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Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l -isoleucinium picrate
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Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate G. Ramasamy, Subbiah Meenakshisundaram ∗ Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
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Article history: Received 7 August 2013 Accepted 12 February 2014 Available online xxx Keywords: Crystal growth Crystal structure Infrared spectroscopy Optical materials
a b s t r a c t A series of l-amino acids, isoleucine, valine, glutamine, methionine, arginine, cystine and aspargine are employed to form picrates with picric acid (1:1). A comparison of cell parameters reveals that expected picrates are formed only in the case of l-valine and l-isoleucine. l-Isoleucinium picrate (LIP), a new nonlinear optical material was grown from aqueous medium by the slow evaporation of equimolar mixture of l-isoleucine and picric acid. The structure of the grown crystal as determined by single crystal XRD diffraction analysis reveals that it belongs to the monoclinic system with space group P21 and the cell ˚ b = 6.425(2) A; ˚ c = 12.871(4) A; ˚ ˇ = 109.54(3)◦ ; V = 770.0(4) A˚ 3 ; Z = 2. parameter values are, a = 9.970(3) A; The presence of functional groups in the LIP is confirmed by FT-IR vibrational patterns and the good crystallinity indicated by powder X-ray diffraction method. The relative second harmonic generation (SHG) efficiency measurements reveal that the LIP is a highly efficient nonlinear optical (NLO) material having an activity 16 times as that of the reference material potassium dihydrogen phosphate. The optical transparency has been studied using UV–vis spectrophotometer and the absorption is minimum in the visible region. Thermogravimetric and differential thermal analyses reveal the purity of the sample and no decomposition is observed up to the melting point. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Picric acid (PA), as an electron acceptor form charge transfer molecular complexes with a number of electron donor compounds such as amines [1–4] through electrostatic or hydrogen bonding interactions. Hence, the picrates are convenient for identification and quantitative analysis of organic compounds. The bonding of these picrate complexes depends on the nature of the donor–acceptor system. Organic nonlinear optical (NLO) materials formed from amino acids have potential applications in second harmonic generation (SHG), optical storage, optical communications, photonics, electro-optic modulation, etc. [5–7]. The structure of nonlinear optical active amino acid picrates such as glycine glycinium picrate [8], l-alanine l-alaninium picrate [9], -alanine -alaninium picrate [10], l-leucine l-leucinium picrates [11], dlphenylalanine dl-phenylalaninium picrate [12], dl-methionine dl-methioninium picrate [13], dl-valine dl-valinium picrate [14] and l-valinium picrate [15] has been reported. The crystal
growth and characterization of glycinium picrate [16–18], glycine glycinium picrate [19], l-prolinium picrate [20–22], l-threoninium picrate [23], l-tryptophanium picrate [24], l-asparaginium picrate [25], l-valinium picrate [26–33], l-alanine l-alaninium picrate [34], -alaninium picrate [35,36], dl-methionine dl-methioninium picrate [33], dl-phenylalanine dl-phenylalaninium picrate [36] and l-leucine l-leucinium picrate [37] have been investigated. Characterization of l-isoleucine crystal morphology from molecular modeling has been reported by Givand et al. [38]. Recently, we have reported the crystal growth, structure, and characterization of p-toluidinium picrate [4]. In the present investigation, a series of l-amino acids, isoleucine, valine, glutamine, methionine, arginine, cystine and aspargine are subjected to investigation and we are reporting the crystal growth, structure and characterization of a new highly efficient NLO material l-isoleucine picrate. 2. Experimental 2.1. Synthesis and crystal growth
∗ Corresponding author. Tel.: +91 4144 221670/9443091274. E-mail address: [email protected] (S. Meenakshisundaram).
l-Isoleucinium picrate crystals were grown from an aqueous solution by stoichiometric incorporation of AR grade of l-isoleucine
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Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036
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G. Ramasamy, S. Meenakshisundaram / Optik xxx (2014) xxx–xxx Table 1 Frequencies of the fundamental vibrations of PA, l-isoleucine and LIP (cm−1 ). PA
l-Isoleucine
LIP
Assignment of vibration
1560 1330 – – – 1235, 1057 1615, 1487 3110 736 780 – – 889 540
– – 2963, 2684 – 3290 – – –
1590 1354 2701 3100 3236 1276, 1123 1633, 1436 – 745 – 1718 1590 909 578
asNO2 sNO2 CH (–CH3 ) sNH (NH3+ ) asNH C O C C -OH ωNO2 NO2 C O asCOO s C C N C C N deformation
– 1760 1577 – –
as – asymmetric stretching; s – symmetric stretching; – scissoring; ω – wagging.
