Accepted Manuscript Synthesis, structure, crystal growth and characterization of a novel semiorganic nonlinear optical l – proline lithium bromide monohydrate single crystal S. Sathiskumar, T. Balakrishnan, K. Ramamurthi, S. Thamotharan PII: DOI: Reference:

S1386-1425(14)01622-9 http://dx.doi.org/10.1016/j.saa.2014.11.004 SAA 12940

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

16 May 2014 22 July 2014 4 November 2014

Please cite this article as: S. Sathiskumar, T. Balakrishnan, K. Ramamurthi, S. Thamotharan, Synthesis, structure, crystal growth and characterization of a novel semiorganic nonlinear optical l – proline lithium bromide monohydrate single crystal, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/ 10.1016/j.saa.2014.11.004

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Synthesis, structure, crystal growth and characterization of a novel semiorganic nonlinear optical l – proline lithium bromide monohydrate single crystal S. Sathiskumara, T. Balakrishnana* K. Ramamurthib and S. Thamotharanc a

Crystal Growth Laboratory, PG & Research Department of Physics, Periyar EVR College (Autonomous), Tiruchirappalli – 620 023, Tamil Nadu, India. b

Crystal Growth and Thin Film Laboratory, Department of Physics and Nanotechnology, SRM University, Kattankulathur – 603 203, Kancheepuram, Tamil Nadu, India. c

Department of Bioinformatics, School of Chemical and Biotechnology, SASTRA University, Thanjavur - 613 401, India.

ABSTRACT L – Proline Lithium Bromide Monohydrate (LPLBM), a promising semiorganic nonlinear optical material, was synthesized and single crystals of LPLBM were grown from solution by slow evaporation technique. Single crystal X – ray structure solution reveals that the grown crystal belongs to monoclinic system with space group P21. Presence of various functional groups was identified by FT – IR and FT - Raman spectral analyses. UV–Vis–NIR spectroscopic study shows that the LPLBM crystal possesses 90 % of transmittance in the range of 250 –1100 nm. Vickers microhardness values, the dielectric constant and dielectric loss of the LPLBM crystal were reported. Elemental analysis by energy dispersive X – ray analysis shows the presence of carbon, nitrogen, oxygen and bromine. The surface morphology of the crystal was investigated using scanning electron microscopic study. The thermal stability of the LPLBM crystal was studied from TGA and DSC analysis. Second harmonic generation efficiency of the LPLBM crystal measured by Kurtz and Perry powder technique using Nd: YAG laser is about 0.3 times that of urea. Key words: Growth from solution, X – ray diffraction, Nonlinear optical material, Thermal characterization, SHG * Corresponding author Tel.: +91 – 9443445535 E – Mail address: [email protected] (T. Balakrishnan) 1

1.

Introduction Nonlinear optical (NLO) crystals find applications in the areas, such as optical

modulation, frequency shifting, opto – electronics, signal processing, sensing and fiber optics communications [1]. Organic materials possess large nonlinear optical coefficients and structural diversity or flexibility when compared to that of the inorganic compounds [2]. However, most of the organic NLO crystals are constituted by weak van der Waals and hydrogen bonds with conjugated π electrons [3]. Hence, the organic materials are soft in nature and difficult to grow large size optical quality crystals. They show poor physico – chemical stability and low mechanical strength. Hence there has been considerable interest in the last few decades to synthesis and grow of semiorganic materials compared to organic crystals, since semiorganic crystals exhibit relatively high mechanical and thermal stability [4]. As a result, the search for novel nonlinear optical semiorganic materials exhibiting large nonlinearity and high resistance to laser induced damage [5-7] has become active. In this regard, amino acid family materials have drawn the attention of many researchers, because they possess high nonlinearity, wide transmission range, high conversion efficiency and high laser damage threshold. Proline, one of the naturally occurring amino acids, is having a unique structure due to the pyrolidine ring with α – carbon. Proline is abundant in collagen and is exceptional among the amino acids because the amino group is a part of a pyrolidine ring, thus making it rigid and directional in the biological systems despite of its conformational flexibility [8]. Single crystals of L – proline belongs to noncentrosymmetric crystal structure and its NLO coefficients have been examined by Boomadevi and Dhanasekaran [9]. Proline combines with CdCl2 [10], ZnCl2 [11], MnCl2 [12-13], SrCl2 [14], HgCl2 [15] and KCl2 [16] to form semiorganic single crystals. Uma Devi et al. [17] have reported synthesis, growth and characterization of L – proline lithium 2

