Quantum chemical calculations, physico-chemical characterizations and crystal structural analysis of a new organic - hydrogen bond networked crystal, 2-aminothiazolium benzilate

Journal of Molecular Structure 1197 (2019) 19e33

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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc

Quantum chemical calculations, physico-chemical characterizations and crystal structural analysis of a new organic - hydrogen bond networked crystal, 2-aminothiazolium benzilate S. Madhan kumar, P. Muthuraja, M. Dhandapani* Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, 641 020, Tamil Nadu, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 20 January 2019 Received in revised form 2 July 2019 Accepted 4 July 2019 Available online 5 July 2019

A new organic proton transfer compound, 2-aminothiazoliumbenzilate (2-ATB) was synthesized and single crystals of the compound were grown by solvent evaporation-solution growth method at ambient temperature. The compound was characterized by elemental analysis, UVeVis NIR, FT-IR, 1H and 13C NMR spectroscopic analyses and single crystal X-ray diffraction (SXRD) structural study. Intermolecular and intramolecular NeH/O and OeH/O hydrogen bonding interactions stabilize the crystal network. The molecular structure was optimized at B3LYP/6-311Gþ(d,p) level using quantum chemical calculations. The natural bonding orbital (NBO) analysis was carried out to explore hyperconjugative interactions and intermolecular charge transfer. Hirshfeld surface analysis reveals that C/H, N/H and O/H interactions build hydrogen bond network in the molecular structure. The HOMO-LUMO energy gap value of 2-ATB is small enough for electron cloud transfer. The Z-scan technique was used to confirm 2-ATB as a third harmonic generating (THG) material for optical limiting device applications. © 2019 Published by Elsevier B.V.

Keywords: Crystal structure Hydrogen bond Hyperpolarizability Natural bond orbital Molecular electrostatic potential

1. Introduction Organic molecules containing p electron conjugation systems can generate nonlinearity in optical activity (NLO). Aromatics and heterocyclics which possess extensive conjugated systems can be utilized for improved optical properties in crystals which are attractive due to their easy design of molecular structure by varying substituents [1,2]. Organic crystals have large optical nonlinearity and low cut-off wavelength in UV region compared to their inorganic counterparts claiming their superiority in optical device applications [3,4]. The large NLO properties of organic molecules are due to their high first order hyperpolarizability (b) values. The b value can be increased by facilitating more intermolecular charge transfer interactions in the molecule by extending the p-conjugated system [5]. The organic molecular network containing hydrogen as well as and electronegative atoms such as O, N and S involve in numerous hydrogen bonding interactions which lead to interesting properties [6]. Heterocyclic ring compounds such as furan, pyridine and thiophene have been reported to have more effective p-conjugation

* Corresponding author. E-mail address: [email protected] (M. Dhandapani). https://doi.org/10.1016/j.molstruc.2019.07.025 0022-2860/© 2019 Published by Elsevier B.V.

between donors and acceptors, resulting in larger nonlinearities due to their lower aromatic stabilization energy than benzene [7]. Heterocyclic molecules having nitrogen in its ring can donate an electron pair as well as receive a proton. 2-aminothiazole has one heterocyclic nitrogen atom and a substituted amino group with two hydrogen atoms (- NH2) apart from heterocyclic S atom [8]. The heterocyclic nitrogen 2-aminothiazole acts as a hydrogen acceptor as well as electron donor [9]. The hydrogen bonding between hydroxyl groups of carboxylic acids and heterocyclic nitrogen atoms has been proved to have the supramolecular network of molecules in several instances [10]. In this work, we have employed a reaction in which the carboxyl group of benzilic acid transfers a proton to the nitrogen of 2-aminothiazole due to strong attraction between electron rich N atom and a proton of benzilic acid. The molecular unit 2-aminothiazolium benzilate (2-ATB) is expected to involve in extensive hydrogen bonding interactions leading to interesting supramolecular architecture of molecules which are further stabilized by weak CeH$$$p interactions. Quantum chemical calculations were also used to explore fascinating molecular properties by utilizing Gaussian 09’ software. Hirshfeld surface analysis, a tool to explore intermolecular interactions present in the solid state was also used to understand the nature and properties of different non covalent interactions in the 2-ATB. Z-scan technique was used to

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investigate the nonlinear optical properties of a symmetrical conjugated system [11e13] by assessing THG activity. Third harmonic generation (THG) is a nonlinear optical phenomenon which can be applied in diverse research areas including interfacial studies, subwavelength light manipulation, and high sensitivity. There is no symmetry requirement for third order NLO effect which permits the extensive research on organic materials [14]. In general, materials having centrosymmetric monoclinic space group (C2/c) are useful in third harmonic generation and find usefulness in optical limiting applications [15]. 2. Experimental details 2.1. Materials The reactants, 2-aminothiazole (Analytical grade: SigmaAldrich) and benzilic acid (Analytical grade: Sigma-Aldrich), were utilized for the synthesis as received without further purification. HPLC grade methanol was used as solvent [16]. 2.2. Synthesis procedure 2-Aminothiazole (10mmole) and benzilic acid (10mmole) were taken in an equimolar stoichiometric ratio (1:1) and were dissolved in methanol solvent. Both the methanolic solutions were mixed together and stirred for about 7 h to get a homogeneous solution of 2-ATB. The chemical reaction is given in Fig. 1. The solution was filtered and the filtrate was kept aside for crystallization without any mechanical disturbance at ambient temperature. The crude 2ATB crystals obtained within a week were re-dissolved and subjected to recrystallization several times to improve quality. Brown coloured transparent single crystals were obtained within a period of fifteen days. Shown in Fig. S1 Photograph of the crystal 2-ATB.

200e800 nm by JASCO (FP-8300) spectrophotometer. Thermogravimetry/Differential thermal analysis (TG/DTA) thermograms were obtained in the temperature range of 25e600  C under nitrogen atmosphere at a heating rate of 10  C per minute in a NETZSCH 409 C/CD thermal analyzer. Z-scan experiment was carried out by using a continuous wave Nd:YAG laser of wavelength 532 nm with power 100 mW which was focused by a lens with a focal length of 103 mm. Both open and closed aperture measurements were taken with a good quality 2ATB crystal of 1 mm thickness. The sample was moved across the focal region (þz to ez) along the direction of propagation of the laser beam. The beam transmitted through 2-ATB was collected by a photodetector through an aperture and the intensity was measured by a digital power meter attached to the detector.

2.4. Crystallographic studies Single crystal X-ray diffraction data were collected using Mo-Ka radiation (l ¼ 0.71073 Å) in an Oxford Xcalibur, Gemini diffractometer equipped with EOS CCD detector at 298 K. CrysAlispro program was used for reduction of data and absorption correction was done by multi j scans. Structure was solved using SHELXS-97 program and was refined by full-matrix least squares against F2 using SHELXL-97 program [17,18]. All the non-hydrogen atoms were revealed in the first difference Fourier map itself. All the hydrogen atoms were positioned geometrically (CeH ¼ 0.93 Å, OeH ¼ 0.82 Å) and refined using a riding model with Uiso (H) ¼ 1.2Ueq and 1.5 Ueq (O). Absorption correction was applied using SADABS [19] and finally crystal packing diagrams were generated using MERCURY software [20]. The presence of various hydrogen bonding interactions were determined by PLATON software [21].

