Ag9I(GeO4)2 – Containing Two‐dimensionally Linked [IAg12] Metallo Complexes

Ag₉I(GeO₄)₂ was obtained for the first time by reacting a stoichiometric mixture of Ag₂O, AgI, and GeO₂, at elevated oxygen pressures, adding a small portion of distilled water. The synthesis was done at 480 °C and 110 MPa of oxygen pressure. It crystallizes in space group C2/m, with the unit cell dimensions a = 17.3736(9) Å, b = 6.9177(4) Å, c = 5.7176(3) Å, β = 105.501(3)°, V = 662.18(6) ų, and Z = 2. The structure refinement was based on 638 independent reflections and resulted in R₁ = 6.26 %. The crystal structure consists of isolated (GeO₄)^4– ions and [IAg₁₂] metallo complexes, the latter are interconnected through each two common edges and corners corresponding to [IAg_6/1Ag_6/2], thus forming infinite layers within the (100) plane. The Ag/I slabs are stacked perpendicular to the a‐axis with an interlayer distance of about 3.4 Å. The (GeO₄)^4– anions are located in the gaps between the silver iodide layers. According to the results of impedance measurements, Ag₉I(GeO₄)₂ is a good silver ion conductor. The compound shows an increase in the ionic conductivity in the temperature range of 30 to 310 °C, and has a silver ion conductivity of 1.1 × 10^–3 Ω^–1 cm^–1 at room temp. The activation energy for silver ion conduction is 0.35 eV, in the temperature range from 25 to 190 °C.     

Ag9I3(SeO4)2(IO3)2 – Synthesis,Crystal Structure,and Ionic Conductivity

Ag₉I₃(SeO₄)₂(IO₃)₂ was obtained for the first time by reacting a stoichiometric mixture of Ag₂O, AgI and SeO₂ at elevated oxygen pressure (255 MPa) and at a temperature of 500 °C. Ag₉I₃(SeO₄)₂(IO₃)₂ was characterized by X‐ray powder diffraction, differential scanning calorimetry, impedance spectroscopy and single crystal structure analysis. The crystal structure was solved by direct methods (I23, Z = 8, a = 12.9584(6) Å, V = 2175.9(2) ų and R₁ = 2.70 %). The crystal structure consists of isolated SeO₄ tetrahedra and trigonal IO₃ pyramids separated by Ag⁺ and I^– ions. Each four of the SeO₄^2– and IO₃^– anions aggregate, forming a novel supramolecular building block, showing a hetero‐cubane like structure. According to the results of impedance measurements, Ag₉I₃(SeO₄)₂(IO₃)₂ is a good silver ion conductor. The compound shows an abrupt increase in the ionic conductivity in the temperature range of 115 to 147 °C, and has a silver ion conductivity of 7.1 × 10^–5 Ω^–1 cm^–1 at 25 °C. The activation energy for silver ion conduction is 0.45 eV, in the temperature range from 25 to 115°.     

Die K4[Ag4O4] — Strukturfamilie

K₄[Ag₄0₄] Structure Type M₄[Ag₄O₄] (M ? Li? Cs) and M₄[Cu₄O₄] (M ? Li? Rb) have been prepared anew; as an example the crystal structure of K₄[Ag₄O₄] has been revised. Contrary to our first report [2, 3] it crystallizes in the space-group I4 m2 with the “ring” [Ag₄O₄]^4? which is not plane, however. Each two O^2? (trans-arrangement) are rather (0.02 Å) above and below the plane of the “ring”, respectively. The new parameters are given in the text. The distances, for example d(Ag⁺·O^2?) = 2.058 Å and the Madelung Part of Lattice Energy, MAPLE, are both in a very good agreement with the measurements and calculations, respectively, which have been done on other ternary oxides with silver.     

Neues über Oxogermanate. 1. Zur Kenntnis von K4GeO4

News on Oxogermanates. 1. On K₄GeO₄ For the first time single crystals of K₄GeO₄ have been prepared by heating KO_0.46 and GeO₂. The structure has been refined. K₄GeO₄: 2565 I₀(hkl), four circle diffractometer PW 1100, ω-scan, AgKα, R = 0.0826, R_w = 0.0837, P1 ; a = 640.56(35), b = 633.87(34), c = 933.68(45) pm; α = 80.26(5)°, β = 107.58(5)°, γ = 113.63(4)°; d_x = 2.94 g/cm³; d_pyk = 2.91 g/cm³; Z = 2. K₄GeO₄ is isotypic with K₄SnO₄. There is, however, an essential difference of the C.P. (Coordination Polyhedra) with respect to K4 and O4. The Effective Coordination Numbers, ECoN, the Mean Fictive Ionic Radii, MEFIR, and the Madelung Part of Lattic Energy, MAPLE, are calculated.     

