Molecular copper centers in potassium tantalate crystals

ESR spectra with resolved hyperfine and superhyperfine structures have been recorded in the 3-cm range at 4.2–800 K for copper-doped KTaO₃ crystals. The axial centers have three orientations. The principal values have been determined for the g tensor and for the hyperfine and superhyperfine interactions tensors. The g factor is explained in a simple crystalline-field model incorporating covalency effects. An MO LCAO model is used to interpret the hyperfine structure and to determine the bond covalencies along the axis of the CuO ₄ ^2– molecular centers and also for bonds perpendicular to that axis. The numbers of lines and the magnitudes and angle dependences for the superhyperfine splittings reveal details in the molecular structure of these centers. The scope for interpreting the results in terms of Jahn-Teller centers is discussed. The measurements do not indicate features characteristic of Jahn-Teller centers, so preference is given to the molecular-center model.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 562–568, September–October, 1988.     

Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals

Single crystals of KNbO₃ (KN), KTaO₃ (KT), and KTa_1−xNb_xO₃ (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 °C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date.     

The low temperature thermal properties of potassium tantalate niobate crystal

The thermal properties of KTN crystal were investigated at low temperatures by DSC and TM. The phase transition enthalpies and the average specific heats of the crystal were measured. Results are analyzed and discussed.     

Anharmonic metastable charge transfer vibronic exciton in potassium tantalate

This study provides an experimental evidence of a non-linear state of charge transfer vibronic excitons (CTVE) and its well-defined metastable behaviors in KTaO₃. An IR source could induce the same green CTVE-recombination luminescence band as that by a UV pumping. This up-conversion luminescence is characterized by a relaxation time τ (τ  60 s at 3 K), and theoretically explained as a result of IR-induced transfer of occupation of a metastable anharmonic CTVE state into a harmonic luminescent CTVE state. The observed temperature dependence of τsuggests that the relaxation is controlled by resonant and phonon-induced tunneling processes.     

Investigation on the formation of potassium trimolybdate via thermal decomposition of a new oxomolybdenum(VI) oxalato complex

The complex K₄(NH₄)₂ [Mo₆O₁₅(C₂O₄)₆(H₂O)₄] (PAMO) was prepared and characterized on the basis of chemical analysis and IR spectral data. Its thermal decomposition was studied by using TG and DTA techniques. PAMO loses its water between 190 and 225°C followed by the decomposition of anhydrous PAMO, which takes place in three stages. The first two stages occur in the temperature ranges 225–245°C and 245–270°C, to give the intermediates with tentative compositions K₁₂(NH₄)₂ [Mo₁₈O₄₅(CO₃)₄(C₂O₄)₁₂ and K₁₂[Mo₁₈O₅₄(CO₃)₂(C₂O₄)₄] respectively, the latter then decomposing in the third stage between 270 and 335°C to give the end product, potassium trimolybadate (K₂Mo₃O₁₀). The end product was characterized by chemical analysis, IR spectral and X-ray studies.

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Zusammenfassung Die Komplexverbindung K₄(NH₄)₂[Mo₆O₁₅(C₂O₄)₆(H₂O)₄] (PAMO) wurde hergestellt und auf der Basis von chemischer Analyse und IR-Spektrum characterisiert. Mittels TG und DT Techniken wurde die thermische Zersetzung untersucht. Zwischen 190 und 225°C gibt PAMO alles Wasser ab, anschlieend erfolgt in drei Schritten eineZersetzung des dehydratierten PAMO. Die ersten zwei Schritte verlaufen in den Temperaturbereichen 225–245°C bzw. 245–270°C und liefern Zwischenprodukte der Zusammensetzung K₁₂(NH₄)₂[Mo₁₈O₄₅(CO₃)₄(C₂O₄)₁₂] bzw. K₁₂[Mo₁₈O₅₄(CO₃)₂(C₂O₄]. Letzteres zerfällt dann in einem dritten Schritt zwischen 270 und 335° C und liefert Kaliumtrimolybdat (K₂Mo₃O₁₀) als Endprodukt, welches mittels Elementaranalyse, IR- und Röntgendiffraktionsuntersuchungen

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The authors are thankful to Dr. M. C. Jain, Head of the Department and professor L. N. Mittal, Principal of the Institution for providing the research facilities. One of the authors (S. P. G.) is also thankful to U. G. C. for providing financial assistance.     

