Structure of the 18-Crown-6 Complex with Ammonium Hexafluorosilicate and Water

The crystalline host–guest type complex [(18-crown-6NH₄)₂][SiF₆]4H₂Ohas been obtained as the result of the interaction of SiF₄2NH₃ with 18-crown-6 (18C6) in an aqueous medium. Crystal data: monoclinic, space groupC 2 c, a=26.541(2), b=8.363(2), c=20.469(2) Å, = 122.43(1)°and Z=4. The final R-value is 0.070 for 3253 reflections with I 2(I).The crystals consist of the complex [NH₄18C6]⁺ cations, [SiF₆]^2-anions and water molecules. The ammonium cation is hydrogen bonded by three of its H-atoms to the crown ether oxygen atoms with N(1) O separations2.923(5)–2.940(5) Å and by the fourth H-atom to the fluorine atom of thehexafluorosilicate anion, the N(1)F(4) distance being 2.797(6) Å.The conformation of the macrocycle and the hydrogen-bond geometry in thecomplex cation closely resemble those in related adducts between 18-crown-6and ammonium salts. All crystal components are connected via a system of hydrogen bonds into a ribbon along the b axis in the unit cell.     

The behaviour of cellulose in hydrated melts of the composition LiXċn H2O (X=I−, NO3−, CH3COO−, ClO4−)

The dissolution behaviour of cellulose in low temperature molten salts was investigated. Depending on the chosen anions in the melt, cellulose shows different reaction behaviour in different Li⁺containing melts. Dissolution of the polymer was observed in molten LiClO₄3H₂O and molten LiI2H₂O. In the hydrated melts of LiCH₃COO2H₂O and LiNO₃3H₂O a fine distribution of cellulose was stated. Cellulose can be regenerated by cooling the melt and removing the salt by dissolution in water.The structure of the recrystallized product is determined by the used low temperature molten salt.     

Catalytic properties of nitrides in ammonia synthesis

Ammonia synthesis on nitrides CeN, UN_1.70 and iron catalyst CA-1 has been examined at pressures of up to 100 bar. Reaction kinetics is described by the Temkin-Pyzhev equation. Activation energy for all samples is similar and equals about 200 kJ/mol. Specific catalytic activity of nitrides is lower than that of the iron catalyst by a factor of 3–4 for uranium and 10 for cerium.

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100 CeN, UN_{1, 70} CA-1. -. 200 /. : 3–4 10 .

     

Reactivity of alkyl and polychloroalkyl radicals toward 1-hexene

The kinetics of CCl₃ radical addition to 1-hexene in CCl₃Br and CCl₄ media has been studied. The rate constant of CCl₃ addition to the double bond is shown to be independent of the solvent. The ratios between the rate constants of transfer and allyl chain termination for the alkyl and polychloroalkyl radicals have been estimated by competition methods. Activation parameters for the calculated rate constants are given.

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CCl₃- 1- CCCl₃Br CCl₄. , . . .

     

Heat evolution during hydration of Ca4(Al6O12)(SO4)

The hydration of the sulphatealuminate phase Ca₄(Al₆O₁₂)(SO₄) at room temperature was observed by means of differential calorimetry and quantitative X-ray diffraction phase analysis in situ. The results were used to evaluate the kinetics of the hydration process and to explain the causes of the exothermic effects: an initial surface reaction, the formation of a highly dispersed system, and the crystallization of monosulphate, Ca₄(Al₂O₆)(SO₄) · 12H₂O, and gibbsite, Al(OH)₃. The experiments showed an increase in efficiency of hydration with a higher mass ratio of water to solid phase (from 143.8 kJ/mol) atw/s=1 to 170.0 kJ/mol atw/s=10).

