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Piperazinium bis (5-chlorosalicylate) – A new third order nonlinear optical single crystal
Journal of Molecular Structure 1228 (2021) 129728
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Piperazinium bis (5-chlorosalicylate) – A new third order nonlinear optical single crystal G. Parvathy a, R. Kaliammal a, K. Velsankar a, G. Vinitha b, K. Sankaranarayanan a, R. Mohan Kumar c, S. Sudhahar a,∗ a b c
Department of Physics, Alagappa University, Karaikudi-630 003, India Division of Physics, School of Advanced Sciences, VIT university, Chennai-600 127, India Department of Physics, Presidency College, Chennai-600 005, India
a r t i c l e
i n f o
Article history: Received 13 June 2020 Revised 9 November 2020 Accepted 3 December 2020 Available online 7 December 2020 Keywords: Crystal structure Optical properties Third order NLO material Thermal stability Mechanical stability
a b s t r a c t A new organic single crystal viz, piperazinium bis(5-chlorosalicylate) (P5C) was grown by low temperature solution growth method and its physico-chemical properties were established. The unit cell param˚ b = 8.7592 A, ˚ c = 9.3103 A, ˚ α = 90°, β = 100.95°, γ = 90°) were determined eters (a = 11.9306 A, by single crystal X-ray diffraction data. The presence of various functional groups in the structure was elucidated by FTIR, Raman and proton NMR spectral studies. The P5C crystal exhibits the good optical tansmittance in the region of 400 to 1200 nm. From photoluminescence studies, the violet emission spectrum was observed under the excitation wavelength of 380 nm. The thermal behaviour of the P5C crystal was analyzed by TG-DSC analysis. The mechanical strength of the grown material classifies it as soft material. The results from Z-scan technique validate the NLO properties. Theoretical calculations like optimized geometry, HOMO-LUMO, mulliken population analysis, natural bond analysis were determined using Gaussian 09W with B3LYP method. © 2020 Elsevier B.V. All rights reserved.
1. Introduction The development of highly efficient NLO materials, increasing the research activity in a variety of applications such as in the area of optical communication, harmonic generation, frequency mixing, laser lithography, diode lasers, etc. [1–2]. Organic materials have great attention by the reason of the wide transparent window, thermal stability, high NLO response, fabrications, and integrating into devices [3]. Recently, researchers mainly concentrate on single crystals of organic because of the easy procedure for synthesis, rapid nonlinear response, and probable of various device fabrications [4–8]. The organic molecules have a π -electron conjugated system connecting donor and acceptor groups are largely polarizable entities that may contribute to triggering the organic crystals for nonlinear optical applications [9]. Third order NLO characterization of organic molecules progresses rapidly because of the promising applications in the area of optical signal processing, optical limiting etc., [10]. There are the variety of methods for analyzing 3rd order nonlinearities, Z-scan technique [11] is one of the easiest and most significant methods to measure both the magni-
∗
Corresponding author. E-mail address: [email protected] (S. Sudhahar).
https://doi.org/10.1016/j.molstruc.2020.129728 0022-2860/© 2020 Elsevier B.V. All rights reserved.
tude and sign of the real part due to nonlinear refraction as well as the imaginary part due to nonlinear absorption of the material science [12,13]. The third order (χ 3 ) coefficients are important for centrosymmetric material where the χ 2 coefficients are equal to zero. The theoretical calculation based density functional theory (DFT) method is generally used to optimize the structure, the charge transfer interaction, hyperpolarizability, etc. It is the most efficient tool for analyzing the theoretical calculation, molecular geometry, and modeling to understand the properties of NLO and forming the novel materials. In this present case, the base material of piperazine is an organic salt and it has piperazinium cation that makes an active role in synthesizing many complex molecules for their interactions between the hydrogen bonds and vibrational analysis [14]. It is a strong basic diamine which consists of two -NH groups. Piperazine used in various biological compounds including drug discovery, the ring of piperazine is used a significant part of pharmaceuticals [15,16], not only that the piperazine derivatives have been subjected to both vibrational and crystallographic analysis [17,18]. The acid material of 5-chlorosalicylic acid has a carboxylic group with two potential coordination such as COOH and OH and there is a high possibility of proton transfer mainly in N-heterocyclic organic salts. Both piperazine and salicylic acid derivative crystals are promising organic material for higher order nonlinear optical applications [19–22]. In this work, the P5C
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 1. Reaction scheme of P5C crystal.
Fig. 2. (a) As-grown P5C crystal and (b) Solubility curve of P5C crystal.
crystal has been synthesized and characterized by structural, spectral, thermal, mechanical, and higher order NLO properties. Also, the theoretical quantum chemical calculations by the method of density functional theory with the 6-311++G (d,p) basis set working in the GAUSSIAN 09 program.
the nature of positive solubility. The solubility nature of P5C is depicted in Fig. 2(b).
3. Results and discussion 2. Experimental section 3.1. Single crystal and powder X-ray diffraction studies 2.1. Material synthesis and crystal growth P5C crystal was characterized by single crystal X-ray diffraction (SXRD) study using Brukker Kappa APEX II X-ray diffractometer with the radiation of MoKα . The P5C structure was determined using direct methods by manipulating the SHELXS-97 [23] and done the refinement of full-matrix least squares on F2 . From structure analysis, it is found that the crystal exhibit monoclinic system having the center of inversion with spacegroup P21 /c resulting with R factors equal to 0.0614 and 0.1253. The calculated lattice pa˚ b = 8.7592 A, ˚ rameters of the grown material are a = 11.9306 A, ˚ α = 90°, β = 100.95° and γ = 90°. The density c = 9.3103 A, ˚ and volume of P5C were determined at 1.499 Mg/m3and 955.21 A3
The piperazine (C4 H10 N2 ) and 5-chlorosalicylic acid (C7 H5 ClO3 ) were taken in the molar ratio of 1:1 for the synthesis of the P5C compound. The calculated amount of both piperazine and 5chlorosalicylic acid materials were dissolved in a suitable solvent mixture of ethanol: water taken in 5:1 volume ratio. The solution was stirred well using a magnetic stirrer to promote homogeneity. After that, the solution was filtered using whatman filter paper and transferred to a beaker which was then covered with a thick perforated polythene sheet for evaporation at room temperature. The proposed chemical reaction scheme of the synthesis of P5C material is depicted in Fig. 1. The purity of the present material was improved by the re-crystallization process. Single crystal was harvested within 5–6 weeks. The picture of an as-grown crystal is shown in Fig. 2(a).
with Z = 2. The crystallographic data file (CIF) of P5C has been deposited in CCDC no. 2010472. The ORTEP diagram and the crystal structure of P5C compound are shown in Fig. 3. The crystal structure of P5C exhibits the deprotonated 5-chlorosalicylate anion and protonated piperazinium cation having intermolecular interaction of hydrogen bonding as seen in the packing diagram (Fig. 4). The asymmetric unit of P5C compound 2(C7 H5 ClO3 ).(C4 H10 N2 ) has 5chlorosalicylate anion and half of piperazinium cation. Cation and anion are linked by the N-H…O hydrogen bond and the anion is connected by the O-H…O hydrogen bond. The structure refinement and crystal data are presented in Table 1. The details of hydrogen bondings are listed in Table 2 after the refinement of structure. The additional data are given in supp. Tables (1–5). Powder XRD pattern recorded on the grown material in the range of 10–80° at the rate of 1°/min shown in Fig. 5 (a). The hkl values were indexed and the observed sharp Bragg’s peaks exhibit the high crystallinity of the grown P5C crystal.
2.2. Solubility The solubility study was taken out from varying temperature between 30 °C and 60 °C with interval of 10 °C utilizing constant temperature bath (CTB) with control efficiency. The amount of P5C salt was added slowly to the mixed solvent of ethanol:water (5:1) and control at 30 °C with repeatedly stirring using a magnetic stirrer. Once it reached the saturation level the equilibrium concentration was measured. The same procedure is repetition for 40, 50 and 60 °C temperatures to measure the solubility. The dissolvation of P5C salt quantity is increased with respect to temperature and therefore the obtained results clearly indicates the P5C crystal has 2
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 3. The molecular structure of the P5C with atom numbering scheme for the atoms and 50% probability displacement ellipsoids. Table 1 Crystal data and structure refinement for P5C. Identification code
P5C
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
C18 H20 Cl2 N2 O6 431.26 296(2) K 0.71073 A˚ Monoclinic P21 /c a= 11.9306(11) A˚ b = 8.7592(9) A˚ c = 9.3103(10) A˚ ˚ 955.21(17) A3
Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 25.242° Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
α = 90°. β = 100.957(2)°. γ = 90°.
2 1.499 Mg/m3 0.379 mm-1 448 0.300 × 0.250 × 0.200 mm3 2.904 to 29.941°. -16< = h< = 16, -12< = k< = 12, -13< = l< = 13 17253 2771 [R(int) = 0.0491] 99.9 % Semi-empirical from equivalents 0.7460 and 0.5626 Full-matrix least-squares on F2 2771 / 0 / 128 1.083 R1 = 0.0403, wR2 = 0.1062 R1 = 0.0614, wR2 = 0.1253 n/a ˚ 0.210 and -0.474 e.A-3
Table 2 Hydrogen bonds for P5C [A˚ and °].
Table 3 FT-IR and Raman spectral vibrational assignments of P5C compound.
