Synthesis, spectral, structural and thermal characterization of NLO active crystal: 2-hydroxyethylammonium-4-nitrobenzoate

Accepted Manuscript Title: Synthesis, spectral, structural and thermal characterization of NLO active crystal: 2-hydroxyethylammonium-4-nitrobenzoate Authors: Ganesan Vadivelan, Venkatesan Murugesan, Munusamy Saravanabhavan, Marimuthu Sekar PII: DOI: Reference:

S0030-4026(17)30456-4 http://dx.doi.org/doi:10.1016/j.ijleo.2017.04.053 IJLEO 59095

To appear in: Received date: Revised date: Accepted date:

8-8-2014 11-4-2017 14-4-2017

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Synthesis, spectral, structural and thermal characterization of NLO active crystal: 2-hydroxyethylammonium-4-nitrobenzoate Ganesan Vadivelana, Venkatesan Murugesanb, c, Munusamy Saravanabhavanb, d, and Marimuthu Sekarb* a

Research & Development centre, Bharathiar university, Coimbatore, Tamil Nadu, India.

b

Post-Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore - 641 020, Tamil Nadu, India.

c

Pachamuthu college of Arts and Science for Women, Dharmapuri - 636 705, Tamil Nadu, India.

d

Dr. NGP College of Engineering and technology, Coimbatore, Tamil Nadu, India.

______________________________________________________________________________ ABSTRACT An organic crystal, 2-hydroxyethylammonium-4-nitrobenzoate (EANB) was synthesized and single crystals grown by the slow evaporation solution growth method at ambient temperature. The Fourier Infrared (FT-IR) spectral analysis was used to confirm the presence of various functional groups in the grown crystal. The formation of molecular compound and crystal has been confirmed by single crystal X-ray diffraction and NMR spectroscopic techniques. The title crystal crystallizes in monoclinic system, space group P21/c. The thermal stability of crystal was established using Thermogravimetry (TG) and Different Thermal Analysis (DTA) simultaneously. Nonlinear optical (NLO) property in the grown crystal was investigated by the modified Kurtz–Perry powder test. Keywords: Proton transfer; Solution growth; Crystal structure; Thermal analysis and NLO. ______________________________________________________________________________ 1. INTRODUCTION Nonlinear optical materials find a variety of application due to their feature of interest such as frequency conversion, light modulation, optical switching, etc., In addition to this, organic crystalline material have a high nonlinear efficiency compared to inorganic and also high thermal stability owing to the presence of intermolecular H-bonding between counter ions. These intermolecular H-bonding is formed by the interaction of an electron donor and an electron acceptor of organic molecules [1-11]. Furthermore, to exploration and design for the

development of organic materials with high NLO efficiency, various theories and models have been put forth to explain the phenomena associated with NLO organic materials. Among organic NLO materials, salts of p-nitrobenzoic acid are one of the directions for searching for new NLO materials, Carboxylic acids contain hydrogen bond donor and acceptor serve as unique and versatile scaffolds and host prevalent functional groups in crystal engineering and also carboxylic acids are ideal candidates for multi component crystals, because they form persistent super molecular heterosynthons with various complementary functional groups such as amine and aromatic nitrogen etc.,[12-17]. We herein, report the “Growth, spectral, structural and nonlinear optical studies on 2-hydroxyethylammonium-4-nitrobenzoate”.

2. Experimental work 2.1. Materials, instruments and methods All reagents used were chemically pure and AR grade. Solvents were purified and dried according to the standard procedure. Elemental analyses were determined by FLASH EA series 1112 CHNS analyzer. FT-IR spectrum was recorded using KBr pellet technique in the range 4000-400 cm-1 using JASCO-5300 FT-IR spectrophotometer. 1H and

13

C NMR spectra were

recorded employing a Bruker 500 MHz spectrometer in DMSO-d6 solvent using TMS as the internal reference standard. The electronic absorption spectrum has been recorded on a Cary 100 Bio UV–Visible spectrophotometer at room temperature in the range 200-800 nm in liquid state. Photoluminescence spectrum was recorded at room temperature on a Horiba Jobin Yvon Fluoromax-4 spectroflurometer. Thermogravimetric and Differential Thermal Analysis (TG-DTA) were carried out using NETZSCH Jupiter thermal analyzer under nitrogen atmosphere at heating rate of 20 °C/min from 30 to 500 °C by using alumina crucible.