Solubility studies in aqueous media: I. Solubility product of silver permanganate and standard electrode potentials of silver—silver permanganate electrode in aqueous media

The solubility and solubility product of silver permanganate in water have been determined at the temperatures ranging from 15 to 35°C over 5°C intervals in the presence of an added electrolyte, sodium perchlorate. The solubility of silver permanganate ranges from 0.966 x 10^?5 mol 1^?1 at 15°C to 1.420x10^?5 moll^?1 at 35°C and the corresponding solubility product 0.933 x 10^?10 mol² 1^?2 at 15°C to 2.017 x 10^?10 mol² 1^?2 at 35°C. The standard potentials of the Ag(s)/AgMnO₄(s)/ MnO^?₄ electrode have been calculated at these temperatures. The mean activity coefficients of silver permanganate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgMnO₄(s)→Ag⁺ (aq)+MnO^?₄(aq) have been calculated at these temperatures.     

Thermodynamic relations among olivine,spinel, and phenacite structures in silicates and germanates: I. Volume relations and the systems NiOMgOGeO2 and CoOMgOGeO2

An experimental approach is outlined to systematically obtain free energy differences among olivine, spinel, and phenacite forms of silicates and germanates from the thermodynamics of terminal solid solutions in ternary systems. This is applied to the ternary systems NiOMgOGeO₂ and CoOMgOGeO₂ at 1200°C in air and to the system NiOMgOGeO₂ at 800°C and 0.57 kbar water pressure. From the location of conjugation lines, activity-composition relations along each orthogermanate join are calculated. The free energies of transformation from the olivine to the spinel structure at 1200°C are estimated to be +1.6, ?3.5, and ?8.2 kcal/mole for Mg₂GeO₄, Co₂GeO₄, and Ni₂GeO₄, respectively.Volume changes for the spinel-olivine and olivine-phenacite transitions are estimated for the silicates and germanates of Mg, Mn, Fe, Co, Ni, and Zn.     

Non-isothermal decomposition of silver maleate dihydrate and anhydrous silver fumarate

The non-isothermal decompositions of silver maleate dihydrate (C₄H₂O₄Ag₂2H₂O) and anhydrous silver fumarate (C₄H₂O₄Ag₂) were studied up to 500°C, in a dynamic atmosphere of air, by means of TG and DTA measurements. Both compounds showed some sublimation (at 120°C for silver maleate and at 180°C for silver fumarate) prior to the onset of decomposition (at 170°C for silver maleate and at 280°C for silver fumarate). The gaseous decomposition products of both compounds were found, using IR spectroscopy, to be dominated by maleic anhydride and CO₂. Minor proportions of ethylene, ethyl alcohol, acetone, methane and isobutene were also identified. Metallic silver was the final solid product, as identified by X-ray diffractometry. NMR analysis was used to monitor the isomerization of the maleate radical into the more stable fumarate above 230°C. Kinetic parameters (E _a and lnA) were calculated from the effect of heating rate, (2, 5, 10, and 20 deg min^?1) on the DTA measurements. A mechanism is suggested for the decomposition pathways of these compounds, on basis of the results obtained and, also, on similarities with analogous systems.     

Phase formation in the Ag3VO4-ScVO4 quasi-binary system

Subsolidus phase formation in the Ag₃VO₄-ScVO₄ quasi-binary system was studied using X-ray powder diffraction and DTA in air under atmospheric pressure over the entire range of component concentrations in 5 mol % steps between 20 and 800°C. Two compounds were found to form: Ag₃Sc(VO₄)₂ and Ag₃Sc₂(VO₄)₃, both melting incongruently at 750 ± 5 and 960 ± 5°C, respectively. A T-x diagram of the Ag₃VO₄-ScVO₄ quasi-binary system was constructed. A eutectic (T _m = 450 ± 5°C) is between the compounds Ag₃VO₄ and Ag₃Sc(VO₄)₂; Ag₃VO₄ concentration is ～5 mol %.     

Darstellung und Struktur von Ag2C4O4

Preparation and Structure of Ag₂C₄O₄ Ag₂C₄O₄ occurs in a yellow and a colourless modification. Both forms decompose to metallic silver upon heating. Ag⁺ is coordinated in two different fashions in the yellow Ag₂C₄O₄. Ag(1) shows distorted tetrahedral coordination, Ag(2) is coordinated in an unusual distorted square planar manner. The connection of Ag⁺ and C₄O₄^2? leads to a complicated three-dimensional framework. C₄O₄^2? is planar with C? O and C? C bonds lengths typical of complete delocalization of the π-electron system.     

