A combined computational and experimental study on the hydrogen bonding with chloride ion in a crab-claw like site of a new chromium Schiff base complex Mahmoud Zendehdel a,b , Narges Yaghoobi Nia c , Mojtaba Nasr-Esfahani a,⇑ , Pooria Farahani d,e , Mohamad Reza Karbaschi a a Department of Chemistry, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran b K.S.R.I. (Kimia Solar Research Institute), Kimia Solar Company, Isfahan, Iran c C.H.O.S.E. (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome ‘‘Tor Vergata’’, via del Politecnico 1, Rome 00133, Italy d Department of Chemistry – Ångström, The Theoretical Chemistry Programme, Uppsala University, P.O. Box 518, SE-75120 Uppsala, Sweden e Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, 05508-000 São Paulo, SP, Brazil article info Article history: Received 10 December 2015 Received in revised form 4 March 2016 Accepted 30 March 2016 Available online 6 April 2016 Keywords: Hydrogen bonding TD-DFT Chromium complex Crystallography Parabolic diagram abstract A combined experimental and computational study to understand the nature of the hydrogen bonding in a crab-claw site of a new synthesized chromium Schiff base complex is reported. The fully optimized equilibrium structures of the Cr(III) complex in the presence and absence of chloride ion are obtained at the B3LYP functional in conjunction with LanL2DZ basis set. The crystal structure of the chromium Schiff base complex consists of [CrL 2 ] + cation, in which L is a tridentate Schiff base ligand with full name of N-(2-(2-hydroxyethylamino)ethyl)5-methoxysalicylideneimine, and a chloride anion, in the asymmet- ric unit. The chromium(III) cation possesses a distorted octahedral geometry, coordinated with four nitro- gen and two phenoxo oxygen atoms derived from two chelate Schiff base ligands. The harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the complexes are also reported. The scaled computational geometry and vibrational wavenumbers are in very good agreement with the experimental values of single crystal X-ray diffraction and FT-IR, respectively. The electronic properties calculations of the complexes are also performed at the TD-B3LYP/LanL2DZ level of theory. The spectroscopic excitation parameters obtained for frontier molecular orbitals of the complexes are reported as well. These findings are in good agreement with the experimental UV–Vis diffuse-reflectance spectroscopy. Parabolic diagrams are derived for the chloride insertion and hydrogen bonding in the crab-claw site with the average optimized HÁÁÁH distances of the effective hydrogen atoms in the crab- claw site as reaction coordinate. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen bonding plays a key role in chemical, catalytic and biochemical processes, as well as in supramolecular chemistry and crystal engineering [1,2]. In the last few decades, considerable attention has been drawn to Schiff bases and their complexes in the fields of coordination and biological chemistry [3,4]. Aromatic Schiff bases and the corresponding metal complexes have recently attracted researchers’ attention due to some interesting properties such as catalyzing reactions on oxygenation [5], hydrolysis [6], electro-reduction [7], and decomposition [8], biological activities like antimicrobial [9], antifungal [10], antiviral [11], synergistic action on insecticides [12], plant growth regulator [13], anti-tumor and cytotoxic activities [14]. Chromium is an earth-abundant metal, and surrounding Cr(III) ions with appropriate ligands can produce powerful photooxidants [15]. The excited state properties of Cr(III) tris-diimine (e.g., bpy, phen) complexes are well-known, and the observed long lifetimes (ls) make these compounds potentially useful for dye-sensitized hole-injection photovoltaic devices and/or photooxidative catalytic schemes [15–17]. Enhanced solution stability may be addressed by increasing the density of the ligand(s) chelating the chromium center [18]. Photo- chemical studies on a few ligated complexes by multidentate amine ligands [19,20] or tethered bipyridines [21] have uncovered long-lived 2 E excited states. It is worth noting that all of these http://dx.doi.org/10.1016/j.ica.2016.03.040 0020-1693/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: mnstd@yahoo.com, m-nasresfahani@iaun.ac.ir (M. Nasr- Esfahani). Inorganica Chimica Acta 447 (2016) 150–161 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica