Synthesis, crystal growth, structural and physicochemical studies of novel binary organic complex: 4-chloroaniline-3-hydroxy-4-methoxybenzaldehyde

Article abstract of DOI:10.1016/j.jssc.2012.02.019

The solid-state reaction, which is solvent free and green synthesis, has been adopted to explore the novel compound. The phase diagram of 4-chloroaniline (CA) and 3-hydroxy-4-methoxybenzaldehyde (HMB) system shows the formation of a novel 1:1 molecular complex, and two eutectics on either sides of complex. Thermochemical studies of complex and eutectics have been carried out for various properties such as heat of fusion, entropy of fusion, Jacksons parameters, interfacial energy and excess thermodynamic functions. The formation of molecular complex was also studied by IR, NMR, elemental analysis and UV-Vis absorption spectra. The single crystal of molecular complex was grown and its XRD study confirms the formation of complex and identifies the crystal structure and atomic packing of crystal of complex. Transmission spectra of grown crystal of the complex show 70% transmittance efficiency with cut off wavelength 412 nm. The band gap and refractive index of the crystal of complex have also been studied.

Full text of DOI:10.1016/j.jssc.2012.02.019

Journal of Solid State Chemistry 190 (2012) 226–232
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Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Synthesis, crystal growth, structural and physicochemical
studies of novel binary organic complex:
4-chloroaniline–3-hydroxy-4-methoxybenzaldehyde
K.P. Sharma, R.S.B. Reddi, S. Bhattacharya, R.N. Rai n
Department of Chemistry, Centre of Advance Study, Banaras Hindu University, Varanasi-221005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The solid-state reaction, which is solvent free and green synthesis, has been adopted to explore the
novel compound. The phase diagram of 4-chloroaniline (CA) and 3-hydroxy-4-methoxybenzaldehyde
(HMB) system shows the formation of a novel 1:1 molecular complex, and two eutectics on either sides
of complex. Thermochemical studies of complex and eutectics have been carried out for various
properties such as heat of fusion, entropy of fusion, Jackson’s parameters, interfacial energy and excess
thermodynamic functions. The formation of molecular complex was also studied by IR, NMR, elemental
analysis and UV–Vis absorption spectra. The single crystal of molecular complex was grown and its XRD
study confirms the formation of complex and identifies the crystal structure and atomic packing of
crystal of complex. Transmission spectra of grown crystal of the complex show 70% transmittance
efficiency with cut off wavelength 412 nm. The band gap and refractive index of the crystal of complex
have also been studied.
Received 6 June 2011
Received in revised form
26 January 2012
Accepted 5 February 2012
Available online 17 February 2012
Keywords:
Phase equilibria
Crystal growth
Optical properties
Crystal packing: X-ray diffraction
Band gap
& 2012 Elsevier Inc. All rights reserved.
1. Introduction
However there is no report for synthesis of this complex adopting
solid state reaction, phase diagram, and various other studies
The metallic systems are potential candidates for technological
applications as well as for fundamental studies till the revolution
of organic materials. The limited choices of materials, density
driver convection effect, opacity, high transformation tempera-
ture, difficulties involved in experimentation and cost factors, are
the limiting factors to work with the metallic systems [1,2]. To
cater the needs of current civilization, synthesis and characteriza-
tion of novel materials with special features and of low cost are
demanding. Organic materials are known for their various pro-
mising properties [3,4] and the pure as well as binary organic
materials have been found worthwhile for nonlinear optical,
fluorescent and white light emitting materials [5–8]. Further,
organic systems, their eutectics and addition compounds/com-
plexes are the analogs of metallic systems [9], and initially the
organic systems were considered as model systems to study the
mysteries of various fundamental aspects which affect the prop-
erties of materials. However, the synthesis of novel materials
utilizing solid state reaction has additional merits such as 100%
yield of materials and solvent free synthesis. The synthesis of
complex of 2-methoxy-5-[[(4-chlorophenyl)imino] methyl] phe-
nol (Registry No. 115095-36-8) is reported by other method [10].
which are being mentioned in this article. With view to explore
the concept of phase diagram and solid state reaction, a binary
organic system involving 4-chloroaniline (CA) and 3-hydroxy-4-
methoxybenzaldehyde (HMB) was selected. The solid state reac-
tion was employed [11] to establish the phase diagram and to
synthesis of binary materials. In this communication the phase
diagram study, and the synthesis and physicochemical studies of
addition compound and two eutectics, along with crystallization
behavior of pure and binary materials, are reported. The interac-
tion between CA-HMB molecules, single crystal growth, atomic
packing, optical characterization, band gap and refractive index of
the newly synthesized addition compound are also reported.
