Journal of Crystallization Process and Technology, 2013, 3, 123-129
http://dx.doi.org/10.4236/jcpt.2013.34020 Published Online October 2013 (http://www.scirp.org/journal/jcpt)
123
Synthesis, Growth, Crystal Structure and Characterization
of the o-Toluidinium Picrate
Kandasamy Mohana Priyadarshini1, Angannan Chandramohan1*, Thangarak Uma Devi2
1Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore, India; 2Department of
Physics, Government Arts College for Women, Pudukottai, India.
Received July 23rd, 2013; revised July August 23rd, 2013; accepted August 30th, 2013
Copyright © 2013 Kandasamy Mohana Priyadarshini et al. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
A new organic charge transfer molecular complex salt of o-toluidinium picrate (OTP) was synthesised and the single
crystals were grown by the slow solvent evaporation solution growth technique using methanol as a solvent at room
temperature. Formation of the new crystal has been confirmed by single crystal X-ray diffraction (XRD) and NMR
spectroscopic techniques. The crystal structure determined by single crystal X-ray diffraction indicates that both the
cation and the anion are interlinked to each other by three types of intermolecular hydrogen bonds, namely
N(4)-H(4A)···O(7), N(4)-H(4B)···O(5) and N(4)-H(4C)···O(7). The title compound (OTP) crystallizes in monoclinic
crystal system with the centrosymmetric space group P21/c. Fourier transform infrared (FT IR) spectral analysis was
used to confirm the presence of various functional groups in the grown crystal. The optical properties were analyzed by
the UV-Vis-NIR and fluorescence emission studies.
Keywords: Single Crystal; Organic Molecules; Solution Growth; X-Ray Diffraction; Characterization; Nonlinear
Optical
1. Introduction
The organic materials with aromatic ring, which are of
great interest for second and third-order nonlinear optical
applications due to their high nonlinearity, high optical
damage threshold and their ultrafast, almost purely elec-
tronic response. Based on the concepts of the molecular
and crystal engineering, the organic molecules offer
many possibilities to tailoring the substances with desired
properties through optimization of the microscopic hy-
perpolarizabilities and the incorporation of the molecules
in a crystalline lattice [1-4]. Mulliken suggested that the
charge transfer interactions from two aromatic molecules
can arise from the transfer of an electron from Lewis
base to Lewis acid and these complexes have attracted
great attention for nonlinear optical materials. Generally,
proton transfer interactions between electron donor and
electron acceptor molecules absorb radiation in the visi-
ble region leading to the formation of intensely colored
charge transfer complexes [5-10]. Picric acid forms crys-
talline picrates of various organic molecules through io-
nic and hydrogen bonding and π-π interactions and the
presence of phenolic OH in the picric acid favors the
formation of the salts with various organic bases [11].
The formation of charge transfer complex depending on
the nature of the donor-acceptor system and the orientation
of anionic and cationic species facilitates the formation
of expected N-H·····O hydrogen bonds between amino
hydrogen and phenolic oxygen [12]. It has been reported
that intramolecular hydrogen bonding interactions are
absent in most of the picrate salts [13] and picric acid
derivatives are interesting candidates, as the presence of
phenolic OH and electron withdrawing nitro groups fa-
vors the formation of salts with various organic bases
such as N,N-dimethylanilinium picrate [11], 3-Methyl
aniliniumpicrate [14], 2-Chloroanilinium picrate [15],
Anilinium picrate [16], p-toluidinium picrate [13], 8-
hydroxyquinolinium picrate [17], 1,3-Dimethylurea di-
methyl ammonium picrate [18], N,N-Dimethyl anilinium
picrate [19] have already been reported. The title salt
crystallizes in the monoclinic crystal system with cen-
trosymmetric space group P21/c, an analogue of p-Tolu-
idinium picrate. In the present work, we report the syn-
thesis, crystal growth, structural, spectral and optical stu-
dies of o-toluidinium picrate single crystal.
*Corresponding author.

