Growth, characterization and theoretical parameter study of benzimidazole L-tartrate single crystal: a nonlinear optical material HIRAL RAVAL 1,2 , P S RAVAL 1,2 , B B PAREKH 1, * and M J JOSHI 3 1 Pandit Deendayal Petroleum University, Gandhinagar 382007, India 2 L D College of Engineering, Ahmedabad 380015, India 3 Department of Physics, Saurashtra University, Rajkot 360005, India *Author for correspondence ([email protected]) MS received 13 July 2020; accepted 30 August 2020 Abstract. Good quality, non-hygroscopic and transparent crystals of organic benzimidazole L-tartrate (BILT) were grown successfully with a slow evaporation method. The powder X-ray diffraction patterns were analysed with Powder-X software which confirms the monoclinic crystal structure. The charge distribution, transport mechanism and intramolecular bonding mechanism have been investigated with the help of natural bond orbital analysis and molecular electrostatic potential diagram. The presence of various functional groups was confirmed with the help of FTIR–ATR response. The values were compared with the values obtained from computational output with the help of Gaussian software. The crystalline quality was further analysed with UV–visible spectral analysis. The lower cut-off wavelength of 288 nm and further optical parameters like band gap, change in refractive index with wavelength and extinction coefficient values support the usage of the material for optoelectronic devices. With band gap of 4.2 eV, the reactivity of material has been observed with the HOMO and LUMO study. The TGA and DTA analyses confirm the thermal stability of the material up to 192°C. The lower dielectric constant and lower dielectric loss support the usage of the material for an NLO device. The hopping motion and Joncher’s power law parameters were also obtained. The material decomposes in single-phase which observes in a range of 180–250°C. The second harmonic generation capacity of the material is found to be 2.69 times that of the KDP with the help of Kurtz and Perry powder technique. Keywords. Crystal growth; organic nonlinear optical material; second harmonic generation; DFT; UV–visible. 1. Introduction The synthesis of multicomponent crystals like salts, moi- eties, co-crystals and solvates attracts researchers due to their versatile properties and applications in the area of optoelectronic devices and NLO properties. The formation of co-crystals has been achieved with the help of a stoi- chiometric ratio mixture of two or more compounds. The intramolecular assembly is mainly with the help of hydro- gen bonding, bond interactions and charge transfer activities [1,2]. The advanced requirements of optical image pro- cessing, photonics, communication and storage devices require a large spectrum of NLO materials with stability and efficient conversion capabilities can be accomplished with the help of such mentioned frames of molecular assemblies [3–6]. In addition to the same, the molecular assemblies of multi-component materials can be unfailingly formed with the help of carboxylic acids [7]. The recent work for the development of powerful NLO materials shows promising results with hydrogen bonding between carboxylic groups and other groups like hydroxyl group, heterocyclic aromatic group [8–11]. The supramolecular assembly framework can be established with the help of carboxylic and heterocyclic compounds through building blocks that self-assemble via N–H…H–O, O–H…O, N–H…O, and C–H…O hydrogen bonds when crystallized [12,13]. Based on the same, in this present work, the effect of a combination of the carboxyl group with bicyclic fusion aromatic compounds in non- linear behaviour has been reported. The various analyses have been carried out which confirm the application of the title compound as potential NLO material. 2. Experimental and computational details 2.1 Synthesis The AR grade L-tartaric acid (Merk Millipore) was dis- solved in water along with the same grade benzamida- zolium (Sigma Aldrich), were dissolved in methanol in Bull. Mater. Sci. (2021)44:38 Ó Indian Academy of Sciences https://doi.org/10.1007/s12034-020-02320-2
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Growth, characterization and theoretical parameter studyof benzimidazole L-tartrate single crystal: a nonlinearoptical material
HIRAL RAVAL1,2, P S RAVAL1,2, B B PAREKH1,* and M J JOSHI3
1Pandit Deendayal Petroleum University, Gandhinagar 382007, India2L D College of Engineering, Ahmedabad 380015, India3Department of Physics, Saurashtra University, Rajkot 360005, India
The synthesis of multicomponent crystals like salts, moi-
eties, co-crystals and solvates attracts researchers due to
their versatile properties and applications in the area of
optoelectronic devices and NLO properties. The formation
of co-crystals has been achieved with the help of a stoi-
chiometric ratio mixture of two or more compounds. The
intramolecular assembly is mainly with the help of hydro-
gen bonding, bond interactions and charge transfer activities
[1,2]. The advanced requirements of optical image pro-
cessing, photonics, communication and storage devices
require a large spectrum of NLO materials with stability and
efficient conversion capabilities can be accomplished with
the help of such mentioned frames of molecular assemblies
[3–6]. In addition to the same, the molecular assemblies of
multi-component materials can be unfailingly formed with
the help of carboxylic acids [7]. The recent work for the
development of powerful NLO materials shows promising
results with hydrogen bonding between carboxylic groups
and other groups like hydroxyl group, heterocyclic aromatic
group [8–11]. The supramolecular assembly framework can
be established with the help of carboxylic and heterocyclic
compounds through building blocks that self-assemble via
N–H…H–O, O–H…O, N–H…O, and C–H…O hydrogen
bonds when crystallized [12,13]. Based on the same, in this
present work, the effect of a combination of the carboxyl
group with bicyclic fusion aromatic compounds in non-
linear behaviour has been reported. The various analyses
have been carried out which confirm the application of the
title compound as potential NLO material.
