Untersuchungen am Chlordiphenyl‐ und Tribenzylstiban sowie am Tribenzyldibromstiboran – Molekülstrukturen und Isotypie

Element–Element Bonds. X. Studies of Chloro(diphenyl)stibane, Tribenzylstibane and Tribenzyldibromostiborane – Molecular Structures and Isotypism Chlorodiphenylstibane ( 1 d ) {P2₁/c; Z = 4; a = 1191.8(1); b = 853.4(1); c = 1112.0(1) pm; β = 93.60(1)°; –100 ± 2 °C} crystallizes isotypically with a series of homologous (H₅C₆)₂E–X compounds (E = As, X = Cl, Br, I; E = Sb, X = Br, I); the structure type of tribenzylstibane ( 5 d ) {Pbca; Z = 8; a = 832.1(2); b = 2681.3(5) pm; c = 1600.9(3); –100 ± 3 °C} is already known from tribenzylmethanol, ‐silanol and ‐silane. Tribenzyldibromostiborane ( 6 ) {P2₁/n; Z = 4; a = 938.4(2); b = 2292.4(5); c = 1019.7(2) pm; β = 112.71(1)°; –100 ± 3 °C} does not show an analogous relationship to known structure types. Characteristic mean bond lengths and angles are { 1 d , Sb–Cl 240.9(1), Sb–C 214.0 pm, Cl–Sb–C 93.8°, C–Sb–C 98.6(1)°; 5 d , Sb–C 217.5(3) pm, C–Sb–C 94.9(6)°; 6 , Sb–Br 264.6; Sb–C 217.0(8) pm, Br–Sb–Br 179.4(1)°; C–Sb–C 120°; Br–Sb–C 84.8(2)° to 94.7(2)°}. Stiborane 6 exhibits very weak intermolecular Sb‥Br interactions of 417 pm which, however, affect the molecular conformation in a striking way.     

Real molecules as models for mathematical chemistry

A [2]-catenane consisting of methylene groups and two additional acetylated aza groups has been synthesized in a multi-step sequence. After splitting off the acetyl bonds, the resulting secondary diamine should provide a good starting material for stepreaction (condensation or addition, respectively) polymerization.     

13C n.m.r. spectra of N,N-dialkylamides

Carbon-13 n.m.r. spectra of formic, acetic, propionic and butyric acid amides with N,N-di-n-alkyl substituents have been completely assigned with the aid of extensive double resonance experiments. The data obtained were used to study long range steric effects on chemical and solvent shifts.     

Local limit theorems for transition densities of Markov chains converging to diffusions

We consider triangular arrays of Markov chains that converge weakly to a diffusion process. Local limit theorems for transition densities are proved. Received: 28 August 1998 / Revised version: 6 September 1999 / Published online: 14 June 2000     

Diaryldichalcogenide radical cations

One-electron oxidation of two series of diaryldichalcogenides (C₆F₅E)₂ (13a–c) and (2,6-Mes₂C₆H₃E)₂ (16a–c) was studied (E = S, Se, Te). The reaction of 13a and 13b with AsF₅ and SbF₅ gave rise to the formation of thermally unstable radical cations [(C₆F₅S)₂]˙⁺ (14a) and [(C₆F₅Se)₂]˙⁺ (14b) that were isolated as [Sb₂F₁₁]^– and [As₂F₁₁]^– salts, respectively. The reaction of 13c with AsF₅ afforded only the product of a Te–C bond cleavage, namely the previously known dication [Te₄]²⁺ that was isolated as [AsF₆]^– salt. The reaction of (2,6-Mes₂C₆H₃E)₂ (16a–c) with [NO][SbF₆] provided the corresponding radical cations [(2,6-Mes₂C₆H₃E)₂]˙⁺ (17a–c; E = S, Se, Te) in the form of thermally stable [SbF₆]^– salts in nearly quantitative yields. The electronic and structural properties of these radical cations were probed by X-ray diffraction analysis, EPR spectroscopy, and density functional theory calculations and other methods.     

F3CCN5S3, A BICYCLIC MULTIFUNCTIONAL SULFUR-NITROGEN LIGAND

The bicyclic sulfur-nitrogen heterocycle F₃CCN₅S₃ (1) was investigated as a donor and acceptor toward H⁺, metal cations, and F^?. Whereas the protonated species F₃CCN₅S₃H⁺ AsF₆ ^? (2) can be isolated, the product of the reaction with F^? is unstable and decomposes among other products to TAS⁺ F₃CCN₅S₃NC(NH₂)CF₃ ^? (3), which is isolated from this reaction in small amounts.