2.3. Physico-chemical characterizations

2.5. Computational details

The elemental analysis (C, H, N and S) was performed in a PerkinElmer 240C, elemental analyzer. The percentage compositions of carbon, hydrogen, nitrogen and sulphur are found to be C ¼ 62.71% (61.03), H ¼ 4.76% (5.27), N ¼ 19.15% (14.8) and S ¼ 10.3% (11.9) theoretically calculated values are given in the parenthesis. The Fourier transform infrared (FT-IR) spectrum was recorded in a FT-IR 8000 spectrophotometer in the wavenumber region of 4000e400 cm1 using KBr pellet method. Nuclear magnetic resonance (NMR) spectroscopic data (1H and 13C) were collected from a BRUKER AV III 500 MHz spectrophotometer instrument using deuterated dimethylsulphoxide (DMSO - D6) solvent. The electronic absorption spectrum of 0.05 M methanolic solution of 2-ATB was recorded using a JASCO (V-770) UV-Vis spectrophotometer in the range of 200e800 nm. The emission spectrum of 2-ATB was recorded using methanol as a solvent, in the spectral region of

Computational calculations were performed using Gaussian'09 version E.01 software package using B3LYP, B3LYP-D3 and M06-2X functionals at 6-311 þ G (d, p) basis level of theory [22]. Molecular structures were visualized using Gauss view 50 software package. From the optimized structure from Gaussian output file, computational calculations of molecular electrostatic potential (MEP), frontier molecular orbitals (FMO), Mulliken atomic charge distribution and NLO parameters including dipole moment, polarizability and hyperpolarizability were carried out. The natural bond orbital (NBO) calculations were performed using NBO 3.1 program [23]. Hirshfeld surface calculations were performed by using the Crystal Explorer 3.1 program [24] with.cif input file. The Hirshfeld surfaces and associated 2D fingerprints were simulated based on the electron distribution as the sum of the spherical atom electron densities [25,26].

Fig. 1. Synthesis of 2-ATB.

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3. Results and discussion 3.1. FT-IR spectroscopic analysis The FT-IR spectrum of the 2-ATB is shown in Fig. 2. The formation of the proton transfer compound by the reaction between 2aminothiazole and benzilic acid is strongly evidenced by presence of characteristic bands in the spectrum. A broad band from 3460 to 3180 cm1 is due to OeH, NeH and CeH stretching vibrations in the compound. The broadness is due to excessive hydrogen bonding interactions. The band at 2372 cm1 is due to the stretching of NHþ group in 2-aminothiazolium moiety which is a strong evidence for the formation of 2-ATB [27]. The characteristic vibrational frequency at 1712 cm1 is due to eC]O group of carboxylate anion. The vibrational frequencies at 1619 and 1420 cm1 indicate

Fig. 2. FT-IR spectrum of 2-ATB.

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asymmetric and symmetric stretching vibrations of COO respectively which confirm the deprotonation process. The NeH in-plane bending vibrational frequency of primary amino group (-NH2) is observed as a band at 1480 cm1. The band at 1345 cm1 is due to CeO stretching vibration of carboxylate moiety. The vibrational frequency at 1173 cm1 is due to the CeN stretching vibration of amino group while the band at 1055 cm1 is due to aromatic CeH in plane bending vibration. The wave numbers at 954, 843 and 742 cm1 are due to various out of plane bending vibrations of OeH, NeH and CeH respectively. 3.2. NMR spectroscopy 3.2.1. 1H NMR spectroscopic studies The 1H NMR spectrum of 2-ATB shown in Fig. 3 has seven distinct signals indicating the presence of seven chemically and magnetically different proton sets. The signal at d7.319 ppm is assigned to a set of four protons, H14, H16, H9 and H7 of same kind in benzilate moiety. Another set of protons, H13, H15, H8 and H6 generate a single signal at d 7.273 ppm. A short peak appears at d 7.022 ppm is due to a set of equivalent H10 and H17 protons of phenyl ring. Another signal at d 7.378 ppm is due to the presence of heterocyclic ring proton H3 of 2-aminothiazolium moiety. A peak at d 6.566 ppm is due to the identical NH2 protons of 2aminothiazolium moiety. The signal at d 6.952 ppm is due to a signal from H2 of 2-aminothaizolium moiety. The NeHþ proton of thiazole moiety in the compound produce a signal at d 2.501 ppm in the upfield of the spectrum. The peak due to proton of carboxylic acid moiety is missing in the (expected around 10.5e12.0 ppm range) spectrum due to deprotonation during the compound formation [28]. 3.2.2. 13C NMR spectroscopic studies The 13C NMR spectrum in Fig. 4 shows nine different carbon signals in the spectrum there by establishing the carbon skeleton arrangement of 2-ATB. The deshielded carbon signal at d 175.29 ppm is due to carbonyl carbon atom C11 surrounded by electronegative oxygen atoms of benzilate moiety. The signal at d144.22 ppm is assigned to chemically equivalent C12 and C5

Fig. 3. 1H NMR spectrum of 2-ATB.

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Fig. 4.

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C NMR spectrum of 2-ATB.

aromatic carbon atoms of anionic moiety. The signal at d138 ppm is due to a set of four carbon atoms namely, C14, C16, C9 and C7 of ring carbon atoms of same anionic benzilate moiety. The signal appearing at d128.12 ppm is due to another set of chemically equivalent C17, C13, C10 and C6 carbon atoms of benzilate moiety. The C15 and C8 carbon atoms of the same kind in acid moiety generate a signal at d127.67 ppm. The C3 carbon of 2-aminothiazolium moiety shows a signal at d127.55 ppm. The C2 carbon shows a signal at d 107.11 ppm whereas the C4 carbon of benzilate moiety produces a signal at d80.73 ppm. The carbon atom (C1) bearing the amino substituent generates a signal at d 169.4 ppm. The solvent peak (DMSO-D6) is observed at around 40 ppm.

3.3. Single crystal X-ray diffraction study The 2-ATB crystallizes in monoclinic crystal system with space group C2/c and the unit cell parameters are a ¼ 22.317(3) Å, b ¼ 8.7611(9) Å, c ¼ 17.134(2) Å, a ¼ g ¼ 90.00, b ¼ 109.755(4) and the unit cell volume is 3152(7) Å3. The crystallographic refinement data of 2-ATB are given in Table .1. 2-Aminothiazole is a heterocyclic molecule containing one nitrogen and one sulphur in the ring skeleton with one eNH2 group substituted in the second position next to the heterocyclic nitrogen. On reaction with benzilic acid, 2-aminothaizole forms a proton transfer compounds, 2-aminothiazolium benzilate (2-ATB). In

Table 1 Crystallographic information of 2-ATB. Chemical Formula

C17 H16 O3N2S

Formula Weight Crystal System Space group Unit cell dimension

328.38 Monoclinic C2/c a ¼ 22.317(3)Å a ¼ 90 b ¼ 8.7611(9)Å b ¼ 109.755(4) c ¼ 17.134(2)Å g ¼ 90 ; 3152.9(7)Å3 8 1.384 Mg/m3 0.222 mm1 1376 0.11  0.20  0.3 mm3 290 K 34 < h<þ 34, 13 < k<þ 13, 26 < l<þ 26 4424 0.041 5888 R1 ¼ 0.0480, WR2 ¼ 0.1339, s ¼ 1.02 0.45 and 0.38 e.Å3

Volume Z Density (calculated) Absorbtion coefficient F(000) Crystal Size Temperature (K) Index ranges Observed Data R(int) Reflections collected Final R indices[I > 2 sigma(I)] Largest diff. peak and hole

