Das Stabilitätsfeld des Calcium-Langbeinits

The Stability of the “Calcium-Langbeinit” Structure The Stability of the Calcium-Langbeinit structure K₂Ca₂(SO₄)₃ was investigated by exchanging the potassium ion by other alkali metals. It could be shown, that there exist compounds with 40 mol% sodium, 50 mol% rubidium, and 10 mol% cesium. These compounds convert at elevated temperature into a cubic structure of Langbeinit-type. Unit cell constants of the orthorhombic phases and of the cubic modifications are given.     

Thermophysics of alkali and related azides II. Heat capacities of potassium,rubidium, cesium,and thallium azides from 5 to 350 K

The heat capacities of potassium, rubidium, cesium, and thallium azides were determined from 5 to 350 K by adiabatic calorimetry. Although the alkali-metal azides studied in this work exhibited no thermal anomalies over the temperature range studied, thallium azide has a bifurcated anomaly with two maxima at (233.0±0.1) K and (242.04±0.02) K. The associated excess entropy was 0.90 cal_th K^?1 mol^?1. The thermal properties of the azides and the corresponding structurally similar hydrogen difluorides are nearly identical. Both have linear symmetrical anions. However, thallium azide shows a solid-solid phase transition not exhibited by thallium hydrogen difluoride. At 298.15 K the values of C_p^o, S^o, and $\text{?{G}{}^{\mathrm{o}}\text{(T)?H}{}^{\mathrm{o}}\text{(0)}}\text{T}$, respectively, are 18.38, 24.86, and 12.676 cal_th K^?1 mol^?1 for potassium azide; 19.09, 28.78, and 15.58 cal_th K^?1 mol^?1 for rubidium azide; 19.89, 32.11, and 18.17 cal_th K^?1 mol^?1 for cesium azide; and 19.26, 32.09, and 18.69 cal_th K^?1 mol^?1 for thallium azide. Heat capacities at constant volume for KN₃ were deduced from infrared and Raman data.     

Possible explanation of unstable superconducting phase in KxC60 with Tc=21 K

EPR and MMMA methods revealed two K₃C₆₀ phases, the unstable one with T_c=21.0 K containing C¹⁻₆₀ centers and a stable one with T_c=18.0 K constituting of C₆₀ molecules in the form of C³⁻₆₀ ions. The metastable phase appears only in the first stage of potassium intercalation of fullerene at the C₆₀/K₃C₆₀ phase boundary. This phase is being transformed to a stable one on further doping to K₃C₆₀. The appearance of a metastable phase is related to the instability of the fullerene C₆₀ fcc structure during the process of octahedral sites being filled by potassium ions. The critical temperature T_c shift upwards from 18.5 to 21.0 K is ascribed to the possible process of potassium transient back charge transfer valency, i.e. K₃¹⁺C₆₀³⁻↔K₂¹⁺K¹⁻C₆₀¹⁻ [3K¹⁺+C³⁻₆₀⇔2K¹⁺+K¹⁻+C₆₀¹⁻], which could enlarge the unit cell necessary to shift a superconducting critical temerature according to T_c on volume dependence.     

Highly conducting solid electrolytes based on poly (ethylene oxide-co-propylene oxide)

The conducting properties of solid electrolytes comprising random poly(ethylene oxide-co-propylene oxide) (of 84 : 16 monomer units mole ratio) and lithium, sodium, potassium, cesium, and rubidium salts have been studied. The systems containing some lithium or sodium salts achieved conductivity levels as high as 10^?5–10^?4 S/cm at ambient temperature and greater than 10^?3 S/cm at 100°C. However, the systems with rubidium and cesium salts exhibit conductivities a few orders of magnitude smaller. DSC studies show that the electrolytes studied are characterized by a high content of an amorphous phase (95–100%). It is suggested that the copolymer exhibits lower complexing abilities than that of poly(ethylene oxide), which results in a higher flexibility of electrolytes containing small cations and poor dissociation of the salts having large cations. © 1995 John Wiley & Sons, Inc.     