However, the other characterizations of crystalline and polycrys-
talline binary addition compound are in progress.
2. Experimental procedure
2.1. Materials and purification
Starting materials, 4-Chloroaniline and 3-hydroxy-4-methoxy-
benzaldehyde were obtained from Sigma Aldrich, Germany. Both
the materials were purified by recrystallization from ethanol. The
melting temperatures of purified CA and HMB were found to be
n Corresponding author. Fax: þ91 542 2307321.
E-mail address: rn_rai@yahoo.co.in (R.N. Rai).
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2012.02.019

K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
227
69.0 and 113.0 1C, respectively. The values of melting temperature
are in agreement with their respective literature values [6,7].
of parent components and its complex were also recorded in
ethanol solution using the same instrument.
2.2. Phase diagram
3. Results and discussions
The phase diagram of CA–HMB system was established in the
form of melting temperature–composition curve [12]. The mix-
tures of two components covering the entire range of composi-
tions were taken in separate test tubes. The mouth of each test
tube was sealed and the melt of mixtures of two components
were homogenized by repeating the process of melting followed
by chilling in ice cooled water for 4 times. The melting points of
the various compositions, thus synthesized, were determined
using Toshniwal melting point apparatus attached with a preci-
sion thermometer of accuracy 70.5 1C.
3.1. Phase diagram
The phase diagram of the CA-HMB system, established in
terms of composition and their respective melting temperatures,
is given in Fig. 1. The melting point of HMB (113.0 1C) decreases
with the addition of CA and attains the minimum temperature
(99.0 1C) at 0.225 mol fraction of CA. This point is known as the
first eutectic point (E1) of the system. Further addition of CA in
HMB the melting point rises and reaches to a maximum melting
temperature (138.5 1C) at point C, where the composition of CA
and HMB are 1:1 M ratio. This composition forming the molecular
complex or addition compound melts congruently, i.e., liquid
has identical composition of the solid. When mole fraction of
CA increases beyond this composition, the melting point again
decreases till the second eutectic (E2). The melting temperature
and mole fraction of CA at E2 are 64.0 1C and 0.920, respectively.
The addition of CA thereafter causes an increase in the melting
point till 69.0 1C, which is the melting point of CA. The finding of
maximum melting temperature, even more than parent compo-
nents, of complex and flat nature of curve suggests the formation
of a stable new entity [14]. This observation also infers that the
complex does not dissociate in molten state. For each eutectic, the
molecular complex behaves as one of the parent component. The
phase diagram study reveals that there are three invariant points,
eutectic-1, complex and eutectic-2, in the HMB-CA system.
2.3. Enthalpy of fusion
The values of heat of fusion of the pure components, the
eutectics and the complex were determined by differential scan-
ning calorimeter (Mettler DSC-4000 system). Indium sample was
used to calibrate the system and the amount of test sample
and heating rate were about 5–7 mg and 10 1C minꢀ1, respec-
tively. The values of enthalpy of fusion are reproducible within
70.01 kJ molꢀ1
.
2.4. Growth kinetics
The solidification behavior of pure components, eutectics and
addition compound were determined by measuring the rate of
movement of solid liquid interface in a thin glass U-tube with
about 150 mm horizontal portion and 5 mm internal diameter.
Molten samples were separately taken in U-tube and placed in a
silicone oil bath. The temperature of oil bath was maintained
using microprocessor temperature controller of accuracy 70.1 1C.
