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Growth, structural, optical and thermal properties of an organic NLO material: l -Argininium hydrogen squarate
Optik 127 (2016) 1660–1664
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Growth, structural, optical and thermal properties of an organic NLO material: l-Argininium hydrogen squarate P. Prabu a , M. Kayalvizhi b , C. Ramachandra Raja c,∗ , G. Vasuki b a b c
Department of Physics, Periyar Maniammai University, Thanjavur 613 403, Tamilnadu, India Department of Physics, Kunthavai Naachiar Government Arts College (W) (Autonomous), Thanjavur 613 007, Tamilnadu, India Department of Physics, Government Arts College (Autonomous), Kumbakonam 612 001, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 13 April 2015 Accepted 9 November 2015 Keywords: Optical materials Organic compounds Crystal growth X-ray diffraction Thermogravimetric analysis (TGA)
a b s t r a c t l-Argininium hydrogen squarate (LAHS) is an organic nonlinear optical material grown by slow evaporation solution growth technique. The crystal structure was confirmed by single crystal X-ray diffraction analysis and the crystal system is identified as triclinic system. The thermal stability and decomposition process were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The crystal is stable up to 238 ◦ C. The optical transparency range and lower cut-off wavelength of grown crystal have been identified by UV–vis–NIR spectroscopy method. The existence of second harmonic generation (SHG) signal was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. The SHG efficiency is compared with potassium di-hydrogen phosphate (KDP) and urea. © 2015 Elsevier GmbH. All rights reserved.
1. Introduction In present day much attention is being paid on exploration of novel and good quality nonlinear optical (NLO) materials. These materials play vital role in industry which includes telecommunication, optoelectronics technology, optical data storage and signal processing [1–5]. As the amino acids have chiral symmetry and crystallize in non-centrosymmetric space groups, they are interesting and important materials for NLO applications. The amino acids with organic salts are capable materials for optical second harmonic generations. Organic NLO materials are superior to their inorganic counterparts due to high conversion efficiency for second harmonic generation and good transparency [6] in the visible region. The optical properties of amino acid crystals are increased by addition of organic acids because of their high range of transparency [7,8]. Amino acids are biologically important organic compounds contain proton accepting amino (NH2 ) group and proton donating carboxyl (COOH) functional group in them. One such interesting amino acid is l-arginine (C6 H14 N4 O2 ). It is widely found in animal sources, plant sources and biological substances. l-Arginine forms
∗ Corresponding author at: Government Arts College, Kumbakonam 612 001, India. Tel.: +91 9976696277. E-mail address: crraja [email protected] (C. Ramachandra Raja). http://dx.doi.org/10.1016/j.ijleo.2015.11.047 0030-4026/© 2015 Elsevier GmbH. All rights reserved.
a number of complexes by reacting with organic acid and salts to produce a marvellous material for NLO applications. Hydrogen bonding is one of the principal intermolecular interactions that frequently play key roles in molecular recognition and self-assembly as well as in crystal engineering research and has been used effectively to predict and design supramolecular assemblies in one, two and three dimensions [9]. Supramolecularly organized systems with a variety of novel features are widely generated through hydrogen-bonding. Hydrogen-bonded systems generated from organic cations and anions are of special interest since they are likely to show stronger hydrogen bonds than neutral molecules thus enabling the simple acid–base chemistry to tune the donor and acceptor properties of the counter ions [10]. Squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) which is popularly known as quadratic acid (C4 H2 O4 ), is a white crystalline powder with highly acidic and chemically stable compound and it was first synthesized in 1959. Squaric acid was shown to be an unusually strong organic acid and one of the series of hydrogen-bonded ferroelectrics [11]. Squaric acid has been of much interest because of its cyclic structure and possible aromaticity. Several basic aspects of the properties of squaric acid have been reported to assess its potentialities for NLO applications. In particular, squaric acid and several optically active amino acids cocrystallize under the form of non-centrosymmetric lattice that are expected to present large second-order susceptibilities [12]. The
P. Prabu et al. / Optik 127 (2016) 1660–1664
