The solid state and solution chemistry of dichlorobis(pyridine)cobalt(II)

The thermal decomposition of dichlorobisquinolinecobalt(II) was investigated. Kinetic analyses were performed on the dynamic and isothermal curves. The dynamic and d.s.c. studies revealed two simultaneously reactions while the isothermal reactions represented single processes. The scheme of thermal decomposition is:

Kristallstruktur von Hexamincyclotriphosphazen,P3N3(NH2)6

Crystal Structure of Hexamine Cyclotriphosphazene, P₃N₃(NH₂)₆ In the presence of KNH₂ hexamine cyclotriphosphazene semi ammoniate (molar ratio 12:1) in NH₃ gives crystals of solvent free P₃N₃(NH₂)₆ within 5 d at 130°C and p(NH₃) = 110 bar. The structure was solved by X-rax methods: P₃N₃(NH₂)₆: P2₁/c, Z = 4, a = 10.889(6) Å, b = 5.9531(6) Å, c = 13.744(8) Å, β = 97.83(3)°, Z(F_o) = 1 721 with (F_o)² ≥ 3σ(F_o)², Z(var.) = 157, R/R_w = 0,036/0,041 The structure contains columns of molecules P₃N₃(NH₂)₆ all in the same orientation. The six-membered rings within one molecule have boat conformation. The columns are stacked together in a way that one is surrounded by four others shifted by half a lattice constant in direction [010]. Strong hydrogen bridge-bonds N? H…?N connect molecules within the columns and between them.     

Dynamik linearer Molekülanionen in den Hydrogensulfiden von Natrium,Kalium und Rubidium: Differential-Scanning-Kalorimetrie,Röntgen- und Neutronenbeugung

Dynamical Behaviour of Linear Molecular Anions in the Hydrogensulfides of Sodium, Potassium and Rubidium: Differential Scanning Calorimetry, X-ray and Neutron Diffraction Hydrogensulfides of the alkali metals M ? Na, K, Rb were prepared in autoclaves by the reaction of the corresponding metals with H₂S and D₂S, respectively, in the temperature range from 50°C to 150°C. Differential scanning calorimetry, X-ray and neutron diffraction methods reveal that both, the HS^?-and DS^?-compounds occur in three crystalline modifications with HT ? high-, MT ? medium- and LT ? low-temperature form: The temperatures and enthalpies for the changes of modifications of the H- and D-compounds are given and the atomic arrangements revealed mainly by neutron diffraction data are discussed, in relation to, for example, size of cations.     

Kinetic and spectroscopic study of 1O2 generation from H2O2 catalyzed by LDH-MoO4(2-) (LDH=layered double hydroxide)

Layered double hydroxides (LDHs), exchanged with molybdate, decompose H2O2 to form one molecule of singlet-state dioxygen (1O2) from two molecules of H2O2. The dependence of the kinetics of H2O2 decomposition on Mo and H2O2 concentrations and on temperature has been related to structural characteristics of the material (X-ray diffraction (XRD), scanning electron microscopy (SEM), IR spectroscopy, N2 adsorption, thermogravimetry) and to molybdate speciation as revealed by in-situ studies in the presence of peroxide (FT Raman, diffuse reflectance UV/visible spectroscopy). The H2O2 decomposition rate is linearly correlated with the amount of LDH-exchanged molybdate, except when a considerable fraction of the molybdate occupies less accessible interlayer positions. A maximum in the H2O2 decomposition rate as the H2O2 concentration is increased is due to the successive formation of mono-, di-, tri-, and tetraperoxomolybdates. This behavior was modeled successfully by using the equilibrium constants for formation of the Mo-peroxo complexes, and the rate constants for decay of the peroxomolybdates with 1O2 liberation. Time-resolved diffuse reflectance and Raman observations of the various MoO4(2-)-peroxide adducts are in line with the proposed kinetic scheme. Of all the Mo-peroxo species on the LDH, the triperoxomolybdate has the highest rate for decay to 1O2. Comparison with the kinetics of dissolved molybdate shows that the monomolecular decay of all peroxomolybdate species proceeds much faster at the LDH surface than in solution. Consequently, maximal rates per Mo atom are at least twice as high for the heterogeneous LDH catalyst as for the homogeneous systems.     

Darstellung und Kristallstruktur von K3La(NH2)6

Preparation and Crystal Structure of K₃La(NH₂)₆. Single crystals of K₃La(NH₂)₆ were obtained by the reaction of the metals (3 K + 1 La) during five days at 200°C and 4000 atm NH₃ pressure. The compound crystallizes monoclinic with a = 6.74, b = 11.67, c = 7.23 Å and β = 108.1°; the space group is C2/m (No. 12). The lattice contains 2 formula units. The amide ions are arranged in a strongly distorted cubic closepacking. All cations occupy edging anion-octahedra.     

Reactivity of singlet oxygen toward strained substrates and a novel non-photochemical method for determination of quenching constants of singlet oxygen.

Rate constants for quenching of ¹O₂ by a number of strained molecules have been determined by the competitive rubrene photooxidation method; the rate constant for quenching by Q may be evaluated by adaption of a kinetic analysis already in the literature for the rubrene photooxidation method.     

Two-proton correlations in the target fragmentation region of nuclear collisions at 200A GeV

Correlations between protons are studied in the target fragmentation region of reactions of protons and¹⁶O with C, Cu, Ag, Au and of³²S with Al and Au at 200A GeV. The emitted protons were measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The comparison of the correlation function with calculations, assuming a spherical, gaussian shaped source with a lifetime τ=0 fm/c, allows the extraction of radius parameters. The values are very close to those expected from the geometry of the target nuclei and increase with the target mass as αA _Target ^1/3 . Even in proton induced reactions the whole target nucleus is involved. The dependence of the radii on centrality, polar angleθ _lab, and energy, and their relation to measured proton yields are presented.     

The role of additional solvents in transition metal complex catalyzed asymmetric reductions in ionic liquid containing systems

When ionic liquids (ILs) are employed as solvents for transition metal complex (TMC) catalyzed reductions, a second solvent can be added to increase the efficiency of the catalytic cycle and the solubility of the reactant in the IL phase. Two industrially relevant asymmetric hydrogenations, the enantioselective reductions of methyl 2-acetamidoacrylate with Rh-EtDuPHOS and methyl acetoacetate with Ru-BINAP, were performed in different catalytic systems including 1-butyl-3-methylimidazolium hexafluorophosphate/ tetrafluoroborate as ILs. Product separation and TMC recycling was performed by extracting the product from the reaction mixture. This can be accomplished by cooling the system, by adding an excess of the second solvent or by adding a third solvent. A high solubility of the second solvent in the IL catalytic phase favors the reaction activity, but can induce leaching of the IL and TMC.