Synthesis, characterization, crystal structure and DFT study of two new polymorphs of a Schiff base (E)-2-((2,6-dichlorobenzylidene) amino)benzonitrile

Two new polymorphs of Schiff base, (E)-2-((2,6-dichlorobenzylidene)amino)benzonitrile, were prepared from the condensation of 4-amino-benzonitrile and 2,6-dichlorobenzaldehyde. The two polymorphs crystallize in two different space groups: P21/c for polymorph (I) with volume 1264.23(2) angstrom(3) and Pbca for polymorph (II) with volume 2469.3(2) angstrom(3). The two polymorphs have been characterized by FT-IR and UV-VIS spectroscopy. The crystal structures of both compounds were determined by single X-ray analysis. The difference between the two polymorphs was observed at the angle between the two phenyl rings which is 4.81 degrees for the first one and 82.27 degrees for the second one. Both crystal structures are built on the basis of moderate and weak hydrogen bonds. Theoretical calculations on isolated molecules at the MP2 cc-pVDZ level show that the two polymorphs correspond to two molecular conformations that are within less than 1 kJ mol(-1) and DFT periodic calculations indicate that (II) is more stable than (I) by 4.1 kJ mol(-1) of formula unit. Additionally, we performed TD-DFT calculation for free ligands to support the experimental data. (C) 2015 Elsevier B.V. All rights reserved.