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Zusammenfassung Die Hydration der Sulfat-aluminat-Phase Ca₄(Al₆O₁₂)(SO₄) bei Zimmertemperatur wurde mittels Differentialkalorimetrie und quantitativer in-situ-Röntgenbeugungs-Phasenanalyse verfolgt. Ein vergleich der Ergebnisse erlaubte die Kinetik des Hydratationsprozesses abzuschätzen und die Ursache der exothermen Effekte zu klären: Anfängliche Oberflächenreaktion, Bildung eines hochdispersen Systems, Kristallisation von Monosulfathydrat Ca₄(Al₂O₆)SO₄·12H₂O und Hydrargillit Al(OH)₃. Die Versuche zeigten eine Zunahme der Hydratationseffektivität mit steigendem Verhältnis Wasser: Feststoff (w/s) von 143,8 kJ mol^–1 beiw/s=1 auf 170,0 kJ mol^–1 beiw/s=10.

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in situ ₄(l₆)(S₄). , , ₄(l₂₆)(S₄) · 122 l()₃. : 143,8 ^–1 1 170,0 · ^–1 10.

     

Catalytic ammoxidation of coal

Ammoxidation of coal on oxide catalyts has shown the possibility of hydrocyanic acid formation at sufficiently low temperatures.

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. .

     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Selective oxidation of methanol on cuprate catalysts

The catalytic activity of BaCuO₂, Ba₂Cu₃O₅ and YBa₂Cu₃O_7–x has been compared in the selective oxidation of methanol to formaldehyde. Ba₂Cu₃O₅ shows the highest activity.

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BaCuO₂, Ba₂Cu₃O₅ YBa₂Cu₃O_7–x . Ba₂Cu₃O₅ .

     

Ru(III) catalysis in the oxidation of arenes by periodate. A kinetic study

The title reactions are zero order in periodate and first order in Ru(III). All substrates show a first order dependence except for p-xylene and fluorene which follow a Michaelis-Menten behavior. The Hammett plot gives a values of-2.0. A mechanism involving metal arene -interaction is discussed.

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Ru(III). , - , -. =–2,0. . , -- .

     

n-Hexane cracking over heteropoly acids, 3. Silica supported heteropoly acids

Silica supported heteropoly acids are active in n-hexane cracking, while the pure compounds (except H₃PW₁₂O₄₀) are inactive. This result is explained by a partial transformation of H₆P₂W₁₈O₆₂ and H₆P₂W₂₁O₇₁ (H₂O)₃ into H₃PW₁₂O₄₀. In the case of H₄SiW₁₂O₄₀, the polyanion in interaction with silica leads to superacidic species upon thermal treatment.

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, , -, ( H₃PW₁₂O₄₀) . H₆P₂W₁₈O₆₂ H₆P₂W₂₁O₇₁ (H₂O)₃ H₃PW₁₂O₄₀. H₄SiW₁₂O₄₀ , , .

     

