A New Polymorph of 4-Pyridinethione Containing a Helical Assembly Based on N−H···S Hydrogen Bonds

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.