Phase formation in the Ag3PO4-ScPO4 quasi-binary system

The phase formation in the subsolidus region of the Ag₃PO₄-ScPO₄ quasi-binary system was studied by X-ray powder diffraction and differential thermal analyses throughout the range of concentration ratios of the initial components at an interval of 10 mol % within the temperature range 20–1000°C in air at atmospheric pressure. A T-x section was constructed. The formation of the binary phosphate Ag₃Sc₂(PO₄)₃ melting incongruently at 1300 ± 5°C was detected. The composition of an eutectic (with the melting point 900 ± 5°C) is between those of the compounds Ag₃PO₄ and Ag₃Sc₂(PO₄)₃.     

FTIR studies of butane, toluene and nitric oxide adsorption on Ag exchanged NaMordenite

In this work, we studied the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts of silver. The reactions that occurred when the adsorbed hydrocarbons interacted with NO and the effect of water adsorption were also addressed. Different silver species were formed after ion exchange and they were detected by TPR analysis. Highly dispersed Ag₂O particles were reduced at temperatures lower than 300 °C whereas Ag⁺ exchanged ions showed two TPR peaks, which can be ascribed to species exchanged at different mordenite sites. The TPD experiments after adsorption of NO at 25 °C showed that the only desorbed species was NO₂ which was formed by the total reduction of Ag₂O particles. When the adsorbed butane was exposed to NO (1000 ppm), isocyanate species were formed on Ag⁺ ionic sites as well as Ag⁺–(NOx)–CO species. Toluene adsorption was stronger than butane since adsorbed toluene molecules were held even at 400 °C. The characteristic bands of the aromatic ring C=C bond was observed as well as that of methyl groups interacting with Ag⁺ and Na⁺ ions. However, the appearance of carboxylic groups at temperatures above 300 °C in inert flow indicated the partial oxidation of toluene due to Ag₂O species present in the samples. After contacting adsorbed toluene with NO, different FTIR bands correspond to organic nitro-compounds, isocyanate, cyanide and isocyanide species adsorbed on Ag⁺ ions, were detected. The presence of water inhibited the formation of NO₂ species and the hydrocarbon adsorption on Na⁺ sites but did not affect the toluene-Ag⁺ interaction.     

Solid state electrochemical study of the phase diagram and thermodynamics of the ternary system CuGeO

Coulometric titrations using solid zirconia ionic conductors have been employed to determine the phase diagram of the ternary system CuGeO in the temperature range from 750 to 950°C. CuGeO₃ was found to be the only existing ternary compound in the system. It is in equilibrium with Cu₂O, CuO, GeO₂, and oxygen of atmospheric pressure. Cu and Cu₂O may coexist with GeO₂. The standard Gibbs energy of formation of CuGeO₃ was found to be ΔG°_f (CuGeO₃) = ?424.5 kJ/mole at 900°C. The standard enthalpy and entropy of formation are ΔH⁰_f = ?756.8 kJ/mole and ΔS°_f = ?283 J/mole·K, respectively.     

Thermally stimulated processes in Eu-containing oxide films with silver and gold nanoparticles

The influence of the nature of the matrix on the properties of Eu-containing oxide films doped with silver and gold was studied by spectral-luminescent methods, X-ray diffraction, and electron microscopy as depending on the temperature of thermal treatment in air. The nature of the matrix was shown to determine the character of processes that occurred in GeO₂-Eu₂O₃-Ag-Au and Al₂O₃-Eu₂O₃-Ag-Au films and to substantially influence the properties of these films. The Ag⁺-Ag⁰-Au⁰ optical centers formed in films based on GeO₂ at 800°C; these centers effectively sensitized europium ion luminescence. In films based onAl₂O₃, silver was strongly bound by the matrix, and the effectiveness of the sensitization of europium ion luminescence decreased. Original Russian Text ? S.V. Vashchenko, Yu.V. Bokshits, A.P. Stupak, G.P. Shevchenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 528–533.     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. XXXIV. Das tetramere Silber(I)-Tri-tert-Butoxysilanthiolat

Contributions to the Chemistry of Silicon Sulfur Compounds. XXXIV. Tetrameric Silver(I)-tri-tert-butoxysilanethiolate Silver(I)-tri-tert-butoxysilanethiolate is formed as a tetramere by reaction of tritert-butoxysilanethiol with AgNO₃. The compound crystallizes as colourless triclinic plates and sublimes in vacuum at 170°C without decomposition. F.I. mass spectra shows only the mass of the tetrameric unit (m/e = 1 548), whereas this unit is observed in E.I. mass spectra with lower intensity. The ²⁹Si n.m.r. spectrum shows a remarkable splitting of the signal around ?68.54 ppm, which is explained by Si? Ag couplings. The central unit of the molecule is a nearly plane alternating Ag₄S₄ eight-membered ring with threefold bonded sulfur and twofold bonded silver atoms. Most important are the significant deviations from colinear S? Ag? S bonds (172.3°) resulting from shifts of the silver atoms toward the center of the eight-membered Ag₄S₄ ring (Ag? Ag = 313.5 pm). This effect is taken as a strong indication for high order direct Ag(I)-to-Ag(I) interactions. Related details of the structure are discussed. (Molecule symmetry is 2-C₂; space group P1 ; a = 1 769.7, b = 2012.8, c = 1 266.8 pm, α = 119.63°, β = 82.22°, γ = 95.08°; Z = 2; R = 0.067; 7 656 reflections h kl.)     