Endo and Exo Coordination to Cofacial Binuclear Copper(II) Complexes

A structural study of internal (endo) and external (exo) coordination to cofacial binuclear complexes is reported.Cu₂(NBA)₂(NBAH₂=3,3'-[2,7-naphthalenediylbis(methylene)]-bis(2,4-pentanedione)) is large enough to accommodate 2-methylpyrazine as an intramolecularly coordinated guest molecule Cu₂(NBA)₂((2Mepyz))4CH₂Cl₂Cu₂C₅₃H₅₈N₂O₈Cl₈, orthorhombic, space group Pnma (No. 62); a = 22.4674(11); b = 22.230(2); c = 11.4520(6) Å V = 5719.6(6) ų (at 100 K); Z = 4; R = 0.058; R _w = 0.167 for 344 parameters and 5339 reflections with I > 2(I). The Cu₂(NBA)₂(-(2-Mepyz)) molecules possess crystallographic m symmetry, with the CuCu vector (CuCu' 7.4801(8) Å) perpendicular to the mirror plane; this requires disorder in the 2-Mepyz guests. The two ``Cu(acac)₂' moieties (acacH = 2,4-pentanedione) are not quite parallel (dihedral angle between (acac)₂ planes = 3.93(7)^circ), forming a slightly wider opening on the side of the methyl group in the 2-Mepyz guest. On the other hand, the cavity in Cu₂(XBA)₂ (XBAH₂ = 3,3'-[1,3-phenylenebis(methylene)]-bis(2,4-pentanedione)) is smaller, so that CH₃CN must bind externally.Cu₂(XBA)₂(CH₃CN)₂1.5CH₃CNH₂O,Cu₂C₄₃H_52.5N_3.5O₉, monoclinic, space group P2₁/c (No. 14); a = 11.7361(16); b = 14.197(3); c = 13.299(3) Å; = 92.22(2)^{^}; V = 2214.3(7) ų (at 100 K); Z = 2; R = 0.044; R _w = 0.124 for 275 parameters and 4983 reflections with I > 2 (I). This structure contains centrosymmetric Cu₂(XBA)₂ units (CuCu' 4.8302(12) Å) with externally coordinated CH₃CN ligands. The crystal packing in Cu₂(NBA)₂((2Mepyz))4CH₂Cl₂,which contains close contacts between layers of Cu₂(NBA)₂(-(2-Mepyz)) moieties, is also similar to that in three other crystalline host–guest adducts M₂(NBA)₂(-G). Cu₂(XBA)₂(CH₃CN)₂1.5CH₃-CNH₂O does not contain similar layers of molecules, presumably because the adduct molecules do not have the same type of exposed flat surfaces.     

Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

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Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

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Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

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(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Thermal decomposition of some imidazole and N-methyl substituted imidazole complexes of palladium(II)

We describe in this paper the thermal decomposition in air of several complexes of palladium(II) chloride with imidazole and N-methylimidazole. Although the final process of the decomposition gives (PdCl₂)_n which then decomposes to pa ladium which oxidizes to PdO, there are interesting differences in the initial decomposition path. The reasons for these differences appear to be related to the trans-effect and to the presence in the imidazole complexes of hydrogen bonds which break down at temperatures of around 220.

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Zusammenfassung In diesem Beitrag wird die thermische Zersetzung verschiedener Komplexe des Palladium(II)chlorids mit Imidazol und N-Methylimidazol in Luft beschrieben. Obwohl der Endvorgang der Zersetzung (PdCl₂)_n ergibt, welches dann zu Palladium zersetzt und zu PdO oxidiert wird, bestehen interessante Unterschiede im Anfangsschritt der Zersetzung. Die Ursachen dieser Unterschiede scheinen mit dem Trans-Effekt und der Anwesenheit von Wasserstoffbindungen in den Imidazolkomplexen verbunden zu sein, welche bei Temperaturen um 220 zerstört werden.

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Résumé La décomposition thermique dans l'air de plusieurs complexes du chlorure de palladium(II) avec l'imidazole et le méthyl-4-imidazole est décrite. Bien que l'étape finale de la décomposition donne (PdCl₂)_n qui se décompose ensuite en palladium qui s'oxyde en PdO, des différences intéressantes apparaissent dans les étapes initiales de la décomposition. Les causes de ces différences sont en rapport avec l'effet trans et la présence, dans les complexes avec l'imidazole, de liaisons hydrogÊne qui se rompent vers 220.

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(II) -. (PdCl₂)_n, , PdO, . , - , 220.

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One of us (M.C. Navarro Ranninger) would like to thank the D.G.E.S.I. for a grant that allowed her to work on this research.     

Hydrogen forms of zeolites obtained by electrolysis

The catalytic activity in cumene cracking and the infrared spectra of the H-forms of Y-zeolite obtained by electrolysis from ammonium forms have been compared. It is concluded that the electrolytic method makes it possible to prepare samples with properties similar to those of ion-exchanged samples.

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- H- , NH ₄ ⁺ -, . , NH ₄ ⁺ - .

