Intermolecular hydrogen bond complexes by in situ charge transfer complexation of o-tolidine with picric and chloranilic acids

Article abstract of DOI:10.1016/j.saa.2011.03.058

A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA)₂] and [(o-TOL)(CA)₂] have been prepared. The ¹³C NM

Full text of DOI:10.1016/j.saa.2011.03.058

Spectrochimica Acta Part A 79 (2011) 672–679
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Intermolecular hydrogen bond complexes by in situ charge transfer
complexation of o-tolidine with picric and chloranilic acids
Moamen S. Refata,b,∗, Hosam A. Saadb,c, Abdel Majid A. Adamb
a Department of Chemistry, Faculty of Science, Port Said, Port Said University, Egypt
b Department of Chemistry, Faculty of Science, Taif University, 888 Taif, Saudi Arabia
c Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and
picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA)2] and [(o-TOL)(CA)2] have been
prepared. The 13C NMR, 1H NMR, 1H-Cosy, and IR show that the charge-transfer chelation occurs via
the formation of chain structures O–H· · ·N intermolecular hydrogen bond between 2NH2 groups of o-
TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning
the two reactions in methanol were performed and the measurements show that the donor–acceptor
molar ratio was found to be 1:2 using the modified Benesi–Hildebrand equation. The spectroscopic data
were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole
moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer com-
plexes showed that the complexes were more stable than their parents. The thermodynamic parameters
were estimated from the differential thermogravimetric curves. The results indicated that the formation
of molecular charge transfer complexes is spontaneous and endothermic.
Received 27 January 2011
Received in revised form 28 March 2011
Accepted 31 March 2011
Keywords:
o-Tolidine (o-TOL)
13C NMR
1H NMR
Charge transfer
Thermal analysis
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
in analytical, clinical and forensic chemistry, such as in the analyt-
ical determination of gold. Numerous studies have been [15,16]
The charge transfer interactions of significant interactions,
which have many applications in various fields, therefore, received
considerable attention in recent years by many researchers [1–5].
CT complexes have applications in many fields such as electron-
ics, solar cells [6], optical devices and electrical conductivities [7].
Charge transfer complexes have also been recognized as an impor-
tant phenomenon in drug receptor binding mechanism and in
many biological processes like photosynthesis and oxidative pro-
cesses [8]. The charge transfer reactions have successfully utilized
in pharmaceutical analysis as given the drug (donor) with different
acceptors [9–12].
o-Tolidine (Formula I) is slightly soluble in water and has a melt-
ing point of 129 ◦C. It readily forms salts with acids [13]. o-Tolidine
is a commercially important aromatic amines used mainly for dye
production, but also for the production of certain elastomers. o-
Tolidine is an intermediate for the production of soluble azo dyes
and insoluble pigments used particularly in the textile, leather and
paper industries [14]. Also it is widely used as a reagent or indicator
devoted to aromatic amines suspected of having mutagenic or car-
cinogenic properties.
H3C
CH3
H2N
NH2
In continuation of our aimed studies on such type of interac-
tions [17–20], herein this paper was reported the spectral tools
in order to investigate the intermolecular hydrogen bond of the
charge transfer complexes of o-tolidine (o-TOL) with picric (PA)
and chloranilic (CA) acids. A literature survey reveals that no
work on the formation of charge transfer complexes between o-
tolidine and either PA or CA acids have been investigated. In view
of this, we described the synthesis and spectroscopic character-
izations such as UV–vis, FT-IR, 1H NMR, 13C NMR and 1H-Cosy
in the present study to interpretative the mechanism of interac-
tion of o-tolidine with PA and CA acceptors. To track the status
of the thermal stability of charge transfer complexes formed the
thermo gravimetric/differential thermo gravimetric analysis and
kinetic thermodynamic parameters (E*, ꢀS*, ꢀH* and ꢀG*) were
employed.
∗
Corresponding author at: Department of Chemistry, Faculty of Science,
Taif University, 888 Taif, Saudi Arabia. Tel.: +966 561926288.
