Supramolecular network through NH…O, OH…O and CH…O hydrogen bonding interaction and density functional theory studies of 4-methylanilinium-3-carboxy-4-hydroxybenzenesulphonate crystal

Accepted Manuscript Supramolecular network through N-H...O, O-H...O and C-H...O hydrogen bonding interaction and density functional theory studies of 4-methylanilinium-3-carboxy-4hydroxybenzenesulphonate crystal

M. Rajkumar, P. Muthuraja, M. Dhandapani, A. Chandramohan PII:

S0022-2860(17)31344-3

DOI:

10.1016/j.molstruc.2017.10.013

Reference:

MOLSTR 24384

To appear in:

Journal of Molecular Structure

Received Date:

11 August 2017

Revised Date:

03 October 2017

Accepted Date:

04 October 2017

Please cite this article as: M. Rajkumar, P. Muthuraja, M. Dhandapani, A. Chandramohan, Supramolecular network through N-H...O, O-H...O and C-H...O hydrogen bonding interaction and density functional theory studies of 4-methylanilinium-3-carboxy-4-hydroxybenzenesulphonate crystal, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.10.013

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ACCEPTED MANUSCRIPT Highlights  4MABS salt was synthesized and grown as single crystals  The title salt involves extensive N-H...O, O-H...O and C-H...O hydrogen bonding interactions.  The grown crystal is thermally stable up to 235 ºC.  The first hyperpolarizability (β) is found to be 5.01 times that of urea.  The Vickers microhardness studies confirm the soft nature of the grown crystal.

ACCEPTED MANUSCRIPT Graphical abstract

ACCEPTED MANUSCRIPT Supramolecular network through N-H...O, O-H...O and C-H...O hydrogen bonding interaction and density functional theory studies of 4-methylanilinium-3-carboxy-4hydroxybenzenesulphonate crystal M. Rajkumara,b, P. Muthurajaa, M. Dhandapania, A. Chandramohana* a Post-Graduate

and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya

College of Arts and Science, Coimbatore - 641 020, Tamil Nadu, India. b

Department of Chemistry, KIT-Kalaignarkarunanidhi Institute of Technology, Coimbatore-

641 402, Tamil Nadu, India. Abstract By utilizing the hydrogen bonding strategy, 4-methylanilinium-3-hydroxy-4-corboxybenzenesulphonate (4MABS), an organic proton transfer molecular salt was synthesized and single crystals of it were successfully grown by slow solvent evaporation solution growth technique at ambient temperature. The 1H and

13C

NMR spectra were recorded to establish

the molecular structure of the title salt. The single crystal XRD analysis reveals that the title salt crystallizes in monoclinic crystal system with centrosymmetric space group, P21/n. Further, the title salt involves extensive intermolecular N-H...O, O-H...O and C-H...O as well as intramolecular O-H...O hydrogen bonding interactions to construct supramolecular architecture. All quantum chemical calculations were performed at the level of density functional theory (DFT) with B3LYP functional using 6-311G (d,p) basis atomic set. The photoluminescence spectrum was recorded to explore the emission property of the title crystal. The presence of the various vibrational modes and functional groups in the synthesized salt was confirmed by FT-IR studies. The thermal behaviour of title crystal was established employing TG/DTA analyses. The mechanical properties of the grown crystal

ACCEPTED MANUSCRIPT were determined by Vicker’s microhardness studies. Dielectric measurements were carried out on the grown crystal at a different temperature to evaluate electrical properties. Keywords: Crystal structure, Hydrogen bonding, Fluorescence, Thermal analysis, DFT *Corresponding author Tel.: +919994283655. E-mail address: [email protected] (A. Chandramohan) 1. Introduction The design and construction of multicomponent functional materials (cocrystals/organic salts) have attracted considerable attention in recent years owing to their potential applications in the optics and nonlinear optics. These materials can be achieved by the utilization of intermolecular non covalent interactions such as hydrogen bond, stacking, electrostatic and charge-transfer interactions [1]. Of these interactions, hydrogen bond interactions are the most powerful supramolecular interactions through which many topology structures such as an infinite 1-D chain, 1-D tapes, 2-D sheet, and 3-D networks have been assembled [2]. Recently, hydrogen bonding interactions have been widely utilized in the field crystal engineering, material science and supramolecular chemistry as well as biological recognition [3-6]. The application of intermolecular hydrogen bonds is well established in the field of the crystal designing to synthesis co crystals and organic salts due to its strength and directional properties [7]. The acid strength of aromatic sulfonic acids ensures the formation of proton transfer compounds from their reaction with most Lewis bases. Moreover, the availability of O atoms of the sulfonate group as proton-accepting centers for hydrogen bonding associations can be utilized for supramolecular assembly [8]. Especially, 5sulfosalicylic acid is an important acid possessing three potential groups such as OH, COOH and SO3H which leads to form construct supramolecular arrays through strong hydrogen

ACCEPTED MANUSCRIPT bonding interactions when it interacted with organic bases (aliphatic and aromatic amines, and heterocyclic compounds containing N atoms) [9-12]. In this background, we report the formation of the proton transfer molecular salt obtained from the reaction of 4-methylaniline with 4-methylanilinium-3-carboxy-4-hydroxybenzenesulphonic acid. Crystal structure, supramolecular assembly through hydrogen bonding interactions, theoritical calculations, thermal, mechanical and electrical properties of the title crystal are presented in this paper. 2. Experimental details 2.1. Material synthesis and growth of single crystal AR grade 4-methylaniline and 3-carboxy-4-hydroxybenzenesulphonic acid were used for

the

synthesis.