2.2. Single crystal X-ray diffraction studies Single crystal X-ray diffraction data of EANB compound was collected on Oxford Gemini Diffractometer equipped with EOS CCD detector at 298 K. Monochromatic MoKa radiations (0.71073°A) was used for the measurements. The data was reduced by using SAINTPLUS [18]. The structure of the compound was solved by direct methods using SHELXS-97 [19] which revealed the position of all non-hydrogen atoms and was refined by fullmatrix least squares on F2 (SHELXL-97) [20]. All non-hydrogen atoms were refined

anisotropically, while the hydrogen atoms were placed in calculated positions and refined as rigid atoms.

2.3. Material synthesis and Growth of single crystal 2-hydroxyethylammonium-4-nitrobenzoate crystal was synthesized by reacting equimolar ratio of methanolic solutions of 2-hydroxyethylamine and 4-nitrobenzoic acid. The solution were mixed together and stirred well at room temperature for 3 h using magnetic stirrer to attain homogenous solution. The solution was then filtered using Whatman No 41 filter paper to remove suspended impurities and kept aside without any mechanical disturbance for growth of crystals by slow evaporation at room temperature [21]. The colourless and transparent crystals were collected after five days. The collected crystals were purified by repeated recrystallization process. The reaction scheme is depicted in Fig.1

3. Results and discussion 3.1. Micro analysis (CHN) The purity and contribution of elements (CHN) of the synthesized compound were checked by the elemental analysis. The analysis results show that the compound EANB contains C: 47.37 % (47.35 %), H: 5.30 % (5.35 %), N: 12.28 % (12.30 %). The analysis data further indicate that the experimentally determined values are in good agreement with theoretical values (within the bracket). The result indicates that EANB is free from impurities and confirms the formation of the compound in the stoichiometry proportion (1:1). 3.2. UV-Vis absorption spectrum UV-Vis absorption spectrum of EANB is shown in Fig.2. The recorded spectrum gives information about the molecular structure because the absorption of UV-Visible light involves promotion of the electron in the s and p orbital from ground state to higher state. The spectrum shows a peak at 275 nm corresponding to n-π* transition and another weak peak at 223 nm is attributed to π-π* transition.

3.2. 1. Determination of optical band gap

The band gap energy (E) was determined from absorption spectra for the EANB crystal according to the following equation [22]. Eg= hc / λ Where, h = Planck’s constant (Js), C = velocity of light (m/s) and λ= wavelength (nm). Using the above equation, band gap energy was calculated and its value was found to be 4.4 eV.

3.3. Emission spectral analysis The emission spectrum of the grown EANB crystal was recorded using spectroflurometer in the range 250-600 nm with the excitation wavelength of 275 nm and the recorded spectrum taken for both the solid and solution is shown in Fig. 3a and 3b. The spectrum exhibits a peak centered at about 454 nm confirming the blue emission and their after no other visible emission was observed. In general, the shift in the emission peak of the sample from shorter to longer wavelengths depends on the strength of their intermolecular interaction which is lower for solution and higher for solids [23]. Moreover, the occurrence of little change in emission peak is related to the physical form of the sample such as concentration for solution or thickness for crystal [24].

3.4. Vibrational spectral analysis The experimental vibrational wavenumbers of EANB assignments are given in Table 4. The experimental FT-IR spectrum of EANB in the region of 4000–400 cm-1 is shown graphically in Fig.4. The broad band exhibited in longer wave number region confirms the presence of hydrogen bonding in EANB crystal. In general, the O-H group exhibits three vibrations, such as stretching, in-plane and out-planes bending vibrations. The hydroxyl stretching vibrations of EANB is observed at precisely at 3500 cm-1 and in-plane and out-plane bending vibrations are observed at 1205 and 982 cm-1 respectively. The N–H stretching vibration of 2-hydroxyethylammonium cation exhibits a broad band at 3290 cm-1. The observed N–H wagging mode of 2-hydroxyetylammonium moiety appears at 796 cm-1 and N–H deformation mode of 2-hydroxyetylammonium moiety is observed at 1563 cm-1. The band observed in the spectrum at 2975 cm-1 assigned to aromatic C-H stretching vibrations of 4-nitrobenzoate moiety. The C-H in-plane bending vibration of aromatic compounds appears in the spectrum at 1146 cm-1 while the respective out-plane bending vibrations of the compound are exhibited according to the expected values at 794 and

