Synthesis, vibrational, thermal, mechanical and third-order nonlinear optical properties of sodium 4-methyl-3-nitrobenzoate monohydrate crystal for optical limiting applications

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Synthesis, vibrational, thermal, mechanical and third-order nonlinear optical properties of sodium 4-methyl-3-nitrobenzoate monohydrate crystal for optical limiting applications M. Divya Bharathi , R. Bhuvaneswari , G. Ahila , G. Vinitha , G. Anbalagan PII: DOI: Reference:

S0577-9073(19)31020-2 https://doi.org/10.1016/j.cjph.2019.12.019 CJPH 1042

To appear in:

Chinese Journal of Physics

Received date: Revised date: Accepted date:

17 September 2019 21 November 2019 17 December 2019

Please cite this article as: M. Divya Bharathi , R. Bhuvaneswari , G. Ahila , G. Vinitha , G. Anbalagan , Synthesis, vibrational, thermal, mechanical and third-order nonlinear optical properties of sodium 4-methyl-3-nitrobenzoate monohydrate crystal for optical limiting applications, Chinese Journal of Physics (2019), doi: https://doi.org/10.1016/j.cjph.2019.12.019

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Synthesis, vibrational, thermal, mechanical and third-order nonlinear optical properties of sodium 4-methyl-3-nitrobenzoate monohydrate crystal for optical limiting applications M. Divya Bharathia, R. Bhuvaneswaria, G. Ahilaa, G. Vinithab, G. Anbalaganc,* a

Department of Physics, Presidency College, Chennai-600005, India

b

Department of Physics, VIT University, Chennai-600127, India

c*

Department of Nuclear Physics, University of Madras, Chennai-600025, India

Corresponding author: [email protected] (G.Anbalagan) Declaration of interests: None

Highlights A new metal-organic material Na4M3N was synthesized and single crystals were grown by slow cooling method.  The LDT value of Na4M3N crystal is found to be superior to that of KDP and Urea.  Enhanced nonlinear susceptibility and polarizability leads to the large third order NLO

properties.  The measured value of thermo-optic coefficient (-3.5 ×10-5 K-1) indicates the self-

defocusing effect.

ABSTRACT A nonlinear optical (NLO) sodium 4-methyl-3-nitrobenzoate monohydrate (Na4M3N) single crystal was synthesized and grown by the slow cooling solution growth method using an ethanol-water (1:1) mixed solvent.

Powder X-ray diffraction (PXRD) reveals the

crystallinity of Na4M3N compound. The Na4M3N crystal was estimated with a single crystal

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XRD instrument and it was identified to be in the centrosymmetric space group (P21/c) having a monoclinic system. The vibrational, proton (1H) and carbon (13C) NMR spectral analysis substantiates the functional groups, hydrogen and carbons in the synthesized compound. The Hirshfeld surfaces analysis was executed to know the different type of interactions present in the crystal. From the UV-vis spectrum, the optical band gap and cutoff wavelength of the Na4M3N crystal are endowed to be 5.06 eV and 254 nm respectively. The Na4M3N crystal was subjected to a thermogravimetric as well as differential thermal analysis for discerning the thermal characteristics. The LDT value of crystal was endowed to be 5.8 GW/cm2 using Nd: YAG laser and the value is superior to that of KDP and Urea. The emission region of the compound was identified by the photoluminescence emission spectrum. The crystalline quality was again confirmed by lifetime measurements. The thermo-optic coefficient (dn/dt) was determined to be -3.5 ×10-5 K-1. The reverse saturable absorption observed by third-order NLO studies dictates the suitability for optical limiting applications. Vickers microhardness test showed that Na4M3N crystal was a soft material. The average etch pit density (3.2  103 cm-2) was determined from chemical etching studies. The complex dielectric constant, electric modulus and electrical conductivity values were measured as a function of frequency to get information on the conduction mechanisms. Keywords: Metal-organic crystal; Crystal growth; Optical materials; Impedance analysis; Optical limiting properties 1. Introduction In recent years, there has been notable attraction towards the synthesis of metalorganic materials with good fluorescence and NLO properties which makes them probable material for use in light-emitting diodes, tele-communication, optical data storage, optical computing and optical information [1, 2]. It is established that the in-organic compounds have large mechanical strength, degree of chemical inertness and melting point, but have very

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penurious NLO efficiency when compared to organic compounds [3, 4]. As for dissimilarity, organic crystals have high NLO efficiency, but they have lesser transparency, mechanical strength, laser damage threshold, optical band gap and thermal properties [5, 6]. Device applications need an optically quality crystal which is difficult in organic materials [7]. Such difficulties are settled by selecting metal-organic materials. Metal organic materials are achieved by combining the organic as well as inorganic materials and with that a crystal was grown using the solution growth technique [8]. It is noticed that nonlinearity exists in the crystal because of the good thermal and mechanical properties present in the combinational compound [9, 10]. In addition to that these compounds exhibit carboxylic acid to metal charge transfer by an electron movement from carboxylic acid to metal and metal to carboxylic acid owing to the π electron delocalization which is an essential property for a crystal to exhibit NLO activity. The organic material 4-methyl-3-nitrobenzoic acid (4M3N) is carboxylic acid and its counterpart derivative compounds exhibit narcotic action [11]. The 4M3N donates hydrogen to the chosen base. The acid of either aqueous or molten form has the tendency to form gaseous products and metal salt on reacting with active metals. Divya Bharathi et al described the crystal structure and growth aspects of a 4M3N single crystal [12]. Sodium hydroxide (NaOH) is a metal type of alkali which is extensively utilized because of its higher charge density and its ability to combine with organic materials. Sodium can form a variety of complexes like sodium hydrogen oxalate hydrate [13], sodium 2, 4dinitrophenolate [14], sodium succinate hexahydrate (β phase) [15], sodium tetraborate decahydrate [16], sodium barium orthoarsenate (V) nonahydrate [17], sodium hydrogen maleate trihydrate [18], sodium para-nitrophenolate para-nitrophenol dihydrate [19], hydrated sodium borate [20] and anhydrous sodium formate [21]. Metal organic crystals play an important role in NLO applications because it has higher third-order nonlinear behaviour. Sodium derivatives are known to be interesting photonic materials in view of their large

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third-order optical nonlinearity and optical limiting properties. In this point of view we have chosen sodium and 4-methyl-3-nitrobenzoic acid as a starting material to synthesis sodium 4methyl-3-nitrobenzoate monohydrate single crystal. The grown materials are having higher third-order NLO efficiency when compared with other metal-organic crystals. The Na4M3N metal-organic crystal having a centrosymmetric space group enacts a decisive role in third harmonic generation which finds a vast range of utilization in optical signal processing, optical communication networks, optical power limiting for sensor production and integrated optics [15]. Thermal diffusivity of crystals is significant for designing photonic devices and optical limiters. It is essential to scrutinize the reliance of the refractive index on temperature by assessing the thermo-optic coefficient, as the comparative enhancement in beam divergence ensues from the nonlinear refractive index and the effect of thermal lensing.Nonlinear optical materials, especially those with 2-dimensional structures, are the fundamental building blocks of future laser optics, photonic circuits and optical communications and they have attracted significant interest [22]. Besiding the metal organic materials, other type of 2-dimensional materials such as Titanium disulfide [23], MXene Ti3C2Tx [24], Metal organic framework [Ni:MOF] [22], Bismuthene [25] and Antimonene [26] are also exhibiting saturable absorption behaviour. Hence these types of materials are also having third-order nonlinear optical properties. In this research work, we report the synthesis, structure, third-order nonlinear and optical limiting properties of a metal-organic Na4M3N single crystal. 2. Experimental procedure The analytical grade NaOH (99% pure) and Sigma Aldrich product of 4-methyl-3nitrobenzoic acid were taken as the starting materials to synthesize Na4M3N. The quantity measuring 9.057 g of 4-methyl-3-nitrobenzoic acid was dissolved in ethanol-water (1:1) and

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the measured amount of NaOH (2g) was added to the solution slowly with continuous stirring for 4 h to get a homogeneous mixture. The fine powder of Na4M3N crystal was used for the solubility study and it was executed as a function of temperature between 30-45oC with an interval of 5oC using a constant temperature bath (CTB) with an accuracy ± 0.01oC. On starting with a temperature of 30°C, 5.78 g of synthesized salt was dissolved in 100 ml of ethanol-water solvent and was allowed continuous stirring to ensure homogenization over the entire volume of the solution for attaining supersaturation. After attaining supersaturation, 10 ml of the clear solution was pipetted into a Petri dish and was allowed to dry at room temperature and weighed. The quantity of salt present in the 10 ml solution was determined which gives the solubility. The same procedure was espoused for all the temperatures from 30 to 45°C. The solubility of the Na4M3N crystal was found to be 13.25 g/100 ml in ethanol-water solvent at 45oC. The temperature dependence of the solubility curve (Fig.1) reveals the positive solubility gradient, and thus, the slow cooling technique helps to grow the Na4M3N crystal. The transparent solution obtained was filtered using A1 filter paper and the solution in the beaker was shielded with a polythene cover with limited holes allowed for evaporation. The solution was kept undisturbed at 35oC in constant temperature bath with an accuracy of ± 0.01oC and the temperature was reduced at a lowering rate of 0.1oC per day. Good quality pale yellow coloured crystals was grown after 20 days. The dimension of the grown crystal is 8 × 8 × 3 mm3; the photograph of the crystal is shown in Fig.2 (a). 3. Characterization techniques 3.1. X-ray diffraction analysis 3.1.1. Morphology study The morphology of the Na4M3N crystal is generated with thehelp of WINXMORPH computer software and the morphology of the grown crystal is presented in Fig. 2(b). The