Investigation on the interaction on and the rotation of C60 in alkali-doped complexes AXA′3-XC60 (X = 1, 2, 3; A,A′ = alkali)

The interaction on and the rotation of C₆₀ in akali-doped C₆₀ solids, A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = alkali), have been calculated with Buckingham potential model. The results show that the total interaction on C₆₀ changes dramatically when the pure C₆₀ solid is alkali-doped into K₃C₆₀. The interaction on C₆₀ in K₃C₆₀ is about 20 times greater than that in pure C₆₀. And the main component in the former, occupying > 90% is electrostatic, while in the latter, the main components, occupying > 90%, are dispersive and repulsive. The results also show that in contrast to the whole-region free rapid rotation of C₆₀ molecule in its pure solid, the rotation of C₆₀ in K₃C₆₀ is mostly forbidden due to a 10 times increase (reaching about 300 kJ/mol) in potential barrier, except for the region from 0° to 50° where a broad, smooth, and shallow potential well exists. Calculations for alkali-doped complexes other than K₃C₆₀, i.e., A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs), come to the same conclusion. Finally, an interesting and meaningful result is that the superconducting transition temperatures of A_XA′_3-XC₆₀ (X = 1, 2, 3; A, A′ = K, Rb, Cs) change inversely with the total interactions on C₆₀. © 1995 John Wiley & Sons, Inc.     

Thermochemical study of gaseous salts of oxygen-containing acids: XXVII. Antimonites of alkali metals

Vaporization of sodium, potassium, rubidium, and cesium antimonates was studied. Vapors above the studied antimonates contain dimeric (MSbO₂)₂ molecules in addition to monomeric antimonites MSbO₂. Standard enthalpies of formation of these gaseous molecules were determined.     

Hydrothermal extraction of potassium,sodium, rubidium and cesium from rocks by lithium hydroxide and determination at very low natural levels

The selective extraction of Na, K, Rb and Cs from rocks is described. The method is particularly designed for low levels of rubidium and cesium in basic and ultrabasic rocks. The rocks are decomposed with lithium hydroxide solution at 180°C. Only part of the aluminium and chromium accompany the alkali metals into solution; all other rock constitutents are left behind as insoluble lithium silicate, hydroxides of divalent metals, etc. Concentration of rubidium and cesium too low to be determined directly by flame emission spectrometry are pre-concentrated up to 25-fold by liquid-liquid extraction. Quantitative recovery (>99.5%) of the two metals is achieved by coprecipitation with potassium tetraphenylboron within the organic phase (di-isobutyl ketone) for subsequent back-extraction and dissolution in an acidic aqueous phase. Detection limits are 1 mg kg^?1 Na or K, 0.1 mg kg^?1 Rb and 0.05 mg kg^?1 Cs in the rock for the direct determination and 0.003 mg kg^?1 Rb and 0.001 mg kg^?1 Cs after preconcentration. Methods are described for the purification of lithium hydroxide and the potassium nitrate used as carrier. Results are presented for the Na₂ O, K₂O, Rb and Cs contents and the K/Rb values for 23 geochemical references samples (basic and ultrabasic rocks, and iron formation samples).     

Potassium Cationic Conduction in K3 – xP1 – xExO4 (E = S,Cr, Mo,W)

Solid solutions of cubic structure based on K₃PO₄are synthesized in the systems K_{3 – x} P_{1 – x} E _x O₄(E = S, Cr, Mo, W). Approximate boundaries of single-phase regions and the temperature and concentration dependences of electroconductivity are studied. The transport numbers, measured by a modified Tubandt method, confirm a potassium cationic character of conduction. Electric parameters of the electrolytes are compared with those of sodium and rubidium conducting solid solutions in similar systems. Factors that affect transport properties of synthesized phases are discussed.     

Syntheses and Characterization of 1,4‐Phenylenebisphosphonates,A[HO3PC6H4PO3H2] (A = Li,K, Rb,Cs, Tl,Ag and NH4) and Crystal Structure of 1,4‐Phenylenebisphosphonic Acid

Seven 1,4‐phenylenebisphosphonates of monovalent ions, A(HO₃PC₆H₄PO₃H₂) (A = Li, K, Rb, Cs, Tl, Ag and NH₄), were synthesized and characterized by single‐crystal X‐ray diffraction, spectroscopic and thermal methods. These compounds and the reported sodium analogue have four structure types. The sodium compound, one‐dimensional lithium compound and pillared‐layered cesium compounds have different structure types, whereas the potassium, rubidium, thallium, ammonium and silver compounds have a pillared ladder‐like structure. They undergo initial thermal decomposition in the range of 120–270 °C. Moreover, the single crystal X‐ray structure of 1,4‐phenylenebisphosphonic acid was determined.     

Solubilities, Densities and Refractive Indices of Rubidium Chloride or Cesium Chloride in Ethanol Aqueous Solutions at Different Temperatures

The data of solubilities, densities and refractive indices of rubidium chloride or cesium chloride in the system CEHsOH-H2O were measured by using a simple accurate analytical method at different temperatures, with mass fractions of ethanol in the range of 0 to 1.0. In all cases, the presence of ethanol significantly reduced the solubility of rubidium chloride and cesium chloride in aqueous solution. The solubilities of the saturated solutions were fitted via polynomial equations as a function of the mass fraction of ethanol. The CsC1-C2H5OH-H2O ternary system appeared in two liquid phases： alcoholic phase and water phase, when the mass fractions of ethanol were in the range of 10.37% to 49.59% at 35 ℃. Density and refractive index were also determined for the same ternary systems with varied unsaturated salt concentrations. Values for both experiment and theory were correlated with the salt concentrations and proportions of alcohol in the solutions. The equations proposed could also account for the saturated solutions.     