E-mail address: msrefat@yahoo.com (M.S. Refat).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.058

M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
673
3.0
2. Experimental
o-Tolidine (o-TOL) was of analytical reagent grade (Aldrich Co.).
Both ␲-acceptors (PA and CA) were purchased from Aldrich. Stock
solutions of o-TOL and acceptors were freshly prepared and the
spectroscopic grade methanol (BDH) was used as received.
2.5
2.0
1.5
1.0
0.5
0.0
2.1. Synthesis of o-TOL/PA and o-TOL/CA charge-transfer
complexes
o-TOL
CA
CT-Complex
The two solid CT-complexes of o-TOL with PA or CA were pre-
pared by mixing a saturated solution of the o-TOL donor in 10 ml
MeOH to each of saturated solutions of PA or CA in the same solvent
with continuously stirring for about 45 min at room temperature.
The solutions were allowed to evaporate slowly at room tempera-
ture, the resulted complexes in the solid state filtered and washed
several times with little amounts of solvent, and dried under vac-
uum over anhydrous calcium chloride. Charge-transfer complexes
of o-TOL/PA formed with empirical formula C26H22N8O14 with
molecular weight 670.5 g/mol and o-TOL/CA formed with empirical
formula C26H20N2Cl4O8 with molecular weight 630.3 g/mol.
200
300
400
500
600
Wavelength (nm)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
[(o-TOL)(PA)2]: Color: yellow, yield: 84%, Calc. (%): C = 46.53%,
H = 3.28% and N = 16.70%, Found (%): C = 46.34%, H = 3.21% and
N = 16.47%.
[(o-TOL)(CA)2]: Color: violet, yield: 87%, Calc. (%): C = 49.50%,
H = 3.17% and N = 4.44%, Found (%): C = 49.27%, H = 3.13% and
N = 4.35%.
o-TOL
PA
CT-Complex
2.2. Analysis
The electronic UV–vis. spectra of the o-TOL, PA, CA and the
resulted CT complexes were recorded in the region of (200–800 nm)
by using a Jenway 6405 Spectrophotometer with quartz cells,
1.0 cm path in length. IR measurements (KBr discs) of the o-TOL,
acceptor and both CT complexes were carried out on a Bruker FT-
IR spectrophotometer (400–4000 cm−1). The NMR spectra were
obtained on a Bruker DRX-250 spectrometer, operating at 250.13
and 62.90 MHz for 1H and 13C, respectively using a dual 5 mm
probe head. The measurements were carried out in DMSO-d6 solu-
tion at ambient temperature. The chemical shift was referenced
to tetramethylsilane (TMS), standard experiments with 30◦ pulses,
1 s relaxation delays, 16 K time domain points, zero-filled to 64 K
for protons and 32 K for carbons were performed. The distortion-
less enhancement by polarization transfer (DEPT) spectra were
recorded under the same conditions as the 13C NMR spectra and
ꢁ = (21JCH) − 1 = 3.45 ␮s was used. The 2D 1H/1H correlated spectra
(COSY) were performed with spectral width 2200 Hz, relaxation
delay 2 s, number of increments 512, and size 1 K × 1 K. The 2D
1H/13C heteronuclear multiple quantum coherence (HMQC) exper-
iments were carried out with a spectral width of 2200 Hz for 1H and
9000 Hz for 13C, relaxation delay 1.5 s, FT size 1 K × 256 W. The ther-
mal analysis (TGA/DTG) was carried under nitrogen atmosphere
with a heating rate of 10 C/min using a Shimadzu TGA-50H thermal
analyzers.
