H. Ban-Oganowska, J. Hanuza, M. Ma̧czka
Jul 3, 2001
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Journal
Vibrational Spectroscopy
Abstract
Abstract The crystal structure of 3-iodo-2,6-dimethyl-4-nitropyridine N-oxide (IDMNPNO) is shown to be not isomorphic with the previously studied 3-chloro- and 3-bromo-derivatives. The compound crystallizes in monoclinic structure, space group C 2/ c , with eight molecules per unit cell of dimensions a =28.051(6), b =4.884(1), c =13.384(3) A, β =96.82(3)°. The molecular conformation is similar to that of the two other derivatives, i.e. the N-oxide group, two methyl C-atoms and the I-atom are coplanar with the ring plane, while the two O-atoms of the nitro group are above and below the plane by 0.54 and −0.59 A, respectively. The main feature of the present structure is the presence of an intermolecular interaction between the ring H-atom and nitro group instead of hydrogen bonding between the NO group and the ring H-atom, as observed in case of the chloro- and bromo-derivatives. Another structural feature of the crystal studied is the presence of very short distance between the I-atom and the N-oxide group. The molecules are arranged into layers parallel to the ac -plane. The IR and Raman spectra, measured at ambient temperature in the region 3500–50 cm −1 , are consistent with the X-ray data giving strong evidence for the importance of the short contact I⋯O. The assignment of the spectra is based on a semiempirical molecular calculation and a comparison with the previously obtained results for the Br- and Cl-derivatives.