Philips Xpert Pro Triple-axis X-ray diffractometer. The XRD data is analyzed by Rietveld method with RIETAN-2000. The FT-IR was recorded in the range 4000–500 cm−1 using AVATAR 330 FT-IR by KBr pellet technique. The UV–vis analysis was carried out between 200 and 800 nm using the Perkin Elmer Lambda 35 model spectrophotometer. TG and DTA were performed using STD Q 600 in the temperature range 0–600 ◦ C at a heating rate of 100 ◦ C/min in the nitrogen atmosphere. The second harmonic generation test on the crystals was performed by the Kurtz powder SHG method [40].
3. Results and discussion Fig. 1. Crystal photographs of (a) LIP, (b) l-valinium picrate, (c) l-glutamine–picric acid (1:1) system, (d) l-methionine–picric acid (1:1) system, (e) l-arginine–picric acid (1:1) system, (f) l-cystine–picric acid (1:1) system, and (g) l-aspargine–picric acid (1:1) system.
(Merck) and picric acid (Qualigens) in the molar ratio of 1:1. The reactants were dissolved in triple distilled water, left for 3 h under stirring to ensure homogeneity and then the solution was tightly covered with a perforated paper. Under the identical experimental conditions, the same procedure was employed for the other amino acids, l-valine (Merck), l-glutamine (sd-fine), l-methionine (Merck), l-arginine (sd-fine), l-cystine (sd-fine) and l-aspargine (Merck). The crystallization took place within a week and the high quality transparent crystals were harvested from the aqueous growth medium. Best quality and highly transparent seed crystals are used in the preparation of bulk crystals. Bulk crystals were grown using optimized growth parameters. The photograph of the as-grown crystals are shown in Fig. 1.
2.2. Characterization techniques In order to ascertain the structure, purity and identification of the grown crystal, single crystal X-ray diffraction data were collected with a specimen 0.30 mm × 0.20 mm × 0.20 mm cut out from the grown crystals using an Oxford Diffraction Xcalibur-S CCD sys˚ tem equipped with graphite monochromated MoK␣ ( = 0.71073 A) radiation at 293 K. The structure was solved by direct methods (SHELXS-97) and refined by full-matrix least squares against F2 using SHELXL-97 software [39]. The molecular structure was drawn using ORTEP-3. The powder XRD analysis was performed by using
A close observation of crystal data (Table 1) reveals that in the case of l-methionine, l-arginine, l-cystine and l-aspargine the expected product picrate is not formed but only the picric acid crystallizes out from the equimolar solution of amino acid and picric acid. Interestingly, the product in l-glutamine–picric acid (1:1) system is ammonium picrate although there is some difference concerning the unit cell dimensions, particularly ‘a’ values. Complete mismatch of unit cell parameters with that of precursors are observed only in l-isoleucine and l-valine, indicating a facile formation of picrate. Formation of picrate complex depends on the nature of donor–acceptor system. Simply, it depends on the nature of the amino acid. Interesting to observe is that the good quality crystals are grown from the aqueous solution only in the case of amino acids, l-isoleucine, l-valine and to a lesser extent in l-glutamine. The crystalline qualities are poor in other amino acid–picric acid (1:1) systems (Fig. 1). The functional groups of LIP are confirmed by recording the FT-IR spectrum in the range 4000–500 cm−1 (Fig. 2). Shifts in peak positions indicate the product formation. The assignments of well defined bands are given in Table 2 and these are found to be in good agreement with those of similar compounds. It has been established by IR that a complex was formed by transferring a proton from the acceptor picric acid to the donor, l-isoleucine [43]. The charge transfer complex is evidenced by the presence of main characteristic IR bands of donor and acceptor in the spectrum of the product. In the present investigation, the proton transfer complex is clearly shown by the single crystal XRD analysis ORTEP and packing diagram (Fig. 3). The extreme intermolecular hydrogen bonding was identified by shifting of bands due to stretching and bending modes of various functional groups. The asymmetric vibration of –NO2 group is stronger than the symmetric one. The N+ –H vibration is observed as sharp peak at ∼3100 cm−1 . The C -O stretching vibration appears as a strong band in the region 1300–1200 cm−1 . In the case of LIP, the band corresponding to this vibration is shifted to 1276 cm−1 .
Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036
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Fig. 3. (I) ORTEP (II) packing diagram of LIP.
Fig. 2. FT-IR spectrum of (a) picric acid, (b) LIP, and (c) l-isoleucine.
The UV spectrum reveals that the cut-off wavelength () is ∼440 nm. Absorption is minimum in the 440–800 nm range. It clearly implies that this crystal has a good transparency in the visible region, a required property for a good NLO material (Fig. 4). The TG and DTA curves of l-isoleucinium picrate crystal is given in Fig. 5. The thermal analysis shows that there is no physically absorbed water in the molecular structure of crystals grown from aqueous medium. Studies reveal the purity of the material. The compound is stable and there is no phase transition till it melts. No decomposition up to the melting point ensures that suitability of the material for application in laser where the crystals are required to withstand high temperatures. The TG curve shows three mass loss processes at inflection temperatures 196.5, 298.6 and 445.8 ◦ C. Sharp endothermic peaks in DTA indicate a good degree of crystallinity of the grown crystal. The melting point was also determined by using Sigma instrument melting point apparatus (196 ◦ C). The powder XRD pattern of LIP crystal (Fig. 6) shows that the sample is of single phase without detectable impurity. Narrow peaks confirm the good crystallinity of the material. Unit cell parameters of picric acid and isoleucine are completely different in comparison with that of LIP (Table 1) and this mismatch very
Fig. 4. UV–vis spectrum of (a) picric acid and (b) LIP.
much supports the product formation. The proton from the phenolic –OH group of the picric acid is transferred to the amino group of l-isolecuine. This behavior is similar to that observed in many picrate salts [16–34]. The structure is determined with a low value of R factor (0.0380) using 7257 reflections (R(int) = 0.0193) and goodness of fit (F2 ) = 1.072. The monoclinic crystal structure with space group P21 of LIP comprises monovalent isoleucininium cations, charge counter balanced by picrate anions (Fig. 3). The packing arrangement reveals stronger – interactions. Bond lengths in the carboxylic COOH group are typical for C O and C OH bonds ˚ respectively). (C7 O9 and C4 O7 distances are 1.218 A˚ and 1.321 A,
Table 2 Crystal data of as-grown crystals. System
Picric acid l-Isoluecine l-Picrate l-Valine picrate Glutamine + picric acid (1:1) Ammonium picrate l-Methonine + picric acid (1:1) l-Arginine + picric acid (1:1) l-Cystine + picric acid (1:1) l-Aspargine + picric acid (1:1)
Cell parameters a/Å
b/Å
c/Å
V/Å3
9.25 9.709 9.970(3) 9.950(3) 15.16(2) 13.45 9.16(2) 9.134(18) 9.24(3) 9.24(2)
9.68 5.291 6.425(2) 6.285(2) 19.97(3) 19.74 9.60(2) 9.594(19) 9.71(3) 9.66(2)
19.08 14.018 12.871(4) 12.621(4) 7.099(10) 7.12 18.93(5) 18.90(4) 19.13(5) 19.09(4)
– – 770.0(4) 739.1(4) 1872(6) – 1664(7) 1656(7) 1717(8) 1703(10)
Crystal system
Space group
References
Orthorhombic Monoclinic Monoclinic Monoclinic Orthorhombic Orthorhombic Orthorhombic Orthorhombic Orthorhombic Orthorhombic
PCa P21 P21 P21 – Ibca – – – –
[41] [38] Present work Present work Present work [42] Present work Present work Present work Present work
Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036
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G. Ramasamy, S. Meenakshisundaram / Optik xxx (2014) xxx–xxx Table 3 SHG output (input 5.1 mV/pulse). System
I2ω /mV
KDP PA LIP
27 70 432
asymmetric units of LIP could be the main reason for high SHG efficiency. 4. Conclusion
Fig. 5. TG-DTA curves of LIP.