200
300
400
500
600
Wavelength (nm)
Fig. 1. Electronic absorption spectra of o-TOL/CA and o-TOL/PA reactions in MeOH.
covered along the range from 1:0.25 to 1:4.00. The UV–vis spec-
tra of o-TOL/PA and o-TOL/CA systems were shown in Fig. 1A and
B. The measured spectra were detected definite absorption bands
which are not existed in both spectra of the free donor and accep-
tors. These bands are noticed at (352 and 419 nm) and (335 and
532 nm) due to CT-complexes formed from the reactions of o-TOL
with PA and CA, respectively. Photometric titration curves based on
charge transfer bands are shown in Fig. 2A and B. These photomet-
ric titration curves were obtained according to well known method
[21] and it is refereed to formation of 1:2 CT complexes. The 1:2 Eq.
(1) [22] was used in the calculations.
CA◦2 CD◦
1
Kε
1
ε
=
+
.CA◦ (4CD◦ + CA◦ )
(1)
A
where CA◦2 and C2◦ are the initial concentration of the ␲-acceptor (PA
and CA) and donor (o-TOL), respectively, and A is the absorbance
of the detected CT-band. The data obtained CD◦ , CA◦2 , CA◦ (4CD◦ + CA◦ )
and (CA◦2 .CD◦ )/A in methanol were calculated. By plotting (CA◦2 .CD◦ )/A
values vs CA◦ (4CD◦ + CA◦ ), straight lines were obtained with a slope
of 1/ε and an intercept of 1/kε as shown in Fig. 3A and B.
The oscillator strength f was obtained from the approximate
formula [23].
3. Results and discussion
3.1. UV–vis spectral studies
f = (4.319 × 10−9)εmax.v1/2
where ꢂ1/2 is the band-width for half-intensity in cm−1 and εmax
is the maximum extinction coefficient of the CT-band. The oscilla-
tor strength values are given in Table 1. The data resulted reveals
(2)
UV–vis absorption spectra of o-TOL/PA and o-TOL/CA CT-
complexes were scanned in MeOH solvent. The concentration of
o-TOL in the reaction mixture was kept fixed at 1.0 × 10−4 M in
MeOH solvent, while, the concentration of PA or CA was changed
from 0.25 × 10−4 M to 4.0 × 10−4 M. These concentrations were

674
M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
500
400
300
200
100
0
o-TOL/CA
50
0
10
20
30
40
-10
o-TOL/CA
o
o
o
C
(4C +C )10
d a
d
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
ml added of CA
1800
1600
1400
1200
1000
800
600
400
200
0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
o-TOL/PA
200
0
50
100
150
-10
o
o
o
C
(4C +C )10
d
d
a
o-TOL/PA
4.0 4.5
Fig. 3. The plot of Cd◦ (4 Cd◦ + Ca◦) values against (Cd ·Ca◦/A) values for the o-TOL/CA
◦2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
and o-TOL/PA systems at 532 and 419 nm, respectively.
ml added of PA
Fig. 2. Photometric titration curves for the o-TOL/CA and o-TOL/PA systems at 532
and 419 nm, respectively.
[27,28];
−4
ID(ev) = 5.76 + 1.53 × 10
v
CT
(4)
where ꢂCT is the wavenumber in cm−1 corresponding to the CT
band formed from the interaction between donor and acceptor.
The electron donating power of a donor molecule is measured by
its ionization potential which is the energy required to remove an
electron from the highest occupied molecular orbital.
several items. (i) The o-TOL/PA and o-TOL/CA systems show high
values of both formation constant (K) and molar absorptivity (ε).
This high value of (K) reflects the high stability of the o-TOL com-
plexes as a result of the expected high donation of the o-TOL which
contains two of amino and methyl groups. (ii) The different values
of the oscillator strength, f, increases with increasing in the dielec-
tric constant (D) of the solvent. This result could be explained on the
basis of competitive solvent interactions with the acceptors [24,25].
The transition dipole moment (ꢃ) of the o-TOL CT-complexes,
Table 1, has been calculated from Eq. (3) [26];
The energy of the charge-transfer complexes ECT of the o-TOL
complexes is calculated using Eq. (5) [26];
ECT = (hꢂCT) = 1243.667/ꢄCT (nm)
(5)
where, ꢄCT is the wavelength of the complexation band.
