Crystal Structure Study of the Metastable β-modification of Glycine and its Transformation into the α-modification

Crystal structure refinement was performed of the metastable modification of glycine (space gr. P2₁, a = 5.092(2) , b = 6.273(3) , c = 5.384(3), = 113.17(4)°, Z = 2, R = 0.0274). The crystals were obtained by a new method (not described in the literature): they were precipitated from a water solution with the addition of glacial acetic acid. The crystal structure of the glycine modification [space gr. P2₁/n, a =5.106(1) , b = 11.979(5) , c = 5.463(2) , = 111.75(2)°:, Z =4] was refined for comparison. Transition from the to the modification in a damp atmosphere was revealed, resulting in the formation of a strongly strained crystal of a mosaic structure. The orientation of the crystallographic axes in the newly formed crystal of the modification relative to the axes in the initial crystal of the modification was determined. It is shown that as in glycine, the lengths of the intramolecular C—O bonds in the modification are fairly similar [1.248(2) and 1.253(2) ] and the previously found significant difference between them is most likely due to the errors of the photomethod. A comparative analysis of the crystal structures of the and glycine modifications (glycine zwitterion packings and structure of intermolecular hydrogen bond networks) was performed. Data of the analysis are used to discuss the properties of the glycine modifications, the possible reasons for the stability of the modification in dry air, the difficulties of crystal growth from solutions, and the ease of crystallization of the modification under various conditions.     

Synthesis and Crystal Structure of the (batre)[CuBr4] Complex, where Batre is bis‐1,1′‐(4‐amino‐1,2,4‐triazolio)ethane

The (batre)[CuBr₄] complex is produced by the reaction of CuBr₂ and (batre)Br₂ in concentrated HBr; its crystal structure is determined. The acentric unit cell (Pn space group) has the following parameters: a = 7.626(2), b = 8.945(2), c = 11.702(2), = 96.69(3)°, V = 792.8(3)³, and Z=1 ((batre)[CuBr₄] composition). The structure of the complex is built up of [CuBr₄]^2- tetrahedral anions and (batre)²⁺ uncoordinated cations. The Cu—Br distances are 2.362–2.385 and the BrCuBr angles are 99.73–129.79°.     

Novel chromium trinuclear trifluoroacetate complexes Cr3(μ3-O)(CF3COO)6(CH3COOH)2(CF3COO) and Cr3(μ3-O)(CF3COO)6(CH3COOH)2(THF): Synthesis and crystal structure

Novel anhydrous trinuclear ₃-oxo complexes of Cr(III), Cr₃(₃-O)(CF₃COO)₆(CH₃COOH)₂(CF₃COO) (I) and of Cr(III,III,II), Cr₃(₃-O)(CF₃COO)₆(CH₃COOH)₂(THF) (II) (where THF is (CH₂)₄O) are synthesized by anodic dissolution of metallic chromium in solutions of trifluoroacetic acid in acetonitrile and in tetrahydrofuran and their structures are studied by X-ray diffraction analysis. Complex I forms orthorhombic crystals with space group Pna2₁, a = 9.778(1) , b = 16.042(2) , c = 22.851(4) , Z = 4, R ₁ = 0.0332; complex II crystallizes in monoclinic system: space group P2₁/c, a = 9.866(1) , b = 17.895(2) , c = 21.167(4) , = 100.75(2)°, Z = 4, R = 0.0422. The average Cr-(₃-O) distances in compounds I and II are almost equal (1.943(3) and 1.927(3) ). An average length of the Cr-O bond in octahedral surrounding of metal atoms is different in complexes I and II (1.985(4) and 2.003(3) , respectively), which is specified by different oxidation states of the metal atom. The CrCr distances lie in an interval of 3.366(1)–3.337(1) .__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 266–272.Original Russian Text Copyright © 2005 by Glazunova, Boltalin, Troyanov.     

Synthesis, Structure, and Thermal Decomposition of Chloropentamminerhodium(III) Hexabromoplatinate(IV)

The binary complex salt [Rh(NH₃)₅Cl][PtBr₆] was synthesized and studied by Xray structural analysis. The crystallographic data are as follows: a = 12.013(2) , b = 8.401(2) , c = 15.999(3) , = 91.13(3)°, V = 1614.3(6) ³, space group P2₁/m, Z = 4, d_x = 3.70 g/cm³, R = 0.086. The thermal decomposition of the salt in a hydrogen atmosphere is shown to produce a Rh_0.5Pt_0.5 solid solution with an FCC cell [a = 3.864(2) . The thermal decomposition of the salt in a helium atmosphere proceeds via the formation of metallic Pt and RhBr₃ and finally results in a mixture of several solid solutions.     

