The unique molecular disorder of crystalline 4-chloro-2,6-dimethyl-3-iodopyridine N-oxide. An X-ray and spectroscopic study

Abstract

The crystal structure of 4-chloro-2,6-dimethyl-3-iodopyridine N-oxide has been determined at ambient temperature. The compound crystallizes in monoclinic structure, space group P2₁/n. The asymmetric unit consists of two formula units, one of which shows positional disorder. The shortest intermolecular contacts form a medium strong hydrogen bond of the type C–H · · · O. The IR and Raman spectra, measured in the region 50–3500 cm^–1, are in agreement with predictions based on the X-ray structural data. The observed electron absorption bands have been attributed to transitions between singlet levels, whereas the emission originates from transitions between the excited triplet level and the ground singlet level. The splitting of the strongest absorption band (225–242 nm) into three components has been explained to be a result of expansion of the valence shell of the iodine atom (d-orbital resonance).