chloride monohydrate. Recently Mohd. Shkir et al. [18] reported synthesis, growth, crystal structure, energy dispersive X-ray analysis (EDAX), UV-Vis-NIR, Differential Scanning Calorimetry (DSC) studies of L- Proline lithium bromide monohydrate (LPLBM). We have also simultaneously carried out the work on the synthesis and growth of LPLBM material and we report on the properties that are not investigated by Mohd. Shkir et al. [18]. 2.

Experimental Procedure

2.1

Synthesis L – Proline lithium bromide monohydrate salt was synthesized by dissolving analar grade

lithium bromide (LiBr - LOBA Chemie) and L – proline (C5H9NO2 - LOBA Chemie) in stoichiometric ratio in double distilled water at room temperature and continuously stirred well using magnetic stirrer. Slow evaporation of the solvent at room temperature yielded LPLBM salt in about three days. The purity of the synthesized salt was improved by successive recrystallization process. The reaction mechanism of the synthesis of LPLBM material is shown in scheme 1. 2.2

Crystal Growth The solubility of LPLBM was determined at four different temperatures, viz., 38 °C

(51.5 g/100 ml ), 45 °C (61.1 g/100 ml), 50 °C (68.3 g/100 ml ) and 55 °C (76.1 g/100 ml) by following gravimetric analysis [19]. The material exhibits positive coefficient of solubility and the value of solubility, given in parenthesis, increases linearly with temperature. Saturated aquasolution of LPLBM was prepared at room temperature using the recrystallized salt and the solution was filtered using Whatman filter paper. Filtered solution was taken in a beaker, which 3

was tightly closed with thick polythene paper and a few perforations were made on it. Slow evaporation of the solvent at room temperature yielded transparent LPLBM single crystals of 20 × 4 × 3 mm3 dimensions in a growth period of three days. Harvested LPLBM single crystals are shown in Fig. 1. As the solubility of the LPLBM material is sufficiently high slow evaporation of the solvent yields relatively larger size crystals in a growth period of three days. Further, it is also evident from the solubility data that controlled slow evaporation of the solvent shall lead to the growth of transparent bulk crystals. 3.

Results and Discussion

3.1

Single crystal X – ray diffraction study The crystal structure of LPLBM was determined from single crystal X–ray diffraction

analysis. The X-ray intensity data for the title salt was measured on an Enraf Nonius CAD4 - F diffractometer with graphite monochromated Mo Kα (λ= 0.71073 Å) radiation. Since the LPLBM is isomorphous with its chloride analogue [17], it was refined with the co - ordinates of the chloride analogue after removing chloride anion and H atoms using SHELXL – 97 [20]. The position of the bromide anion was located from a difference Fourier map and refined anisotropically. The H atoms bound to C atoms were placed in geometrically idealized positions (C–H = 0.97– 0.98 Å) with Uiso (H) = 1.2Ueq(C) and constrained to ride on their parent atoms. The H atoms of amino group and water molecule were located from a difference Fourier map and refined using DFIX option with N–H = 0.85(2) Å, water O–H = 0.95(2) Å and water H…H distance restrained to 1.55(2) Å. The details of data collection and refinement statistics are presented in Table 1. CCDC 1011575 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data 4