D-H···A
d(D-H)
d(H···A)
d(D···A)
<(DHA)
FT-IR (cm−1 )
Raman (cm−1 )
Assignments
Reference
C(6)-H(6)···Cl(1)#2 C(8)-H(8A)···O(3)#3 C(9)-H(9A)···Cl(1)#1 C(9)-H(9B)···O(2)#2 O(3)-H(3A)···O(2) O(3)-H(3A)···O(2)#4 N(1)-H(1A)···O(2)#5 N(1)-H(1B)···O(1)#2
0.93 0.97 0.97 0.97 0.82 0.82 0.89 0.89
2.98 2.53 2.87 2.55 1.83 2.51 1.98 1.78
3.8652(16) 3.2438(19) 3.6931(16) 3.4054(19) 2.5568(17) 3.0518(17) 2.8069(17) 2.6619(17)
160.5 130.5 142.9 147.5 146.5 124.6 154.9 170.2
3248
3304 3215 3081, 3024, 2968 1557 1434 1349 1226 1141 1067 810 640
ν O-H ν N-H ν C-H ν C = O + ν N-H ν C-H + ν N-H ν C-H + ν N-H + ν C-N ν C-O + ν C-C + ν C-N ν C-C + ν C-N ν C-H ν N-H ν N-H
[24–26] [8,24–26] [8,24–28] [8,24,26] [24,25] [24,25] [24,25,29] [8,24,25] [24] [24,26] [24]
3010, 2815 1588 1438 1314 1270 1146 1075 819 643
Symmetry transformations used to generate equivalent atoms: #1 -x+2,-y,-z+1 #2 -x+1,-y,-z+1 #3 x+1,y,z+1. #4 -x,-y,-z #5 -x+1,y+1/2,-z+1/2.
3.2. FT-IR and Raman spectral analyses
trum [8,24–26]. The CH stretching modes are assigned at 3010, 2815 cm−1 in the FT-IR spectrum and these bands are appeared in the Raman spectrum in the region of 3081-2968 cm−1 [8,24– 28]. The band appeared at 1588 cm−1 in the FT-IR spectrum and 1557 cm−1 in the Raman spectrum, which is attributed to the C = O stretching and N-H deformation vibrations [8,24–26]. The band appeared at 1438 cm−1 in the FT-IR spectrum and 1434 cm−1 in the Raman spectrum, which is attributed to the C-H stretching
The FT-IR and Raman spectra of the title compound P5C are shown in Fig. 5(b) and (c) respectively, and their assignments are summarized in Table 3. The phenolic OH and NH stretching modes are assigned at 3248 cm−1 in the FT-IR spectrum and these bands are appeared at 3304 cm−1 for OH and 3215 cm−1 for NH in the Raman spec3
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
The bands appeared at 1075 cm−1 is assigned to the C-H and the bands at 819 and 643 cm−1 are assigned to the N-H group in the FT-IR spectrum. These bands are also found at 1067 cm−1 , 810 & 640 cm−1 in the Raman spectrum respectively [24,26]. 3.3. Nuclear magnetic resonance 1 H-NMR (d6 -DMSO, 400MHz, δ in ppm): 3.34 (s, 8H, 4xCH ), 2 6.74, 6.76 (d, 4H, J= 8Hz, 2xNH2 + ), 7.24-7.26 (t, 6H, J= 8Hz, C3,4,5 HSalicylate ring ), 7.66 (s, 2H, OHSalicylate ring ).The NMR spectroscopy is one of the efficient techniques used to study the crystal structure of organic materials [30]. In the 1 H NMR spectrum of the symmetric organic crystal P5C, a sharp singlet peak showed at 3.348 ppm, which is assigned to the four methylene (4xCH2 ) protons [31] and a doublet peak showed at 6.74 and 6.76 ppm is attributed to the ammonium (2xNH2 + ) protons of the piperazine1,4-diium moiety which confirms all the protons are transferred from 5-Chlorosalicylic acid to Piperazine. The aromatic protons of the 5-Chlorosalicylate moiety show a peak at 7.24-7.26 ppm. A singlet peak at 7.66 ppm is assigned to the phenolic -OH of the 5-Chlorosalicylate moiety. The 1 H-NMR spectrum of P5C did not show the chemical shift for the free carboxylic acid. From this it is justified and confirmed that the structure of the grown symmetric crystal P5C is shown in Fig. 6.
Fig. 4. Crystal packing diagram of P5C crystal.
and asymmetric bending N-H vibrations [24,25]. The C-H, N-H and C-N groups showed a band at 1314 cm−1 in the FT-IR spectrum and 1349 cm−1 in the Raman spectrum [24,25]. The band at 1270 and 1226 cm−1 are ascribed to stretching vibrations of C-O, C-N and C-C in the FT-IR and Raman spectra respectively [24,25,29]. The C-N and C-C bonds are showed a band at 1146 cm−1 in the FT-IR spectrum and 1141 cm−1 in the Raman spectrum [8,24,25].
3.4. UV-Vis spectral study The optical property of the grown material was measured using ocean optics HR 20 0 0 UV-Vis spectrophotometer. UV-Vis spec-
Fig. 5. (a) The powder XRD, (b) FT-IR and (c) Raman. 4
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 6. NMR spectra of P5C crystal.
3.5. Photoluminescence spectrum
trum provides the massive information about a molecular electronic transition of π - conjugated system which involves the promotion of an electron in σ and π orbitals from the ground level to a higher energy level due to absorption [32]. The optical properties are very important for crystals to study the lattice vibrations, impurity levels, excitons, energy band structure, etc. [33]. The transitions between the absorption bands of π -π ∗ , n-π ∗ (lone pairs and π orbitals) take place in aromatic compounds. Defects are being impurities, the cracks, the inclusion of solvent and grain boundaries which usually diminish the optical quality of the crystal [34]. The absorption spectrum of P5C crystal was recorded and is shown in Fig. 7(a). The cutoff wavelength is observed at 340 nm and the grown crystal is transparent about 75% in the region between 4001100 nm which is an important parameter needed for NLO materials. This lower cut-off at 340 nm is owing to the excitation of aromatic material contains hydrogen and nitrogen [35]. The optical absorption coefficient is based on the energy of photons (hν ) and helps to identify the type of transition of electrons and band structure [36]. The transmittance (T) evaluated using the absorption spectrum was used to measure the absorption coefficient (α ) by using the relation (1),
α = 2.3026 log(1/T )/d
The PL spectrum of P5C crystal was observed using the varian cary eclipse spectrofluorometer to analyze the defects and optical properties of the grown material. The luminescence of organic molecules depends on π -electron systems occurring in the internal individual organic fragments. Generally, the PL signal is based on changing the excitation point and wavelength, the density of excited electrons and the intensity of the incident beam. The recorded emission spectrum in the range of 30 0–80 0 nm under 380 nm excitation wavelength is shown in Fig. 7 (c). A strong violet emission was measured at 445 nm, which may be owing to the π -π ∗ interaction in the salicylate and piperazine molecules.
3.6. TG-DSC analysis The Fig. 7(d) shows the result of the thermogravimetry (TGA) and differential scanning calorimetry (DSC) analysis on P5C single crystal in a nitrogen gas atmosphere and in the temperature range of 30 to 500 °C at the heating rate of 10 °C/min using SDT Q600 V20.9 Build 20. A sample mass of 1.666 mg was taken for analysis and placed in the alumina crucible during the study. TGA plot indicates that the P5C crystal is stable up to 160 °C and the decomposition of the material was noted in the temperature range of 180 °C–300 °C. The TG curve also suggests that no phase transition occurred until the grown material melts. The sharp endothermic peak at 236.62 °C in the DSC curve indicates the melting point of the grown crystal. The sharpness implies the phase purity and good crystallinity of the P5C sample [37]. The melting point of P5C is larger than a few of the derivatives of piperazine like PBA (197 °C) [38], MPHP (217 °C) [39] etc. This improvement in the melting point is an added advantage for NLO applications.
(1)
d is the thickness of the grown crystal. The band gap (Eg ) was calculated by using the formula (2),
(α hν )2 = A(Eg − hν )
(2)
Where α indicates the absorption coefficient, A is constant, Eg is the optical band gap, h is Planck’ s constant, ν is the frequency of photons Fig. 7 (b) exhibits the graph between the variation of (α hν )2 with ‘hν ’ which is used to calculate the optical band gap. The band gap energy of the P5C crystal is about 4.1 eV. 5
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 7. (a) UV-Vis absorbance, (b) optical band gap energy (Eg ), (c) PL and (d) TG-DSC of P5C crystal.
behavior of ISE is n<2. The n>2 is a behavior of reverse ISE. P5C crystal exists a soft material category because of n>2. The fracture toughness (kc ) explains how much fracture stress is enforced under uniform loading. The Kc is given by the following formula,
3.7. Microhardness studies The information on mechanical strength is an important parameter for practical application of the studied crystal. The hardness value was evaluated for varying loads of 10, 25, 50, and 100 g with a fixed indentation time of 5 s for all loads. For every load, the d of the diagonal length of the indentation mark was measured at different indentation sites and an average of these values was taken. The Vicker’s microhardness number (Hv ) can be estimated by using the formula,
Hv = 1.854 P/d2 Kg/mm2
Kc = P/β0 l3/2 ; if l ≥ d/2
(3)
Where P indicates the applied load and d refers to the diagonal length. A graph was attained between the hardness number (Hv ) and applied load (P) and was shown in Fig. 8(a) where in the Hv increases with the applied load (P) up to 100 g, and that behavior was attributed to reverse indentation size effect [40]. The increase of applied load beyond 100 g led to the formation of cracks on the crystal surface and thus the study was restricted up to the load of 100 g. Fig. 8(b) depicted the graph of HV versus indentation diagonal length d. The easiest way to explain the ISE is Meyer’s law [41], the relationship between the load P and size of indentation (d) is given by the relation,
P = Adn
(5)
Where β 0 is a constant (β 0 = 7), l represents the crack length, d indicates the diagonal length. The plot between P versus l3/2 is shown in Fig. 9 (b). The brittleness is one of the essential properties and it deals with the fracture induced in a crystal without any observable deformation. The brittleness index (Bi ) value is calculated by using the formula [42],
Bi = HV /KC
(6)
Further, the yield strength (σ y ) of a grown crystal can be measured by using HV and Meyer’s index as 2.25 by using the equation,
σy =
Hv 12.5(n − 2 ) [1 − (n − 2 )] 2.9 1 − (n − 2 )
n−2
(7)
Fig. 9(c) exhibits the graph between the load (P) and Yield strength (σ y ). The elastic stiffness constant (C11 ) was measured by using Wooster’s relation [43]. It provides a deep idea about the interatomic bonding strength of the crystals.