Determination of resonance energy (RN) [29] theoretically
derived from (Eq. (6));
1/2
m(Debye) = 0.0958[εmax
v1/2/vmax
]
(3)
7.7 × 10−4
εmax
=
(6)
hꢂCT /[RN − 3.5]
The transition dipole moment is useful for determining if tran-
sitions are allowed, that the transition from a bonding ␲ orbital to
an antibonding ␲* orbital is allowed because the integral defining
the transition dipole moment is nonzero.
The ionization potential (Ip) of the o-TOL donor in the charge
transfer complexes of (o-TOL/PA and o-TOL/CA) are calculated
using empirical equation derived by Aloisi and Piganatro Eq. (4)
where εmax is the molar absorptivity of the CT-complexes at max-
imum CT band, ꢂCT is the frequency of the CT peak and RN is the
resonance energy of the complex in the ground state, which, obvi-
ously is a contributing factor to the stability constant of the complex
(a ground state property). The values of RN for the (PA and CA)
complexes under study have been given in Table 1.
Table 1
Spectrophotometric results of the o-TOL CT-complexes; (A) [(o-TOL)(CA)] and (B) [(o-TOL)(PA)].
Complex
ꢄmax (nm)
ECT (eV)
K (l mol−1
)
εmax (l mol−1 cm−1
)
f
ꢃ
Ip
D
RN
ꢀG◦(25 ◦C) (KJ mol−1
)
A
B
532
419
2.34
2.97
0.073 × 1010
0.112 × 1010
0.1314 × 106
0.1143 × 106
45.40
49.37
71.64
66.30
8.64
9.41
33
33
0.572
0.711
6.48 × 1013
5.43 × 1013

M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
675
The standard free energy changes of complexation (ꢀG◦) were
calculated from the formation constants by the following Eq. (7)
[30];
tors, ꢂ(N–H) of NH2 group of o-TOL donor and some of stretching
motions of ꢂ(C–H) respected to the aromatic rings.
3412 s + 3375 s + 3338 ms (o-TOL free donor) →
3414 vw + 3386 w + 3357 vw(o-TOL/CA complex)
3400 s + 3328 s (o-TOL/PA complex)
ꢀG◦ = −2.303RT log KCT
(7)
where ꢀG◦ is the free energy change of the CT-complexes
(KJ mol−1), R is the gas constant (8.314 J mol−1 K), T is the tempera-
ture in Kelvin degrees (273+ ◦C) and KCT is the formation constant of
the complexes (l mol−1) in different solvents at room temperature.
Found that the values characteristic of both the –OH and the
–NH2 groups happened to shifted to a lower values and also
decreased in the intensities of vibration motions, which indicates
that the interactions placed among the –OH group of each of CA
and PA and –NH2 group of o-TOL through the hydrogen bonding
(region 3000–2000 cm−1) existed at 2757 sh, 2643 w, 2571 w for
o-TOL/CA and 2728 vw, 2657 vw, 2571 w, 2543 w for o-TOL/PA.
These new bands were attributed to the stretching vibration of a
proton attached to the donation site (–NH2) of the donor and form-
ing +NH3 group [31]. These results caused by the protonation of
both NH2 group of the o-TOL donor through one protons transfer
from the acidic center on the CA or PA acceptors via –OH group to
the basic center on the donor NH2 group.
3.2. Infrared spectral studies
Infrared spectral studies sheds light on the place of donation in
donor species and the differences occurs in the spectra of both PA
and CA charge transfer complexes. Comparison between the spec-
tra of both CT-complexes and the data of o-TOL donor and receptors
have been studied and recorded in Table 2. The full spectra of o-
TOL/CA and o-TOL/PA were shown in Fig. 4A and B.
