The radical ions of acenaphtho[1,2-b][1,4]dithiine derivatives and acenaphtho[1,2-b][1,4]oxathiine: Solution EPR and ENDOR studies. The X-ray crystal structures of 8,9-bis(methylsulfanyl)acenaphtho[1,2-b][1,4]dithiine and its complexes with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), 2,5-dibromo-TCNQ and iodine

Abstract

Syntheses of acenaphtho[1,2-b][1,4]oxathiine 4 and 8,9-bis(methylsulfanyl)acenaphtho[1,2-b][1,4]dithiine 5 are reported. The fairly persistent radical ions of acenaphtho[1,2-b][1,4]dithiine 1, acenaphtho[1,2-b][1,4]benzodithiine 2, acenaphtho[1,2-b]thieno[3,4-e][1,4]dithiine 3, and 4, i.e. 1^˙+–4^˙+ and 1^˙––4^˙–, were generated from their neutral precursors and their EPR and ENDOR spectra are reported. Oxidation to the radical cations implies an electron removal from the heteroatoms of the donor dithiine or oxathiine moiety which houses the bulk of the spin population. Accordingly, in the EPR spectra of 1^˙+–4^˙+, the ¹H-hyperfine pattern is only 0.25–0.70 mT wide, while the ³³S satellites extend over 2–3 mT. Upon reduction of 1–4 to their radical anions, the extra electron resides in the acenaphthylene π-system. Thus, the EPR spectra of 1^˙––4^˙– have a total width of ca. 2.2 mT with no observable ³³S satellites. The g factors of the radical cations comply with the values for oxidised S-donors, whereas those of the corresponding anions are typical of reduced π-systems without heteroatoms. The crystal structure of 5 is characterised by pseudo-dimers of molecules folded by 54° along the S· · ·S vector of the 1,4-dithiine ring. The structural motif of both 5∶TCNQ and 5∶Br₂TCNQ comprises mixed stacks of donor and acceptor moieties. The bond lengths in 5∶TCNQ and 5∶Br₂TCNQ show minor perturbation compared with pure 5, which can be attributed to a small degree of charge transfer. The asymmetric unit of 5∶(I₇^–) comprises one radical cation 5^˙+, two I₂ molecules and one I₃^– anion. The radical cation, in contrast with the structures of 5, 5∶TCNQ and 5∶Br₂TCNQ, shows only a minor boat-like distortion, and the radical cations form a stepwise stack, parallel to the b axis. Iodine species form an infinite zig-zag chain, running in the general direction of the c axis, i.e. normal to the stacks. The conductivity values of these complexes are low (σ_rt = ≤ 10^–8 S cm^–1).