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general, 2-amino substituted compound leads to hydrogen bonding interaction forming a R22 (8) ring graph set [29]. The protonated heterocyclic nitrogen acts as hydrogen donor while the deprotanated carboxylic oxygen acts as hydrogen acceptor. The ORTEP view at 50% probability of 2-ATB shown in Fig. 5 clearly presents a benzilate anion and an aminothiazoilium cation in the asymmetric unit. The intermolecular hydrogen bonding network in 2-ATB is due to NeH/O and OeH/O interactions as well as CeH/O intramolecular interactions. Supramolecular motifs found in 2-ATB are R22 (8), R22 (10), R12 (7), R22 (11) and R66 (16) as shown Fig. 6. The large ring motif, R66 (16) arises due to interactions of neighbouring benzilate moieties utilizing two eOH and two -COO- groups. In all the ring graph sets, hydrogen bonds are found to be either strong or moderately strong due to cyclic NeH/O interactions. In 2-ATB, among the three hydrogen bonds, the moderately strong hydrogen bonding is O3eH1/O2 with the length of 3.001 Å while the other two interactions, namely, N2eH2A … O3 (2.741 Å) and N1eH1/O2 (2.700 Å) are found to be strong hydrogen bonds [30]. The shortest centroid … centroid distance found in 2-ATB is 4.1801(11) Å (symmetry operation 1-x, y, ½) where the association occurs between heterocyclic 2-aminothiazolium and benzilate ring. Another centroid … centroid interaction with the distance of 4.8243 (11) Å (symmetry operation: x, y, z) is observed between two adjacent benzilate rings. The C10eH10 … p interaction is observed at a distance of 3.548 Å between the rings (symmetry operation ½-x, ½-y, ½-z). A noticeable noncovalent interaction, C5eO3 … p interaction in 2-ATB is due to the association of carboxylate oxygen with the neighbouring thiazole ring with the distance of 3.983 Å (symmetry operation: 1-x, 2-y, 1-z). The CeO bond lengths of carboxylate anion C5eO2 and C5eO3 are 1.264 and 1.239 Å respectively. The small difference (0.015 Å) arises due

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to the formation of CeO … p interactions. In neutral 2-aminothiazole molecule, the expected C1eN1eC3 bond angle is 116.4 [31]. In 2-ATB molecule (thaiozlium cation), the same is found to be 113.4 which is a strong evidence for the proton transfer during the synthesis. The protonation on the N site of the cation is also confirmed from increased CeN bond distance. The normal bond lengths C3eN1 and C1eN1in an uncharged 2aminothiazole moiety [31] are 1.38 Å and 1.30 Å respectively which are found to have altered in 2-ATB as 1.39 Å (C3eN1) and 1.33 Å (C1eN1) proving the transfer of proton from benzilicacid to 2-aminothiazole during the reaction. The hydrogen bond geometrical parameters of 2-ATB are presented in Table 2. In 2-ATB, since both oxygen atoms of the COO group participate in the hydrogen bonding interactions (N1eH1/O2 and N2eH2A … O3), there is a lengthening of C4eC5 value to 1.560 Å from normal value of 1.375 Å due to the formation of intermolecular hydrogen bonding interaction. Hydrogen bonding interactions also influence the variation in the bond angles. The O2eC5eO3 bond angle is increased to 126.5 from normal bond angle of 120 . The exocyclic angles C5eC4eC12 (105.9 ), C5eC4eC6 (112.47 ) and C6eC4eO1 (106.80 ) also found to vary from normal tetrahedral angle of 109.5 due to strong hydrogen bonding in the crystal structure. There are other intramolecular hydrogen bond interactions involving benzilate anions also found in 2-ATB and the distances are 2.982 (C7eH7/O3) and 2.823 Å (C17eH17/O1). Crystallographic data of 2-ATB have been deposited in Cambridge Crystallographic Data Centre. (CCDC NO: 1537597).

3.4. UV-visible spectroscopic analysis The UV-Vis spectrum of 2-ATB is shown in Fig. S2. The qualitative absorbtion profile of 2-ATB was obtained in methanolic

Fig. 5. ORTEP of 2-ATB at 50% probability level.

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Fig. 6. Different graph sets involving hydrogen bonding in 2-ATB.

Table 2 Hydrogen bond parameters of 2-ATB. Donar - H … Acceptor

D-H[Å]

H … A[Å]

D … A[Å]

D-H … A[ ]

N (1) eH (1) … O(2) O (1) eH (1A) … O(2) N (2) eH (2A) … O(3) N (2) eH (2B)/O(1) C (7) eH (7) … O(3) C (17) eH (17) … O(1)

0.86 0.82 0.86 0.86 0.93 0.93

1.85 2.22 1.90 2.21 2.43 2.51

2.700 3.001 2.741 2.993 2.982 2.823

170 160 165 151 118 100

solution. Two absorptions at 224 and 258 nm observed in the spectrum are due to p-p* and n-p* transitions. There is no absorption between 330 and 800 nm showing a good transparency window in the visible region [32]. Molar extinction coefficients (ε) were calculated and are found to be 181 and 181.5 l mol1cm1 at 224 and 258 nm respectively.

1-x,1-y,1-z x,1 þ y,z

159  C in DTA corresponds to melting point of the crystal. It is concluded that decomposition starts as soon as the compound melts. Absence of either endothermic or exothermic peaks below 159  C indicates that there was no phase transition before melting also. Good thermal stability of 2-ATB is useful in optical device

3.5. Photoluminescence studies The emission spectrum is one of the powerful tools to afford direct information about the physical properties of materials of the molecular level. The delocalized p electrons in aromatic phenyl rings of benzilate anion get excited from ground energy state to higher energy state by absorbing visible light and re-emit the same at higher wavelength and the same is responsible for photoluminescence spectrum [33]. The emission spectrum of 2ATB is shown in Fig. S3. After excitation at 250 nm, the photoluminescence spectrum shows two broad peaks at 312 and 370 nm which indicates that the crystal can be used for optical applications [34]. 3.6. Thermal analysis The thermal stability of the crystal was investigated by thermogravimetry (TG) and differential thermal analysis (DTA) [35]. The TG-DTA curves of 2-ATB are shown in Fig. 7. TG curve shows that there is no weight loss up to 159  C. The endothermic dip at

Symmetry

Fig. 7. TG/DTA thermograms of 2-ATB.

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applications up to 159  C [36].

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2.1%. Based on the Hirshfeld surface analysis, it is inferred that CeH … p interactions have a greater contact over the entire molecular structure of 2-ATB.

4. Theoretical calculations 4.1. Hirshfeld surface analysis

4.2. Optimized geometry

The crystal structure of 2-ATB is greatly influenced by NeH/O, OeH/O, CeH/O, CeH … p, CeO … p and p … p interactions. Hirshfeld surface analysis is an excellent tool to explore the major non-covalent interactions and to calculate the proportion/contribution in percentage. The results of Hirshfeld surface analysis very well agreed with the results of X-ray crystal structure analysis of 2ATB and elucidated the intermolecular interactions in a novel visual manner. The Hirshfeld surfaces mapped with properties such as di, de, dnorm, shape index, curvedness and the 2D fingerprint plots of 2ATB are shown in Figs. 8 and 9 respectively. The Hirshfeld surfaces of 2-ATB have been mapped over the distances are given in parenthesis for the properties, d norm (0.1-1.5 Å), shape index (0.1-1.5 Å), and curvedness (0.1-1.5 Å). Since both anions as well as cations possess abundant hydrogens which greatly increase The H/H contacts in 2-ATB crystal amount to 47.3% due to abut ant hydrogen present in both cation and anion. Surprisingly C/H/H/C contacts are higher in % (23.7%) when compared to O/H/H/O contacts (13.3%), which clearly/ expose the stacking interactions in 2-ATB. The dnorm surfaces with dark red spots illustrate such hydrogen bonding interactions. The contribution of C/C contacts is reduced to 1.2% because of CeH … p interactions. The curvedness diagram having larger flat green areas separated by blue colour outline indicates the nature of stacking interactions. Similarly, the shape index also illustrates the p-p stacking interactions with red hollows and blue humps. Despite 2-ATB having CeO … p interactions, the contribution C/O/ O/C is only 0.3%. Other interactions such as N/H/H/N and O/S/ S/O, also contribute to the total Hirshfeld surface to the level of

