Polymorphism in 2-(4-hydroxy-2,6-dimethylanilino)-5,6-dihydro-4H-1,3- thiazin-3-ium chloride

Details of the structures of two conformational polymorphs of the title compound, C₁₂H₁₇N₂OS⁺·Cl ^-, are reported. In form (I) (space group P1̄), the two N - H groups of the cation are in a trans conformation, while in form (II) (space group P2₁/c), they are in a cis arrangement. This results in different packing and hydrogen-bond arrangements in the two forms, both of which have extended chains lying along the a direction. In form (I), these chains are composed of centrosymmetric R₄²(18) (N - H⋯Cl and O - H⋯Cl) hydrogen-bonded rings and R₄ ²(18) (N - H⋯O) hydrogen-bonded rings. In form (II), the chains are formed by centrosymmetric R₄²(18) (N - H⋯Cl and O - H⋯Cl) hydrogen-bonded rings and by R₄ ²(12) (N - H⋯Cl) hydrogen-bonded rings.