present work reports on the growth and characterization of squaric acid and amino acid based single crystal. 2. Experimental details 2.1. Synthesis and crystal growth The title compound was grown from aqueous solution by slow evaporation solution growth technique. l-Arginine and squaric acid were taken in equimolar ratio and thoroughly dissolved in deionized water. The solution was stirred well for 6 h at room temperature using magnetic stirrer with 680 rpm to yield a homogenous mixture of solution. Then the saturated solution was filtered using Whatmann filter paper to eliminate unwanted impurities and transferred to a beaker. The beaker was covered with a perforated transparent polythene paper and kept at a dustless environment for slow evaporation. Good and transparent crystals were grown in a period of 3 weeks. The reaction involved in the process may be written as shown in Fig. 1. 2.2. Characterization The grown LAHS crystal was subjected to various characterization techniques like single crystal X-ray diffraction, UV–vis–NIR, thermal analysis and nonlinear optical studies. In order to obtain the cell parameters and crystal data of LAHS crystal, X-ray diffraction studies were carried out using crystal diffractometer equipped with a CCD detector (Bruker Kappa APEX II ULTRA), a rotating ˚ anode (Bruker AXS, FR591) with MoK␣ radiation ( = 0.71073 A). The UV–vis–NIR optical absorption spectral analysis was carried out between 200 and 1100 nm, using Lambda 25 spectrophotometer. Thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were carried out using SDT Q600 V8.3 Build 101 thermal analyzer instrument, ranging from room temperature to 1000 ◦ C at the heating rate of 20 ◦ C per minute under nitrogen atmosphere. The second harmonic generation efficiency was measured using Kurtz and Perry powder technique using Nd:YAG laser beam of energy 4.6 mJ/pulse. 3. Result and discussion 3.1. Crystal structure and X-ray diffraction analysis The intensity data were collected at 296 K on a Bruker AXS Kappa APEX2 CCD Diffractometer [13] system using MoK␣ graphite monochromated radiation. The molecular structure of the LAHS crystal (C10 H16 N4 O6 ) was refined by the least squares method using anisotropic thermal parameters: R = 3%. The compound crystallizes in triclinic, P1. The parameter values calculated are ˚ b = 8.2364(9) A, ˚ c = 14.7926(16) A, ˚ and Z = 2. This a = 5.0901(5) A, value is in good agreement with earlier report [14] which was recorded at 292 K. The asymmetric unit of the title compound contains two 5-((amino(imino)methyl)amino)-2-amminopentanoate (C1–C6/O1/O2/N1–N4 and C11–C16/O7/O8/N5–N8) and two 2-hydroxy-3,4-dioxocyclobut-1-enolate (O3–O6/C7–C10 and
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O9–O12/C17–C20). The C N bond distances of the NH2 groups ˚ N2–C6 = 1.315(9) A, ˚ N5–C16 = 1.325(3) A˚ and N1–C6 = 1.315(8) A, ˚ respectively, which is short for a C N single N6–C16 = 1.310(1) A, ˚ but still not quite as contracted as one would expect for bond 1.47 A, ˚ These bond length feaa fully established C N double bond 1.27 A. tures are consistent with an imino resonance form as it commonly found for C N single bonds involving sp2 hybridized C and N atoms ˚ C1–O2 = 1.238(3) A, ˚ [15]. The bond distances C1–O1 = 1.256(3) A, ˚ ˚ ˚ C11–O7 = 1.237(1) A, C11–O8 = 1.254(2) A, C8–O4 = 1.230(9) A, ˚ ˚ ˚ C9–O5 = 1.217(6) A, C10–O6 = 1.249(1) A, C17–O9 = 1.232(1) A, ˚ respectively, C18–O10 = 1.214(8) A˚ and C19–O11 = 1.243(8) A, clearly indicate the presence of C O double bonds, including those also generated through resonance. The H atoms attached to the squaric groups (O6 and O11) are transferred to the basic centers N6 and N2 respectively, generating the iminium groups. Also the carboxylic H-atoms on O1 and O8 have been transferred to N4 and N8, respectively, to generate the common amino acid zwitterions. The C O double bonds generated through resonance in the ˚ in molecule A and squaric acid anion [C10 O6 (1.249(1) A) ˚ in molecule B] are shorter than normal sinC19 O11 (1.243(8) A) ˚ and slightly longer than normal double C O gle C O bond (1.426 A) ˚ Both molecules (A and B) are involved in inter and bond (1.23 A). intra molecular N H· · ·O hydrogen bonds. Intramolecular C H· · ·O and N H· · ·O hydrogen bonds lead to the formation of a five-, six-, seven-, eight-, nine- and ten-membered ring motif S(5), S(6), S(7), S(8), S(9) and S(10), respectively [16]. The crystal structure of the compound is further stabilized by intermolecular C H· · ·O and N H· · ·O hydrogen bonds. The LAHS crystal data, experimental conditions and structural refinement parameters are presented in Table 1. The molecular structure, crystal packing and unit cell packing diagrams of LAHS are shown in Figs. 2–4, respectively. For the title compound, data collection was done using the computer program APEX2 [13], cell refinement was done using the computer program APEX2/SAINT [13] and data reduction was done by using SAINT/XPREP [13]. The structure of the title compound was solved by using the computer program SIR92 [17] and refined using SHELXL-97 [18]. The molecular graphics were done using the computer programs ORTEP [19], Mercury [20] and PLATON [21]. All the H atoms were positioned geometrically and treated as riding on their parent atoms, with C H = 0.98 A˚ (methine), and 0.97 A˚ (methylene), and refined using a riding model with Uiso (H) = 1.2 Ueq and 1.5 Ueq (parent atom).