Distortion of the Cucurbituril Molecule by an Included 4‐Methylpyridinum Cation

The crystal and molecular structures of a guest–host complex of cucurbituril with 4methylpyridinium, {(4MePyH) (C₃₆H₃₆N₂₄O₁₂)}(NO₃) · 4H₂O, were determined by Xray structural analysis. The crystals are monoclinic with a = 26.276(3) , b = 25.861(2) , c = 17.375(2) , = 124.17(1)°, V_cell =9768.6(18) ³, space group Cc, and Z = 8. The structure contains two crystallographically independent supramolecular complexes. They are arranged in pillars oriented along the a axis. In each pillar, the complexes are parallel to each other. The pillars are shifted with respect to each other by onehalf of the crystallographic translation. The centers of the supermolecules are arranged according to a pseudobodycentered motif. Distortions of the cucurbituril molecule depending on the guest type have been analyzed with the use of results obtained in the present and previous studies.     

Studies on clathrasils: VII. A new clathrate compound of silica: Synthesis,crystallographic, and thermal properties

Using l-aminoadamantane a new type of silica host framework has been stabilized. The clathrasil is rhombohedral with a=13.887 and c=40.989 for the hexagonal unit cell. Heating the compound on a thermal analyser shows that from 500°C on the guest molecule evaporates. The silica framework only very slowly breaks down when heated at 1100°C for several hours yielding cristobalite. Since l-aminoadamantane stabilizes, at higher temperatures of synthesis, dodecasil 1H the new clathrasil is regarded as low temperature form for this particular guest molecule.     

Crystal and Molecular Structure of Monoammonium Salt of 5‐nitroaminotetrazole

Xray structural investigation of the monoammonium salt of 5nitroaminotetrazole was performed. The crystals are orthorhombic: a = 10.077(1), b = 17.009(1), c = 6.6472(6), V = 1139.33(17)³, space group Pbca, Z =8, _calc = 1.715 g/cm³. Monodeprotonation of 5nitroaminotetrazole during formation of the salt occurs at the N(4) nitrogen atom of the heterocycle. The anion has an almost flat structure; the bond lengths suggest delocalization of electron density in the molecule. The negative charge is distributed among three nitrogen atoms and two oxygen atoms of the anion. Changes in the geometrical parameters of 5nitroaminotetrazole on monodeprotonation are considered.     

Configurations of the [Pd(NO2)4]2- Complex Anion: Crystal Structure of Ag4A2[M(NO2)4]3 (M = Pd, Pt; A = K, Rb)

An integrated Xray diffraction study was performed on polycrystals and single crystals of three new isostructural phases with general formula Ag₄A₂[M(NO₂)₄]₃ (M = Pd, Pt; A = K, Rb). Data on the crystal structure solution (CAD4 diffractometer, MoK radiation, graphite monochromator = 2–30° are presented. In one crystallographically independent [M(NO₂)₄]^2- complex anion, the planar square coordination of the central atom is completed to 4 + 2 by two oxygen atoms at a distance of 3.02–3.12 in the other anion, it is completed to 4 + 1 + 1 by an oxygen atom at a distance of 3.12–3.30 and an Ag⁺ cation at a distance of 3.04–3.11 . Part of the Ag⁺ cations form Ag - Ag dimers with a distance of 3.03–3.07. Crystalchemical analysis of known structures containing [Pd(NO₂)₄]^2- complex anions was performed. It has been established that in none of the cases do any of the possible limiting configurations occur.     

Crystal and Molecular Structure of 2‐nitro‐1‐ureidoguanidine

An Xray structural investigation of 2nitro1ureidoguanidine has been carried out. The crystals are monoclinic: a = 4.4690(2), b = 15.566(1), c = 9.4131(7), = 94.896(5)°, V = 652.4(3)> ³, space group P2₁/n, Z = 4, _calc = 1.650 g/cm³. The molecule consists of two planar fragments: carbamide and nitroguanidine. The geometrical characteristics of the molecule are analyzed. The system of intra and intermolecular hydrogen bonds in the crystal is considered.     

Experiences with the use of DSC in the determination of vapor pressure of organic compounds

This paper describes the arrangement of measuring apparatus for vapor pressure determination by means of DSC according to the dynamic method (measurement of boiling temperatures at various pressures). Measuring conditions, main test parameters, typical disturbances and measuring errors are discussed. In the measuring range accessible (0.1 to 7000 kPa/ –30 to 600°C), certain boiling points and vapor pressure curves plotted therefrom agree very well with values specified in the literature. Extrapolation of these vapor pressure curves to the pressure range up to 0.1 mPa gives approximate values, the orders of magnitude of which are in agreement with those measured by means of other methods. Vapor pressure curves of oleochemical substances are presented.

