Chemical Bonding and Pressure‐Induced Change of the Electron Configuration of Ytterbium in β‐YbAgGa2

Single‐phase polycrystalline samples of the intermetallic compound β‐YbAgGa₂ were synthesized by inductive heating and subsequent annealing for eight weeks at 670 K. Magnetic properties were characterized by susceptibility measurements and indicated intermediate valence of ytterbium at ambient pressure. Angle‐dispersive X‐ray powder diffraction data of orthorhombic β‐YbAgGa₂ indicate stability of the phase in the investigated pressure range from 0.1 MPa (ambient pressure) to 19 GPa. The pressure‐induced volume decrease is accompanied by an increase of the effective valence from 2.17 at ambient conditions to 2.71 at 16 GPa as evaluated by X‐ray absorption spectroscopy at the Yb L_III threshold. Analysis of the chemical bonding in β‐YbAgGa₂ by integrating the electron density of the polyanion in basins as defined by the electron localization function results in an electron count Yb^2.7+[(Ag^0.2—)(Ga1(3b)^1.0—)(Ga2(4b)^1.5—)]. This finding is close to the expected values calculated by means of the Zintl rules and fits well the results of magnetic susceptibility measurements and XAS investigations.     

Stabilization of Th ions into mixed-valence thorium fluoride

The unusual oxidation state +3 of the thorium has been stabilized into a lithium containing non-stoichiometric mixed-valence (III/IV) thorium fluorinated phase with formula Li_2+xTh₁₂F₅₀ (0<x<1.8). This phase is closely related to the Li_5.5Ce₁₂F₅₀ one, the structure of which has been determined from the combined single-crystal X-ray diffraction and high resolution synchrotron powder diffraction. In these phases, the Li⁺ ions can be divided into two groups and are located either in locked positions or in open channels of the three dimensional framework. The amount of Li⁺ ions in open channels can be variable, so that the afore mentioned single phase may be considered as an insertion compound. The Li⁺ insertion is accompanied by the simultaneous reduction of a part of the Th⁴⁺ ions, resulting in a mixed-valence III/IV thorium fluoride. The electrochemical insertion of Li⁺ ions into the open channels of the host matrix has been carried out at 60 °C, using an alkylcarbonate PC-LiClO₄ 1 M electrolyte. The Li⁺ and Th³⁺ contents, both in the starting composition and the Li⁺ inserted ones, were investigated by high resolution solid state ⁷Li NMR and EPR, respectively.     

Dimers of Ag2+ Ions – Synthesis and Characterization of the Quaternary Silver Fluoride Ag2ZnZr2F14 with [Ag2F7]3– Units

Deep blue‐violet colored powder samples of Ag₂ZnZr₂F₁₄ were synthesized by heating Zn(NO₃)₂·4H₂O, Ag and ZrOCl₂·8H₂O at 300 °C under fluorine atmosphere. The crystal structure of Ag₂ZnZr₂F₁₄ was refined from X‐ray powder diffraction data using the Rietveld method (C2/m, a = 9.0206(1) Å, b = 6.6373(1) Å, c = 9.0563(1) Å, β = 90.44(1)°, Z = 2). The structure is derived from the isotypic Ag₃Zr₂F₁₄ by replacing only one of the two crystallographically different Ag²⁺ ions with Zn²⁺ ions, thus leading to discrete Ag₂F₇ dimers. These dimers are connected via nearly linear Ag–F···F–Ag bridges with short F···F distances of 2.33 Å to form two‐legged ladders. Magnetic susceptibility measurements and density functional calculations show that the two Ag²⁺ ions in each Ag₂F₇ dimer are strongly coupled antiferromagnetically.     

Thermodynamic properties of the silver ion in alcohol + water solvent mixtures from electromotive force measurements and thermodynamic solubility product constants of AgX (X = Cl,Br, I or CNS) at different temperatures

The standard potentials of the silver-silver ion electrode in alcohol+water solvent mixtures containing 10 and 20 wt% methanol, ethanol, 1-propanol and 2-propanol have been determined from the electromotive force measurements of the cell Ag(s), AgCl(s), NaCl(c), NaNO₃(c)// NaNO₃(c), AgNO₃(c), Ag(s) at seven different temperatures in the range 5–35°C. The standard potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the electrode reaction, the primary medium effects of various solvents upon Ag⁺, and the standard thermodynamic quantities for the transfer of 1 g-ion of Ag⁺ from water to the respective alcohol + water media have been evaluated and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents. From the values of the standard potentials of the Ag/Ag⁺ and Ag/AgX, X^? electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide, silver iodide and silver thiocyanate have been determined in alcohol + water solvent mixtures at different temperatures.     

Neue Ternäre Silber(II)-fluoride: Ag3IIM2IVF14 (MIV = Zr,Hf)

New Ternary Silver (II) Fluorides: Ag M F₁₄ (M^IV = Zr, Hf) Single crystals of deeply blue violet coloured fluorides Ag₃^IIM₂^IVF₁₄ (M^IV = Zr, Hf) have been obtained by heating powder samples under F₂/N₂ (1:2) at T ≈? 600°C. The isotypic compounds crystallizes monoclinic with a = 924.9, b = 668.6, c = 907.3 pm, β = 90.30° (Ag₃Hf₂F₁₄) and a = 922.5, b = 667.6, c = 906.3 pm, β = 91.30° (Ag₃Zr₂F₁₄) (Four circle diffractometer data, Philips PW 1100), spcgr. C2/m-C_2h³ (No. 12), Z = 2. There are two different sorts of Ag²⁺:Ag(1) with coordination number C.N. [Ag(1)] = 4 + 2 and Ag(2) with C.N.[Ag(2)] = 4 + 4 against F^?. Ag(1) can be substituted by Cu²⁺, Ni²⁺, Zn²⁺, Mg²⁺ (all of blue/red violet colour), Ag(2) by Ca²⁺, Cd²⁺, Hg²⁺ (bright green). From (preliminary) powder data CuAg₂Zr₂F₁₄ with a = 912.3(4), b = 661.2(2), c = 899.4(2) pm, β = 90.70° (3) is isotypic, the other compounds seems to be of closely related type of structure.     

Membrane Transport of Pb(II) with a Cooperative Carrier Composed of Dibenzyldiaza‐18‐Crown‐6 and Palmitic Acid

A chloroform membrane system containing a given mixture of dibenzyldiaza‐18‐crown‐6 and palmetic acid was applied for transport of Pb²⁺ ions. The transport was capable of moving metal ions “uphill”. Thus, it was possible to follow the transfer of Pb(II) from the aqueous source phase to the organic layer and from the organic layer to the receiving phase. The effects of thiosulfate concentration in the receiving phase, palmetic acid and dibenzyldiaza‐18‐crown‐6 concentration in the organic phase on the efficiency of the transport system were examined. By using S₂O₃^2? ion as metal ion acceptor in the receiving phase, the amount of lead ion transport across the liquid membrane after 150 minutes is 96 ± 1.5%. The selectivity and efficiency of lead transport from aqueous solution containing Cu²⁺, Tl⁺, Ag⁺, Co²⁺, Ni²⁺, Mg²⁺, Zn²⁺, Hg²⁺, Cd²⁺, Ca²⁺ were investigated. In the presence of thiosulfate as a suitable masking agent in the source phase, the interfering effects of Ag⁺ and Cu²⁺ were diminished drastically.     

Potentiometric investigation of the silver(I) complexes of a series of sulphur-containing α,ω-diamines

The composition and the stability constants of the complexes formed between Ag(I) and ligands of the type where n,m = 2,2; 2,3; 2,4; 3,3; 3,4; 4,4, have been determined by a pH/pM-metric method at 25°C in a 0.5 M (K)NO₃ medium. The determination of the stability constants proceeded by a combination of a graphical method and a least squares minimization procedure. The complex formation is discussed in comparison with silver complexes formed with S-containing mono-amines and in terms of the Taft σ*-parameters for the substituents. Below pH = 4, the protonated complexes AgLH₂³⁺ and AgL₂H₄⁵⁺ are formed and the thioethergroup is the only coordinating centre. In neutral and alkaline medium there was evidence for the species AgLH²⁺, Ag₂L₂H₂⁴⁺, Ag₂L₂H³⁺, Ag₂L₂²⁺, AgL₂H₃⁴⁺, AgL₂H²⁺, AgL₂ + and Ag₂L²⁺ in which Ag⁺? S and Ag⁺? NH₂ bonds are involved. It is shown that in the Ag₂L₂²⁺ and Ag₂L²⁺ complexes the ligands effectively coordinate through all available donor centres.     