Equimolar

solutions

of

4-methylaniline

and

3-carboxy-4-

hydroxybenzenesulphonic acid were prepared separately in methanol and millipore water of resistivity 18.2 mΩ, respectively. The two solutions were henceforth mixed together, stirred well for about an hour and heated gently to get the uniform concentration of the entire solution. The resulting solution was filtered through a quantitative Whatmann 41 grade filter paper to eliminate all the suspended impurities. The filtrate was then collected in a 100 ml beaker and kept aside unperturbed in an atmosphere most suitable for the growth of single crystals. Good optical quality single crystals of the title compound were harvested for about eight days time period. The reaction scheme and the photograph of as-grown crystals are shown in Figs.1and 2, respectively. 2.2. Instrumentation techniques Elemental analysis was performed on a Perkin Elmer 240C elemental analyzer. UVvisible spectrum was recorded employing a systronics make double beam UV-vis spectrophotometer 2202 in the range of 200-800 nm and DMSO was used as solvent. The title salt crystal was subjected to FT-IR spectral analysis on a Perkin Elmer FT-IR 8000

ACCEPTED MANUSCRIPT spectrophotometer in the frequency range 4000-400cm-1 using the KBr pellet method. Photoluminescence emission spectrum was recorded by exciting the sample with a radiation of wavelength 290 nm in the wavelength range 300-550 nm using a Horiba Jobin Yvon model FL3-22 Fluorolog spectrofluorimeter. NMR spectra were performed in DMSO solvent employing a Bruker AV III 500 MHz spectrometer. TG and DTA thermal analyses were simultaneously carried out on a NETZSCH STA 409 C/CD TG/DTA thermal analyzer in the temperature range 40-575 ºC in nitrogen atmosphere at a heating rate of 10 ºC min-1. The mechanical property was determined by Vickers microhardness tester (HMV SHIMADZU, make: HMV-2T). Dielectric studies were carried out in the frequency range from 50 Hz to 5 MHz at different temperatures using Hioki LCR 3532-50 LCR meter. Single crystal X-ray diffraction data were collected on well grown single crystal at 298 K on a Bruker SMARTAPEX CCD diffractometer equipped with a fine focused sealed tube. The unit cell parameters were determined and the data collections were performed using a graphitemonochromated Mo Kα (λ = 0.71073 Å) radiation by φ and ω scans. Further, the collected data were reduced by SAINT program [13] and the empirical absorption corrections were carried out using the SADABS program [14]. The structure were solved by direct methods [15] using SHELXS-97 which revealed the position of all non-hydrogen atoms, and it was refined by full-matrix least squares on F2 (SHELXL-97) [16]. All non-hydrogen atoms were refined anisotropically, while the hydrogen atoms were placed in calculated positions and refined as riding atoms. 2.3. Theoretical calculations The molecular geometry of the title compound was optimized by using the DFT method with a hybrid functional B3LYP (Becke3-Lee-Yang-Parr) using Gaussian 09 program package with 6-311G (d,p) basis set [17]. The optimized structure, bond parameters,

ACCEPTED MANUSCRIPT HOMO-LUMO, MEP, NBO and NLO calculations were performed at the same level using Gauss view(version 5) program[18] . 3. Results and discussion 3.1. Elemental analysis Elemental analysis is an essential tool to determine the percentage composition of the elements, stoichiometry proportion and the purity of the compound. The percentage composition of the elements present in the 4MABS salt are C = 51.76% (51.68%), H = 4.56% (4.65%), N = 4.23% (4.31%). The elemental analysis data indicates that the experimental and calculated (given in brackets) values are in good agreement with each other within the permissible error. Further, it confirms that the title salt is free from and devoid of water molecules. 3.2. UV-Visible absorption Studies UV-Visible spectroscopy provides the information about the electronic structure of the organic molecules. UV-Visible absorption spectrum was obtained due to excitation of the ground state electrons to higher energy states by the absorption of light energy. The UVVisible absorption spectrum was recorded and the corresponding spectrum is shown in Fig.3. The spectrum exhibits the characteristic absorption bands attributed to the usual π-π* and nπ* transitions occurring in title salt crystal. The strong bands observed at 210 and 236 nm are attributed to the most probable π-π* transition and a weak band appearing at 310 nm is assigned to the symmetry forbidden n- π* transitions. 3.3. Fluorescence emission studies Fluorescence can be observed in molecules that are aromatic or contain multiple conjugated system double bonds with a high degree of resonance stability [19]. The

