Pr6C2‐Doppeltetraeder in Pr6C2Cl10 und Pr6C2Cl5Br5

Pr₆C₂‐Bitetrahedra in Pr₆C₂Cl₁₀ and Pr₆C₂Cl₅Br₅ The compounds Pr₆C₂Cl₁₀ and Pr₆C₂Cl₅Br₅ are prepared by heating stoichiometric mixtures of Pr, PrCl₃, PrBr₃ and C in sealed Ta capsules at 810 ? 820 °C. They form bulky transparent yellow to green and moisture sensitive crystals which have different structures: space groups C2/c, (a = 13.687(3) Å, b = 8.638(2) Å, c = 15.690(3) Å, β = 97.67(3)° for Pr₆C₂Cl₁₀ and a = 13.689(1) Å, b = 10.383(1) Å, c = 14.089(1) Å, β = 106.49(1)° for Pr₆C₂Cl₅Br₅). Both crystal structures contain C‐centered Pr₆C₂ bitetrahedra, linked via halogen atoms above edges and corners in different ways. The site selective occupation of the halogen positions in Pr₆C₂Cl₅Br₅ is refined in a split model and analysed with the bond length‐bond strength formalism. The compound is further characterized via TEM investigations and magnetic measurements (μ_eff = 3.66 μ_B).     

Reactions of Cl2P3/2: Absolute rate constants for reaction with H2, CH4, C2H6, CH2Cl2, C2Cl4, and c?C6H12

The absolute rate constants have been measured for several gas-phase chlorine atom-molecule reactions at 25°C by resonance fluorescence. These reactions and their corresponding rate constants in units of cm³ mole^?1 sec^?1 are: The effects of varying the substrate pressure, total pressure, light intensity and chlorine-atom source on the value of the bimolecular rate constants have been investigated for all these reactions. Conditions under which no competing side reaction occurs were established and the reported rate constants were measured under these conditions. For reactions (2), (5), (6), (7), and 8, there is a discrepancy of a factor of two between the rate constants measured in this work and values in the literature; it is suggested that this is due to an error in the previously measured value of k/k upon which the relative measurements in the literature ultimately depend.     

Mechanism of pyrolysis of C2Cl6

Using published data on the kinetics of pyrolysis of C₂Cl₆ and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations: The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease. From the analysis, the bond dissociation energy DH⁰(C₂Cl₅? Cl) is found to be 70.3 ± 1 kcal/mol and ΔH_f300⁰(·C₂Cl₅) = 7.7 ± 1 kcal/mol. The resulting π? bond energy in C₂Cl₄ is 52.5 ± 1 kcal/mol.     

Zur Bildung gasförmiger MCl2-Komplexe. Vergleichende Untersuchung zur Eignung von Al2Cl6, Ga2Cl6, In2Cl6, Fe2Cl6, SiCl4, TiCl4, PCl5, TaCl5 und U2Cl10 als Komplexbildner

Formation of Gaseous MCl₂ Complexes. Comparative Study on the Suitability of Al₂Cl₆, Ga₂Cl₆, In₂Cl₆, Fe₂Cl₆, SiCl₄, TiCl₄, PCl₅, TaCl₅, and U₂Cl₁₀ as Complex Former The thermodynamic data for reactions of the type MCl_2,s + L₂Cl_6,g = ML₂Cl_8,g are – as expected – nearly independent on L(Al, Ga, In, Fe). Transport rates e. g. of CoCl₂ something smaller with L ? Ga may be traced back on uncertainties concerning the Ga₂Cl₆ dissociation, and with L ? Fe they may be traced back on the incorporation of FeCl₂ into MCl_2,s. SiCl₄ and TiCl₄ cause no noticable transport of CoCl₂ or CuCl₂ in a temperature gradient, which leads to a short bond consideration. PCl₅ and TaCl₅ cause the transport of small amounts of CoCl₂. U₂Cl₁₀/UCl₅ are able to transport a remarkable amount of CaCl₂ and CoCl₂, respectively.     

