Synthesis, crystal structure, crystal growth and physical properties of N,N-diethyl anilinium picrate

Journal of Crystal Growth 334 (2011) 159–164

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Synthesis, crystal structure, crystal growth and physical properties of N,N-diethyl anilinium picrate R. Subramaniyan @ Raja, G. Anandha Babu n, P. Ramasamy Centre for Crystal Growth, SSN College of Engineering, SSN Nagar 603110, Tamilnadu, India

a r t i c l e i n f o

abstract

Article history: Received 5 April 2011 Received in revised form 21 August 2011 Accepted 24 August 2011 Communicated by M. Roth Available online 5 September 2011

Crystalline substance of N,N-diethyl anilinium picrate (NNDEAP) has been synthesized and single crystals of NNDEAP were successfully grown for the first time by the slow evaporation solution growth technique at room temperature with dimensions 14  10  10 mm3. The formation of the new crystal has been confirmed by single crystal X-ray diffraction studies. The structural perfection of the grown crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups of NNDEAP have been identified by Fourier transform infrared spectral studies. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have also been carried out and the thermal behavior of NNDEAP has been studied. The UV–vis–NIR studies have been carried out to identify the optical transmittance and the cut off wavelength of NNDEAP is identified. The dielectric loss and the dielectric constant as a function of frequency and temperature were measured for the grown crystal and the nature of variation of dielectric constant er and dielectric losses (tan d) were studied. Vicker’s hardness test has been carried out on NNDEAP to measure the load dependent hardness. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. & 2011 Elsevier B.V. All rights reserved.

Keywords: A1. X-ray diffraction A2. Growth from solutions B1. Organic compounds

1. Introduction There is a great deal of interest in organic materials for their high nonlinearities. In a centrosymmetric structure the even-order nonlinear susceptibilities are zero in the electric dipole approximation [1]. Among the organic materials picric acid draws much more attention because of its tendency to form salts or charge transfer molecular complexes with many organic compounds particularly with aromatic amines, aliphatic amines, aromatic hydrocarbons, etc. The bonding of electron-donor–acceptor picric acid complexes strongly depends on the nature of the partners. A number of picrate complexes form crystalline solids and their crystal structures were studied in the past. Picric acid contains an activating  OH group and highly deactivating nitro groups. It not only acts as a good p acceptor due to the presence of three electron withdrawing nitro groups [2] but also as an acidic ligand to form salts through specific electrostatic or hydrogen bonding interactions [3]. The picrate charge transfer adducts of picric acid with basic organic compounds have been prepared and their crystal structures investigated thoroughly to know their binding modes [4]. The crystal and molecular structures of anilinium picrate, dimethylanilinium picrate and acenaphthene picrate have been reported [5]. All these complexes

n

Corresponding author. Fax: þ91 44 27469756. E-mail address: [email protected] (G. Anandha Babu).

0022-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2011.08.038

are formed through ionic and hydrogen bonding in the crystalline state. The proton transfer from the donor to the acceptor molecule is confirmed in the complexes such as dimethylanilinium picrate, 4-dimethylaminopyridinium picrate and caffeinium picrate. In the successive series efforts were made to grow NNDEAP crystals from solutions in order to study their properties. However no structure reports and systematic studies of NNDEAP have been made. Hence in the present investigation we report the synthesis, structure, growth, optical, thermal, dielectric and laser damage threshold studies of NNDEAP single crystals.

2. Experimental procedure 2.1. Material synthesis Picric acid and N,N-diethyl aniline were employed for the synthesis of the title compound N,N-diethyl anilinium picrate (NNDEAP). The title compound was synthesized by dissolving picric acid in analar grade N,N-diethyl aniline. The resulting product was stirred well when an yellow crystalline precipitate of NNDEAP was obtained. The proton is transferred from the electron donor group of the acid to the electron acceptor group of the base. The picric acid OH group necessarily protonates the nitrogen of the N,N-diethyl aniline. Fig. 1 presents the reaction scheme for the formation of NNDEAP.

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C 2H 5

C 2H 5

OH

O2N

N NO2

O2N

C2H5 N

H..................... O

NO2

C2H5 O2N

NO2 [N, N-diethyl aniline]

[Picric acid]

[N, N-diethyl anilinium picrate] Fig. 1. Reaction scheme for NNDEAP.

35

Solubility (g/100 ml)

30 25 20 15 10 5 0 15

20

25 30 Temperature (°C)

35

40

Fig. 3. Grown crystals of NNDEAP.

