Thianthren‐Radikalkation‐Tetrachloroaluminat

Structures and Molecular Properties of Charge‐Perturbed Molecules, 53 [1,2] . — Thianthrene Radical Cation Tetrachloroaluminate One‐electron oxidation of thianthrene, which exhibits a reversible half‐wave potential at + 1.3 V and an irreversible one at + 1.65 V, under aprotic conditions with AlCl 3 /H 2 CCl 2 yields the violet radical cation salt [H 4 C 6 S 2 C 6 H 4 ⊕ ][AlCl 4 ⊖ ]. Its single‐crystal structure analysis at 90 K reveals an interplanar angle between the phenyl rings of 174° and demonstrates that the neutral sulfur heterocyclic molecule, bent by 128°, is considerably flattened upon one‐electron removal. Semiempirical enthalpy of formation hypersurfaces allow to rationalize the experimental results by a double‐minimum potential for the bent neutral molecule with a rather low inversion barrier and a single minimum one for a planar radical cation. Other radical cation properties such as the spin distribution deduced from its ESR spectrum or the visible absorption maxima near \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document} = 11000 and at 18250 cm ‐1 corresponding to π → π * and π → σ * transitions are also satisfactorily reproduced by PM3 calculations partly including configuration interaction based on the experimental structure.