723 cm-1 respectively. The carboxylate group has two strongly coupled resonant bands whose bond strength is intermediate between C-O and C=O. The carboxyl C=O stretching vibration mode can easily be recognized in IR spectrum of aromatic acids. Aromatic acids in cationic form depending on the strength of interaction are expected to give a band around 1700 cm-1 due to stretching motion of C=O atoms. The symmetrical hydrogen bond reduces the intensity of carboxyl C=O band in IR as observed at 1649 cm-1 in 2-hydroxyethylammonium-4nitrobenzoate. The C=C stretching (ring) vibrations are observed at 1580, 1500, 1473 cm-1. The nitro group in the title compound exhibit distinct absorption bands due to asymmetric and symmetric stretching vibrations of NO2 group at 1555 and 1347 cm-1 respectively. The band at 871 cm-1 is assigned to C-N stretching vibration.

3.5. NMR Spectral Analysis Nuclear magnetic resonance (NMR) is versatile technique for identification of molecular structure of the organic compounds. The 1H NMR and 13C NMR spectra of EANB were recorded using deutrated DMSO as solvent using TMS as internal standard reference. The chemical shifts and their assignments are tabulated in Table 2. The 1H NMR spectrum of EANB crystal is shown in Fig.5. In the spectrum, the doublet appearing at δ 8.17 is attributed to C3 and C5 aromatic protons of 4-nitrobenzoate moiety. A proton signal at δ 8.061 is split into doublet owing to the influence of the adjacent C-H group in 4nitrobenzoate moiety. A singlet at δ 2.8 is attributed to OH proton of 2-hydroxyethylammonium moiety. The two CH protons of the 2-hydroxyethylammonium moiety exhibit at δ 3.2. The signal due to N-H does show at δ 7.1. The

13

C NMR spectrum of EANB crystal is shown in Fig.6. Every carbon atom at

different environment produces different signal. The sharp and intense signal at δ 130 is due to C2 and C6 carbon atoms of the 4-nitrobenzoate moiety. Another intense signal of C3 and C5 carbon atoms resonates at δ 123. The presence of signal at δ 168 is due to carboxylate carbon of 4-nitrobenzoate. Signals at δ 148 and δ 142 are assigned to C4 and C1 aromatic carbons. The aliphatic carbons of 2-hydroxyethylammonium moiety are exhibited at δ 63 and δ 42.

3.6. Thermal Analysis

In order to examine the thermal stability, the title material has been studied over the temperature range of 50 ºC-800 ºC under nitrogen atmosphere and the obtained thermogram is presented in Fig. 7. From the thermogram, TG curve inferred that the major weight loss takes place at 170 ºC before the start of the decomposition. It seems that there is no absorption of water in the material. In DTA curve, a sharp endothermic dip at 170 ºC indicates the melting point of the material. The sharpness of this endothermic peak shows good degree of crystallinity and purity of the material. This is further confirmed by melting point apparatus. Further heating above 170 ºC results in the formation of volatile substances, probably carbon dioxide, ammonia, and CH and CO molecule. The next stage of decomposition corresponds to the decomposition of residues. Thus, from thermal analyses, it is seen that the crystal can be utilized for device applications in the field of optoelectronics and photonics up to 170 ºC.