If we take into account the changes that have taken place in the
region of 4000–3000 cm−1, we find that this area includes some
stretching vibration motions; the ꢂ(OH) group of CA and PA accep-
To place greater emphasis on the interactions between the
donor and both acceptors, the 2000–1000 cm−1 region was inves-
tigated. This region contain the bending vibration motions of –NH2
group (ı(NH2)) which influenced by charge transfer complexation
Table 2
Infrared frequenciesa (cm−1) and tentative assignments for o-TOL, CA, PA, [(o-TOL)(CA)], and [(o-TOL)(PA)] CT-complexes.
o-TOL
CA
PA
o-TOL/CA
o-TOL/PA
Assignmentsb
3475 s
3412 s
3375 s
3420 s,br
3235 s, br
3416 br
3103 ms
3471 vw
3414 vw
3386 w
3400 s
3328 s
ꢂ(O–H)
ꢂ(N–H); NH2
3338 ms
3213 ms
3019 m
3357 vw
3143 sh
–
–
2980 sh
2872 w
3200 s,br
3114 sh
3057 w
2986 vw
2929 vw
2857 vw
2814 vw
2728 vw
2657 vw
2571 w
2543 w
1614 vs
1557 s
ꢂ(C–H); aromatic rings
2982 ms
2940 mw
2898 w
2856 w
–
–
2957 vw
2914 vw
2857 vs,br
ꢂs(C–H); CH3
ꢂas(C–H); CH3
–
–
2757 sh
2643 w
2571 w
Hydrogen bonding
1870 ms
1625 vs
1574 s
1520 w
1489 m
1458 s
1384 s
1321 s
1295 s
1269 vs
1154 vs
1065 s
1039 s
1664 ms
1630 vs
1861 ms
1632 vs
1608 vs
1529 vs
1618 s
1485 vs
Overtone of ı(CH)
ꢂas(NO2); PA
ꢂ(C O) + ␯(C C)
ı(NH2)
Ring breathing bands
ıas(CH3) + ıs(CH3)
ꢂs(NO2); PA
ꢂ(C–C) + ꢂ(C–N) + ꢂ(C–O)
In-plane bending
1528 s
1486 vs
1368 s
1432 s
1428 vw
1386 s
1357 vw
1300 vs
1214 s
1171 s
1143 vw
1043 s
1400 s
1386 s
1357 s
1342 w
1328 s
1217 vs
1214 s
1171 s
1114 s
1014 w
928 s
1263 vs
1207 w
1168 w
1343 ms
1312 w
1263 w
1150 ms
1086 s
986 s
944 ms
902 s
887 s
855 ms
829 vs
777 ms
735 s
682 s
661 s
609 s
583 s
525 s
425 s
981 vs
851 vs
752 vs
917 vs
829 w
781 s
732 s
971 s
(C–H) bend
Aromatic rings vibrations
900 m
857 m
843 vs
800 s
886 s
828 s
800 s
757 s
728 w
714 s
690 vs
569 vs
703 s
652 sh
522 ms
643 w
600 w
586 vs
543 vs
443 vs
686 vs
642 s
586 w
528 s
428 s
Aromatic rings vibrations of ortho substituted
Skeletal vibrations
a
s, strong; w, weak; m, medium; sh, shoulder; v, very; br, broad.
ꢂ, stretching; ı, bending.
b

676
M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
Fig. 5. 1H NMR spectrum of [(o-TOL)(CA)] CT complex.
Fig. 4. (a) Infrared spectrum of [(o-TOL)(CA)] CT complex. (b) Infrared spectrum of
[(o-TOL)(PA)] CT complex.
Fig. 6. 13C NMR spectrum of [(o-TOL)(CA)] CT complex.
and shifted to lower wavenumbers and consequently the inten-
sity was distorted, this results can be summarized as the following
explanatory equation;
Hc
O
O
H3
N
Hb
O
Cl
O
O
Ha
1625 vs + 1574 s (o-TOL free donor) →
1618 s + 1485 vs (o-TOL/CA complex)
1614 vs + 1557 s (o-TOL/PA complex)
HO
Cl
Cl H3C
CH3 Cl
OH
Ha
As expected, the bands characteristic for the o-TOL unit in
[(o-TOL)(CA)] and [(o-TOL)(PA)] CT-complexes are existed with
small changes in band intensities and frequency values. This could
be attributed to the expected symmetry and electronic structure
changes upon the formation of the CT-complexes.