Electronic structure of C84 and KxC84: Comparison to C60 and graphite

X ray photoemission spectra show ～10 valence band features in C₆₀ and C₈₄ films, although they are less distinct in C₈₄ because of the increased number of valence electrons and the decreased molecular symmetry. The presence of inequivalent carbon atoms in C₈₄ is reflected by the fact that the C 1s main line is ～0.2 eV wider than in C₆₀. The C 1s satellite region of C₈₄ exhibits four features within 15 eV of the main line and shows that the HOMO-LUMO π-π* excitation energy of C₈₄ is ～0.5 eV smaller than in C₆₀. Potassium 2p spectra for K-doped C₈₄ films suggest the formation of a phase with composition K₃C₈₄ with two spectroscopically-distinguishable K sites. A new spectral feature emerges when the K content is increased beyond K₃C₈₄, suggesting a phase transition and a saturated composition of K₆C₈₄, as for K_xC₆₀. These similarities are intriguing since K_xC₈₄ is insulating for all x while K₃C₆₀ is metallic and superconducting.     

Electroreduction of Oxalate Complexes of Ruthenium(III) on a Dropping Mercury Electrode: Effect of Alkali Metal Cations and Solution Acidity

It is established that the reaction of recharging trioxalate complexes of ruthenium(III) occurs in the case of solutions with excess supporting oxalate salts of alkali metals K⁺, Na⁺, and Cs⁺ in reversible conditions, and limiting recharge currents are caused by diffusion. At the same time, values of diffusion coefficients for complex anion [Ru(C₂O₄)₃]^–3 decrease by almost two times upon going from potassium to sodium and cesium electrolytes. Substantial differences in the limiting currents in solutions containing excess amounts of the above salts are explained by the formation, at least in the case of cesium and sodium electrolytes, of ionic associates whose reduction rate at a fixed potential is lower than that of nonassociated anion [Ru(C₂O₄)₃]^–3. With solution dilution by supporting salts, transition is observed from reversible recharge conditions to absolutely irreversible conditions and a change in the above sequence of the effect of supporting cations on the recharge rate; at a fixed potential, the process decelerates in the series Cs⁺ > K⁺ > Na⁺. The reduction wave of the ruthenium(II) oxalate complexes in solutions with excess supporting electrolyte happens to depend on pH and, probably, is determined by simultaneous formation of adsorbed atoms of hydrogen (or ruthenium hydride) on atoms of ruthenium(0).     

Isomorphism in Alkali Metal Uranophosphates APUO6 · nH2O

A possibility for the isomorphous substitution of sodium, potassium, and rubidium ions for hydroxonium ion in uranophosphoric acid HPUO₆ · 4H₂O was found, and characteristics of the process were estimated. These solid solutions can be described by the regular model. The lithium and cesium derivatives do not form solid solutions with the hydroxonium derivatives.     

Indirect complexometric titration of potassium,rubidium, cesium,thallium and ammonium

A titrimetric method using EDTA for the determination of potassium, rubidium, cesium, thallium and ammonium has been developed. These cations are precipitated as M₂Ag[Co(NO₂)₆] and the blue cobalt thiocyanate complex in acetone-water mixed system is titrated with EDTA. Milligram quantities have been determined in the present work     

Kinetics of solid-phase H<Superscript>+</Superscript>/M<Superscript>+</Superscript> ion exchange on hafnium hydrogen phosphate

The kinetics of solid-phase reactions between hafnium hydrogen phosphate and alkali metal chlorides were studied by thermogravimetry with subsequent analysis of leaving gases. For sodium and potassium chlorides, the reaction occurs in two stages; the first stages produces MHHf(PO₄)₂, and the second yields the MHf₂(PO₄)₃ NASICON phosphate. For rubidium chloride, the reaction is one stage and produces Rb₂Hf(PO₄)₂. For cesium chloride, the reaction is an analogue of the reaction for rubidium chloride, but has two stages. Kinetic data were used to determine interdiffusion coefficients for hydrogen and alkali-metal ions at various temperatures and the activation energies of interdiffusion.     