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observed well developed faces of Na4M3N crystal are (0 0 -1), (1 0 -1), (0 1 -1), (1 1 -1), (-1 -1 0), (-1 0 1), (0 0 1), (0 -1 -1), (-1 -1 1), (1 1 0), (-1 0 0) and (1 0 0). The most prominent face of the Na4M3N crystal is (1 0 0) which is utilized for various characterizations. 3.1.2. Powder XRD analysis Powder X-ray diffraction (XRD) analysis was carried out using D8 Advance (Bruker) by employing CuKα (1.5408 Å) in the range between 10 - 70º with the scanning rate 0.5º min at ambient temperature. The crushed powder sample was used to collect the X-ray diffraction data of the Na4M3N compound. Fig. 3(a), displays the powder XRD pattern of Na4M3N compound. The crystallinity of crystal is identified from the diffraction pattern. The data were indexed using Powder-X software. The sharp peak confirms the good crystallinity of the Na4M3N crystal. 3.1.3. Single crystal XRD study The Na4M3N crystal was allowed for the above-mentioned analysis with the help of an instrument (Bruker AXS Kappa APEX II CCD Diffractometer) furnished with graphite monochromated MoKα radiation (λ=0.7023 Å) at ambient temperature and the crystal possessing dimension of 0.3 × 0.2 × 0.25 mm3 was used for data collection. Accurate lattice parameters were established from the 36 frames of reflections contemplated in three disparate crystallographic zones using the difference vector system. The SHELXS-2016 program was used to decide the Na4M3N structure using direct methods procedure and it was refined by the method of Full-matrix least squares on F2 using the SHELXL-2016 program. The structure was originally rectified to a high R index value of 9.89% and the map shows a difference Fourier (∆ρmax = 0.74 eÅ-3) which is observed to be a relatively larger peak. A preliminary check with the Twin Rot Mat routine of PLATON shows that the crystal has the non-merohedral twin, having rotational twinning about the c-axis with a twin matrix of (-0.998 0 -0.499/ 0 -1 0 /-0.009 0 0.998). The ratio of twin domains is found to be 85:15 and

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an HKLF5 file format is generated using the twin matrix, after applying the twin correction the structure refined to an upgraded R index of 5.40 %, with an appreciable Fourier map of embellished difference (∆ρmax = 0.39 e Å-3) and BASF of 0.15. All the atoms which have an absence of hydrogen (H) were employed for anisotropic refinement, whereas the H was rectified isotropically. The H atoms bound to the C atoms were treated as riding atoms with distances of d(C-H) = 0.96Å (for CH3) with Uiso(H) = -1.5Uequ(C) and d(C-H) = 0.93Å (for aromatic CH) with Uiso(H) = -1.2 Uequ(C). The H-atom associated with water, oxygen atoms were identified from the disparity electron density peak and were geometrically optimized. Tables 1 and 2 represent the refinement of the structure’s details, bond length and bond angles. The molecular graphics are equipped with the program ORTEP [27] and Mercury [28] software. The emigration Ellipsoid Plot of the compound Na4M3N pinched at 50% probability level showing the asymmetric unit is depicted in Fig. 3(b) and the coordination of the Na (I) atom with five oxygen atoms in the crystal structure is demonstrated in Fig. 3(c). The Na4M3N compound crystallizes in monoclinic with space group P21/c. The sodium (I) atom is a five-coordinated in distorted trigonal - bipyramidal geometry. The Na atom is coordinated with four, 4-methyl-3-nitrobenzoate anion and a water molecule. The connection between the adjacent Na (I) ions is enchanted by two oxygen atoms of the carboxylate group of the 4-methyl-3-nitrobenzoate anion resulting in the configuration of a coordination polymer. In the anion (4-methyl-3-nitrobenzoate), the surrogated nitro group is warped away from the phenyl plane with a dihedral angle of 37.58(2)º, whereas the carboxylate group plays a part in coordinating with the metal atom in plane with the phenyl group. The crystal structure is made up of a 2-dimensional coordination polymer or a complex of Na (I) cation and 4-methyl-3-nitrobenzoate anion. Here the adjacent Na (I) atoms are bridged by the carboxylate oxygen atoms O3 and O4 alternately which generates a one-

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dimensional chain made of Na(I)-O coordination bonds extending along the crystallographic [0 0 1] direction. In the chain the adjacent trigonal - bipyramidal geometry of the Na atoms is connected over the center of inversion at (0, 0, 0), (0, 0, 1/2) and (0, 0, 1) etc. Adjacently, [0 0 1], the Na (I)-O coordinates are further bridged by the carboxylate carbon atom C7 (bonded with O3 and O4) to form a two-dimensional coordination network extending parallel to the (1 0 0) crystallographic plane. These inorganic 2D networks perpendicular to the a-axis are separated by a distance equal to the length of the a-axis [16.779(2) Å], and the 4-methyl3-nitrobenzoate anion bonded to the Na(I) atom is projected on both sides of the 2D network. Also, the coordinated water molecules from the two O-H…O hydrogen ones bond with the oxygen atoms of the nitro group and one C-H…O interaction [Table 3] which doesn’t make any change in the molecular network; rather it strengthens the molecular packing of the crystal. These hydrogen bonds may have an impact over the physico-chemical properties of the crystal as they are electrostatic in nature. The crystallographic data with CCDC No. 1535485 have been stowed with the Cambridge Crystallographic Data Centre,12, Union Road, Cambridge CB21EZ, UK and the copies of the structure details can be fetched free of cost (e-mail: deposite@ ccdc.cam.ac.ukwww:http://www.ccdc.cam.ac.uk). 3.2. Vibrational analysis The FT-IR and Raman vibrational analysis were carried out to scrutinize the existence of functional groups and their vibrations in the Na4M3N compound. The FT-IR spectrum was recorded using a Perkin Elmer spectrometer in the province of 450 - 4000 cm-1 having a resolution score as 1 cm-1 by KBr Pellet method. The BRUKER RFS 27 containing Nd: YAG laser having a wavelength of 1064 nm was utilized to acquire the Raman spectrum in the region 50-4000 cm-1 with a resolution 2 cm-1. The traced FT-IR spectrum is shown in Fig.4 while the Raman spectrum is in Fig.5 and the analogous vibrational assignments are given in

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Table 4. The band at 3596, 3381 and 3260 cm-1 observed in the FT-IR spectrum is ascertained to the O-H stretching vibration. The peaks obtained at 3106 and 3073 cm-1 in the FT-IR and the equivalent band in the Raman spectrum at 3080 as well as in 3035 cm-1 are due to the C-H asymmetric vibration and symmetric stretching respectively. The CH3 asymmetric as well as symmetric stretching vibration was observed in the FT-IR at 2996 and 2929 cm-1 and in the Raman spectrum at 2995 and 2930 cm-1[12]. The absorption peaks at 2963 cm-1 in the FT-IR and Raman at 2965 cm-1 are due to the C-H stretching vibration. The presence of lattice water in the FT-IR is recognized by the H-O-H bending at 1652 cm-1[29]. Basically, the strong asymmetrical stretching (υas) band for carboxylate ion occurs amid 1650-1550 cm-1 and the weak symmetrical stretching (υs) bands present nearby -1400 cm-1. The asymmetric COO- stretching vibration was observed at 1602 cm-1 in the FT-IR spectrum and the corresponding peak appears at 1615 cm-1 in the FTRaman spectrum. The band in the FT-IR spectrum at 1403 cm-1 and in the Raman spectrum at 1406 cm-1 is due to the symmetric COO- stretching vibration [30]. The absence of a peak positioned at 1716 cm-1 in the FT-IR and Raman spectra affirms that there is no COOH group present in the Na4M3N compound. Generally, the NO2 groups strongly absorb at 1530-1500 cm-1 and weakly absorb at 1370-1330 cm-1. The asymmetric NO2 stretching vibrations in the FT-IR and Raman spectrum were observed at 1524 cm-1 and 1519 cm-1 respectively. The bands at 1353 and 1358 cm-1 are due to the symmetric NO2 stretching vibration in the FT-IR and Raman spectrum respectively. The band that occurs in the Raman spectrum at 1593 cm-1 is ascertained to the C-N asymmetric stretching vibration. The peak observed in the FT-IR spectrum at 1075 cm-1 and in the Raman spectrum positioned at 1080 cm-1 is ascertained to the C-N symmetric stretching vibration. The observed peaks at 1555 and 1492 cm-1 present in the FT-IR spectrum and at 1549 and 1445 cm-1 in the Raman spectrum are assigned to the C=C stretching vibration. The peaks observed

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in the FT-IR spectrum at 1380, 1026 and 940 cm-1 and in the Raman spectrum at 1380 and 1001 cm-1 is due to the C-C stretching vibration. The stretching mode of C-N vibration peak is noticed in the Raman spectrum at 1306 cm-1. The band at 1267 cm-1 positioned in the FT-IR spectrum and the corresponding peak observed in the Raman spectrum at 1263 cm-1 are due to the C-O stretching vibration. The band of medium intensity produced in the FT-IR spectrum at 1204 and 1141 cm-1 and in the Raman spectrum at 1206 and 1145 cm-1 is assigned to C-H deformation. The peaks at 1161, 915 and 677 cm-1 occurred in a spectrum of FT-IR and also in the Raman spectrum at 1163, 919 and 671 cm-1 are due to the C-H in-plane bending. The C-H bending vibration occurs out of plane in the FT-IR spectrum at 862, 826 and 755 cm-1 and the corresponding vibration peak is noticed in the Raman spectrum at 828 and 741 cm-1. The peak that absorbs at 706 cm-1 in both the FT-IR and Raman spectrum is attributed to the C-H deformation. The band at 635 cm-1 positioned in the FT-IR spectrum and in the Raman spectrum at 632 cm-1 is due to C-NO2 stretching vibration. The Na-O stretching occurs in the FT-IR and Raman spectrum at 520 cm-1 and 519 cm-1 [15]. The peak observed in the Raman spectrum at 484 cm-1 is due to Na-OH2 wagging vibration. This band affirms the existence of a sodium atom that was coordinated to the water molecule [31,32]. The absorption of the peak at 354 cm-1 is ascertained to the C-CH3 bending vibration occurring inplane in Raman spectrum. Four peaks were observed under 300 cm-1 in the Raman spectrum at 280, 184, 145 and 84 cm-1 attributed to lattice vibration in Na4M3N compound. 3.3. NMR spectral analysis

NMR is an analytical method utilized to verify the molecular structure of the Na4M3N compound. The 1H as well as 13C NMR spectrum was chronicled using AVANCE III 500 NMR spectrometer with an internal standard tetramethylsilane (TMS) using DMSO d6

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solvent. The recorded proton and carbon NMR spectra of Na4M3N are shown in Fig.6 (a & b) and the corresponding assignments are given in Table 5. 3.3.1. Proton NMR In the 1H NMR spectrum (Fig.6 (a)), the singlet shift that appeared at 2.5 ppm was assigned to the para position of the methyl group (H-3) protons of 4-methyl-3-nitrobenzoate. The chemical shift that appeared at 3.474 is due to the water molecule present in the title compound. The doublet peak at 7.395 ppm was attributed to the meta position (H-2) of the carboxyl group. The ortho position of aromatic protons (H-4 and H-1) that appear as two doublet signals at 8.396 and 8.0775 ppm is owing to the olefinic hydrogen (HC=CH). There is no other shift for the carboxylic acid (COOH) proton which usually comes between 10.5 and 12 ppm. It confirms the molecular geometrical structure of the Na4M3N compound through carboxylic acid by deprotonation.