3.2. Thermal analysis Thermogravimetric analysis is an analytical technique used to determine thermal stability and fraction of volatile compound of a crystal by monitoring the weight change that occurs as the crystal is heated. The TGA, DTA and DSC of LAHS crystal were carried between room temperature to 1000 ◦ C at the heating rate of 20 ◦ C per minute under nitrogen inert atmosphere. The resulting TGA/DTA and DSC curves are shown in Figs. 5 and 6, respectively. The initial mass of the crystal subjected to analyses was 4.9670 mg and the final mass left out after the experiment was 5.163% of the initial mass. The TGA trace appears nearly straight
Fig. 1. Chemical reaction.
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Fig. 2. The molecular structure of the two independent molecules of LAHS crystal, showing atom numbering, with displacement ellipsoids drawn at the 50% probability level.
Fig. 3. Crystal packing of LAHS crystal in the unit cell, viewed along the c-axis, showing C H· · ·O and N H· · ·O interactions as dashed lines.
Fig. 4. Unit cell packing of LAHS single crystal.
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Table 1 Crystal data and structure refinement for LAHS crystal. Crystal data Chemical formula Formula weight Crystal system Space group Temperature (K) a b c ˛ ˇ Volume Z Absorption coefficient Crystal size (mm)
C6 H15 N4 O2 ·C4 HO4 288.27 Triclinic P1 296 ˚ 5.0901(5) A, ˚ 8.2364(9) A, 14.7926(16) A˚ 92.980◦ (5) 96.301◦ (5) 99.862◦ (5) 605.72(11) A˚ 3 2 0.13 mm−1 0.30 × 0.20 × 0.20
Data collection Diffractometer Absorption correction Tmin , Tmax No. of measured, independent and observed [I > 2(I)] reflections Rint (sin /max ) (Å−1 ) Refinement R[F2 > 2(F2 )], wR(F2 ), S No. of reflections No. of parameters No. of restraints Refinement method Goodness-of-fit on F2 Final R indices [I > 2(I)] R indices (all data) Absolute structure parameter Largest diff. peak and hole
Bruker AXS Kappa APEX2 CCD Diffractometer Multi-scan SADABS (Bruker, 2004) 0.932, 0.991 12,761, 5177, 4232
0.030 0.639 0.037, 0.093, 1.04 5177 403 5 Full-matrix least-squares on F2 1.041 R1 = 0.0374, wR2 = 0.0829 R1 = 0.0559, wR2 = 0.0933 −0.4 (9) 0.256 and −0.204 e A˚ −3
up to 210 ◦ C. The appearance of endotherm in the DSC and DTA at 238 ◦ C corresponds to TGA results. The endotherm at 238 ◦ C in the DSC trace shows the decomposition of LAHS crystal. From the TGA, DTA and DSC analyses, it is clearly observed that the crystal is stable up to 238 ◦ C. Hence, it can be said that melting and decomposition takes place simultaneously. There is a gradual and significant weight loss as the temperature is increased above the melting point. A total decomposition of the compound takes place at a temperature about 1000 ◦ C. There is no evidence of entrapped water in the crystal lattice or any adsorbed water on the crystal
Fig. 5. TGA/DTA curves of LAHS.
Fig. 6. DSC curve of LAHS.
surface as there is no weight loss up to 238 ◦ C. From the studies it is observed that the crystal is thermally stable till 238 ◦ C after this the sample undergoes appreciable weight loss. The crystal could be used for any optical application below this temperature. 3.3. UV–vis–NIR studies The UV optical absorption spectral analysis of LAHS single crystal was carried out between 200 nm and 1100 nm to ensure the optical activeness [22]. The recorded spectrum is shown in Fig. 7. The optical transmittance window and transparency lower cut off wavelength is very essential for the realization of SHG output. The absorption spectrum illustrates that the lower cut-off wavelength of the crystal was found to be 300 nm. The crystal is transparent in the wavelength range of 300–1100 nm. This study confirms that the crystal is transparent within a wide range of spectrum from UV to IR region, which enables it to be a potential candidate for optoelectronic applications and the second harmonic generation of the Nd:YAG laser. The spectrum shows an absorption peak at 268 nm, which is due to the → * transition. The band gap energy of the material is calculated using the formula, Eg = h
C × 6.2415 × 1018 eV
Fig. 7. Optical absorption spectrum of LAHS.
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Table 2 SHG efficiency of LAHS crystal.