Metal-ion recognition-competitive bulk liquid membrane transport of transition and post-transition metal cations using a thioether donor acyclic ionophore

The competitive bulk liquid membrane transport of Cr³⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations with a new synthetic sulfur donor acyclic ligand (pseudo-cyclic ionophore), i.e. 1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl]ethylsulfanyl)-3-phenoxy-2-propanol; (C₂₀H₂₆O₄S₂), was examined using some organic solvents as membranes. The membrane solvents include: chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl₃-NB) and chloroform-dichloromethane (CHCl₃-DCM) binary mixtures. The transport process was driven by a back flux of protons, maintained by the buffering the source and receiving phases with pH 5 and 3, respectively. The aqueous source phase consisted of a buffer solution (CH₃COOH/CH₃COONa) at pH = 5 and containing an equimolar mixture of these seven metal cations. The organic phase contained the acyclic ligand, as an ionophore and the receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. For these systems that displayed transport behaviour, sole selectivity for Ag⁺ cation was observed under the employed experimental conditions in this investigation. The amount of Ag⁺ transported follows the trend: 1,2-DCE > CHCl₃ > DCM > NB in the bulk liquid membrane studies. The transport of the metal cations in CHCl₃-NB and CHCl₃-DCM binary solvents is sensitive to the solvent composition. The influence of the stearic acid, palmitic acid and oleic acid in the membrane phase on the ion transport was also investigated.     

Pressure Effects on 3dn (n=4, 9) Insulating Compounds: Long Axis Switch in Na3MnF6 not Due to the Jahn-Teller Effect

The pressure-induced switch of the long axis of MnF₆³⁻ units in the monoclinic Na₃MnF₆ compound and Mn³⁺-doped Na₃FeF₆ is explored with the help of first principles calculations. Although the switch phenomenon is usually related to the Jahn-Teller effect, we show that, due to symmetry reasons, it cannot take place in 3dⁿ (n=4, 9) systems displaying a static Jahn-Teller effect. By contrast, we prove that in Na₃MnF₆ the switch arises from the anisotropic response of the low symmetry lattice to hydrostatic pressure. Indeed, while the long axis of a MnF₆³⁻ unit at ambient pressure corresponds to the Mn³⁺−F₃⁻ direction, close to the crystal c axis, at 2.79 GPa the c axis is reduced by 0.29 Å while b is unmodified. This fact is shown to force a change of the HOMO wavefunction favoring that the long axis becomes the Mn³⁺−F₂⁻ direction, not far from crystal b axis, after the subsequent relaxation process. The origin of the different d-d transitions observed for Na₃MnF₆ and CrF₂ at ambient pressure is also discussed together with changes induced by pressure in Na₃MnF₆. The present work opens a window for understanding the pressure effects upon low symmetry insulating compounds containing d⁴ or d⁹ ions.     

Isolation of Homo-/Mixed-Valence Ag12, Ag29, and Ag8 Clusters Stabilized by Cyclic Alkyl(amino) Carbene-Anchored Monoanionic Phosphorus Ligand

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag₁₂Cl₃, Ag₂₉, and Ag₈ cores [((cAAC)P)₆Ag₁₂Cl₃](OTf)₃ ( 1 ), [((cAAC)P)₆Ag₂₉] ( 2 ), and [((cAAC)P)₄Ag₈] ( 3 ) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP⁻) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1 , and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P⁻) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P−B(NⁱPr₂)₂ through cleavage of the P−B bond with the help of a triflate anion (OTf⁻) as a weak nucleophile. Equivalent number of the (cAAC)P⁻ anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)₂P₂ leading to the generation of Ag⁰ ions in solution for the formation of the unprecedented mixed-valence Ag NC 2 . Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf₂. The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1 – 3 , further providing a three- ( 1 , 2 )/two- ( 3 ) fold stand. The Ag₁₂Cl₃ NC ( 1 ) with a tricationic core [Ag^I₁₂Cl₃] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag₂₉ ( 2 ) and Ag₈ ( 3 ) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag⁰ at room temperature.     