3.3.2. Carbon NMR In the

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C spectrum (Fig.6 (b)), the singlet peak of carbon (C-8) at 19.929 ppm is

attributed to the methyl group in the 4-methyl-3-nitrobenzoate. The DMSO solvent peaks are in the range of 39.419 to 40.421. The signal that arises at 111.446 ppm was ascertained to the C=C carbon atom (C-3) of aromatic rings. The various carbon atoms C-1, C-5, C-6 and C-7 appear as singlet signals at 133.832, 125.087, 148.82 and 140.066 ppm respectively. The doublet signal for carbon C-2 was observed at 132.334 ppm. The singlet peak that appeared at 168.137 ppm was assigned to the carboxylate (COO-) carbon (C-4) with more number of electronegative oxygen atom in benzoate. The total number of carbon that exists in the title compound is 8 and this carbon count is exactly matching the carbon spectrum and it confirms the molecular structure of the Na4M3N compound.

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3.4. Hirshfeld surface analysis Hirshfeld surface analysis and finger print plots of the title compound were carried out using the crystal information CIF file output in the Crystal Explorer software [33]. The intermolecular contact of the compound can also observed by this method. This method is a graphical tool for visualization of intermolecular interactions using colour-codes on the Hirshfeld surface. The normalized contact distance depends on both di and de (distance from the point to the adjacent nucleus internal to the surface) and (distance from the point to the adjacent nucleus external surface) [34]. The Hirshfeld surface is illustrated in Fig.7(a). The red colour corresponds to closer distances, while the white colour indicates the near distances and blue represents longer distances. The 2D fingerprint plot (Fig.7(b)) furnishes additional

information about the individual contribution of all interactions in the crystal packing. The 2D fingerprint plots are dominated by H⋅⋅⋅H, C…C, O⋅⋅⋅H, C⋅⋅⋅H and N…O contacts. The contributors

to the crystal packing interactions are H···H (28.3%), C…C (9.5%), C…H/H…C (6.5%), O…N/N…O (2.1%) and O···H/H···O (29%). 3.5. Optical studies The UV-Vis transmittance spectrum of the Na4M3N crystal was recorded at ambient temperature by utilizing a SHIMADZU 1800 UV-Vis spectrometer in the wavelength region between 190 and 900 nm with the thickness of 1 mm. Fig.8 (a) depicts the recorded transmittance spectrum of the Na4M3N compound. From the spectrum, it is observed that it positions a good transparency (69%) including the cut-off wavelength which is lower for the Na4M3N crystal (254 nm) and this is due to the π-π* transition. The absorption is found absent in the range between 254 - 850 nm and makes the title crystal desirable for optoelectronic applications. The parameters including linear absorption coefficient (α) have been determined from the transmittance (T) as well as thickness (t) of the sample using the following relation [35]:

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1 2.303 log  T   t (1) The absorption coefficient which is linear can be demonstrated in a number of ways as

explained by Tauc's relation [30]:

(h )  AE g  h 

m

(2)

where Eg is the optical band gap, hυ is the photon energy, m is the index that symbolizes the optical absorption process and A is the constant. The values of m for each transition as direct allowed (1/2), indirect allowed are (2) with the direct forbidden (3/2) and indirect forbidden (3) transitions respectively. The graph plotted between (αhυ)2 vs. photon energy is depicted in Fig.8(b). The optical energy gap Eg (5.06 eV) is obtained from the interpolated line with the hυ axis. The optical band gap and cut-off wavelength of the title crystal is compared with other compound and it is given in Table 6. The larger energy band gap shows that the defect concentration in the grown crystals is very low [36]. Reflectance is a significant notion in the field of tele-communication, solar thermal energy, optics and radar and it is based on the polarization of radiation [37]. The reflectance of the Na4M3N crystal may be explained in terms of the absorption coefficient (α), R

1  1  exp  t   exp t  1  exp  t 

(3)

Fig.9(a) illustrates the changing reflectance as a function of wavelength which indicates that, the reflectance increases with increasing wavelength in the lower absorption range and beyond this range it was saturated. The refractive index (no) of an optical material was calculated using the relation [30], no 

 R  1   3R 2  10 R  3 2R  1

(4)

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The calculated refractive index of the Na4M3N crystal is 2.24 and the plot is illustrated in Fig.9 (b). This refractive index value of the Na4M3N crystal proves its good optical nature and also this value is used to calculate the third-order susceptibility values. Variation of the refractive index with respect to wavelength shows the normal dispersion nature of the crystal which is a significant factor in communications. The refractive index of the title crystal suggests that the material will enhance the performance of optical and photovoltaic devices such as solar cells [38], Bragg gratings [39], photonic crystals [40] and waveguide-based optical circuits [41]. 3.5.1. Deduction of optical electro-negativity The nature of bonding between the composed material can be identified by deducing the optical electro negativity (Δ*). If optical electronegativity is high (more than 1.7), the materials are ionic in nature and if its magnitude between 0 to 1.7 then the materials is covalent in nature [42]. It is also observed that for the molecules if the optical electronegativity is low and the molecules should also have high refractive index. Duffy explained the theory of optical electro- negativity obtained using the following relation [43]:

 *  0.2688E g where,

(5)

* *  *   anions   cations

The Eg value of the compound was substituted in eq. (5), to identify the nature of bonding in the Na4M3N crystal. The electro-negativity of Na4M3N was found to be 1.36. From the obtained result, it is clear that Na4M3N is a polar covalent bonded material. 3.6. TG-DTA analysis Thermal stability was recognized utilizing the model TGA Q500 V20.10 Build 36 instrument in a nitrogen atmosphere at a heating pace of 20°C/min in the temperature assortment from ambient temperature to 900°C and the respective TG-DTA trace is

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represented in Fig.10. Three stages of decomposition are noticed in the TG curve. The first stage of decomposition starts from 30°C to 79°C owing to the volatilization of ethanol with the mass loss of 11.7%. The combination of the anion and cation moieties of water molecules is dehydrated showing a percentage mass loss of 30.1% in the temperature from 79°C to 127°C. The major decomposition of Na4M3N between the temperatures 314°C and 343°C is owing to the decomposition of 4-methyl-3-nitrobenzoic acid into carbon dioxide (CO2). The DTA curve of the thermogram shows three exothermic peaks in which the first peak at 83°C corresponds to the removal of ethanol and the second peak at 123°C was owing to the removal of water. At last the third exothermic peak exhibits a major decomposition (89%) of the substance at 327°C. The high crystallinity of the crystal is identified by the sharpness of its peak. The thermal stability of the grown compound is compared with other compound and it is given in Table 6. 3.7. LDT study Laser damage threshold study (LDT) is one of the most essential factors that can be utilized to analyze the withstanding capacity of the crystal and the laser damage spot decides the application of high intensity induced laser radiation [44]. A Q-switched high energy Nd: YAG laser (λ=1064 nm) operating in EPM2000 was used as the source, with pulse width 6 ns and repetition rate of 10 Hz. The pace of thermal conduction across the atomic lattice in the long pulse reign (τ > 100 ps) as well as optical breakdown and different nonlinear ionization mechanisms become important in the short pulse reign (τ < 100 ps) are controlling the damage that occurs in the crystal [45]. The crystal was attached on an X-Y translator that enables in bringing various areas of the material for exposure to the laser. The onset damage can be noticed. The output intensity of the laser beam was measured with a variable attenuator and the pulse energy of the shot was calculated utilizing the grouping of the phototube and oscilloscope. The LDT value was derived from the subsequent expression,

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Power density (Pd) =

E r 2

(6)

where E is the intensity of the irradiated laser beam in mJ, r is the radius of the spot in mm and τ is the pulse width in nanosecond. The LDT value of the Na4M3N crystal is endowed to be 5.8 GW/cm2 and this value was compared with some important NLO crystals and it is specified in Table 7 [44, 12 and 46]. The LDT analysis divulges that the Na4M3N crystal can tolerate the laser beam which has a higher power of up to 5.8 GW/cm2. From the results, it can be concluded that the crystal possesses good laser damage tolerance. Thus, the Na4M3N crystal is useful for high power laser applications [47]. 3.8. Photoluminescence (PL) analysis As the energies of the emission peaks are inferior to the band gap energy, the observed PL is not connected to a direct transition amid the valence and conduction bands. Hence it could be related to the radiative recombination connecting the trapped electrons and holes which occur amid localized states located in the band gap [48]. The PL emission spectrum was traced by utilizing Jobin Yvon Fluoromax-4-Spectrofluorometer (Horiba, USA) with an excitation wavelength of 300 nm. Two emission peaks were noticed in Fig.11 (a), one at 423 and the other 471 nm. The peak that arises at 423 nm is due to defects in the crystal which are attributed to mechanical disturbance during the growth process. The emission peak, which is sharp at 471 nm, is assigned to blue emission. The PL emission of the Na4M3N crystal may find applications in blue light emitting diodes and the sharp peak indicates the crystalline quality of the crystal. To understand the emission of the crystal visualized from CIE diagram and it can be utilised in the display devices. The CIE chromaticity coordinates were determined (x = 0.1285, y = 0.1069) using the emission spectra and the colour regime was mentioned with a ‘circle’ in the chromaticity graph in Fig. 11(b). From the diagram, one can observe that the tile compound has blue emission.

