Aleksandra Tyl

Electron-Induced Phase Transition in Hydrogen-Bonded Solid-State 2-Pyridone

This paper presents the results of experimental studies of hydrogen-bonded 2-pyridone crystal IR spectra. Spectral studies have demonstrated the existence of two anhydrous solid-state phases of each compound, namely the α and the β phases. Hydrogen bonds in the high-temperature α phase of these crystals have been estimated to be 40% stronger than the hydrogen bonds in the β phase, which are stable at room temperature. The mechanism of the phase transition in the solid-state 2-pyridone is proposed on the basis of the IR spectral data. This was possible by taking into account small changes in the geometry of heterocyclic molecular skeletons, which accompany the electron density redistribution in the hydrogen bonds occurring during the transition. The phase transition is connected with a partial change in the hydrogen bond nature from the N(+)-H···O(-) in the α phase, to the N-H···O hydrogen bonds in the β phase crystals.

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.

X-ray, Hirshfeld surface analysis, spectroscopic and DFT studies of PAHs: fluoranthene and acenaphthene

The X-ray structure, theoretical calculation, Hirshfeld surfaces analysis, IR and Raman spectra of fluoranthene and acenaphthene were reported. The acenaphthene crystallizes in the orthorhombic crystal system and space group P 2 1 ma , with crystal parameters a = 7.2053 (9) A, b = 13.9800 (15) A, c = 8.2638 (8) A, Z = 4 and V = 2135.5 (4) A 3 . In turn, the grown crystals of fluoranthene are in monoclinic system with space group P2 1 /n. The unit cell parameters are a = 18.349 (2) A, b = 6.2273 (5) A, c = 19.861 (2) A, β = 109.787 (13) °, Z = 8 and unit cell volume is 832.41 (16) A 3 . The structure was solved by direct methods and refined by full-matrix least squares based on F2 with weight w=1/[σ 2 (F 0 2 )+(0.0702P) 2 +0.5131P] where P=(F 0 2 +2F c 2 )/3 and w=1/[σ 2 (F 0 2 )+(0.0589P) 2 ] where P = (F 0 2 +2F c 2 )/3 for fluoranthene and acenaphthene respectively . Theoretical calculations of the title compounds isolated molecule have been carried out using DFT at the B3LYP level. The intermolecular interactions in the crystal structure, for both the title PAHs, were analyzed using Hirshfeld surfaces computational method.