4-[(E)-(2,4-Difluorophenyl)(hydroxyimino)methyl]piperidinium picrate

Abstract

The title compound, C12H15F2N2O+·C6H2N3O7−, a picrate salt of 4-[(E)-(2,4-difluorophenyl)(hydroxyimino)methyl]piperidine, crystallizes with two independent molecules in a cation–anion pair in the asymmetric unit. In the cation, a methyl group is trisubstituted by hydroxyimino, piperidin-4-yl and 2,4-difluorophenyl groups, the latter of which contains an F atom disordered over two positions in the ring [occupancy ratio 0.631 (4):0.369 (4)]. The mean plane of the hydroxy group is in a synclinical conformation nearly orthogonal [N—C—C—C = 72.44 (19)°] to the mean plane of the piperidine ring, which adopts a slightly distorted chair conformation. The dihedral angle between the mean plane of the 2,4-difluorophenyl and piperidin-4-yl groups is 60.2 (3)°. In the picrate anion, the mean planes of the two o-NO2 and single p-NO2 groups adopt twist angles of 5.7 (2), 25.3 (7) and 8.3 (6)°, respectively, with the attached planar benzene ring. The dihedral angle between the mean planes of the benzene ring in the picrate anion and those in the hydroxyimino, piperidin-4-yl and 2,4-difluorophenyl groups in the cation are 84.9 (7), 78.9 (4) and 65.1 (1)°, respectively. Extensive hydrogen-bond interactions occur between the cation–anion pair, which help to establish the crystal packing in the unit cell. This includes dual three-center hydrogen bonds with the piperidin-4-yl group, the phenolate and o-NO2 O atoms of the picrate anion at different positions in the unit cell, which form separate N—H...(O,O) bifurcated intermolecular hydrogen-bond interactions. Also, the hydroxy group forms a separate hydrogen bond with a nearby piperidin-4-yl N atom, thus providing two groups of hydrogen bonds, which form an infinite two-dimensional network along (011).