3.2. Growth kinetics
In order to study the crystallization behaviors of the pure
components, eutectics, and the complex, the crystallization rate
(v) are determined at different undercoolings (
the rate of movement of solid-liquid interface in a thin glass
U-tube. The plots between log T and log v for pure compounds
At different undercoolings (DT), a seed crystal of the same
DT) by measuring
composition was added to start nucleation, and the rate of
movement of the solid–liquid interface (v) was measured using
a traveling microscope and a stop watch [12].
D
and binary materials are given in Fig. 2. The graph, for each
material, shows the linear dependence which is in accordance
2.5. Spectral studies
with following equation
n
Infrared spectra of the parent components and the complex
were recorded in the spectral region 400–4000 cmꢀ1 via pelletiz-
ing the materials that was dispersed in KBr using Perkin–Elmer
RX-1, FT-IR spectrophotometer. The 1H and 13C NMR spectra were
measured in JEOL 300 FTNMR using CDCl3 as a solvent. The data
of elemental analysis for complex compound was recorded using
the CHN/Elemental Analyzer (Exeter Analytical, Inc. Model 440,
USA).
v ¼ uðDTÞ
ð1Þ
where u and n are constants depending on the solidification
behavior of the materials. The experimental values of these
constants for pure components, eutectics and addition compound
are given in Table 1. From the values of u, it can be inferred that
the growth velocity of eutectic E1 is less than those of its
components namely HMB and addition compound while that of
E2 lies in between CA and addition compound. In case of E1, the
melting point of addition compound is higher than that of HMB
and hence addition compound nucleates first followed by the
nucleation of HMB and the two phases grow by the alternate
nucleation mechanism. On the other hand in E2 the addition
compound, with higher melting point than CA, nucleates first
followed by nucleation of CA and the two phases grow following
the side by side mechanism [15].
2.6. Single crystal growth and study of atomic packing
The single crystal of the novel complex was grown from the
saturated ethanol solution at room temperature by slow evapora-
tion technique. X-ray diffraction data of single crystal were
collected using the Xcalibur oxford CCD diffractometer. The data
reduction was carried out using Chrysalis Pro software. Structure
solution and refinement were carried out utilizing SHELXS and
SHLEXL-97 [13].
3.3. Thermochemistry
2.7. Optical characterization
3.3.1. Enthalpy of fusion
The experimental values of enthalpy of fusion of the pure
components, the eutectics and the addition compound are given
in Table 2. For the purpose of comparison the heats of fusion of
eutectics are calculated by the mixture law [9] and have tabulated
The optical transmittance of the grown crystal was recorded in
UV–Vis–NIR spectrophotometer [JASCO V-670, Tokyo, Japan] in
the range of 190–950 nm. For comparison, the absorbance spectra

228
K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
Fig. 1. Phase diagram of 4-chloroaniline–3-hydroxy-4-methoxybenzaldehyde system.
Table 1
Values of n and u for pure components and their eutectics, and complex.
Material
u (mm sꢀ1 degꢀ1
CA
n
)
2.67
5.51 ꢂ 10ꢀ4
HMB
0.87
2.76
0.85
1.16
7.76 ꢂ 10ꢀ3
6.54 ꢂ 10ꢀ7
6.29 ꢂ 10ꢀ4
7.53 ꢂ 10ꢀ3
Eutectic-1
Eutectic-2
Complex
suggested [16]; quasi-eutectic for
cules for
highly negative value of enthalpy of mixing in both eutectics
DmixH40, clustering of mole-
mixHo0 and molecular solution for DmixH¼0. The
D
suggests that there is associative interaction in the molecules in
the eutectic melt. The entropy of fusion (DfusS) values, for
different materials, has been calculated by dividing the enthalpy
of fusion by their corresponding absolute melting temperatures
(Table 2). The positive values suggest that the entropy factor
favors the melting process.
3.3.2. Interfacial energy and size of critical radius
During crystallization process, when liquid is cooled below its
melting temperature it does not solidify spontaneously because
under equilibrium condition the melt contains number of clusters
of molecules. As long as the clusters are well below the critical
size, they can not grow to form crystals. The critical size (rn) of
nucleus is related to interfacial energy (
Tfus
fusH ꢁ
where Tfus DfusH and DT are melting temperature, heat of fusion,
s) by [17].
