An unexpected tautomer : synthesis and crystal structure of N-[6-amino-4-(methylsulfanyl)-1,2-dihydro-1,3,5-triazin-2-ylidene]benzenesulfonamide

The title compound, C₁₀H₁₁N₅O₂S₂, consists of an unexpected tautomer with a protonated nitro-gen atom in the triazine ring and a formal exocyclic double bond C=N to the sulfonamide moiety. The ring angles at the unsubstituted nitro-gen atoms are narrow, at 115.57 (12) and 115.19 (12)°, respectively, whereas the angle at the carbon atom between these N atoms is very wide, 127.97 (13)°. The inter-planar angle between the two rings is 79.56 (5)°. The mol-ecules are linked by three classical hydrogen bonds, forming a ribbon structure. There are also unusual linkages involving three short contacts (< 3 Å) from a sulfonamide oxygen atom to the C-NH-C part of a triazine ring.