Fig. 2. Solubility curve of NNDEAP in acetone–methanol (1:1).

2.2. Solubility The selection of solvent is important to grow good quality single crystals of considerable size. The solubility test can be performed to choose the solvent for crystal growth. The solubility was measured by taking excess amount of NNDEAP in the solvent at constant temperature (30 1C) and it is continuously stirred to achieve uniform concentration over the entire volume of the solution. The solubility experiments were carried out several times at constant temperatures (20–35 1C) with an interval of 5 1C for various solvents such as acetone, methanol, ethanol and mixed solvents also. These studies were carried out in the constant temperature bath controlled to an accuracy of 70.01 1C, provided with a cryostat for cooling below the room temperature. It is observed that NNDEAP is highly soluble in acetone–methanol (1:1) solvent mixture when compared to other solvents. The solubility almost increases linearly with the increase of temperature. Hence acetone–methanol (1:1) solvent mixture was selected for the growth of single crystals. Fig. 2 shows the solubility curve for NNDEAP. 2.3. Growth of single crystals of NNDEAP A saturated solution of NNDEAP in 1:1 acetone–methanol mixture in accordance with the estimated solubility curve was prepared at the room temperature. The solution was stirred well for 6 h using magnetic stirrer to attain homogeneity throughout the entire volume of the solution. Suspended impurities were removed by filtering the solution. The clear filtrate thus obtained was kept at room temperature at approximately 32 1C and undisturbed in an environment conducive for single crystal growth. Then the solution was allowed to evaporate at room temperature approximately 32 1C.

In a span of fifteen days, well defined bright yellow single crystals of NNDEAP with an average dimension of 14  10  10 mm3 were obtained. The well grown crystals were harvested. The grown NNDEAP crystals are shown in Fig. 3.

3. X-ray diffraction studies The grown crystals were subjected to X-ray diffraction studies. The unit cell parameters and the crystal structure were determined from single-crystal X-ray diffraction studies using Bruker AXS Kappa Apex II CCD diffractometer. The crystal structure was solved by a direct method with the SHELXS-97 program [6] and refined by full matrix least squares with SHELXS-97 program to an R-value of 0.0522. The ORTEP drawing was performed with the ORTEP III program [7]. The X-ray diffraction intensity data for NNDEAP were measured at 293 K. The wavelength l of the MoKa radiation ˚ The intensity of 17,140 (graphite monochromator) is 0.71073 A. reflections was recorded in the range 1.961–251 of which 3172 unique reflections were recorded. The XRD data show that the crystal belongs to monoclinic system with the space group P21/c. NNDEAP belongs to centrosymmetric space group. The ˚ b¼12.1028(4) A, ˚ c¼ lattice parameters values are a¼7.3991(2) A, ˚ a ¼901, b ¼91.908(2)1, g ¼901 and volume of the unit 20.1744(6) A, cell is 1805.61(9) A˚ 3. The ORTEP diagram of NNDEAP is shown in Fig. 4. The crystal packing diagram is shown in Fig. 5. The crystal data and structure refinement for NNDEAP are given in Table 1. The crystallographic information file has been deposited by us in the Cambridge structure database (CCDC 801618). These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data-request/cif, by e-mailing [email protected] or by contacting the Cambridge CB21 EZ, UK; Fax, þ44 1223 336033.

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161

Fig. 4. ORTEP diagram of NNDEAP.

Table 1 Crystal data and structure refinement for NNDEAP. Empirical formula Formula weight Temperature Wavelength

C16H18N4O7 378.34 293(2) K 0.71073 A˚

Crystal system, space group Unit cell dimensions

Monoclinic, P21/c ˚ a ¼901 a ¼7.39919(2) A,

Volume

˚ b ¼ 91.908(2)1 b ¼ 12.1028(4) A, ˚ g ¼901 c ¼ 20.1744(6) A, 1805.61(9) A˚ 3

Z, Calculated density Absorption coefficient F(000) Crystal size Theta range for data collection Limiting indices

Fig. 5. Packing diagram of NNDEAP.

