ferrocenecarboxylic, ferroceneacetic, or ferrocenepropionic parts. Their interaction with double stranded DNA (dsDNA) was studied kinetically and electrochemically. Association rate constants of these ligands were found to correlate with their intramolecular stacking ability between the ferrocene and naphthalene diimide planes: ligands which can adopt a stacked conformation in buffer solution were unfavorable in the association with dsDNA, resulting in a smaller association rate constant. Dissociation rate constants of these ligands carrying the bulky piperazino linker were smaller than that of those carrying an N-methylamino one. Binding constants were dictated by the balance of these two factors. These ligands were applied to the electrochemical detection of the amount of dsDNA on the electrode. Ligand 6 having the highest affinity for dsDNA gave rise to the largest current increase upon dsDNA formation in the electrochemical hybridization assay.