Crystal structure, spectroscopic and theoretical studies on two Schiff base compounds of 2,6-dichlorobenzylidene-2,4-dichloroaniline and 2,4-dichlorobenzylidene-2,4-dichloroaniline Alireza Soltani a,⇑ , Fereshteh Ghari b , Aliakbar Dehno Khalaji c , E. Tazikeh Lemeski d , Karla Fejfarova e , Michal Dusek e , Masoomeh Shikhi a a Young Researchers and Elite Club, Gorgan Branch, Islamic Azad University, Gorgan, Iran b Department of Chemistry, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran c Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran d Department of Chemistry, Gorgan Branch, Islamic Azad University, Gorgan, Iran e Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague 8, Czech Republic highlights  2,6-dichlorobenzylidene-2, 4-dichloroaniline and 2, 4-dichlorobenzylidene-2, 4-dichloroaniline are investigated.  The synthesized compounds were theoretically and experimentally characterized using X-ray, IR, and 1 H NMR.  The theoretical calculations were carried out using B3LYP method at 6-31G / and STO-3G basis sets.  The calculated the electronic properties and atomic charges were presented. graphical abstract article info Article history: Received 12 May 2014 Received in revised form 27 September 2014 Accepted 23 October 2014 Available online 15 November 2014 Keywords: Schiff base Single-crystal DFT Electronic properties abstract The crystal structures of two Schiff base compounds, 2,6-dichlorobenzylidene-2,4-dichloroaniline (1) and 2,4-dichlorobenzylidene-2,4-dichloroaniline (2) have been determined from single-crystal X-ray diffrac- tion and characterized by FT-IR and 1 H NMR spectroscopy. The electronic structures of compounds 1 and 2 in the gas phase were computed by the density functional theory (DFT) method. The obtained theoret- ical results were supported by the crystallographic data. In addition, theoretical configurations of the title compounds were relaxed and studied in terms of the combined analysis of HOMO–LUMO energy gap, total density of states (DOS), molecular electrostatic potential (MEP), NMR spectra and harmonic vibra- tional frequencies. Ó 2014 Elsevier B.V. All rights reserved. Introduction Schiff base (azomethine) is a compounds including imine group (AC@NA), which has been studied as an organic ligand in the field of coordination chemistry [1]. This compound possesses interest- ing features like antimicrobial activity, special electrochemical and thermal properties, anionic sensitivity, photochromism and thermochromism, and non-linear optical properties [2–5]. In continuation of our studies on Schiff base compounds [1–4], we report the synthesis, characterization and crystal structures of http://dx.doi.org/10.1016/j.saa.2014.10.099 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +98 938 4544921. E-mail address: alireza.soltani46@yahoo.com (A. Soltani). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 271–278 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa