The hydrothermal decomposition of aluminum fluoride trihydrate. Kinetics and mechanism

The hydrothermal decomposition of AlF₃.3H₂O in water suspension was investigated by chemical and X-ray analyses at temperatures ranging from 114 to ca. 143°C. It was found that this process runs from a trihydrate to a monohydrate composition according to a zero order rate equation to give subsequently Al(OH,F)₃.H₂O and β -AlF₃.H₂O direct from solution and α -AlF₃.H₂O by conversion of solid trihydrate. Reactions involved in the process are discussed in detail.     

High temperature crystallization of aluminum fluoride. Course,hydrolysis, solid phases.

A study for AlF₃ crystallization from water solution was performed in the temperature range 100 to 200°C.Four solid phases were found to be precipitated, AlF₃.3H₂O (up to ca.120°C, cubic α-AlF₃.H₂O (decomposition of AlF₃.3H₂O in suspension), hexagonal β -AlF₃.H₂O (direct from solution) and the hydroxyfluoride Al(OH,F)₃.H₂O with an F/Al ratio of ca. 2.5 (hydrolysis of AlF₃). The extent of hydrolysis was established as a function of the initial AlF₃ concentration.X-ray diffraction and thermogravimetric data for the monohydrates were given and differences between the two indicated.     

PMR study of Cd(II) complexes with 2,2′-bipyridine

The NMR method has been used to study the structure of the complexes [Cd(bipy)]SO₄.4H₂O, [Cd(bipy)](NO₃)₂.2H₂O, [Cd(bipy)₂](NO₃)₂.$\text{1}\text{2}$H₂O and [Cd(bipy)₃](NO₃)₂.7H₂O. The influence of the central ion and of diamagnetic currents of the rings in these complexes on the PMR spectrum has been investigated. In the complexes [Cd(bipy)](NO₃)₂.2H₂O and [Cd(bipy)]SO₄.4H₂O two kinds of hydration isomers, with different PMR spectra, have been obtained.     

The reaction of alf3 solution with aluminium hydroxide and some reactions of the aluminium hydroxyfluoride obtained

AlF₃ solution (150 g/l) reacts with Al(OH)₃ in the m.ratio 2:1 in excess of ca. 115°C to produce Al(OH,F)₃.H₂O with an F/Al at. ratio > 2. At lower temperatures, e.g. 110°C, or at higher reactants ratios, e.g. 3-11, formation of Al(OH,F)₃.H₂O may be accompanied by crystallization of AlF₃-hydrates as AlF₃.3H₂O and/or /gb-AlF₃.H₂O. When crystallization of β - AlF₃.H₂O occurs to a greater extent, Al(OH,F)₃.H₂O may vary in its F/Al at.ratio from ca. 2.5 to 1, during the reaction.Al(OH)F₂.H₂O reacts readily with NaOH, NaF and NH₄F solutions to give sodium and ammonium cryolite. Reactions with NaHF₂ and H₂SiF₆ were unsuccessful, while with AlF₃ solution an increase of the F/Al ratio in the Al basic fluoride used resulted.     

Selective Acetylation of Primary Alcohols: Acetyl and Formyl Transfer Reactions with Copper(II) Salts

The efficient esterification of primary and secondary alcohols in acetic acid was achieved in the presence of Cu(NO₃)₂.3H₂O in high yields. Selective acetylation of primary in the presence of secondary hydroxyl groups in excellent yields were performed in EtOAc. Formylation of primary and secondary alcohols was also achieved easily in ethyl formate. High retention of configuration was observed in the acetylation and formylation of (-) menthol in the presence of Cu(NO₃)₂. 3H₂O and Cu(OAc)₂.H₂O.     