(4)
C11 = (HV )7/4
Where A is an arbitrary constant for a grown material and n is the work hardening coefficient of P5C single crystal. The n value can be calculated by using Meyer’s graph between log P and log d as seen in Fig. 9(a). The n value was calculated to be at 2.25. The normal
(8)
A plot between the load (P) and stiffness constant (C11 ) for a grown material, is shown in Fig. 9(d). The numerical values of above these parameters of P5C material for varying loads are given in Table 4. 6
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 8. (a) Plot of Hardness number (Hv ) vs. load (P) and (b) Plot of Hardness number (Hv ) vs. diagonal (d).
Fig. 9. (a) log d vs log ‘P’, (b) log ‘P’ vsl3/2 (c) Plot of yield strength (σ y) vs. load P and (d) Variation of stiffness constant (C11 ) with Load P.
Table 4 Microhardness (Hv ), Yield strength (σ v ), Stiffness Constant (C11 ), Fracture toughness (Kc ) and Brittleness (Bi ) for different loads. Load (g) 10 25 50 100
Hv
Meyer’s index 2
(kg/mm ) 51.30 58.10 64.90 69.00
(n) 2.25 2.25 2.25 2.25
σv 2
(GN/m ) 18.94 21.46 23.96 24.37
7
C11 x 1014
Kc
(Pa) 9.83 12.59 13.27 15.28
(gμm 0.0487 0.0681 0.0829 0.1047
Bi −3/2
)
(μm−1/2 ) 10.5 8.67 7.34 6.30
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 10. (a) Open aperture curve and (b) Closed aperture of P5C crystal.
Table 5 Calculated Z-scan results of nonlinear refractive index (n2 ), nonlinear absorption coefficient (β ), third order nonlinear susceptibility (χ 3 ) of the P5C crystal.
3.8. Z-scan analysis Third order nonlinear optical properties were analyzed by Zscan technique to determine both nonlinear refractive index ‘n2 ’ and nonlinear absorption coefficient ‘β ’ and third order nonlinear susceptibility ‘χ 3 ’ which is complex in nature. The Z-scan method to study under closed and open apertures (CA and OA) for P5C crystal using semiconductor diode laser (λ = 532 nm). The given sample attains a maximum reached an intensity at foci (z = 0) which symmetrically minimized towards both sides of positive and negative Z values and it start from +15 to -15, the light may be transmitted and P5C crystal was analyzed using digital meter. The final data are plotted against the sample position is called as Zscan curve of P5C crystal. Fig. 10(a) exhibits the open aperture (OA) curve for which corresponds to nonlinear transmittance decreasing with increasing intensity that exhibits the reverse saturable absorption. To calculate the value of nonlinear absorption coefficient ‘β ’ using the following equation [44],
β
√ 2 2 T = ( m/W ) IoLe f f
NLO parameters Calculated values
Re χ ( 3 ) =
(9)
χ (3 ) =
α indicates the linear absorption coefficient (λ = 532 nm). L denotes the thickness. To evaluate the closed aperture provides the data around the sign and magnitude of n2 . The CA of P5C crystal is depicted in Fig 10 (b). The peak to valley determines that the crystal carried out self-defocusing which shows the negative nonlinear behaviour of grown crystal [45]. To calculate the nonlinear refractive index using the relation [46],
(11)
10−4 εoC 2 n2 n2o
π
10−2 εoC 2 λβ n2o 4π 2
(14)
(15)
Re
2 χ (3) + Im χ (3)
(16)
The geometrical parameters were theoretically analyzed using DFT B3LYP functional with 6-311G++ (d,p) basis set. The theoretical calculations have been analyzed using Gaussian 09W to provide an optimized structure of P5C compound [47] and the structure is viewed by Gaussview 5.0 [48]. The SXRD CIF file of P5C was used as input. The optimized structure, HOMO-LUMO, mulliken charge analysis, hyperpolarizability, natural bond analysis was theoretically analyzed using Gaussian 09W program.
(12)
S denotes the linear transmittance and it can be calculated using the relation,
S = 1 − exp −2ra 2 /wa 2
4.01 × 10−7
3.9. Computational details
Where ∅ indicated as on axis phase shift and it calculated by using the following relationship,
| ∅| = TP−V /0.406(1 − S )0.25
3.756 × 10
χ 3 [esu] −9
The calculated values of third-order NLO parameters, i.e. nonlinear refractive index (n2 ), absorption co-efficient (β ), and third order susceptibility (χ 3 ) of P5C crystal were observed to be n2 = 1. 875 × 10−14 m2 /W, β = 3.756 × 10−9 m/W, (χ 3 ) = 4.01 × 10−7 esu respectively is shown in Table 5. The open aperture curve shows a decrease the transmittance with increasing intensity. This determines the existence of reverse saturable absorption (RSA) which leads to a grown material for optical limiting applications.
(10)
∅ K IoLe f f
β [Mw−1 ]
To calculate the third order nonlinear susceptibility (χ 3 ) of P5C crystal by using the following equation,
Where T indicates the valley value from OA curve. I0 indicates the input intensity. Leff represents the thickness of the sample, it can be examined by using the formula
n2 =
1.875 × 10
−14
In the above equation ra represent the radius of the aperture and laser beam radius was represented by wa . The real and imaginary parameters of the third-order nonlinear optical susceptibility (χ 3 ) of P5C crystal were obtained using the relations:
Im χ (3 ) =
Leff = 1 − e−α L /α
n2 [m2 W−1 ]
(13) 8
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728 Table 6 Experimental and optimized geometry parameters of P5C crystal computed by B3LYP/6-311++G (d,p) basis set.
Fig. 11. Optimized molecular structure of P5C crystal.
3.9.1. Optimized molecular structure The optimized molecular parameters of P5C molecule like bond length, angles and dihedral angles were obtained from theoretical studies of B3LYP method and those values compared to experimental data. The obtained optimized structure is depicted in Fig. 11. From XRD, the protons are transferred from 5-Chlorosalicylic acid to piperazine. The structure of P5C bond length C-C is placed be˚ ˚ A˚ in experimental and 1.380 A-1.500 A˚ for tween 1.375 A–1.508 theoretical. The C8 –C9 bond distance is larger compared with other bond distance, it is owing to the presence of piperazinium. The CH bond length range 0.930 A˚ for XRD and 1.08 A˚ for B3LYP almost all C-H bond distances are approximately equal. The C2 –O3 ˚ bond distance is larger when compared with other C(1.358 A) O bond distance. The C5 –Cl1 bond distance is 1.742 A˚ in theoretical and 1.759 A˚ in experimental. The obtained N-H bond distance value obtained 0.890 A˚ in XRD and 1.010 A˚ in B3LYP respectively. The bond angles of O3-C2-C1 (122.1°) are higher when compared with other angles, it is owing to the presence of carboxyl. The experimental and theoretical values are listed in Table 6. 3.9.2. Analysis of frontier molecular orbitals (FMO) The study of understanding the FMO is an effective way to examine the chemical reactivity and optical properties of molecules. The excitation of electrons from occupied (HOMO) to unoccupied (LUMO) molecular orbital makes a significant role in optical property. The FMO pictorial representation is depicted in Fig. 12. Which evidentiary exhibit the HOMO is occupied over 5-chlorosalicylate and the LUMO is delocalized over piperazinium. The theoretical energy values are -2.0438 eV in HOMO and -6.5010 in LUMO. The obtained energy gap is 4.4 eV, which is nearly equal to the experimental value (4.1 eV). HOMO energy has the capability to give an electron while the LUMO has the capability to access the electron [49]. The energy gap between them indicates the properties of electrical and it affirms that placed charge transfer action in the molecule. The implementation of LUMO has the strong energy level because of the electron access group is placed. The red and green colour indicates the positive and negative region is depicted in Fig. 12. The energy gap is a most important part because it provides chemical stability [50]. The other important parameters of chemical hardness (η), Electrophilicity (ω), Ionization potential (I), Chemical potential (μ), Electron affinity (A), Global softness (S), Electronegativity (χ ) of P5C molecule can be determined by applying the koopman’s theorem [51] is provided in Table 7.
˚ Bond length (A) Geometric parameters
Experimental values
B3LYP/6-311++G(d, p)
C1-C6 C1-C2 C1-C7 C2-O3 C2-C3 C3-C4 C3-H3 C4-C5 C4-H4 C5-C6 C5-Cl1 C6-H6 C7-O1 C7-O2 C8-N1 C8-C9 C8-H8A C8-H8B C9-H9A C9-H9B O3-H3A N1-H1A N1-H1B
1.397 1.401 1.494 1.358 1.394 1.378 0.930 1.386 0.930 1.375 1.742 0.930 1.248 1.277 1.487 1.508 0.970 0.970 0.970 0.970 0.820 0.890 0.890
1.406 1.415 1.472 1.343 1.402 1.383 1.082 1.399 1.082 1.380 1.759 1.081 1.332 1.230 1.377 1.500 2.410 1.086 1.089 1.081 0.983 1.009 1.010
Bond Angles(°) Geometric parameters
Experimental value
B3LYP/6-311++G(d, p)
C6-C1-C2 C6-C1-C7 C2-C1-C7 O3-C2-C3 O3-C2-C1 C3-C2-C1 C4-C3-C2 C4-C3-H3 C2-C3-H3 C3-C4-C5 C3-C4-H4 C5-C4-H4 C6-C5-C4 C6-C5-Cl1 C4-C5-Cl1 O2-C7-C1 N1-C8-C9 N1-C8-H8A C9-C8-H8A N1-C8-H8B C8-C9-H9B
119.0 119.5 121.4 118.0 122.1 119.8 120.5 119.7 119.7 119.3 120.3 120.3 121.0 119.1 119.8 117.4 109.7 109.7 109.7 109.7 109.7
119.6 121.1 119.2 117.8 123.0 119.1 120.6 121.0 118.3 119.9 120.2 119.8 120.7 119.9 119.3 123.0 126.9. 113.3 119.6 109.8 120.1
Dihedral Angles(°) Geometric parameters
Experimental value
B3LYP/6-311++G(d, p)
C6-C1-C2-O3 C7-C1-C2-O3 C6-C1-C2-C3 C7-C1-C2-C3 O3-C2-C3-C4 C1-C2-C3-C4 C2-C3-C4-C5 C3-C4-C5-C6 C3-C4-C5-Cl1 Cl1-C5-C6-C1 C2-C1-C6-C5 C7-C1-C6-C5 C2-C1-C7-O1 C6-C1-C7-O2
179.6 0.1 0.2 179.5 179.7 0.3 0.4 0.4 179.3 179.4 0.2 179.5 -176.6 -177.5
179.9 0.03 0.04 179.9 179.9 0.03 0.01 0.0 179.9 179.9 0.03 179.4 -179.9 -179.8
Global softness (S) = 1/(η)……(4) Chemical potential (μ) = - (I+A/2)…..(5) Electronegativity (χ ) = (I+A/2)……(6) Electrophilicity (ω) = μ2 /2 η……(7)
Ionization potential (I) = -Homo energy….. (1) Electron affinity (A) = -Lumo energy…..(2) Chemical hardness (η) = (I-A/2)…..(3) 9
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728 Table 8 The polarizability and first-order hyperpolarizability of P5C. Polarizability
α components (a.u) α xx α xy α yy α xZ α yz α zz α tol (e.s.u.)