Complexation of Cd2+, Ni2+, and Ag+ metal ions with 4,13-didecyl-l,7,10,16-tetraoxa-4,13-diazacyclooctadecane in acetonitrile-ethylacetate binary mixtures

Conductometric titrations have been performed in acetonitrile-ethylacetate (AN-EtOAc) binary solutions at 288, 298, 308, and 318 K to obtain the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of Cd²⁺, Ni²⁺, and Ag⁺ cations with 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (cryptand 22DD). The stability constants of the resulting 1: 1 complexes formed between the metal cations and the ligand were determined by computer fitting of the conductance-mole ratio data. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of ethylacetate in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the Cd²⁺, Ni²⁺, and Ag⁺ cations with the ligand changes with the nature of the solvent. The standard enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, the complexation processes of the metal cations with the C22DD, is mainly entropy governed and the values of thermodynamic parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Specific Uphill Transport of Zinc as Zn(SCN)42− Ion using Na+-Dicyclohexyl-18-Crown-6 as Carrier

Sodium-dicyclohexyl- 18-crown-6 complex cation was used as carrier for the uphill transport of zinc as Zn(SCN)₄^2? complex anion. By using L-cysteine as a metal ion acceptor in the receiving phase at the optimized pH of 7.6, the amount of zinc transport through the liquid membrane after 90 min was 97.2 ± 1.0%. The selectivity and efficiency of zinc transport from aqueous solutions containing equimolar mixtures of Ag⁺, Cd²⁺ Co²⁺, Cu²⁺, Fe²⁺, Ni²⁺, Pb²⁺, Pd²⁺, Sr²⁺, Bi³⁺, Cr³⁺ and Fe³⁺ ions was investigated. In the presence of NH₂OH.HCl as a suitable masking agent in the source phase, the interfering effect of Cu²⁺ and Pb²⁺ ions was diminished drastically.     

New Silver Tellurates – The Crystal Structures of a Third Modification of Ag2Te2O6 and of Ag4TeO5

Single crystals of a third modification of Ag₂Te₂O₆ (denoted as Ag₂Te₂O₆–III) and of Ag₄TeO₅ have been obtained as minor by‐products during hydrothermal phase formation experiments in the system Ag‐Hg‐Te‐O. The crystal structure of Ag₂Te₂O₆–III (P2₁/c, Z = 4, a = 6.4255(10), b = 6.9852(11), c = 13.204(2) Å, β = 90.090(3)°, 1885 independent reflections, R[F² > 2σ(F²)] = 0.0334, wR2(F² all) = 0.0817) comprises tellurium in oxidation states +IV and +VI and is topologically related to the structure of the Ag₂Te₂O₆–I modification, which consists of similar layers and interjacent layers of Ag⁺ cations. Ag₄TeO₅ (C2/c, Z = 8, a = 16.271(2), b = 6.0874(10), c = 11.4373(16) Å, β = 106.730(10)°, 2372 independent reflections, R[F² > 2σ(F²)] = 0.0288, wR2(F² all) = 0.0737) is made up of a layer‐like arrangement of isolated [Te^VI₂O₁₀] double octahedra and of Ag⁺ cations situated both in layers parallel and inside the layers of the anionic moieties.     

Study of Complex Formation between N-Phenylaza-15-Crown-5 with Mg2+, Ca2+, Ag+ and Cd2+ Metal Cations in Some Binary Mixed Aqueous and Non-aqueous Solvents using the Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H₂O) and propanol (PrOH)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K _f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag⁺>Cd²⁺>Ca²⁺>Mg²⁺, but in the case of neat AN is Ca²⁺>Cd²⁺>Mg²⁺>Ag⁺. The values of thermodynamic parameters (ΔH _c ^o , ΔS _c ^o ) for formation of Ph-N15C5–Mg²⁺, Ph-N15C5–Ca²⁺, Ph-N15C5–Ag⁺ and Ph-N15C5–Cd²⁺ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

Expanding the Hierarchy of Metal-Oxide Building Blocks from Fragments via Clusters to Networks: A ∞2 [({Mo17(NO)2}3{MoV2}3{FeIII}6)(FeII1.5)]-Type Layer Compound

A planar network consisting of {Mo₁₇(NO)₂}₃{Mo^V ₂}₃{Fe₆^III} cluster entities that are interlinked to layers via {Fe^II(H₂O)₄}²⁺ groups is formed stepwise from building units. The corresponding mixed-valence compound exhibits a variety of different formal oxidation states: {MoNO}³⁺, Mo^V, Mo^VI, Fe^II, and Fe^III. This compound also represents an extension of building-block hierarchy from the molecular level to extended networks.     