The bond lengths of C3–C4 and C4–C5 are 1.398(3) A˚ and 1.456(3) A˚ respectively which are longer and deviate from regular aromatic ˚ which is interC C values. The C4 O7 value of LIP is 1.321(3) A, mediate between the single and double bonds. Loss of hydroxyl proton at the O7 leading to specific electron delocalization around C4 is observed. These observations are in agreement with the other picrates subjected to proton transfer [4,44,45]. It has been established that the orientation of anion and cation molecules facilitates the formation of expected N H· · ·O hydrogen bonds between amino nitrogen and phenolic oxygen [44]. The crystal structure is also stabilized by O H· · ·O hydrogen bonds and specific short contacts. The doubling of frequency was confirmed by the green color of the output radiation whose characteristic wavelength is 532 nm. KDP was used as a reference material in the present measurement. The relative SHG conversion efficiency of LIP is found to be 16 times that of KDP (Table 3). This may be attributed to the molecular structure of l-isoleucine in which the carboxyl group of the isoleucinium residue is engaged in a strong hydrogen bond with the picrate anion. The amino group of the l-isoleucinium cation and the picrate anion are held together by an intermolecular hydrogen bond. This type of strong intermolecular hydrogen bonding enhances the NLO properties of the material [46]. Also, it has been reported that the –* transition occurs in the carboxyl group which gives rise to NLO properties in this compound [21]. LIP is a donor–acceptor molecular compound in which l-isoleucinium cation act as donor and picrate anion act as an acceptor. Presence of donor–acceptor
Fig. 6. Powder XRD pattern of LIP.
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Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate G. Ramasamy, Subbiah Meenakshisundaram ∗ Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
a r t i c l e
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Article history: Received 7 August 2013 Accepted 12 February 2014 Available online xxx Keywords: Crystal growth Crystal structure Infrared spectroscopy Optical materials
a b s t r a c t A series of l-amino acids, isoleucine, valine, glutamine, methionine, arginine, cystine and aspargine are employed to form picrates with picric acid (1:1). A comparison of cell parameters reveals that expected picrates are formed only in the case of l-valine and l-isoleucine. l-Isoleucinium picrate (LIP), a new nonlinear optical material was grown from aqueous medium by the slow evaporation of equimolar mixture of l-isoleucine and picric acid. The structure of the grown crystal as determined by single crystal XRD diffraction analysis reveals that it belongs to the monoclinic system with space group P21 and the cell ˚ b = 6.425(2) A; ˚ c = 12.871(4) A; ˚ ˇ = 109.54(3)◦ ; V = 770.0(4) A˚ 3 ; Z = 2. parameter values are, a = 9.970(3) A; The presence of functional groups in the LIP is confirmed by FT-IR vibrational patterns and the good crystallinity indicated by powder X-ray diffraction method. The relative second harmonic generation (SHG) efficiency measurements reveal that the LIP is a highly efficient nonlinear optical (NLO) material having an activity 16 times as that of the reference material potassium dihydrogen phosphate. The optical transparency has been studied using UV–vis spectrophotometer and the absorption is minimum in the visible region. Thermogravimetric and differential thermal analyses reveal the purity of the sample and no decomposition is observed up to the melting point. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Picric acid (PA), as an electron acceptor form charge transfer molecular complexes with a number of electron donor compounds such as amines [1–4] through electrostatic or hydrogen bonding interactions. Hence, the picrates are convenient for identification and quantitative analysis of organic compounds. The bonding of these picrate complexes depends on the nature of the donor–acceptor system. Organic nonlinear optical (NLO) materials formed from amino acids have potential applications in second harmonic generation (SHG), optical storage, optical communications, photonics, electro-optic modulation, etc. [5–7]. The structure of nonlinear optical active amino acid picrates such as glycine glycinium picrate [8], l-alanine l-alaninium picrate [9], -alanine -alaninium picrate [10], l-leucine l-leucinium picrates [11], dlphenylalanine dl-phenylalaninium picrate [12], dl-methionine dl-methioninium picrate [13], dl-valine dl-valinium picrate [14] and l-valinium picrate [15] has been reported. The crystal
