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The compound [(PyH)3Br][AlBr4]2 is formed by melting stoichiometric amounts of AlBr/PyHBr in a ratio of 2:3. It crystallizes in the orthorhombic space group Pbca with lattice constants a = 1365.5(2), b = 1616.0(2), c = 2783.7(3) pm, Z = 8, Dc = 2.21 g/cm3. The structure was solved from 2810 diffractometer measured intensities (Cu -Kα radiation) and refined to Rw (F) = 0.071. The cation shows three pyridinium ions attached via N - H - Br hydrogen bonds to a central bromide ion. The N - Br distances are 321(1), 321(2) and 332(2) pm.
Crystal and molecular structure analysis of the electron rich title compound exhibits an undistorted, yet sterically shielded tetra(primary alkyl)-substituted double bond system with alternating anti-periplanar CH2SiMe3 substituents. The diastereotopic methylene protons have been located and their position correlated to the 1HNMR data and to the ESR hyperfine coupling constants of the corresponding radical cation. In contrast to the highly inert all-carbon derivative, tetraneopentylethene, the more electron-rich and more flexible organosilicon title compound reacts with bromine. Close to orthogonal arrangement between the C-C(H2)-Si planes and the ethene plane ensures effective, fourfold σ/π-hyperconjugation.
Crystal and molecular structure analysis of the title compound 1, a most electron rich carbosilane, exhibits a shallow boat conformation for the cyclohexadiene ring which is shielded by four bulky Me3Si groups. Multiple hyperconjugative interaction occurs between the two non-conjugated olefinic π systems and the four rather long (192 pm) carbon-silicon o bonds which form an angle of about 34° with the assumed π axis. The HOMO destabilization caused by this unique structural arrangement explains the energetically facile formation and subsequent reactivity of the cation radical 1+ which was found to undergo oxidative desilylation to the aromatic 1,4-bis(trimethylsilyl) benzene precursor in the single electron transfer reaction with TCNE.
The structurally different radical anions M⊖ of peralkylated 1-sila-2,5-diazacyclopentane-3,4-dithione and of tetrakis(isopropylthio)-p-benzoquinone are generated by reduction with potassium/2.2.2-cryptand under aprotic conditions in THF solution. On addition of Li⊕B(C6H5)4⊖, both form hitherto elusive sulfur-containing contact ion pairs, which are characterized by their ESR/ENDOR spectra.
For the first time, 107,109Ag ENDOR measurements in solution are reported. In addition, the formation of the known paramagnetic contact ion pair [Ag⊕(PR3)2(R2H2C6O2·⊖] on reduction of 3,5-di(tert-butyl)-o-benzoquinone in THF solution containing soluble silver salts and triphenylphosphine is studied by cyclic voltammetry.
[MONCl3 · NC - C2Cl3]2 has been prepared by the reaction of MONCl3 with trichloromethyl isocyanidedichloride, CCl3NCCl2 , in CH2Cl2 suspension. The compound forms redbrown. mois-ture sensitive crystals, which were characterized by their IR spectrum as well as by a crystal structure determination (2482 independent observed reflexions, R = 0.048). Crystal data (-70 °C): Space group P21/c, Z = 2, a = 674.2(2); b = 2128.2(11); c = 786.0(4) pm: β = 102.81(3)°. [MONCl3 • NC-C2Cl3]2 forms centrosymmetric dimeric molecules via chloro bridges with Mo-Cl bond lengths of 240.7 and 276.0 pm. The longer MoCl bond of the MOCl2MO ring is caused by the trans influence of the nitride ligand; the MoN bond length of 167 pm corresponds with a triple bond. The 2,3,3-trichloroacrylnitrile ligand is bonded by its nitrogen atom with a bond length of Mo -N = 216 pm; the Mo-N≡C-C sequence is almost linear with a remarkable short C-C bond of 143.0 pm.