ACCEPTED MANUSCRIPT fluorescence emission spectrum was recorded in the range 500 to 900 nm with the excitation wavelength of 290 nm and depicted in Fig.4. The two broad bands observed in the range 380450 and 450-580 nm confirm the blue and green fluorescence emission of the 4MABS crystal respectively. 3.4. FT-IR Spectral analysis Infrared spectroscopy has proven to be a potential tool not only for the recognition of proton transfer and hydrogen bonding interactions but also for the identification of their functional groups present in the organic compounds [20]. The FT-IR spectrum of 4MABS crystal was recorded and the spectrum is depicted in Fig.5. The characteristic vibrational bands of the functional groups and their assignments are given in Table 1. The strong and broad bands in the range of around 3700-3100 cm-1 are the characteristic of hydrogen bonded O-H and N-H stretching vibrational frequencies [21]. A sharp band at 3241 cm-1 represents phenolic N+-H asymmetric stretching vibration which further widened up to 3150 cm-1 due to the presence of hydrogen bonded O-H stretching vibration. The absorption band at 3079 cm-1 corresponds to aromatic C-H stretching vibration. The aliphatic C-H asymmetric stretching in the salt is observed at 2972 cm-1 and the corresponding symmetric stretching vibration appears at 2870 cm-1. The appearance of e carboxylic C=O stretching vibrations at 1682 cm-1 confirms that the COOH group remains unionised. As has been expected aromatic ring, aromatic C=C stretching vibrations are observed at 1616, 1594 and 1517cm-1. Two distinct bands observed at 1488 and 1375 are characteristics of asymmetric and symmetric C-H inplane-bending vibrations, respectively. The asymmetric and symmetric S=O stretching vibration appear at 1354 and 1161cm-1, respectively which are distinct of the deprotonated sulphonate group [20]. The C-N stretching vibration is observed at 1341 cm-1. The absorption band at 1293 cm-1 corresponds to the C-O stretching vibration. The absorption at 921 cm- is

ACCEPTED MANUSCRIPT consistent with O-H out-of-plane bending vibration. The S-O stretching vibration appears at 907 cm-1. The band at 805 cm-1 owes to the aromatic C-H out-of-plane bending mode. 3.5. NMR spectral analysis NMR spectroscopy is the most powerful tool to elucidate the structure of the organic compound.

1H

and

13C

NMR spectra were recorded in deuterated methanol and shown in

Fig.6. The proton NMR spectrum pronounces seven signals at different position under the influence of the magnetic field which confirms the presence of the seven different kinds of protons in the title compound. A singlet signal at δ 8.34 ppm owes to the C2 aromatic protons of 3-carboxy-4-hydroxybenzenesulfonate moiety. The C6 proton signal of 3-carboxy-4hydroxybenzenesulfonate moiety is observed as a doublet at δ 7.90 ppm. Another doublet signal at δ 7.33 ppm owes to C2 and C6 aromatic protons of the same kind in the 4methylaniline moiety. The signal due to C3 and C5 aromatic protons of the same kind in the 4-methylaniline moiety resonates as a doublet at δ 7.27 ppm. The appearance of doublet signal at δ 6.9 ppm represents the C5 protons of 3-carboxy-4-hydroxybenzenesulfonate moiety. A broad singlet at δ 4.98 ppm is attributed to the proton of phenolic O-H group present in the 3-carboxy-4-hydroxybenzenesulfonate moiety. The most intense signal at δ 2.38 ppm owes to the methyl protons of 4-methylaniline moiety. The signal due to COOH does not appear because of fast deuterium exchange taking place in this group. The 13C NMR spectrum exhibits twelve distinct carbon signals which unambiguously confirm the formation of the molecular salt. The highly deshielded carboxyl carbon of the 3carboxy-4-hydroxybenzenesulfonate moiety appears in the downfield region at δ 171.55ppm. The carbon signal at δ 163.11 ppm is assigned to the C4 carbon of 3-carboxy-4hydroxybenzenesulfonate moiety. The ipso carbon of the 4-methylaniline moiety is observed at δ 139.20 ppm. The carbon signal at δ 135.98 ppm is attributed to the C1 carbon of 3carboxy-4-hydroxybenzenesulfonate moiety. The signal observed at δ 132.72 ppm is

ACCEPTED MANUSCRIPT attributed to the C6 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety. The signal at δ 130.28 ppm owes to the C2 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety. The signal at δ 128.28 ppm is due to the C3 and C5 carbon of the same kind in 4-methylaniline moiety. The signal at δ 127.80 ppm is due to the C2 and C6 carbons of the same kind in 4methylaniline moiety. The signal at δ 122.46 ppm is due to the C4 carbon of 4-methylaniline moiety. The signal at δ 116.81ppm is attributed to the C5 carbons of the 3-carboxy-4hydroxybenzenesulfonate moiety. The signal at δ 111.83 ppm is attributed to the C3 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety. The signal at δ 19.6 ppm is due to methyl carbon of 4-methylaniline moiety. The 1H and