Centre via www.ccdc.cam.ac.uk/data_request/cif. As shown in the ORTEP diagram (Fig. 2), the asymmetric unit contains a proline molecule, one Li cation, one Br- anion and a water molecule. The Li cation has a distorted tetrahedral geometry and surrounded by a water molecule and three carboxylate oxygen atoms of the amino acid molecule as observed in chloride analogue of the title compound and in catena-Poly[[[aqua(glycine-κO)lithium]-μ-glycine-κ2O:O]bromide] [21]. Selected intermolecular bond lengths and angles are given in Table 2. The conformation of the pyrolidine ring of the proline residue can be described by five endo - cyclic torsion angles χ1 (N1–C2–C5–C4) = 23.2(7)°, χ2 (C2–C5–C4–C3) = -37.5(7)°, χ3 (C5–C4–C3–N1) = 36.4(9)°, χ4 (C4–C3–N1–C2) = -22.3(10)° and χ5 (C3–N1–C2–C5) = -0.8(8)°. The pyrolidine ring adopts envelope conformation on atom C4 with a pseudo-rotation angle Δ = 268.9° and a maximum torsion angle φm = 38.8° [22]. The hydrogen – bonding parameters are listed in Table 3. As shown in Fig. 3, the carboxylate group of proline residue acts as a bridging ligand connecting neighbouring Li ions to an infinite chain parallel to the b axis. The amino group of the proline is involved in an intramolecular hydrogen bond (N1–H1N…O2) and which generates S(6) loop. The adjacent polymeric chains are interlinked via intermolecular O1w–H…Br- and N1–H…Brinteractions. It is interesting to note that the water molecule only acts as a donor for two crystallographically independent Br- anions. 3.2

Powder X – ray diffraction analysis Finely crushed powder of LPLBM single crystal was characterized by powder X – ray

diffraction analysis using a SEIFERT JSO DEBYEFLEX (Model 2002) X – ray powder diffractometer with CuKα (λ = 1.5408 Å) radiation. The sample was scanned over the 2θ ranging from 10° to 70° at a scan rate 1°/min. Fig. 4 represents the X – ray powder diffraction

5

pattern of LPLBM. The peaks have been indexed using AUTOX 97 software. The XRD peak (303) has the maximum intensity. 3.3

FT – IR and FT – Raman spectral analysis Fourier Transform Infrared (FT – IR) and FT – Raman spectral analysis were carried out

to confirm the molecular structure of the synthesized salt. The FT - IR and FT – Raman spectrum of LPLBM crystal was recorded using Perkin Elmer Spectrophotometer in the range of 400 to 4000 cm-1 by KBr pellet technique and BRUKER RFS27 FT – Raman spectrometer in the range of 50 – 4000 cm-1 as shown in Fig. 5 and Fig. 6 respectively. The peak at 3398 cm-1 and 3239 cm-1 is assigned to O – H asymmetric and symmetric stretching vibration of water molecules respectively. The low intensity sharp peaks appear at 3185 cm-1 and 3077 cm-1 are attributed to (N – H) asymmetric and symmetric stretching vibrations respectively. The absorption band at 2960 cm-1 in IR and 2953 cm-1 in Raman spectra are assigned to the CH stretching vibration. The band at 1425 cm-1 in IR and 1428 cm-1 in Raman spectra are due to the COO- symmetric stretching vibration. The peak at 1620 cm-1 is assigned to asymmetric stretching vibration of C=O. The C – H bending vibration mode is observed at 1366 cm-1 in IR spectra. The peaks observed at 1328 and 1030 cm-1 [15] are assigned to CH2 wagging and C – N stretching vibration respectively. The peak observed at 1277 cm-1 in Raman spectrum is due to CH2+ twisting mode of vibration. The strong band occurring about 845 cm-1 in Raman and at 842 cm-1 in IR is attributed to the CH2 rocking vibration. The medium intensity IR band occurs in 660 cm-1 and a weak Raman band at 655 cm-1 are attributed to the COO- wagging mode of vibration. The peak at 565 cm-1 in Raman spectrum is due to the NH torsional vibration. The vibrational frequencies of various functional groups of LPLBM and their tentative band assignments [23, 24] are presented in Table 4. 6

3.4

UV – Vis – NIR spectral studies The optical transmittance and absorption spectrum of LPLBM single crystal was

recorded in the wavelength range from 190 to 1100 nm using Varian Cary 5E spectrophotometer and is shown in Fig. 7. One of the optical quality single crystals of thickness about 3 mm was used for this study. The UV lower cut off wavelength for the grown crystal is at 238 nm. The LPLBM crystal exhibits the transparency of 90 % in the 250 – 1100 nm range and hence the crystal may be used for nonlinear optical (NLO) application. 3.5

Mechanical hardness Hardness of a crystal is the measure of the resistance of the local deformation and

hardness measurement of crystals gives important information for the understanding of the nature of the crystalline material. The hardness of the materials depends on the different parameters such as lattice energy, Debye temperature, heat of formation and interatomic spacing [25]. The Vickers hardness indentations were carried out on the grown LPLBM single crystal employing Shimadzu HMV - 2000 microhardness tester. Transparent crystals free from cracks were selected for microhardness measurement. The indentations were made on the sample with load ranging from 25 to 100g and the indentation time was 10 seconds.