Δ
2
s
rn ¼
ð2Þ
Fig. 2. Linear velocity of crystallization at various degrees of undercooling for pure
D
DT
components, eutectics and complex.
,
and degree of undercooling, respectively. However, the interfacial
energy is computed by using the expression [17]
in the same table. The values of enthalpy of mixing which is the
difference of experimental and the calculated values of the
enthalpy of fusion of the eutectic-1 and eutectic-2 are found to
be ꢀ5.1 and ꢀ1.7 kJ molꢀ1. As such, three types of structures are
C ꢁ
Dfush
s
¼
ð3Þ
1=3
2=3
ðNAÞ ðVm
Þ

K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
229
Table 2
Melting point, heat of fusion, entropy of fusion and interfacial energy of pure. components and their eutectics, and complex.
Materials
Melting temperature
(K)
Heat of fusion
Heat of mixing
Entropy of fusion
Interfacial energy
(kJ mꢀ2) ꢂ 10ꢀ6
(kJ molꢀ1
)
(kJ molꢀ1
)
(J molꢀ1 Kꢀ1
)
CA
342.0
386.0
22.38
29.55
65.44
76.55
46.43
48.42
HMB
Eutectictic-1
(Exp.)
372.0
22.84
27.90
ꢀ5.10
ꢀ1.70
61.40
47.98
(Cal.)
Eutectictic-2
(Exp.)
337.0
411.5
21.18
22.88
23.28
62.85
56.57
46.57
47.43
(Cal.)
Complex
Table 3
3.4. Spectral studies
Critical radius of pure components and their eutectics, and complex.
To understand the nature of interaction between HMB and CA
molecules, the infrared and NMR studied have been done and the
significant changes due to the bond formation have been con-
sidered. The FT-IR spectrum of CA gives two sharp peaks at
3380 cmꢀ1 and 3470 cmꢀ1 due to symmetric and antisymmetric
N–H stretching and another sharp peak at 1614 cmꢀ1 due to N–H
deformation of –NH2 group while a sharp peak at 1672.7 cmꢀ1
was assigned for C¼O group in FT-IR spectrum of HMB. In the
FT-IR spectrum of complex formed; the peaks for –NH2 and C¼O
groups were disappeared and a new peak at 1582.5 cmꢀ1 was
appeared which corresponds to the C¼N stretching.
Critical radius ꢂ 10ꢀ8 cm
Undercooling
DT 1C)
CA
HMB
Eutectic-1
Eutectic-2
Complex
3.0
3.5
4.37
4.94
4.23
4.0
3.55
2.84
5.0
5.5
2.69
1.98
1.35
6.0
2.37
2.11
7.0
2.40
1.68
7.5
8.0
1.58
1.26
The proton NMR spectra of HMB shows a signal at
to the carbonyl proton (–CHO) and CA gives a peak at
–NH2 protons. In the NMR spectra of complex both peaks
d
9.87 due
10.0
11.0
12.0
15.0
18.0
20.0
d
4.0 due to
1.05
1.30
1.04
0.87
0.78
1.40
1.12
disappear and a new signal at
d 8.37 was recorded which could
be due to the –N¼CH– proton.
In 13C NMR spectra, HMB shows a peak at
d
190 due to
144.8
corresponding to C–NH2 carbon. In the addition compound both
signals disappear and a new peak at 161.9 appears which also
carbonyl (–CHO) carbon and CA shows a signal at
d
d
Table 4
Excess thermodynamic functions for eutectics.
corresponds to the –N¼CH– carbon. From the spectral studies it
could be concluded that –NH2 group of CA and –CHO group of
HMB are involved in the bond formation and give strong indica-
tive for the formation of new complex.
The elemental analysis gives the quantitative information
about % composition of the elements (C, H and N) present in the
compound. The experimental elemental analysis of the complex
compound for C, H and N are found to be 64.206, 4.410 and
4.987%, respectively, and these values are very close to their
respective computed values (64.249, 4.622 and 5.352%).