O
N
Hb
H3
Hc
The full analysis recorded is, 1H NMR (Fig. 5)
(CDCl3) for symmetrical 2,2ꢀ-[(3,3ꢀ-dimethylbiphenyl-4,4ꢀ-
diyl)bis(aminohydroxy)]bis(3,6-dichloro-5-hydroxy-benzo-1,4-
quinone), gave a signals at:
3.3. 3.3. 1H NMR, 13C NMR and 1H–1H-Cosy spectral studies
ı = 1.25 (br, 2H, 2OH), 1.57 (br, 2H, NH2), 2.22 (s, 3H, CH3), 6.73
(d, 1Hb, J = 7.5 Hz, Ar–H), 7.24 (d, 1Hc, J = 7.5 Hz, Ar–H), 7.26 (s, 1Ha,
Ar–H). 1H–1H-Cosy indicates (Fig. 7) that Hc coupled with Hb as
ortho coupling as shown in spectrum. 13C NMR (CDCl3); ı = 17.6
(CH3), 115.3, 122.5, 125.0, 128.6, 128.8, 130.9, 132.1, 134.2 and
143.1 (Ar–C and C O).
On the other hand, the reaction between picric acid and o-TOL
in methanol formed an ionic compound on the bases of hydrogen
transfer from picric acid –OH to –NH2 of o-TOL also in ratio 2:1
PA-to-o-TOL. The spectral studies for 1H, 13CNMR (Figs. 8 and 9)
proved formation of symmetrical compound between electron rich
molecule, o-TOL, and electron deficient, picric acid.
The reaction between chloranilic acid and o-tolidine in
methanol carried out in 2:1 ratio through formation of hydro-
gen bond between –OH of CA and –NH2 group of o-TOL. The
1H and 13C NMR spectroscopic data (Figs. 5 and 6) proved the
formation of symmetrical compound with 6 types of hydrogen pro-
tons, five on o-TOL molecule and one for the OH of CA, also, the
13C NMR spectrum (Fig. 6) for the same product showed signals
for 10 different carbons 7 for o-TOL molecule and 3 for CA, this
means that, presence of axis of symmetry for the formed product
(Formula II).

M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
677
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
[(o-TOL)(CA)]
1.8
0
100 200 300 400 500 600 700 800
Temp [oC]
2.0
1.5
1.0
0.5
0.0
Fig. 7. 1H–1H-Cosy spectrum of [(o-TOL)(CA)] CT complex.
[(o-TOL)(PA)]
0
100 200 300 400 500 600 700 800
Temp [oC]
Fig. 10. TG curves of o-TOL CT complexes.
NO2
H3C
Ha Hb
Hc
O2N
O
O2N
H3N
NH3
O
NO2
NO2
Hb
CH3
Hc
Ha
Fig. 8. 1H NMR spectrum of [(o-TOL)(PA)] CT complex.
O2N
The full analysis recorded is, 1H NMR (CDCl3) for
symmetrical 3,3ꢀ-dimethylbiphenyl-4,4ꢀ-diaminium di(2,4,6-
trinitrophenolate), gave a signals at:
ı = 2.87 (s, 3H, CH3), 5.42 (br, 3H, NH3+), 8.56 (d, 1Hb, J = 7.8 Hz,
Ar–H), 8.91 (d, 1Hc, J = 7.8 Hz, Ar–H), 8.89 (s, 1Ha, Ar–H), 10.5 (s, 2H,
Ar–H, picrate).