growth and characterization of glycinium picrate [16–18], glycine glycinium picrate [19], l-prolinium picrate [20–22], l-threoninium picrate [23], l-tryptophanium picrate [24], l-asparaginium picrate [25], l-valinium picrate [26–33], l-alanine l-alaninium picrate [34], -alaninium picrate [35,36], dl-methionine dl-methioninium picrate [33], dl-phenylalanine dl-phenylalaninium picrate [36] and l-leucine l-leucinium picrate [37] have been investigated. Characterization of l-isoleucine crystal morphology from molecular modeling has been reported by Givand et al. [38]. Recently, we have reported the crystal growth, structure, and characterization of p-toluidinium picrate [4]. In the present investigation, a series of l-amino acids, isoleucine, valine, glutamine, methionine, arginine, cystine and aspargine are subjected to investigation and we are reporting the crystal growth, structure and characterization of a new highly efficient NLO material l-isoleucine picrate. 2. Experimental 2.1. Synthesis and crystal growth
∗ Corresponding author. Tel.: +91 4144 221670/9443091274. E-mail address: [email protected] (S. Meenakshisundaram).
l-Isoleucinium picrate crystals were grown from an aqueous solution by stoichiometric incorporation of AR grade of l-isoleucine
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Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036
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G. Ramasamy, S. Meenakshisundaram / Optik xxx (2014) xxx–xxx Table 1 Frequencies of the fundamental vibrations of PA, l-isoleucine and LIP (cm−1 ). PA
l-Isoleucine
LIP
Assignment of vibration
1560 1330 – – – 1235, 1057 1615, 1487 3110 736 780 – – 889 540
– – 2963, 2684 – 3290 – – –
1590 1354 2701 3100 3236 1276, 1123 1633, 1436 – 745 – 1718 1590 909 578
asNO2 sNO2 CH (–CH3 ) sNH (NH3+ ) asNH C O C C -OH ωNO2 NO2 C O asCOO s C C N C C N deformation
– 1760 1577 – –
as – asymmetric stretching; s – symmetric stretching; – scissoring; ω – wagging.
Philips Xpert Pro Triple-axis X-ray diffractometer. The XRD data is analyzed by Rietveld method with RIETAN-2000. The FT-IR was recorded in the range 4000–500 cm−1 using AVATAR 330 FT-IR by KBr pellet technique. The UV–vis analysis was carried out between 200 and 800 nm using the Perkin Elmer Lambda 35 model spectrophotometer. TG and DTA were performed using STD Q 600 in the temperature range 0–600 ◦ C at a heating rate of 100 ◦ C/min in the nitrogen atmosphere. The second harmonic generation test on the crystals was performed by the Kurtz powder SHG method [40].
3. Results and discussion Fig. 1. Crystal photographs of (a) LIP, (b) l-valinium picrate, (c) l-glutamine–picric acid (1:1) system, (d) l-methionine–picric acid (1:1) system, (e) l-arginine–picric acid (1:1) system, (f) l-cystine–picric acid (1:1) system, and (g) l-aspargine–picric acid (1:1) system.
(Merck) and picric acid (Qualigens) in the molar ratio of 1:1. The reactants were dissolved in triple distilled water, left for 3 h under stirring to ensure homogeneity and then the solution was tightly covered with a perforated paper. Under the identical experimental conditions, the same procedure was employed for the other amino acids, l-valine (Merck), l-glutamine (sd-fine), l-methionine (Merck), l-arginine (sd-fine), l-cystine (sd-fine) and l-aspargine (Merck). The crystallization took place within a week and the high quality transparent crystals were harvested from the aqueous growth medium. Best quality and highly transparent seed crystals are used in the preparation of bulk crystals. Bulk crystals were grown using optimized growth parameters. The photograph of the as-grown crystals are shown in Fig. 1.
