Two crystal forms of 4-{(2E)-2-[1-(4-methoxyphenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quinoline

Abstract

The Schiff base, 4-{(2E)-2-[1-(4-methoxy-phenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quino-line, crystallizes in two polymorphic forms depending on the solvent. One of these forms is monoclinic (1M), space group P2 1/c with a = 10.2906(10) Å, b = 8.9211(7) Å, c = 18.4838(15), β = 97.271(8)°, and the other is orthorhombic (1O), space group Pbca, unit-cell parameters: a = 13.6485(12) Å, b = 9.0588(9) Å, c = 27.400(2) Å. The molecules in either crystalline form have similar bond lengths and angles, but one is nearly planar while the other has a significant twist. In monoclinic form the dihedral angle between terminal ring planes is 17.26(8)° while in the orthorhombic one it is 26.11(5)°, and in this latter case the central chain is almost coplanar with the quinoline ring system while in the former these two planes are significantly twisted. The crystal structures of both forms are determined by the interplay of van der Waals forces and weak directional interactions C-H...F, π...π stacking, and-in the case of 1M-short intermolecular C-F...N contact. The crystals of 1M decomposes slowly into the powder while the other form is stable. The powder diffraction pattern of the product of decomposition of 1M is similar to that calculated for 1O. This suggests that the decomposition is a consequence of the phase transition of the less stable monoclinic into more stable orthorhombic form. © The Author(s) 2012.