Acknowledgements
Compound
SHG signal (mV)
KDP (reference) Urea LAHS
122 312 65
where, h = Planks constant = 6.626 × 10−34 J s, C = Speed of light = 3.0 × 108 m/s, = Cut-off wavelength = 300 × 10−9 m. The band gap energy of the crystal is found to be 4.1 eV. This indicates that the crystal has dielectric behavior to induce polarization when powerful radiation is incident on the material. 3.4. SHG efficiency The nonlinear optical property was tested by Kurtz and Perry powder method [23]. A Q-switched solid state Nd:YAG laser that delivers a fundamental beam of 1064 nm at a repetition rate of 10 Hz with a pulse width of 8 ns was used as light source. The input beam energy was 4.6 mJ/pulse. The 1064 nm was guided by various optical arrangements before being focused on the sample. The SH signal (532 nm) was selected by monochromator and then collected by photo multiplier tube and finally fed into the oscilloscope for measurement. To eliminate the experimental error, urea and KDP samples of the same particle size were also tested in the same setup and the efficiency were evaluated as a ratio. The experiment was carried out in pure KDP, urea and later in the sample. The second harmonic generation efficiency was found to be 0.208 times with respect to urea, 0.532 times with respect to KDP. The SHG efficiency of LAHS crystal is given in Table 2. 4. Conclusions Single crystal of LAHS was grown successfully by slow evaporation solution growth technique. The crystal structure and lattice parameters were identified by single crystal XRD analysis. The thermal stability of the grown crystal was analyzed by TG/DTA technique and it reveals that the crystal is stable up to 238 ◦ C. It is found from optical absorption study that the crystal is transparent in the range of wavelength 300–1100 nm. Kurtz and Perry powder method conforms the emission of SHG from the grown crystal and the efficiency was found to be 0.208 times with respect to urea and 0.532 times with KDP.
The authors are thankful to Prof. P.K. Das, Indian Institute of Science (IISC), Bangalore, India for support with laser facilities for SHG measurements and also extend their gratitude to the authorities of Sophisticated Analytical Instrument Facility (SAIF), IIT, Chennai, India for single crystal data collection and also authors acknowledge the Centre for Electrochemical Research Institute (CECRI) Karaikudi, India for TGA-DTA and DSC measurements. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic molecules and Crystals, Academic Press, New York, 1987. [2] S.S. Gupte, A. Marcano, R.D. Pradhan, C.F. Desai, J. Melikechi, Appl. Phys. 89 (2001) 4939. [3] P.R. Newman, L.F. Warren, P. Cunningham, T.Y. Chang, D.E. Cooper, G.L. Burdge, P. Polok-Dingels, C.K. Lowe-Ma, Mater. Res. Soc. Symp. Proc. 173 (1990) 557. [4] H.S. Nalwa, S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, CRC Press Inc., New York, 1997. [5] R.A. Hann, D. Bloor (Eds.), Organic Materials for Nonlinear Optics, The Royal Society of Chemistry, 1989. [6] M. Blanchard-Desce, C. Runser, A. Fort, M. Barzoukas, J.M. Lehn, V. Bloy, V. Alain, Chem. Phys. 199 (1995) 253. [7] M.N. Bhat, S.M. Dharmaprakash, J. Cryst. Growth 236 (2002) 376–380. [8] J.F. Nicoud, R.J. Twieg, D.S. Chemla, J. Zyas, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, London, 1987. [9] O.Z. Yes¸ilel, H. Pas¸ao˘glu, O.O. Yilan, O. Büyükgüngör, J. Chem. Sci. 62b (2007) 823–828. [10] H.K. Fun, W.S. Loh, A. Johnson, S. Yousuf, E. Eno, Acta Crystallogr. E 69 (2013) o353–o354. [11] X. Xue, C. Wang, W.J. Zhong, Mater. Sci. Technol. 20 (2004) 206–208. [12] M. Spassova, T. Kolev, I. Kanev, D. Jacquemin, B. Champagne, J. Mol. Struct. (THEOCHEM) 528 (2000) 151–159. [13] Bruker, SAINT-Plus, XPREP and SADABS, Bruker AXS Inc., Madison, WI, USA, 2004. [14] O. Angelova, V. Velikova, T. Kolev, V. Radomirska, Acta Crystallogr. C 52 (1996) 3252–3256. [15] M. Sethuram, G. Bhargavi, M. Dhandapani, G. Amirthaganesan, M. Nizam Mohideen, Acta Crystallogr. E 69 (2013) o1301–o1302. [16] J. Bernstein, R.E. Davis, L. Shimoni, N.L. Chang, Angew. Chem. Int. Ed. Engl. (1995) 1555–1573. [17] M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano, C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 36 (2003) 1103. [18] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112–122. [19] L.J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849–854. [20] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J. Pearson, R. Taylor, Acta Crystallogr. B 58 (2002) 389–397. [21] A.L. Spek, Acta Crystallogr. D 65 (2009) 148–155. [22] C.N.R. Rao, Ultraviolet and Visible Spectroscopy, Chemical Applications, Plenum Press, 1975. [23] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical materials, J. Appl. Phys. 39 (1968) 3798–3814.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Growth, structural, optical and thermal properties of an organic NLO material: l-Argininium hydrogen squarate P. Prabu a , M. Kayalvizhi b , C. Ramachandra Raja c,∗ , G. Vasuki b a b c
Department of Physics, Periyar Maniammai University, Thanjavur 613 403, Tamilnadu, India Department of Physics, Kunthavai Naachiar Government Arts College (W) (Autonomous), Thanjavur 613 007, Tamilnadu, India Department of Physics, Government Arts College (Autonomous), Kumbakonam 612 001, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 13 April 2015 Accepted 9 November 2015 Keywords: Optical materials Organic compounds Crystal growth X-ray diffraction Thermogravimetric analysis (TGA)
a b s t r a c t l-Argininium hydrogen squarate (LAHS) is an organic nonlinear optical material grown by slow evaporation solution growth technique. The crystal structure was confirmed by single crystal X-ray diffraction analysis and the crystal system is identified as triclinic system. The thermal stability and decomposition process were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The crystal is stable up to 238 ◦ C. The optical transparency range and lower cut-off wavelength of grown crystal have been identified by UV–vis–NIR spectroscopy method. The existence of second harmonic generation (SHG) signal was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. The SHG efficiency is compared with potassium di-hydrogen phosphate (KDP) and urea. © 2015 Elsevier GmbH. All rights reserved.
