Temperature-dependent Raman, IR and X-ray studies of 2-ethylimino-4-nitropyridine N-oxide

The X-ray crystal structure of 2-ethylimino-4-nitro-pyridine N-oxide has been determined at room and 105 K temperature. The structure is monoclinic, space group P21/c. The asymmetric unit consists of two C7H8N3O3 formula units, slightly differing in the interatomic bond distances. The intermolecular hydrogen bonds of NH⋯O type between the same chemical groups of the two components form a three-dimensional network of molecules in the crystal structure. The X-ray data show that CH3 end-group of the ethylimino moiety performs enhanced thermal movements about the crystal a-axis. At low temperature these rotations become hindered, but it does not influence the crystal symmetry. In addition to X-ray studies, IR and Raman spectra have been measured and assignment of the vibrational modes have been discussed on the basis of the quantum chemical calculations. The measured spectra are consistent with the established crystal structure and they show very clearly the presence of hydrogen bonds and hindrance of the ethylimino group rotation.