The molecular structure of 2-ATB in the ground state was optimized and the structural parameters were computed by Gaussian 09 program using B3LYP method 6-311 þ G(d,p) basis set. Optimized molecular structure of 2-ATB with atom labelling is presented in Fig. 10 and the optimized bond lengths and angles are presented in Tables 3 and 4 respectively along with experimental results obtained from SXRD study. The CeH bond length in 2-ATB molecule has a value of 0.930 Å in SXRD measurements and the corresponding computed value is 1.082 Å. The N1eH1 and N2eH2 bond lengths are found to be 0.860 Å from the X-ray structural analysis whereas N1eH1, N2eH2A and N2eH2B bond length values are found to be 1.116 Å, 1.061 Å and 1.006 Å respectively in the optimized geometry of 2-ATB. The experimental C3eN1 and C1eN1 bond distances are 1.390 and 1.392 Å respectively, while the calculated values are 1.383 and 1.324 Å respectively. Both the experimental and computed values are found to be less than normal CeN single bond distance (1.480 Å) [37]. The intermolecular hydrogen bond lengths, N4eH5/O14 (1.615 Å) and N2eH3/O15 (1.443 Å) are appreciably shorter than van der Waals separation (2.72 Å) between O and H atom. The hydrogen bridges facilitate (H5/O14 and H3/O15) the electron flow through the ring motif in which NeH act as a hydrogen bond donor (2aminothiazolium ion) and oxygen of benzilate anion acts as a hydrogen bond acceptor. The experiment was repeated with two other theoretical calculations, namely, DFT-D3 and M06-2X apart from B3LYP. The linear regression plots have been drawn (Fig. S4) for the experimental and computed structural parameters of 2-ATB. From the plots, the linear regression coefficients (r2) were

Fig. 8. Hirshfeld surfaces mapped on 2-ATB (i) di, (ii) de, (iii) dnorm (iv) Shape index and (v) Curvedness.

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Fig. 9. 2D fingerprint plots of 2-ATB.

calculated and are 0.9607, 0.9705 and 0.9401 corresponding to B3LYP, B3LYP-D3 and M06-2X functionals, respectively. This statistical analysis endorses the result of (B3LYP-D3) DFT functional to be more reliable and close to the experimental results than the others functionals. The relative electronic energies of the structure are predicted as 1391.13 a.u. (B3LYP), 1391.27 a.u.(B3LYP-D3) and-1390.71 a.u. (M06-2X), The low energy value obtained at B3LYP-D3 functional leads to more structural stability attesting this functional as the best. The optimized bond lengths and angles are presented in Tables S5 and S6 respectively along with experimental results obtained from SXRD study. 4.3. Molecular electrostatic potential In order to understand the reaction mechanism and hydrogen bonding interactions, MEP analysis was carried out using B3LYP method by 6-311 þ G(d,p) level of theory for both the reactants and the product 2- ATB. In order to understand the mechanism of the reaction, MEP of reactants were also individually mapped. MEP diagrams of, 2-aminothiazole and benzilic acid 2-ATB are presented in Fig. 11aec respectively. The red, green and blue colours represent the most negative, neutral and most positive electrostatic potential

regions in the molecule respectively [38]. The formation of 2-ATB is confirmed by analyzing the MEP of reactants and product. It is clear from Fig. 11 (a) that high electronegative potential is developed on the heterocyclic nitrogen of the five member ring of 2-aminothiazole. In the case of benzilic acid (Fig. 11b), high electropositive potential developed on the carboxyl hydrogen (blue colour). Due to more electropositive potential on acid hydrogen and more electronegative potential on heterocyclic nitrogen, the migration of proton is easily facilitated. After the formation of the product (Fig. 11c), electropositive potential appears on the NHþ group and hydroxyl hydrogen (eOH) while electronegative potential prevails over carboxylate oxygen with the development of yellow colour. The contour maps of reactants and 2-ATB also shown in Fig. 11d, 11e and 11. f demonstrate the formation of the product. It is found that there is an electron density spread over heterocyclic nitrogen in the 2-aminthiazole moiety before reaction. The disappearance of the density in the product clearly confirms the formation of 2-ATB. 4.4. NBO analysis NBO analysis is one of the best tools for the investigation of

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Fig. 10. Optimized structure of 2-ATB.

intermolecular and intramolecular interactions arising out of conjugative and hyperconjugative interactions in a molecular system [39]. The NBO analysis was performed using the NBO 3.1 program as implemented in the Gaussian 09 package at B3LYP method at 6311 þ G(d,p) basis set. The charge transfer from non-bonding orbitals of oxygen atom to anti-bonding orbitals stabilizes the molecule. The stabilization energy E2 is associated with the deprotonation of donor (i), acceptor (j) was calculated on the basis of second order perturbation theory [40]. The delocalization of CeN atoms of thiazolium moiety brings about high stabilization energy and this energy is due to electron transfer from non-bonding orbital of nitrogen atom to anti-bonding orbital of carbon. In the product 2-ATB, the LP(1) N4 /p* N2eC7 conjugative interaction has the highest stabilization energy (94.3 kcalmol-1) in the 2-aminothiazolium ring, which makes the N4eH5/O14 and N2eH3/O15 hydrogen bonding interactions feasible. The energies of hyperconjugative interactions LP(3)O14/LP*(1)C19 and LP(3) O15/LP*(1) C19 are 180.55 and 176.99 kJ/mol and this high energy is due to the involvement of hydrogen bonding interactions by O14 and O15 in the neighborhood of C19. The stabilization energy values associated with hyperconjugative interactions LP (1) O14/ s*N4eH5 and LP (1) O15/ s*N2eH3 are 5.51 and 5.57 kcal/mol respectively. In 2-ATB, the intramolecular interactions are formed by the orbital over lapping through p- p* conjugative interactions such as p(C16eC22) / p*(C26eC36), p(C17eC20) / p*(C24eC30), p(C24eC30) / p*(C28eC32), p(C26eC36) / p*(C16eC22), p(C28eC32) /p*(C17eC20) with stabilization energies of 20.43, 19.94, 21.51, 20.06, 19.29 kcal/mol, respectively. The highest stabilization energy of 229.66 kJ/mol is observed for p*(C34eC38) /p*(C16eC22) conjugative interaction, which leads to intramolecular charge transfer

process enhancing optical properties of 2-ATB molecule. Table S1.

4.5. Bader's topology analysis Hydrogen bonding interactions in a compound can be better understood by calculations of parameters such as electron density (r(r)) and Laplacian electron density (V2r(r)). The V2r(r) clearly differentiates the conventional hydrogen bonds from covalent bonding in the system. Topological parameters such as r(r), V2r(r) nuclear critical point (NCP), bond critical point (BCP), ring critical point (RCP) and cage critical point (CCP) can be useful in validating the existence of NeH/O and OeH/O hydrogen bonding interactions [41,42]. Atoms in molecules analysis (AIM) provide the important topological parameters and the results are shown in Table 5. The 2-ATB molecule contains N4eH5/O14 and N2eH3/O15 hydrogen bonding interactions. AIM analysis confirms the presence of 39 NCPs, 45 BCPs,7 RCPs, and 0 CCP, which satisfy the PoincareHopf relationship (n e b þ r e c ¼ 1, i.e. 39e45 þ 70 ¼ 1), which is in decreasing order: BCP>NCP>RCP. Fig. S5 illustrates various critical points in 2-ATB. The electron density and Laplacian density of NeH/O and OeH/O hydrogen bonding interactions are listed in Table 5 which clearly show the positive value for Laplacian electron density (V2 r(r) > 0).This proves that the interaction between donor and acceptor is dominated by the contraction of r(r) towards each nucleus [42]. The values of r(r) are found to be 0.0904 and 0.0573 while the values of V2r(r) are 0.1281 and 0.1392 for RCP in R22 (8) motif formed via N4eH5/O14 and N2eH3/O15 interactions between cationic and anionic moieties.