Conductance Studies on Complex Formation Between Aza-18-Crown-6 with Ag+, Hg2+ and Pb2+ Cations in DMSO–H2O Binary Solutions

The complexation reactions between Ag⁺, Hg²⁺ and Pb²⁺ metal cations with aza-18-crown-6 (A18C6) were studied in dimethylsulfoxide (DMSO)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes in most cases is 1:1(ML), but in some cases 1:2 (ML₂) complexes are formed in solutions. A non-linear behaviour was observed for the variation of log K _f of the complexes vs. the composition of the binary mixed solvents. Selectivity of A18C6 for Ag⁺, Hg²⁺ and Pb²⁺ cations is sensitive to the solvent composition and in some cases and in certain compositions of the mixed solvent systems, the selectivity order is changed. The values of thermodynamic parameters (ΔH _c^o, ΔS _c^o) for formation of A18C6–Ag⁺, A18C6–Hg²⁺ and A18C6–Pb²⁺ complexes in DMSO–H₂O binary systems were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

Die Kristallstruktur von AgIIF[AgIIIF4]

Crystal structure of Ag^IIF[Ag^IIIF4] For the first time dark brown single crystals of mixedvalent AgF[AgF₄] were isolated under solvothermal conditions out of anhydrous HF/F₂. The compound crystallizes in a new type of structure, triclinic with a = 499.9(2) pm, b = 1108.7(5) pm, c = 735.7(3) pm, α = 90.05(3)°, β = 106.54(4)°, γ = 90.18(4)°, spcgr. P1¯ — C_i¹ (No. 2) and Z = 4.     

Selective and efficient liquid membrane transport of gold as gold cyanide using an anion carrier

The facilitated transport of Au(III) from cyanide solutions through a bulk liquid membrane is reported. The organic phase consisted of a chloroform solution containing Victoria blue dye as the Au(CN)⁻₄ carrier. The effects of pH of source phase, potassium cyanide concentration in source phase, Victoria blue concentration in the organic phase and sodium hydroxide in the receiving phase on the efficiency of transport process were examined. Under optimum conditions the extent of Au(CN)⁻₄ transport across the liquid membrane was about 97% after 180 min. The carrier can selectively and efficiently transport Au(CN)⁻₄ ion from the aqueous solutions containing other cations such as alkali and alkaline earth, Zn²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Ag⁺, Co²⁺, Fe²⁺, Pt²⁺, Pd²⁺ and Ni²⁺.     

Crown-containing butadienyl dyes 8. Structures and complexation of chromogenic dithia-15(18)-crown-5(6) ethers

The structures of new butadienyl dyes of the benzothiazole series containing the dithia-15-crown-5 (2a) or dithia-18-crown-6 (2b) fragments were established by X-ray diffraction. Complexation of dyes 2a,b with Hg²⁺, Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, and alkaline-earth cations in aqueous-acetonitrile solutions was studied by spectrophotometry. At a high percentage of water in solutions (P _w ≈ 50%), these dyes have a very low ability to bind Pb²⁺ cations (logK < 2) and virtually do not bind Cd²⁺, Zn²⁺, and alkaline-earth cations. At the same time, these dyes form stable 1: 1 complexes with Hg²⁺ and Ag⁺ cations at all P _w. The stability constants of complexes with the Ag⁺ cation increase with increasing P _w because the free energy of hydration of this cation is much lower than the free energy of solvation in acetonitrile. In the P _w range from 0 to 75%, the stability constants of the complexes of dyes 2a,b with the Hg²⁺ cation are larger than those of the corresponding complexes with the Ag⁺ cation by more than four orders of magnitude. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 90–96, January, 2006.     

Mechanism of silver nucleation upon the radiation-induced reduction of its ions in polyphosphate-containing aqueous solutions

Long-lived (hours to days) silver clusters, Ag ₄ ²⁺ , Ag ₄ ⁺ , Ag ₈ ²⁺ , etc., are formed upon the radiation-induced reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The efficiency of the cluster formation decreases and the stability of the clusters increase with a rise in the concentration of the polymeric stabilizer. In the course of the aggregation of clusters, their sizes increase, quasi-metallic particles emerge, and the process terminates with the formation of silver nanoparticles. The mechanism of silver nucleation upon the radiation-induced reduction of silver ions in aqueous solutions is discussed.