The Vickers diamond

pyramidal indentor attached to microscope with an adapted video camera was used to measure the diagonal indentation lengths. Two indentations were made and the arithmetic mean value of the measured two diagonals was used for calculation of hardness. Vickers microhardness number (Hv) was calculated using the relation Hv = 1.8544 P/d2 (kg/mm2) where, P is the applied load and d is the average diagonal length of the indentation impression in μm. The values of Hv determined were plotted in Fig. 8 as a function of the applied load at room temperature. The 7

hardness value of LPLBM increases with increasing load. The increase in the hardness number can be attributed to the electrostatic attraction between the zwitterions present in the molecule. A plot obtained between log P and log d gives a straight line. It is observed from the graph that there is absence of indentation size effect (ISE) [26]. In order to analyze the reverse indentation size effect (RISE) in the hardness testing it needs to fit the values using Meyer’s power law, which correlates the applied load P and indentation length d by the relation P=Adn, where A is the arbitrary constant for a given material and n is the Meyer’s index or work hardening exponent that has been calculated from the slope of the straight line. In this study, the work hardening coefficient n calculated by the least square curve fitting method is 3. According to Onitsch [27], the value of n lies between 1 and 1.6 for hard materials and n is greater than 1.6 for soft materials. Thus the value of n obtained reveals that LPLBM crystal belongs to the soft materials category. 3.6

Dielectric studies Studies on the dielectric constant and dielectric loss of materials give important

information about the nature of atom, ions and their bonding in the materials. The dielectric constant and dielectric loss of LPLBM crystal was studied using HIOKI 3532 LCR HITESTER in the frequency range from 50 Hz to 2 MHz. The dielectric constant measured as a function of frequency at different temperature is shown in Fig. 9, while the corresponding dielectric loss is depicted in Fig. 10. The dielectric constant is evaluated using the relation εr = Cd/ε0A, where d is the thickness of the grown crystal, ε0 is the free space permittivity, C is the capacitance and A is the area of the crystal. The dielectric constant decreases with increasing frequency which may be attributed to the dependence on the electronic, ionic, orientational and space charge polarizations 8

[28]. Fig.10 shows decrease of dielectric loss of LPLBM as a function of frequency. It is also observed that as the temperature increases, the value of dielectric constant also increases to a considerable value. The increase at higher temperatures is mainly attributed to the thermally generated charge carriers and impurity dipoles. The same trend is observed in the case of dielectric loss versus frequency as well (Fig.10). The larger values of dielectric loss at lower frequency may be attributed to space charge polarization, which depends on the purity and perfection of the sample. 3.7

Surface morphology and Elemental composition study The nature of the surface morphology of the grown crystal was studied by a scanning

electron microscope (SEM) using a JSM 253 SEM analyzer. The transparent growth plane of the LPLBM crystal was scanned at two different magnifications. The image of surface of LPLBM with magnification of 2000× and 4000× is shown in Fig. 11a and Fig. 11b respectively. From the image of 4000× magnification, it is observed that the surface consists of regular morphological habits of the arrangement of atoms (Fig. 11b) thus showing a perfect growth surface with some microcrystallites on the surface. Compositional analysis of LPLBM crystal was made using energy dispersive X-ray analysis (EDAX) and the EDAX spectrum is presented in Fig. 12. Elemental analysis by energy dispersive X - ray spectrum shows that the presence of carbon, nitrogen, oxygen and bromine. The percentage of various elements present in the crystal LPLBM is given in the Table 5. 3.8

Thermal analysis Thermal stability of LPLBM crystal was studied using Perkin Elmer thermal analyzer in

the temperature range 25 °C - 800 °C in nitrogen gas atmosphere at a heating rate of 10 °C/ min. 9