198.550 85.313 458.003 75.528 156.986 189.578 2.82 ∗ 10−23
First order hyperpolarizability β components (a.u)
β xxx β xxy β xyy β yyy β xxz β xyz β yyz β xzz β yzz β zzz β tol (e.s.u.)
3276.73 4382.532 5835.231 10747.261 2611.253 3339.410 5291.376 1984.441 2769.025 1791.548 1.415∗ 10−28
mined by 3 × 3 × 3 matrix. The twenty seven components of 3 dimensional matrix are diminished to ten elements which is owing to the kleimann symmetry [54-57]. The charge transfer action and π -conjugation presented in P5C molecule lead to trigger the hyperpolarizability may cause of high transfer. The low energy gap certainly indicates the charge transfer takes place in a molecule via conjugation and therefore increased the NLO response [58,59]. The hyperpolarizability value of P5C is β = 1.415 × 10−28 and polarizability is α = 2.82 × 10−23 . For P5C, the largest element is obtained for β yyy direction and it represents the charge transfer action. The observed value represent the hyperpolarizability is 1.415 × 10−28 e.s.u, it shows the NLO response and the value indicates polarizability is 2.82 × 10−23 e.s.u. Fig. 12. Frontier molecular orbital (FMO) of P5C.
3.9.4. Mulliken charge analysis The mulliken population analysis is one of the efficient methods to find relevance in quantum calculations to indicate the distribution of charge in each atom placed in a molecule. The values of atomic charges were attained by mulliken charge analysis [60] of P5C molecule is calculated by using the B3LYP method with 6-311++G (d,p) as a basis set. The P5C structure with atomic charge is depicted in Fig. 13. The charges have ranged from 0.062 to 0.509. In P5C molecule the charge C15, C18, C13 acquires a positive charge, whereas other carbon atoms are negative. The N9 atom charge is negative and all the hydrogen atoms are positive. The Cl (0.509) is the highest positive charge and C2 possess the smallest negative charge of remaining atoms in P5C molecule.
Table 7 HOMO-LUMO energy gap and their related molecular properties of P5C molecule. Molecular properties (B3LYP/6-311G (d,p) HOMO energy LUMO energy HOMO-LUMO energy gap Ionization potential (I) Electron affinity (A) Chemical hardness (η ) Reciprocal of hadrness (S) Chemical potential (μ) Electronegativity (χ ) Electrophilicity (ω )
-6.5010 eV -2.0438 eV 4.4 eV 6.5011 eV 2.0438 eV 5.4792 eV 0.1825 eV -7.523 eV 7.523 eV 5.161 Ev
3.9.5. Natural bond analysis (NBO) NBO analysis helps to understand inter and intramolecular energies of interaction both acceptor and donor relation using 2nd order fock matrix. NBO gives all the probable interactions of bonding and antibonding with the help of delocalization calculation and rehybridization in the molecule [61,62]. A bonding and antibonding orbitals play a role in donor and acceptor. The strong hydrogen bonded relation between the lone pair (LP) and antibonding orbital of N-H and O-H bonds. The interactions LP(3)O(21)-π ∗ (C19 -C20 ), LP(3)O(21)-σ ∗ (H5 -N9 ), LP(1)O(21)- σ ∗ (H5 -N9 ) which corresponds to the high stabilization energies of 43.85, 33.32, 20.21 Kcal/mol which proved the occurrence of intramolecular relation with P5C. The strong interactions are π (C13 -C14 )-π ∗ (C19 -C20 ) which corresponds to the maximum energies of 16.93 Kcal/mol. The next strong relation is σ (C1 -C2 )-σ ∗ (H6 -N9 ) which have the energies of 7.49 Kcal/mol. The strong ICT relation of P5C is increased with respect to the interaction energy and stabilization. The different hyperconjugative interactions are given in supp. Table 6.
The softness and chemical hardness are linked to stability of materials [52]. Electronegativity helps to observe the capability to invite the shared electrons. Electron affinity represents the ability to access electron from a donor. Softness represents the properties of materials indicates the chemical reactivity of P5C molecule. 3.9.3. Hyperpolarizability Quantum chemical calculations attend with DFT method is the efficient way to know between structure and NLO role in organic materials through the description of NLO characteristics of materials [53]. The hyperpolarizability makes an efficient role in stability of materials and enhancement of properties of optical materials and the components are provided in Table 8. The first order hyperpolarizability is a type of 3rd rank tensor and that can be deter10
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 13. Mulliken atomic charges plot of P5C.
4. Conclusion
Acknowledgements
A new organic crystal viz., piperazinium bis (5-chlorosalicylate) was grown by the solution growth method at 35 °C. The SXRD reveals that the grown crystal possesses monoclinic system with a P21 /c space group. The molecular structure of grown material was further ascertained by FTIR, Raman, and proton NMR spectral studies. P5C crystal exhibited a cut-off wavelength at 340 nm and the optical bandgap of the material was measured to be 4.1 eV. The PL study identifies a violet emission peak at 445 nm. TG-DSC analysis validate the thermal stability up to 160 °C and the melting point at 236.42 °C for the present material. The mechanical property of the P5C crystal was analyzed and it belongs to the category of soft material. The nonlinear refractive index n2 = 1. 875 × 10−14 m2 /W, absorption co-efficient (β ) = 3.756 × 10−9 m/W, and third order susceptibility (χ 3 ) = 4.01 × 10−7 esu of P5C crystal were evaluated by Z-scan technique. From FMO analysis, the obtained bandgap energy is 4.4 eV which is nearly equal to the experimental value 4.1 eV. The bonding interaction of P5C was observed by Mulliken analysis. The first order hyperpolarizability of P5C crystal was β = 1.415 × 10−28 e.s.u. These results conclude that the newly grown P5C crystal is suitable for NLO applications.
The authors acknowledge the scheme MHRD-RUSA PHASE-2.0 (grant sanctioned vide Letter No. F.24-51/2014-U, Policy (TN MultiGen), Dept. of Edn. Govt. of India, Dt. 09.10.2018) New Delhi and DST-PURSE-II, New Delhi-India for a grant. Also, the authors express their thanks to UGC-SAP, DST-FIST and Alagappa University, Karaikudi-03, Tamilnadu, India. Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2020.129728. References [1] R.L. Sutherland, Handbook of Nonlinear optics, Materials Dekker, Inc, 1996. [2] M. Krishna kumar, S. Sudhahar, A. Silambarasan, B.M. Sornamurthy, R. Mohan kumar, Crystal growth, structural, linear and nonlinear optical studies of 4-methyl-4’-N’-methylstilbazolium tosylate single crystals, Optik 125 (2014) 751–755. [3] P.N. Prasad, D.J. Wollians, Introduction to nonlinear optical effects in molecules and polymers, Wiley-Interscience, Newyork, 1991. [4] T. Chem, Z. Sun, C. Song, Y. Ge, J. Luo, W. Lin, M. Hong, Bulk crystal growth and optical and thermal properties of the nonlinear optical crystal L-histidinium-4nitrophenolate 4-nitrophenol (LHPP) cryst, Growth Des. 12 (2012) 2673–2678. [5] G.A. Babu, P. Ramasamy, Investigation of crystal growth, structural, optical, dielectric,mechanical and thermal properties of a novel organic crystal: 4,4’-dimethylbenzophenone, J. Cryst. Growth 310 (2008) 3561–3567. [6] S. Manivannan, S. Dhanuskodi, S.K. Tiwari, J. Philip, Laser induced surface damage, thermal transport and microhardness studies on certain organic and semiorganic nonlinear optical crystals, Appl. Phys. B 90 (2008) 489–496. [7] D. Satheesh, A. Rajendran, K. Chithra, Synthesis of some new protic N1-benzyl/butyl-2-methyl-4-nitro-1H-imidazol-3-ium salts with 3,5-diaminobenzoate, 3,5-dinitrobenzoate, (E)-3-(4-hydroxy-3-methoxyphenyl) acrylate and 2-carboxy-5-nitrobenzoate as organic anions, Results in Chem. 2 (2020) 10 0 033. [8] D. Satheesh, A. Rajendran, K. Chithra, R. Saravanan, Synthesis and antimicrobial evaluation of N1 -benzyl/butyl-2-methyl-4-nitro-3-imidazolium 3 -chloroperoxy benzoates, Chem. Data Collect. 28 (2020) 100406. ´ [9] P. Tansuri, K. Tanusree, B. Gabriele, R. Lara, Morphology, crystal structure, and thermal and spectral studies of semiorganic nonlinear optical crystal LAHCIBr, Cryst., Growth Des. 4 (2004) 743–747. [10] M. Somac, A. Somac, B.L. Davies, M.G. Humphery, Wong M S third-order optical nonlinearities of oligomers, dendrimers and polymers derived from solution Z-Scan studies, Opt. Mater. 21 (2002) 485–488.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement G. Parvathy: Conceptualization, Investigation, Writing - original draft. R. Kaliammal: Formal analysis, Resources. K. Velsankar: Methodology, Software. G. Vinitha: Formal analysis. K. Sankaranarayanan: Supervision, Visualization. R. Mohan Kumar: Validation, Data curation. S. Sudhahar: Project administration, Supervision, Writing - review & editing. 11
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Piperazinium bis (5-chlorosalicylate) – A new third order nonlinear optical single crystal G. Parvathy a, R. Kaliammal a, K. Velsankar a, G. Vinitha b, K. Sankaranarayanan a, R. Mohan Kumar c, S. Sudhahar a,∗ a b c
Department of Physics, Alagappa University, Karaikudi-630 003, India Division of Physics, School of Advanced Sciences, VIT university, Chennai-600 127, India Department of Physics, Presidency College, Chennai-600 005, India
a r t i c l e
i n f o
Article history: Received 13 June 2020 Revised 9 November 2020 Accepted 3 December 2020 Available online 7 December 2020 Keywords: Crystal structure Optical properties Third order NLO material Thermal stability Mechanical stability
a b s t r a c t A new organic single crystal viz, piperazinium bis(5-chlorosalicylate) (P5C) was grown by low temperature solution growth method and its physico-chemical properties were established. The unit cell param˚ b = 8.7592 A, ˚ c = 9.3103 A, ˚ α = 90°, β = 100.95°, γ = 90°) were determined eters (a = 11.9306 A, by single crystal X-ray diffraction data. The presence of various functional groups in the structure was elucidated by FTIR, Raman and proton NMR spectral studies. The P5C crystal exhibits the good optical tansmittance in the region of 400 to 1200 nm. From photoluminescence studies, the violet emission spectrum was observed under the excitation wavelength of 380 nm. The thermal behaviour of the P5C crystal was analyzed by TG-DSC analysis. The mechanical strength of the grown material classifies it as soft material. The results from Z-scan technique validate the NLO properties. Theoretical calculations like optimized geometry, HOMO-LUMO, mulliken population analysis, natural bond analysis were determined using Gaussian 09W with B3LYP method. © 2020 Elsevier B.V. All rights reserved.