Effect of outer cations and water of crystallization on the radiolytic decomposition of nitrates

The -ray induced decomposition of several inorganic nitrates CsNO₃, TlNO₃, Mg/NO₃/₂.6H₂O, Ca/NO₃/₂.4H₂O, Hg/NO₃/₂, Hg/NO₃/₂.2H₂O, Pb/NO₃/₂ and Al/NO₃/₃.9H₂O has been studied at an absorbed dose of {5 Mrads. G/NO ₂ ^– / is affected by the outer cation and depends mainly on its valency and ionic size. G/NO ₂ ^– / for hydrated mercuric nitrate is always higher as compared to that for the anhydrous mercuric nitrate at various doses. Water of crystallization might provide extra factors to facilitate the decomposition of the hydrated nitrate compared to that for the anhydrous salts. In most cases G/NO ₂ ^– / decreases exponentially with dose but in cases of CsNO₃, Mg/NO₃/₂.6H₂O and Al/NO₃/₃.9H₂O it varies linearly.     

Mössbauer study of surface films on steels formed in phosphate environments under stress-corrosion cracking conditions

A study on the composition of the surface films and corrosion products of mild and low-alloy (2% Cr) steels in 1M NaH₂PO₄ under stress-corrosion cracking (SCC) conditions has been carried out using Mössbauer spectroscopy. At potentials in the SCC region the films formed on both steels contain Fe₃(PO₄)₂.4H₂O, Fe₃(PO₄)₂.8H₂O and FePO₄.xH₂O. The precipitates in the solution formed under these conditions consist of FePO₄.xH₂O and iron(III) hydrogen phosphate [most probably Fe(H₂PO₄)₃.2H₂O]. An attempt has been made to relate the surface film composition to SCC susceptibility.     

Free Radical Reactions of N2O Molecules

Experimental data are presented on the spectral (ESR, IR, and optical) and thermochemical characteristics of a complex between the (Si–O)₃Si^.radical and an N₂O molecule. The rate constants of separate reactions in the systems (Si–O)₃Si^.+ N₂O and (Ge–O)₃Ge^.+ N₂O are found. The results of quantum chemical calculations of potential energy surfaces and spectral characteristics are presented for the following systems: H^.+ N₂O, H₃C^.+ N₂O, H₃Si^.+ N₂O, F₂HSi^.+ N₂O, F₃Si^.+ N₂O, and F₃Ge^.+ N₂O. The latter three systems served as molecular models for experimentally found systems. Based on experimental and theoretical data, the product of N₂O addition to (Si–O)₃Si^.has the structure Si–N=N–O^.. The reactions of free radicals H^., H₃C^., H₃Si^., F₂HSi^., F₃Si^., (Si–O)₃Si^., and (Ge–O)₃Ge^.with N₂O are compared. The spectrum of optical absorbance of the (Si–O)₃Si–O^.radical is recorded and qualitatively characterized.     

The reaction of aluminum fluoride solution with cryolite

The title reaction was investigated kinetically and the products obtained were analyzed and examined by physicochemical methods. The reaction was found to result in the formation of NaAlF₄.H₂O and its solid solutions with aluminum fluoride with compositions down to Na_0.5AlF_3.5.1.3H₂O, except in the presence of chiolite seed crystals, which cause the reaction to give it as the final product.It was suggested that the solid solution are brought about by coprecipitation of approximately monohydrated hexagonal ° -AlF₃ direct from solution, both compounds being presumably isostructural each other.Differences in the infrared spectra of Na₂AlF₆, Na₅Al₃F₁₄ and NaAlF₄.H₂O were indicated.Homogenous mixtures of Na₃AlF₆ and NaAlF₄.H₂O are found to react exothermally at 350°C to give Na₅Al₃F₁₄, while NaAlF₄.H₂O alone decomposes into Na₅Al₃F₁₄ and AlF₃.     

Separation and kinetic study of chromium(III) chloro complexes by capillary electrophoresis

