Crystal structure of single crystals of nonlinear optical L-histidinium trichloroacetate S. Gokul Raj a , G. Ramesh Kumar a , R. Mohan a, * , Babu Varghese b , R. Jayavel c a Department of Physics, Presidency College, Chepauk, Chennai 600 005, India b Sophisticated Analytical Instrument Facility, IIT, Chennai 600 025, India c Crystal Growth Centre, Anna University, Sardar Patel Road, Chennai 600 025, India Received 14 November 2005; received in revised form 10 April 2006; accepted 17 April 2006 Available online 5 June 2006 Abstract Single crystals of a new histidinium salt: L-histidinium trichloroacetate {abbreviated as LHTCA; [(C 3 N 2 H 4 ) CH 2 CH (NH 3 ) (CO 2 )] + CCl 3 COO  } were grown by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in a non-centro- symmetric space group P2 1 of monoclinic system with cell parameters a = 5.4505(18) A ˚ , b = 25.769(8) A ˚ , c = 9.210(2) A ˚ and b = 99.98(2)° with Z = 4. The structure has been refined to an R-value of 0.05 for 2539 observed reflections using three-dimensional X-ray diffraction data. The vibrational structure of the compound confirms the presence of various functional groups in the molecule. The UV–Vis–NIR spectrum shows a good transparency in the whole of the region from ultraviolet to near IR. The Kurtz–Perry powder SHG measurement confirms the frequency doubling of the crystal and its powder SHG efficiency was measured as d eff = 0.33 d eff (KDP). Ó 2006 Elsevier B.V. All rights reserved. Keywords: Single crystal; Optical materials; Crystal growth; L-histidinium trichloroacetate 1. Introduction Amino acids are naturally occurring chiral species; crys- tallize in non-centrosymmetric space groups, which is an essential criterion for nonlinear optical (NLO) application [1]. Especially, L-arginine and L-histidine derivatives are serving as potential second harmonic (SHG) generators [2–5]. L-histidine has been extensively studied because of its ability of imidazole moiety to act as a proton donor, a proton acceptor and a nucleophilic reagent [6]. Hence there has been a great interest in counterparting the organic/in- organic materials such as fluoride, tartaric acid, phosphoric acid and orthoarsenic acid crystal, etc., with histidine [7–10]. In a similar way L-histidinium trichloroacetate (LHTCA), a new NLO material, is chosen for our study. In the present work, we report the crystal structure and properties of another L-histidine derivative, LHTCA, with chemical formula L-His-CCl 3 COOH. 2. Experimental procedure 2.1. Preparation of LHTCA The starting compounds, L-histidine (Lancaster 98%) and trichloroacetic acid (Merck 99%), were mixed in the ratio 1:1. The growth solution was prepared by dissolving equimolar quantities of L-histidine and trichloroacetic acid in deionized water. The solution was stirred for 24 h con- tinuously and the homogeneous solution was left standing for several days. Good quality crystals of L-histidinium tri- chloroacetate were prepared by successive recrystallization by slow evaporation from an aqueous solution. 2.2. Crystallography Three-dimensional intensity data of a transparent good quality crystal were collected on an Enraf-Nonius 0022-2860/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2006.04.023 * Corresponding author. Tel.: +91 44 2854 4894; fax: +91 44 2851 0732. E-mail addresses: gokulrajs@yahoo.com (S. Gokul Raj), professormohan@yahoo.co.in (R. Mohan). www.elsevier.com/locate/molstruc Journal of Molecular Structure 825 (2006) 158–164