13C

NMR chemical shift values and their

corresponding assignments are summarized in the Table 2. 3.6. Single crystal X-ray diffraction analysis The single crystal XRD analysis has been carried out on the grown single crystal which indicates that the crystal belongs to monoclinic crystal system with centrosymmetric space group, P21/n. The crystallographic data and structure refinements of the crystal are given in Table 3. Lattice parameters are a= 9.4932(8), b= 12.2889(12) c= 12.5382(11) Å, α = 90, β =98.907(8), γ =90° and the unit cell volume is 1445.1(2) Å3. Fig. 7(a) shows the ORTEP of the molecule viewed drawn at 50 % probability thermal displacement ellipsoids with the atom numbering scheme. The proton 5-sulfosalicylic acid is transferred to the N atom of 4-methylaniline to form molecular salt. Here, only the proton of the 5-sulfosalicylic acid has transferred to the N atom of 4-methylaniline whereas the protons of both COOH and OH remain unionized due to the strong acidic nature of SO3H group than that of carboxylic and phenolic groups. The selected bond lengths and bond angles are given in Tables 4 and 5, respectively. The S-O bond distances in the SO3- group are ranging from 1.4331(19) to 1.4579(19) Å which are in the range of the deprotonated sulphonic group [20]. The C-O (O (6)-C (4), 1.343(3) Å) bond distance also indicates unionisation phenolic group. As per free

ACCEPTED MANUSCRIPT COOH group concerned, two C-O bond lengths are quiet different between (O (4)-C(7), 1.304(3) Å) and (O(5)-C(7), 1.221(3) Å). In the asymmetric unit of the crystal packing, there was the existence of one 4-methylanilinium and one 3-carboxy-4-hydroxybenzenesulfonate ions. The packing arrangement of the molecule viewed down ‘a’, ‘b’ and ‘c’-axes is as shown in Fig.8. The 4-methylaniline ion is connected to 5-sulfosalicylate ion through N(1) -H(10A) ...O(5) intermolecular hydrogen bonding to form a heterodimer. As expected for the 5sulfosalicylate moiety, it shows O (6)-H (2)...O (5) intramolecular hydrogen bonding with OO distance of 2.587(3) Å [22]. It is noted that there is head to tail arrangement of acid moieties viewed along the c-axis where the carboxylic hydrogen approaches sulphonic oxygen and gives raised to a supramolecular O-H...O hydrogen boning interaction. The centroid-centroid distance of acid and base moieties is 3.864 Å which also illustrates the supramolecular architecture developed from π...π interactions. The hydrogen bond interactions involved in the 4MABS is shown in Table 6. 3.7. Optimized molecular geometry The molecular structure of 4MABS salt crystal was optimized using density functional theory employing B3LYP method with 6-311G (d,p) basis set and the resulting optimized structure is depicted in Fig.7(b). The comparison of the bond lengths and bond angles obtained from the optimized structures are given in Table 4 which is in agreement with the values of the X-ray crystal structure data with slight variations. The calculated bond lengths for S1-O1, S1-O2 and S1-O3 are 1.650, 1.657 and 1.646 Å, respectively and the corresponding experimental values are 1.4579(19), 1.442(2) and 1.4331(19) Å, respectively. The optimized C=O band length is 1.247 where as the C-O band length is 1.353 Å. The calculated C-C band lengths of the aromatic ring are found in the range of 1.37-1.41 while the experimental values are in the range of 1.36-1.39 Å. It was found that slight variations of optimized bond lengths have been observed from experimental values which could be

ACCEPTED MANUSCRIPT attributed to the fact that the theoretical calculations were performed for isolated gaseous phase molecules whereas the experimental results were obtained for solid phase in which intermolecular interactions exist. 3.8. HOMO-LUMO band gap and electronic descriptors The frontier molecular orbitals play pivotal role in the determination of electrical properties, electron conductivity and chemical reactivity of a molecule as well as in recognizing the molecular interaction between the constituents [23, 24]. The surface energy of HOMO and LUMO is presented in Fig.9. For the title salt crystal, the calculated HOMOLUMO energy gap in gas phase was found to be 1.0645 eV. Moreover, the title crystal is hard and less reactive due to small HOMO-LUMO energy gap value. As seen from contour plot of frontier molecular orbital, HOMO is spread over 4-methylaniline moiety and LUMO electron density is localized over 3-carboxy-4-hydroxy benzenesulphonate moiety which leads to intermolecular charge transfer in the title molecular salt crystal. Parr [25] proposed global electrophilicity index (ω) as electrophilicity power of molecule and measured the stabilization energy when system acquires an additional electronic charge from the environment. The calculated values of electronegativity, chemical potential, chemical hardness, softness and electrophilicity index for the title salt are 0.161055 eV, 0.161055 eV, 0.152245 eV, 3.28418 eV and 0.0851 eV, respectively. 3.9. Molecular electrostatic surface potential (MESP) Molecular electrostatic surface potential provides information about the net electrostatic effect produced at a point in space by the total charge distribution over the molecule [26]. Further, it paves the way to visualize the relative polarity, to predict the reactivity of molecule towards electrophilic and nucleophilic reactions and helps to study drug-receptor interactions, biological recognition and hydrogen bond interactions [27-29]. To