2.2. Characterization techniques In order to ascertain the structure, purity and identification of the grown crystal, single crystal X-ray diffraction data were collected with a specimen 0.30 mm × 0.20 mm × 0.20 mm cut out from the grown crystals using an Oxford Diffraction Xcalibur-S CCD sys˚ tem equipped with graphite monochromated MoK␣ ( = 0.71073 A) radiation at 293 K. The structure was solved by direct methods (SHELXS-97) and refined by full-matrix least squares against F2 using SHELXL-97 software [39]. The molecular structure was drawn using ORTEP-3. The powder XRD analysis was performed by using
A close observation of crystal data (Table 1) reveals that in the case of l-methionine, l-arginine, l-cystine and l-aspargine the expected product picrate is not formed but only the picric acid crystallizes out from the equimolar solution of amino acid and picric acid. Interestingly, the product in l-glutamine–picric acid (1:1) system is ammonium picrate although there is some difference concerning the unit cell dimensions, particularly ‘a’ values. Complete mismatch of unit cell parameters with that of precursors are observed only in l-isoleucine and l-valine, indicating a facile formation of picrate. Formation of picrate complex depends on the nature of donor–acceptor system. Simply, it depends on the nature of the amino acid. Interesting to observe is that the good quality crystals are grown from the aqueous solution only in the case of amino acids, l-isoleucine, l-valine and to a lesser extent in l-glutamine. The crystalline qualities are poor in other amino acid–picric acid (1:1) systems (Fig. 1). The functional groups of LIP are confirmed by recording the FT-IR spectrum in the range 4000–500 cm−1 (Fig. 2). Shifts in peak positions indicate the product formation. The assignments of well defined bands are given in Table 2 and these are found to be in good agreement with those of similar compounds. It has been established by IR that a complex was formed by transferring a proton from the acceptor picric acid to the donor, l-isoleucine [43]. The charge transfer complex is evidenced by the presence of main characteristic IR bands of donor and acceptor in the spectrum of the product. In the present investigation, the proton transfer complex is clearly shown by the single crystal XRD analysis ORTEP and packing diagram (Fig. 3). The extreme intermolecular hydrogen bonding was identified by shifting of bands due to stretching and bending modes of various functional groups. The asymmetric vibration of –NO2 group is stronger than the symmetric one. The N+ –H vibration is observed as sharp peak at ∼3100 cm−1 . The C -O stretching vibration appears as a strong band in the region 1300–1200 cm−1 . In the case of LIP, the band corresponding to this vibration is shifted to 1276 cm−1 .
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Fig. 3. (I) ORTEP (II) packing diagram of LIP.
Fig. 2. FT-IR spectrum of (a) picric acid, (b) LIP, and (c) l-isoleucine.
The UV spectrum reveals that the cut-off wavelength () is ∼440 nm. Absorption is minimum in the 440–800 nm range. It clearly implies that this crystal has a good transparency in the visible region, a required property for a good NLO material (Fig. 4). The TG and DTA curves of l-isoleucinium picrate crystal is given in Fig. 5. The thermal analysis shows that there is no physically absorbed water in the molecular structure of crystals grown from aqueous medium. Studies reveal the purity of the material. The compound is stable and there is no phase transition till it melts. No decomposition up to the melting point ensures that suitability of the material for application in laser where the crystals are required to withstand high temperatures. The TG curve shows three mass loss processes at inflection temperatures 196.5, 298.6 and 445.8 ◦ C. Sharp endothermic peaks in DTA indicate a good degree of crystallinity of the grown crystal. The melting point was also determined by using Sigma instrument melting point apparatus (196 ◦ C). The powder XRD pattern of LIP crystal (Fig. 6) shows that the sample is of single phase without detectable impurity. Narrow peaks confirm the good crystallinity of the material. Unit cell parameters of picric acid and isoleucine are completely different in comparison with that of LIP (Table 1) and this mismatch very
Fig. 4. UV–vis spectrum of (a) picric acid and (b) LIP.