17

3.8.1. Lifetime (τ) analysis For prolific utilization of the material for any realistic application, it is vital to identify the lifetime of the excited states [49]. The Time-Correlated Single Photon Counting system was utilized to calculate the lifetime profile [37]. The decay time spectrum of the Na4M3N crystal is displayed in Fig.12 (a). Generally, the decay curve is multi-exponential in nature with fast and slow decay components. However, in a recent study it could be analysed as twoexponential or ‘biexponential’ [50]. Therefore, the real behaviour of the decay curve can be written as, F (t) = B1 e−t/τ1 + B2 e−t/τ2

(7)

where, τ1 is a constant corresponding to fast decay (Prompt) and τ2 slow decay (Delayed). B1 and B2 are the co-efficients that signify the percentage of the fast and slow decay components, respectively. The decay constants for prompt and delayed components have been determined by the curve fitting method and the values are endowed to be 7.18 ns (35.46%) and 28.7 ns (64.54%). The inset of Fig.12 (b) illustrates the residual fitting which indicates the best fit with reference to the actual data. The perfectness of the curve fit could be measured from the residuals, and the value of the reduced non-zero second-order molecular polarizability (χ2=1.22) ratio. Hence, the smaller lifetime value of the molecules in the compound Na4M3N proves it the good crystalline nature with lesser defects [51]. 3.9. Third-order nonlinear studies The Na4M3N crystal is subjected to optical nonlinearity measurement (Z-scan technique) and it is utilized to establish the sign and magnitude of susceptibility of third-order nonlinear. The experiment is executed utilizing a 532 nm continuous wave (CW) Nd: YAG (4.5 kW/cm2) laser beam attentive by a lens of focal length (3.5 cm) and also by translating a crystal during the beam waist. The equivalent transmitted intensity throughout the sample was gathered by a photo-detector and it was measured by a digital power meter. Based on the

18

relation between laser wavelength and band gap, the third-order nonlinear optical response can be divided into two types, i.e., resonant third-order nonlinear optical response [52] and non-resonant third-order nonlinear optical response [53]. The 633 nm (1.96 eV) wavelength is closer to the quasidirect band gaps of 1.43 eV than that of 532 nm (2.33 eV). In our experiment we have used 532 nm. Relatively, laser wavelength at 633 nm is much closer to the resonant band gap while non-resonance absorption occurs at 532 nm. The non-resonant third-order nonlinear optical response is considered to be an ultrafast process [26]. The imaginary part of third order nonlinear susceptibility (Imχ(3)) related with the nonlinear absorption can be calculated from open aperture (OA) curve. The real third order nonlinear susceptibility (Reχ(3)) is calculated from the division of the “closed aperture (CA)” by the “OA” Z-scan traces, which are connected to the nonlinear refraction of the compound. If the nonlinear absorption transmittance is the minimum around the focal point, it corresponds to positive which is owing to the reverse saturable absorption, and if the transmittance is the maximum around the focal point, it is negative and it is owing to the saturable absorption response [54]. Basically the nonlinear refraction is a “valley-peak” that corresponds to positive (self focusing) and the “peak-valley” corresponds to a negative (self-defocusing) response [55]. In Fig.13 (a, b and c), the scattered circles represent the experimental data and the solid line represents the theoretical fit as proposed by Sheik-Bahae. The normalized transmittance of the CA as a function of the sample position and nonlinear refractive index is theoretically evaluated by using the relation [56], TCA ( Z ,  o )  1 

where x 

4 x (1  x 2 )(9  x 2 )

(8)

Z is the diffraction length. The OA curve was assessed theoretically by utilizing Zo

the following expression [49],

19



TOA ( Z , S  1)   m 0

 qo (Z ,0)m , q (m  1)

3

2

o



I o Leff  Z2  1  2   Z  o  

(9)

where Z is position of the sample position, qo is the free factor and Zo (= kωo2/2 ) is the Rayleigh duration of the beam. The nonlinear optical coefficients such as nonlinear refractive index, nonlinear absorption coefficient and nonlinear optical susceptibilities are calculated using standard equations, which are being formulated for calculating nonlinear optical coefficients [57]. At a molecular level, χ(3) is directly connected to the second hyperpolarizability, γ, utilizing the following equation: Re  

 

Re  (3) Nf 4

(10)

where N is the number density of the corresponding molecules and f is attributed to the local

 2  2  . The third-order susceptibility field factor of correction which can be estimated by  no  3  (χ(3)) was calculated to be 12.11×10-6 esu and the corresponding second-order hyperpolarizability, γ as 3.233×10-35 esu. The calculated value of the linear refractive index is no = 2.24, and refractive index in nonlinear- is n2 = - 6.70×10-8 cm2/W, absorption coefficient is β = 0.09×10-4 cm/W. The real and imaginary susceptibilities of third-order (χ(3)) values are 12.10 ×10-6 esu and 0.57 ×10-6 esu. These values are compared with the related crystal and they are illustrated in Table 8. This work also aimed at a comparison of different types of lasers as depicted in Table 9. These results support the conclusion that the order of magnitude of third-order nonlinear susceptibility in Na4M3N material obtained from Nd: YAG continuous wave laser is higher than that of MXeneTi3C2Tx, antimonene and Bismuthene [24 - 26]. The MXeneTi3C2Tx, antimonene and Bismuthene third-order nonlinear optical properties are investigated by SSPM (spatial self-phase modulation) experiment. Na4M3N

20

material can be considered as a potential candidate for all optical switching and optical communication applications. The COO- ions act as an electron donating group in the structure of the title compound and it leads to raise the nonlinearity. Third order non-linearity occurs because of non-linear absorption, two photon absorption, saturable absorption, reverse saturable absorption and non-linear refraction. Nonlinear absorption and refraction are strongly associated NLO effects. The non-parametric and parametric mechanisms are responsible to these nonlinearities. The non-parametric mechanisms increase the nonlinear absorption and refraction but the parametric contributions provide small nonlinear response except for intense light pulses [58]. The Im χ(3) > Re χ(3) which means that the contribution of β is more dominant than the n2, is inferred from Fig.13(b) where the peak is larger than that of valley. It has been utilized for a diversity of applications such as waveguide switches, optical switching, optical limiting, optical data processing, optical logic gates and optical communications[59].

3.9.1. Thermo-optic coefficient Thermal diffusivity is the property that specifies how quickly heat is conducted on materials. The value of thermal diffusivity is calculated to be 2.192 × 10-6 m2s-1 by using the Photoacoustic spectrometer and the specific heat capacity (Cp) is determined using the NETZSCH STA 449 F3 Jupiter thermal analyzer and the value at 100oC as 3.0546 Jg-1K-1 and the thermal conductivity (κ) were obtained using thermal diffusivity × specific heat capacity × density. The determined value of κ is 0.1078 W m-1 K-1. When a laser light is passed on the grown material part of the light will be absorbed and the absorbed light is converted into heat, so a temperature gradient is created in the crystal along with thermal

21

expansion. The same amount of heat is absorbed by the material at the time the crystal with a high specific heat has a lesser temperature gradient than a material with a low specific heat having a high temperature gradient. If a crystal has having a large specific heat, then the crystal also has a higher value of damage threshold. In the present case, the value of specific heat is 3.0546 Jg-1K-1 due to this the crystal has high (5.8 GW/cm2) value of the laser damage threshold. The thermo-optic effect in the crystal can be valuable in the production of optical devices like optical switches and couplers. The temperature effective nonlinear refractive index (dn/dT) is given as,

dn 4n2  dT a 2

(11) where, α is the linear absorption coefficient (3.63×102), and ωa is the beam waist radius at the focal point (1.5×102). The thermo-optic coefficient can be positive or negative and a negative sign is due to self-focusing while the positive is due to self-defocusing [60]. The measured value of the thermo-optic coefficient (-3.5 ×10-5 K-1) indicates the self-defocusing effect.

3.10. Optical limiting study The optical limiting behaviour originated due to different nonlinear mechanisms such as two-photon absorption, free carrier absorption, reverse saturable absorption and nonlinear scattering [59]. Optical limiting is a method in which the transmitted intensity from the crystal increases and it remains constant at high input power which can be utilized to shield the eyes from the intensity of high power laser beams. Since the source used to investigate the nonlinear material is a low power continuous wave laser, the optical nonlinearity in Na4M3N crystal observed here is likely to be of thermal origin, arising from the temperature dependence of refractive index [61]. The response time of the material as recorded by an

22

oscilloscope is found to be in millisecond regime, which is to be expected in the case of such nonlinearity [62]. This is executed by placing the Na4M3N crystal at a post focus position and measuring the power over the aperture for diverse incident laser powers and it is depends on aperture limited geometry. The optical limiting plot of Na4M3N crystal is represented in Fig.13(d). The material show very good optical limiting behaviour arising from nonlinear refraction [62]. The defocusing effect appears at a certain threshold value, which results in a more cross sectional region and reduces the relative intensity of the beam passing the aperture. The optical limiting study reveals that at a low power region, the output power increases with an increase in the input power and saturates from the threshold of 38.5 mW. The linear transmission initiates to move away from linearity at high input power of the laser. Therefore, the Na4M3N crystal reveals good limiting input intensity and it is an excellent candidate for photonic applications like optical limiters [63]. 3.11. Mechanical studies For device fabrication quality single crystals are required and NLO properties are always from the more ideal part in single crystals [64]. The quality crystals are necessary not only with a good optical behaviour but with excellent mechanical recital [65]. Vickers microhardness analysis was executed utilizing a Futuretech FM-800 type-E series microhardness instrument to estimate the mechanical strength of the grown crystal and this strength depends purely on the lattice energy, molecular structure and chemical composition of the crystal. Indentations were made on the Na4M3N crystal for the loads ranging from 1 to 100 g. The static indentation was made at ambient temperature with a constant indentation time of 7 s for indentations. The microhardness number (Hv) is ascertained by utilizing the subsequent relation, HV 

1.8544  P  kg   2  d2  mm 

(12)

23

The geometrical feature of the diamond pyramid is noted as 1.8544, diagonal length of the indentation is expressed as d in mm and the load, P in g. The variation Hv with P is presented in Fig.14. From the figure, it is noticed that the HV is increased with rising P up to 100 g, which indicates reverse indentation size effect (RISE) [66]. On increasing the load further, a crack develops on the smooth surface of the crystal and is due to the release of internal stresses created locally by indentation [67]. The relation linking P and d can be determined from the Meyer’s law, P = k1dn, where k1 is a constant and n is the work hardening coefficient or Meyer’s number. The graph is traced amid log P vs. log d (Fig. 15) which furnishes a straight line. The slope of the straight line gives the value of n and is 2.78. According to Onitsch, for a hard material n ˂ 1.6 and for a soft material n ˃1.6 [68]; hence, the grown crystal comes under the soft materials category. The Meyer’s number of the Na4M3N crystal is compared with other compound and it is displayed in Table 6. From the HV, the yield strength of the Na4M3N crystal can be estimated using the relation, for n ˃ 2; then