1. Introduction The development of highly efficient NLO materials, increasing the research activity in a variety of applications such as in the area of optical communication, harmonic generation, frequency mixing, laser lithography, diode lasers, etc. [1–2]. Organic materials have great attention by the reason of the wide transparent window, thermal stability, high NLO response, fabrications, and integrating into devices [3]. Recently, researchers mainly concentrate on single crystals of organic because of the easy procedure for synthesis, rapid nonlinear response, and probable of various device fabrications [4–8]. The organic molecules have a π -electron conjugated system connecting donor and acceptor groups are largely polarizable entities that may contribute to triggering the organic crystals for nonlinear optical applications [9]. Third order NLO characterization of organic molecules progresses rapidly because of the promising applications in the area of optical signal processing, optical limiting etc., [10]. There are the variety of methods for analyzing 3rd order nonlinearities, Z-scan technique [11] is one of the easiest and most significant methods to measure both the magni-
∗
Corresponding author. E-mail address: [email protected] (S. Sudhahar).
https://doi.org/10.1016/j.molstruc.2020.129728 0022-2860/© 2020 Elsevier B.V. All rights reserved.
tude and sign of the real part due to nonlinear refraction as well as the imaginary part due to nonlinear absorption of the material science [12,13]. The third order (χ 3 ) coefficients are important for centrosymmetric material where the χ 2 coefficients are equal to zero. The theoretical calculation based density functional theory (DFT) method is generally used to optimize the structure, the charge transfer interaction, hyperpolarizability, etc. It is the most efficient tool for analyzing the theoretical calculation, molecular geometry, and modeling to understand the properties of NLO and forming the novel materials. In this present case, the base material of piperazine is an organic salt and it has piperazinium cation that makes an active role in synthesizing many complex molecules for their interactions between the hydrogen bonds and vibrational analysis [14]. It is a strong basic diamine which consists of two -NH groups. Piperazine used in various biological compounds including drug discovery, the ring of piperazine is used a significant part of pharmaceuticals [15,16], not only that the piperazine derivatives have been subjected to both vibrational and crystallographic analysis [17,18]. The acid material of 5-chlorosalicylic acid has a carboxylic group with two potential coordination such as COOH and OH and there is a high possibility of proton transfer mainly in N-heterocyclic organic salts. Both piperazine and salicylic acid derivative crystals are promising organic material for higher order nonlinear optical applications [19–22]. In this work, the P5C
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728
Fig. 1. Reaction scheme of P5C crystal.
Fig. 2. (a) As-grown P5C crystal and (b) Solubility curve of P5C crystal.
crystal has been synthesized and characterized by structural, spectral, thermal, mechanical, and higher order NLO properties. Also, the theoretical quantum chemical calculations by the method of density functional theory with the 6-311++G (d,p) basis set working in the GAUSSIAN 09 program.
the nature of positive solubility. The solubility nature of P5C is depicted in Fig. 2(b).
3. Results and discussion 2. Experimental section 3.1. Single crystal and powder X-ray diffraction studies 2.1. Material synthesis and crystal growth P5C crystal was characterized by single crystal X-ray diffraction (SXRD) study using Brukker Kappa APEX II X-ray diffractometer with the radiation of MoKα . The P5C structure was determined using direct methods by manipulating the SHELXS-97 [23] and done the refinement of full-matrix least squares on F2 . From structure analysis, it is found that the crystal exhibit monoclinic system having the center of inversion with spacegroup P21 /c resulting with R factors equal to 0.0614 and 0.1253. The calculated lattice pa˚ b = 8.7592 A, ˚ rameters of the grown material are a = 11.9306 A, ˚ α = 90°, β = 100.95° and γ = 90°. The density c = 9.3103 A, ˚ and volume of P5C were determined at 1.499 Mg/m3and 955.21 A3
The piperazine (C4 H10 N2 ) and 5-chlorosalicylic acid (C7 H5 ClO3 ) were taken in the molar ratio of 1:1 for the synthesis of the P5C compound. The calculated amount of both piperazine and 5chlorosalicylic acid materials were dissolved in a suitable solvent mixture of ethanol: water taken in 5:1 volume ratio. The solution was stirred well using a magnetic stirrer to promote homogeneity. After that, the solution was filtered using whatman filter paper and transferred to a beaker which was then covered with a thick perforated polythene sheet for evaporation at room temperature. The proposed chemical reaction scheme of the synthesis of P5C material is depicted in Fig. 1. The purity of the present material was improved by the re-crystallization process. Single crystal was harvested within 5–6 weeks. The picture of an as-grown crystal is shown in Fig. 2(a).
with Z = 2. The crystallographic data file (CIF) of P5C has been deposited in CCDC no. 2010472. The ORTEP diagram and the crystal structure of P5C compound are shown in Fig. 3. The crystal structure of P5C exhibits the deprotonated 5-chlorosalicylate anion and protonated piperazinium cation having intermolecular interaction of hydrogen bonding as seen in the packing diagram (Fig. 4). The asymmetric unit of P5C compound 2(C7 H5 ClO3 ).(C4 H10 N2 ) has 5chlorosalicylate anion and half of piperazinium cation. Cation and anion are linked by the N-H…O hydrogen bond and the anion is connected by the O-H…O hydrogen bond. The structure refinement and crystal data are presented in Table 1. The details of hydrogen bondings are listed in Table 2 after the refinement of structure. The additional data are given in supp. Tables (1–5). Powder XRD pattern recorded on the grown material in the range of 10–80° at the rate of 1°/min shown in Fig. 5 (a). The hkl values were indexed and the observed sharp Bragg’s peaks exhibit the high crystallinity of the grown P5C crystal.
2.2. Solubility The solubility study was taken out from varying temperature between 30 °C and 60 °C with interval of 10 °C utilizing constant temperature bath (CTB) with control efficiency. The amount of P5C salt was added slowly to the mixed solvent of ethanol:water (5:1) and control at 30 °C with repeatedly stirring using a magnetic stirrer. Once it reached the saturation level the equilibrium concentration was measured. The same procedure is repetition for 40, 50 and 60 °C temperatures to measure the solubility. The dissolvation of P5C salt quantity is increased with respect to temperature and therefore the obtained results clearly indicates the P5C crystal has 2
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 3. The molecular structure of the P5C with atom numbering scheme for the atoms and 50% probability displacement ellipsoids. Table 1 Crystal data and structure refinement for P5C. Identification code
P5C
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
C18 H20 Cl2 N2 O6 431.26 296(2) K 0.71073 A˚ Monoclinic P21 /c a= 11.9306(11) A˚ b = 8.7592(9) A˚ c = 9.3103(10) A˚ ˚ 955.21(17) A3
Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 25.242° Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
α = 90°. β = 100.957(2)°. γ = 90°.
2 1.499 Mg/m3 0.379 mm-1 448 0.300 × 0.250 × 0.200 mm3 2.904 to 29.941°. -16< = h< = 16, -12< = k< = 12, -13< = l< = 13 17253 2771 [R(int) = 0.0491] 99.9 % Semi-empirical from equivalents 0.7460 and 0.5626 Full-matrix least-squares on F2 2771 / 0 / 128 1.083 R1 = 0.0403, wR2 = 0.1062 R1 = 0.0614, wR2 = 0.1253 n/a ˚ 0.210 and -0.474 e.A-3
Table 2 Hydrogen bonds for P5C [A˚ and °].
Table 3 FT-IR and Raman spectral vibrational assignments of P5C compound.
D-H···A
d(D-H)
d(H···A)
d(D···A)
<(DHA)
FT-IR (cm−1 )
Raman (cm−1 )
Assignments
Reference
C(6)-H(6)···Cl(1)#2 C(8)-H(8A)···O(3)#3 C(9)-H(9A)···Cl(1)#1 C(9)-H(9B)···O(2)#2 O(3)-H(3A)···O(2) O(3)-H(3A)···O(2)#4 N(1)-H(1A)···O(2)#5 N(1)-H(1B)···O(1)#2
0.93 0.97 0.97 0.97 0.82 0.82 0.89 0.89
2.98 2.53 2.87 2.55 1.83 2.51 1.98 1.78
3.8652(16) 3.2438(19) 3.6931(16) 3.4054(19) 2.5568(17) 3.0518(17) 2.8069(17) 2.6619(17)
160.5 130.5 142.9 147.5 146.5 124.6 154.9 170.2
3248
3304 3215 3081, 3024, 2968 1557 1434 1349 1226 1141 1067 810 640
ν O-H ν N-H ν C-H ν C = O + ν N-H ν C-H + ν N-H ν C-H + ν N-H + ν C-N ν C-O + ν C-C + ν C-N ν C-C + ν C-N ν C-H ν N-H ν N-H
[24–26] [8,24–26] [8,24–28] [8,24,26] [24,25] [24,25] [24,25,29] [8,24,25] [24] [24,26] [24]
3010, 2815 1588 1438 1314 1270 1146 1075 819 643
Symmetry transformations used to generate equivalent atoms: #1 -x+2,-y,-z+1 #2 -x+1,-y,-z+1 #3 x+1,y,z+1. #4 -x,-y,-z #5 -x+1,y+1/2,-z+1/2.