much supports the product formation. The proton from the phenolic –OH group of the picric acid is transferred to the amino group of l-isolecuine. This behavior is similar to that observed in many picrate salts [16–34]. The structure is determined with a low value of R factor (0.0380) using 7257 reflections (R(int) = 0.0193) and goodness of fit (F2 ) = 1.072. The monoclinic crystal structure with space group P21 of LIP comprises monovalent isoleucininium cations, charge counter balanced by picrate anions (Fig. 3). The packing arrangement reveals stronger – interactions. Bond lengths in the carboxylic COOH group are typical for C O and C OH bonds ˚ respectively). (C7 O9 and C4 O7 distances are 1.218 A˚ and 1.321 A,
Table 2 Crystal data of as-grown crystals. System
Picric acid l-Isoluecine l-Picrate l-Valine picrate Glutamine + picric acid (1:1) Ammonium picrate l-Methonine + picric acid (1:1) l-Arginine + picric acid (1:1) l-Cystine + picric acid (1:1) l-Aspargine + picric acid (1:1)
Cell parameters a/Å
b/Å
c/Å
V/Å3
9.25 9.709 9.970(3) 9.950(3) 15.16(2) 13.45 9.16(2) 9.134(18) 9.24(3) 9.24(2)
9.68 5.291 6.425(2) 6.285(2) 19.97(3) 19.74 9.60(2) 9.594(19) 9.71(3) 9.66(2)
19.08 14.018 12.871(4) 12.621(4) 7.099(10) 7.12 18.93(5) 18.90(4) 19.13(5) 19.09(4)
– – 770.0(4) 739.1(4) 1872(6) – 1664(7) 1656(7) 1717(8) 1703(10)
Crystal system
Space group
References
Orthorhombic Monoclinic Monoclinic Monoclinic Orthorhombic Orthorhombic Orthorhombic Orthorhombic Orthorhombic Orthorhombic
PCa P21 P21 P21 – Ibca – – – –
[41] [38] Present work Present work Present work [42] Present work Present work Present work Present work
Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036
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G. Ramasamy, S. Meenakshisundaram / Optik xxx (2014) xxx–xxx Table 3 SHG output (input 5.1 mV/pulse). System
I2ω /mV
KDP PA LIP
27 70 432
asymmetric units of LIP could be the main reason for high SHG efficiency. 4. Conclusion
Fig. 5. TG-DTA curves of LIP.
The bond lengths of C3–C4 and C4–C5 are 1.398(3) A˚ and 1.456(3) A˚ respectively which are longer and deviate from regular aromatic ˚ which is interC C values. The C4 O7 value of LIP is 1.321(3) A, mediate between the single and double bonds. Loss of hydroxyl proton at the O7 leading to specific electron delocalization around C4 is observed. These observations are in agreement with the other picrates subjected to proton transfer [4,44,45]. It has been established that the orientation of anion and cation molecules facilitates the formation of expected N H· · ·O hydrogen bonds between amino nitrogen and phenolic oxygen [44]. The crystal structure is also stabilized by O H· · ·O hydrogen bonds and specific short contacts. The doubling of frequency was confirmed by the green color of the output radiation whose characteristic wavelength is 532 nm. KDP was used as a reference material in the present measurement. The relative SHG conversion efficiency of LIP is found to be 16 times that of KDP (Table 3). This may be attributed to the molecular structure of l-isoleucine in which the carboxyl group of the isoleucinium residue is engaged in a strong hydrogen bond with the picrate anion. The amino group of the l-isoleucinium cation and the picrate anion are held together by an intermolecular hydrogen bond. This type of strong intermolecular hydrogen bonding enhances the NLO properties of the material [46]. Also, it has been reported that the –* transition occurs in the carboxyl group which gives rise to NLO properties in this compound [21]. LIP is a donor–acceptor molecular compound in which l-isoleucinium cation act as donor and picrate anion act as an acceptor. Presence of donor–acceptor
Fig. 6. Powder XRD pattern of LIP.
