Crystallochemical Aspect of Phase Formation in the γ-FeOOH-H2O-NaOH System

Phase transition of metastable -FeOOH into -FeOOH and its chemical transformation into -Fe₂O₃ upon hydrothermal treatment in 0-5 M NaOH solutions at 100-230°C were studied. The regions of formation of the above phases were specified. The probable composition of the crystallizing complexes formed in the solutions and the reactions occurring at their incorporation into various atomically smooth faces of -FeOOH and -Fe₂O₃ were considered.     

The thermolysis of zinc bis(citrato)ferrate(III) dodecahydrate

The thermolysis of zinc bis(citrato)ferrate(III)dodehydrate has been investigated from ambient temperature to 600 °C using various physico-chemical techniques, i.e., simultaneous TG-DTG-DTA, XRD, Mössbauer and I.R. spectroscopy. After dehydration at 200 °C, the anhydrous complex undergoes oxidative decomposition to yield -Fe₂O₃ and ZnO at 350 °C. Subsequently, the cations remix to yield fine particles of zinc ferrite, ZnFe₂O₄ as a result of solid state reaction between -Fe₂O₃ and ZnO at a temperature (450 °C) much lower than for ceramic method.     

Mössbauer spectroscopic and X-ray diffraction study of the thermal decomposition of Fe(CH3COO)2 and FeOH(CH3COO)2

Thermal decomposition of iron(II) acetate, Fe(CH₃COO)₂, and iron(III) acetate hydroxide, FeOH(CH₃COO)₂, has been studied using⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction. Samples were thermally treated in air atmosphere between 150°C and 1000°C. The formation of maghemite '-Fe₂O₃, and hematite, -Fe₂O₃, is discussed. Hematite appears as the final decomposition product.     

Physico-chemical studies on thermal analyses of sodium hexa/carboxylato/ferrates/III/

The thermolysis of sodium hexa/benzoato/ferrate/III/, i. e. Na₃[Fe/C₆H₅COO/₆].4.5H₂O has been investigated at different temperatures in air using Mössbauer, infrared spectroscopic and derivatographic techniques /DTG, DTA, TG/. The thermal decomposition proceeds without the reduction of iron/III/. An increase in particle size of -Fe₂O₃ formed during thermolysis has been observed with increasing temperature. The end product, -NaFeO₂ is formed as a result of the solid state reaction between -Fe₂O₃ and sodium carbonate.     

Mössbauer study of the thermal decomposition of alkali dihydroxo tetrapropionato ferrates(III)

Thermal decomposition of alkali dihydroxo tetrapropionato ferrates(III), M₃[Fe(C₂H₅COO)₄(OH)₂]xH₂O (M=Li, Na, K) has been studied upto 973 K. The complexes were calcined isothermally at various temperatures i. e., 473, 573, 773 and 973 K. The intermediates/products have been characterized by Mössbauer, infrared spectroscopies and XRD powder diffraction. The anhydrous complexes directly decompose to give -Fe₂O₃ and alkali metal carbonate without undergoing reduction to iron(II) moiety. An increase in the particle size and internal magnetic field of -Fe₂O₃ has been observed with increasing decomposition temperature. At higher temperature (973 K) MFeO₂ is formed as the final thermolysis product due to a solid state reaction between -Fe₂O₃ and alkali metal carbonate.     

The unusual morphological structure of the aging products of coprecipitated Fe(III)-Al(III) hydroxides

Aluminum-substituted hematite ( ^*-Fe₂O₃) with an unusual morphological structure is formed upon the aging of coprecipitated Fe(III)-Al(III) hydroxides with excess Fe(III). The crystals of this hematite are found in separate layers and includes seams of an aluminum-containing phase. In samples with excess Al(III) content, the ^*-Fe₂O₃ crystals are found as seams in mixed aggregates of boehmite and ^*-Fe₂O₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 931–933, April, 1990.     

Mössbauer studies on thermal decomposition of some alkali tris (malonato) ferrate (III) tetrahydrates

Thermal decomposition of some alkali tris (malonato) ferrate (III) tetrahydrates, i. e. M₃ [Fe(CH₂C₂O₄)₃]·4H₂O (M=Na, K) has been studied in the temperature range of 433–973 K in static air atmosphere using Mössbauer, IR and TG-DTG-DTA techniques. Mössbauer spectra are reported at different stages to study the mechanism of decomposition. The anhydrous complex decomposed into -Fe₂O₃ of varying particle sizes and alkali metal malonate/carbonate in successive stages. In the final stage of remixing of cations, a solid state reaction between -Fe₂O₃ and alkali metal carbonate/oxide gives fine particles of the respective ferrites at temperatures lower than for oxalate precursor or even for ceramic method. Thermal stability obeys the order: sodium > potassium > lithium tris(malonato) ferrate (III).     