ACCEPTED MANUSCRIPT predict the reactive sites of the title molecule, the electrostatic potential map from optimized geometry is shown in Fig.10. From the MESP, it is evident that negative charge is spread over the oxygen atoms of sulphonate, carboxy and hydroxy groups which prefer electrophilic attack whereas the positive region is mostly located around the hydrogen atoms for nucleophilic attack. These sites give information about region where the title salt can have intermolecular interactions. 3.9. Mulliken charge analysis The Mulliken charge analysis is an effective method for population analysis and finds applications in quantum mechanical calculations to represents the charge distribution of each atom present in a molecular system. The dipole moment, polarizability and electronic structure are strongly influenced by charge distributions of a molecule [30]. The atomic charge values calculated by Mulliken charge distribution method are shown in Fig.11. The charge of nitrogen atom of the molecular salt is highly negative and its protonated hydrogen atoms possess higher positive charge compared to other hydrogen atoms. The charge of sulphur atom is found to most positive among all the atoms whereas the oxygen atoms attached to sulphur atom show remarkable negative charge. Further, the eight carbon atoms of the phenyl rings (C7, C12, C13, C24, C26, C29, C32 and C34) are negative due to the withdrawing substituents in its surrounding while the remaining five carbon atoms attached to electronegative atoms are positive (C6, C10, C15, C17 and C28). It is also observed that the hydrogen atoms of phenolic and carboxyl groups show reasonably higher value owing to the presence of intra molecular O-H…O hydrogen bonding. 3.10. Hyperpolarizability calculations Quantum calculations accompanied with DFT approach are precious tool for predicting relationship between electronic structure and NLO response of organic materials

ACCEPTED MANUSCRIPT thereby identification of the molecular NLO properties of the material [31]. Nonlinear optical properties of a material find wide range of applications in the emerging technologies such as optics and electro-optics. The calculated dipole moment (μ), polarizability (α) and first order hyperpolarizability(β) of the 4MABS crystal are given in Table 6. The first hyperpolarizability value of the title compound is found to be 5.01 times that of urea (0.3728 x 10-30 esu). The enhancement in the hyperpolarizability owes to the charge transfer from the electron donating group through the π-conjugation system to the electron accepting group to extent the conjugation of the molecular salt crystal. Hence, the large β value indicates that the title salt crystal is an attractive material for NLO applications. 3.11. TG/DTA Thermal analyses The thermal properties of 4MABS crystal were studied by thermo gravimetric and differential thermal analyses. The powdered sample weighing 4.840 mg was analyzed and the thermogram is depicted in Fig.12. From TG curve, it is understood that the substance is stable up to 235°C and moisture free and it decomposes immediately after melting. The TG curve shows a two stage weight loss pattern when the material was heated from 50 to 600 ºC. The first stage decomposition commences immediately after melting at 235 ºC with the elimination of 38.01 % of material into gaseous products. The second stage decomposition noticed between the temperature 300 and 250 ºC incurs a weight loss of 68.66 % of the material into various gaseous products. The DTA curve shows two endothermic dips occurring at 240 ºC and 550 ºC. The first sharp endothermic dip at 240 ºC is attributed to the melting point of the compound which is in good agreement with the melting point verified using the capillary melting point apparatus. This is followed by another small endothermic dip at 330ºC which coincides with the second decomposition curve in TG thermogram. Hence, 4MABS crystal is thermally stable up to 235 ºC and it has high thermal stability than that of N,N-dimethylanilinium-3-carboxy-4-hydroxybenzenesulphonate [20].

ACCEPTED MANUSCRIPT 3.12. Micro hardness study The mechanical hardness is related to structure and nature of bonding in the crystalline materials. Microhardness test is one of the important methods used to understand the mechanical properties of materials such as yield strength, fracture behavior, molecular bindings, cracking temperature and elastic constants [32, 33]. Microhardness study was carried out using a Shimadzu microhardness tester (make: HMV-2T) fitted with a diamond pyramidal indenter. Hardness of the crystals was calculated using the relation

()

Hv = 1.8544

P

2

d

Kg/mm2

Where, Hv is Vicker’s microhardness number, P is the indenter load and d is the diagonal length of the impression. The microhardness measurements are carried out on a well-developed crystal at room temperature with a constant indentation time of 15 S for all indentations. The variation of microhardness profile as a function of applied load is shown in Fig.13 (a). From the microhardness study, it is understood that hardness increases with increasing applied load (Reverse Indentation Size Effect). When the load was increased to 100g, cracks were developed on the smooth surface of the crystal due to the release of internal stress generated locally by indentations. The plot of log P against log d is shown in Fig.13(b). The work hardening coefficient of grown crystal was determined by the leastsquares fit method. According to Onitsch, the work hardening coefficient (n) lies between 1.0 and 1.6 for hard materials and above 1.6 for soft materials [34]. The work hardening coefficient of the grown crystal is found to be 4.66. Like other organic salt crystals, the grown crystal also belongs to soft material category and it could be used as good engineering material for device fabrication. 3.13. Dielectric studies

ACCEPTED MANUSCRIPT The dielectric measurement of the material provides information about electrical properties that determine suitability for practical device applications [35]. The dielectric constant of 4MABS crystal was measured as a function of frequency varies from 50 Hz to 5 MHz at temperature ranging from 303-373 K. The dielectric constant was calculated using the following formula

