Growth and characterization of 2-amino-4-picolinium toluene sulfonate single crystal

Article abstract of DOI:10.1016/j.saa.2011.08.003

2-Amino-4-picolinium toluene sulfonate (2A4PTS), a new organic material, was synthesized and grown as single crystals in room temperature by slow evaporation solution growth technique using water as solvent. The crystal structure of 2A4PTS has been determ

Full text of DOI:10.1016/j.saa.2011.08.003

Spectrochimica Acta Part A 82 (2011) 521–526
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Growth and characterization of 2-amino-4-picolinium toluene sulfonate
single crystal
G. Anandha Babu∗, P. Ramasamy
Centre for Crystal Growth, SSN College of Engineering, SSN Nagar, Kalavakkam 603 110, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
2-Amino-4-picolinium toluene sulfonate (2A4PTS), a new organic material, was synthesized and grown
as single crystals in room temperature by slow evaporation solution growth technique using water as sol-
vent. The crystal structure of 2A4PTS has been determined using single crystal X-ray diffraction studies.
2A4PTS belongs to monoclinic crystal system. The molecular arrangements in the crystal were studied.
The structural perfection of the grown crystals has been analysed by high-resolution X-ray diffraction
(HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectral studies have been
performed to identify the functional groups. The optical transmittance window and the lower cutoff
wavelength of the 2A4PTS have been identified by UV–Vis–NIR studies. The nonlinear optical properties
have been investigated by Z-scan method. The nonlinear refractive index and linear absorption coeffi-
cient of the 2A4PTS are found to be in the order of 10−8 cm2/W and 10−4 cm/W, respectively. The laser
induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. Thermal
analysis carried out on the compound reveals that 2A4PTS is stable up to 133 ◦C. The microhardness test
was carried out and the load dependent hardness was measured.
Received 11 June 2011
Received in revised form 25 July 2011
Accepted 7 August 2011
PACS:
61.66.Hq
42.70.Nq
81.10.Dn
61.10.−i
Keywords:
Optical materials
Organic compounds
Crystal growth
Crystal structure
Defects
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
In this paper, we report on synthesis, crystal growth, single crys-
tal structure determination by single-crystal X-ray diffraction, high
The origins of the nonlinear processes are well understood
and the progress now depends on the development of materi-
als technology compatible with the various device embodiments
[1]. Compared to the extensive amount of research conducted on
the synthesis and characterization of new molecular structures for
second-order nonlinear optical applications, the study of third-
order nonlinear processes on molecular materials has received
relatively limited attention. Recently, the scope for the synthesis
and characterization of third-order materials has expanded consid-
erably. The impetus for this increased activity has been a quest for
fundamental understanding of the structure property relationship
and the strong technological interest in all optical signal process-
ing provided by the third-order processes [2]. Development of
novel molecular and crystal design techniques for assembling such
materials is of great current interest [3,4]. The desirable proper-
ties of 2A4PTS which include stable physio-chemical properties and
absence of any phase transition highlight this material as a potential
candidate for nonlinear optical applications, and thereby attracted
our interests towards a thorough investigation of this compound.
resolution X-ray diffraction, optical, thermal, laser-induced sur-
face damage threshold, NLO properties by Z-scan technique and
mechanical properties of 2A4PTS presented for the first time.
2. Material synthesis and single crystal growth
The 2A4PTS salt was obtained by dissolving 2 Amino 4-Picoline
and p-Toluene sulfonic acid in methanol at room temperature in the
molar ratio 1:1. The reaction scheme and the chemical structures
are illustrated in Fig. 1. The salt was purified by the recrystalliza-
tion process. The single crystals were grown from aqueous solution.
Single crystal of size 15 × 8 × 5 mm3 has been obtained after a typ-
ical period of 90 days. Grown single crystals of 2A4PTS are shown
in Fig. 2. As highlighted by the chemical bonding theory of single
crystal growth, the growth shape of 2A4PTS single crystals is closely
correlated to their crystallographic characteristics [5–10].
3. Sample characterization
3.1. Single-crystal X-ray diffraction study
∗
The crystal structure was determined from the single crystal
X-ray diffraction data obtained with a three-circle Enraf Nonius
Corresponding author. Tel.: +91 4427475166; fax: +91 4427475166.
E-mail address: anandcgc@gmail.com (G. Anandha Babu).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.08.003

