Thianthrene and Related Heterocycles

Abstract

Liquid SO₂ was used as a solvent for complexation as well as redox reactions based on thianthrene and related heterocyclic molecules. With silver salt, AgX (X = BF₄^-, SbF₆^-), the complexes [Ag₂(TA)₂][BF₄]₂ · 3 SO₂ (1) and [Ag₂(TA)₃][SbF₆ ]₂ · 5 SO₂ (2), and with gold(III) chloride, the complex [AuCl₂(TA)₂][AuCl₄] (3) were obtained. The oxidation products contain radical cations of thianthrene, TA^·+, as found in the structure of (TA^·)(HSO₄) · H₂SO₄ (5) and (TA^·)[FeCl₄] (6), radical cation of selenanthrene in the structure of (SA^·)[AlCl₄] (8) and (SA^·)₂[SO₄(BF₃)₂] (10), and a structure with a bridging oxygen of <i>µ</i>-oxy-selenanthrene(2+), SAO(HSO₄)₂ (9). The reaction between thianthrene and aluminum chloride was also performed without solvent, resulting in an adduct [AlCl₃(TA)] (4) and a unique thianthrene "triple decker", (TA₃)[Al₂Cl₇]₂ (7). An unexpected phenazine salt, (H₂PAz)(HSO₄)₂ (11) was obtained from phenazine in an oxidative environment. All compounds were examined by single crystal <i>X</i>-ray diffractometry. The gold and aluminum complexes were additionally characterized by UV-Vis, IR and Raman spectra, calorimetry and conductivity measurements. Cyclic voltammetry measurements of thianthrene in SO₂ at room temperature were performed using a self-made pressure-tight electrochemical cell and electrodes with the result that liquid SO₂ does not reduce the oxidation potential of thianthrene. The influence of SO₃, which is often present in liquid SO₂ as impurity, was also studied, confirming its role in the oxidation of thianthrene. The use of liquid SO₂ combined with weak coordinating anions allows complexation of silver ion with higher coordination number, bonded to thianthene via S atoms. SO₃ as an impurity in liquid SO₂ is the most probable source for oxidation reaction leading to the compounds containing radical cations. Thianthrene undergoes self-oxidation processes in the presence of AlCl₃, both with or without solvent. Close TA · · · TA arrangements in the crystal structures should be an indication of the electrical semiconductivity.