Untersuchung des Systems Silbertellurid-Silberchlorid

Investigation of the System Silver Telluride—Silver Chloride The system Ag₂Te? AgCl has been investigated by differential-thermal X-ray-phase, and micro-structural analysis within the concentration range from 0 to 100 mole-% silver telluride. Equilibrium samples were obtained by tempering for 480 hours at 330°C. The system silver telluride—silver chloride is of an eutectic type, with an eutectic point corresponding to 80 mole-% AgCl and 377°C. At 510°C and 33 mole-% AgCl, one observes the formation of a compound of a peritectic type with the probable composition Ag₅Te₂Cl.     

Ag2Pb8O7Cl4, Ein neues Blei(II)-oxidhalogenid mit Silber

Ag₂Pb₈O₇Cl₄, a New Member of Lead(II) Oxyhalides with Silver Ag₂Pb₈O₇Cl₄ is one among other products of the thermal decomposition of AgPb₄O₄Cl. Ag₂Pb₈O₇Cl₄ can be prepared directly by heating the binary components within a temperature range from 590°C to 620°C. The crystal structure was solved by single crystal X-ray methods. The compound crystallizes monoclinic with a = 12.411(4) Å, b = 17.99(3) Å, c = 14.785(4) Å, β = 147.01(2)°, Z = 4 with the space group P2₁/c. Ag₂Pb₈O₇Cl₄ shows remarkable structural features, e.g. silver tetrahedrally surrounded by chlorine.     

Kinetics of electrochemical reactions on the Ag(Hg)/Ag4RbI5 interface

The electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ interface is investigated by a potentiostatic pulse method. It is found that the rate-determining step of the electrode reaction is electron transfer with an exchange current density of 68 mA cm^–2 and a transfer coefficient of approximately 0.45. The order of the electrochemical reaction for silver oxidation is estimated from polarization investigations of silver amalgam in various concentrations. From this it is deduced that the mercury is ionized and is implanted in the electrolyte together with silver under anodic polarization: 15Ag+85Hg–100e^–→15Ag⁺+85Hg⁺. From comparison of the electrochemical behaviour of the Ag(Hg)/Ag₄RbI₅ and Ag/Ag₄RbI₅ interfaces it is concluded that the rate of anodic silver dissolution on the Ag/Ag₄RbI₅ interface is limited by crystallization effects. Electronic Publication     

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.     

Solid solubility and cation distribution in the system Co2GeO4Mg2GeO4

In the system Co₂GeO₄Mg₂GeO₄, solid solubilities in spinel and olivine structures were studied on samples prepared by solid state reaction at temperatures of 1000–1300°C. The solubility limits were determined from the identification by X-ray powder pattern and the change of the lattice constant of spinel with composition. The relation between temperature and the free energy difference ΔG° which was estimated from the solubility limits agreed qualitatively with the fact that the spinel phase of Mg₂GeO₄ is stable at low temperatures under atmospheric pressure. The spinels were also synthesized at 800°C under the pressure of 20 kb. Over the whole range of composition, the cation distribution was found to be normal with u = 0.375. Above 1000°C under 20 kb in the presence of water, the spinels, except Co₂GeO₄, were found to react with water to form enstatite and probably magnesium hydroxide in an amorphous state.     

Bis(4‐aminopyridine)silver(I) nitrate and tris(2,6‐diaminopyridine)silver(I) nitrate

The bis(4‐aminopyridine)silver(I) cation in [Ag(C₅H₆N₂)₂]NO₃ has the Ag atom on a twofold axis and displays an N—Ag—N angle of 174.43 (15)° and an Ag—N distance of 2.122 (3) Å. The two ligands are planar and the angle between the two ligand planes is 79.45 (9)°. The pyridine rings are stacked in piles with an interplanar distance of 3.614 (5) Å, a distance that strongly suggests that pyridine π–π interactions have an appreciable importance with respect to the non‐bonded crystal organization. The tris(2,6‐diaminopyridine)­silver(I) cation in [Ag(C₅H₇N₃)₃]NO₃ has Ag—N distances of 2.243 (2), 2.2613 (17) and 2.4278 (18) Å, and N—Ag—N angles of 114.33 (7), 134.91 (7) and 114.33 (7)°. The Ag⁺ ion is situated 0.1531 (2) Å from the plane defined by the three pyridine N atoms.