3.4. Thermogravimetric studies
The thermo gravimetric analysis give an idea about the thermal
stabilities of the prepared charge transfer complexes and also show
the different in physical behavior between the starting and result-
ing compounds. TG curves of o-tolidine CT complexes are shown
in Fig. 10. The o-TOL donor beginning decomposed at ∼129 ◦C with
maximum decomposition at 244 ◦C. The thermal decomposition of
o-TOL occurs sum in one step which was detected at 244 ◦C within
the range of 200–800 ◦C corresponding to loss of C12H16N2 organic
moiety representing a weight loss of obs = 88.65%, calc = 88.70%
then leaving residual carbon as final product.
Fig. 9. 13C NMR spectrum of [(o-TOL)(PA)] CT complex.
TG curve of [(o-TOL)(CA)] CT-complex was thermally decom-
posed in nearly two decomposition steps within the temperature
rang 25–800 ◦C. The first decomposition step (obs = 27.00%,
calc = 27.92%) within the temperature range 25–288 ◦C, may be
assigned to the liberation of 2Cl2 + H2O + 0.5O2 molecules. The
The formation of ionic NH3 was confirmed by the 1H NMR
+
(Fig. 8) formed at ı = 42 and disappearance of the signal due to OH
proton of picric acid (Formula III).

678
M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
Table 3
Kinetic parameters of [(o-TOL)(CA)] and [(o-TOL)(PA)] CT-complexes.
Complex
n
Parameter
E (J mol−1
)
Z
(s−1
)
ꢀS (J mol−1 K−1
)
ꢀH (J mol−1
)
ꢀG (J mol−1
)
r
[(o-TOL)(CA)]
CR
HM
[(o-TOL)(PA)]
CR
HM
1
1
157
75.6
2.62 × 1013
4.31 × 105
−7.45
−1.42
152
71.4
148
144
0.9882
0.9975
1
1
182
129
4.5 × 1016
2.78 × 105
−169.2
−241
178
125
141
151
0.9979
0.9990
n = number of decomposition steps.
-11.0
-11.2
-11.4
-11.6
-11.8
-12.0
-12.2
-12.4
-13.2
-13.4
-13.6
-13.8
-14.0
-14.2
-14.4
-14.6
-14.8
-15.0
Coats-Redfern curve
0.00196 0.00198 0.00200
-12.6 Coats-Redfern curve
0.00202
0.00204
0.00180
0.00182
1/T (K-1
0.00184
0.00186
1/T (K-1)
)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
Horowitz and Metzger curve
70 80 90 100
Horowitz and Metzger curve
50
60
θ (Κ)
-5
0
5
10
15
20
25
30
θ (Κ)
Fig. 12. Kinetic curves of decomposition steps of [(o-TOL)(PA)] complex using Coats
and Redfern (CR) and Horowitz and Metzger equations.
Fig. 11. Kinetic curves of decomposition steps of [(o-TOL)(CA)] complex using Coats
and Redfern (CR) and Horowitz and Metzger equations.
tion energy (E*), frequency factor (A), enthalpy of activation (H*),
entropy of activation (S*), free energy of activation (G*). From TG
data employing Coats–Redfern [32] and Horowitz and Metzger [33]
equations various kinetic thermodynamic parameters have been
calculated. The kinetic data obtained for the non isothermal decom-
position of complexes are given in Table 3 and Figs. 11 and 12.
Generally, the value of (A) increases with decrease in E* and higher
value of activation energy suggests the higher thermal stability.
second decomposition step found within the temperature range
288–800 ◦C (obs = 22.00%, calc = 22.52%) which are assigned by the
removal of 6H2O and 2NH3 molecules with remaining a many car-
bon atoms as a final residual.
