Structural Characterization of Two Polymorphs of 1-(4-Methylpyridin-2-yl)thiourea and Two Derived 2-Aminothiazoles

Two polymorphic forms of 1-(4-methylpyridin-2-yl)thiourea (1) and the crystal and molecular structures of the 2-aminothiazolesN-(4-methylpyridin-2-yl)-4-(pyridin-2-yl)thiazol-2-amine (2) andN-(4-methylpyridin-2-yl)-4-(pyrazin-2-yl)thiazol-2-amine (3), derived from1and the respective alpha-bromoketone via the Hantzsch reaction, are described. Both polymorphic forms 1 alpha (space group P2(1)/c, Z = 4) and 1 beta (space group P2(1)/n, Z = 8) crystallize in the monoclinic system but exhibit distinctly different intermolecular hydrogen bonding patterns. Compound 2 (orthorhombic, space group Pca2(1), Z = 8) forms polymeric N-HMIDLINE HORIZONTAL ELLIPSISN hydrogen-bonded zigzag tapes in the polar crystal structure, with a significant twisting between the thiazole and pyridine rings. In contrast, the crystal structure of3(monoclinic, space group P2(1)/c, Z = 4) features nearly planar centrosymmetric N-H center dot center dot center dot N hydrogen-bonded dimers, which are laterally joined through long C-H center dot center dot center dot N contacts, affording a pi center dot center dot center dot pi stacked layered structure.

Automated summary

Two polymorphic forms of thiourea and two compounds derived from it have been studied, showing distinct crystalline forms and hydrogen bonding patterns. Compound 2 forms zigzag tapes in a polar crystal structure, while compound 3 features planar centrosymmetric dimers in a layered structure.