3.2. FT-IR and Raman spectral analyses
trum [8,24–26]. The CH stretching modes are assigned at 3010, 2815 cm−1 in the FT-IR spectrum and these bands are appeared in the Raman spectrum in the region of 3081-2968 cm−1 [8,24– 28]. The band appeared at 1588 cm−1 in the FT-IR spectrum and 1557 cm−1 in the Raman spectrum, which is attributed to the C = O stretching and N-H deformation vibrations [8,24–26]. The band appeared at 1438 cm−1 in the FT-IR spectrum and 1434 cm−1 in the Raman spectrum, which is attributed to the C-H stretching
The FT-IR and Raman spectra of the title compound P5C are shown in Fig. 5(b) and (c) respectively, and their assignments are summarized in Table 3. The phenolic OH and NH stretching modes are assigned at 3248 cm−1 in the FT-IR spectrum and these bands are appeared at 3304 cm−1 for OH and 3215 cm−1 for NH in the Raman spec3
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Journal of Molecular Structure 1228 (2021) 129728
The bands appeared at 1075 cm−1 is assigned to the C-H and the bands at 819 and 643 cm−1 are assigned to the N-H group in the FT-IR spectrum. These bands are also found at 1067 cm−1 , 810 & 640 cm−1 in the Raman spectrum respectively [24,26]. 3.3. Nuclear magnetic resonance 1 H-NMR (d6 -DMSO, 400MHz, δ in ppm): 3.34 (s, 8H, 4xCH ), 2 6.74, 6.76 (d, 4H, J= 8Hz, 2xNH2 + ), 7.24-7.26 (t, 6H, J= 8Hz, C3,4,5 HSalicylate ring ), 7.66 (s, 2H, OHSalicylate ring ).The NMR spectroscopy is one of the efficient techniques used to study the crystal structure of organic materials [30]. In the 1 H NMR spectrum of the symmetric organic crystal P5C, a sharp singlet peak showed at 3.348 ppm, which is assigned to the four methylene (4xCH2 ) protons [31] and a doublet peak showed at 6.74 and 6.76 ppm is attributed to the ammonium (2xNH2 + ) protons of the piperazine1,4-diium moiety which confirms all the protons are transferred from 5-Chlorosalicylic acid to Piperazine. The aromatic protons of the 5-Chlorosalicylate moiety show a peak at 7.24-7.26 ppm. A singlet peak at 7.66 ppm is assigned to the phenolic -OH of the 5-Chlorosalicylate moiety. The 1 H-NMR spectrum of P5C did not show the chemical shift for the free carboxylic acid. From this it is justified and confirmed that the structure of the grown symmetric crystal P5C is shown in Fig. 6.
Fig. 4. Crystal packing diagram of P5C crystal.
and asymmetric bending N-H vibrations [24,25]. The C-H, N-H and C-N groups showed a band at 1314 cm−1 in the FT-IR spectrum and 1349 cm−1 in the Raman spectrum [24,25]. The band at 1270 and 1226 cm−1 are ascribed to stretching vibrations of C-O, C-N and C-C in the FT-IR and Raman spectra respectively [24,25,29]. The C-N and C-C bonds are showed a band at 1146 cm−1 in the FT-IR spectrum and 1141 cm−1 in the Raman spectrum [8,24,25].
3.4. UV-Vis spectral study The optical property of the grown material was measured using ocean optics HR 20 0 0 UV-Vis spectrophotometer. UV-Vis spec-
Fig. 5. (a) The powder XRD, (b) FT-IR and (c) Raman. 4
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 6. NMR spectra of P5C crystal.
3.5. Photoluminescence spectrum
trum provides the massive information about a molecular electronic transition of π - conjugated system which involves the promotion of an electron in σ and π orbitals from the ground level to a higher energy level due to absorption [32]. The optical properties are very important for crystals to study the lattice vibrations, impurity levels, excitons, energy band structure, etc. [33]. The transitions between the absorption bands of π -π ∗ , n-π ∗ (lone pairs and π orbitals) take place in aromatic compounds. Defects are being impurities, the cracks, the inclusion of solvent and grain boundaries which usually diminish the optical quality of the crystal [34]. The absorption spectrum of P5C crystal was recorded and is shown in Fig. 7(a). The cutoff wavelength is observed at 340 nm and the grown crystal is transparent about 75% in the region between 4001100 nm which is an important parameter needed for NLO materials. This lower cut-off at 340 nm is owing to the excitation of aromatic material contains hydrogen and nitrogen [35]. The optical absorption coefficient is based on the energy of photons (hν ) and helps to identify the type of transition of electrons and band structure [36]. The transmittance (T) evaluated using the absorption spectrum was used to measure the absorption coefficient (α ) by using the relation (1),
α = 2.3026 log(1/T )/d
The PL spectrum of P5C crystal was observed using the varian cary eclipse spectrofluorometer to analyze the defects and optical properties of the grown material. The luminescence of organic molecules depends on π -electron systems occurring in the internal individual organic fragments. Generally, the PL signal is based on changing the excitation point and wavelength, the density of excited electrons and the intensity of the incident beam. The recorded emission spectrum in the range of 30 0–80 0 nm under 380 nm excitation wavelength is shown in Fig. 7 (c). A strong violet emission was measured at 445 nm, which may be owing to the π -π ∗ interaction in the salicylate and piperazine molecules.
3.6. TG-DSC analysis The Fig. 7(d) shows the result of the thermogravimetry (TGA) and differential scanning calorimetry (DSC) analysis on P5C single crystal in a nitrogen gas atmosphere and in the temperature range of 30 to 500 °C at the heating rate of 10 °C/min using SDT Q600 V20.9 Build 20. A sample mass of 1.666 mg was taken for analysis and placed in the alumina crucible during the study. TGA plot indicates that the P5C crystal is stable up to 160 °C and the decomposition of the material was noted in the temperature range of 180 °C–300 °C. The TG curve also suggests that no phase transition occurred until the grown material melts. The sharp endothermic peak at 236.62 °C in the DSC curve indicates the melting point of the grown crystal. The sharpness implies the phase purity and good crystallinity of the P5C sample [37]. The melting point of P5C is larger than a few of the derivatives of piperazine like PBA (197 °C) [38], MPHP (217 °C) [39] etc. This improvement in the melting point is an added advantage for NLO applications.
(1)
d is the thickness of the grown crystal. The band gap (Eg ) was calculated by using the formula (2),
(α hν )2 = A(Eg − hν )
(2)
Where α indicates the absorption coefficient, A is constant, Eg is the optical band gap, h is Planck’ s constant, ν is the frequency of photons Fig. 7 (b) exhibits the graph between the variation of (α hν )2 with ‘hν ’ which is used to calculate the optical band gap. The band gap energy of the P5C crystal is about 4.1 eV. 5
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 7. (a) UV-Vis absorbance, (b) optical band gap energy (Eg ), (c) PL and (d) TG-DSC of P5C crystal.
behavior of ISE is n<2. The n>2 is a behavior of reverse ISE. P5C crystal exists a soft material category because of n>2. The fracture toughness (kc ) explains how much fracture stress is enforced under uniform loading. The Kc is given by the following formula,
3.7. Microhardness studies The information on mechanical strength is an important parameter for practical application of the studied crystal. The hardness value was evaluated for varying loads of 10, 25, 50, and 100 g with a fixed indentation time of 5 s for all loads. For every load, the d of the diagonal length of the indentation mark was measured at different indentation sites and an average of these values was taken. The Vicker’s microhardness number (Hv ) can be estimated by using the formula,
Hv = 1.854 P/d2 Kg/mm2
Kc = P/β0 l3/2 ; if l ≥ d/2
(3)
Where P indicates the applied load and d refers to the diagonal length. A graph was attained between the hardness number (Hv ) and applied load (P) and was shown in Fig. 8(a) where in the Hv increases with the applied load (P) up to 100 g, and that behavior was attributed to reverse indentation size effect [40]. The increase of applied load beyond 100 g led to the formation of cracks on the crystal surface and thus the study was restricted up to the load of 100 g. Fig. 8(b) depicted the graph of HV versus indentation diagonal length d. The easiest way to explain the ISE is Meyer’s law [41], the relationship between the load P and size of indentation (d) is given by the relation,
P = Adn
(5)
Where β 0 is a constant (β 0 = 7), l represents the crack length, d indicates the diagonal length. The plot between P versus l3/2 is shown in Fig. 9 (b). The brittleness is one of the essential properties and it deals with the fracture induced in a crystal without any observable deformation. The brittleness index (Bi ) value is calculated by using the formula [42],
Bi = HV /KC
(6)
Further, the yield strength (σ y ) of a grown crystal can be measured by using HV and Meyer’s index as 2.25 by using the equation,
σy =
Hv 12.5(n − 2 ) [1 − (n − 2 )] 2.9 1 − (n − 2 )
n−2
(7)
Fig. 9(c) exhibits the graph between the load (P) and Yield strength (σ y ). The elastic stiffness constant (C11 ) was measured by using Wooster’s relation [43]. It provides a deep idea about the interatomic bonding strength of the crystals.
(4)
C11 = (HV )7/4
Where A is an arbitrary constant for a grown material and n is the work hardening coefficient of P5C single crystal. The n value can be calculated by using Meyer’s graph between log P and log d as seen in Fig. 9(a). The n value was calculated to be at 2.25. The normal
(8)
A plot between the load (P) and stiffness constant (C11 ) for a grown material, is shown in Fig. 9(d). The numerical values of above these parameters of P5C material for varying loads are given in Table 4. 6
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 8. (a) Plot of Hardness number (Hv ) vs. load (P) and (b) Plot of Hardness number (Hv ) vs. diagonal (d).