εr =

C pd εoA

Where, Cp is the measured parallel capacitance, d is the thickness of the crystal, A is the electrode area, εr dielectric constant and εₒ is the vacuum permittivity (8.85 x 10-12 F/m). Fig.14 (a) and (b) illustrate the relationship between dielectric constant and dielectric loss with respect to applied frequencies at different temperatures. From the results, it is clear that both the dielectric constant and loss decrease with increasing in frequency for all the temperatures and remain constant at higher frequencies. The high value of dielectric constant at low frequencies owes to the presence of all the four polarizations such as space charge, orientation, ionic and electronic polarizations at higher frequencies, these polarizations cannot follow the applied electric field; hence the dielectric constant is deceased to minimum level [36]. The high value of dielectric loss at low frequencies is due to the oscillation of dipoles and at higher frequencies, all the polarizations are not operative. So no energy is spent to rotate dipoles hence dielectric loss is high. Moreover, as the temperature increases, dipoles are free and respond to the applied electric field so the dielectric constant gets increased. Additionally, the low dielectric constant and dielectric loss at higher frequencies clearly reveals that the title crystal possesses high optical quality and has low defects which are most important and desirable property of the crystalline materials for nonlinear optical applications [37]. Therefore, 4MABS crystal reveals normal dielectric behaviour as like other organic salt crystals such as N,N-dimethylanilinium-3-carboxy-4-hydroxybenzenesulphonate

ACCEPTED MANUSCRIPT [20], 2-amino-4-picolinium 4-aminobenzoate [38], 4-aminopyridinium 4-nitrophenolate 4nitrophenol [39] and 3-hydroxypyridinium 4-nitrobenzoate [40]. 4. Conclusion 4-methylanilinium-3-hydroxy 4-carboxy-benzene sulphonate, an organic molecular salt was synthesized and grown as single crystals by slow solvent evaporation solution growth technique at ambient temperature. The formation of molecular salt was confirmed by NMR spectral studies. Single crystal XRD analysis indicates that the crystal belongs to monoclinic crystal system with centrosymmetric space group, P21/n. Furthermore, the N-H...O hydrogen bond is the foremost intermolecular force to link the 4-methylanilinium moiety with 3hydroxy-4-carboxy-benzene sulphonate moiety for the construction of supramolecular assembly. Since the potentially hydrogen bonding phenol group is present in the ortho position to the carboxyl group in 3-hydroxy 4-carboxy-benzene sulphonate moiety, it forms the more facile intramolecular O-H...O hydrogen bonding. There is also C-H...O and π-π interactions. From the quantum chemical studies, the experimental and theoretically optimized structures were identical with slight variations in their bond lengths and angles. The HOMO-LUMO energies and MEP map of the title salt crystal reveal their electronic transitional properties, relative polarity and chemical reactivity. The first hyperpolarizability value of the title compound is found to be 5.01 times that of urea. The TG/DTA indicates that the grown crystal is thermally stable up to 235 ºC without any phase transitions. The Vickerss microhardness measurement confirms the soft nature of the grown crystal. The dielectric constant and loss of 4MTBS crystal ascertain the dielectric behaviour which is a requisite for optoelectronic device applications. Acknowledgements

ACCEPTED MANUSCRIPT The authors gratefully acknowledge the School of Chemistry, University of Hyderabad, Hyderabad for providing instrumental facilities. One of the authors M. Rajkumar thanks the UGC Networking Centre, School of Chemistry, University of Hyderabad, for the award of visiting research fellowship to use the facilities at school of chemistry, University of Hyderabad, Hyderabad and grateful to Prof. S. K. Das, University of Hyderabad, Hyderabad for his support and help. Supplementary data CCDC 1413819 contains the crystallographic data for this paper. This data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or E-mail: [email protected]. References [1] D. Ž. Veljković, G. V. Janjić, and S. D. Zarić, Are C–H⋯O interactions linear? The case of aromatic CH donors, CrystEngComm 13 (2011) 5005 [2] S. Jin, M. Guo, D. Wang, H. Cui, Salt and co-crystal formation from 2-(imidazol-1-yl)-1phenylethanone and different acidic components, J. Mol. Struct. 1006 (2011) 128-135. [3] M. Rajkumar, A. Chandramohan, Synthesis, spectral, thermal, mechanical and structural characterization of NLO active organic salt crystal: 3,5-Dimethylpyrazolium-3Nitrophthalate, Mater. Lett.181 (2016) 354-357. [4] G.A. Jeffrey, W. Saenger, Hydrogen Bonding in Biological Structures, Springer-Verlag, Berlin, 1991.

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ACCEPTED MANUSCRIPT Figure captions Fig.1. Reaction scheme of 4MABS crystal Fig.2. Photograph of as-grown crystals of 4MABS from methanol Fig.3. UV-Visible spectrum of the 4MABS crystal Fig.4. Fluorescence emission spectrum of 4MABS crystal Fig.5. FT-IR spectrum of 4MABS crystal Fig.6. 1H and 13C NMR of 4MABS crystal Fig.7(a)-(b). ORTEP diagram of 4MABS crystal with displacement ellipsoids are drawn at 50 % probability level and Optimized molecular geometry Fig.8. Packing diagram of 4MABS crystal viewed along a, b and c axes Fig.9. Frontier molecular orbitals of 4MABS crystal Fig.10. Molecular Electrostatic potential of 4MABS crystal Fig.11. Mulliken’s atomic charges of the optimized molecular structure of 4MABS crystal Fig.12. TG/ DTA thermogram of 4MABS crystal Fig.13(a)-(b). Vickers hardness profile as a function of the applied load and Plot of log d vs. log p for 4MABS crystal Fig.14(a)-(b). Variation of the dielectric constant and dielectric loss with log frequency at different temperatures for 4MABS crystal

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Fig.1. Reaction scheme of 4MABS crystal

Fig.2. Photograph of as-grown crystals of 4MABS from methanol.