Summary Three Cr(III) species (dichlorotetraaquachromium (III), [CrCl₂(H₂O)₄]⁺; monochloropentaaquachromium(III), [CrCl(H₂O)₅]²⁺; and hexaaquachromium(III), [Cr(H₂O)₆]³⁺) have been separated and determined by capillary electrophoresis. The first two complexes could be detected in direct mode in phosphate buffer, but because the absorption of complex [Cr(H₂O)₆]³⁺ is poor in the UV range, indirect UV detection had to be used. For indirect detection 5 mM imidazole was added to the buffer solution. The formation and decomposition of the different Cr(III) complexes were monitored in time after the preparation of solutions of CrCl₃.6H₂O. The slowest process was the decomposition of [CrCl(H₂O)₅]²⁺; 300 h after preparation of a solution of CrCl₃.6H₂O of pH 1 the solution contained only [Cr(H₂O)₆]³⁺. The effects of pH and the content of some matrix ions on the rates of conversion of the complexes were studied. The kinetic characteristics of this complex system could be investigated adequately by means of capillary electrophoresis. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Versatile coordinating behaviour of bis(acylhydrazone) ligands derived from imino- and methyl-iminodiacetic acid diethyl ester. Antimicrobial properties of their trinuclear copper(II) complexes

The coordinating properties of a new bis(pyridylhydrazone) ligand derived from iminodiacetic acid diethyl ester and 2-pyridinecarboxaldehyde (picolinaldehyde) H₃Imdp and of the bis(salicylhydrazone) H₅Imds and H₄MeImds ligands derived, respectively, from iminodiacetic acid diethyl ester and from methyl-iminodiacetic acid diethyl ester and salicylaldehyde were considered, by means of analytical and spectroscopic methods, towards first row transition metal ions. These ligands showed various coordination modes in complexation with Cu(II), Co(II), Mn(II) and Zn(II) ions. In particular, we have synthesized and characterized, by analytical, ¹H NMR and IR techniques, tri-, di- and mononuclear metal complexes of formula Co₃(HImdp)(NO₃)₄·2H₂O, Cu₃(HImdp)(NO₃)₄·C₂H₅OH·H₂O, Cu₃(HImdp)Cl_4, Zn₂(H₃Imdp)(ClO₄)₄·2H₂O, Co₃(HImds)Cl₂·CH₃OH·H₂O, Zn₂(H₃Imds)Cl₂·2H₂O, Co(H₄Imds)NO₃·2H₂O, Mn(H₄Imds)Cl·CH₃OH·H₂O, Cu(H₃Imds)·CH₃OH·H₂O and Cu(H₂MeImds)^.CH₃OH·3H₂O. Antibacterial, antifungal and antiprotozoal properties of H₅Imds and H₃Imdp together with three copper(II) trinuclear species of H₅Imds of formula Cu₃(HImds)(NO₃)₂^.2CH₃OH·2H₂O, Cu₃(HImds)(ClO₄)₂^.EtOH·2H₂O and Cu₃(HImds)SO₄·4H₂O are also discussed. The H₅Imds ligand and their trinuclear copper(II) complexes showed good activities versus Trichomonas vaginalis, Staphylococcus epidermidis and Acanthamoeba castellanii.     

Hydrate numbers of scandium sulfate as deduced from solubility data

A simple method for determination of the hydrate numbers of saturating multi-hydrate salts in developed. The method demonstrated for scandium sulfate is based upon estimation of the enthalpy of solution of the hydrates from the solubility smoothing equations. It is shown that in the Sc₂(SO₄)₃–H₂O system, contrary to common opinion, the equilibrium solid phases are: Sc₂(SO₄)₃.6H₂O at 273–295 K, Sc₂(SO₄)₃.5H₂O at 295–333 K and Sc₂(SO₄)₃.4H₂O at 333–373 K. The solubility smoothing equations for the hexa-, penta- and tetrahydrate of scandium sulfate are given.     

Vibrational Spectra of Magnesium Hydrogenphosphate Trihydrate and of its Manganese Analogue

Abstract

The infrared (IR) and Raman spectra of MgHPO₄. 3H₂O and of a series of partially deuterated analogues as well as the IR spectra of MnHPO₄. 3H₂O have been recorded and interpreted. The analysis of the IR spectra in the HOD bending region rules out the possibility of existence of H₃OC⁺ ions in the structure.     