Dissociative electron attachment to CH2Cl2, CHCH3Cl2, and C(CH3)2Cl2

We perform theoretical studies of dissociative electron attachment (DEA) for the compounds CH(2-n)(CH(3))(n)Cl(2), n = 0, 1, 2, by combining the finite-element discrete model with the resonance R-matrix theory. An unexpectedly low DEA cross section for CH(2)Cl(2) is likely due to the relatively large resonance width for this compound that confirms experimental observations. However, there are some quantitative discrepancies with the experimental results. Since DEA cross sections are very sensitive to the resonance width, a slight adjustment of its value can significantly improve agreement between theory and experiment. Our calculation of the thermal rate coefficients show that there are some inconsistencies between beam and swarm measurements and between different swarm measurements of the rate coefficients for DEA to CH(2)Cl(2). Further experimental and theoretical studies are warranted.     

Condensed two- and three-dimensional aromatic systems: a theoretical study on the relative stabilities of isomers of CB19H16+, B20H15Cl, and B20H14Cl2 and comparison to B12H10Cl22-, C6H4Cl2, C10H7Cl, and C10H6Cl2

DFT studies (B3LYP/6-31G) on mono- and dichloro derivatives of benzene, naphthalene, B12H12(2-), four-atom-sharing condensed systems B20H16, and monocarborane isomers of B20H16 are used to compare the variation of relative stability and aromaticity between condensed aromatics. The trends in the variation of the relative energies and aromaticity in these two- and three-dimensional systems are similar. Aromaticity, estimated by NICS values, does not change considerably with condensation or substitution. The minor variation in the relative energies of the isomers of chloro derivatives is explained by the topological charge stabilization rule of Gimarc. The compatibility of the cap and ring orbitals decides the relative stability of CB19H16+.     

Reaction of Cl atoms with C6F13CH2OH, C6F13CHO, and C3F7CHO

The Cl atom initiated oxidation of C(6)F(13)CH(2)OH, C(6)F(13)CHO, and C(3)F(7)CHO was investigated at 298 K and 1000 mbar pressure of air in a photoreactor using in situ Fourier transform infrared (FTIR) analysis. The rate coefficient for the reaction Cl + C(6)F(13)CH(2)OH (reaction 2) was measured using a relative method: k(2) = (6.5 +/- 0.8) x 10(-13) cm(3) molecule(-1) s(-1). C(6)F(13)CHO was detected as the major primary product, while CO and CF(2)O were found to be the major secondary products. A fitting procedure applied to the concentration-time profiles of C(6)F(13)CHO provided a production yield of (1.0 +/- 0.2) for this aldehyde in reaction 2, and the rate coefficient for the reaction Cl + C(6)F(13)CHO (reaction 4) was k(4) = (2.8 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1). A high CO yield observed in the oxidation of C(6)F(13)CH(2)OH, (52 +/- 1)%, is attributed to the Cl atom initiated oxidation of C(6)F(13)CHO. High CO yields, (61 +/- 2)% and (85 +/- 5)%, were also measured in the Cl atom initiated oxidation of C(3)F(7)CHO in air and nitrogen, respectively. These high CO yields suggest the occurrence of a decomposition reaction of the perfluoroacyl, C(6)F(13)CO, and C(3)F(7)CO radicals to form CO which will compete with the combination reaction of these radicals with oxygen to form perfluoroacyl peroxy radicals in the presence of air. The latter radicals C(n)F(2)(n)(+1)CO(O)(2) (n = 6-12), through their reaction with HO(2) radicals, are currently considered as a possible source of persistent perfluorocarboxylic acids which have been detected in the environment. The consequences of the present results would be a reduction of the strength of this potential source of carboxylic acids in the atmosphere.     