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Fig.3. UV-Visible spectrum of the 4MABS crystal Fig. 3. Transmission spectrum and Tacu’s Plot (inset) of 4MABS crystal

Fig.4. Fluorescence emission spectrum of 4MABS crystal

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Fig.5. FT-IR spectrum of 4MABS crystal

Fig.6. 1H and 13C NMR of 4MABS crystal

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Fig.7(a)-(b). ORTEP diagram of 4MABS crystal with displacement ellipsoids are drawn at 50 % probability level and Optimized molecular geometry

Fig.8. Packing diagram of 4MABS crystal viewed along a, b and c axes

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Fig.9. Frontier molecular orbitals of 4MABS crystal

Fig.10. Molecular Electrostatic potential of 4MABS crystal

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Fig.11.The Mulliken’s atomic charges of the optimized molecular structures of 4MABS crystal

Fig.12. TG/ DTA thermogram of 4MABS crystal

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Fig.13 (a)-(b). Vickers hardness profile as a function of the applied load and Plot of log d vs log p for 4MABS crystal

Fig.14(a)-(b). Variation of the dielectric constant and dielectric loss with log frequency at different temperatures for 4MABS crystal

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Table captions Table 1 FT-IR spectral assignments of 4MABS crystal Table 2 NMR spectral data of 4MABS crystal Table 3 Crystallographic data and structure refinement of 4MABS crystal Table 4 Comparison of experimental band lengths [Å] and angles [°] with optimized values of 4MABS crystal Table 5 Hydrogen bonding parameters of 4MABS crystal Table 6 Dipole moment, the average polarizability and the first hyperpolarizability of 4MABS crystal

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Table 1 FT-IR spectral assignments of 4MABS crystal Infrared frequencies (cm-1) Assignments 3241

Phenolic O-H stretching frequency

3191

N+-H stretching vibration

3079

Asymmetric aromatic C-H stretching vibration

2972

Asymmetric aliphatic C-H stretching vibration

2870

symmetric aliphatic C-H stretching vibration

2586

overtone and combination bands

1682

C=O stretching vibration of carbonyl group

1616,1594 and 1517

C=C stretching vibration

1488

Asymmetric bending vibration of CH3

1375

symmetric bending vibration of CH3

1354

Asymmetric S=O Stretching vibration

1341

C-N stretching vibration

1325

O-H in-plane-bending vibration

1293

C-O stretching vibration

1161

Asymmetric S=O Stretching vibration

1030

C-H in-plane-bending vibration

921

O-H out-of-plane bending vibration

907

S-O Stretching vibration

805

C-H out-of-plane bending vibration

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Table 2 NMR spectral data of 4MABS crystal Chemical shift Assignments values (ppm) 1H

NMR

8.34

C2 aromatic protons of 3-carboxy-4-hydroxybenzenesulfonate moiety

7.90

C6 proton of 3-carboxy-4-hydroxybenzenesulfonate moiety

7.33

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

7.27

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

6.9

C5 protons of 3-carboxy-4-hydroxybenzenesulfonate moiety

4.98

Phenolic O-H of the 3-carboxy-4-hydroxybenzenesulfonate moiety

2.38

Methyl protons of 4-methylanilinium moiety

13C

NMR

171.55

Carboxyl carbon of the 3-carboxy-4-hydroxybenzenesulfonate moiety

163.11

C4 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety

135.98

C1 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety

132.72

C6 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety

130.28

C2 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety

128.28

C3 and C5 carbon of the same kind in 4-methylanilinium moiety

127.80

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

122.46

C4 carbon of 4-methylanilinium moiety

116.81

C5 carbons of the 3-carboxy-4-hydroxybenzenesulfonate moiety

111.83

C3 carbon of 3-carboxy-4-hydroxybenzenesulfonate moiety

19.6

Methyl carbon of 4-methylanilinium moiety

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Table 3 Crystallographic data and structure refinement of 4MABS crystal Empirical formula

C14H15NO6S

Formula weight

325.33

Temperature

293(2) K

Wavelength

0.71073 Å

Crystal system,

Monoclinic

Space group

P 21/n

Unit cell dimensions

a = 9.4932(8) A α = 90° b = 12.2889(12) A

β = 98.907(8)°

c = 12.5382(11) A γ = 90° Volume

1445.1(2) Å3

Z, Calculated density

4, 1.495 Mg/m-3

Absorption coefficient

0.254 mm-1

F(000)

680

Theta range for data collection 2.92 to 29.08° Limiting indices

-8<=h<=11, -16<=k<=13, -12<=l<=17

Reflections collected / unique

6382 / 3273 [R(int) = 0.0334]