Attempts have been made to synthesize and good picrates with series of l-amino acids. Interestingly, only the precursor picric acid crystallizes out from a equimolar solution of amino acid and picric acid (1:1) for many of the amino acids studied. We are reporting a new NLO material from the amino acid family, l-isoleucinium picrate (LIP) grown from an equimolar aqueous solution by slow evaporation solution growth technique and characterized. The cell parameter values mismatch with that of precursors and it crystallizes in a noncentrosymmetric space group P21 . The vibrational patterns in FT-IR evidence the product formation. High transmittance is observed and the cut-off is ∼440 nm. The relative second harmonic generation efficiency measurements reveal that LIP has a superior NLO activity (16× of KDP). Intermolecular hydrogen bonds, –* transitions in the carboxyl group and the presence of strong electron acceptor–donor are the prime reasons for the large SHG efficiency possessed by this material. References [1] C. Muthamizhchelvan, K. Saminathan, J. Fraanje, R. Peschar, K. Sivakumar, Crystal structure of 2-chloroanilinium picrate, X-ray Struct. Anal. Online 21 (2005) x61–x62. [2] K. Saminathan, J. Fraanje, R. Peschar, K. Sivakumar, 3-Methylanilinium picrate, Acta Cryst. E 61 (2005) o1153–o1155. [3] C. Muthamizhchelvan, K. Saminathan, K. SethuSankar, K. Sivakumar, Cyclohexylammonium picrate, Acta Cryst. E 61 (2005) o3605–o3607. [4] K. Muthu, Subbiah Meenakshisundaram, Crystal growth, structure, and characterization of p-toluidinium picrate, J. Cryst. Growth 352 (2012) 163–166. [5] T. Pal, T. Kar, Optical, mechanical and thermal studies of nonlinear optical crystal l-arginine acetate, Mater. Chem. Phys. 91 (2005) 343–347. [6] K. Meera, R. Muralidharan, R. Dhanasekaran, P. Manyum, P. Ramasamy, Growth of nonlinear optical material: l-arginine hydrocholoride and its characterization, J. Cryst. Growth 263 (2004) 510–516. [7] S. Aruna, G. Bhagavannarayana, M. Palanisamy, P.C. Thomas, B. Varghese, P. Sagayaraj, Growth, morphological, mechanical and dielectric studies of semi organic NLO single crystal: l-argininium perchlorate, J. Cryst. Growth 300 (2007) 403–408. [8] V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, Glycine glycinium picrate – reinvestigation of the structure and vibrational spectra, Spectrochim. Acta A78 (2011) 128–132. [9] V.V. Ghazaryan, M. Fleck, A.M. Petrosyan, Structure and vibrational spectra of l-alanine l-alaninium picrate monohydrate, J. Mol. Struct. 1015 (2012) 51–55. [10] K. Anitha, B. Sridhar, R.K. Rajaram, -Alanine -alaninium picrate, Acta Crystallogr. E60 (2004) o1630–o1632. [11] K. Anitha, S. Athimoolam, R.K. Rajaram, l-Leucine l-leucinium picrate, Acta Crystallogr. E61 (2005) o1604–o1606. [12] K. Anitha, R.K. Rajaram, dl-Phenylalanine dl-phenylalaninium picrate, Acta Crystallogr. E61 (2005) o589–o591. [13] K. Anitha, S. Athimoolam, R.K. Rajaram, dl-Methionine dl-methioninium picrate, Acta Crystallogr. E62 (2006) o8–o10. [14] K. Anitha, S. Annavenus, B. Sridhar, R.K. Rajaram, dl-Valine dl-valninium picrate, Acta Crystallogr. E60 (2004) o1722–o1724. [15] K. Anitha, B. Sridhar, R.K. Rajaram, l-Valinium picrate, Acta Crystallogr. E60 (2004) o1530–o1532. [16] T. Uma Devi, N. Lawrence, R. Ramesh Babu, K. Ramamurthi, G. Bhagavanarayana, Structural, electrical and optical characterization studies on glycine picrate single crysal: a third order non-linear optical material, J. Miner. Mater. Charact. Eng. 8 (2009) 755–763. [17] T. Uma Devi, N. Lawrence, R. Ramesh Babu, K. Ramamurthi, Growth and characterization of glycine picrate single crystal, Spectrochim. Acta A 71 (2008) 340–343. [18] Mohd. Shakir, S.K. Kushwaha, K.K. Maurya, G. Manju Arora, Bhagavannarayanan, Growth and characterization of glycine picrate – remarkable second
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Please cite this article in press as: G. Ramasamy, S. Meenakshisundaram, Studies on amino acid picrates: Crystal growth, structure and characterization of a new nonlinear optical material l-isoleucinium picrate, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.02.036