522
G. Anandha Babu, P. Ramasamy / Spectrochimica Acta Part A 82 (2011) 521–526
SO3
CH3
SO3H
CH3
CH3
N
+
N
H
NH2
NH2
CH3
Fig. 1. Reaction of 2 Amino 4-Picoline with p-Toluene sulfonic acid.
Fig. 4. Packing diagram of 2A4PTS.
file has been deposited by us in the Cambridge structure database
(CCDC 781115).
2A4PTS crystallizes in the centrosymmetri−c space group P21/c
+
Fig. 2. Grown single crystals of 2A4PTS.
with four formula units of C6H7N2 ·C7H7SO3 in the unit cell. A
formula unit consists of one 2-amino-4-picolinium cation and one
toluene sulfonate anion as shown in Fig. 3.
˚
CAD4-MV31 (graphite-monochromated, CuK␣ = 1.54180 A). The
crystal structure was solved by a direct method with the SIR97 [11]
program and refined by full matrix least-squares with SHELX97 [12]
program to an R value of 0.0544. The structure was solved by direct
methods and full-matrix least-squares refinements were per-
formed on F2 using all unique reflections. All nonhydrogen atoms
were refined with anisotropic atomic displacement parameters
and the hydrogen atoms were refined with isotropic displacement
factors. Drawings of the molecular structure (Fig. 3) and the pack-
ing diagram (Fig. 4) were obtained using PLATON. Further crystal
data, experimental conditions and structural refinement param-
eters are presented in Table 1. The crystallographic information
The protonated N1 atom has lead to a slight increase in the
C5–N1–C1 angle to 122.2(2)◦. The bond lengths and angles are nor-
mal [13]. In the crystal packing (Fig. 4), the protonated N1 atom
and 2-amino group (N2) are hydrogen-bonded to the sulfonate oxy-
gen atoms (O2, O3 and O4) via a pair of N–H· · ·O hydrogen bonds
and protonated N1 atom is hydrogen bonded sulfonate sulfur atom
via a N–H· · ·S hydrogen bond. The crystal structure is stabilized by
intramolecular hydrogen bonds to form a three-dimensional net-
work. It should be mentioned that hydrogen bonds are a kind of
NLO functional bonds in the crystallographic frame, which was first
highlighted by Xue et al. [14–17].
Fig. 3. ORTEP diagram of 2A4PTS.