3.7. Single crystal analysis The grown EANB single crystal was subjected to single crystal X-ray diffraction analysis. The crystal structure was solved by direct method with the SHELXS-97 method and refined by full matrix least squares with SHELXS-97 method. The obtained crystallographic data are given in the Table 3. From the single crystal X-ray diffraction data, it is confirmed that the grown crystal belongs to monoclinic system with space group P21/c. The lattice parameters obtained are a = 6.1995(6) Å, b = 8.6976(8) Å, c = 19.7323(18) Å, α = 90°, β= 91.014(2)°, γ= 90° and the unit cell volume is 1063.81(17) Å3. The EANB crystal consists of one 2-hydroxyethylammonium cation and one 4-nitrobenzoate anion. The crystal data confirms the synthesized crystal crystallized as mono protonated 2-hydroxyethylamine and deprotonated 4nitro benzoic acid. Thus the charge transfer between the donor and acceptor group approves the Donor –  – Acceptor type structure of the molecule. A proton is transferred to nitrogen atom of 2-hydroxyethylamine from the carboxylic group of acid. The carboxylate anion forms a strong O⋯H–N hydrogen bond with ethylamine. The hydrogen bond distance relatively smaller than the normal hydrogen bond distance. This indicates a strong hydrogen bonding in the molecule. The atom H5O of O5 forms intermolecular hydrogen bonding interactions with the atom O1. The 2-hydroxyethylammonium is linked with 4-nitrobenzoate anion through N+—H---O– intermolecular hydrogen bond to stabilize the counter ions in the crystal packing. The structure of the compound is stabilized by N-H⋯O and O-H⋯O hydrogen bonding interactions. The

pattern of the ORTEP view of the compound is shown in Fig.8. The crystal packing diagram is shown in Fig.9. The blue colour line in packing diagram indicates the hydrogen bonds in the crystal. The C-O bond lengths of C7-O1 and C7-O2 are found to be 1.252 and 1.234 Å respectively in 4-nitrobenzoate moiety which further confirms that hydrogen atom of COOH is deprotonated and the resultant carboxylate involves in the resonance.

3.8. SHG studies The study of second harmonic generation conversion efficiency was carried out using modified experimental set up of Kurtz-Perry powder technique [25]. A Q-switched ND: YAG laser beam of wavelength 1064 nm, with input power of 5.75 mJ and pulse width of 8 ns with a repetition rate of 10 Hz was used. The grown EANB crystal and KDP crystal were ground into a powder of particle size 100–150 mm and separately and packed densely between two transparent glass slides and exposed to laser radiation. The detector was used to detect second harmonic intensity connected to power meter to read the energy input and output. The generation of SHG was confirmed by the emission of green light. The modified Kurtz and Perry powder technique shows that the SHG efficiency of EANB was six times higher than that of KDP. 4. Conclusion An organic proton transfer compound of EANB was synthesized and single crystals were grown by the slow evaporation solution growth method at ambient temperature. The grown crystal has been characterized by 1H and 13C NMR, UV–Vis, FT-IR spectroscopy and elemental analysis. The electronic absorption spectrum suggests that electronic transitions are due to n- π* and π-π* transition of the constitute ions present in the compound. The presence of various functional groups in the title crystal has been confirmed by FT-IR spectroscopy. The proton and carbon positions were analyzed by NMR spectra which establish molecular structure of the crystal. The thermal analysis indicates that the title crystal is thermally stable up to 170ºC without any phase transitions and there was no water inclusion. The single crystal XRD study reveals that the compound crystallizes in a monoclinic system with space group P21/c. the Powder SHG test with Nd: YAG laser radiation shows high SHG efficiency than that of standard KDP materials. Hence, EANB crystal seems to be a promising material for NLO applications. Acknowledgements

The authors gratefully acknowledge the School of Chemistry, University of Hyderabad, Hyderabad for their instrumental facilities. One of the authors V. Murugesan thanks the UGC-Networking Centre, School of Chemistry, University of Hyderabad, for the award visiting research fellowship to use the facilities at school of chemistry, University of Hyderabad, Hyderabad. And also grateful to prof. Samar Kumar Das, School of Chemistry, University of Hyderabad, Hyderabad for providing research facilities at laboratory. Supplementary data CCDC 963859 contains the crystallographic data for compounds. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

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16. C.M. Grossel, A.N. Dwyer, M.B. Hursthouse, J.B. Orton, Cryst. Eng. Comm., 8 (2006) 123. 17. 14. B.R. Bhogala, A. Nangia, New J. Chem., 32 (2008) 800. 18. SAINT: Software for the CCD Detector System, Bruker Analytical X-ray Systems, Inc., Madison, WI, 1998. 19. G.M. Sheldrick, SHELXS-97, Program for Structure Solution, University of Gottingen, Gottingen, Germany, 1997. 20. G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Analysis, University of Gottingen, Gottingen, Germany, 1997. 21. V. Sasikala, D. Sajan, K. Job Sabu, T. Arumanayagam, P. Murugakoothan, Spectrochim. Acta Part A, 139 (2015) 555-572. 22. K. Balaji, s. C. Murugavel, J. Polym. Sci. Part A: Polym. Chem., 49 (2011) 4809–4819. 23. X. Zeng, D. Zhang, L. Duan, L. Wang, G. Dong, Y. Qiu, Appl. Surf. Sci., 253 (2007) 6047–6051. 24. S. Dai, J. Yang, L. Wen, L. Hu, Z. Jiang, J. Lumin., 104 (2003) 55–63. 25. S. K. Kurtz, T.T. Perry, J. Appl. Phys., 39 (1968) 3798-3813.

