Spectrochimica Acta Part A 75 (2010) 293–298 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Crystal studies, vibrational spectra and non-linear optical properties of l-histidine chloride monohydrate A. Ben Ahmed a,∗ , H. Feki a , Y. Abid a , H. Boughzala b , C. Minot c a Laboratoire de Physique Appliquée (LPA), Faculté des Sciences 3018, BP802 Sfax, Tunisia b Laboratoire de cristallochimie Faculté des Sciences de Tunis, Tunisia c Laboratoire de Chimie Théorique (LCT), Université Pierre et Marie Curie, Paris VI, France article info Article history: Received 3 June 2009 Received in revised form 3 October 2009 Accepted 13 October 2009 Keywords: l-Histidine NLO Hyperpolarizability DFT TD-DFT abstract This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a non-linear optical material l-histidine chloride monohydrate. Due to the lack of sufficiently precise information on geometric parameters available in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of l-histidine chloride monohydrate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro-symmetric space group P2 1 2 1 2 1 of orthorhombic system. IR spectrum has been recorded in the range [400–4000 cm -1 ]. All the experimental vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our calculations. The opti- mized geometric bond lengths and bond angles obtained by using DFT//B3LYP/6-31G (d) method show a good agreement with the experimental data. The calculated vibrational spectra are in well agreement with the experimental one. To investigate microscopic second-order non-linear optical NLO behavior of the examined complex, the electric dipole , the polarizability ˛ and the hyperpolarizability ˇ were computed using DFT//B3LYP/6-31G (d) method. The time-dependent density functional theory (TD-DFT) was employed to descript the molecular electron structure of the title compound using the B3LYP/6-31G (d) method. According to our calculations, l-histidine chloride monohydrate exhibits non-zero ˇ value revealing microscopic second-order NLO behavior. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The development and focus on new materials possessing non- linear optical properties have been diverted from traditional inorganic solids such as LiNbO 3 and KH 2 PO 4 to organic and inor- ganic systems due to numerous reasons [1]. In fact, considerable efforts have been made to combine amino acid with various inter- esting organic and inorganic matrices to produce materials having a non-Centro-symmetric cell, large polarizability and a strong non-linear optical coefficient. However, in conjunction with some recent work on these compounds [2–5], the crystal structure and vibrational spectra of l-histidine oxalate, l-histidine bromide and l-histidinium dihydrogen phosphate–phosphoric acid have been investigated in our laboratory [6–8]. In the previous study, the crystal structure of l-histidine chloride monohydrate has been pub- lished by various authors ODA et al. [9], Fuess et al. [10] and Dietmar et al. [11]. To the best of our knowledge, experimental data on geometric parameters and especially that of hydrogen bonds and ∗ Corresponding author. Tel.: +216 96 933 658. E-mail address: ahmedlpa@yahoo.fr (A.B. Ahmed). theoretical calculations on the structure and vibrational spectra of l-histidine chloride monohydrate are not available in the literature. Then, for a proper comparison with our theoretical calculations, the re-determination of the crystal structure is essential. In this work, we report X-ray and IR spectroscopy study of l-histidine chloride monohydrate. To obtain a more reliable assignment of the experi- mental bands, we have calculated the vibrational frequencies in the ground states using DFT method. The non-linear optical properties are also addressed theoretically. The electric dipole moment  tot , the isotropic polarizability ˛ tot and the first hyperpolarizability ˇ tot of the title compound are calculated. 2. Experimental 2.1. Preparation l-Histidine chloride monohydrate crystal was produce from aqueous solution with equimolar proportion of l-histidine (purity 99%) and hydrochloric acid. The synthesized compound was dis- solved in doubly distilled water using a magnetic stirrer and filtered twice to remove the suspended impurities in the solution. Two weeks later, transparency crystals were obtained. 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.10.026