SYNTHESIS, PROPERTIES, AND X-RAY STRUCTURE OF 6-AZA-5,7,12,14-TETRATHIAPENTACENE AS A NOVEL POLYHETEROCYCLIC ELECTRON-DONOR, AND RELATED-COMPOUNDS

Two new compounds, 1-aza-2,3-dichlorothianthrene (5) and 6-aza-5,7,12,14-tetrathiapentacene (6) have been prepared by reaction of 2,3,5,6-tetrachloropyridine (4) and 1,2-benzenedithiol in dimethylformamide (DMF) in the presence of sodium bicarbonate. On the other hand, the synthesis of two known compounds, 1-azathianthrene (7) and 5,7,12,14-tetrathiapentacene (8) have been improved by using the same synthetic procedure as above, starting from 2,3-dichloropyridine and 1,2,4,5-tetrachlorobenzene, respectively. The radical cations of 6-8 have been generated in fluid solution and they are stable enough to be analyzed by electron paramagnetic resonance (EPR). The hyperfine coupling (hfc) constants in the EPR spectra have been assigned according with those from thianthrene radical cation (10), reported in the literature, and with semiempirical estimations (McLachlan method). The cyclic voltammogram of 6 exhibits a redox couple (E degrees = 1.07 V vs SCE) which is attributed to the oxidation to its radical cation 6(.+), and a second irreversible peak (E(p)(a) = 1.25 V) which is ascribed to the formation of the unstable dication 6(2+). X-ray structure of 6 shows that the molecule has a stable chair-shaped conformation with an interplanar angle between benzenes and pyridine ring of 134.7(1)degrees. The crystal packing presents a stacking pattern and the molecules overlap showing diagonal shifts in the stack.