Material
gE (kJ molꢀ1
)
hE (kJ molꢀ1
)
sE (kJ molꢀ1 Kꢀ1
)
Eutectic-1
Eutectic-2
ꢀ0.1138
25.157
0.0679
0.0661
ꢀ14.628
ꢀ0.0436
where NA is the Avogadro number, Vm is the molar volume, and
the values of parameter C lies between 0.34 and 0.45. The
interfacial energy and critical nucleus at different undercoolings,
for different materials, are reported in Tables 2 and 3, respec-
tively. It is evident from the table that the radius of critical
nucleus decreases with increasing undercooling.
3.5. Single crystal growth and crystal X-ray diffraction
The single crystal of newly synthesized complex was grown
from saturated solution of ethanol using slow evaporation tech-
nique at 303 K. The transparent crystal of the size 22 ꢂ 4 ꢂ 2 mm3
was grown in 30 day (Fig. 3). In literature, the crystal structures of
HMB was found monoclinic with space group P21/a and lattice
3.3.3. Excess thermodynamic functions
The deviation from the ideal behavior can best be expressed in
terms of excess thermodynamic functions, namely, excess free
energy (gE), excess enthalpy (hE), and excess entropy (sE) which give
a more quantitative idea about the nature of molecular interactions.
The excess thermodynamic functions can be calculated by using
earlier reported equations [16, 18], and the calculated various excess
thermodynamic functions are given in Table 4.The negative value of
excess free energy; gE for E1 suggests that the interactions between
unlike molecules are stronger than those between like molecules
while the positive value for E2 infers the strong interaction
between like molecules [17]. The values of hE and sE, comple-
mentary to gE, are the measure of excess enthalpy and excess
entropy of mixing, respectively.
˚
˚
˚
constants a¼8.51 A, b¼13.42 A, c¼6.43 A [19], and CA has
reported for orthorhombic crystal structure with Pn21a space
˚
˚
˚
group and lattice constants a¼8.665 A, b¼7.397 A and c¼9.281 A
[20]. However, the single crystal X-ray diffraction analysis of
complex infers that it has crystallized in monoclinic unit cell with
P21/n space group. The lattice parameters as well as various other
crystallographic parameters of the crystal are given in Table 5,
and selected bond angle and bond length between different atoms
of complex molecule have given in Table 6. The picture of
experimental powder X-ray diffraction (PXRD) pattern of complex
compound has been given in Supplementary Fig. S-I. The molecular

230
K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
Fig. 3. Photograph of the grown crystal of complex.
Table 5
Crystal data and structure refinement table for
complex crystal.
Fig. 4. The molecular structure and numbering scheme of complex.
Empirical formula
Mw
C14H12ClNO2
261.70
T (K)
293
Crystal system
Space group
Monoclinic
P21/n
15.0582(7)
˚
a (A)
5.3092(2)
˚
b (A)
15.8846(7)
˚
c (A)
99.396(4)
b
(deg.)
3
1255.13(9)
˚
V (A )
Z
4
Exptl. crystal density
m
1.385 mg/mm3
0.297
(Mo K /mmꢀ1
)
a
Final R indices
R1¼0.046
wR2¼0.1164
R1¼0.075
R2¼0.1279
I (I42s (I))
R indices all data
GOF on F2
˚
0.927 A
Table 6
Selected bond lengths and bond angles for com-
plex crystal.
Fig. 5. Crystal packing and hydrogen bonding in the grown crystal of complex.
Bond
˚
Length (A)
of OH group of a complex molecule and the N-atom of another
neighboring complex molecule (Fig. 5). Each N–H bond length is
Cl1–C01
O02–C11
O02–C14
O01–C10
N01–C07
N01–C04
C08–C07
1.745 (2)
1.354 (2)
1.434 (2)
1.354 (2)
1.274 (2)
1.418 (2)
1.453 (2)
˚
found to be 1.976 A. Besides this interaction, another interaction
between hydrogen atoms and -electron cloud, i.e., intermolecular
C–H–
interaction was also observed. The centeroide to H distance is
p
p
˚
found to be 4.07 A, (Fig. 6). The two phenyl rings of the complex
molecule are non-planar and the interplanar angle was found to be
40.121.