Cu3AlCl6 und Cu2Al2Cl8, die Gaskomplexe im System CuCl/Al2Cl6

Cu₃AlCl₆ and Cu₂Al₂Cl₈, Gas Complexes in the System CuCl/Al₂Cl₆ Investigations by mass spectroscopy in the system CuCl_s/Al₂Cl_6,gestablished that only Cu₃AlCl₆ and Cu₂Al₂Cl₈ are observed as principal gas complexes. Results of flow measurements published by LAUGHLIN and Gregory (1976) which were attributed erroneously by these authors to the complex CuAlCl₄ may be described by the equilibria given in “Inhaltsübersicht”. The complexes cu₃AlCl₆ and Cu₂Al₂Cl₈ are supposed to have a cube type structure similar to Cu₄Cl₄.     

Calculation of 13C shielding of the isotopomers CH3Cl,CH2DCl,CHD2Cl,and CD3Cl

The ¹³C shielding of the isotopomers CH₃Cl, CH₂ DCl, CHD₂Cl, and CD₃Cl has been calculated for a range of temperatures from an self-consistent field (SCF) shielding surface computed by Buckingham and Olegario. It is found that each successive deuterium substitution increases the shielding by about 0.19 ppm and that a very slight nonadditivity occurs. The principal factor which governs the nuclear motion correction for each isotopomer is the stretching of the bonds with both first- and second-order terms being significant. Angle bending contributions are very small at first order but quite substantial at second order. Not only should the ¹³C-isotope shifts in this experimentally uninvestigated series be easily measured but the temperature dependence of the shielding in any one isotopomer should be observable provided that careful measurements are made. The ¹³C-shielding difference between CH₃ ³⁵Cl and CH₃ ³⁷Cl has also been calculated and is found to agree well with experiment. © 1996 John Wiley & Sons, Inc.     

Darstellung von trans-[Mo6Cl8]Cl4Br22−ausgehend von kristallisierten [Mo6Cl8]Cl4(H2O)2 und die Kristallstruktur von [(C6H5)4As]2[Mo6Cl8]Cl4Br2

Preparation of trans-[Mo₆Cl₈]Cl₄Br₂^2? Starting from Crystalline [Mo₆Cl₈]Cl₄(H₂O)₂ and Crystal Structure of [(C₆H₅)₄As]₂[Mo₆Cl₈]Cl₄Br₂ The synthesis of the title compound is successful if the crystallized [(Mo₆Cl₈)Cl₄(H₂O)₂] containing the H₂O molecules in trans-position reacts with HBr + [(C₆H₅)₄As]Br in ethanol in a heterogeneous reaction. The X-ray structure investigation confirms the existence of discrete trans-Br-substituted cluster anions of composition [(Mo₆Cl₈)Cl₄Br₂]^2? in the crystal. The reaction in homogeneous solutions proceeds to Br-enriched compounds. [(C₆H₅)₄As]₂[(Mo₆Cl₈)Cl₄Br₂] crystallizes in the triclinic space group P¯1 with a = 11.071(2), b = 11.418(2), c = 12.813(2) Å, α = 116.10(2), β = 95.27(2) and γ = 94.41(2)° (?133°C). The crystal structure at ?133°C was determined from single crystal X-ray diffraction data (R₁ = 0.026). The [(Mo₆Cl₈)Cl₄Br₂]^2?-anions are not completely ordered but distributed statistically among the three positions which are possible within the limits of the ordered [Mo₆Cl₈]-cores (ratio 11:5:4). The frameworks of the anions consist of Mo₆ cluster units with (slightly distorted) octahedral arrangement of the metal atoms (d(Mo? Mo): 2.600(1) up to 2.614(1) Å), which are coordinated by the halogeno ligands in a square-pyramidal manner. The details of the structure will be discussed and compared with similar [(Mo₆X₈)Y₄] cluster units (X, Y ? Cl, Br).     

