Effect of intermolecular =C-H-O interaction on the crystal structure and vibrational properties of 2,6-dimethyl-4-nitropyridine N-oxide

The crystal structure of 2,6-dimethyl-4-nitropyridine N-oxide (DMNPO) has been determined at ambient temperature. The compound crystallizes as a monoclinic structure, space group P2/n, with 12 molecules per unit cell. The unit cell contains three non-equivalent formula units. The nitro group is not coplanar with the pyridine ring. Through a system of =C-H ... O hydrogen bonds the molecules are arranged into a two-dimensional network of layers parallel to the axe plane. The IR and Raman spectra, measured in the 3500-100 cm region at ambient temperature, are correlated with X-ray structural data. The assignment of IR and Raman bands is given, The appearance of characteristic vibrational features in the spectra of this compound and the observed shifts of the =C-H and N-O IR active stretching modes, when the sample is dissolved in CCl4, is discussed in terms of the relatively strong =C-H ... O hydrogen bonds present in this crystal. (C) 1998 Elsevier Science B.V.