Electron-induced phase transition in hydrogen-bonded anhydrous solid state 4-pyridone

Spectral studies of hydrogen bonded 4-pyridone crystal have demonstrated the existence of two anhydrous solid-state phases of the compound, namely the α and the β-phase. Hydrogen bonds in the high-temperature α-phase have been estimated to be 40% stronger than hydrogen bonds in the β-phase. It was proved that the crystals of the two polymorphs are identical with the crystals of the previously determined structures. The α polymorph is monoclinic while the β is orthorhombic. The mechanism of the phase transition 4-pyridone is proposed on the basis of the crystalline polarized IR spectra measured in the νOH and νOD band frequency ranges. It is connected with a partial change in the hydrogen bond nature, from the N+H⋯O− in the α-phase, to the NH⋯O in the β-phase crystals. This involves small changes in the geometry of hydrogen bonds, which accompany the electron density redistribution in the hydrogen bonds during the phase transition.