1. Introduction In present day much attention is being paid on exploration of novel and good quality nonlinear optical (NLO) materials. These materials play vital role in industry which includes telecommunication, optoelectronics technology, optical data storage and signal processing [1–5]. As the amino acids have chiral symmetry and crystallize in non-centrosymmetric space groups, they are interesting and important materials for NLO applications. The amino acids with organic salts are capable materials for optical second harmonic generations. Organic NLO materials are superior to their inorganic counterparts due to high conversion efficiency for second harmonic generation and good transparency [6] in the visible region. The optical properties of amino acid crystals are increased by addition of organic acids because of their high range of transparency [7,8]. Amino acids are biologically important organic compounds contain proton accepting amino (NH2 ) group and proton donating carboxyl (COOH) functional group in them. One such interesting amino acid is l-arginine (C6 H14 N4 O2 ). It is widely found in animal sources, plant sources and biological substances. l-Arginine forms
∗ Corresponding author at: Government Arts College, Kumbakonam 612 001, India. Tel.: +91 9976696277. E-mail address: crraja [email protected] (C. Ramachandra Raja). http://dx.doi.org/10.1016/j.ijleo.2015.11.047 0030-4026/© 2015 Elsevier GmbH. All rights reserved.
a number of complexes by reacting with organic acid and salts to produce a marvellous material for NLO applications. Hydrogen bonding is one of the principal intermolecular interactions that frequently play key roles in molecular recognition and self-assembly as well as in crystal engineering research and has been used effectively to predict and design supramolecular assemblies in one, two and three dimensions [9]. Supramolecularly organized systems with a variety of novel features are widely generated through hydrogen-bonding. Hydrogen-bonded systems generated from organic cations and anions are of special interest since they are likely to show stronger hydrogen bonds than neutral molecules thus enabling the simple acid–base chemistry to tune the donor and acceptor properties of the counter ions [10]. Squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) which is popularly known as quadratic acid (C4 H2 O4 ), is a white crystalline powder with highly acidic and chemically stable compound and it was first synthesized in 1959. Squaric acid was shown to be an unusually strong organic acid and one of the series of hydrogen-bonded ferroelectrics [11]. Squaric acid has been of much interest because of its cyclic structure and possible aromaticity. Several basic aspects of the properties of squaric acid have been reported to assess its potentialities for NLO applications. In particular, squaric acid and several optically active amino acids cocrystallize under the form of non-centrosymmetric lattice that are expected to present large second-order susceptibilities [12]. The
P. Prabu et al. / Optik 127 (2016) 1660–1664
present work reports on the growth and characterization of squaric acid and amino acid based single crystal. 2. Experimental details 2.1. Synthesis and crystal growth The title compound was grown from aqueous solution by slow evaporation solution growth technique. l-Arginine and squaric acid were taken in equimolar ratio and thoroughly dissolved in deionized water. The solution was stirred well for 6 h at room temperature using magnetic stirrer with 680 rpm to yield a homogenous mixture of solution. Then the saturated solution was filtered using Whatmann filter paper to eliminate unwanted impurities and transferred to a beaker. The beaker was covered with a perforated transparent polythene paper and kept at a dustless environment for slow evaporation. Good and transparent crystals were grown in a period of 3 weeks. The reaction involved in the process may be written as shown in Fig. 1. 