H 12.5(n  2)   y  V 1  (n  2)  2.9  1  (n  2) 

n2

(13)

If n ˂ 2 then the above relation reduces to

y 

HV 3

(14)

Wooster’s empirical formula can be utilized to estimate the elastic stiffness constant for various loads. C11 = (HV)7/4 and its offering nature of bonding with neighbouring atoms. This is the property by the asset of which it can absorb the maximum energy before the fracture happens in the Na4M3N crystal. The selection of a Na4M3N crystal for device fabrication depends on fracture toughness (Kc) where the load outstrips the limit or yield point. The Kc (g/μm3/2) is given by:

24

Kc 

P

C 

3 2

(15)

where C is the middle of the indentation mark for the cracking tip and β (β=7) is the geometrical constant for the Vickers indenter. The variation of Kc with P is presented in Fig. 16 (a). Brittleness is an imperative property of the crystal which affects the mechanical behaviour and also it provides an idea around the fracture induced in a grown crystal without any detectable deformation. The brittleness index Bi (1/μm1/2) for the various loads was estimated using the relation,

Bi 

HV KC

(16)

Fig.16 (b) represents the dissimilarity of Bi with P for the Na4M3N crystal. The calculated parameters Hv, C11, σy, Kc and Bi are specified in Table 10. 3.12. Chemical etching study Etching study is a significant tool to identify the crystal defects and grain boundaries in the grown crystal [69]. The Na4M3N crystal was tested by a Wilson microhardness instrument with a mixed solvent (water-ethanol) at room temperature using 100 x resolution microscope. The Na4M3N crystal was engrossed in the etchant for 20, 30 and 40 s and the crystal was cleaned with tissue paper. Fig. 17 depicts the etch pit pattern observed for the Na4M3N crystal before etching and with etching times of 20, 30, 40 s. The characteristic of the grown crystal can be understood by evaluating the distribution of dislocations and density of the crystal. The calculated average etch pit density of 3.2  103 cm-2 designates the growth pattern of the crystal with minimum dislocations. 3.13. Impedance analysis Impedance spectroscopy is one of the appropriate tools to investigate the electrical properties of the Na4M3N crystal for a broad range of frequencies. The measurements were

25

executed using an impedance analyzer (Model: CHI604E) with a frequency range of 1 to 500 Hz to determine the impedance of the material. The complex impedance of Z* = Z'- jZ" in which Z' is real and Z" is the imaginary part of the impedance respectively

Z'

Z"

Rg 1  (Rg C g ) 2

Rg 1  (Rg C g )

2





Rgb 1  (RgbC gb ) 2

Rgb 1  (RgbC gb ) 2

(17)

(18)

where ω is the angular frequency, Rg the grain resistance, Rgb the grain boundary resistance, Cg the grain capacitance and Cgb the grain boundary capacitance. Fig.18 (a&b) depicts the dissimilarity of real and imaginary part of impedance with frequency. It shows that Z' decreases with the rise in frequency, symbolizing the increasing conductivity with frequency [70]. The high value of Z' at low frequency shows low ion mobility in the crystal and this may result in better NLO characteristics of the sample [71]. The value of Z" increases up to 1.48 Hz which is assumed to be the relaxation frequency and on further increase of frequency Z'' gradually decreases which is due to the immobile charges exhibited by the sample [72]. 3.13.1. Dielectric studies The dielectric property of the Na4M3N crystal furnishes a lucid insight into the lattice dynamics, molecular dynamics, molecular anisotropy and electro-optical properties [73]. Various polarization and electrical processes in the crystal were displayed by analysing the dielectric behaviour with frequency. Thus, for the present work, the dielectric constant (') as well as dielectric loss (tan ) is calculated using the given below relation:

 '

" t Z" t Z' . 2 . 2 ,  " , tan   2 2 ' A 0 Z '  Z " A 0 Z '  Z "

(19)

26

where A and t represent the cross section and thickness of the pellet respectively. The dielectric constant and tan  with frequency is displayed in Fig.19 (a and b). From the figure, it is observed that the value of ' and tan  decreases with increasing frequency and become almost constant at high frequency. The high value of ' at low frequency is due to the different polarization mechanisms, i.e. space charge, orientation, electronic and ionic polarization. At high frequency, the ' value is low which is owing to the consequence of the loss of any of these polarizations steadily. The low values of dielectric loss at high frequencies suggest that the Na4M3N crystal possesses improved optical quality with lesser defects which is a crucial parameter for NLO applications [74]. The σac (a.c conductivity) of the Na4M3N crystal was calculated utilizing the following equation,

 ac 

t Z' . 2 A Z '  Z "2

(20)

The increase of conductivity with increase in frequency displayed in Fig.20 is owing to the charge carrier hopping pace and dispersion. 3.13.2. Electric modulus analysis The electrical transport phenomena like carrier hopping pace and conductivity relaxation of the materials can be investigated by the complex modulus spectroscopy. The electric modulus of the complex is given as follows, M* = M' + jM''

(21)

The real and imaginary values of the modulus are calculated from the following relation, M '

'  '  "2

(22)

M "

"  '  "2

(23)

2

2

27

It can be noticed from Fig.21 (a), that at low frequency M' is approximately zero and M' increases with frequency up to 214.8 Hz and then decreases on further increase of frequency. This type of variation can be understood as; at a low frequency region, electrode polarization is active and the charge carriers are able to move within a long range regime under the influence of the applied electric field. Also, due to the lack of restoring force, M' attains the minimum value at room temperature. Fig. 21 (b) illustrates that the imaginary part of the modulus (M'') shows broad and asymmetric crests, which signify the non-Debye type relaxation. 4. Conclusion A metal-organic NLO crystal was synthesized and successfully grown from an ethanol-water (1:1) solvent by the slow cooling technique. PXRD pattern shows the quality of the compound. The lattice parameters and crystal structure of the Na4M3N crystal were attained from a single crystal XRD. The modes of vibration in the title compound are established from the vibrational analysis. The

13

C and 1H predicts the chemical structure of

the Na4M3N compound. The 2-dimensional fingerprint analysis revealed that the H…H and C…H interactions are more dominant in the Na4M3N compound. An optical study showed the crystal having a transparency of about 69% with lower cut-off wavelength around 254 nm and the optical band gap is endowed to be 5.06 eV. TG-DTA analysis reveals the Na4M3N material decomposition starts from 79oC. The value of LDT of the Na4M3N crystal is 5.8 GW/cm2 which is superior to that of standard materials (KDP and urea). The PL spectrum explains that the Na4M3N crystal is suitable for blue light emitting diodes. The prompt and delayed values are calculated with the help of the lifetime measurement. The nonlinear absorption coefficient (β = 0.09×10-4 cm/W) and n2 = -6.70×10-8 cm2/W were determined from the third-order nonlinear studies. The thermal conductivity and specific heat capacity of the Na4M3N crystal suggests the possibility of a high laser damage threshold. Optical

28

limiting study demonstrates the low value of the laser threshold, which is desirable for optoelectronic and device applications. The mechanical measurement itemizes the variation of the hardness number, stiffness constant, yield strength, crack toughness and brittleness index with the applied load. The determined etch pit density values (3.2  103 cm-2) specify the minimum dislocations in the Na4M3N crystal. The electric property of the crystal is elucidated from the complex impedance analysis. The low values of the dielectric constant and loss at high frequency imply that this material can be utilized for the manufacture of photonic and electro-optic devices. Hence from the observations the Na4M3N crystal can well be utilized for NLO applications. Acknowledgment The author (M. Divya Bharathi) thanks the University Grants Commission, New Delhi for providing financial support (UGC-NFOBC-63129 dated 01-04-2017). References [1] R.Medishetty, J.K. Zaręba, D. Mayer, M. Samoć, and R.A.Fischer, Chem. Soc. Rev. 46(16) (2017) 4976-5004. [2] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic molecule and crystals, Academic Press, New York, 2012. [3] M. Marinescu, Synthesis and Nonlinear Optical Studies on Organic Compounds in LaserDeposited Films, Appl. Surf. Sci. Intech Open, 2018. [4] M.Thangaraj, G. Ravi, T.S Girisun, G.Vinitha, and A. Loganathan, Spectrochim. Acta A Mol. Biomol. Spectrosc. 138 (2015) 158-163. [5] Y.R. Shen, The Principles of Nonlinear Optics, Wiley, New York, 1984. [6] M.S. Kajamuhideen, K. Sethuraman, K.Ramamurthi, and P. Ramasamy, J. Cryst. Growth 483 (2018) 16-25.

29

[7] B. Uma, Rajnikant, K. Sakthi Murugesan, S. Krishnan, B. Milton Boaz, Prog. Nat. Sci. 24 (2014) 378–387. [8] A Subashini, K Rajarajan and Suresh Sagadevan, Mater. Res. Express 4 (2017) 026202. [9] R. Masse, J. Zyss, J. Mol. Eng 1 (1991) 141-152. [10] A. Arunkumar, P. Ramasamy, K.Vishnu, M. K. Jayaraj, J. Mater. Sci., 49(10) (2014) 3598-3607. [11] O.D.Tyagi, M. Yadav, Text Book of Synthetic Drugs. Fifth Edition, Anmol Publications, New Delhi, 1990. [12] M. Divya Bharathi, G. Ahila, J. Mohana, G. Chakkaravarthi, G.Anbalagan, J. Phys. Chem. Solids 98 (2016) 290–297. [13] C.Ramki, R.Ezhil Vizhi, Mater. Chem. Phys. 197 (2017) 70-78. [14] L.Guru Prasad, V.Krishnakumar, R.Nagalakshmi, Spectrochim. Acta, Part A: Mol Biomol Spectrosc. 110 (2013) 377-382. [15] P.S. Latha Mageshwari, R. Priya, S. Krishna, V. Joseph, S. Jerome Das, Opt. Laser Technol. 85 (2016) 66-74. [16] R. Ezhil Vizhi, J. Cryst. Growth 452 (2016) 184-188. [17] F. Edhokkar, A. Hadrich, T. Mhiri, M. Graia, J. Mol. Struct. 1059 (2014) 260-264. [18] R. Omegala Priakumari, D. Grace Sahaya Sheba, M. Gunasekaran, J. Mol. Struct. 1102 (2015) 63-70. [19] E. Selvakumar, Maria Susai Boobalan, S. Anthuvan Babu, S. Ramalingam, A. Leo Rajesh, J. Mol. Struct. 1125 (2016) 1-11. [20] W. Zhao, J. Mol. Struct. 1127 (2017) 252-256. [21] C. Amuthambigai, C.K. Mahadevan, X. Sahaya Shajan, Curr. Appl. Phys. 16 (2016) 1030-1039.