Fig. 9. (a) log d vs log ‘P’, (b) log ‘P’ vsl3/2 (c) Plot of yield strength (σ y) vs. load P and (d) Variation of stiffness constant (C11 ) with Load P.
Table 4 Microhardness (Hv ), Yield strength (σ v ), Stiffness Constant (C11 ), Fracture toughness (Kc ) and Brittleness (Bi ) for different loads. Load (g) 10 25 50 100
Hv
Meyer’s index 2
(kg/mm ) 51.30 58.10 64.90 69.00
(n) 2.25 2.25 2.25 2.25
σv 2
(GN/m ) 18.94 21.46 23.96 24.37
7
C11 x 1014
Kc
(Pa) 9.83 12.59 13.27 15.28
(gμm 0.0487 0.0681 0.0829 0.1047
Bi −3/2
)
(μm−1/2 ) 10.5 8.67 7.34 6.30
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 10. (a) Open aperture curve and (b) Closed aperture of P5C crystal.
Table 5 Calculated Z-scan results of nonlinear refractive index (n2 ), nonlinear absorption coefficient (β ), third order nonlinear susceptibility (χ 3 ) of the P5C crystal.
3.8. Z-scan analysis Third order nonlinear optical properties were analyzed by Zscan technique to determine both nonlinear refractive index ‘n2 ’ and nonlinear absorption coefficient ‘β ’ and third order nonlinear susceptibility ‘χ 3 ’ which is complex in nature. The Z-scan method to study under closed and open apertures (CA and OA) for P5C crystal using semiconductor diode laser (λ = 532 nm). The given sample attains a maximum reached an intensity at foci (z = 0) which symmetrically minimized towards both sides of positive and negative Z values and it start from +15 to -15, the light may be transmitted and P5C crystal was analyzed using digital meter. The final data are plotted against the sample position is called as Zscan curve of P5C crystal. Fig. 10(a) exhibits the open aperture (OA) curve for which corresponds to nonlinear transmittance decreasing with increasing intensity that exhibits the reverse saturable absorption. To calculate the value of nonlinear absorption coefficient ‘β ’ using the following equation [44],
β
√ 2 2 T = ( m/W ) IoLe f f
NLO parameters Calculated values
Re χ ( 3 ) =
(9)
χ (3 ) =
α indicates the linear absorption coefficient (λ = 532 nm). L denotes the thickness. To evaluate the closed aperture provides the data around the sign and magnitude of n2 . The CA of P5C crystal is depicted in Fig 10 (b). The peak to valley determines that the crystal carried out self-defocusing which shows the negative nonlinear behaviour of grown crystal [45]. To calculate the nonlinear refractive index using the relation [46],
(11)
10−4 εoC 2 n2 n2o
π
10−2 εoC 2 λβ n2o 4π 2
(14)
(15)
Re
2 χ (3) + Im χ (3)
(16)
The geometrical parameters were theoretically analyzed using DFT B3LYP functional with 6-311G++ (d,p) basis set. The theoretical calculations have been analyzed using Gaussian 09W to provide an optimized structure of P5C compound [47] and the structure is viewed by Gaussview 5.0 [48]. The SXRD CIF file of P5C was used as input. The optimized structure, HOMO-LUMO, mulliken charge analysis, hyperpolarizability, natural bond analysis was theoretically analyzed using Gaussian 09W program.
(12)
S denotes the linear transmittance and it can be calculated using the relation,
S = 1 − exp −2ra 2 /wa 2
4.01 × 10−7
3.9. Computational details
Where ∅ indicated as on axis phase shift and it calculated by using the following relationship,
| ∅| = TP−V /0.406(1 − S )0.25
3.756 × 10
χ 3 [esu] −9
The calculated values of third-order NLO parameters, i.e. nonlinear refractive index (n2 ), absorption co-efficient (β ), and third order susceptibility (χ 3 ) of P5C crystal were observed to be n2 = 1. 875 × 10−14 m2 /W, β = 3.756 × 10−9 m/W, (χ 3 ) = 4.01 × 10−7 esu respectively is shown in Table 5. The open aperture curve shows a decrease the transmittance with increasing intensity. This determines the existence of reverse saturable absorption (RSA) which leads to a grown material for optical limiting applications.
(10)
∅ K IoLe f f
β [Mw−1 ]
To calculate the third order nonlinear susceptibility (χ 3 ) of P5C crystal by using the following equation,
Where T indicates the valley value from OA curve. I0 indicates the input intensity. Leff represents the thickness of the sample, it can be examined by using the formula
n2 =
1.875 × 10
−14
In the above equation ra represent the radius of the aperture and laser beam radius was represented by wa . The real and imaginary parameters of the third-order nonlinear optical susceptibility (χ 3 ) of P5C crystal were obtained using the relations:
Im χ (3 ) =
Leff = 1 − e−α L /α
n2 [m2 W−1 ]
(13) 8
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728 Table 6 Experimental and optimized geometry parameters of P5C crystal computed by B3LYP/6-311++G (d,p) basis set.
Fig. 11. Optimized molecular structure of P5C crystal.
3.9.1. Optimized molecular structure The optimized molecular parameters of P5C molecule like bond length, angles and dihedral angles were obtained from theoretical studies of B3LYP method and those values compared to experimental data. The obtained optimized structure is depicted in Fig. 11. From XRD, the protons are transferred from 5-Chlorosalicylic acid to piperazine. The structure of P5C bond length C-C is placed be˚ ˚ A˚ in experimental and 1.380 A-1.500 A˚ for tween 1.375 A–1.508 theoretical. The C8 –C9 bond distance is larger compared with other bond distance, it is owing to the presence of piperazinium. The CH bond length range 0.930 A˚ for XRD and 1.08 A˚ for B3LYP almost all C-H bond distances are approximately equal. The C2 –O3 ˚ bond distance is larger when compared with other C(1.358 A) O bond distance. The C5 –Cl1 bond distance is 1.742 A˚ in theoretical and 1.759 A˚ in experimental. The obtained N-H bond distance value obtained 0.890 A˚ in XRD and 1.010 A˚ in B3LYP respectively. The bond angles of O3-C2-C1 (122.1°) are higher when compared with other angles, it is owing to the presence of carboxyl. The experimental and theoretical values are listed in Table 6. 3.9.2. Analysis of frontier molecular orbitals (FMO) The study of understanding the FMO is an effective way to examine the chemical reactivity and optical properties of molecules. The excitation of electrons from occupied (HOMO) to unoccupied (LUMO) molecular orbital makes a significant role in optical property. The FMO pictorial representation is depicted in Fig. 12. Which evidentiary exhibit the HOMO is occupied over 5-chlorosalicylate and the LUMO is delocalized over piperazinium. The theoretical energy values are -2.0438 eV in HOMO and -6.5010 in LUMO. The obtained energy gap is 4.4 eV, which is nearly equal to the experimental value (4.1 eV). HOMO energy has the capability to give an electron while the LUMO has the capability to access the electron [49]. The energy gap between them indicates the properties of electrical and it affirms that placed charge transfer action in the molecule. The implementation of LUMO has the strong energy level because of the electron access group is placed. The red and green colour indicates the positive and negative region is depicted in Fig. 12. The energy gap is a most important part because it provides chemical stability [50]. The other important parameters of chemical hardness (η), Electrophilicity (ω), Ionization potential (I), Chemical potential (μ), Electron affinity (A), Global softness (S), Electronegativity (χ ) of P5C molecule can be determined by applying the koopman’s theorem [51] is provided in Table 7.
˚ Bond length (A) Geometric parameters
Experimental values
B3LYP/6-311++G(d, p)
C1-C6 C1-C2 C1-C7 C2-O3 C2-C3 C3-C4 C3-H3 C4-C5 C4-H4 C5-C6 C5-Cl1 C6-H6 C7-O1 C7-O2 C8-N1 C8-C9 C8-H8A C8-H8B C9-H9A C9-H9B O3-H3A N1-H1A N1-H1B
1.397 1.401 1.494 1.358 1.394 1.378 0.930 1.386 0.930 1.375 1.742 0.930 1.248 1.277 1.487 1.508 0.970 0.970 0.970 0.970 0.820 0.890 0.890
1.406 1.415 1.472 1.343 1.402 1.383 1.082 1.399 1.082 1.380 1.759 1.081 1.332 1.230 1.377 1.500 2.410 1.086 1.089 1.081 0.983 1.009 1.010
Bond Angles(°) Geometric parameters
Experimental value
B3LYP/6-311++G(d, p)
C6-C1-C2 C6-C1-C7 C2-C1-C7 O3-C2-C3 O3-C2-C1 C3-C2-C1 C4-C3-C2 C4-C3-H3 C2-C3-H3 C3-C4-C5 C3-C4-H4 C5-C4-H4 C6-C5-C4 C6-C5-Cl1 C4-C5-Cl1 O2-C7-C1 N1-C8-C9 N1-C8-H8A C9-C8-H8A N1-C8-H8B C8-C9-H9B
119.0 119.5 121.4 118.0 122.1 119.8 120.5 119.7 119.7 119.3 120.3 120.3 121.0 119.1 119.8 117.4 109.7 109.7 109.7 109.7 109.7
119.6 121.1 119.2 117.8 123.0 119.1 120.6 121.0 118.3 119.9 120.2 119.8 120.7 119.9 119.3 123.0 126.9. 113.3 119.6 109.8 120.1
Dihedral Angles(°) Geometric parameters
Experimental value
B3LYP/6-311++G(d, p)
C6-C1-C2-O3 C7-C1-C2-O3 C6-C1-C2-C3 C7-C1-C2-C3 O3-C2-C3-C4 C1-C2-C3-C4 C2-C3-C4-C5 C3-C4-C5-C6 C3-C4-C5-Cl1 Cl1-C5-C6-C1 C2-C1-C6-C5 C7-C1-C6-C5 C2-C1-C7-O1 C6-C1-C7-O2
179.6 0.1 0.2 179.5 179.7 0.3 0.4 0.4 179.3 179.4 0.2 179.5 -176.6 -177.5
179.9 0.03 0.04 179.9 179.9 0.03 0.01 0.0 179.9 179.9 0.03 179.4 -179.9 -179.8
Global softness (S) = 1/(η)……(4) Chemical potential (μ) = - (I+A/2)…..(5) Electronegativity (χ ) = (I+A/2)……(6) Electrophilicity (ω) = μ2 /2 η……(7)
Ionization potential (I) = -Homo energy….. (1) Electron affinity (A) = -Lumo energy…..(2) Chemical hardness (η) = (I-A/2)…..(3) 9
G. Parvathy, R. Kaliammal, K. Velsankar et al.
Journal of Molecular Structure 1228 (2021) 129728 Table 8 The polarizability and first-order hyperpolarizability of P5C. Polarizability
α components (a.u) α xx α xy α yy α xZ α yz α zz α tol (e.s.u.)