Mössbauer spectroscopic studies of thermal decomposition of substituted pentacyanoferrate(II) complexes

The thermal behaviour of substituted pentacyanoferrates(II) of the type Na₃[Fe(CN₅)L]·xH₂O, whereL=n-, sec-, tert- oriso-butylamine,di-iso-butylamine ortri-n-butylamine, was investigated with the aid of Mössbauer spectroscopy, XRD and TG-DTG-DTA. The Mössbauer spectra of these complexes exhibit a quadrupole doublet with E _Q=0.70–0.83 mm s^–1 at room temperature. The isomer shift, =0.00±0.03 mm s^–1 suggests that the iron atom is in the +2 low-spin state. The complexes start to decompose at 50°C, yielding a residual mass of 5.8 –21.3% in the temperature range 900–950°C. The Mössbauer spectra recorded after heating at 150 and 300°C exhibit an asymmetric doublet, suggesting partial decomposition. The Mössbauer spectra at higher temperature are complex. At different stages of the thermal process, the presence of -Fe₂O₃, -Fe₂O₃, -Fe, Fe₃C and Fe₃O₄ was demonstrated.On leave from A. N. College, Anandwan-442 914, IndiaWe are grateful to the Monbusho (Ministry of Education, Science, Sports and Culture) for the award of a fellowship to RBL and for financial assistance for the research work. Thanks are also due to Dr. T. Nakamoto for valuable cooperation.     

Triterpene glycosides of alfalfa. III. Medicoside I

On the basis of chemical transformations and with the aid of physicochemical results, the structure of glycoside I isolated from the roots of the plantMedicago sativa has been established as hederagin 3-O-[O--L-arabinopyranosyl-(1 2)--D-glucopyranosyl-(1 2)--L-arabinopyranoside] 28-O--D-glucopyranoside. Compound (I), C₅₂H₈₄O₂₂, mp 210–212°C, [] _D ²¹ +38.4° (c 1.48; methanol). Acid hydrolysis of (I) led to hederogenin (II) — C₃₀H₄₈O₄, mp 326–330°C, [] _D ²³ +84.2° (c 0.19; pyridine. The Hakomorimethylation of glycoside (I) yielded the permethylate (IV) — C₆₅H₁₁O₂₂ [] _D ²³ +41.6° (c 1.79; methanol). The GLC analysis of the products of the methanolysis of compound (IV) showed the presence of 3,4,6-tri-O-methyl-D-glucopyranose, 2,3,4,6-tetra-O-methyl-D-glucopyranose, 3,4-di-O-methyl-L-O-arabinopyranose, and 2,3,4-tri-o-methyl-L-arabinopyranose. The alkaline hydrolysis of glycoside I gave compound (III) with mp 230–233°C, [] _D ²¹ +35.2° (c 0.21; methanol), which was identified as medicoside C. Details of the PMR spectrum are given for compound (IV) and of the IR spectrum for compound (I).Institute of the Chemistry of Plant Substances of the Uzbek Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 607–610, September–October, 1986.     

M?ssbauer study of transformation mechanism of Fe cations in olivine after thermal treatments in air

The transformation mechanism of Fe cations in natural olivine after thermal treatments in air has been studied using mainly⁵⁷Fe Mössbauer spectroscopy. -Fe₂O₃ nanoparticles appear as the primary Fe³⁺ phase in Mössbauer spectra of olivine samples heated at 600-900 °C. These nanoparticles are thermally unstable and they are transformed to -Fe₂O₃ with the increase of heating time. Another transformation mechanism of iron related with the complete decomposition of olivine structure has been observed at temperatures of 1000 °C and higher. The mixed oxide MgFe₂O₄ with the spinel structure and enstatite MgSiO₃ were identified as iron-bearing decomposition products.     

Mössbauer study on thermal decomposition of cesium tris(oxalato) ferrate(III) dihydrate

The thermal decomposition of cesium tris(oxalato) ferrate(III) dihydrate, Cs₃ Fe(ox)₃ 2H₂O has been studied at various temperatures in air, employing Mössbauer and infrared spectroscopies, and thermogravimetric methods. The complex undergoes reduction to an iron(II) intermediate at 473 K. The particle size of -Fe₂O₃ formed during thermolysis increases with increasing decomposition temperature. Finally, a solid state reaction between -Fe₂O₃ and cesium carbonate/oxide occurs, leading to the formation of fine particles of cesium ferrite (CsFeO₂).     

Structure of the X-ray emission CuLα-line in YBa2Cu3O7−δ and CuO based on the SCFXα-SW calculation

Using the SCF X-SW method we have calculated the final states of the X-ray L-transition of the CuO ₄ ^–6 cluster modeling the nearest environment of the copper atom (one of two types) in YBa₂Cu₃O_7- and the nearest environment of copper in CuO. The energies of transitions forming the L-spectrum (with or without many-electron excitations) have been calculated. It has been shown that for interpretation of the main singularities of the X-ray emission L-spectrum, not only should the Coster-Kronig transitions be considered but also the shake-up excitation 2b_1g3b_1g processes and the multiple ionization satellites 3p^–1. An experimental schame has been suggested that allows separation of the effects of different many-electron processes on the L-spectrum.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 3–9, July–August, 1993.Translated by L. Smolina     

Withasteroids ofPhysalis VI.1H and13C NMR spectra of withasteroids ixocarpalactone A and ixocarpanolide

The¹H and¹³C NMR spectra of two withasteroids isolated fromPhysalis ixocarpa Brot. have been studied in detail. Their spectral characteristics are discussed. A comparison of the results obtained has led to the identification of a withasteroid with the composition C₂₈H₄₀O₈, mp 291–292°C (from methanol) as ixocarpalactone A, in spite of some difference in its physical constants. The other compound, with mp 252–253°C (from methanol), had the composition C₂₈H₄₀O₆, [] _D ²⁰ +27±4°, is new and has been called ixocarpanolide. The structure of 5,20R-dihydroxy-1-oxo-6, 7-epoxy-22R-witha-2-enolide has been proposed for it.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 326–332, May–June, 1986.     