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S. Madhan kumar et al. / Journal of Molecular Structure 1197 (2019) 19e33

Table 3 Experimental and calculated bond lengths [Å] in 2-ATB. Atomic labelling S1eC1 S1eC2 O1eC4 O1eH1A O3eC5 O2eC5 N1eC1 N1eC3 N1eH1 N2eC1 N2eH2A N2eH2B C12eC17 C12eC13 C12eC4 C6eC7 C6eC11 C6eC4 C4eC5 C7eC8 C7eH7 C17eC16 C17eH17 C11eC10 C11eH11 C13eC14 C13eH13 C9-10 C9eC8 C9eH9 C10eH10 C8-8 C15eC16 C15eC14 C15eH15 C14eH14 C16eH16 C3eC2 C3eH3 C2eH2 RMSD values for Bond length in

Observed [Å] 1.7227 (12) 1.729 (2) 1.4314 (13) 0.8200 1.2395 (15) 1.2648 (15) 1.3295 (17) 1.3905 (19) 0.8600 1.3140 (18) 0.8600 0.8600 1.3858 (17) 1.3943 (17) 1.5300 (16) 1.3832 (18) 1.3928 (16) 1.5241 (16) 1.5595 (15) 1.390 (2) 0.9300 1.400 (2) 0.9300 1.391 (2) 0.9300 1.390 (2) 0.9300 1.370 (2) 1.373 (2) 0.9300 0.9300 0.9300 1.371 (3) 1.375 (3) 0.9300 0.9300 0.9300 1.334 (2) 0.9300 0.9300 0.0016 Å

Table 4 Experimental and calculated bond angles [ ] in 2-ATB. Observed [ ]

Calculated [Å]

Atomic labelling

1.754 1.761 1.421 0.971 1.274 1.247 1.324 1.383 1.116 1.324 1.061 1.006 1.400 1.398 1.547 1.398 1.399 1.540 1.564 1.395 1.081 1.392 1.082 1.392 1.082 1.396 1.082 1.394 1.392 1.082 1.082 1.085 1.395 1.392 1.084 1.085 1.085 1.345 1.080 1.077

C1eS1eC2 90.61 (7) C4eO1eH1A 109.5 C1eN1eC3 113.65 (11) C1eN1eH1 123.2 C3eN1eH1 123.2 C1eN2eH2A 120.0 C1eN2eH2B 120.0 H2A-N2-H2B 120.0 C17eC12eC13 118.52 (12) C17eC12eC4 121.03 (11) C13eC12eC4 120.35 (11) C7eC6eC11 118.30 (11) C7eC6eC4 123.64 (10) C11eC6eC4 118.05 (11) O1eC4eC6 106.80 (9) O1eC4eC12 110.73 (9) C6eC4eC12 111.46 (9) O1eC4eC5 109.45 (9) C6eC4eC5 112.47 (9) C12eC4eC5 105.97 (9) O3eC5eO2 126.52 (11) O3eC5eC4 117.56 (10) O2eC5eC4 115.89 (10) C6eC7eC8 120.59 (13) C6eC7eH7 119.7 C8eC7eH7 119.7 C12eC17eC16 120.14 (13) C12eC17eH17 119.9 C16eC17eH17 119.9 C10eC11eC6 120.59 (14) C10eC11eH11 119.7 C6eC11eH11 119.7 C14eC13eC12 120.86 (14) C14eC13eH13 119.6 C12eC13eH13 119.6 N2eC1eN1 124.42 (11) N2eC1eS1 124.28 (10) N1eC1eS1 111.29 (10) C10eC9eC8 119.62 (13) C10eC9eH9 120.2 C8eC9eH9 120.2 C9eC10eC11 120.35 (14) C9eC10eH10 119.8 C11eC10eH10 119.8 C9eC8eC7 120.53 (15) C9eC8eH8 119.7 C7eC8eH8 119.7 C16eC15eC14 119.95 (14) C16eC15eH15 120.0 C14eC15eH15 120.0 C15eC14eC13 119.99 (15) C15eC14eH14 120.0 C13eC14eH14 120.0 C15eC16eC17 120.54 (14) C15eC16eH16 119.7 C17eC16eH16 119.7 C2eC3eN1 113.38 (15) C2eC3eH3 123.3 N1eC3eH3 123.3 C3eC2eS1 111.05 (13) C3eC2eH2 124.5 S1eC2eH2 124.5 RMSD values for Bond Angle in 0.4864

4.6. Atomic charge analysis Mulliken atomic charge analysis of 2-ATB was carried out using the B3LYP basis set at 6311 þ G(d,p) level of theory. The data and related Mulliken atomic charge distribution chart are given in Table S2 and Fig. S6 respectively. In this study, distribution of positive and negative charges over various atoms of the 2-ATB molecule is analyzed. All the hydrogen atoms of 2-ATB possess positive charge, especially the hydrogen atoms H3 (0.6047) and H5 (0.4153) have higher values than others. This is due to involvement of these atoms in the N2eH3/O15 and N4eH5/O14 intermolecular hydrogen bonding interactions. In the 2-ATB, the carbon atoms C7 has negative charge due to its attachment with more electronegative nitrogen atoms N2 and N4 which suggests that atom C7 is acting as the centre for charge transfer between the thiazolium to carboxylate moiety. Out of the three oxygen atoms present in 2ATB, two oxygen atoms, O14 and O15 possess high negative charges. The atoms O14 (0.3379) and O15 (0.47184) enforce a large negative charge on C19 (0.75777) due to resonance [43].

4.7. Frontier molecular orbital analysis The frontier molecular orbital analysis helps to explore the electric and optical properties of a material [44]. Highest occupied molecular orbital (HOMO) acts as an electron donor and the lowest

Calculated [ ] 90.9 104.6 114.1 121.0 124.9 118.6 120.4 121.0 118.6 117.9 123.5 118.7 119.7 121.6 108.6 108.9 111.3 107.8 109.7 110.3 125.7 114.7 119.6 121. 119.9 120.4 120.8 119.0 120.8 120.7 119.4 120.0 120.6 119.6 119.8 123.3 125.5 111.2 119.3 120.3 120.4 120.4 120.3 119.5 120.4 120.1 119.5 119.3 120.4 120.4 120.5 120.1 119.5 120.4 120.1 119.6 114.4 126.8 118.7 1104 129.0 120.6

unoccupied molecular orbital (LUMO) largely acts as an electron acceptor. The energy difference (EHOMO eELUMO) influences the chemical stability as well as reactivity of the molecule. The HOMOLUMO plots were obtained by using B3LYP method at 6311 þ G(d,p) basis set level. While the energy of HOMO is directly related to ionization potential and LUMO is the energy of electron affinity. In the 2-ATB molecule, HOMO is fully spread over entire

S. Madhan kumar et al. / Journal of Molecular Structure 1197 (2019) 19e33 Table 5 Topological analysis parameters of 2-ATB using B3LYP method at 6-311 þ G(d,p) theory. Hydrogen bonds

Critical points

Electron density, r(r), (a.u)

Laplacian electron density, V2 r(r), (a.u)

H13eO12/H23 N4eH5/O14 N2eH3/O15 O12eH13 ….O15 C20eH21/O14

71 75 60 54 59

0.0173 0.0573 0.0904 0.0329 0.0144

0.076 0.1392 0.1281 0.1265 0.0506

benzilate anion and LUMO has covered the 2-aminothiazlium cation completely. The energies of HOMO and LUMO are computed as 6.2441eV and 1.5784eV respectively, the difference in their energy gap is 4.6659 eV shown in Fig. 12(a). The HOMO-

Table 6 Dipole moment, Polarizibility and hyperpolarizibility values of 2-ATB. Dipole moment m (D)

Polarizibility (a)

