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A phase equilibrium study of the system aluminiumbromide and pyridiniumbromide has been carried out. The phase diagram of the system indicates the existence of three congruently melting com pounds of the molar ratio AlBr3/PyHBr 1:1, 1:3, 2 :3 and one incongruently melting compound of the molar ratio 1:2 and is therefore similar to the AlCl3-PyHCl system [1].
From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX62- . A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A2TeX6 (A = Rb. Cs: X = Cl, Br) the averaged structure (m3̅m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar SnX62 compounds. Distortions therefore are very small and are evident from FTIR spectroscopic measurements only. Here very broad T1u-deformation vibration bands are observed down to temperatures <10 K without splitting: Astatically distorted species could not be frozen out. In contrast to XeF6 for TeX62- the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T1u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments.
The title compound has been prepared from (PPh4)2[Mo2(O2C-Ph)4Cl2] and CCl4 in CH2Cl2 solution as moisture sensitive crystals, which are black in reflexion and yellow in transmission. (PPh4)2[Mo2(O2C-Ph)4Cl4] · 2 CH2Cl2 was characterized by a X-ray crystal structure determination (7873 observed independent reflexions. R = 0.048). It crystallizes in the space group P1̄ with one formula unit in the unit cell; the lattice constants are a = 1186.4; b = 1404.0; c = 1451.0 pm; α = 61.98°; β = 78.91°; γ = 78.26°. The structure consists of PPh4⊕ ions. CH2Cl2 molecules and centrosymmetric anions [Mo2(O2C-Ph)4Cl4]2⊝ containinga molybdenum d3 d3 unit with a relatively long Mo=Mo bond of 249.6 pm. The Mo≡Mo group is spanned in a chelate manner by four O atoms of two benzoate groups and by two further single O atoms of two further benzoate groups. Two terminal Cl atoms on each Mo atom complete the pentagonal bipyramidal coordination spheres about the Mo atoms.
MoF4(NCl) has been prepared as a yellow crystal powder by the reaction of diluted fluorine with MoCl3(N3S2) at room temperature. The compound is associated via fluorine bridges, according to the IR spectrum. With acetonitrile, the monomeric complex [CH3CN -MoF4(NCl)] is obtained, which was characterized by its IR and 19F NMR spectra as well as by an X-ray structure determination. Crystal data: space group Pm, Z = 2 (1068 observed, independent reflexions, R = 0.03). Lattice dimensions at -90 °C: a = 507.1. b = 704.8, c = 995.8 pm, β = 102.02°. The unit cell contains two crystallographically independent molecules [CH3CN -MoF4(NCl)], the Mo≡N-Cl groups being linear (bond angles 176°, 178°) with bond lengths MoN = 172 and NCI = 159, 162 pm. In the trans position to the MoNCl group, the nitrogen atom of the acetonitrile molecule is coordinated.
Cp2TiSe5 has been prepared by the reaction of trim ethyltetradecylammonium-polyselenide with Cp2TiCl2 in ethanol solution and subsequent extraction of the dry residue with dichloromethane. Cp2TiSe5 crystallizes in the space group P1 with two formula units in the unit cell (2559 observed, independent reflexions, R = 0.074). The cell dimensions are a = 808.6, b = 822.6, c = 1190.7 pm, α - 96.28°, β - 106.06°, γ = 108.78°. The structure consists of discrete Cp2TiSe5 molecules with the TiSe5, ring in the chair conformation.
Coordination of substitutionally inert [Ru(bpy)2]2+ fragments (bpy: 2,2′-bipyridine) to the a-iminoketone chelate ligands pyrazine-2-dimethylcarboxamide (4) and 4,7-phenanthroline-5,6-dione (5) yields the complexes [(N,O-4)Ru(bpy)2]2⊕, [(O,O′-5⊖)Ru(bpy)2]⊕ and {(N,O; N′,O′-5)[Ru(bpy)2]2}4⊕ which exhibit a rich electrochemistry. The distinctly different electronic structures of the complexes are evident from the ESR behaviour of paramagnetic intermediates: N.O-coordinated complexes have the unpaired electron residing in the ligand n system upon reduction, albeit with g<2 for the binuclear complex of 5. The paramagnetic O,O′-coordinated mononuclear complex with 5 has its redox potentials shifted positively relative to that of the binuclear system. These results are particularly noteworthy because 4 and 5 can be regarded as model compounds for the flavin and methoxatin dehydrogenase cofactors.
(NBu4)[CoCl3(PPh3)] reacts with Se(SiMe3)2 to form the new clusters [Co8Se8(PPh3)6][CoCl3(PPh3)] (6) and [Co8Se8(PPh3)6][Co6Se8(PPh3)6] (7). The structures of 6 and 7 have been determ ined by X-ray diffraction. 6 and 7 crystallize in the space group P1̄ with two formula units per unit cell and with the following lattice constants at 180 K: 6: a = 1413.8(10), b - 2224.2(23), c = 2348.4(17) pm, α = 86.06(5), β = 86.58(5), γ = 76.11(5)°; 7: a = 1465.9(4), b = 1627.6(6), c = 2505.7(6) pm, α - 98.69(2), β = 96.23(2), γ = 113.06(2)°. The cluster structures of the [Co8Se8(PPh3)6]n (n = 0, 1 +) depend on the total number of electrons in the cluster units.
Photoelektronen-Spektren und Moleküleigenschaften, 110 [1,2]. Tricyanmethan-Derivate X—C(CN)3
(1987)
The photoelectron spectra of tricyanomethane derivatives X-C(CN)3 with substituents X = H, CH3, Br and C6H5 have been recorded and are assigned based on MNDO calculations as well as on radical cation state comparison with the iso(valence)electronic P(CN)3, within the series of cyanomethanes H4-nC(CN)n, and with each other. For HC(CN)3, no traces of the isomeric dicyano, ketimine HN = C=C(CN)2 are detected in the gas phase. Tricyanomethylbenzene, H5C6-C(CN)3, exhibiting the highest first ionization energy of any known singly acceptor substituted phenyl derivative, demonstrates the tremendous electron withdrawing effect of the -C(CN)3 group.
Trifluoromethyl azide decomposes in a low-pressure flow system at rather high temperatures by splitting off N2. The nature of the resulting products depends largely on the wall material of the pyrolysis tube: using molybdenum above 1120 K, FCN is observed exclusively. Neither F2C=NF nor F3C-N=N-CF3 can be detected as intermediates by comparing their PE spectra with those continuously recorded while increasing the temperature. F3C-N = N - CF3 fragments already at 870 K to give N2 and F3C-CF3. The PE spectra of F3CN3 and F2C=NF are assigned based on MNDO calculations.
The HCl elimination from β-chloroethyl azide (1-azido-2-chloroethane) over potassium tert. butanolate at 350 K in a low pressure flow system is optimized using PE spectroscopic real-time gas analysis. The highly explosive vinyl azide formed can be purified by cool-trapping the by-products. Its subsequent and virtually hazard-free pyrolysis yields 2H-azirine, which can be isolated at temperatures below 240 K.
In contrast, the direct pyrolysis of β-chloroethyl azide requires temperatures above 710 K and results in a simultaneous split-off of both HCl and N2, yielding acetonitrile as the main thermolysis product. No intermediates such as β-chloroethanimine or ketenimine are observed, a result which is interpreted in terms of chemical activation.