G. Anandha Babu, P. Ramasamy / Spectrochimica Acta Part A 82 (2011) 521–526
523
Table 1
Crystal data and structure refinement of 2A4PTS.
Empirical f ormula
Formula weight
Temperature
C13H16N2O3S
280.34
293(2) K
˚
Wavelength
1.54180 A
Crystal system
Space group
Unit cell dimensions
Monoclinic
P21/c
◦
˚
a = 7.2442(8) A, ˛ = 90
◦
˚
˚
b = 13.359(3) A, ˇ = 98.152(13)
◦
c = 14.655(3) A, ꢀ = 90
3
˚
Volume
1404.0(4) A
Z
4
Calculated density
Absorption coefficient
F (0 0 0)
Crystal size
Theta range for data collection
Limiting indices
Reflections collected/unique
Completeness to theta
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
1.326 g/cm3
2.110 mm−1
592
0.30 × 0.20 × 0.20 mm3
4.50–65.14◦
−8 ≤ h ≤ 8, 0 ≤ k ≤ 15, −17 ≤ l ≤ 0
2499/2399 [R(int) = 0.0365]
65.14, 99.8%
Fig. 5. High-resolution X-ray diffraction curve recorded for a typical 2A4PTS single
crystal specimen using (2 0 0) diffracting planes.
Psi-scan
0.7882 and 0.6511
Full-matrix least-squares on F2
2399/0/190
is somewhat more than that expected from the plane wave theory
of dynamical X-ray diffraction [21], for an ideally perfect crystal but
close to that expected for nearly perfect real life crystals. This much
broadness with good scattered intensity along both the wings of the
DC indicates that the crystal contains both vacancy and interstitial
type of defects [22]. More details may be obtained from the study of
high-resolution diffuse X-ray scattering measurements [23], which
is not the main focus of the present investigation.
1.084
R1 = 0.0514, wR2 = 0.1365
R1 = 0.0613, wR2 = 0.1446
0.0206(15)
0.384 and −0.307 e/A
3
˚
3.2. Multicrystal X-ray diffractometry
The crystalline perfection of the grown single crystals was
characterized by HRXRD by employing multicrystal X-ray
3.3. Fourier transform spectral analysis
a
diffractometer developed at NPL [18]. The well-collimated and
monochromated MoK␣1 beam obtained from the three monochro-
mator Si crystals set in dispersive (+, −, −) configuration has been
used as the exploring X-ray beam. The specimen crystal is aligned
in the (+, −, −, +) configuration. Due to dispersive configuration,
though the lattice constant of the monochromator crystal(s) and
the specimen are different, the unwanted dispersion broadening
in the diffraction curve (DC) of the specimen crystal is insignifi-
cant. The specimen can be rotated about the vertical axis, which
is perpendicular to the plane of diffraction, with minimum angu-
lar interval of 0.4ꢀꢀ. The rocking or diffraction curves were recorded
by changing the glancing angle (angle between the incident X-ray
beam and the surface of the specimen) around the Bragg diffraction
peak position ꢁB (taken as zero for the sake of convenience) start-
ing from a suitable arbitrary glancing angle and ending at a glancing
angle after the peak so that all the meaningful scattered intensities
on both sides of the peak are included in the diffraction curve. The
DC was recorded by the so-called ω scan wherein the detector was
kept at the same angular position 2ꢁB with wide opening for its
slit. This arrangement is very appropriate to record the short range
order scattering caused by the defects or by the scattering from
local Bragg diffractions from agglomerated point defects or due to
low angle and very low angle structural grain boundaries [19].
Before recording the diffraction curve to remove the non-
crystallized solute atoms which remained on the surface of the
crystal and the possible layers which may sometimes form on the
surfaces on crystals grown by solution methods [20] and also to
ensure the surface planarity, the specimen was first lapped and
chemically etched in a non preferential enchant of water and ace-
tone mixture in 1:2 volume ratio.
The FTIR spectrum was recorded using Perkin Elmer FTIR spec-
trophotometer (KBr pellet technique) in the range 4000–450 cm−1
.
The recorded FTIR spectrum of 2A4PTS is shown in Fig. 6. The
aromatic C N stretching vibration appears as a sharp band at
1677 cm−1. As expected the asymmetric deformation mode of
sulfonyl groups appears at 1385 cm−1 and the corresponding sym-
metric mode exhibits a band at 1176 cm−1. The aromatic C
C
stretching vibration brings forth a sharp band at 1486 cm−1. The
aromatic C–H in plane bending modes are at 1033 cm−1 and
1008 cm−1. The observed wave numbers and the assignments made
from the recorded spectra for 2A4PTS crystal are given in Table 2.
3.4. UV–visible spectral analysis
The UV–Vis–NIR transmission spectrum of the as grown 2A4PTS
crystal has been recorded using a Perkin Elmer UV–Vis–NIR spec-
trophotometer in the wavelength range 200–1100 nm and is shown
100
80
464
60
40
563
20
683
Fig. 5 shows the high-resolution diffraction curve (DC) recorded
for a typical 2A4PTS crystal grown by SEST method using (2 0 0)
diffracting planes. As seen in Fig. 5, the DC contains a single peak and
indicates that the specimen is free from structural grain boundaries.
The FWHM (full width at half maximum) of the curve is 34ꢀꢀ which
0
4000
3500
3000
2500
2000
1500
1000
500
wavenumber (cm-1)
Fig. 6. FTIR spectrum of 2A4PTS.

