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).     

Sensing the ortho Positions in C6Cl6 and C6H4Cl2 from Cl2− Formation upon Molecular Reduction

The geometrical effect of chlorine atom positions in polyatomic molecules after capturing a low-energy electron is shown to be a prevalent mechanism yielding Cl₂⁻. In this work, we investigated hexachlorobenzene reduction in electron transfer experiments to determine the role of chlorine atom positions around the aromatic ring, and compared our results with those using ortho-, meta- and para-dichlorobenzene molecules. This was achieved by combining gas-phase experiments to determine the reaction threshold by means of mass spectrometry together with quantum chemical calculations. We also observed that Cl₂⁻ formation can only occur in 1,2-C₆H₄Cl₂, where the two closest C–Cl bonds are cleaved while the chlorine atoms are brought together within the ring framework due to excess energy dissipation. These results show that a strong coupling between electronic and C–Cl bending motion is responsible for a positional isomeric effect, where molecular recognition is a determining factor in chlorine anion formation.     

Reactions between rubidium atoms and C6F6, C2Cl4, C2HCl3, CH2=CCl2 or trans-C2H2Cl2 in crossed molecular beams

Molecular and fragment negative ions are produced from the collisions between rubidium atoms and several kinds of halogenated unsaturated organic molecules in crossed supersonic beams. Their apparent electron affinities and the bond dissociation energies are measured.     

The pyrolysis of CCl4 and C2Cl6 in the gas phase. Mechanistic modeling by thermodynamic and kinetic parameter estimation

A detailed radical reaction mechanism is proposed to describe the thermal reactions of CCl₄ and C₂Cl₆ in the gas phase quantitatively. A consistent set of activation energies and preexponential factors for all elementary reactions, in combination with enthalpies of formation and entropies for all species involved, is computer optimized to fit experimental pressure-rise curves and concentration profiles. For this purpose new experimental results on the pyrolysis of CCl₄ are used, together with published kinetic data on the pyrolysis of C₂Cl₆ (in the absence and in the presence of Cl₂). © 1996 John Wiley & Sons, Inc.     

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 the pyrolysis of C2HCl5, molecular and radical steps

An analysis of the thermochemistry of the kinetic parameters of the elementary reactions involved in the pyrolysis of pentachloroethane has resolved several disputed, unclarified, or inconsistent aspects of the reaction mechanism. The resulting mechanisms for the inhibited and uninhibited pyrolysis account for all reported experimental findings. On the basis of this interpretation, first experimentally based values have been derived for the following: DH⁰(CCl₃–CHCl₂) = 79.0 ± 1.0 kcal/mol, ΔH${}_{\text{f}}^{\text{0}}$(CHCl₂) = 25.7 ± 1.0 kcal/mol, and E₁ = 59.7 ± 1.0 kcal/mol C₂HCl₅ .     

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).     

ESR study of the photolysis of C60Cl6

The photolysis of C₆₀Cl₆ in the presence of α-phenyl-N-tert-butylnitron (PBN) as a spin trap was studied by ESR spectroscopy. It was shown that a C−Cl bond undergoes homolytic cleavage to give a stable fullerenyl radical of the cyclopentadienyl type, whose formation was confirmed by quantum-chemical computations. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 752–754, April, 2000.     

NaEu2Cl6 und Na0,75Eu2Cl6: Gemischtvalente Chloride des Europiums mit Natrium

NaEu₂Cl₆ and Na_0.75Eu₂Cl₆: Mixed Valent Chlorides of Europium with Sodium The reaction of Na₂EuCl₅ with Eu metal in sealed gold tubes yields blue single crystals of NaEu₂Cl₆. It crystallizes with the hexagonal crystal system (space group P6₃/m) with a = 755.74(8) pm, c = 429.81(5) pm, Z = 1; the structure is closely related to the UCl₃-type. Green single crystals of Na_0.75Eu₂Cl₆ were first obtained as a by-product in the synthesis of Na₂EuCl₅ in evacuated silica tubes and may be prepared by reduction of EuCl₃ with sodium. Na_0.75Eu₂Cl₆ crystallizes isotypic to NaEu₂Cl₆ with a = 753.69(11) pm and c = 416.3(2) pm.     

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.     

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.     

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+.