Four Dysprosium(III) Compounds Based On 1H‐Benzimidazole‐5,6‐dicarboxylic Acid via Hydrothermal Synthesis

Four compounds [Dy(H₂bidc)(Hbidc)(H₂O)₈] · 8H₂O ( 1 ), {[Dy(Hbidc)(H₂O)₂(Htzac)] · 3H₂O}_n ( 2 ), [Dy(C₂O₄)_0.5(Hbidc)(H₂O)₃]_n ( 3 ), {[Dy₂(Hbidc)₂(H₂O)(SO₄)] · H₂O}_n ( 4 ) (H₃bidc = 1H‐benzimidazole‐5,6‐dicarboxylic acid, H₂tzac = 1H‐3‐amino‐5‐carboxy‐1,2,4‐triazole) were synthesized with hydrothermal synthesis and structurally characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. X‐ray analysis revealed that the four coordination compounds have different structures: Compound 1 is a three dimensional supermolecular structure joined by hydrogen bonding interactions based upon dinuclear units. Compound 2 is a three dimensional supermolecular structure combined by hydrogen‐bonding interactions based upon one dimensional coordination chain including a T4(1)‐type water cluster chain. The structure of compound 3 is built of two dimensional (3,6)‐connected kgd‐type (4³)₂(4⁶.6⁶.8³) layers with a right‐handed and a left‐handed helical chain, which are further extended into three dimensional supramolecular architecture by hydrogen bonding interactions. Compound 4 displays a three dimensional framework containing a dinuclear dysprosium building unit with a (3,8)‐connected (4.5²)₂(4².5¹⁰.6¹².7.8³) topological framework. In addition, the photoluminescent property of compound 3 was investigated.     

Reaction of Lanthanum Carbonates with Nickel in Aqueous Medium

The system La₂(CO₃)₃-NiCO₃-H₂O and separate fragments of the systems Ni(OH)₃-NiCO₃-H₂O and LaNiO_{2 . 5}-CO₂-H₂O were studied by the isothermal crystallization technique. The compounds La₂(CO₃)₃·8H₂O, LaNi₅(CO₃)_{6 . 5}·xH₂O, and Ni(CO₃)_{0 . 6}(OH)_{0 . 8}·3H₂O and solid solutions based on lanthanum carbonate and lanthanum-nickel mixed carbonates were detected in the system. The intermetallic compound LaNi₅, which is highly competitive in characteristics with LaNi₅ cast alloy, was obtained by reduction of LaNi₅(CO₃)_{6 . 5}·xH₂O.     

The radiolysis of mixtures of carbon dioxide and hydrogen

The self-radiolysis of CO₂ in excess tritium (³H₂) has been studied at pressures of 0.1 to 1.0 atm, temperatures of ?80° to +100°C, and in the presence of added H₂O, He, or Ar. The primary products of decomposition are CO and ³H₂O. Secondary products are C³H₄, C₂³H₄, and a white polymer. The rates of disappearance of CO₂ and formation of products and G-;values were measured. The disappearance of CO₂ initially obeys first-order kinetics, then slows down with time at a rate depending upon the initial pressure of ³H₂. The initial rates are proportional to pressures of CO₂ and ³H₂. They are independent of temperature, decreased by addition of H₂O vapor, and increased by addition of He or Ar. The proposed mechanism of decomposition of CO₂ and formation of products involves ionization of CO₂ followed by dissociative recombination forming CO and O. Then the O reacts with a hydrogen-containing species forming OH and H₂O, and a back reaction forms CO₂ from CO and OH.     

Phenol as a guest molecule in clathrate compounds

Phenol, having favourable physical and chemical properties, can be enclosed as the guest component in the clathrates of tetracyano complexes. Six compounds of Hofmann and similar type clathrates M(NH₃)₂M' (CN)₄.nG and M(en)_m M'(CN)₄.nG were prepared and identified: Ni(NH₃)₂Pt.2C₆H₅OH; Ni(en)₂Pt(CN)₄.O.14C₆H₅OH; Ni(NH₃)₂Pt(CN)₄.C₆H₅OH.H₂O; Zn(NH₃)₂Ni(CN)₄.O.1C₆H₅OH.H₂O; Cu(NH₃)₂Ni(CN)₄. 2C₆H₅OH and Fe(NH₃)₂Ni(CN)₄.2C₆H₅OH. The phenol containing clathrates are more stable than clathrates containing other guest molecules. In the case of Ni(en)₂ Pt(CN)₄.O.14C₆H₅OH thermal loss of the guest molecule leaves the host lattice intact, but further heating results in the rupture of the host lattice. The compounds were capable in the solid state of sorbing other organic molecules once they had been heated to the temperature required for almost complete loss of guest molecule i.e. n→o.     

