Chalcogen-nitrogen rings

Weak interactions may occur between molecules (intermolecular association) as well as within a molecule (intramolecular) for chalcogen-nitrogen ring systems. This behaviour is especially significant for odd electron species, e.g., [EsNa]" (4.14, E = S, Se) and [PhCNaEa] (4.15, E = S, Se), both of which are seven r-electron molecules. As mentioned in the previous section, it also occurs for the eight r-electron dithiatriazines 4.10... 

Chalcogen-Nitrogen Rings Containing Phosphorus(III) or Other p-Block Elements... 

The thermal or base-promoted elimination of SO2 from E(NSO)2 gives rise to chalcogen-nitrogen ring systems. For example, the reactions of 39a or 39b with TiCU produce the polymeric adducts [ESN2 TiGUj (E=S, Se). The cyclometallathiazene 40 is formed upon the treatment of 39a with [Pt(CH2=CH2)(PPh3)2]. ... 

The structures of chalcogen-nitrogen compounds are frequently unpredictable. For example, the reactions of heterocyclic systems often result in substantial reorganization of their structural frameworks, e.g. ring expansion or contraction. The formation of acyclic products from ring systems (or vice versa) is also observed. 

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