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Zusammenfassung Der Aufbau eines Meßplatzes zur Dampfdruckbestimmung mit der DSC nach der dynamischen Methode (Messung der Siedetemperaturen bei verschiedenen Drücken) wird beschrieben. Meßbedingungen, wesentliche Versuchsparameter, typische Störungen und Meßfehler werden diskutiert. Im zugänglichen Meßbereich (0,1 bis 7000 kPa/–30 bis 600°C) bestimmte Siedepunkte und daraus ermittelte Dampfdruckkurven stimmen sehr gut mit Literaturangaben überein. Die Extrapolation der Dampfdruckkurven in den Druckbereich bis 0,1 mPa liefert näherungsweise Werte, die mit nach anderen Verfahren gemessenen Werten in der Größenordnung übereinstimmen. Dampfdruckkurven von fettchemischen Substanzen werden vorgestellt.

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, / /. , , . , 0,1–7000 –30° 600°, . 0,1 , , . .

     

The consistency of repeated H2?O2 titration cycles on supported Pt catalysts

H₂ and O₂ uptakes at 296 K on a Pt/Al₂O₃ catalyst remained constant during repeated H₂–O₂ titration cycles conducted in a high vacuum adsorption system. Previously reported variations in these uptakes are attributed to adsorption of contaminants during desorption conditions. Also, it was found that nearly 40% of the H₂ adsorbed could be removed by degassing at 296 K for 1 hr.

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H₂ O₂ 296 Pt/Al/₂O₃ H₂–O₂, . . , 40% H₂ 1 296 .

     

Improved activity and selectivity in carbon-oxygen double bond hydrogenation with Ru/TiO2

Ru/TiO₂ hydrogenates the carbonyl function with priority to other unsaturated parts in the molecule as opposed to Ru/SiO₂. This is connected with an increase in activity towards carbonyl hydrogenation.

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Ru/TiO₂, Ru/SiO₂, , . .

     

Effect of Isomorphic Incorporation of Titanium on the Structure and Absorption Properties of VPI-8 Zeolites

We have synthesized titanium silicate analogs of VPI-8 zeolite with a broad range of ratios of Si and Ti atoms. We have shown that introduction of titanium into the zeolite lattice is accompanied by an increase in the unit cell parameter from 13.05 to 14.85 , and also an increase in the sorption capacity and a decrease in the characteristic methanol adsorption energy. X-ray phase analysis, IR and UV spectroscopy have confirmed the isomorphic incorporation of Ti in a tetrahedral environment into the structure of VPI-8 zeolite, up to Ti/(Si+Ti) = 0.05.     

Structure of 2,4,4,5,5‐pentamethyl‐2‐imidazoline‐1‐oxyl‐3‐oxide

The crystal and molecular structures of the stable nitroxide radical 2,4,4,5,5pentamethyl2imidazoline1oxyl3oxide was determined. The N—O bond lengths are 1.279(2) and 1.280(2), respectively. The O^-—N⁺=C—N— O fragment is nearly planar with carbon atoms of the ethyl fragment that deviated from the O—N⁺=C—N—O plane by –0.204(5) and +0.176(5). The minimum intermolecular distance between the oxygen atoms of NO groups is 4.094.     

Synthesis and structure of isomeric (μ-H)Os<Subscript>3</Subscript>(μ,η<Superscript>2</Superscript>-(O,N)-6,6-clusters of dimethyl-2-methylene-bicyclo[3.1.1]heptan-3-one oxime)(CO)<Subscript>10</Subscript>. Crystal structure of one of the isomers

(-H)₂Os₃(,²-(O,N)-6,6-dimethyl-2-methylene-bicyclo[3.1.1]heptan-3-one oxime)(CO)₁₀ isomeric clusters have been synthesized, separated chromatographically, and investigated by IR and NMR spectroscopy. The crystal structure of one of the isomers has been determined (Enraf-Nonius CAD-4 automatic diffractometer, graphite monochromator, MoK , /2 scan mode at a variable rate). The crystals are monoclinic with unit cell parameters: a = 9.125(2) , b = 13.629(3) , c = 10.098(2) , = 90.16(3)°, V = 1255.8(4) ³, space group P2₁, Z = 2, composition (-H)₂Os₃(,²-ONC₁₀H₁₄)(CO)₁₀, d _calc = 2.647 g/cm³. The structure is molecular; the planes of the Os₃ triangle and the OsONOs bridging ligand are linked according to the butterfly pattern with an angle of 102.0° between the planes. The Os-Os bonds vary within the range 2.840 –2.882 .Original Russian Text Copyright © 2004 by V. A. Maksakov, N. V. Pervukhina, S. V. Korenev, N. V. Podberezskaya, V. P. Kirin, and A. V. TkachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 698–705, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Di- and tri-nuclear osmium carbonyl chloride complexes: x-ray structures of Os2(CO)8Cl2 and Os3(CO)12Cl2