Thermogravimetric analysis curve of LPLBM is shown in Fig. 13. A sample of weight 3.551 mg was taken for investigation. TGA curve shows that there are three major step of weight loss in the thermogram. The first step of weight loss is observed between 151 °C and 218 °C. This weight loss is due to the loss of water of hydration present in the crystal lattice and a resulting weight loss of 10% of the total weight of the material. The second step of weight loss starts at 218 °C and ends at 393 °C. In this interval a total weight loss of 45% is observed. This step of weight loss is assigned to decomposition of L – proline molecules. The remaining material of about 45% decomposes in third step gradually. In the final step of weight loss is due to the loss of lithium bromide molecules between the temperature 393 °C and 715 °C. Differential Scanning Calorimetry (DSC) was carried out using Perkin Elmer DSC 7 calorimeter with a heating rate of 10 °C/min. The sample was scanned over the temperature range from 25 °C to 400 °C. For this a small piece of the crystal weighing 1.0 mg was placed in aluminium pan. The DSC curve of LPLBM is shown in Fig. 14. The endothermic peaks are observed between the temperature ranges 112 °C to 218 °C. These endothermic peaks are indicating the loss of water molecule. The loss of water is also reflected in the TGA curve within the same region. 3.9

Second harmonic generation efficiency The second harmonic generation (SHG) efficiency of LPLBM crystal was examined

using the Kurtz and Perry [29] powder technique. The powdered sample of LPLBM crystal is illuminated by the fundamental beam of Nd: YAG laser (λ = 1064 nm). The input pulse energy was 0.680 J/pulse and the pulse widths of 8ns with a repetition rate of 10Hz were used. The second harmonic signal generated was confirmed from the emission of green light of wavelength 10

532 nm from the powdered sample. The 532 nm radiation was collected by a monochromator after separating the 1064 nm pump beam with an infra – red blocking filter. The second harmonic radiation generated by the randomly oriented micro crystals was focused by a lens and detected by a photo multiplier tube. The outcome of SHG signal with the energy 3.2 mJ confirms the nonlinear behavior of the grown LPLBM crystal and its SHG efficiency is 0.3 times that of urea crystal. 4.

Conclusion A novel semiorganic nonlinear optical material of LPLBM was synthesized and optical

quality single crystals were grown from aqueous solution by solvent evaporation technique at room temperature. Single crystal X – ray diffraction studies reveal that the crystal LPLBM belongs to monoclinic system with space group P21 and isomorphous with its chloride analogue reported earlier. Powder X – ray diffraction pattern confirmed the formation of LPLBM. The FT – IR and FT – Raman spectrum of LPLBM crystal confirms the presence of various functional groups. The observed wide transmittance range indicates that the LPLBM is a suitable candidate for nonlinear optical application. Vickers microhardness values increases with increasing loads and the crystal experiences cracks for loads above 100g. The microstructure of LPLBM analyzed using SEM photograph shows a smooth surface with the attachment of microcrystals. The value of

dielectric

constant

and

dielectric

loss

decreases

with

increase

of

frequency.

Thermogravimetric analysis reveals that this compound is stable up to 151 °C. Kurtz powder SHG test confirmed the frequency doubling of the grown crystal and SHG efficiency observed is 0.3 times that of urea.

11

Acknowledgement The authors T. B and S. S would like to acknowledge the University Grant Commission (UGC), New Delhi, India for providing financial support [Project ref. No. 41 – 956/2012(SR)]. The authors gratefully acknowledge the scientific supports extended by Sophisticated Analytical Instrument Facility (SAIF), Indian Institute of Technology Madras, Chennai – 600 036, India, and Department of Physics, B. S. Abdur Rahman University, Vandalur, Chennai –600 048, for providing facilities for characterization. One of the authors (ST) thanks the management of SASTRA University, Thanjavur - 613 401, India for the financial support (TRR grant). References [1] Tanusri Pal, Tanusree Kar, Gabriele Bocelli, Lara Rigi, Cryst. Growth Des. 3 (2003) 13 – 16. [2] D.S. Chemla, J. Zyss (Eds.), Nonlinear optical properties of organic molecules and crystals, Vol. 1 and 2 (1987) Academic Press, New York. [3] X.J. Liu, Z.Y. Wang, D. Xu, X.Q. Wang, Y.Y. Song, W.T. Yu. W.F. Guo, J. Alloys Compd. 441 (2007) 323 – 326. [4] Tanusri Pal, Tanusree Kar, J. Cryst. Growth 234 (2002) 267 - 271. [5] G. Xing, M. Jiang, D. Yuan, Z. Sao, D. Xu, Chin. J. Lasers 14 (1987) 302 - 308. [6] N. Zhang, M. Jiang, D. Yuan, D. Xu, X. Tao, Chin. Phys. Lett. 6 (1989) 280 - 289. [7] H.O. Marcy, L.F. Warren, M.S. Webb, C.A. Ebbers, S.P. Velsko, G.C. Kennedy, G.C. Catella, Appl. Opt. 31 (1992) 5051 - 5060. [8] S. Myung, M. Pink, M.H. Baik, D.E. Clemmer, Acta Crystallogr. C61 (2005) o506 – o508. [9] R. Dhanasekaran, S. Boomadevi, J. Cryst. Growth 261 (2004) 70 – 76. [10] A. Kandasamy, R. Siddeswaran, P. Murugakoothan, P. Suresh Kumar, R. Mohan, Cryst. Growth Des. 7 (2007) 183 – 186. 12

