A new polymorph of 4-pyridinethione containing a helical assembly based on N-H⋯S hydrogen bonds

Abstract

Tautomerization of 4-mercaptopyridine in absolute ethanol at two different temperatures leads to the formation of two polymorphs. In the polymorph 1, obtained by refluxing the ethanolic solution of 4-mercaptopyridine and layering with ether, the molecules are arranged in a helical conformation through N-H⋯S hydrogen bonds. On the other hand, the previously reported polymorph 2 is an N-H⋯S bonded zigzag chain and can be prepared by layering an ethanolic solution of 4-pyridinethione with ether at 5°C. Apart from the different structural motifs, N-H⋯S, C-H⋯S hydrogen bonds, π⋯π and C-H⋯π interactions make a significant difference between the two structures. Both polymorphs exhibit solid-state photoluminescence due to π-π* transition.