Synthesis, Growth, Crystal Structure and Characterization of the o-Toluidinium Picrate
124
2. Experimental Procedure
2.1. Material Synthesis
Analar grade o-toluidine (1.07 g, 0.01 mol) and Picric
acid (2.29 g, 0.01 mol) were dissolved in pure methanol
separately in equimolar ratio and the two solutions were
mixed together. The solution was stirred well for about
one hour, when a yellow colored crystalline precipitate of
the charge transfer complex salt of o-toluidinium picrate
was obtained as a result of the acid-base reaction be-
tween picric acid and o-toluidine. The precipitate was
filtered off and recrystallised many times in methanol to
enhance the degree of purity of the product. The reaction
involved is illustrated in the Scheme 1.
2.2. Growth and Characterization of OTP Single
Crystals
A saturated methanolic solution of OTP was prepared,
stirred well for about five hours and filtered through a
quantitative whatmann 41 grade filter paper to eliminate
the unwanted suspended impurities present in the solu-
tion. The clear filtrate so obtained was kept aside unper-
turbed in a dust-free room for the growth of single crys-
tals. Well-defined, yellow colored crystals were collected
at the end of the 8th day. The photograph of as-grown
crystals of OTP is shown in Figure 1. The grown OTP
crystal was subjected to various characterization tech-
niques like 1H and 13C NMR spectral analyses, single
crystal X-ray diffraction studies, Fourier transform infra-
red (FT IR), UV-Vis-NIR spectral analysis and Fluores-
cence emission studies. The detailed results are presented
in the following sections.
CH
3
NH
2
HO
O
2
N
O
2
N
NO
2
CH
3
NH
3
O
O
2
N
O
2
N
NO
2
o-Toluidine
Picric acido-To
l
u
i
d
i
n
i
um
p
i
crate
Scheme 1. Reaction mechanism of o-toluidinium picrate.
Figure 1. As-grown single crystals of OTP.
3. Results and Discussion
3.1. Nuclear Magnetic Resonance Studies
The 1H and 13C NMR spectra were recorded using the
BRUKER AVANCE III 500 MHz (AV 500) spectrome-
ter with TMS as the internal reference standard and
DMSO as the solvent.
The 1H NMR spectrum of the title crystal (Figure 2)
shows four proton signals indicating the presence of four
different proton environments in the OTP crystal. The
broad hump appearing at δ 9.66 ppm is assigned to the
highly deshielded +NH3 protons of o-toluidinium moiety.
The intense singlet signal appearing at δ 8.61 ppm has
been assigned to C3 and C5 aromatic protons of the same
kind in picrate moiety. The complex multiplet signal
centered at δ 7.32 ppm is arising due to the overlap be-
tween two triplets attributed to C4 and C5 aromatic pro-
tons and two doublets due to C3 and C6 aromatic protons
of o-toluidinium moiety in the salt. The triplet and dou-
blet signals coalesce into a multiplet due to the closeness
of the coupling constant values. The singlet signal at δ
2.32 ppm has been assigned to the methyl protons of o-
toluidinium moiety.
The 13C NMR spectrum of OTP is depicted in Figure
3. The appearance of eleven distinct peaks in the spec-
trum establishes the molecular structure of the OTP
complex salt. The weak carbon signal at δ 161.30 ppm
owes to the ipso carbon (C1) of picrate moiety. The C2
and C6 aromatic carbon atoms of the same kind in pi-
crate moiety appear at δ 142.28 ppm. The highly in-
tense peak at δ 125.70 ppm is due to C3 and C5 aromatic
carbon atoms of the same kind in picrate moiety. The
weak signal at δ 124.89 ppm is assigned to C4 carbon
atom of the same moiety in the complex salt. The peaks
appearing at δ 132.03, 131.83, 131.12, 128.66, 127.63
and 123.59 ppm have been assigned respectively to C2,
C3, C4, C5, C6 and C1 carbon atoms in o-toluidinium
moiety in the complex. The signal at δ 17.23 ppm is at-
tributed to the methyl carbon of o-toluidinium moiety.
Figure 2. 1H NMR spectrum of OTP.

Synthesis, Growth, Crystal Structure and Characterization of the o-Toluidinium Picrate
125
Figure 3. 13C NMR spectrum of OTP.