30

[22] Xiantao Jiang, Liangjing Zhang, Shunxiang Liu, Yiyue Zhang, Zhiliang He, Wenjia Li, Feng Zhang, Yihuang Shi, Wei Lü, Yu Li, Qiao Wen, Jiagen Li, Jun Feng, Shuangchen Ruan, Yu-Jia Zeng, Xi Zhu, Yuerui Lu, and Han Zhang, Adv. Optical Mater. 2018, 1800561 – 11. [23] Yanqi Ge, Zhengfeng Zhu, Yanhua Xu, Yunxiang Chen, Si Chen, Zhiming Liang, Yufeng Song, Yousheng Zou, Haibo Zeng, Shixiang Xu, Han Zhang, and Dianyuan Fan, Adv. Optical Mater. (2018) 1701166 - 10. [24] Xiantao Jiang, Shunxiang Liu, Weiyuan Liang, Shaojuan Luo, Zhiliang He, Yanqi Ge, Huide Wang, Rui Cao, Feng Zhang, Qiao Wen, Jianqing Li, Qiaoliang Bao, Dianyuan Fan, and Han Zhang, Laser Photonics Rev. (2017) 1700229 - 10 [25] Lu Lu, Zhiming Liang, Leiming Wu, YunXiang Chen, Yufeng Song, Sathish Chander Dhanabalan, Joice Sophia Ponraj, Biqin Dong, Yuanjiang Xiang, Feng Xing, Dianyuan Fan, and Han Zhang, Laser Photonics Rev. (2017) 1700221. [26] L. Lu, X. Tang, R. Cao, L. Wu, Z. Li, G. Jing, B. Dong, S. Lu, Y. Li, Y. Xiang, J. Li, D. Fan and H. Zhang, Adv. Optical. Mater. (2017) 1700301 - 9 [27] L.J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849-854. [28] C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P. Shields, R. Taylor, M. Towler and J. van de Streek, J. Appl. Cryst., 39 (2006) 453-457. [29] R.L. Frost, J. Kristof, G.N. Paroz, and J.T. Kloprogge, J. Colloid Interface Sci,208 (1) (1998) 216-225. [30] M. Divya Bharathi, G. Ahila, J. Mohana, G. Chakkaravarthi, G. Anbalagan, Mater. Chem. Phys. 192 (2017) 215 - 227. [31] D.Lin-Vien, N.B. Colthup, W.G.Fatley, J.G.Grassselli, The Hand book of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academic Press, New York, 1991.

31

[32] R.A. Nuquist, R.O. Kagel, The Handbook of Infrared and Raman Spectra of Inorganic Compounds, Chemical physics research laboratory, New York, 1971. [33].

S.K.Wolff,

D.J.Grimwood,

J.J.McKinnon,

M.J.Turner,

D.Jayatilaka

and

M.A Spackman, Crystal Explorer Version 3.0 (Perth: University of Western Australia) 2012. [34] S.K. Seth, N.C.Saha, S.Ghosh and T.Kar, Chem. Phys. Lett. 506 (2011) 309-314. [35] S. Sudha, M. Peer Mohamed, G. Vinitha, C. Rathika Thaya Kumari, P. Sangeetha, M. Lydia Caroline, Chinese J. Phys. 57 (2019) 211–225. [36] M.K. Gupta, N. Sinha, B. Kumar, Physica B: Condensed Matter, 406 (1) (2011) 63 - 67. [37] S. Kandhan, B. Tamil Arasan, P. Krishnan, S. Aravindhan, S. Srinivasan, S. Gunasekaran, J. Mol. Struct. 1180 (2019) 512-522. [38] Bayram Gunduz, Polym.Bull.72 (2015) 3241-3267. [39] A. Cusano, A. Iadicicco, D. Paladino, S. Campopiano, A. Cutolo, M. Giordano, Opt. Fiber Technol. 13 (2007) 291–301. [40] T. Kohoutek, J. Orava, T. Sawada, H. Fudouzi, J. Colloid. Interface Sci. 353 (2011) 454458. [41] W.F.Ho, M.A.Uddin, H.P.Chan, Polym. Degrad. Stab. 94 (2009) 158–161. [42] R.R. Reddy, Y. Nazeer Ahammed, K. Rama Gopal, D.V. Raghuram, Opt. Mater. 10 (1998) 95–100. [43] J.A. Duffy, Phys. C 13 (1980) 2979-2989. [44] G.C. Bhar, A.K. Chaudhary, P. Kumbhakar, Appl. Surf. Sci. 161 (2000) 155-162. [45] RO.MU. Jauhar, S. Kalainathan, P. Murugakoothan, J. Cryst. Growth 424 (2015) 42-48. [46] P. Mythili, T. Kanagasekaran, Shailesh N. Sharma, R. Gopalakrishnan, J. Cryst. Growth 306 (2007) 344 – 350. [47] P. Karuppasamy, Muthu Senthil Pandian, P. Ramasamy, Sunil Verma, Opt. Mater. 79 (2018) 152 – 171.

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[48] G. Shanmugam, S. Brahadeeswaran, Spectrochim. Acta Part A 95 (2012) 177-183. [49] Sonia, N. Vijayan, Mahak Vij, Kanika Thukral, Naghma Khan, D.Haranath, Rajnikant, M.S. Jayalakshmy, Chin. J. Chem. Eng, 27 (2019) 701-708. [50] N. Vijayan, J. Philip, D. Haranath, B. Rathi, G. Bhagavannarayana, S.K. Halder, N. Roy, M.S. Jayalakshmy, S. Verma, Spectrochim. Acta A: Mol Biomol Spectrosc. 122 (2014) 309 – 314. [51] N. Durairaj, S. Kalainathan, M.V. Krishnaiah, Mater. Chem. Phys., 181 (2016) 529-537. [52] T. Sakai, Y. Kawabe, H. Ikeda, R. Hasegawa, K. Kawasaki, in Conf. on Lasers & Electro-Optics, Optical Society of America, Baltimore, 26 (19930 303. [53] A. Faccinetto, S. Mazzucato, D. Pedron, R. Bozio, S. Destri, W. Porzio, Chem. Phys. Chem. 9 (2008) 2028. [44] K. Iliopoulos, I. Guezguez, A.P. Kerasidou, A. El-Ghayoury, D. Branzea, G. Nita, N. Avarvari, N., H. Belmabrouk, S. Couris, B. Sahraoui, Dyes Pigm. 101 (2014) 229-233. [45] B.Kulyk, A.P. Kerasidou, L. Soumahoro, C. Moussallem, F.Gohier, P. Frère, B. Sahraoui, RSC Adv. 6(18) (2016) 14439-14447. [46] F.L.S. Cuppo, A.M. Figueiredo Neto, S.L. Gomez, P. Palffy-Muhoray, J. Opt. Soc. Am. B 19 (2002) 1342-1348. [47] M. Saravanan, T.C. Sabari Girisun, G. Vinitha, J. Mater. Sci. 51 (2016) 3289- 3296 [58] G. De la Torre, M. Nicolau, and T.Torres, Supramolecular Photosensitive and Electroactive Materials, 2001, 1–111. [59] B. Thirumalaiselvam, R. Kanagadurai, D. Jayaraman, V. Natarajan, Opt. Mater., 37 (2014) 74–79. [60] D.E. Gray, ed., The American Institute of Physics Handbook, Section 6b, McGraw-Hill, New York 1972, 6-12.

33

[61] Ramamurthy, N., Dhanuskodi, S., Manjusha, M.V. and Philip, J., Opt. Mater. 33(4) (2011) 607-612. [62] Kaladevi Sendhil, C. Vijayan, M.P. Kothiyal, Opt. Mater. 27 (2005) 1606–1609. [63] N.P. Rajesh, V. Jabha Ananthi, G. Vinitha, J. Cryst. Growth 511 (2019) 25-32. [64] M.Saravanan, A.Senthil, S.Abraham Rajasekar, Opt. Mater. 48 (2015) 226 - 232. [65] J.N. Sherwood, Pure Appl. Opt. 7 (1998) 229–238. [66] V.Revathi, K. Karthik, J. Mater. Sci. Mater. Electron 29(20) (2018) 17323-17332.

[67] T. Uma devi, N. Lawrence, R. Ramesh Babu, K. Ramamurthi, J. Cryst. Growth 310 (2008) 116-123. [68] E.M. Onitsch, Mikroskopie, 95 (1956) 12-14. [69] L. Chandra , J. Chandrasekaran, , K. Perumal , B. Babu , V. Jayaramakrishnan, Mater Sci-Poland, 35(1) (2017) 126-134. [70] R.Gomathi, S. Madeswaran, D.Rajan Babu, Mater. Chem. Phys. 207 (2018) 84-90. [71] G.Emerson Robin, U.Sankar, T.Chithambarathanu, P.Selvarajan, Int. J. Innov. Res. Adv. Eng. 2 (2015) 195-199. [72] T. Badapanda, R.K. Harichandan, S.S. Nayak, A.Mishra, S. Anwar, P. Appl. Ceram. 8 (2014) 145-153. [73] N.R. Rajagopalan, P. Krishnamoorthy, K. Jayamoorthy, J. Inorg. Organomet. Polym. Mater. 27 (2017) 739 - 756. [74] P.S. Latha Mageshwari, R. Priya, S. Krishnan, V. Joseph, S. Jerome Das, Optik 125 (2014) 2289 – 2294.