The N,N'-bis(trimethylsilyl)benzamidinato complexes [C6H5 -C(NSiMe3)2MCl3]2(M = Ti. Zr) have been prepared by the reactions of N,N,N'-tris(trimethylsilyl)benzamidine [C6H5-C(NSiMe3)N(SiMe3)2] with titanium tetrachloride, and zirconium tetrachloride, respec-tively. The compounds form moisture sensitive, dark red (Ti) and white (Zr) crystals, which were characterized by crystal structure determinations. [C6H5-C(NSiMe3)2TiCl3]2 : space group P21/rc. Z = 2, 4373 observed independent reflexions, R = 0.034. Lattice dimensions (-90 °C): a - 959.0(8); b = 1196.5(8); c = 1770.9(11) pm; β = 93.79(4)°. [C6H5-C(NSiMe3)2ZrCl3]2 : space group P21/n. Z = 2, 3160 observed independent reflexions, R = 0.031. Lattice dimensions (-90 °C): a = 971.6(7); b = 1222.2(9); c = 1792.9(10) pm; β = 93.51(5)°.
Both complexes crystallize isotypically, forming centrosymmetric dimeric molecules via chloro bridges with bond lengths of 242.0 and 253.8 pm (Ti), and of 253.7 and 264.9 pm (Zr). The metal atoms complete their distorted octahedral surroundings with two chlorine ligands and the nitrogen atoms of the chelating amidinato ligand. The N atoms of the amidinato group are in equatorial and axial positions. This accounts for the different metal-nitrogen bond lengths of 207 pm (ax) and 199 pm (eq) in the titanium compound and 219 pm (ax) and 214 pm (eq) in the zirconium complex.
WCl4(NCl) has been prepared as a red-brown crystal powder by the reaction of tungsten hexacarbonyl with excess nitrogen trichloride in boiling CCl4. The complex is associated via chloro bridges, forming dimeric units, according to the IR spectrum. Thermal decomposition at 200 °C leads to tungsten nitride trichloride, WNCl3,. With acetonitrile, WCl4(NCl) reacts with formation of the monomeric complex [CH,CN-WCl4(NCl)], which was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P21/m, Z = 2 (1387 independent observed reflexions, R = 0.07). Lattice dimensions at 20 °C: a = 590.4(3), b = 729.0(3), c = 1124.6(4) pm, β = 100.63(2)°. The complex forms monomeric molecules, in which the tungsten atom has a distorted octahedral environment of four chlorine atoms in equatorial positions, and the acetonitrile molecule in trans-position to the group. Bond lengths WN = 172 and NCI = 161 pm; bond angle WNCl = 175.5°.
Di(methylthio)acetylene H3CS-C≡C-SCH3 reacts with S2C12 in AlCl3/H2CCl2 solution to the tetra(thiomethyl)thiophene radical cation (H3CS)4C4S·⊕ and with H3CSCl to the tetra(thiomethyl)ethene radical cation (H3CS)2C·=⊕C(SCH3)3. Their ESR spectra are assigned by comparison with literature data or those of analogous products obtained from other acetylene derivatives R-C≡C-R with R = SCH2CH3, CH3, C6H5 as well as based on HMO arguments. The possible course of the oxidative sulfuration is discussed.
[Na-15-Crown-5][MoF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with MoF4(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR and 19F NMR spectra as well as by an X-ray structure determination. Crystal data: space group P21/n, Z = 4 (3736 observed, independent reflexions, R = 0.034). Lattice dimensions at -70 °C: a = 823.5(4). b = 1612.2(9), c = 1383.4(8), β = 99.35(3)°. The compound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether molecule and by two fluorine ligands of the [MoF5(NCl)]- unit with Na-F distances of 228.3 and 249.6 pm. The Mo=N-Cl group of the anion is nearly linear (bond angle 175.8°) with bond lengths MoN = 172.9 and NCl = 161.8 pm.