Bond
Angle (deg.)
3.6. Optical characterization
C11–O02–C14
C07–N01–C04
O02–C11–C10
O02–C11–C12
N01–C07–C08
O01–C10–C11
O01–C10–C09
Cl1–C01–C02
Cl1–C01–C06
117.0 (1)
119.2 (2)
115.4 (1)
125.5 (2)
125.5 (2)
116.0 (1)
124.0 (2)
119.5 (2)
120.1 (2)
The optical transmittance spectrum of 2 mm thick and hand
polished single crystal of complex was determined in the region 190
to 850 nm and has shown in Fig. 7. The transmittance of the crystal
was found to be 70% and it was transparent from 412 to 850 nm.
Below 412 nm wavelength, the crystal was opaque. For comparative
study of the nature of complex, the absorption technique was also
extended for pure components and complex in ethanol solution. The
absorption peaks of complex compound were significantly different
from the absorption peaks of parent components (Fig. 8) which
further supports the formation of complex.
structure and numbering scheme of complex are shown in (Fig. 4).
The complex molecules are bonded with each other via intermole-
cular hydrogen bonding. The hydrogen bond exists between H-atom

K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
231
Fig. 8. Absorption spectra of parent compounds and complex.
Fig. 6. C–Hyp interaction in complex molecules.
Fig. 7. Transmittance spectra of the grown crystal of complex.
α
3.6.1. Energy band gap and refractive index
Fig. 9. Plot of
a versus photon energy for complex crystal.
The optical absorption coefficient,
a, for complex crystal at
different wavelength was calculated by using the following
relation,
refractive index of complex crystal was calculated using the
relation
1
a
¼
logð1=TÞ
ð4Þ
d
qffiffiffiffiffiffiffiffiffiffiffiffiffi
n2ꢀ1
where T is the transmittance and d the thickness of the crystal. As
an indirect band gap material, the crystal has an absorption
coefficient (
energies (h
¼ 1ꢀ Eg=20
ð6Þ
n2 þ2
a) obeying the following relation for high photon
proposed by Dimitrov and Sakka [22]. The calculated refractive
index of complex crystal was found to be 2.45.
n
)
2
ðhvꢀEgÞ
a
¼ A
ð5Þ
hv
4. Conclusions
where Eg is the optical band gap of the crystal and A is a constant.
2
The variation of (
ahn
)
versus (h
n
), for complex crystals is shown
The binary phase diagram of 4-chloroaniline and 3-hydroxy-4-
methoxybenzaldehyde shows the formation of an addition/com-
plex compound and two eutectics on either sides of complex. The
in Fig. 9, and Eg was evaluated [21] from an extrapolation of the
linear portion of the curve and it was found to be 2.74 eV. The

232
K.P. Sharma et al. / Journal of Solid State Chemistry 190 (2012) 226–232
newly synthesized complex and eutectics have been studied for
their various thermochemical properties such as heat of fusion,
entropy of fusion, interfacial energy and excess thermodynamic
functions. The spectral studies, FT-IR, proton and 13C NMR,
conclude that parent compounds are covalently bonded, where
–NH2 group of CA and –CHO group of HMB are involved in the
bond formation, to produce the complex molecule. The experi-
mental elemental analysis of the complex compound for C, H and
N is in agreement with the calculated values. The single crystal
grown from the saturated solution indicates that the optical
quality crystal of complex could be grown. The X-ray diffraction
of crystal infers that the complex has crystallized in monoclinic
unit cell with P21/n space group. The XRD confirms the covalent
bonding between parent components to engineer the complex
compound. Apart from the covalent bonding there is H- bonding
Appendix A. Supplementary materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.jssc.2012.02.019.
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p interac-
tion. The grown single crystal of the complex was transparent
from 412 to 850 nm with 70% transmittance efficiency. The
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Acknowledgments
The authors sincere thank to Board of Research in Nuclear
Science, Department of Atomic Energy, Mumbai, India for finan-
cial support.