2.2. Characterization The grown LAHS crystal was subjected to various characterization techniques like single crystal X-ray diffraction, UV–vis–NIR, thermal analysis and nonlinear optical studies. In order to obtain the cell parameters and crystal data of LAHS crystal, X-ray diffraction studies were carried out using crystal diffractometer equipped with a CCD detector (Bruker Kappa APEX II ULTRA), a rotating ˚ anode (Bruker AXS, FR591) with MoK␣ radiation ( = 0.71073 A). The UV–vis–NIR optical absorption spectral analysis was carried out between 200 and 1100 nm, using Lambda 25 spectrophotometer. Thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were carried out using SDT Q600 V8.3 Build 101 thermal analyzer instrument, ranging from room temperature to 1000 ◦ C at the heating rate of 20 ◦ C per minute under nitrogen atmosphere. The second harmonic generation efficiency was measured using Kurtz and Perry powder technique using Nd:YAG laser beam of energy 4.6 mJ/pulse. 3. Result and discussion 3.1. Crystal structure and X-ray diffraction analysis The intensity data were collected at 296 K on a Bruker AXS Kappa APEX2 CCD Diffractometer [13] system using MoK␣ graphite monochromated radiation. The molecular structure of the LAHS crystal (C10 H16 N4 O6 ) was refined by the least squares method using anisotropic thermal parameters: R = 3%. The compound crystallizes in triclinic, P1. The parameter values calculated are ˚ b = 8.2364(9) A, ˚ c = 14.7926(16) A, ˚ and Z = 2. This a = 5.0901(5) A, value is in good agreement with earlier report [14] which was recorded at 292 K. The asymmetric unit of the title compound contains two 5-((amino(imino)methyl)amino)-2-amminopentanoate (C1–C6/O1/O2/N1–N4 and C11–C16/O7/O8/N5–N8) and two 2-hydroxy-3,4-dioxocyclobut-1-enolate (O3–O6/C7–C10 and
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O9–O12/C17–C20). The C N bond distances of the NH2 groups ˚ N2–C6 = 1.315(9) A, ˚ N5–C16 = 1.325(3) A˚ and N1–C6 = 1.315(8) A, ˚ respectively, which is short for a C N single N6–C16 = 1.310(1) A, ˚ but still not quite as contracted as one would expect for bond 1.47 A, ˚ These bond length feaa fully established C N double bond 1.27 A. tures are consistent with an imino resonance form as it commonly found for C N single bonds involving sp2 hybridized C and N atoms ˚ C1–O2 = 1.238(3) A, ˚ [15]. The bond distances C1–O1 = 1.256(3) A, ˚ ˚ ˚ C11–O7 = 1.237(1) A, C11–O8 = 1.254(2) A, C8–O4 = 1.230(9) A, ˚ ˚ ˚ C9–O5 = 1.217(6) A, C10–O6 = 1.249(1) A, C17–O9 = 1.232(1) A, ˚ respectively, C18–O10 = 1.214(8) A˚ and C19–O11 = 1.243(8) A, clearly indicate the presence of C O double bonds, including those also generated through resonance. The H atoms attached to the squaric groups (O6 and O11) are transferred to the basic centers N6 and N2 respectively, generating the iminium groups. Also the carboxylic H-atoms on O1 and O8 have been transferred to N4 and N8, respectively, to generate the common amino acid zwitterions. The C O double bonds generated through resonance in the ˚ in molecule A and squaric acid anion [C10 O6 (1.249(1) A) ˚ in molecule B] are shorter than normal sinC19 O11 (1.243(8) A) ˚ and slightly longer than normal double C O gle C O bond (1.426 A) ˚ Both molecules (A and B) are involved in inter and bond (1.23 A). intra molecular N H· · ·O hydrogen bonds. Intramolecular C H· · ·O and N H· · ·O hydrogen bonds lead to the formation of a five-, six-, seven-, eight-, nine- and ten-membered ring motif S(5), S(6), S(7), S(8), S(9) and S(10), respectively [16]. The crystal structure of the compound is further stabilized by intermolecular C H· · ·O and N H· · ·O hydrogen bonds. The LAHS crystal data, experimental conditions and structural refinement parameters are presented in Table 1. The molecular structure, crystal packing and unit cell packing diagrams of LAHS are shown in Figs. 2–4, respectively. For the title compound, data collection was done using the computer program APEX2 [13], cell refinement was done using the computer program APEX2/SAINT [13] and data reduction was done by using SAINT/XPREP [13]. The structure of the title compound was solved by using the computer program SIR92 [17] and refined using SHELXL-97 [18]. The molecular graphics were done using the computer programs ORTEP [19], Mercury [20] and PLATON [21]. All the H atoms were positioned geometrically and treated as riding on their parent atoms, with C H = 0.98 A˚ (methine), and 0.97 A˚ (methylene), and refined using a riding model with Uiso (H) = 1.2 Ueq and 1.5 Ueq (parent atom).