524
G. Anandha Babu, P. Ramasamy / Spectrochimica Acta Part A 82 (2011) 521–526
Table 2
Spectral data and their assignments for 2A4PTS.
FTIR (cm−1
)
Assignments
3274
3131
2924
2777
1677
1486
1385
1176
1637
1033
1008
812
ꢂas(NH2)
ꢂ(NH+)
ꢂ(C–H)
ꢂ(C–H) of CH3 group
ꢂ(C N)
ꢂ(C C)
ꢂas(SO3)
ꢂs(SO3)
ıin plane(N–H)
ıin plane(C–H)
ıin plane(C–H)
ıout plane(C–H)
ıout plane(N–H)
683
in Fig. 7. From the spectrum, it is noted that the UV transparency
cutoff occurs at 350 nm, and there is no remarkable absorption in
the entire region of the spectra. The transmittance of 2A4PTS is
30–40%, which is good enough for the generation of higher har-
monic light using infrared lasers through NLO phenomena. Since
the crystal is transparent in the region 350–1100 nm, one can use
2A4PTS as third harmonic generator of Nd:YAG (ꢃ = 1064 nm) laser
to produce ∼354.6 nm.
Fig. 8. TG–DTA curves of 2A4PTS.
length 80 mm. The sample is placed 1 cm away from the focus. The
onset of damage can be determined by visual damage and audible
cracking.
The utility of NLO crystal depends not only on the linear
and nonlinear optical properties but also largely on its ability
to withstand high power lasers. The bulk materials appear more
damage-resistant than the surfaces. The damage threshold depends
on a great number of laser parameters such as wavelength, energy,
pulse duration, transverse and longitudinal mode structure, beam
size, location of beam etc. The diameter of the focused spot is cal-
culated to be 1.08 mm using knife edge method. Single shot and
multiple shot (150 pulses) surface laser damage thresholds are
determined to be 0.55 GW/cm2 and 0.36 GW/cm2, respectively, at
532 nm laser radiation.
The damage pattern of 2A4PTS shows tiny circular blobs sur-
rounding the core of the damage. Such circular blobs are generally
seen in crystals where the damage is mainly due to thermal effects
resulting in melting and solidification or decomposition of the
material. It is most likely that in the present case damage occurs due
to decomposition of the crystal. Hence, in 2A4PTS we can expect the
damage to be of thermal origin. However, one cannot rule out other
mechanisms being operative simultaneously, as the damage mech-
anism is quite complex and depends on the nature of the material
and various experimental parameters.
3.5. Thermal analysis
Thermal analysis for 2A4PTS was taken using SDT Q 600 sys-
tem. The TG results reveal no weight loss below 200 ◦C and hence
the crystal is found to be free from physically absorbed lattice-
entrapped water. There is a major weight loss close to 250 ◦C
resulting in the decomposition of the compounds of the crystal. The
TG/DTA curves of 2A4PTS are shown in Fig. 8. Fig. 8 shows that there
is a sharp endothermic reaction with the maximum temperature at
133 ◦C which is assigned to the melting of the crystal.
3.6. Laser damage threshold measurement
A Q-switched Nd:YAG Innolas laser of pulse width 7 ns and 10 Hz
repetition rate operating in TEM00 mode is used as the source. The
energy per pulse of 532 nm laser radiation attenuated using appro-
priate neutral density filters is measured using an energy meter
(Coherent EPM 200) which is externally triggered by the Nd:YAG
laser. For both single and multiple shot experiments, the sample is
mounted on an X–Y translator which facilitates in bringing differ-
ent areas of the sample for exposure precisely. For surface damage,
the sample is placed at the focus of a plano-convex lens of focal
3.7. Z-scan measurements
The third-order nonlinear refractive index n2 and the nonlin-
ear absorption coefficient ˇ of aqueous solution of the 2A4PTS
was evaluated by the Z-scan technique. A diode-pumped Nd:YAG
(Coherent Compass TM 215M-50) laser of wavelength 532 nm was
used as source. The Gaussian profile laser beam was focused on a
1 mm cuvette containing the 1 mM concentration solution by lens
of focal length 3.5 cm to produce a beam waist ωo of 15.84 ␮m.
The sample is translated from −10 mm to 10 mm with Z = 0 at the
focus of the lens in order to vary the incident intensity falling on
the sample and the corresponding output transmittance was mea-
sured. The transmission of the beam through an aperture placed in
the far field was measured using a photo detector fed to the dig-
ital power meter. For the open aperture Z-scan, a lens to collect
the entire laser beam transmitted through the sample replaced the
aperture.
40
30
20
10
0
|ꢄϕo|, the on-axis phase shift at the focus is related to the dif-
200
400
600
800
1000
1200
ference in the peak and valley transmission, |Tp–v|, as
wavelength (nm)
Tp–v = 0.406(1 − S)0.25|ꢄϕo|
(1)
Fig. 7. UV–Vis spectrum of 2A4PTS.

