The peri-bridged naphthalenes Cl0I+,XY with XY = SS, SSe, STe, SeSe, SeTe, TeTe all exhibit low first vertical ionization potentials at about 7.1 eV and, therefore, can be oxidized using AIC13/H2CC12. The radical cations generated (XY = SS to SeTe) are stable at room temperature. The chalcogen bridges dominate the species M'@ regarding spin population as well as charge distribution and, correspondingly, the ESR spectra reflect the effect of increasing spin/orbit inter- A novel and elegant synthesis6) reacting a THF solution of l,%dilithio-naphthalene at -78°C with powdered chalcogens has been extended successfully to prepare the mixed derivatives with SSe-, STe-, and SeTe-bridges7). Starting from known molecular properties of bis(methy1thio)-substituted naphthalenes3) as well as of Chem. Ber. 114(1981) 0 Verlag

Trimethylsilyl substituents have a differential effect on the individual molecular states of neighboring K systems: In general they act as K acceptors in radical anions[3a1 or carbanions[3b1, are weak donors in the ground state of the neutral and-as will be shown in the present communication-are able to considerably delocalize the positive charge in iadical cations.Experience shows[41 that radical cations M" can be generated in solution from molecules M having first ionization energies l E l 5 8 eV and characterized by ESR spectroscopy. Thus the first band in the photoelectron spectrum of the tetrasilyl-substituted ethylene derivative 2,2,4,4,6,6,8,8-octamethyl-2,4,6,8-tetrasilabicyclo[3.3.O]oct-l-ene~51 occurs at 7.98 eV, and the ESR spectrum of its radical cation is observed after reaction with AlCI, in CH2C12 at 180 K (Fig. 1).

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Ein neuer Typ „persistenter”︁ Radikalionen ist durch Oxidation sowie durch Reduktion eines tetrasilylsubstituierten Ethylens zugänglich. Wie aus den ESR‐Spektren des Kations (1) und des Anions (2). ‐und der damit isoelektronischen Radikalkationen entsprechender Hydrazinderivate ‐ hervorgeht, liegen diese Spezies in Lösung nicht als π‐, sondern als σ‐Radikale vor.magnified image

The oxidation of hexakis(alky1thio)ethanes (RS),C -C(SR), by AICI,/H2CCI2, NOBF,, or I, yields tetrakis(alky1thio)ethene radical cations (RS),C'~C(SR),. The dark violet tetrahydrotetrathiafulvalenium triiodide 1 . I, (n = 2) has been obtained as acrystalline solid.Other derivatives such as the dibenzotetrathiafulvalene (2) and the quinodimethane (4) radical cations have been characterized by ESR spectroscopy in solution: The coupling constants and the y values reveal that the spin density accumulates preferentially at the S centers. The alkyl proton coupling is rationalized advantageously by angle-independent spin polarization. For tetrathiafulvalene, geometry-optimized MNDO calculations predict a lengthening of the central C = C bond on oxidation and the positive charge centered predominantly at sulfur.Elektronenreiche Chalkogen-Verbindungen sind von aktuellem Interesse, da ihre stapelartigen CT-Komplexe, wie z. B. der aus Tetrathiafulvalen und Tetracyanchinodimethan, elektrische Leitfahigkeiten bis 300 R-cm-aufweisen4). Allgemein besitzen Molekiile mit mehreren Schwefelatomen niedrige erste Ionisierungsenergien s- ' ) -so Tetrakis(methy1thio)ethen 7.75 eV ' ) -und lassen sich daher meist auch in Losung oxidieren -1 3 ) -so zu Tetrakis(methy1thio)ethen-Radikalkationen *).Ein weiterer Prototyp elektronenreicher Schwefelverbindungen sind Hexakis(alky1-thio)-oder -(arylthio)ethane9. 14, 15), aus denen oberhalb 370 K als Hauptprodukte's) Tetrakis(alky1-oder ary1thio)ethene entstehen. Bei dieser Zersetzung lasseh sich ESR-