Absorption correction

Semi-empirical from equivalents

Max. and min. transmission

1.00000 and 0.88441

Refinement method

Full-matrix least-squares on F2

Data / restraints / parameters

3273 / 0 / 203

Goodness-of-fit on F^2

1.033

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

R1 = 0.0546, wR2 = 0.1183

R indices (all data)

R1 = 0.0890, wR2 = 0.1379

Largest diff. peak and hole

0.250 and -0.432 e.A-3

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Table 4 Comparison of experimental band lengths [Å] and angles [°] with optimized values of 4MABS crystal

S(1)-O(3) S(1)-O(2) S(1)-O(1) S(1)-C(1) O(4)-C(7) O(5)-C(7) C(4)-O(6) C(4)-C(3) C(4)-C(5) C(5)-C(6) C(5)-C(7) C(6)-C(1) C(1)-C(2) C(3)-C(2) N(1)-C(8) C(9)-C(8) C(9)-C(10) C(13)-C(8) C(13)-C(12) C(10)-C(11) C(11)-C(12) C(11)-C(14)

Observed 1.4331(19) 1.442(2) 1.4579(19) 1.757(2) 1.304(3) 1.221(3) 1.343(3) 1.390(3) 1.391(3) 1.388(3) 1.475(3) 1.379(3) 1.385(3) 1.371(3) 1.467(3) 1.368(3) 1.375(3) 1.369(3) 1.376(3) 1.380(4) 1.384(4) 1.507(3)

Calculated 1.646 1.650 1.657 1.850 1.353 1.247 1.339 1.418 1.432 1.390 1.470 1.397 1.406 1.377 1.490 1.390 1.394 1.392 1.396 1.406 1.403 1.509

O(3)-S(1)-O(2) O(3)-S(1)-O(1) O(2)-S(1)-O(1) O(3)-S(1)-C(1) O(2)-S(1)-C(1)

113.89(14) 111.50(12) 112.00(12) 107.16(12) 106.77(10)

113.3 113.3 113.3 107.7 107.4

O(1)-S(1)-C(1) O(6)-C(4)-C(3) O(6)-C(4)-C(5) C(3)-C(4)-C(5) C(6)-C(5)-C(4) C(6)-C(5)-C(7) C(4)-C(5)-C(7) C(1)-C(6)-C(5) C(6)-C(1)-C(2) C(6)-C(1)-S(1) C(2)-C(1)-S(1) C(2)-C(3)-C(4) O(5)-C(7)-O(4) O(5)-C(7)-C(5) O(4)-C(7)-C(5) C(3)-C(2)-C(1) C(8)-C(9)-C(10) C(8)-C(13)-C(12) C(9)-C(8)-C(13) C(9)-C(8)-N(1) C(13)-C(8)-N(1) C(9)-C(10)-C(11) C(10)-C(11)-C(12) C(10)-C(11)-C(14) C(12)-C(11)-C(14) C(13)-C(12)-C(11)

Observed 104.87(12) 117.5(2) 122.74(19) 119.8(2) 119.94(19) 120.2(2) 119.8(2) 120.0(2) 119.6(2) 119.9(2) 120.46(16) 119.5(2) 123.0(2) 122.1(2) 114.9(2) 121.1(2) 118.6(2) 118.8(2) 121.5(2) 119.1(2) 119.4(2) 121.8(2) 117.6(2) 121.0(3) 121.3(3) 121.5(3)

Calculated 105.6 116.8 122.7 120.5 119.3 121.8 118.9 118.1 123.9 117.6 118.4 118.0 123.0 122.8 114.2 118.0 118.7 118.7 121.8 119.0 119.2 121.3 118.3 120.7 121.0 121.3

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Table 5 Hydrogen bonding parameters of 4MABS crystal Donor- H....Acceptor

D - H H...A D...A

D - H...A

O(4)-H(1)…O(1)

0.82

1.79

2.612(3) 175

O(6)-H(2)…O(5)

0.82

1.87

2.587(3) 146

N(1)-H(10A)…O(5)

0.89

2.29

2.749(3) 112

N(1)-H(10A)…O(1)

0.89

2.59

3.460(3) 166

N(1)-H(10B)…O(3)

0.89

1.95

2.826(3) 170

N(1)-H(10C)…O(2)

0.89

1.95

2.831(3) 171

C(6)-H(5)…O(2)

0.93

2.50

2.884(3) 105

C(6)-H(5)…O(4)

0.93

2.41

2.723(3) 100

Table 6 Dipole moment, the average polarizability and the first hyperpolarizability of 4MABS crystal Dipole moment (debye) Polarizability (esu)

Hyperpolarizability (esu)

μx

1.9522

α xx -26.5975

βxxx

218.1599

μy

1.0724

α xy -2.4525

βyyy

38.4253

μz

-4.1694

α yy -116.522

βzzz

-30.8073

μtot

4.7271

α zz -127.363

βxyy

-74.6556

α xz -6.4752

βxxy

93.5536

α yz -1.5019

βxxz

31.4356

1.43145 x10 -23 βxzz

18.7679

βyzz

11.0329

βyyz

1.6233

βxyz

-33.9451

βtot

1.8687x10-30

αtot