3.2. FT-IR Spectroscopy
The characteristic vibrational frequencies of the func-
tional groups of OTP are identified from the fourier
transform infrared (FT-IR) spectrum recorded in the
range of 4000 - 400 cm−1 employing Perkin-Elmer FT-IR
spectrometer by using the KBr pellet technique. The
formation of charge transfer complex during the acid-
base interaction of o-toluidine with picric acid is strongly
evidenced through the realization of important bands of
donor and acceptor in the resultant spectrum of the com-
plex salt (Figure 4). The absorption at 3194 cm−1 is due
to the +N-H stretching vibration. The absorption band at
3060 cm−1 corresponds to aromatic C-H asymmetric
stretching vibration. The broad absorption bands in the
region 2940 to 2813 cm−1 are due to the overlapping of
C-H asymmetric and symmetric stretching vibration of
methyl group and aromatic C-H symmetric stretching
vibration. The absorptions at 1535 and 1359 cm−1 con-
firm the asymmetric and symmetric stretching vibrations
of NO2 group respectively. The C-O stretching vibration
is observed at 1192 cm−1. The band at 836 cm−1 is due to
C-N stretching vibration. The presence of C=C stretch-
ing vibration of aromatic ring is revealed from the ab-
sorption bands at 1606, 1570 and 1479 cm−1. The as-
signment is in very close agreement with data of the
complex salts reported already [7-9].
3.3. Single Crystal X-Ray Diffraction Studies
Single crystal XRD analysis for the grown o-toluidi-
nium picrate has been carried out to identify the unit
cell parameters and the crystal structure using “ENRAF
(BRUKER) NONIUS CAD4” diffractometer with graph-
ite monochromated MoKα radiation (λ = 0.71073 Å).
The structure was solved by direct methods procedure as
implemented in SHELXS 97 [20] program. Cell refine-
ment and data reduction were carried out using SAINT
program. All the hydrogen atoms were fixed geometri-
cally and allowed to ride on their parent atoms. All
non-hydrogen atoms were refined using anisotropic dis-
placement parameters.
The crystal structure analyses of OTP reveals that OTP
crystallized in a monoclinic crystal structure with cen-
trosymmetric space group P21/c, and the unit cell pa-
rameters are a = 11.6475(2) Å, b = 16.4763(5) Å, c =
7.5702(4) Å. Table 1 summarizes the crystal data, inten-
sity data collection and refinement details for the OTP
single crystals. The selected bond lengths and bond an-
gles of OTP charge transfer complex salt are given in
Tables 2 and 3 respectively. The protonation on the N1
site of the cation is confirmed from C-N bond distances
and C-N-C bond angles. All the bond distances and bond
angles of the two molecules in the asymmetric unit are
agreed with each other. The crystal structure of OTP
consists one molecule each of o-toluidinium cation and
picrate anion. The ORTEP of the charge transfer com-
plex OTP is clearly shown in the Figure 5 and the atom
numbering scheme adopted. A well-defined yellow col-
our single crystal of OTP with dimension 0.30 × 0.20 ×
0.20 mm was selected for diffraction analysis. A total of
12528 reflections (2541 Unique, R(int) = 0.0239) were
collected by using ω/2θ scan mode at 293(2) K in the
range of 2.15˚ < θ < 25˚ with the index ranges −13 <= h
= 13, −19 <= k <= 19, −7 <= 1 <= 9. The refinement
converged to final R-factor of 0.04%. The packing dia-
gram (Figure 6) indicates the existence of intermolecular
hydrogen bonds in the three dimensional network be-
tween the constituent molecules. The structure is based
on asymmetric part of o-Toluidinium picrate which con-
tains 2-methyl anilinium cation and picrate anion con-
nected by three intermolecular N-H····O hydrogen bonds
with a donor-acceptor distance of 2.7697(19), 2.853(2)
and 2.762(2) Å. The corresponding data for the H-bonds
are listed in Table 4. In the charge transfer complex of
OTP, the carbon skeleton of the anionic picrate species
Figure 4. FT-IR spectrum of OTP.

Synthesis, Growth, Crystal Structure and Characterization of the o-Toluidinium Picrate
126
Table 1. Crystallographic data for OTP.