34

14

Concentration (g/100 ml)

Ethanol-Water (1:1)

12

10

8

6 30

35 40 o Temperature ( C)

Fig.1. Solubility curve of Na4M3N crystal

45

35

Fig.2 (a). Photograph and (b) Morphology of Na4M3N crystal

36

(200)

5000

3000

(303)

(412)

(302) (-610)

(112) (501)

(-300) (-211) (301)

1000

(-411)

2000

(111)

Intensity (a.u)

4000

0 10

15

20

25

30

35

2 (degree)

Fig.3(a). Powder XRD pattern for Na4M3N crystal

40

37

Fig.3 (b) ORTEP diagram for Na4M3N compound drawn at 50% probability level showing the asymmetric unit

38

Fig. 3 (c). The coordination of Na (I) atom with five oxygen atoms in the crystal structure for Na4M3N crystal

0 3500 1602

3000 1353

791

1492

100

1500

-1

1000

Wavenumber ( cm )

Fig.4. FT-IR spectrum for Na4M3N compound 520

1204 1161 1139 1075 1026 940 915 862 826 755 706 677 635

1267

2929

2996 2963

60

1403 1385

3260 3106 3073

40 1652

3381

80

1555 1524

20 3596

Transmittance (%)

39

Na4M3N

500

40

Na4M3N

1358

0.30

84 1206 1163 1145 1080 1001 919 828 741793 706 671 632 519 484 354 280 184 145

1263

1519 1445

2965

0.05

1306

1406 1615

0.10

1549

3035

0.15

1380

1593 2995 2930

0.20

3080

Intensity (a.u)

0.25

0.00 3500

3000

1500

1000

500

-1

Wavenumber (cm ) Fig.5.Raman spectrum of Na4M3N crystal recorded at room temperature

41

Fig.6(a). Proton NMR of Na4M3N crystal

42

Fig. 6(b). Carbon NMR of Na4M3N crystal

43

Fig.7(a) Hirshfeld surface and (b) 2D fingerprint plot of Na4M3N compound

44

80

(a)  =254 nm cut 750

(b)

2

600 h (0 ) (eV/m)

450

-6

40



Transmittance (%)

60

300 150

20

5.06 eV

0 2

0 200

300

400

3 4 Photon energy (eV)

500

600

700

5

800

Wavelength (nm)

Fig.8 (a) Uv-vis transmittance spectrum (b) Tauc’s plot of Na4M3N crystal

45

(a) 2.8

Refractive index (n)

Reflectance (a.u)

0.3

0.2

0.1

(b)

2.6 2.4 2.2 2.0 1.8

300

400

500

600

700

800

Wavelength (nm)

0.0 300

400

500

600

700

800

Wavelength (nm) Fig.9 (a & b). Reflectance and refractive index of Na4M3N crystal

79 C o 127 C

46

o

TGA DTA

o

o

80

0.8

60 0.6 0.4

o

o

83 C 123 C

40

20

0.2 0.0

0 0

200

400

600

800

o

Temperature ( C)

Fig.10. TG-DTA trace of Na4M3N compound

1000

DTA (mW/mg)

Endo

Mass (%)

1.2 1.0

343 C

100

314 C

o

327 C

47

1.2 Na4M3N 471 nm

6

Intensity (10 ) (a.u)

1.0 0.8 0.6 0.4 0.2

423 nm

0.0 300

350

400

450

500

550

Wavelength (nm)

Fig.11(a). PL spectrum of Na4M3N crystal excited at 300 nm

48

Fig.11(b). The CIE chromaticity diagram for Na4M3N crystal under the excitation of 300 nm

49

12000 (a)

Residuals

10000

Prompt4 Decay Fit 2

Counts

8000 6000

(b)

0 -2

4000

-4

200

400

600

800

1000

Time (ns)

2000 0 0

200

400

600

800

Time (ns) Fig.12 (a) Lifetime spectrum (b) residual fit of Na4M3N crystal

1000

50

1.12

Experimental Theoretical

Normalized transmittance

1.10 1.08 1.06 1.04 1.02 1.00 -15

-10

-5

0

5

Z (mm) Fig. 13(a). Open aperture for Na4M3N crystal

10

15

51

Normalized transmittance

1.5

Theoretical Experimental

1.2

0.9

0.6

0.3

0.0 -15

-10

-5

0

5

Z (mm) Fig.13 (b). Closed aperture for Na4M3N crystal

10

15

52

Experimental Theoretical

Normalized transmittance (a.u)

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -15

-10

-5

0

5

10

Z (mm)

Fig.13(c). Ratio of Z-scan data for Na4M3N crystal

15

53

350 Na4M3N

Output power (mW)

300 250 200 150 100 50 0 0

5

10

15

20

25

30

Input power (mW)

Fig.13(d). Optical limiting for Na4M3N crystal

35

40

45

54

2

Hardness number (HV) (kg/mm )

300

250

200

150

100

50 0

20

40

60

80

100

Load P (g) Fig.14. Variation of hardness number with applied load for Na4M3N crystal

55

2.0

n = 2.78 2 R =0.9978

Na4M3N Linear fit

log P

1.5

1.0

0.5

0.0 0.75

0.90

1.05

1.20

1.35

log d Fig.15. Plot of log P vs log d for Na4M3N crystal.

1.50

56

1800 3/2

)

(b)

Brittleness index Bi (m

-1/2

)

Fracture toughness KC(g/m

1500 1200 900 600

(a)

4 3 2 1 0

300

0

20

40

60

80

100

Load P (g)

0 0

20

40

60

80

100

Load P (g)

Fig. 16 (a). The variation of Kc and (b) Bi with applied load of Na4M3N crystal

57

Fig.17. Etch pattern produced on the Na4M3N crystal (a) Before etching (b) 20 s (c) 30 s (d) 40 s

58

(a) 800

800 (b)

600

Z' ()

Z'' ()

600

400

400 200 0 0.5

200

1.0

1.5

2.0 2.5 log Hz)

3.0

3.5

0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

log  (Hz) Fig.18(a) Real and (b) imaginary part of impedance versus log ω for Na4M3N crystal

59

80 1.5 Dielectric loss

(a)

Dielectric constant

60

(b)

1.2 0.9 0.6 0.3 0.0

40

0.5

1.0

1.5

2.0

2.5

3.0

3.5

log z)

20

0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

log (Hz)

Fig.19. Variation of (a) dielectric constant and (b) dielectric loss with frequency

60

-2.1 -2.4

-1

-1

logac ( m )

-2.7 -3.0 -3.3 -3.6 -3.9 1.0

1.5

2.0

2.5

3.0

3.5

log  (Hz)

Fig.20. Variation of ac conductivity with log ω for Na4M3N crystal

61

0.025

0.20

(b)

(a)

M'' ()

0.15

0.10

M'()

0.020 0.015 0.010 0.005 0.000

1.0

1.5

0.05

2.0 2.5 log z

3.0

3.5

0.00 1.0

1.5

2.0

2.5

3.0

3.5

log z) Fig.21. (a) Real and (b) imaginary part modulus plot of Na4M3N crystal

62

Table 1. Crystal data and structure refinement for Na4M3N Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions

Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection

Index ranges Reflections collected Independent reflections Completeness to theta = 24.998° Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole

Na4M3N C8 H8 N Na O5 221.14 293(2) K 0.71073 Å Monoclinic P21/c a = 16.77860(10) Å α= 90°. b = 7.95080(10) Å β=95.252(10)°. c = 6.8669(4) Å γ= 90°. 3 912.22(5) Å 4 1.610 Mg/m3 0.173 mm-1 456 0.350 x 0.250 x 0.250 mm3 2.438 to 24.998° -19<=h<=19, -9<=k<=9, -8<=l<=8 13235 13235 99.80% semi-empirical from equivalents 0.7466 and 0.6506 Full-matrix least-squares on F2 13235 / 3 / 143 1.133 R1 = 0.0540, wR2 = 0.1501 R1 = 0.0620, wR2 = 0.1557 n/a 0.391 and -0.318 e.Å-3

63

Table 2. Bond lengths [Å] and angles [°] for Na4M3N Atoms

Length

Atoms

Length

Atoms

Length

C(1)-C(6) C(1)-C(2)

1.371(5) 1.395(5)

C(7)-O(4) C(7)-O(3)

1.245(4) 1.258(4)

Na(1)-O(5) Na(1)-O(3)

2.325(4) 2.424(3)

C(1)-N(1) C(2)-C(3) C(2)-C(8) C(3)-C(4) C(3)-H(3) C(4)-C(5) C(4)-H(4) C(5)-C(6)

1.468(5) 1.386(6) 1.500(5) 1.373(5) 0.9300 1.383(5) 0.9300 1.379(5)

C(7)-Na(1)1 C(8)-H(8A) C(8)-H(8B) C(8)-H(8C) N(1)-O(1) N(1)-O(2) O(3)-Na(1) O(3)-Na(1)

3.018(4) 0.9600 0.9600 0.9600 1.217(5) 1.219(5) 2.424(3) 2.461(3)

Na(1)-O(4) Na(1)-O(3) Na(1)-C(7) Na(1)-Na(1) Na(1)-Na(1) Na(1)-Na(1) Na(1)-Na(1) O(5)-H(5A)

2.446(3) 2.461(3) 3.018(4) 3.549(3) 3.704(3) 4.0313(6) 4.0313(6) 0.81(4)

C(5)-C(7) C(6)-H(6)

1.504(5) 0.9300

O(4)-Na(1) O(4)-Na(1)

2.325(3) 2.446(3)

O(5)-H(5B) -

0.84(4) -

Atoms

Angles

Atoms

Angles

Atoms

Angles

C(6)-C(1)-C(2) C(6)-C(1)-N(1) C(2)-C(1)-N(1) C(3)-C(2)-C(1) C(3)-C(2)-C(8)

124.0(3) 116.3(3) 119.7(3) 114.8(3) 120.4(4)

H(8B)-C(8)-H(8C) O(1)-N(1)-O(2) O(1)-N(1)-C(1) O(2)-N(1)-C(1) C(7)-O(3)-Na(1)

109.5 123.2(4) 118.9(4) 117.8(4) 105.7(2)

O(3)-Na(1)-Na(1) C(7)-Na(1)-Na(1) O(4)-Na(1)-Na(1) O(5)-Na(1)-Na(1) O(3)-Na(1)-Na(1)

