Synthesis, growth, structural, thermal, optical properties of new metal-organic crystals: Methyltriphenylphosphonium iodide thiourea and methyltriphenylphosphonium iodide chloroform hemisolvate Boris L. Shivachev a,n , Krassimir Kossev a , Louiza T. Dimowa a , Georgi Yankov b , Todor Petrov b , Rositsa P. Nikolova a , Nadia Petrova a a Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria b Institute of Solid State Physics, Bulgarian Academy of Sciences,72, Tzarigradsko Chaussee, Blvd., 1784 Sofia, Bulgaria article info Article history: Received 15 November 2012 Received in revised form 5 April 2013 Accepted 19 April 2013 Available online 29 April 2013 Keywords: A1. X-ray diffraction A2. Growth from solutions B1. Organic compounds B2. Nonlinear optical material abstract Crystals of methyltriphenylphosphonium iodide thiourea (1) and methyltriphenylphosphonium iodide chloroform hemisolvate (2) were obtained for the first time. Fourier transform infrared (FTIR) spectral studies have been performed to identify the functional groups. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study their thermal properties. The optical transmit- tance window and the lower cutoff wavelength have been identified by UV–vis studies. Crystals of the title compounds suitable for single crystal X-ray analyses were successfully grown by slow evaporation and diffraction data were collected to elucidate the molecular structure and interactions. The proton donors (phosphonium) and proton acceptor (iodine) in the structure of 1 provide infrastructure to introduce charge asymmetry while in 2 chloroform molecule is not involved in the charge transfer. An optical quality crystal of 1 (5 Â 4 Â 2 mm 3 ) was obtained by macroseeding. The crystal has developed facets with major ones (001) and (00 ̄ 1). A crystal of 1 was tested with 1060 nm laser radiation and showed second harmonic generation (SHG). & 2013 Elsevier B.V. All rights reserved. 1. Introduction Nonlinear optics is a constantly expanding field of research and technology encompassing knowledge from several scientific fields: physics, chemistry, optics, crystal growth, physical chemistry and engineering. Lately, the search for new nonlinear optic (NLO) media has intensified as a result of the growing demand for such materials, their broadened range of applications and in order to overcome some of the difficulties and limitations of existing NLO materials [1]. Organic and metal-organic non-linear optical materials are attracting consider- able interest because of their potential applications in electro optical modulator, memory, second harmonic generation in QCLs (quantum- cascade lasers), optical switches and other photonic devices [2–6]. The usage of organic molecules as nonlinear media has several advantages such as low cost, low dielectric constant and great diversity of possible organic templates. Furthermore, the nonlinear optical response in organic based NLO materials is microscopic in origin, offering an opportunity to use theoretical modeling to adjust the molecular structure and properties [7]. In order to produce the desired new molecules the theoretical modeling and design of such materials is easily coupled with the flexibility of chemical synthesis [8]. Finally, fine-tuning of the crystal structure and crystal properties is achieved by means of crystal engineering [9, 10]. One should note that the practical implementation of organic NLO materials is hampered mainly by their relative low thermal stability and lack of robustness. The crystal packing in those compounds is governed through weak non-covalent interaction (hydrogen bonds, π–π interactions, etc.) either between the molecules or with the often present solvent inclusions. Unfortunately the end result is a low laser damage threshold [11, 12] generating structural changes, damages, transition etc. Additionally, finding ways to ensure that a bulk material (crystal) is acentric has been a serious hurdle in the design of new NLO materials. Various strategies have been proposed to obtain noncentrosymmetric packing. These include the presence of a chiral center, hydrogen bonding dipole–dipole interaction etc. [13, 14]. Typically the nonlinearity of organic compounds having a π-electron conjugated system is caused by nonlinear polarization that occurs due to the interaction between laser light which comprises a strong electromagnetic wave and the delocalized π electrons in the organic molecule of interest. In order to increase the magnitude of nonlinear polarization of the molecules, a common technique for molecular design involves the introduction into the conjugated system of an electron donating group (donor) or an Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.04.040 n Corresponding author. Tel.: +359 28 700 161; fax: +359 29 797 056. E-mail addresses: blshivachev@gmail.com, bls@clmc.bas.bg (B.L. Shivachev), k_kossev@yahoo.com (K. Kossev), Louiza.Dimova@gmail.com (L.T. Dimowa), gjankov@issp.bas.bg (G. Yankov), tspetrov@issp.bas.bg (T. Petrov), rosica.pn@clmc.bas.bg (R.P. Nikolova), nadia5@mail.bg (N. Petrova). Journal of Crystal Growth 376 (2013) 41–46