Gd10C4Cl18 und Gd10C4Cl17, zwei Seltenerdmetall-Clusterverbindungen mit interstitiellen C2-Gruppen

Gd₁₀C₄Cl₁₈ and Gd₁₀C₄Cl₁₇, Two Lanthanoid Cluster Compounds with Interstitial C₂ Units The compounds Gd₁₀C₄Cl₁₈ ( I ) and Gd₁₀C₄Cl₁₇ ( II ) are prepared by heating stoichiometric amounts of GdCl₃, Gd, and graphite in sealed tantalum tubes at 1070 ( I ) and 1 120 K ( II ). Single crystal investigations ( I : P2₁/c, Z = 2, a = 918.2, b = 1 612.0, c = 1 288.6 pm, β = 119.86°; II : P1 , Z = 1, a = 849.8, b = 917.4, c = 1 146.2 pm, α = 104.56°, β = 95.98°, γ = 111.35°) revealed the occurrence of novel Gd₁₀C₄Cl₁₈ clusters. The metal framework is formed by edge-sharing of two Gd₆ octahedra. These are centred by C₂ units (d_{C? C} = 147 pm) and Cl atoms bridge all available edges of the octahedra. The structure of I corresponds to a packing of such quasi molecular clusters, in II they are linked to chains via common Cl atoms. Both structures are discussed in terms of a model of close packed spheres as well as in the concept of condensed clusters.     

Die Reaktion von Quarzglas mit Al2Cl6,g und mit Alrf + Al2Cl6,g

Reaction of Quartz Glass with Al₂Cl_6,g and with Al,_f + Al₂Cl_6,g The attack of quartz glass by Al₂Cl_6,g at temperatures ≧ 300°C results in the formation of SiCl_4,g. At low temperature the oxygen appears as gaseous oxide chloride (e. g. Al₄OCl₁₀…); above 300°C crystalline AlOCl is observed, whereas at more elevated temperatures Al₂O₃ is formed. With Al + Al₂Cl₆ (1 atm, 20°C) at 400/350°C thin silicon foils with metallic luster deposit on the quartz wall. Discussion of the experimental evidence leads to the suggestion that the reduction of SiCl₄ — formed initially by attack of the quartz vessel — proceeds by reaction with Al₂Cl_4,g.     

KEu2Cl6 und K1, 6Eu1, 4Cl5: Zwei neue gemischtvalente Europiumchloride

KEu₂Cl₆ and K_1.6Eu_1.4Cl₅: Two New Mixed‐Valent Europium Chlorides The reaction of the binary chlorides EuCl₃, EuCl₂ and KCl yields the mixed‐valent compounds KEu₂Cl₆ and K_1.6Eu_1.4Cl₅. KEu₂Cl₆ (hexagonal, P6₃/m, Z = 1, a = 788.87(13), c = 411.41(6) pm, R₁ = 5.40 %) crystallizes with an addition‐variant of the UCl₃‐type of structure with tricapped trigonal prismatic coordination for the europium cations. The K⁺ ions reside in channels along [001] and exhibit extremely large displacement parameters U₃₃. The crystal structure of K_1.6Eu_1.4Cl₅ (orthorhombic, Pnma, Z = 4, a = 1260.49(12), b = 871.05(9), c = 787.18(10) pm, R₁ = 4.77 %) is closely related to that one of K₂EuCl₅ if the K⁺ and the Eu³⁺ ions are partly substituted for Eu²⁺. Absorption spectra show transitions, which can be assigned to Eu²⁺ and Eu³⁺ ions, and additional transitions due to interaction of both cations occupying common positions.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

Kinetics and mechanism of the decomposition of Cs2Pt[CH3]2Cl4 in aqueous solution with concurrent formation of C2H6, C2H4, and C2H5Cl

Reductive elimination of ethane from Cs₂Pt(CH₃)₂Cl₄ in aqueous chloride solutions at 368 K is accompanied by C-H bond scission. A mechanism is proposed for the reaction which includes the intermediate formation of an ethylhydrideplatinum(IV) and an ethylplatinum(II) complex.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 154–158, March–April, 1993.