Fig. 1. Reaction scheme of EANB crystal

Fig. 2. Electronic absorption spectrum of EANB

(a)

(b)

Fig. 3. Emission spectrum of EANB ((a) Soild) and (b) liquid)

Fig. 4. FT-IR spectrum of EANB

Fig. 5. 1H NMR spectrum of EANB

Fig. 6. 13C NMR spectrum of EANB

Fig. 7. TG/DTA thermogram of EANB

Fig.8. ORTEP diagram of EANB

Fig.9. Packing diagram of EANB

Table 1 FT-IR spectral band assignments of EANB crystal Infrared frequencies(cm-1)

Assignments

3500

O-H stretching vibration

3290

N-H stretching vibration

2975

C-H stretching vibration (aromatic)

2898

C-H asymmetric stretching (methyl)

2736

C-H asymmetric stretching (methyl)

1649

C=O stretching vibration

1610

COO- asymmetric stretching Vibration

1512

NO2 asymmetric stretching vibration

1580, 1500,1473

C=C aromatic stretching

1391

COO- symmetric stretching vibration

1347

NO2 symmetric stretching vibration

1205

O-H in-plane bending vibration

982

O-H out-plane bending vibration

871

C-N stretching vibration

Table 2 1H and

13C

NMR chemical shift values of EANB crystal

Chemical shift (δ ppm)

Group Identification 1H

7 (s)

NMR -NH protons of 2-hydroxyethylammonium moiety

8.17 (d)

C3 and C5 protons of the same kind in 4-nitrobenzoate moiety

8.06 (d)

C2 and C6 protons of the same kind in 4-nitrobenzoate moiety

2.8 (s)

OH proton of 2-hydroxyethylammonium moiety

3.6 (s)

OH proton of 2-hydroxyethylammonium moiety

3+

13C

NMR

168

carboxylate carbon of the 4-nitrobenzoate moiety

148

C4 carbon signal of 4-nitrobenzoate moiety

145

C1 carbon signal of 4-nitrobenzoate moiety

130

C2 and C6 carbons of the same kind in 4-nitrobenzoate moiety

123

C3 and C5 carbons of the same kind in 4-nitrobenzoate moiety

63

Methyl carbon (NH3+ substituted)

42

Methyl carbon (OH substituted)

Table 3 Crystallographic data and structure refinements of EANB crystal Empirical formula

C9 H12 N2 O5

Formula weight

228.21

Temperature

298(2) K

Wavelength

0.71073 Å

Crystal system

Monoclinic

Space group

P21/c

Unit cell dimensions

a = 6.1995(6) Å

α = 90˚

b = 8.6976(8) Å

β = 91.014(2)˚

c = 19.7323(18) Å

γ= 90˚

Volume

1063.81(17) Å3

Z

4

Calculated density

1.425 Mg/m3

Absorption coefficient

0.118 mm-1

F(000)

480

Crystal size

0.30 x 0.20 x 0.10 mm

Theta range for data collection

2.06˚ to 28.21˚

Limiting indices

-8<=h<=8, -11<=k<=11, -25<=l<=25

Reflections collected / unique

11988 / 2562 [R(int) = 0.0368]

Absorption correction

Empirical

Max. and min. transmission

0.9883 and 0.9656

Refinement method

Full-matrix least-squares on F2

Data / restraints / parameters

2562 / 0 / 161

Goodness-of-fit on F2

1.087

Final R indices [I>2sigma(I)]

R1 = 0.0656, wR2 = 0.1556

R indices (all data)

R1 = 0.0783, wR2 = 0.1648

Largest diff. peak and hole

0.197 and -0.435 e.A-3