[11] G. Anandha Babu, P. Ramasamy, Mater. Chem. Phys. 113 (2009) 727 – 733. [12] Z. Rzaczynska, R. Mrozek, T. Gklowiak, J. Chem. Crystallogr. 27 (1997) 417 – 422. [13] Kevin Lamberts, Ulli Englert, Acta Crystallogr. B68 (2012) 610 – 618. [14] K. Manoj Gupta, Nidhi Sinha, Binay Kumar, Physica B 406 (2011) 63 – 67. [15] D. Kalaiselvi, R. Jayavel, Appl. Phys. A 107 (2012) 93 – 100. [16] V. Vasantha Kumari, P. Selvarajan, R. Thilagavathi, Inter. J. Advan. Scien. & Technol. Research 5 (2012) 474 – 491. [17] T. Uma Devi, N. Lawrence, R. Ramesh Babu, S. Selvanayagam, Helen Stoeckli – Evans, K. Ramamurthi, Cryst. Growth Des. 9 (2009) 1370 – 1374. [18] Mohd. Shkir, S. Alfaify, M. Ajmal Khan, Ernesto Dieguez, Josefina Perles, J. Cryst. Growth 391 (2014) 104 – 110. [19] A.C. Zettlemoyer (Ed.), Nucleation, Dekker, New York, 1969. [20] SHELXL – 97 CRYSTAL STRUCTURE REFINEMENT – WinGX version, Copyright George, M. Sheldrick, 1993 – 1997. [21] T. Balakrishnan, K. Ramamurthi, J. Jeyakanthan, S. Thamotharan, Acta Crystallogr. E69 (2013) m60 – m61 [22] S.T. Rao, E. Westhof and M. Sundaralingam, Acta Crystallogr. A37 (1981) 421 – 425. [23] K. Nakamoto, Infrared and Raman spectra of Inorganic and Coordination compounds, Wiley, New York, 1978 [24] George Socrates, Infrared and Raman characteristic group frequencies, John Wiley, New York, 2001. [25] Jianghong Gong, J. Mater. Sci. Lett. 19 (2000) 515 [26] S. Mukerji, T. Kar, Cryst. Res. Technol. 34 (1999) 1323 – 1328. [27] M.E. Onitsch, Microskopic. 2 (1947) 131- 134 13

[28] P.C. Smyth, Dielectric Behavior and Structure (McGraw Hill, 1965, New York,) [29] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798 – 3813.

14

Table 1 Crystal data and structure refinement details for LPLBM Formula

C5 H11 Br - Li NO3

Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions

220 293 (2) K 0.71073 Å Monoclinic P21 a = 8.0009 (3) Å α = 90° b = 5.1388 (2) Å β = 104.267 (2)° c = 10.5935 (4) Å γ = 90° 422.12 (3) Å 3 2, 1.731 Mg/m3 4.825 mm-1 220 0.35×0.30×0.30 mm3 2.63 to 24.99° -8 ≤ h ≤ 9, -5 ≤ k ≤ 6, -12 ≤ l ≤ 12 3771 / 1389 [R (int) = 0.0298] 99.3 % Semi – empirical from equivalents 0.3865 and 0.2632 Full – matrix least – squares on F2 1389 / 6 / 116 1.072 R1 = 0.0237, wR2 = 0.0587 R1 = 0.0273, wR2 = 0.0602 0.016 (15) 0.549 and -0.411 e Å -3