Preparation of carrier-free111mCd and105,106mAg and their chemical behavior

It was found that not only^111mCd but also¹⁰⁵Ag and^106mAg sublimate at 1050 °C under a reduced pressure from Pd foils irradiated with -particles. The sublimation method has enabled rapid separation of the isotopes and repeated use of valuable Pd foils. Adsorption onte -Fe₂O₃ and coprecipitation with ferric hydroxide were studied by using radioactive tracers.     

Hard magnetic ferrites with high coercive field

The solid-state reaction between SrCO₃ and -FeOOH was investigated by means of thermal analysis, X-ray diffraction, electron microscopy and magnetic measurements. The high reactivity of this mixture is discussed in comparison with that of the mixture of SrCO₃ and -Fe₂O₃.     

Physico-chemical studies on thermal analysis of cobalt hexa(formato)ferrate(III) decahydrate

Thermal decomposition of cobalt hexa(formato)ferrate(III) decahydrate, Co₃[Fe(HCOO)₆]₂. 10H₂O, has been studied up to 973 K in static air atmosphere, employing TG, DTG, DSC, XRD, ESR, Mössbauer and infrared spectroscopic techniques. Dehydration occurs in two stages in the temperature range of 340–430 K. Immediately after the removal of the last water molecule the anhydrous complex undergoes decomposition till -Fe₂O₃ and cobalt carbonate are formed at 588 K. In the final stage of remixing of cations, a solid state reaction between -Fe₂O₃ and cobalt carbonate leads to the formation of CoFe₂O₄ at a temperature (953 K) much lower than for the ceramic method. A saturation magnetization value of 2310 Gauss of ferrite (CoFe₂O₄) shows its potential to function at high frequencies.     

Kinetics of thermal decomposition of barium zirconyl oxalate

Kinetics of the thermal decomposition of anhydrous barium zirconyl oxalate and a carbonate intermediate have been studied. Decomposition of the anhydrous oxalate, though it could be explained based on a contracting-cube model, is quite complex. Kinetics of decomposition of the intermediate carbonate Ba₂Zr₂O₅CO₃ is greatly influenced by thermal effects during its formation. (-t) curves are sigmoidal and obey a power law equation followed by first order decay. Presence of carbon in the vacuum-prepared carbonate has a strong deactivating effect. Decomposition of the carbonate is accompanied by growth in particle size of the product barium zirconate.

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Die Kinetik der thermischen Zersetzung von Barium-zirkonyl-oxalat

Zusammenfassung Es wurde die thermische Zersetzung von wasserfreiem Barium-zirkonyl-oxalat und dem intermediären Karbonat untersucht. Die Zersetzung des wasserfreien Oxalates ist — obwohl über das contracting-cube-Modell erklärbar — sehr komplex. Die Kinetik der Zersetzung des intermediären Karbonates Ba₂Zr₂O₅CO₃ ist stark von den thermischen Effekten während seiner Bildung abhängig. Die (-t)-Kurven gehorchen einem exponentiellen Gesetz, gefolgt von einem Zerfall erster Ordnung. Die Gegenwart von Kohlenstoff im Karbonat hat einen starken desaktivierenden Effekt. Die Zersetzung des Karbonats wird von einem Wachstum der Partikelgröße des Produktes (Bariumzirkonat) begleitet.

     

Cardiac glycosides ofAcokanthera venenata

Six cardenolides have been isolated from the leaves ofAcokanthera venenata G. Don: AV-1, mp 252–255°C, [] _D ²⁰ +39.4° (MeOH); AV-2, mp 199–208°C, [] _D ²⁰ -59.3° (MeOH); AV-3, mp 269–275°C/300–304°C, [] _D ²¹ –69.8° (MeOH); AV-4, mp 279–289°C; AV-5, mp 222–225°, [] _D ²⁰ -64.3° (MeOH); and AV-6, mp 193–196°C [] _D ²⁰ –23.8° (MeOH — CHCl₃). AV-5 has been identified as acovenoside A. AV-3 is a new cardiac glycoside: it is 1-acetoxy-3-(4-O--D-glucosyl-3-O-methyl--L-talomethylosyloxy)-14-hydroxy-5, 14-card-20(22)-enolide (glucoacovenoside B).Khar'kov State Pharmaceutical Institute. All-Union Scientific Research Institute of Drug, Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 372–376, May–June, 1987.     

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.