4. High-resolution X-ray diffraction studies The crystalline perfection of the grown single crystals was characterized by HRXRD by employing a multicrystal X-ray diffractometer developed at NPL [8]. The well-collimated and monochromated MoKa1 beam obtained from the three monochromator Si crystals set in dispersive ( þ,  ,  ) configuration has been used as the exploring X-ray beam. The specimen crystal is aligned in the ( þ,  ,  ,þ) configuration. Due to dispersive configuration, though the lattice constants of the monochromator crystal(s) and the specimen are different, the unwanted dispersion broadening in the diffraction curve (DC) of the specimen crystal is insignificant. The specimen can be rotated about the vertical axis, which is perpendicular to the plane of diffraction, with minimum angular interval of 0.4 arcsec. The rocking or diffraction curves were recorded by changing the glancing angle (angle between the incident X-ray beam and the surface of the specimen) around the Bragg diffraction peak position yB (taken as zero for the sake of convenience) starting from a suitable arbitrary glancing angle and ending at a glancing angle after the peak so that all the meaningful scattered intensities on both sides of the peak are included in the diffraction curve. The DC was recorded by the so-called o scan wherein the detector was kept at the

Reflections collected/unique Refinement method Data/restraints/parameters Goodness-of-fit on F^2 Final R indices [I42sigma (I)] R indices (all data) Largest diff. peak and hole

4, 1.392 Mg/m3 0.111 mm  1 792 0.30  0.20  0.20 mm3 1.961 to 25.001 –8 o ¼ h o ¼8, –14 o ¼ ko ¼14, –23 o ¼ l o ¼23 17,140/3172 [R (int)¼ 0.0285] Full-matrix least-squares on F2 3172/1/271 1.036 R1¼ 0.0522, wR2 ¼0.1465 R1¼ 0.0730, wR2 ¼0.1657 0.480 and  0.170 e A  3

same angular position 2yB with wide opening for its slit. This arrangement is very appropriate to record the short range order scattering caused by the defects or by the scattering from local Bragg diffractions from agglomerated point defects or due to low angle and very low angle structural grain boundaries [9]. Before recording the diffraction curve to remove the noncrystallized solute atoms, which remained on the surface of the crystal and the possible layers, which may sometimes form on the surfaces on crystals grown by solution methods [10] and also to ensure the surface planarity, the specimen was first lapped and chemically etched in a non preferential etchant of water and acetone mixture in 1:2 volume ratio. Fig. 6 shows the high-resolution diffraction curve (DC) recorded for NNDEAP specimen crystal using (022) diffracting planes in symmetrical Bragg geometry by employing the multicrystal X-ray diffractometer described above with MoKa1 radiation. As seen in Fig. 6, the curve does not contain a single diffraction peak, but contains an additional broad peak. The additional peak seems to be the convolution of many peaks due to mosaic blocks in the crystal.

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40

100

-600

-400 -200 Glancing angle [arc s]

3500

5. FT-IR spectral analysis The room temperature Fourier transform infrared (FTIR) spectrum of NNDEAP was recorded in the region 400–4000 cm  1 in order to analyze the synthesized compound qualitatively for the presence of functional groups in the molecule at a resolution of 75 cm  1 using a Perkin-Elmer FTIR spectrometer, equipped with a TGS detector, a KBr beam splitter, a He-Ne laser source and a boxcar apodization used for 250 averaged interferograms collected for both the sample and the background. In this technique almost all functional groups in a molecule absorb characteristically within a definite range of frequency [12]. The FTIR spectrum of NNDEAP is shown in Fig. 7. The asymmetric and symmetric stretching vibrations of ethyl groups appear at 3069 and 2898 cm  1. The asymmetric C–H stretching appears at 2953 cm  1. The band at 2740 cm  1 occurs due to symmetric C–H stretching. The band at 1632 cm  1 is assigned to the carbonyl stretching vibration. The band at 1564 cm  1 appears due to NO2 asymmetric stretching vibrations. The C–H asymmetric deformation modes of ethyl groups appear at 1489 cm  1. Asymmetric deformation of ethyl groups occurs at 1433 cm  1. The band at 1318 cm  1 is assigned to NO2 symmetric stretching. The C–O stretching appears at 1273 cm  1. The aromatic C–H inplane bending modes are at 1163, 1078 and 1022 cm  1. The presence of very sharp bands at 910 cm  1 owe to the C–NO2 stretching vibration. The NO2 rocking vibration is observed at 556 cm  1.

6. UV–vis–NIR spectral analysis The UV–vis–NIR spectrum is studied by Perkin-Elmer Lambda35 spectrometer with a NNDEAP single crystal of 1 mm thickness in the range of 200–1100 nm. The transmission range and transparency cut off are very important for the crystals. The recorded transmittance spectrum is shown in Fig. 8. NNDEAP crystal presents a cut off

1022 910 1163 1078

1433

2500 2000 1500 Wavenumber (cm-1)

1000

500

Fig. 7. FTIR spectrum of NNDEAP.