Volume Z, Calculated density Absorption coefficient F (000) Crystal size Theta range for data collection Limiting indices Reflections collected / unique Completeness to theta = 24.99 Absorption correction Max. and Min. transmission Refinement method Data / restraints / parameters Goodness – of – fit on F2 Final R indices [ I>2.0 sigma (I) R indices (all data) Absolute structure parameter Largest diff. peak and hole

15

Table 2 Selected bond lengths (Å) and bond angles (°) for LPLBM Li1 – O2i

1.959 (17)

O2 – Li1iv

1.959 (17)

Li1 – O2ii

1.960 (9)

Li1 – O2iii

1.960 (9)

Li1 – O1 W

1.979 (8)

N1 – C3

1.490 (5)

Li1 – O1

1.980 (14)

N1 – C2

1.520 (8)

Li1 – Li1iii

3. 167 (7)

C1 – C2

1.528 (7)

Li1 – Li1ii

3.167 (7)

C2 – C5

1.522 (8)

Li1 – H1 W

2.04 (6)

C3 – C4

1.483 (7)

O1 – C1

1.214 (10)

C4 –C5

1.514 (12)

O2 – C1

1.271 (7)

O2i – Li1 – O2ii

113.3 (5)

C1 – O2 – Li1iv

128.4 (4)

O2i – Li1 – O1W

105.2 (8)

C1 – O2 – Li1iii

113.2 (5)

Li1 – O2 – Li1

i

O2 – Li1 – O1

118.0 (4)

C3 – N1 – C2

108.7 (4)

O2ii – Li1 – O1

107.0 (8)

O1 – C1 – O2

127.4 (5)

O1W – Li1 – O1

99.4 (5)

O1 – C1 – C2

119.4 (5)

O2i – Li1 – Li1iii

135.5 (4)

O2 – C1 – C2

113.1 (7)

36.1 (5)

N1 – C2 – C5

103.5 (4)

116.5 (6)

N1 – C2 – C1

109.4 (5)

O1 – Li1 – Li1iii

71.0 (4)

C5 – C2 – C1

112.0 (4)

O2i – Li1 – Li1ii

36.10 (11)

N1 – C2 – H2

110.6

O2ii – Li1 – Li1ii

78.4 (5)

C5 – C2 – H2

110.6

O1W – Li1 – Li1ii

113.0 (6)

C1 – C2 – H2

110.6

O1 – Li1 – Li1ii

142.1 (5)

C4 – C3 – N1

104.4 (4)

108.5 (4)

C3 – C4 – C5

103.6 (5)

131.4 (5)

C4 – C5 – C2

105.2 (5)

O2 – Li1 – O1W

O2ii – Li1 – Li1iii O1W – Li1 – Li1

iii

Li1 – Li1 – Li1 C1 – O1 – Li1

iii

ii

iv

122.3 (6)

ii

iii

107.8 (4)

Symmetry codes: (i) x, y+1, z; (ii) –x+2, y+1/2, -z; (iii) –x+2, y-1/2, -z; (iv) x, y-1,z. 16

Table 3 Hydrogen Bond Parameters for LPLBM D – H .....A

D–H

H ..... A

D …… A

D – H .....A

N1 – H2N…..O1

0.87 (3)

2.08 (5)

2.696 (6)

128 (5)

N1 – H1N ….Br1v

0.87 (2)

2.88 (5)

3.357 (3)

116 (4)

N1 – H1N ….Br1vi

0.87 (2)

2.65 (5)

3.327 (8)

136 (5)

O1W – H2W…Brv

0.93 (3)

2.42 (3)

3.318 (8)

164 (5)

O1W – H1W – Br1vii

0.92 (3)

2.79 (6)

3.375 (7)

122 (5)

Symmetry codes: (v) x+1, y, z; (vi) –x+1,y-1/2, -z+1; (vii) x+1, y+1, z.