Summary Os₂(CO)₈Cl₂ (1) is orthorhombic P2₁2₁2₁ witha=9.3599(9),b=9.879(2),c=16.014(3), V=1480³, D_c=3.03 Mgm^–3 for Z=4. Structure solved by Patterson methods. Final R=0.038, R_w=0.038 [w=(²F)] for 1270 observed reflections and 141 parameters. Os₃(CO)₁₂Cl₂ (2) is monoclinic C2/m witha=12.105(3), b=10.612(3),c=8.798(1) , =117.02(2)°, V=1006³, D_c=3.22 Mgm^–3 for Z=2. Structure solved by Patterson methods. Final R=0.036, R_w=0.037 (w=(²F)^–) for 821 observed reflections and 75 parameters.Complex(1) has an osmium-osmium single bond 2.897(1), with the chloride ligands in equatorial positions,(2) has a linear triosmium chain with osmium-osmium single bonds 2.893(1) and the chloride ligands occupy equatorial sites on the terminal osmium atoms. Both(1) and(2) are isostructural with their osmium carbonyl iodide analogues.     

Thermal decomposition of some heavy and transition metal benzenesulphonates

The thermal behaviours of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II), Pb(II), and VO(II) benzenesulphonates were studied by simultaneous thermoanalytical methods (DTA, TG, DTG, EGA). The measurements were at times supplemented by X-ray analysis of the decomposition products, as well as by chemical analysis. The decomposition processes of samples were carried out in oxygen, in air and in nitrogen atmospheres. The effect of the atmosphere on the decomposition was studied primarily with regard to the reaction paths of the sulphur content of compounds investigated. The possibility of quantitative analysis of these salts was studied from the aspects of both residues and the sulphur oxide products.

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Zusammenfassung Das thermische Verhalten von Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II), Pb(II) und VO(II)-benzolsulfonaten wurde durch simultane thermoanalytische Methoden (DTA, TG, DTG, EGA) untersucht. Gelegentlich wurden die Messungen durch Röntgenanalyse der Zersetzungsprodukte sowie durch chemische Analyse ergänzt. Die Zersetzungsvorgänge der Proben wurden in Sauerstoff, Luft und Stickstoffatmosphäre durchgeführt. Die Wirkung der Atmosphäre auf die Zersetzung wurde untersucht, mit besonderer Berücksichtigung der Reaktionen entsprechend dem Schwefelgehalt der geprüften Verbindungen. Die Möglichkeit der quantitativen Analyse dieser Salze wurde nach den Resten und den Schwefeloxid-Produkten untersucht.

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Résumé On a étudié par ATD, TG, TGD et AGE simultanées le comportement thermique des benzène-sulfonates de Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II), Pb(II) et VO(II). Occasionnellement, on a complété ces résultats par analyse aux rayons X et par analyse chimique. On a étudié l'effet de l'atmosphère (oxygène, air et azote) sur la décomposition, surtout du point de vue des processus réactionnels liés à la teneur en soufre des composés. On a étudié la possibilité d'une analyse quantitatitive de ces sels à partir des résidus ainsi qu'à partir des oxydes de soufre.

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- Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II),Pb(II)VO(II) (, , ). , . , . . , .

     

Structure and Energetics of β–Diketonates. XI. Molecular Structure of Sc(thd)3 from Gas–Phase Electron Diffraction Data

Electron–diffraction and mass–spectrometric studies of saturated vapor of scandium tris–dipivaloyl–methanate showed that at 135(5)°, the vapor contains only monomeric Sc(thd)₃, whose structural parameters r _a , r _g , and r were determined. The internuclear distances in the chelate ring were found to be rSc=O) = 2.066(5), r(O=C) = 1.272(3), and r(C=C_r) = 1.385(3). The ScO₆ coordination polyhedron has a D ₃ symmetry configuration close to a regular antiprism. The angle of rotation of the O=O=O trigonal faces relative to their position in a regular prism is 25.7(1.5)°.     

Kinetic laws for dehydrogenation of cyclohexane over Pd/C catalysts

A kinetic equation for cyclohexane dehydrogenation at P_O=1.0 MPa has been obtained.

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1,0 .