Empirical formula C13H12N4O7
Formula weight 336.27
Temperature 293(2) k
Wavelength 0.71073 Å
Crystal system, space group Monoclinic, P21/c
Unit cell dimensions
a = 11.6475(2) Å, α = 90˚ b =
16.4763(5) Å, β = 94.1980(10)˚
c = 7.5702(4) Å, γ = 90˚
Volume 1448.88(9) Å3
Z, Calculated density 4, 1.542 Mg/m3
Absorption coefficient 0.128 mm−1
F(000) 696
Crystal size 0.30 × 0.20 × 0.20 mm
Theta range for data collection 2.15 to 25.00 deg
Limiting indices −13 <= h <= 13, −19 <= k <= 19,
−7 <= 1 <= 9
Reflections collected/unique 12528/2541 [R(int) = 0.0239]
Completeness to theta = 25.00 99.9%
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.9924 and 0.9245
Refinement method Full-matrix least-squares on F2
Data/restraints/parameters 2541/0/220
Goodness-of-fit on F2 1.046
Final R indices [I > 2 sigma(I)] R1 = 0.0402, wR2 = 0.1084
R indices (all data) R1 = 0.0468, wR2 = 0.1152
Extinction coefficient 0.0042(11)
Largest diff. peak and hole 0.382 and −0.264 e.Å−3
Figure 5. ORTEP diagram of OTP.
Table 2. Selected bond lengths in OTP (Å).
C(1)-C(6) 1.374(2)
C(1)-C(2) 1.432(2)
C(1)-N(1) 1.461(2)
C(2)-O(7) 1.270(2)
C(2)-C(3) 1.429(2)
C(3)-C(4) 1.365(2)
C(3)-N(2) 1.462(2)
C(4)-C(5) 1.386(3)
C(5)-C(6) 1.380(3)
C(5)-N(3) 1.447(2)
C(7)-C(12) 1.380(2)
C(7)-C(8) 1.386(2)
C(7)-N(4) 1.470(2)
C(8)-C(9) 1.391(3)
C(8)-C(13) 1.503(3)
C(9)-C(10) 1.376(3)
C(10)-C(11) 1.375(3)
C(11)-C(12) 1.380(3)
C(13)-H(13A) 0.9600
N(1)-O(1) 1.216(2)
N(1)-O(2) 1.221(2)
N(2)-O(4) 1.209(2)
N(2)-O(3) 1.213(2)
N(3)-O(6) 1.215(2)
N(3)-O(5) 1.228(2)
N(4)-H(4A) 0.8900
Figure 6. Packing arrangement of molecules showing in-
termolecular N-H···O hydrogen bonding interactions and
π-π interactions viewed down in the c-axis.

Synthesis, Growth, Crystal Structure and Characterization of the o-Toluidinium Picrate
127
Table 3. Selected bond angles in OTP (˚).
C(6)-C(1)-C(2) 124.17(16)
C(6)-C(1)-N(1) 116.84(16)
C(2)-C(1)-N(1) 118.88(15)
O(7)-C(2)-C(3) 122.26(15)
O(7)-C(2)-C(1) 125.48(16)
C(3)-C(2)-C(1) 112.14(14)
C(4)-C(3)-C(2) 125.28(15)
C(4)-C(3)-N(2) 117.71(15)
C(2)-C(3)-N(2) 116.99(14)
C(3)-C(4)-C(5) 118.03(16)
C(6)-C(5)-C(4) 121.50(16)
C(6)-C(5)-N(3) 119.09(16)
C(4)-C(5)-N(3) 119.37(16)
C(1)-C(6)-C(5) 118.77(16)
C(12)-C(7)-C(8) 122.89(16)
C(12)-C(7)-N(4) 118.12(15)
C(8)-C(7)-N(4) 118.98(15)
C(7)-C(8)-C(9) 116.38(17)
C(7)-C(8)-C(13) 122.73(16)
C(9)-C(8)-C(13) 120.89(17)
C(10)-C(9)-C(8) 121.68(18)
C(11)-C(10)-C(9) 120.34(18)
C(10)-C(11)-C(12) 119.74(18)
C(11)-C(12)-C(7) 118.96(17)
C(8)-C(13)-H(13A) 109.5
H(13A)-C(13)-H(13B) 109.5
O(1)-N(1)-O(2) 123.16(18)
O(1)-N(1)-C(1) 118.20(17)
O(2)-N(1)-C(1) 118.65(16)
O(4)-N(2)-O(3) 123.06(17)
O(4)-N(2)-C(3) 118.66(16)
O(3)-N(2)-C(3) 118.24(16)
O(6)-N(3)-O(5) 123.45(16)
O(6)-N(3)-C(5) 119.62(17)
O(5)-N(3)-C(5) 116.93(17)
Table 4. Hydrogen bond parameters in OTP.