Fig. 6. HRXRD curve of NNDEAP single crystal for (022) diffracting plane.

60 50 40 %T

From the angular spread of this broad peak it is understood that these mosaic blocks (structural grain boundaries) are misoriented by each other with tilt angles in the range of few tens of arc sec to few minutes of arc [11]. The interesting thing in the DC is that of the main peak at zero glancing angle (i.e. the Bragg peak of the main crystal block). The FWHM (full width at half maximum) of this main peak is 35 arcsec and indicates that a good portion of the crystal is having reasonably good perfection.

3000

1564

1632

0 4000

0

1489

20

1318 1273

35"

2740

2898

60

200

0 -800

3069

300

556

80

2953

400

%T

Diffracted X-ray intensity [c/s]

100

NNDEAP MoKα1 (+, −, −, +)

30 20 10 0 300

400

500

600 700 800 900 Wavelength (nm)

1000 1100 1200

Fig. 8. Transmittance spectra of NNDEAP.

wavelength at 471 nm. The crystal has 50 percent transmission in the visible region and near infrared region. These studies were carried out without any antireflection coatings. The low percentage of the transmission can be attributed to the purity of the starting material, growth method and surface polishing.

7. Thermal studies The thermal behavior of NNDEAP was studied by the thermogravimetric (TG) and differential thermal analyses (DTA). The TG/DTA for NNDEAP has been recorded using NETZSCHSTA 449F3 instrument. An alumina crucible was used for heating the sample and analyses were carried out in an atmosphere of nitrogen at a heating rate of 10 1C/min in the temperature range of 301–600 1C. The TG–DTA curves of NNDEAP are shown in Fig. 9. The differential thermogram curve of NNDEAP shows the sharp endothermic reaction at 144 1C. This is assigned to the melting point at which no weight loss is occurred. This is in good agreement with the observation of melting point of the material using ‘MONATCH’ melting apparatus. The weight loss of 30% occurs between the temperature 1771 and 240 1C. 11% of the weight loss occurs between the temperature 250 and 350 1C. The residual mass after heating the NNDEAP sample to 597 1C is 46.7%.

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4

20

80

2 DTA TGA

16

90

70 60

0

Dielectric constant

227°C

18

Weight loss (%)

Exo

100

DTA (mW/mg)

163

144°C

200 300 400 Temperature (°C)

10 8 6

2 40

100

12

4

50

0

313K 333K 353K 373K 393K

14

500

0

600

3

2

Fig. 9. TG/DTA curve of NNDEAP.

4 5 Log frequency (Hz)

6

Fig. 10. Variation of dielectric constant with frequency for NNDEAP.

8. Dielectric measurement

9. Vickers microhardness test Hardness is one of the important mechanical properties of the materials. As the hardness of the crystal determines the

0.35 313K 333K 353K 373K 393K

0.30 Dielectric loss

The dielectric constant is one of the basic electrical properties of solids. Studies of the temperature and frequency dependence of dielectric properties unveil useful information about structural changes, defect behavior and transport phenomena [13]. Essentially, dielectric constant er is the measure of how easily a material is polarized in an external electric field. The dielectric constant and the dielectric loss were measured using the Agilent 4284-A LCR meter. Good quality single crystals of NNDEAP were cut and polished on a soft tissue paper with fine grade alumina powder. Two opposite surfaces across the breadth of the sample were treated with good quality graphite in order to obtain good Ohmic contact. Using the LCR meter, the capacitance of this crystal was measured for the frequencies 100 Hz, 1 KHz, 10 KHz, 100 KHz and 1 MHz at various temperatures. The observations were made while cooling the sample. Air capacitance (Cair) was also measured. The dielectric constant of the NNDEAP crystal was measured as a function of frequency at different temperatures (40 1C, 60 1C, 80 1C, 100 1C and 120 1C). The variation of dielectric constant with the frequency at different temperatures is shown in Fig. 10. It is deduced that the dielectric constant is relatively high at lower frequencies and decreases as the frequency increases. The dielectric constant of materials is due to the contribution of electronic, ionic, dipolar and space charge polarizations, which depend on the frequencies. At low frequencies all these polarizations are active [14]. At 100 Hz the dielectric constant of NNDEAP crystal at 393 K is 10.4 whereas the dielectric constant decreases to 2.9 at 313 K. The dielectric constant is relatively high in the lower frequency and almost saturated beyond 100 KHz. Fig. 11 shows the plot between the frequency and dielectric loss at various temperatures. It is observed from the plot that the dielectric loss decreases as the frequency increases. The higher values of the dielectric loss at low frequencies originate from space charge polarization. The low dielectric loss value at higher frequencies indicates that the grown NNDEAP crystal contains minimum defects.