198.550 85.313 458.003 75.528 156.986 189.578 2.82 ∗ 10−23
First order hyperpolarizability β components (a.u)
β xxx β xxy β xyy β yyy β xxz β xyz β yyz β xzz β yzz β zzz β tol (e.s.u.)
3276.73 4382.532 5835.231 10747.261 2611.253 3339.410 5291.376 1984.441 2769.025 1791.548 1.415∗ 10−28
mined by 3 × 3 × 3 matrix. The twenty seven components of 3 dimensional matrix are diminished to ten elements which is owing to the kleimann symmetry [54-57]. The charge transfer action and π -conjugation presented in P5C molecule lead to trigger the hyperpolarizability may cause of high transfer. The low energy gap certainly indicates the charge transfer takes place in a molecule via conjugation and therefore increased the NLO response [58,59]. The hyperpolarizability value of P5C is β = 1.415 × 10−28 and polarizability is α = 2.82 × 10−23 . For P5C, the largest element is obtained for β yyy direction and it represents the charge transfer action. The observed value represent the hyperpolarizability is 1.415 × 10−28 e.s.u, it shows the NLO response and the value indicates polarizability is 2.82 × 10−23 e.s.u. Fig. 12. Frontier molecular orbital (FMO) of P5C.
3.9.4. Mulliken charge analysis The mulliken population analysis is one of the efficient methods to find relevance in quantum calculations to indicate the distribution of charge in each atom placed in a molecule. The values of atomic charges were attained by mulliken charge analysis [60] of P5C molecule is calculated by using the B3LYP method with 6-311++G (d,p) as a basis set. The P5C structure with atomic charge is depicted in Fig. 13. The charges have ranged from 0.062 to 0.509. In P5C molecule the charge C15, C18, C13 acquires a positive charge, whereas other carbon atoms are negative. The N9 atom charge is negative and all the hydrogen atoms are positive. The Cl (0.509) is the highest positive charge and C2 possess the smallest negative charge of remaining atoms in P5C molecule.
Table 7 HOMO-LUMO energy gap and their related molecular properties of P5C molecule. Molecular properties (B3LYP/6-311G (d,p) HOMO energy LUMO energy HOMO-LUMO energy gap Ionization potential (I) Electron affinity (A) Chemical hardness (η ) Reciprocal of hadrness (S) Chemical potential (μ) Electronegativity (χ ) Electrophilicity (ω )
-6.5010 eV -2.0438 eV 4.4 eV 6.5011 eV 2.0438 eV 5.4792 eV 0.1825 eV -7.523 eV 7.523 eV 5.161 Ev
3.9.5. Natural bond analysis (NBO) NBO analysis helps to understand inter and intramolecular energies of interaction both acceptor and donor relation using 2nd order fock matrix. NBO gives all the probable interactions of bonding and antibonding with the help of delocalization calculation and rehybridization in the molecule [61,62]. A bonding and antibonding orbitals play a role in donor and acceptor. The strong hydrogen bonded relation between the lone pair (LP) and antibonding orbital of N-H and O-H bonds. The interactions LP(3)O(21)-π ∗ (C19 -C20 ), LP(3)O(21)-σ ∗ (H5 -N9 ), LP(1)O(21)- σ ∗ (H5 -N9 ) which corresponds to the high stabilization energies of 43.85, 33.32, 20.21 Kcal/mol which proved the occurrence of intramolecular relation with P5C. The strong interactions are π (C13 -C14 )-π ∗ (C19 -C20 ) which corresponds to the maximum energies of 16.93 Kcal/mol. The next strong relation is σ (C1 -C2 )-σ ∗ (H6 -N9 ) which have the energies of 7.49 Kcal/mol. The strong ICT relation of P5C is increased with respect to the interaction energy and stabilization. The different hyperconjugative interactions are given in supp. Table 6.
The softness and chemical hardness are linked to stability of materials [52]. Electronegativity helps to observe the capability to invite the shared electrons. Electron affinity represents the ability to access electron from a donor. Softness represents the properties of materials indicates the chemical reactivity of P5C molecule. 3.9.3. Hyperpolarizability Quantum chemical calculations attend with DFT method is the efficient way to know between structure and NLO role in organic materials through the description of NLO characteristics of materials [53]. The hyperpolarizability makes an efficient role in stability of materials and enhancement of properties of optical materials and the components are provided in Table 8. The first order hyperpolarizability is a type of 3rd rank tensor and that can be deter10
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Journal of Molecular Structure 1228 (2021) 129728
Fig. 13. Mulliken atomic charges plot of P5C.
4. Conclusion
Acknowledgements
A new organic crystal viz., piperazinium bis (5-chlorosalicylate) was grown by the solution growth method at 35 °C. The SXRD reveals that the grown crystal possesses monoclinic system with a P21 /c space group. The molecular structure of grown material was further ascertained by FTIR, Raman, and proton NMR spectral studies. P5C crystal exhibited a cut-off wavelength at 340 nm and the optical bandgap of the material was measured to be 4.1 eV. The PL study identifies a violet emission peak at 445 nm. TG-DSC analysis validate the thermal stability up to 160 °C and the melting point at 236.42 °C for the present material. The mechanical property of the P5C crystal was analyzed and it belongs to the category of soft material. The nonlinear refractive index n2 = 1. 875 × 10−14 m2 /W, absorption co-efficient (β ) = 3.756 × 10−9 m/W, and third order susceptibility (χ 3 ) = 4.01 × 10−7 esu of P5C crystal were evaluated by Z-scan technique. From FMO analysis, the obtained bandgap energy is 4.4 eV which is nearly equal to the experimental value 4.1 eV. The bonding interaction of P5C was observed by Mulliken analysis. The first order hyperpolarizability of P5C crystal was β = 1.415 × 10−28 e.s.u. These results conclude that the newly grown P5C crystal is suitable for NLO applications.
The authors acknowledge the scheme MHRD-RUSA PHASE-2.0 (grant sanctioned vide Letter No. F.24-51/2014-U, Policy (TN MultiGen), Dept. of Edn. Govt. of India, Dt. 09.10.2018) New Delhi and DST-PURSE-II, New Delhi-India for a grant. Also, the authors express their thanks to UGC-SAP, DST-FIST and Alagappa University, Karaikudi-03, Tamilnadu, India. Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2020.129728. References [1] R.L. Sutherland, Handbook of Nonlinear optics, Materials Dekker, Inc, 1996. [2] M. Krishna kumar, S. Sudhahar, A. Silambarasan, B.M. Sornamurthy, R. Mohan kumar, Crystal growth, structural, linear and nonlinear optical studies of 4-methyl-4’-N’-methylstilbazolium tosylate single crystals, Optik 125 (2014) 751–755. [3] P.N. Prasad, D.J. Wollians, Introduction to nonlinear optical effects in molecules and polymers, Wiley-Interscience, Newyork, 1991. [4] T. Chem, Z. Sun, C. Song, Y. Ge, J. Luo, W. Lin, M. Hong, Bulk crystal growth and optical and thermal properties of the nonlinear optical crystal L-histidinium-4nitrophenolate 4-nitrophenol (LHPP) cryst, Growth Des. 12 (2012) 2673–2678. [5] G.A. Babu, P. Ramasamy, Investigation of crystal growth, structural, optical, dielectric,mechanical and thermal properties of a novel organic crystal: 4,4’-dimethylbenzophenone, J. Cryst. Growth 310 (2008) 3561–3567. [6] S. Manivannan, S. Dhanuskodi, S.K. Tiwari, J. Philip, Laser induced surface damage, thermal transport and microhardness studies on certain organic and semiorganic nonlinear optical crystals, Appl. Phys. B 90 (2008) 489–496. [7] D. Satheesh, A. Rajendran, K. Chithra, Synthesis of some new protic N1-benzyl/butyl-2-methyl-4-nitro-1H-imidazol-3-ium salts with 3,5-diaminobenzoate, 3,5-dinitrobenzoate, (E)-3-(4-hydroxy-3-methoxyphenyl) acrylate and 2-carboxy-5-nitrobenzoate as organic anions, Results in Chem. 2 (2020) 10 0 033. [8] D. Satheesh, A. Rajendran, K. Chithra, R. Saravanan, Synthesis and antimicrobial evaluation of N1 -benzyl/butyl-2-methyl-4-nitro-3-imidazolium 3 -chloroperoxy benzoates, Chem. Data Collect. 28 (2020) 100406. ´ [9] P. Tansuri, K. Tanusree, B. Gabriele, R. Lara, Morphology, crystal structure, and thermal and spectral studies of semiorganic nonlinear optical crystal LAHCIBr, Cryst., Growth Des. 4 (2004) 743–747. [10] M. Somac, A. Somac, B.L. Davies, M.G. Humphery, Wong M S third-order optical nonlinearities of oligomers, dendrimers and polymers derived from solution Z-Scan studies, Opt. Mater. 21 (2002) 485–488.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement G. Parvathy: Conceptualization, Investigation, Writing - original draft. R. Kaliammal: Formal analysis, Resources. K. Velsankar: Methodology, Software. G. Vinitha: Formal analysis. K. Sankaranarayanan: Supervision, Visualization. R. Mohan Kumar: Validation, Data curation. S. Sudhahar: Project administration, Supervision, Writing - review & editing. 11
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