17

Table 4 Tentative vibrational band assignments of LPLBM single crystal LPLBM FT – Raman FT - IR 3391 3398 3239 3186 3185 3024 3077 3000 2976 2953 2960 2222 2086 1614 1620 1526 1523 1469 1450 1428 1425 1368 1366 1330 1328 1277 1231 1228 1174 1166 1081 1080 1033 1030 970 969 940 921 908 845 842 777 748 655 660 565 555 426 413

LPLCM [17] FT - IR 1527 1423 1370 1329 1168 1031 972 922 845 778 661 414

18

Band assignments (O – H) asymmetric stretching of (H2O) (O – H ) symmetric stretching of (H2O) NH asymmetric stretching NH symmetric stretching NH3+ symmetric stretching CH2 asymmetric stretching CH stretching NH bending NH torsional C=O asymmetric stretching NH2+ in – plane deformation CH2 scissoring CH2 bending COO- symmetric stretching CH bending CH2 wagging CH2 twisting C – O stretching NH2+ twisting CH2+ rocking C – N stretching C – C – N stretching NH2+ rocking C – C stretching CH2 rocking COO- in – plane deformation COO- wagging NH torsional Br - in plane deformation COO- wagging

Table 5 Compositional analysis of LPLBM crystal from EDAX spectra

Element

Weight %

Atomic %

C

40.60

57.47

N

10.73

13.02

O

22.54

23.95

Br

26.13

5.56

100.00

100.00

Total

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Scheme 1 The reaction mechanism involved in the synthesis of LPLBM

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Fig. 1

Fig. 2 21

Fig. 3

Fig. 4 22

Fig. 5

Fig. 6 23

Fig. 7

Fig. 8 24

Fig. 9

Fig. 10

25

Fig.11a

Fig. 11b 26

Fig. 12

\

Fig. 13 27

Fig. 14

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Figure caption: Fig.1. As grown crystals of LPLBM by slow evaporation technique Fig.2. The ORTEP diagram showing the atom labeling scheme and molecular structure of LPLBM single crystal Fig.3. Crystal packing of the LPLBM projected along the bc plane. For clarity, H atoms bound to carbon atoms have been omitted. Dashed lines indicate hydrogen bonds. Fig.4. Powder X – ray diffraction pattern of LPLBM Fig.5. FT - IR spectrum of LPLBM Fig.6. FT – Raman spectrum of LPLBM Fig.7. UV – Vis – NIR transmittance spectrum of LPLBM Fig.8. Hardness behavior of LPLBM Fig.9. Dielectric constant of LPLBM Fig.10. Dielectric loss of LPLBM Fig.11a. SEM micrograph (2000×) of LPLBM Fig.11b. SEM micrograph (4000×) of LPLBM Fig.12. Energy dispersive X – ray analysis of LPLBM Fig.13. Thermogravimetric analysis of LPLBM Fig.14. DSC plot of LPLBM

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Graphical Abstract (for review)

L – Proline lithium bromide monohydrate (LPLBM), a semiorganic nonlinear optical material was grown from slow evaporation technique at room temperature. The grown single crystals were characterized by XRD, spectral, thermal, optical, Vickers microhardness, dielectric, SEM – EDAX and second order nonlinear optical properties. The grown LPLBM crystallizes into monoclinic system with the space group of P21. The modes of vibrations of different molecular groups present in LPLBM were identified by FT – IR and FT – Raman spectral studies. The optical transparency of the grown crystal was investigated by UV – Vis – NIR spectrum. The scanning electron microscope (SEM) study was carried out to determine the surface morphology of the grown crystal. The thermal stability of the grown crystal was investigated using thermogravimetric (TG) and differential thermal analysis (DTA). Second harmonic generation (SHG) efficiency was found to be 0.3 times that of urea.

Crystal packing of the LPLBM projected along the bc plane.

HIGHLIGHTS



L - proline lithium bromide monohydrate (LPLBM) crystal is grown.



LPLBM crystal belongs to monoclinic system with space group P21.



Mechanical, thermal, dielectric, linear and nonlinear optical are reported.



Presence of Br- is confirmed from energy dispersive X- ray analysis.

Synthesis, structure, crystal growth and characterization of a novel semiorganic nonlinear optical l-proline lithium bromide monohydrate single crystal.

l-Proline lithium bromide monohydrate (LPLBM), a promising semiorganic nonlinear optical material, was synthesized and single crystals of LPLBM were g...
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