Hyperpolarizibility (b)

mx¼8.7823 my ¼ 0.2551 mz ¼ 1.4661 m ¼ 8.9074

axx¼108.58 axy¼0.3331 ayy¼143.144 axz¼2.142 ayz ¼ 1.1228 azz¼132.198 a0 ¼ - 1.8965  1023 esu Da ¼ 4.5773  1024 esu

xxx ¼ 276.35 xxy ¼ 16.1185 xyy ¼ 21.928 yyy ¼ 8.5308 zxx ¼ 20.493 xyz ¼ 12.2926 zyy ¼ 3.5132 xzz ¼ 48.9304 yzz ¼ 2.7459 zzz ¼ 11.891 b tot ¼ 2.6214  1030 esu

29

LUMO energy gap facilitates the charge transfer within the molecule with ease [45]. The experimental band gap energy measured from UV -Vis spectrum for 2-ATB molecule is 4.3 eV(Fig. 12d) which is close to the computed value. The contribution of each fragment orbital to the overall molecular orbitals was investigated from the total density of states (DOS) and partial density of states (PDOS) [46]. The contribution of each fragment such as thiazolium cation, carboxylate anion (COO), OH, NH2 and phenyl rings present in the 2-ATB molecule has been investigated and the results are shown in Fig. 12b and 12. c. The DOS spectrum proves the population analysis per orbital in certain energy range while the PDOS demonstrates the percentage contribution of every individual group to each molecular orbital. The energy range of DOS spectrum is 0 to 20 eV while the PDOS shows the percentage of contribution of various groups to each molecular orbital. The COO and OH groups contribute more in the high energy range of 8 to 10 eV. The contribution of phenyl rings is the highest among all other groups which has substantial influence on nonlinear optical properties and this observation correlates with the findings of FMO analysis where the maximum electron density is spread over these phenyl rings. 4.8. Hyperpolarizability calculations The electric dipole moment(m), polarizability (a), anisotropy of polarizability (Da) and the first order hyperpolarizibility (b) of 2ATB were calculated at B3LYP level of theory using 6311 þ G(d,p) basis set. The movement of electron cloud from donor to acceptor makes the molecule highly polarizable and the inter-molecular charge transfer is responsible for the NLO properties [47]. The study helps in understanding of hydrogen bond interaction and

Fig. 11. Molecular electrostatic potential of (a) 2-aminothiazole, (b) benzilicacid and (c) 2-ATB and contour mapping of (d) 2-aminothiazole, (e) benzilicacid and (f) 2-ATB.

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Fig. 12. (a) HOMO-LUMO plot, (b) DOS, (c) PDOS and (d) band energy gap spectra of 2-ATB.

delocalization of electron density in 2-ATB. Urea was used as a protypical molecule for comparative purpose [48]. The hyperpolarizibility values are listed in Table .6. The calculated dipole moment (m), polarizability (a) and anisotropic polarizability (Da) values of 2-ATB molecule are 8.9074 debye (D), - 1.8965  1023 esu and 4.5773  1024 esu respectively. The first order hyperpolarizibility value (btot) of 2-ATB is 2.6214  1031 esu which is 2.125 times greater than that of reference compound, urea (1.2332  1030 esu). The highest first order hyperpolarizability value (b) is 276.35 au in the bxxx direction which is attributed to more delocalization of electron cloud in this direction. The hyperpolarizability value (b) is an indicator of the quality of optical materials [49]. The presence of NeH/O and OeH/O hydrogen bonding interactions in 2-ATB significantly enhances the polarizability and molecular hyperpolarizability vales which are responsible for more active nonlinear optical response [50]. 5. Z-scan analysis Generally, the Z-scan technique is a very powerful tool to understand the NLO properties and the electronic structure of these organic materials. This study is used for the calculation of refractive

index (n2) and nonlinear coefficient (b) of the material. It is a simple technique in which the sample is investigated along Z-direction using a focused Gaussian beam from continuous wave Nd:YAG laser of wavelength 532 nm with power 100 mW. The calculation of transmittance by both open and closed aperture Z escan methods supply information regarding NLO parameters [51]. The measurements of open and closed apertures are shown in Fig. 13. The third order nonlinear optical properties were calculated standard equation [52]. Electron donating and accepting moieties in organic molecules that involve in the intermolecular interactions influence the focussing properties of laser beam [53]. The calculated nonlinear refractive index (n2), absorbtion coefficient (b) and third order susceptibility (c3) of 2-ATB are 2.778  107 cm2/W, 2.1564  104 cm/W and 7.5090  108 esu respectively. Even though the (c3) seems to be small in magnitude, there are number of reports in which the values are less than are equal to the calculated value [54e57]. In closed aperture curve, a peak is followed by a valley indicating self defocusing and negative nonlinear refraction. In the open aperture curve the transmittance is minimum at z ¼ 0 indicating reverse saturation absorption. The Z-scan studies of 2-ATB reveal the suitability of the crystal for third order nonlinear optical limiting applications. The results presented in

S. Madhan kumar et al. / Journal of Molecular Structure 1197 (2019) 19e33

31

Fig. 13. Z-scan curves in (a) open and (b) closed aperture of 2-ATB.

Table S4 indicate that the material reveal a positive refractive index which results in the self focussing nature due to two-photo absorption process of the crystal. This is one of the essential parameters for optical limiting applications.

6. Conclusion A new third order optical material 2-ATB was synthesized and the structure was confirmed through single crystal XRD analysis. The 2-ATB crystal belongs to monoclinic system with C2/c space group. The FT-IR and NMR spectroscopic analyses proved the proton transfer mechanism during the formation of the molecule. Optimized geometry and NBO analysis clearly prove the presence of NeH/O and OeH/O hydrogen bond interactions in the molecule. High positive and negative charges over the atoms involved in NeH/O and OeH/O interactions found in the Mulliken population analysis confirm hydrogen bonding network in 2-ATB. NBO exposes p conjugative interaction as the prominent charge transfer interaction due to high stabilization energy of 229.66 kJ/mol. The high stabilization energies of hyperconjugative interactions, LP(3)O14/LP*(1)C19 and LP(3)O15/LP*(1)C19 also confirm hydrogen bonding framework in the crystal. MEP analysis of the product, 2ATB shows negative potential on oxygen atoms and positive potential on eNH group which clearly indicate the proton transfer in the formation of 2-ATB. The optical transmittance study shows that 2-ATB has low-energy band gap of 4.3 eV with the lower cut off wavelength of 300 nm, which endorses its suitability for optoelectronic applications. The small HOMO-LUMO energy gap of 4.6 eV facilitates charge transfer within molecule. TG/DTA analysis  confirms the thermal stability of the 2-ATB crystal up to 159 C. The calculated first-order hyperpolarizability of 2-ATB is 2.6214  1031 esu, which is 2.1 times greater than that of urea. Zscan studies show that 2-ATB crystal exhibits good third order susceptibility. The closed aperture study indicates the 2-ATB has negative optical nonlinear refraction confirming self defocusing behaviour which is an additional advantage for optical limiters. The 2-ATB exhibits reverse saturable absorption process in Z-scan which is the most required quality for optical limiting applications.