G. Anandha Babu, P. Ramasamy / Spectrochimica Acta Part A 82 (2011) 521–526
525
Table 3
Nonlinear optical parameters.
Closed
1.4
1.2
1.0
0.8
0.6
0.4
0.2
(a)
Sample
2A4PTS
n2 × 10−8 cm2/W
ˇ × 10−4 cm/W
−7.7
ꢆ(3) × 10−6 esu
−6.8
3.38
normalized transmittance versus sample position, for the cases of
closed and open aperture, allow determination of the nonlinear
refractive index, n2, and the saturation absorption coefficient, ˇ.
Here, since the closed-aperture transmittance is affected by the
nonlinear refraction and absorption, the determination of n2 is
less straight forward from the closed-aperture scans. It is neces-
sary to separate the effect of nonlinear refraction from that of the
nonlinear absorption. A method to obtain purely effective n2 is
to divide the closed-aperture transmittance by the corresponding
open-aperture scans. The ratio of Fig. 9(a) and (b) scans is shown in
Fig. 9(c). The data obtained in this way reflects purely the effects of
nonlinear refraction.
-10
-5
0
5
10
z (mm)
Open
1.030
1.025
1.020
1.015
1.010
1.005
1.000
(b)
The nonlinear absorption coefficient ˇ can be estimated from
the open-aperture Z-scan data.
√
2
2ꢄT
ˇ =
(3)
IoLeff
The nonlinear refraction index coefficient, n2, the nonlinear absorp-
tion coefficient, ˇ, and susceptibility, ꢆ(3), for solution of 2A4PTS
in water using the Z-scan technique with 532 nm diode pumped
Nd:YAG laser is given in Table 3. The Z-scan measurements indi-
cate that the 2A4PTS exhibits negative nonlinear optical properties.
It is shown that the nonlinear absorption can be attributed to a sat-
uration absorption process, while the nonlinear refraction leads to
self-defocusing in the compound.
-10
-5
0
5
10
Z (mm)
3.8. Mechanical hardness
Closed/Open
1.4
1.2
1.0
0.8
0.6
0.4
0.2
The structure and composition of the crystalline solids are invi-
olably related to the mechanical hardness [24–26]. The Vickers
hardness is one of the important deciding factors in selecting the
processing (cutting, grinding and polishing) steps of bulk crystal
in the fabrication of devices based on the crystals. It is, therefore,
important to study the mechanical properties of organic NLO crys-
tals.
Vickers microhardness measurement studies were also carried
out using a MITUTOYO model HM112 hardness tester. Microhard-
ness testing is one of the best methods of understanding the
mechanical properties of materials such as hardness number, crack
length, fracture toughness, brittle index, and elastic stiffness con-
stant. Hardness of a material is a measure of resistance it offers to
local deformation [27]. The hardness measurements were made on
(C)
-10
-5
0
5
10
Z(mm)
40
35
30
25
Fig. 9. (a) Closed aperture scan; (b) open-aperture scan; and (c) the division of (a)
by (b).
where S = 1 − exp(−2ro2/ωo2) is the aperture linear transmittance
with ro denoting the aperture radius and ωo denoting the beam
radius at the aperture in the linear regime. Then nonlinear refrac-
tive index is given by
ꢄϕoꢃ
n2
=
(2)
2ꢅIoLeff
where ꢃ is the laser wavelength, Io is the intensity of the laser
beam at focus Z = 0, Leff = [1 − exp(−˛L)/˛] is the effective thick-
ness of the sample, ˛ is the linear absorption coefficient and L is
the thickness of the sample. Generally the measurements of the
0
20
40
60
80
100
load, P (gm)
Fig. 10. Mechanical behavior of 2A4PTS: load versus hardness number.

526
G. Anandha Babu, P. Ramasamy / Spectrochimica Acta Part A 82 (2011) 521–526
2A4PTS crystal. Loads ranging from 5 to 100 g were used for mak-
ing indentations, keeping the time of indentation constant at 10 s
for all the cases. The diagonal lengths of the indentation mark and
crack length were measured, using the micrometer eyepiece. The
microhardness value was calculated using
Acknowledgment
We thank Dr. G. Bhagavannarayana, National Physical Labora-
tory, New Delhi for HRXRD studies.
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1.8544P
Hv
=
kg/mm2
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Single crystals of 2A4PTS were grown using solution growth
technique. The crystal structure of 2A4PTS was determined
by single crystal X-ray diffraction analysis. The high resolu-
tion X-ray diffraction curve (DC) measurements substantiate the
good quality of the crystals. The functional group was con-
firmed by FTIR. Optical transmittance window and the lower
cutoff wavelength have been identified through UV–Vis–NIR
spectrum. The thermal behavior of the grown crystals was
studied using TG-DTA. Single shot and multiple shot (50
pulses) surface laser damage thresholds are determined to be
0.55 GW/cm2 and 0.36 GW/cm2 at 532 nm laser radiation, respec-
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