D-H···A d(D-H) d(H···A) d(D···A) <(DHA)
N(4)-H(4A)···O(7)#1 0.89 1.89 2.7697(19) 172.0
N(4)-H(4B)···O(5)#2 0.89 2.14 2.853(2) 136.9
N(4)-H(4C)···O(7) 0.89 1.88 2.762(2) 172.5
#1 x, −y + 1/2, z + 1/2; #2 –x + 1, −y, −z + 1.
and cationic o-Toluidinium species is non-planar and is
shown in the torsion angle of N(1)-C(1)-C(2)-C(3),
N(2)-C(3)-C(4)-C(5), N(3)-C(5)-C(6)-C(1), N(4)-C(7)-
C(8)-C(13), C(13)-C(8)-C(9)-C(10), C(10)-C(11)-C(12)-
C(7) which are 179.28(16)˚, −178.89(16)˚, 178.76(16)˚,
−0.8(3)˚, 178.8(2)˚, −0.6(3)˚ respectively.
3.4. UV-Vis-NIR Transmission Studies
The optical transmission spectrum of OTP crystals was
recorded in the region 200 - 1100 nm employing a Shi-
madzu UV-1061 UV-Vis spectrophotometer in solution
using DMSO as the solvent. The recorded transmission
spectrum of OTP is shown in Figure 7. The lower cutoff
wavelength of the OTP crystal was around 488 nm. The
attained percentage of transmittance was around 97 for
OTP complex in the region between 500 and 1100 nm.
Hence, this crystal can be used for the suitable optical
applications due to its wide transparency range in the part
of visible region above 488 nm and in the entire near
infrared region.
3.5. Fluorescence Emission Studies
Fluorescence may be expected generally in molecules
that are aromatic or contain multiple conjugated double
bonds with a high degree of resonance stability [21].The
fluorescence emission spectrum of OTP was recorded
using HORIBA JASCO V-670 FLUOROLOG 3 spectro-
fluorometer. The fluorescence emission spectrum was
recorded in the range from 500 to 900 nm and depicted in
Figure 8. Two peaks at 555 and 607 nm observed in the
emission spectrum indicates that OTP crystal has a green-
orange fluorescence emission.
4. Conclusion
The organic molecular charge transfer complex salt OTP
Figure 7. Optical transmission spectrum of OTP.

Synthesis, Growth, Crystal Structure and Characterization of the o-Toluidinium Picrate
128
Figure 8. Fluorescence emission spectrum of OTP.
was synthesized and the single crystals of it were grown
by slow evaporation solution growth technique using
methanol as the solvent. FT-IR, 1H and 13C NMR spec-
tral techniques confirm the molecular structure of OTP
and also bring forth the evidence for the prevalent charge
transfer activity in the complex salt. The single crystal
XRD study reveals that OTP crystallizes in monoclinic
crystal system with P21/c space group. UV-Vis-NIR
transmittance study shows that the attained percentage of
transmission was around 97% for OTP complex in the
region between 500 - 1100 nm. Hence the title crystal is
a good candidate for suitable optical applications. Fluo-
rescence emission study shows that OTP crystal has a
green-orange fluorescence emission.
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Supplementary Material
CCDC 894814 contains the supplementary crystallo-gra-
phic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/data-request/cif, by
e-mailing data-request @ccdc.cam.ac.uk or by contact-
ing The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB21 EZ, UK; Fax: + 44 1223
336033.