The zwitterion of 4-nitro-2-{(E)-[2-(piperidin-1-yl)eth-yl]imino-meth-yl}- phenol

Abstract

The title Schiff base compound, 4-nitro-1-oxo-2-{(E)-[2-(piperidin-1-yl) eth-yl]iminiometh-yl}cyclo-hexa-dienide, C14H19N3O3, exists as a zwitterion, with the H atom of the phenol group being transferred to the imine N atom. The C=O, CAr - CAr and C - N bond lengths are in agreement with the oxocyclo-hexa-dienide-iminium zwitterionic form. The iminium H atom is engaged in a strong intra-molecular hydrogen bond with the O atom of the keto group (N+ - H⋯O) to form an S(6) motif. Soft C - H⋯O inter-actions in the ac plane lead to the development of hydrogen-bonded tapes, which are π-stacked through the oxocyclo-hexa-dienide ring and iminium group. The significance of this study is in providing crystallographic evidence, supported by NMR and IR data, of the predominance of the oxocyclo-hexa-dienide- iminium zwitterion form over the noncharged canonical form in the title Schiff base. © 2009 International Union of Crystallography.