2. Experimental and computational details
2.1 Synthesis
The AR grade L-tartaric acid (Merk Millipore) was dis-
solved in water along with the same grade benzamida-
zolium (Sigma Aldrich), were dissolved in methanol in
Bull. Mater. Sci. (2021) 44:38 � Indian Academy of Scienceshttps://doi.org/10.1007/s12034-020-02320-2Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)
equal proportion and mixed. The mixture was dried in the
oven at 60�C for 2 h. The powder was again dissolved in
water and filtered with filter paper grade 41. At every stage
of dissolution, the homogeneous solution was prepared with
the help of magnetic stirrer. The solution was kept in beaker
and covered with polythene to enable very slow evapora-
tion. After 26 days, the good quality transparent crystals
(figure 1) were harvested for analysis. The average size of
good quality and the transparent crystal was 129 89 6 mm3.
Furthermore, no hygroscopic nature of crystal was observed
and quality remains the same for a long period.
2.2 Experimental analysis
The grown crystals were subjected to various analyses
which help to identify its potential usage for non-linear
activity. The crystals were analysed by various means
like structural analysis by powder X-ray diffraction
(XRD), thermal analysis with TGA and DTA, optical
quality analysis with UV–visible photo-spectrometer,
functional group analysis with FTIR–ATR spectroscopy,
dielectric analysis with PSM analyzer and second har-
monic generation (SHG) analysis with Kurtz and Perry
powder technique.
2.3 Computational analysis
The theoretical quantum chemical computation of BILT
was carried out with the help of the Gaussian 09 software
[14]. The calculations were carried out with time-dependent
density functional theory (TD-DFT) matrix on the basis set
of B3LYP/6-311 G(d,p). The experimental correlated cal-
culations, such as vibrational response, molecular electro-
static potential (MEP) distribution, natural bond orbital
(NBO), polarizability and HOMO and LUMO calculations
were carried out. All calculations were performed on an
optimized structural output.
3. Results and discussion
3.1 Structural analysis
Structural analysis of BILT crystal was carried out with the
help of fine powder X-ray analysis. The diffraction pattern
was recorded on PANalytical X’pert PRO X-ray diffrac-
tometer from 0 to 90� range with a source of CuKa (k =
1.5418 A) radiation. The data were analysed with Powder-X
software as shown in figure 2. The analysis confirmed that
the BILT crystal belongs to monoclinic crystal structure
system with cell parameters a = 9.227 A, b = 7.278 A and
c = 10.889 A, volume = 731.241 A3 and a = c = 90� and b =
110.50�.The titled compound structure was also optimized for
further theoretical analysis with the help of the Gaussian
09W program package with the TD-SCF DFT method
with the basis point of B3LYP (6-311G). The hydrogen
sharing bond is observed between H21 and H26 with a
sharing bond length of 2.894 A. The bond parameters
observed after optimization are listed in the supplemen-
tary information. The zigzag tartrate structure with car-
bon chain C–C–C–C is observed with torsion angle of
0.0346�. The higher non-linearity and stability are pro-
jected due to the expected zigzag configuration of tartrate
molecules [15].
The benzimidazole and tartrate are aligned with head
to the tail arrangement on the axis. The formation of
chain suggests good stability of the crystalline material.
The diagram is illustrated in figure 3 with bond length.
The aromatic ring and benzene sharing bond is observed
with (C4–N5) and (C3–N2) with bond lengths of 1.407Figure 1. As grown crystal of BILT.
38 Page 2 of 16 Bull. Mater. Sci. (2021) 44:38
Figure 2. Powder X-ray pattern of single crystal BILT.
Figure 3. DFT optimized structure of title compound.
Bull. Mater. Sci. (2021) 44:38 Page 3 of 16 38
Table 1. Optimized structure parameters: bond angles.