Acknowledgements One of the authors, M. Dhandapani, would like to thank the University Grants Commission (UGC), New Delhi, India for the financial support (Major Research Project Grant No. 43e200/ 2014(SR) to carry out the research work. S. Madhankumar, thanks the Dr. R. Nagarajan, School of Chemistry and UGC Networking Centre, Hyderabad, for awarding visiting research fellowship. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.07.025. References [1] M.Y. Balakina, Polymer matrix effects on the nonlinear optical response of incorporated chromophore: new analytical models, ChemPhysChem 7 (2006) 2115e2125. Doi.org/10.1002/cphc.200600263. [2] K.P. Glaser, A. Pietraszko, J. Baran, B. Hilczer, J. Małecki, M. Połomska, P. Ławniczak, Structure and molecular dynamics of bis-1H-1,2,4-triazole succinic acid complex crystals, CrystEngComm 13 (2011) 3698e3709, https://doi.org/10.1039/c0ce00866d. [3] T. Matsukawa, A. Hoshikawa, Y. Ishikawa, T. Ishigaki, Evaluation of hydrogenbonding distance in organic nonlinear optical crystals for high-output terahertz-wave generation, J. Mol. Struct. 1134 (2017) 835e839. Doi.org/ 10.1016/j.molstruc.2017.01.025. [4] H.A. Petrosyan, H.A. Karapetyan, M.Y. Antipin, A.M. Petrosyan, Nonlinear optical crystals of l-histidine salts, J. Cryst. Growth 275 (2005) 1919e1925, https://doi.org/10.1016/j.jcrysgro.2004.11.258. [5] P.S.P. Silva, Cardoso Cl audia, M.R. Silva, A.P. Jose, A.M. Beja, M.H. Garcia, N. Lopes, Crystal structure and experimental and theoretical studies of the second-order nonlinear optical properties of salts of triphenylguanidine with carboxylic acids, J. Phys. Chem. A 114 (2010) 2607e2617. Doi.org/10.1021/ jp909005q. [6] M. Shankar, A. Dennis Raj, R. Purusothaman, M. Vimalan, S. Athimoolam, I. Vetha Potheher, Studies on optical, electrical, mechanical and theoretical investigation of 4-nitrobenzoic acid (3-ethoxy-2-hydroxy-benzylidene)-hydrazide: a novel Schiff base organic NLO material, J. Mol. Struct. 1181 (2019) 348e359, https://doi.org/10.1016/j.molstruc.2018.12.082. [7] P. Muthuraja, M. Sethuram, T. Shanmugavadivu, M. Dhandapani, Single crystal X-ray diffraction and Hirshfeld surface analyses of supramolecular assemblies in certain hydrogen bonded heterocyclic organic crystals, J. Mol. Struct. 1122 (2016) 146e156. Doi.org/10.1016/j.molstruc.2016.05.083. [8] R.M. Ramadan, M. Ali, E. Atrash, M.A. Amany, Ibrahim, Charge transfer

32

[9]

[10]

[11]

[12]

[13]

[14] [15] [16] [17] [18] [19] [20]

[21] [22]

[23] [24]

[25] [26]

[27]

[28] [29]

[30] [31]

[32]

[33]

[34]

S. Madhan kumar et al. / Journal of Molecular Structure 1197 (2019) 19e33 complexes of some thiazoles and benzothiazoles with certain nitrobenzene derivatives, Spectrochim. Acta, Part A 46 (1990) 1305e1312, https://doi.org/ 10.1016/0584-8539(90)80134-k. O.Z. Yesilel, M. Odabasoglu, O. Buyukgungor, Supramolecular squarate and hydrogensquarate compounds with 4-amino-1,2,4-triazole, 2-aminothiazole and 2-aminobenzimidazole, J. Mol. Struct. 874 (2008) 151e158. G.R. Desiraju, Designer crystals: intermolecular interactions, network structures and supramolecular synthons, Chem. Commun (1997) 1475e1482. Doi.org/10.1039/a607149j. S. Karthigha, S. Kalainathan, F. Hamada, M. Yamada, Y. Kondo, Synthesis, growth and third-order nonlinear optical properties of quinolinium single crystal-PCLQI, RSC Adv. 6 (2016) 33159e33169, https://doi.org/10.1039/ C6RA05055G. M. Sheik-Bahae, A.A. Said, E.W. Van Stryland, High-sensitivity, single-beam n2 measurements High-sensitivity, single-beam n2 measurements, Opt. Lett. 14 (1989) 955e957, https://doi.org/10.1364/ol.14.000955. M. Sheik-Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W. Van Stryland, Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron. 26 (1990) 760e769, https://doi.org/10.1109/3.53394. B. Jindawong, S. Chantrapromma, H. k. Fun, C. karalai, ActaCryst E61 (2005) 03237e03239. J.L. Bredas, C. Adant, P. Tackx, A. Persoons, B.M. Pierec, Chem. Rev. 94 (1) (1994) 243e278. A.I. Vogel, Test Book of Practical Organic Chemistry, fifth ed., London, 1989. G.M. Sheldrick, Crystal structure refinement with SHELX-97, Acta Crystallogr. C Cryst. Struct. 71 (2015) 3e8, https://doi.org/10.1107/s2053229614024218. G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. A 64 (2008) 112e122, https://doi.org/10.1107/s0108767307043930. G.M. Sheldrick, SADABS, University of Gottingen, Gottingen, Germany, 2008. C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.R. Monge, R. Taylor, J.V.D. Streek, P.A. Wood, J. Appl. Crystallogr. 41 (2008) 46e470. A.L. Spek, A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, The Netherlands, 1999. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09’, Revision E.01, Gaussian Inc., Wallingford, CT, 2013. E. D. Glendening, A. E. Reed, J. ECarpenter, F. Weinhold, NBO Version 3.1, Theoretical Chemistry Institute, University of Wisconsin, Madison. S.K. Wolf, D.J. Grimwood, J.J. McKinnon, M.J. Turner, D. Jayatilaka, M.A. Spackman, CrystalExplorer Version 3.1, University of Western Australia, 2012. M.A. Spackman, D. Jayatilaka, Hirshfeld surface analysis, CrystEngComm 11 (2009) 19e32, https://doi.org/10.1039/b818330a. M.A. Spackman, J.J. Mckinnon, Fingerprinting intermolecular interactions in molecular crystals, CrystEngComm 4 (2002) 378e392. Doi.org/10.1039/ b203191b. K. Sathya, P. Dhamodharan, M. Dhandapani, Computational, spectral and structural studies of a new non linear optical crystal: 2-hydroxy pyridinium 3, 5-dinitrobenzoate, J. Mol. Struct. 1130 (2017) 414e424, https://doi.org/ 10.1016/j.mol.struc.2016.10.018. H.O. Kalinowski, S. Berger, S. Braun, Carbon-13 NMR Spectroscopy, John wiley & Sons, Chichester, 1988, https://doi.org/10.1016/S0003-2670 (00)81981-9. P. Muthuraja, T. Joselin Beaula, T. Shanmugavadivu, V. Benajothy, M. Dhandapani, Hydrogen bonded R22(8) graph set in inducing charge transfer mechanism in guanidinium-3,5-dinitrobenzoate: a combined experimental, theoretical and Hirshfeld surface study, J. Mol. Struct. 1137 (2017) 649e662, https://doi.org/10.1016/j.mol.struc.2017.02.067. G.C. Pimental, A.L. McClellan, The Hydrogen Bond, Freeman, San Francisco, 1960. F.P. Anderson, J.F. Gallagher, P.T.M. Kenny, A.J. Lough, Redetermination of para-aminopyridine(fampridine, EL-970) at 150 K, Acta Crystallogr. 61 (2005) 1350e1353. A.A. Prasad, K. Muthu, V. Meenatchi, M. Rajasekar, R. Agilandeshwari, K. Meena, J.V. Manonmoni, S.P. Meenakashisundram, Optical, vibrational, NBO, first-order molecular hyperpolarizability and Hirshfeld surface analysis of a nonlinear optical chalcone, Spectrochim. Acta, Part A 140 (2015) 311e327, https://doi.org/10.1016/j.saa.2014.12.011. P. Muthuraja, T. Joselin Beaula, T. Shnmugavadivu, V. Bena jothy, M. Dhandapani, Hydrogen bonded R22(8)graph set in inducing charge transfer mechanism in guanidinium-3,5-dinitrobenzoate: a combined experimental, theoretical and Hirshfeld surface study, J. Mol. Struct. 1137 (2017) 649e662, https://doi.org/10.1016/j.molstruc.2017.02.067. C. Adant, M. Dupuis, J.L. Bredas, Ab initio study of the nonlinear optical

[35]

[36]

[37]

[38] [39]

[40]

[41]

[42]

[43]

[44]

