Synthesis and crystal structure analysis of a 6aλ4-thia-1,2,3,4,6-pentaazapentalene

6aλ⁴-Thia-1,2,3,4,6-pentaazapentalenes 3 are conveniently prepared by reacting 5-imino-Δ³-1,2,4-thiadi-azolines 2 with aromatic diazonium tetrafluoroborates in the presence of pyridine. The first crystal structure analysis of this class of compounds 3g is described and shows properties characteristic of a thiapentalene structure; i.e. long N-S-N bonds (1.85 and 1.975 Å) in a nearly linear arrangement (164°) and comprising a heterobicycle which is strictly planar.