Synthesis, crystal structures and theoretical studies of four Schiff bases derived from 4-hydrazinyl-8-(trifluoromethyl) quinoline

Abstract

The molecular structures of three new Schiff base compounds of the form R – hydrazinyl-8-(trifluoromethyl)-quinoline, and the fourth, a structurally related hydrate, have been examined by X-ray crystallography, B3LYP/6-3 G (d) and Hirshfeld surface and fingerprint calculations. Compound ( I), C 18H 14F 3N 3, crystallizes in the tetragonal, I 4 1 / a space group ( z = 32) while compounds ( II) – C 18H 13BrF 3N 3; P 2 1 / c, ( III) – C 18H 14F 3N 3O·H 2O; P 2 1 / c, and ( IV) – C 22H 16F 3N 3; P 2 1/n , are monoclinic ( z = 4). In ( I) there are two independent molecules in the asymmetric unit. In compounds ( I), ( II) and ( IV) R = ethylidene 1-phenyl, ethylidene 3-bromophenyl and ethylidene naphthalen-2-yl while ( III) consists of a 4-[(1E)-1-{2-[8-(trifluoromethyl)quinolin-4-yl]-hydrazinylidene}ethyl]-phenol hydrate. In all four compounds the trifluoromethyl group lies in the plane of the quinoline ring and the methyl group is in the plane of the hydrazine moiety. The mean plane of the quinoline ring is planar with hydrazine moiety in ( II) and ( IV) and twisted slightly in ( I) and ( III). In all four compounds weak π-stacking interactions are observed between ring centroids of the various naphthalene(benzene) and quinoline (benzene and pyridine) rings which contribute to the crystal packing. A comparison of the angles between mean planes of the benzene and quinoline rings in the crystal and with the DFT theoretical calculation as well as inclusion of strong and weak intermolecular hydrogen-bond interactions has been included for each molecule. Hirshfeld surface analysis for visually analyzing intermolecular interactions in crystal structures employing 3D molecular surface contours and 2D fingerprint plots have been used to examine molecular shapes.