Organic spin science is a well-developed discipline combining chemistry, physics, materials science, and biomedicine of open-shell compounds; of specific interest are S ≥ 1 high-spin species.^1–15 

With chalcogens, organic π-cyclic derivatives of thiazyl [SN]˙ and its putative heavier congeners are essentially important.^{1–3,7,8,16–31}  Some of them, especially 4-R-1,2,3,5-dichalcogenadiazolyls (chalcogen = S, Se), are comprehensively discussed elsewhere.^{1–3,7,32–34}  The present chapter is focused on neutral 1,2,3- and 1,3,2-benzodichalcogenazolyls (1 and 2; Herz and Wolmershäuser radicals, respectively), and anionic 2,1,3-benzochalcogenadiazolidyls and 1,2,3-benzodichalcogenazolidyls (3 and 4, respectively), involved in the design and synthesis of conductive and magnetic materials, including spin-crossover materials. The common feature of 1–4 is a 6–5 bicyclic scaffold and a delocalized antibonding π*-SOMO implying an intrinsic instability (for structural archetypes, see Scheme 7.1). Nevertheless, many of them can be isolated in the form of thermally-stable solids possessing highly-correlated electron systems with strong spin-lattice interactions.^{1–3,7,14,18,19,22,25,26,32–37}  Monocyclic analogues of 1–4 and other relevant ring systems are also discussed where reasonable; open-shell derivatives of 2,2-dioxides of 3 (E = S) and congeners^23,38  are not covered.