134.01(10) 120.49(10) 116.99(10) 117.70(13) 41.06(7)

C(1)-C(2)-C(8)

124.8(4)

C(7)-O(3)-Na(1)

121.4(2)

O(4)-Na(1)-Na(1)

135.94(10)

C(4)-C(3)-C(2) C(4)-C(3)-H(3) C(2)-C(3)-H(3) C(3)-C(4)-C(5) C(3)-C(4)-H(4) C(5)-C(4)-H(4) C(6)-C(5)-C(4) C(6)-C(5)-C(7)

122.3(4) 118.8 118.8 121.2(3) 119.4 119.4 118.1(3) 120.6(3)

Na(1)-O(3)-Na(1) C(7)-O(4)-Na(1) C(7)-O(4)-Na(1) Na(1)-O(4)-Na(1) O(4)-Na(1)-O(5) O(4)-Na(1)-O(3) O(5)-Na(1)-O(3) O(4)-Na(1)-O(4)

98.63(11) 144.1(3) 119.5(2) 96.09(11) 101.79(14) 132.05(12) 126.08(14) 83.91(11)

O(3)-Na(1)-Na(1) C(7)-Na(1)-Na(1) Na(1)-Na(1)-Na(1) O(4)-Na(1)-Na(1) O(5)-Na(1)-Na(1) O(3)-Na(1)-Na(1) O(4)-Na(1)-Na(1) O(3)-Na(1)-Na(1)

40.31(7) 57.64(8) 142.42(11) 49.05(8) 144.18(12) 85.07(9) 102.65(9) 68.06(8)

C(4)-C(5)-C(7) C(1)-C(6)-C(5) C(1)-C(6)-H(6) C(5)-C(6)-H(6)

121.3(3) 119.5(3) 120.2 120.2

O(5)-Na(1)-O(4) O(3)-Na(1)-O(4) O(4)-Na(1)-O(3) O(5)-Na(1)-O(3)

92.32(13) 95.58(11) 91.34(11) 96.87(13)

C(7)-Na(1)-Na(1) Na(1)-Na(1)-Na(1) Na(1)-Na(1)-Na(1) O(4)-Na(1)-Na(1)

107.92(10) 73.83(6) 72.27(6) 141.03(11)

64

O(4)-C(7)-O(3) O(4)-C(7)-C(5) O(3)-C(7)-C(5) O(4)-C(7)-Na(1) O(3)-C(7)-Na(1) C(5)-C(7)-Na(1) C(2)-C(8)-H(8A) C(2)-C(8)-H(8B)

124.2(4) 117.8(3) 118.0(3) 80.1(2) 50.62(19) 149.8(2) 109.5 109.5

H(8A)-C(8)-H(8B) 109.5 C(2)-C(8)-H(8C) 109.5 H(8A)-C(8)-H(8C) 109.5

O(3)-Na(1)-O(3) O(4)-Na(1)-O(3) O(4)-Na(1)-C(7) O(5)-Na(1)-C(7) O(3)-Na(1)-C(7) O(4)-Na(1)-C(7) O(3)-Na(1)-C(7) O(4)-Na(1)-Na(1)

81.37(11) 170.36(12) 150.59(12) 105.70(13) 23.65(9) 84.73(10) 95.54(11) 43.26(8)

O(5)-Na(1)-Na(1) O(3)-Na(1)-Na(1) O(4)-Na(1)-Na(1) O(3)-Na(1)-Na(1) C(7)-Na(1)-Na(1) Na(1)-Na(1)-Na(1) Na(1)-Na(1)-Na(1) Na(1)-Na(1)-Na(1)

54.80(10) 79.30(8) 68.37(8) 119.62(10) 55.71(8) 104.79(8) 101.94(7) 160.90(9)

O(5)-Na(1)-Na(1) 99.31(13) O(3)-Na(1)-Na(1) 120.39(11) O(4)-Na(1)-Na(1) 40.65(7)

Na(1)-O(5)-H(5A) Na(1)-O(5)-H(5B) H(5A)-O(5)-H(5B)

118(4) 130(4) 109(5)

Symmetry transformations used to generate equivalent atoms: 1)-x+2, y+1/2,-z+3/2 2) x,-y+1/2, z-1/2 3) -x+2,-y,-z+1 4) -x+2,y-1/2,-z+3/2 5) x,-y+1/2,z+1/2 6) -x+2,-y,-z+2

Table 3. Hydrogen bonds for Na4M3N crystal [Å and °] D-H...A

d(D-H)

d(H...A)

d(D...A)

<(DHA)

C(6)-H(6)...O(5)

0.93

2.64

3.501(5)

154.8

O(5)-H(5B)...O(3)7

0.84(4)

1.92(4)

2.758(4)

172(5)

O(5)-H(5A)...O(2)8

0.81(4)

2.18(4)

2.972(5)

170(6)

Symmetry transformations used to generate equivalent atoms: 7) x, y-1, z 8) x,-y-1/2,z+1/2

65

Table 4. FT-IR and Raman wavenumbers for Na4M3N crystal Wavenumbers (cm-1)

Assignments

FT-IR

Raman

3596

-

O-H stretching

3381

-

O-H stretching

3260

-

O-H stretching

3106

3080

C-H asymmetric stretching

3073

3035

C-H symmetric stretching

2996

2995

CH3 asymmetric stretching

2963

2965

C-H stretching

2929

2930

CH3 symmetric stretching

1652

-

HOH bending

1602

1615

COO asymmetric stretching

-

1593

C-N asymmetric stretching

1555

1549

C=C stretching

1524

1519

NO2 asymmetric stretching

1492

1445

C=C stretching

1403

1406

COO symmetric stretching

1380

1380

C-C stretching

1353

1358

NO2 symmetric stretching

-

1306

C-N stretching

1267

1263

C-O stretching

1204

1206

C-H deformation

1161

1163

C-H in palne bending

1141

1145

C-H deformation

1075

1080

C-N symmetric stretching

1026

1001

C-C stretching

940

-

C-C stretching

915

919

C-H in palne bending

862

-

C-H out of plane bending

826

828

C-H out of plane bending

791

793

Libration of water molecule

66

755

741

C-H out of plane bending

706

706

C-H deformation

677

671

C-H in plane bending

635

632

C-NO2 stretching

520

519

Na-O stretching

-

484

Na-OH2 wagging

-

354

C-CH3 in plane bending

-

280

Lattice vibration

-

184

Lattice vibration

-

145

Lattice vibration

-

84

Lattice vibration

Table 5. NMR chemical shifts for Na4M3N compound Assignments

Shift Values (δ) ppm

Assignments

Shift Values (δ) ppm

H-1

8.0775

C-3

111.446

H-2

7.3955

C-4

168.135

H-3

2.500

C-5

125.087

H-4

8.396

C-6

148.82

H2O

3.474

C-7

140.066

C-1

133.832

C-8

19.929

C-2

132.334

DMSO

39.419 - 40.421

67

Table 6. Optical and mechanical properties of sodium related compound

Crystals 4-methyl-3-nitrobenzoic acid [12]

Cut-off wavelength (nm) 404

Band gap (eV) 2.91

Thermal stability (ºC) 184

Meyer’s index number (n) 2.50

295

4.07

125

2.00

256

2.40

119

-

296

4.20

67.69

2.39

221

5.64

94.59

-

290

4.27

249.6

2.40

257

2.81

128

1.50

225

-

318

2.68

254

5.06

79

2.78

Sodium hydrogen oxalate [13] Sodium 2,4-nitrophenolate monohydrate [14] Sodium succinate hexahydrate (β phase) [15] Sodium tetraborate decahydrate [16] Sodium hydrogen maleate trihydrate [18] Sodium para-nitrophenolate para nitrophenol dihydrate [19] Anhydrous sodium formate [21] Na4M3N (Present work)

Table 7 Laser damage threshold values of Na4M3N crystal Crystal

Wavelength (nm)

Reference

1064

LDT value (GW/m2) 0.2

KDP Urea

1064

1.32

[44]

4-methyl-3-nitrobenzoic acid

1064

24.33

[12]

Sodium sulfanilate dihydrate

1064

6.40

[46]

Sodium 4-methyl-3nitrobenzoate monohydrate

1064

5.80

Present work

[44]

68

Table 8. Comparison of NLO results with some sodium related crystals Compound

n2 (cm2/W)

χ(3) (esu) 1.40×10-9

Reference

1.01×10-8

β (cm/W) 1.30×10-3

4-methyl-3-nitrobenzoic acid Sodium succinate hexahydrate

1.26×10-6

0.95×10-4

1.73×10-4

[15]

Sodium hydrogen maleate trihydrate

-5.04×10-11

1.08×10-3

6.35×10-7

[18]

Sodium para-nitrophenolate paranitrophenol dihydrate Anhydrous sodium formate

5.35×10-8

5.00×10-7

1.43×10-8

[19]

-0.55×10-6

2.06×10-2

4.6×10-6

[21]

Sodium tetraborate pentahydrate

1.63×10−8

0.03×10−4

1.21×10−6

[16]

Sodium 4-methyl-3-nitrobenzoate monohydrate

-6.70×10-8

0.09×10-4

12.11×10-6

Present work

[12]

Table 9. Nonlinear refractive index and third order susceptibility values of 2D materials Materials

wavelength (nm)

n2 (cm2/W)

χ(3) (esu)

Reference

MXeneTi3C2Tx

1064

10-18

10-14

[24]

Bismuthene

532 & 633

10-5

10-9

[25]

Antimonene

532 & 633

10-5

10-9

[26]

Na4M3N

532

10-8

10-6

Present work

69

Table 10. Mechanical properties of Na4M3N crystal Load P (g)

Hv (kg/mm2)

σy (GPa)

C11(GPa)

Kc (g/μm3/2)

Bi (1/μm1/2)

1

70.054

1.6963

102.2801

0.0408

1716.32

3

79.982

2.1391

116.7753

0.1224

653.186

5

88.252

2.5410

128.8500

0.2040

432.435

10

106.75

3.5429

155.8588

0.4081

261.540

25

132.15

5.1507

192.9419

1.0204

129.507

50

191.05

9.8175

278.9350

2.0408

93.613

100

267.18

17.6568

390.0907

4.0816

65.459

70

Graphical Abstract