Studies of thermal decomposition of hydrazidocarbonates of some first row transition elements

The thermal properties of some hydrazidocarbonates of copper, Cu(N₂H₃COO)₂.0.5H₂O, nickel, Ni(N₂H₃COO)₂.2N₂H₄, and iron, Fe(N₂H₃COO)₂ and N₂H5[Fe(N₂H₃COO)₃].H₂O, were studied in an inert argon atmosphere. The TG, DTG and DSC curves for these compounds were taken. In the case of N₂H₅[Fe(N₂H₃COO)₃].H₂O, intermediates were observed and isolated during the decomposition. The end-products were metal powders oxidized to a greater or lesser degree.

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Zusammenfassung In einer inerten Argonatmosphäre wurden die thermischen Eigenschaften einiger Hydrazidocarbonate von Kupfer, Cu(N₂H₃COO)₂.0.5H₂O, Nickel Ni(N₂H₃COO)₂.2N₂H₄ und Eisen Fe(N₂H₃COO)₂ bzw. N₂H₅[Fe(N₂H₃COO)₃].H₂O ermittelt, d.h. TG-, DTG- und DSC-Kurven wurden angefertigt. Im Falle von N₂H₅[Fe(N₂H₃COO)₃].H₂O konnten während der Zersetzung auch Zwischenprodukte beobachtet und isoliert werden. Die Endprodukte waren mehr oder weniger oxydierte Metallpulver.

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Paper presented at the 6th World Conference for Thermal Analysis, Capri, 1989.

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This work was supported by the Research Council of Slovenia.     

Selecting oxygen source for partial oxidation of methane to methanol using microwave plasmas

The methanol selectivity in partial oxidation of methane in microwave plasma reactors is improved by using H₂O in the presence or absence of O₂. The use of H₂O₂ as an oxygen source has a similar effect, although it is less effective than H₂O. The addition of H₂ to the system has little effect on selectivity. Two pathways are suggested for the formation of methanol. One involves a CH₃O^* or CH₃O₂ ^* intermediate, while the other involves a direct combination of CH₃ ^* and OH^* radicals. The first pathway is favored in the presence of O₂ while the latter is favored in the presence of H₂O or H₂O₂. The best results are obtained for the CH4-O₂-H₂O system when methanol is formed through both pathways.     

Preparative and structural studies of halodimolybdates(II). IV. Synthesis and crystal structure of (pyH)3Mo2Br7(H2O)2

(pyH)₃Mo₂Br₇(H₂O)₂ (pyH = Pyridinium cation) was prepared from the solution of (NH₄)₅Mo₂Cl₉ · H₂O in 1:1 HBr by the addition of pyHBr. The compound has monoclinic unit cell: P 2₁/n with a = 10.250(4), b = 11.891(4), c = 11.971(3) Å and β = 112.86(2)°. Z = 2, D calcd. = 2.54, D obsd. = 2.52(2) g cm^?3. The structure has been refined to the unweighted and weighted residuals of 7.8 and 8.7%. The structure contains Mo₂Br₆(H₂O)₂^2?, C₅H₆N⁺ and Br^? ions. Short Mo? Mo distance 2.130(4) Å reflects the strong bond. H₂O is coordinated to molybdenum at 2.19(3) Å. Distribution of H₂O molecules and Br^? ions around Mo₂ is different from (picH)₂Mo₂X₆(H₂O)₂ (X = Br, I) and determined by the two-fold axes perpendicular to the Mo? Mo direction and the plane defined by two H₂O molecules and 2 Br atoms. Three independent Mo? Br distances are 2.574(4), 2.606(5) and 2.569(5) Å. Specific structure of the Mo₂Br₆(H₂O)₂^2? ion has no synthetic consequences and reaction with neutral aromatic nitrogen bases leads to the known Mo₂Br₄L₄ compounds.