     

Molecular oxidic phases of diluted silica supported vanadia

Different surface phases of silica supported vanadia catalysts have been characterized by static adsorption, reduction, and reoxidation experiments under vacuum conditions. The obvious mobility of vanadium involved in some preparation steps gives rise to a diversification of initial precursor phases as a function of pretreatment conditions and SiOH concentration.

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SiO₂ , . , , SiOH.

     

A mechanistic explanation for the SO2 oxidation rate data of a Cs/V catalyst at high pressures and conversions

A preliminary attempt to modify a molybdena-silica for ethylene homologation was performed by adding copper. Ethylene homologation (3C₂H₄2C₃H₆) was enhanced 2.5 times on copper doped catalyst. Contrary to this, ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) was suppressed in the presence of copper. The selectivity of the homologation to metathesis was increased 7.5 times.

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- , (3C₂H₄2C₃H₆), . 2,5 , (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . 7,5 .

     

Study of interaction between trimethyl-substituted silanes and silica surface

Interaction mechanism of (CH₃)₃SiX silanes (X=Br, I, N₃, NCS, NCO, CN, NCNSi(CH₃)₃ and SO₄Si(CH₃)₃ with dehydrated silica surface has been studied by IR spectroscopy. It has been established that (CH₃)₃SiCN, (CH₃)₃SiBr, (CH₃)₃SiI and [(CH₃)₃Si]₂SO₄ can be used as soft silylating agents for endcapping.

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(CH₃)₃SiX (X=Br, I, N₃, NCS, NCO, CN, NCNSi(CH₃)₃, SO₄Si(CH₃)₃) -. , (CH₃)₃SiCN, (CH₃)₃SiBr, (CH₃)₃SiI [(CH₃)₃Si]₂SO₄ .

     

Influence of molecular nitrogen and irradiation temperature on radiolysis of N2O?Al2O3 system

Molecular nitrogen and irradiation temperature are shown to affect the radiationchemical yield of O _st ^– in the radiolysis of N₂O adsorbed on alumina with large surface areas and to exert no influence in the case of small surface areas of Al₂O₃.

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, - O _st ^– N₂O, Al₂O₃ .

     

Results of thermal analysis for investigation of salt hydrates as latent heat-storage materials

DTA and DSC methods and quasi-isothermal and quasi-isobaric thermogravimetry are of great importance in the investigation of salt hydrates as latent heat-storage materials. However, the transferability of the DTA and DSC results is given only for application in static latent heatstorage units. Special calorimetric methods adapted to the storage principle are preferred for the study of salt hydrates under dynamic storage conditions. The findings are discussed in connection with the examples of Na₂SO₄·10H₂O, CH₃COONa·3H₂O, Na₂S·9H₂O, Na₂S·5H₂O, Mg(NO₃)₂·6H₂O, MgCl₂·6H₂O and the eutectic mixture of Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O.

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Zusammenfassung Bei der Untersuchung von Salzhydraten als Latentwärmespeichermaterialien besitzen DTA-, DSC-Methoden und die quasi-isotherme und quasi-isobare Thermogravimetrie eine wesentliche Bedeutung. Die Übertragbarkeit der DTA- und DSC-Ergebnisse ist jedoch nur für den Einsatz in statischen latentwärmespeichern gegeben. Für das Studium der Salzhydrate under dynamischen Speicherbedingungen werden spezielle, dem Speicherprinzip angepaßte kalorimetrische Methoden bevorzugt. Die Aussagen werden an den Beispielen Na₂SO₄·10H₂O, CH₃COONa·3H₂O, Na₂S·9H₂O, Na₂S·5H₂O, Mg(NO₃)₂·6H₂O, MgCl₂·6H₂O und der eutektischen Mischung von Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O diskutiert.

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, . , . , . Na₂SO₄·10H₂O, CH₃COONa·3H₂O, Na₂S·5H₂O, Na₂S·9H₂O, Mg(NO₃)₂·6H₂O, MgCl₂·6H₂O Mg(NO₃)₂·6H₂O·MgCl₂·6H₂O.