Potassium hydrogen trans‐glutaconate monohydrate at 295, 245 and 40 K,and its rubidium analogue at 298 K

A centrosymmetric and short O—H?O hydrogen bond was found in isomorphic crystals of potassium hydrogen trans‐glutaconate monohydrate (potassium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, K⁺·C₅H₅O₄^?·H₂O), (I), and rubidium hydrogen trans‐glutaconate monohydrate (rubidium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, Rb⁺·C₅H₅O₄^?·H₂O), (II). The O?O distance at room temperature is 2.444 (3) Å in (I), and 2.417 (4) Å in (II). The O?O distance for (I) showed no significant decrease at low temperatures.     

Fullerides: heterometallic superconductors with composition M<Subscript>2</Subscript>M′C<Subscript>60</Subscript> (M = K,Rb; M′ = Yb,Lu, Sc)

One- or two-step reactions of potassium and rubidium fullerides with composition M_k C₆₀ (M = K, Rb; k = 3—6) and K₆C₆₀ + m K mixtures (m = 1, 3) with anhydrous salts MCl₃ (M = La, Pr, Nd, Sm, Gd, Tb, Yb, Lu, Y, Sc) and YbI₂ in a toluene—THF medium afforded heterometallic fullerides M_3–nM_nC₆₀ (n = 1—3). Among these compounds, substituted fullerides with composition M₂MC₆₀ (M = Yb, Lu, Sc) display superconducting properties with critical temperatures of 14—20 K.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1623–1628, August, 2004.     

FIA Potentiometric and Solvent Extraction Studies of Alkali Metal and Alkaline Earth Cation Complexation by bis(Tert-butylbenzo)-21-crown-7

Abstract

A flow injection analysis study of the potentiometric selectivity of bis[4(5)-tert-butylbenzo]-21-crown-7 (D(tBB)21C7) for cesium over the other alkali metal cations and three alkaline earth cations has been conducted. A PVC matrix membrane containing D(tBB)21C7 as an ionophore was coated on the tip of a silver wire incorporated in a flow cell. No selectivity for cesium over rubidium and only low selectivity over potassium were noted. However, very high selectivities for cesium over sodium, lithium, strontium, calcium, and magnesium were observed. Selectivity of D(tBB)21C7 in the solvent extraction of alkali metal cations was determined by the picrate extraction method. The percent extraction into deuteriochloroform decreased in the order cesium, rubidium > potassium » sodium » lithium. Thus good agreement was observed between the responses of D(tBB)21C7 towards alkali metal cations in polymeric membrane electrodes and in solvent extraction.     

The effect of the synthesis method on the parameters of pore structure and selectivity of ferrocyanide sorbents based on natural minerals

Ferrocyanide sorbents were obtained via thin-layer and surface modification of natural clinoptilolite and marl. The effect of modification method on surface characteristics of these sorbents and their selectivity for cesium was studied. It was shown that the modification resulted in an increase of selectivity of modified ferrocyanide sorbents to cesium as compared with the natural clinoptilolite in presence of Na⁺, as well as in an increase of cesium distribution coefficients in presence of K⁺. The nickel–potassium ferrocyanide based on the clinoptilolite showed the highest selectivity for cesium at sodium concentrations of 10^?4—2 mol L^?1: cesium distribution coefficient was lg K _d = 4.5 ± 0.4 L kg^?1 and cesium/sodium separation factor was α(Cs/Na) = 250. In the presence of NH₄ ⁺, all modified sorbents showed approximately equal selectivity for ¹³⁷Cs. Probable applications of the sorbents were suggested.     

Author index for volume 52

Dehydrated samples of zeolite Y containing alkali-metal cations have been reacted with alkali-metal vapor in sealed silica tubes, and the products studied by electron-spin resonance (ESR) spectroscopy. Two distinct species were detected following the reaction of sodium-exchanged zeolite Y with sodium, potassium, or rubidium vapor. Exposure to a low concentration of metal vapor resulted in brightly colored samples with ESR signals characteristic of a stable ionic cluster species Na³⁺₄, in which an unpaired electron is trapped on four equivalent sodium cations in the sodalite cages of the zeolite. Exposure to higher concentrations of metal vapor resulted in dark-colored samples with ESR signals characteristic of small metallic particles located inside the zeolite cavities. A similar ionic cluster species K³⁺₄ was detected following the reaction of potassium-exchanged zeolite Y with sodium or potassium vapor although the potassium cluster was less stable than its sodium counterpart and an ESR signal from small metallic particles was observed at the same time. The corresponding Rb³⁺₄ ionic cluster species was not detected following the reaction of rubidium-exchanged zeolite Y with rubidium vapor; only an ESR signal from small metallic particles was observed. The narrow linewidths of the ESR signals from the small metallic particles suggest an inhibition of the spin-relaxation mechanisms in the bulk metals.