3.2. Thermal analysis Thermogravimetric analysis is an analytical technique used to determine thermal stability and fraction of volatile compound of a crystal by monitoring the weight change that occurs as the crystal is heated. The TGA, DTA and DSC of LAHS crystal were carried between room temperature to 1000 ◦ C at the heating rate of 20 ◦ C per minute under nitrogen inert atmosphere. The resulting TGA/DTA and DSC curves are shown in Figs. 5 and 6, respectively. The initial mass of the crystal subjected to analyses was 4.9670 mg and the final mass left out after the experiment was 5.163% of the initial mass. The TGA trace appears nearly straight
Fig. 1. Chemical reaction.
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Fig. 2. The molecular structure of the two independent molecules of LAHS crystal, showing atom numbering, with displacement ellipsoids drawn at the 50% probability level.
Fig. 3. Crystal packing of LAHS crystal in the unit cell, viewed along the c-axis, showing C H· · ·O and N H· · ·O interactions as dashed lines.
Fig. 4. Unit cell packing of LAHS single crystal.
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Table 1 Crystal data and structure refinement for LAHS crystal. Crystal data Chemical formula Formula weight Crystal system Space group Temperature (K) a b c ˛ ˇ Volume Z Absorption coefficient Crystal size (mm)
C6 H15 N4 O2 ·C4 HO4 288.27 Triclinic P1 296 ˚ 5.0901(5) A, ˚ 8.2364(9) A, 14.7926(16) A˚ 92.980◦ (5) 96.301◦ (5) 99.862◦ (5) 605.72(11) A˚ 3 2 0.13 mm−1 0.30 × 0.20 × 0.20
Data collection Diffractometer Absorption correction Tmin , Tmax No. of measured, independent and observed [I > 2(I)] reflections Rint (sin /max ) (Å−1 ) Refinement R[F2 > 2(F2 )], wR(F2 ), S No. of reflections No. of parameters No. of restraints Refinement method Goodness-of-fit on F2 Final R indices [I > 2(I)] R indices (all data) Absolute structure parameter Largest diff. peak and hole
Bruker AXS Kappa APEX2 CCD Diffractometer Multi-scan SADABS (Bruker, 2004) 0.932, 0.991 12,761, 5177, 4232
0.030 0.639 0.037, 0.093, 1.04 5177 403 5 Full-matrix least-squares on F2 1.041 R1 = 0.0374, wR2 = 0.0829 R1 = 0.0559, wR2 = 0.0933 −0.4 (9) 0.256 and −0.204 e A˚ −3
up to 210 ◦ C. The appearance of endotherm in the DSC and DTA at 238 ◦ C corresponds to TGA results. The endotherm at 238 ◦ C in the DSC trace shows the decomposition of LAHS crystal. From the TGA, DTA and DSC analyses, it is clearly observed that the crystal is stable up to 238 ◦ C. Hence, it can be said that melting and decomposition takes place simultaneously. There is a gradual and significant weight loss as the temperature is increased above the melting point. A total decomposition of the compound takes place at a temperature about 1000 ◦ C. There is no evidence of entrapped water in the crystal lattice or any adsorbed water on the crystal
Fig. 5. TGA/DTA curves of LAHS.
Fig. 6. DSC curve of LAHS.
surface as there is no weight loss up to 238 ◦ C. From the studies it is observed that the crystal is thermally stable till 238 ◦ C after this the sample undergoes appreciable weight loss. The crystal could be used for any optical application below this temperature. 3.3. UV–vis–NIR studies The UV optical absorption spectral analysis of LAHS single crystal was carried out between 200 nm and 1100 nm to ensure the optical activeness [22]. The recorded spectrum is shown in Fig. 7. The optical transmittance window and transparency lower cut off wavelength is very essential for the realization of SHG output. The absorption spectrum illustrates that the lower cut-off wavelength of the crystal was found to be 300 nm. The crystal is transparent in the wavelength range of 300–1100 nm. This study confirms that the crystal is transparent within a wide range of spectrum from UV to IR region, which enables it to be a potential candidate for optoelectronic applications and the second harmonic generation of the Nd:YAG laser. The spectrum shows an absorption peak at 268 nm, which is due to the → * transition. The band gap energy of the material is calculated using the formula, Eg = h
C × 6.2415 × 1018 eV
Fig. 7. Optical absorption spectrum of LAHS.
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Table 2 SHG efficiency of LAHS crystal.