0.25 0.20 0.15 0.10 0.05 0.00 3.0

3.5

4.0 4.5 5.0 Log frequency (Hz)

5.5

6.0

Fig. 11. Variation of dielectric loss with frequency for NNDEAP.

mechanical stability of the crystal, it is an inevitable parameter to be determined. Hardness of the material is a measure of resistance it offers to local deformation [15]. The indentation hardness is measured as the ratio of applied load to the projected area of indentation. Vickers microhardness studies have been performed on NNDEAP. It is carried out using the instrument MITUTOYO model MH 120. Loads ranging from 5 to 50 g were used for making indentations. The microhardness value was calculated as Hv ¼ 1:8544P=d2 kg=mm2 , where Hv is the Vickers hardness number, P is the applied load and d is the diagonal length of the indentation. Fig. 12 shows the variation of Hv as a function of applied load ranging from 10 g to 50 g for NNDEAP crystal. It is observed that Hv increases with the increase of load, which indicates the reverse indentation size effect (ISE). The cracks have been observed beyond 50 g for NNDEAP. According to Onitsch [16], n should lie between 1 and 1.6 for harder materials and above 1.6 for softer materials. The value of n for NNDEAP is 1.8. Therefore NNDEAP belongs to softer material category.

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value is 1.27 GW/cm2 for 1064 nm wavelength of Nd:YAG laser radiation.

20 18

11. Conclusion

Hv (Kg/mm2)

16 14 12 10 8 6 10

20

30 Load P in gm

40

50

Fig. 12. Mechanical behavior of NNDEAP: Load vs hardness number.

NNDEAP has been synthesized. Single crystals of NNDEAP were successfully grown by the slow evaporation solution growth method and its structure is reported for the first time in the literature. The grown crystals have been confirmed using X-ray diffraction studies. NNDEAP belongs to monoclinic system with the space group P21/c. The high-resolution XRD measurements substantiate the quality of the crystal. The presence of functional groups of NNDEAP was confirmed by FT-IR analysis. The cut off wavelength of NNDEAP from the transmittance spectrum is 480 nm. Differential thermal analysis carried out on the grown crystal indicates that the material does not sublime before it melts at 144 1C. The dielectric constant and dielectric loss were measured for the grown NNDEAP crystal, which establishes the normal behavior. Microhardness measurements reveal that the hardness increases with the increase of load. The laser damage threshold value for NNDEAP is 1.27 GW/cm2 for 1064 nm wavelength of Nd:YAG laser radiation.

10. Laser damage threshold measurements Acknowledgments Laser damage threshold value of as grown NNDEAP crystal was measured using Nd:YAG laser. Laser induced breakdown of materials is caused by various physical mechanisms. For transparent materials the damage is due to avalanche and multiphoton ionizations. The damage threshold in the case of strong absorbing materials is due to the temperature rise, which creates strain induced fracture [17]. The laser damage threshold depends on a great number of laser parameters such as wavelength, energy, pulse duration, longitudinal and transverse mode structure, beam size, location of beam, etc. It is known from an earlier report [18] that in the long pulse regime (t 4100 ps), the damage is controlled by the rate of thermal conduction through the atomic lattice and in the short pulse regime (t o100 ps), the optical breakdown and various nonlinear ionization mechanisms become important. For multiple shot experiments, the sample is mounted on an X–Y translator that facilitates in bringing different areas of the sample for exposure precisely. The onset of damage can be determined by visual damage and audible cracking. To investigate the laser damage threshold of NNDEAP crystal, pulse width of 30 ns with a repetition rate of 5 Hz and a fundamental wavelength of 1064 nm was used. The laser beam of diameter 1 mm was focused on the crystal. The sample is placed at the focus of a plano-convex lens of focal length 30 cm. An attenuator was used to vary the energy of the laser pulses with a polarizer and a half wave plate. The pulse energy of each shot was measured using the combination of phototube and oscilloscope. The surface damage threshold of the crystal was calculated using the expression: Power densityðPd Þ ¼ E=tpr 2 where E is the energy (mJ), t the pulse width (ns) and r the radius of the spot (mm). A crack is observed after passing 30 mJ energy in 30 s. The measured multiple shot (150 pulses) laser damage threshold

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