Investigation of the complex formation of technetium with thiourea by spectrophotometry and electromigration

TcO ₄ ^– is reduced by thiourea /tu/ to Tc/III/ in 6N HCl. By capillar electrophoresis three different cations have been identified with electrophoretic mobilities of u=/4.3–4.8/x10^–4 u=/3.2–3.8/x10^–4, and u=/2.2–2.8/x10^–4 cm² v^–1s^–1. These species were assigned to complex cations [Tc/tu/₆]³⁺, [Tc/tu/₅Cl]²⁺, and [Tc/tu/₄Cl₂]⁺, respectively. [Tc/tu/₆]³⁺ was identified by spectrophotometry according to recently published data. [Tc/tu/₅Cl]²⁺ was isolated and chemically characterized. The formation of the monovalent cation [Tc/tu/₅Cl₂]⁺ was concluded from spectrophotometrical measurements.     

Fabrication of potassium tantalate films by hydrothermal electrochemical method at low temperature

Potassium tantalate was formed to pyrochlore structures on the tantalum substrate by hydrothermal or electrochemical method. In synthesizing process of potassium tantalate, a crystal structure of the substrate surface seemed to be an important factor. Potassium tantalate was synthesized with a simple equipment only, low temperature of 323 K or over, low concentration of 2–4 mol per liter potassium hydroxide aqueous solution and short time.     

Complex formation of univalent cations in acetonitrile with other solvents. Study of potassium ion complex formation with a cation-sensitive glass electrode

The formation constants of the complexes formed between potassium ion and other solvents in acetonitrile have been obtained potentiometrically by using a univalent cation-sensitive glass electrode. The formation constants of the mono-complexed potassium ions were 1.5 with dimethylformamide, 2.0 with dimethylacetamide, 2.4 with N-methylpyrrolidone, 2.8 with N-methylformamide, 2.9 with dimethyl sulfoxide, and 6.9 with hexamethylphosphoramide. Within the concentration ranges of the solvents studied (0.35–0.7 M for different solvents), only up to 1:2 K⁺: solvent species were detected, in contrast to the results for other univalent cations. Rubidium ion could not be studied effectively because of unsatisfactory response of the glass electrode. The complex formation constants of various univalent cations in acetonitrile with other solvents are summarized and discussed in detail.     

Investigation of the complex formation of plutonium(VI) with 2-thenoyltrifluoroacetone by solvent extraction

The co-ordination of plutonyl ions with 2-thenoyltrifluoroacetone (HTTA) has been investigated by distribution studies of²³⁹Pu between benzene and aqueous perchlorate medium at 25°C in order to understand the nature of the extracted species and their stability. The formation constants of the first and second complexes have been evaluated by Rydberg's graphical method as well as by least squares analysis of the distribution data using a computer programme. The overall formation constant (β₂) for Pu(VI)-HTTA system has been found to be of the order of 10¹².     

Investigation on the complex of diperoxovanadate with picolinamide

A novel diperoxovanadate complex NH₄[OV(O₂)₂(picolinamide)]·H₂O was synthesized from aqueous solution under physiological conditions. The solution structure of the complex was characterized by multinuclear (¹H, ¹³C, ¹⁴N, and ⁵¹V), variable temperature as well as two-dimensional (DOSY) NMR techniques in the interaction system of NH₄VO₃/H₂O₂/picolinamide at room temperature. The crystal structure of the complex was determined at 223 K by single-crystal X-ray diffraction method. It belongs to the monoclinic space group P21/c with a = 7.323(3) Å, b = 14.255(7) Å, c = 10.022(5) Å, β = 99.524(9)°, V = 1031.7(8) Å³, and Z = 4. The crystal is composed of ammonium ions, picolinamide oxodiperoxovanadate(V) ions, and water molecules, which are held together by ionic and hydrogen bond forces. The species [OV(O₂)₂(picolinamide)]⁻ is seven-coordinated with a distorted pentagonal bipyramidal geometry both in solution and in crystal.     

Analytical applications of complex formation in non-aqueous solutions-I: complexes of bismuth(III) with potassium diphenyldiselenophosphate in organic solvents

Complex formation between bismuth(III) chloride and potassium diphenyldiselenophosphate has been studied spectrophotometrically in acetronitrile, dimethylformamide, acetone, methanol, ethanol and dimethylsulphoxide media. Increased solvation ability is found to shift the maximum absorption band of the complex to longer wavelengths and there is a correlation between the stability constants and the solvent donor strength. Spectrophotometric methods for bismuth(III) determination are proposed, in methanol, ethanol and acetonitrile as media.