Two polymorphs of anhydrous 4-pyridone at 100 K.

Two polymorphs of the title compound, C(5)H(5)NO, (I), have been obtained from ethanol. One polymorph crystallizes in the monoclinic space group C2/c [henceforth (I)-M], while the other crystallizes in the orthorhombic space group Pbca [henceforth (I)-O]. In the two forms, the lattice parameters, cell volume and packing motifs are very similar. There are also two independent molecules of 4-pyridone in each asymmetric unit. The molecules are linked by N-H...O hydrogen bonds into one-dimensional zigzag chains extending along the b axis in the (I)-M polymorph and along the a axis in the (I)-O polymorph, with the graph set C(2)(2)(12). The structures are stabilized by weak C-H...O hydrogen bonds linking adjacent chains, thus forming a ring with the graph set R(6)(5)(28). The significance of this study lies in the analysis of the hydrogen-bond interactions occurring in these structures. Analyses of the crystal structures of the two polymorphs of 4-pyridone are helpful in elucidating the mechanism of the generation of spectroscopic effects observed in the IR spectra of these polymorphs in the frequency range of the N-H stretching vibration band.