[45] [46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

properties of urea: electron correlation and dispersion effects, Int. J. Quantum Chem. 56 (S29) (1995) 497e507, https://doi.org/10.1002/qua.560560853. A.B. Ahmed, H. Feki, Y. Abid, H. Boughzala, C. Minot, A. Mlayah, Crystal structure, vibrational spectra and theoretical studies of l-histidinium dihydrogen phosphate-phosphoric acid, J. Mol. Struct. 920 (2009) 1e7, https:// doi.org/10.1016/j.mol.struc.2008.09.029. M. Sethuram, G. Bargavi, M. Rajasehakaran, M. Dhandapani, G. Amirthaganeshan, Synthesis, crystal, growth and characterization of 2aminomethylpyridinium picrate (2- ampp)- a charge transfer molecular complex and organic optical material, Optic 125 (2014) 55e60. Doi.org/ 10.1016/j.ijleo.2013.06.069. T. Joselin Beaula, I. Hubert Joe, V.K. Rastogi, V. Bena jothy, Spectral investigations, DFT computations and molecular docking studies of the antimicrobial 5-nitroisatin dimer, J. Chem. Phys. Lett. 624 (2015) 93e101, https:// doi.org/10.1016/j.cplett.2015.02.026. M. Suenga, Development of GUI for games/FMO calculations, J. Comput. Chem. Jpn. 7 (2008) 33e54. Doi.org/10.2477/jccj.h1920. A.E. Read, L.A. Curtiss, F. Weinhold, Intermolecular interactions from a natural bond orbital, donor-aceptor view point, Chem. Rev. 88 (1988) 899e926. Doi.org/10.1021/cr00088a005. T. Shanmugavadivu, K. Senthil kumar, M. Dhanadapani, P. Muthuraja, S. Balachandar, M. Sethu Raman, Theoretical and experimental evaluation of a new organic proton transfer crystal aminoguanidinium p-nitrobenzoate monohydrate for optical limiting applications, J. Phys. Chem. Solids 111 (2017) 82e94, https://doi.org/10.1016/j.jpcs.2017.07.015. N. Castillo, C.F. Matta, R.J. Boyd, The first example of a cage critical point in a single ring: a novel twisted a-helical ring topology, Chem. Phys. Lett. 409 (2005) 265e269, https://doi.org/10.1016/j.cplett.2005.04.088. P.S. Vinod kumar, V. Raghavendra, V. Subramanian, Bader's theory of atoms in molecules (AIM) and its applications to chemical bonding, Chem. Sci. 128 (2016) 1527e1536, https://doi.org/10.1007/s12039-016-1172-3. P. Dhamodharan, K. Sathya, M. Dhanadapani, Studies on synthesis, structural, luminescent and thermal properties of a new non-linear optical crystal: 4amino-4H-1,2,4-triazol-1-ium-3-hydroxy-2,4,6-trinitrophenolate, Physica B 508 (2017) 33e40, https://doi.org/10.1016/j.physb.2016.12.009. S. Karthigha, S. Kalainathan, K.U.M. Rao, F. Hamada, M. Yamada, Y. Kondo, Synthesis, Growth, Structural, Optical, Luminescence, Surface and HOMO LUMO analysis of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate organic single crystals grown by slow evaporation technique, J. Cryst. Growth 436 (2016) 113e124. Doi.org/10.1016/ j.jcrysgro.2015.11.028. T. Shimazaki, T. Nakajima, Phys. Chem. Chem. Phys. 18 (2016) 27554, https:// doi.org/10.1039/c6cp04863c. M. Jose, R. Uthrakumar, A.J. Rajendran, S.J. Das, Optical and spectroscopic studies of potassium p-nitrophenolate dihydrate crystal for frequency doubling applications, Spectrochim. Acta 86 (2012) 460e495, https://doi.org/ 10.1016/j.saa.2011.11.002. T. Shanmugavadivu, S. Balachandar, P. Muthuraja, M. Dhandapani, Structural, computational and Hirshfeld surface analysis of a proton transfer crystal, amino (2-(propa n-2-ylidene) hydrazinyl) methaniminium picrate, J. Mol. Struct. 1171 (2018) 793e807, https://doi.org/10.1016/j.molstruc.2018.06.021. J.L. Oudar, Optical nonlinearities of conjugated molecules. Stilbene derivatives and highly polar aromatic compounds, J. Chem. Phys. 67 (1977) 446e457, https://doi.org/10.1063/1.434888. Y. Li, P. Song, J. Liu, R. Su, M. Ahao, Charge transfer and optoelectronic properties in the triartrylamine-based donor-bridge acceptor dyes for dyesensitized solar cells, Mol. Simul. 39 (2013) 521e528, https://doi.org/ 10.1080/08927022.2012.751532. R. Nithya, k. Senthilkumar, Charge transport and optical properties of crossconjugated organic molecules: a theoretical study, Org. Electron. 15 (2014) 1607e1623, https://doi.org/10.1016/j.orgel.2014.04.025. P. Justin, K. Anitha, S.S.R. Inbanathan, G. Giester, M. Fleck, Growth, structural, thermal, mechanical, optical and third order nonlinear optical studies of 3hydroxy 2-nitropyridine single crystal, J. J. Opt. Mat.opt. mat 86 (2018) 562e570, https://doi.org/10.1016/j.optmat.2018.10.047. H.J. Ravindra, A. John Kiran, S.M. Dharmaprakash, N. satheesh Raj, K. Chandrasekharan, B. Kalluraya, F. Rotermund, Growth and characterization of an efficient nonlinear optical D-p-A-p-D type chalcone single crystal, J. Cryst. Growth 310 (2008) 4169e4176. Doi.org/10.1016/ j.jcrysgro.2008.06.045. M. Suriya, B. Milton Boaz, G. Chakkaravarthi, G. Vinitha, K. Sakthi Murugesan, Synthesis, crystal growth, structural, spectral, thermal, optical characteristics and density functional theory calculations of a novel third-order nonlinear optical material: 4-acetylanilinium dihydrogen phosphate (4AADP) single crystals, J. Mol. Struct. 1180 (2019) 330e343, https://doi.org/10.1016/ j.molstruc.2018.12.001. H.C. Kwong, M.S. Rakesh, C.S.C. Kumar, S.R. Maidur, P.S. Patil, C.K. Quah, Y.F. Win, C. Parlak, S. Chandraju, Structureeproperty Relation and Third-Order Nonlinear Optical Studies of Two New Halogenated Chalcones, 2017, https:// doi.org/10.1515/zkri-2017-2098. Z. Lian, K. Jiang, T. Loub, Structures and third-order nonlinear optical properties of two three-dimensional Cd(II) coordination polymers with trinodal (3, 4, 5) and dinodal (4, 5) connected network topologies, RSC Adv. 5 (2015) 82781e82788, https://doi.org/10.1039/c5ra14734d. P. Liu, Q. Liu, N. Zhao, C. Ana, Z. Liana, Structure and third-order nonlinear

S. Madhan kumar et al. / Journal of Molecular Structure 1197 (2019) 19e33 optical properties of the two-dimensional CoII coordination polymer [Co(1,2BIB)(PA)]n {1,2-BIB is 1,2-bis[(1Himidazol-1-yl)methyl]benzene and H2PA is phthalicacid}, Acta Crystallogr. C72 (2016) 890e894, https://doi.org/10.1107/ S2053229616015928. [57] R. Shivaraj, P. Maidur, S. Patil, A. Ekbote, T.S. Chia, C.K. Quah, Molecular

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structure, second- and third-order nonlinear optical properties and DFT studies of a novel non-centrosymmetric chalcone derivative: (2E)-3-(4fluorophenyl)-1-(4-{[(1E)- (4-fluorophenyl)methylene]amino}phenyl)prop2-en-1-one, Spectrochim. Acta Mol. Biomol. Spectrosc. 184 (2017) 342e354, https://doi.org/10.1016/j.saa.2017.05.015.