Acknowledgements
Compound
SHG signal (mV)
KDP (reference) Urea LAHS
122 312 65
where, h = Planks constant = 6.626 × 10−34 J s, C = Speed of light = 3.0 × 108 m/s, = Cut-off wavelength = 300 × 10−9 m. The band gap energy of the crystal is found to be 4.1 eV. This indicates that the crystal has dielectric behavior to induce polarization when powerful radiation is incident on the material. 3.4. SHG efficiency The nonlinear optical property was tested by Kurtz and Perry powder method [23]. A Q-switched solid state Nd:YAG laser that delivers a fundamental beam of 1064 nm at a repetition rate of 10 Hz with a pulse width of 8 ns was used as light source. The input beam energy was 4.6 mJ/pulse. The 1064 nm was guided by various optical arrangements before being focused on the sample. The SH signal (532 nm) was selected by monochromator and then collected by photo multiplier tube and finally fed into the oscilloscope for measurement. To eliminate the experimental error, urea and KDP samples of the same particle size were also tested in the same setup and the efficiency were evaluated as a ratio. The experiment was carried out in pure KDP, urea and later in the sample. The second harmonic generation efficiency was found to be 0.208 times with respect to urea, 0.532 times with respect to KDP. The SHG efficiency of LAHS crystal is given in Table 2. 4. Conclusions Single crystal of LAHS was grown successfully by slow evaporation solution growth technique. The crystal structure and lattice parameters were identified by single crystal XRD analysis. The thermal stability of the grown crystal was analyzed by TG/DTA technique and it reveals that the crystal is stable up to 238 ◦ C. It is found from optical absorption study that the crystal is transparent in the range of wavelength 300–1100 nm. Kurtz and Perry powder method conforms the emission of SHG from the grown crystal and the efficiency was found to be 0.208 times with respect to urea and 0.532 times with KDP.
The authors are thankful to Prof. P.K. Das, Indian Institute of Science (IISC), Bangalore, India for support with laser facilities for SHG measurements and also extend their gratitude to the authorities of Sophisticated Analytical Instrument Facility (SAIF), IIT, Chennai, India for single crystal data collection and also authors acknowledge the Centre for Electrochemical Research Institute (CECRI) Karaikudi, India for TGA-DTA and DSC measurements. References [1] D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic molecules and Crystals, Academic Press, New York, 1987. [2] S.S. Gupte, A. Marcano, R.D. Pradhan, C.F. Desai, J. Melikechi, Appl. Phys. 89 (2001) 4939. [3] P.R. Newman, L.F. Warren, P. Cunningham, T.Y. Chang, D.E. Cooper, G.L. Burdge, P. Polok-Dingels, C.K. Lowe-Ma, Mater. Res. Soc. Symp. Proc. 173 (1990) 557. [4] H.S. Nalwa, S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, CRC Press Inc., New York, 1997. [5] R.A. Hann, D. Bloor (Eds.), Organic Materials for Nonlinear Optics, The Royal Society of Chemistry, 1989. [6] M. Blanchard-Desce, C. Runser, A. Fort, M. Barzoukas, J.M. Lehn, V. Bloy, V. Alain, Chem. Phys. 199 (1995) 253. [7] M.N. Bhat, S.M. Dharmaprakash, J. Cryst. Growth 236 (2002) 376–380. [8] J.F. Nicoud, R.J. Twieg, D.S. Chemla, J. Zyas, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, London, 1987. [9] O.Z. Yes¸ilel, H. Pas¸ao˘glu, O.O. Yilan, O. Büyükgüngör, J. Chem. Sci. 62b (2007) 823–828. [10] H.K. Fun, W.S. Loh, A. Johnson, S. Yousuf, E. Eno, Acta Crystallogr. E 69 (2013) o353–o354. [11] X. Xue, C. Wang, W.J. Zhong, Mater. Sci. Technol. 20 (2004) 206–208. [12] M. Spassova, T. Kolev, I. Kanev, D. Jacquemin, B. Champagne, J. Mol. Struct. (THEOCHEM) 528 (2000) 151–159. [13] Bruker, SAINT-Plus, XPREP and SADABS, Bruker AXS Inc., Madison, WI, USA, 2004. [14] O. Angelova, V. Velikova, T. Kolev, V. Radomirska, Acta Crystallogr. C 52 (1996) 3252–3256. [15] M. Sethuram, G. Bhargavi, M. Dhandapani, G. Amirthaganesan, M. Nizam Mohideen, Acta Crystallogr. E 69 (2013) o1301–o1302. [16] J. Bernstein, R.E. Davis, L. Shimoni, N.L. Chang, Angew. Chem. Int. Ed. Engl. (1995) 1555–1573. [17] M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano, C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 36 (2003) 1103. [18] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112–122. [19] L.J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849–854. [20] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P. McCabe, J. Pearson, R. Taylor, Acta Crystallogr. B 58 (2002) 389–397. [21] A.L. Spek, Acta Crystallogr. D 65 (2009) 148–155. [22] C.N.R. Rao, Ultraviolet and Visible Spectroscopy, Chemical Applications, Plenum Press, 1975. [23] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical materials, J. Appl. Phys. 39 (1968) 3798–3814.