The [(o-TOL)(PA)] CT complex was decomposed thermally
in two definite decomposition steps (250 and 516 ◦C) within
the temperature rang 100–800 ◦C. The first decomposition
step (obs = 36.50%, calc = 36.55%) within the temperature range
100–395 ◦C, may be attributed to the liberation of one molecule
of PA and NH2 group from o-TOL donor. The second decom-
position step existed within the temperature range 395–800 ◦C
(obs = 63.50%, calc = 63.45%), which are reasonably by the loss of one
molecule of PA and C14H14N organic moiety remnant from o-TOL
molecule.
i Coats–Redfern equation is as follows:
ꢀ
ꢁ
ꢀ
ꢁ
− ln(1 − a)
E∗
AR
ϕE∗
Ln
= −
+ ln
(8)
T2
RT
where ˛ is the fraction of the sample decomposed at time T,
where T is the derivative peak temperature, A is frequency fac-
tor, R is the gas constant, E* is the activation energy and ϕ is the
linear heating rate. A plot of left side vs 1/T gives a slope for the
evaluation of activation energy.
3.5. Kinetic thermodynamic studies
The kinetic studies on thermal process are expected to provide
sufficient information regarding Arrhenius parameters viz. activa-

M.S. Refat et al. / Spectrochimica Acta Part A 79 (2011) 672–679
679
ii Horowitz–Metzger equation is as follows:
[2] S.-L. Wang, J.-M. Lin, S.-E. Shu, C.-Y. Chern, J. Photochem. Photobiol. A: Chem.
210 (1) (2010) 54.
[3] N. Singh, A. Ahmad, J. Mol. Struct. 977 (1–3) (2010) 197.
[4] I.M. Khan, A. Ahmad, J. Mol. Struct. 977 (1–3) (2010) 189.
[5] A. Chakraborty, K.L. Barbu-Debus, A. Zehnacker-Rentien, N. Guchhait, J. Pho-
tochem. Photobiol. A: Chem. 213 (2–3) (2010) 164.
[6] K. Takahasi, K. Horino, T. Komura, K. Murata, Bull. Chem. Soc. Jpn. (1993) 66.
[7] P.J. Trotter, P.A. White, Appl. Spectrosc. 32 (1978) 323.
[8] R.A. Marcus, Rev. Mod. Phys. 65 (1993) 599.
[9] H. Duymus, M. Arslan, M. Kucukislamoglu, M. Zengin, Spectrochim. Acta Part A
65 (5) (2006) 1120.
ꢂ
ꢃ
w˛
w
E∗Â
log log
=
− log 2.303
(9)
2
2.303RTs
where  = T − Ts, w = w˛ − w, w˛ = mass loss at the comple-
tion of the reaction; w = mass loss up to time t. The plot of
log[log(w˛/w )] vs  was drawn and found to be linear from the
slope of which E* was calculated.
[10] I.M. Khan, A. Ahmad, M. Oves, Spectrochim. Acta Part
A
77 (5) (2010)
1059.
The entropy of activation, ꢀS*, was calculated from the follow-
ing equations. The enthalpy activation, ꢀH*, and Gibbs free energy,
ꢀG* were calculated from;
[11] M. Pandeeswaran, K.P. Elango, Spectrochim. Acta Part
1462.
[12] P. Singh, P. Kumar, A. Katyal, R. Kalra, S.K. Dass, S. Prakash, R. Chandra, Spec-
trochim. Acta Part A 75 (3) (2010) 983.
[13] C.R. Noller, Textbook of Organic Chemistry, Springer Verlag, 1960.
[14] G. Gangadhar, Chemoshere 32 (2) (1996) 267.
[15] G.M. Malanoski, E.A. Elliot, Epidemiol. Rev. 3 (1981) 203.
[16] G. Pfizenmair, T. Pflaum, Naturwissenschaften 3 (1995) 40.
[17] M.S. Refat, H.M.A. Killa, I. Grabchev, M.Y. El-Sayed, Can. J. Anal. Sci. Spectrosc.
52 (2) (2007) 75.
A
75 (5) (2010)
ꢀH∗ = E∗ − RT
and ꢀG∗ = DH∗ − TꢀS∗
(10)
(11)
The higher values of ‘E*’ and lower values of (A) favor the reaction
to proceed slower than normal [34]. The activation energy values
(E*) of CT-complexes arranged with order of thermal stability as:
[(o-TOL)(PA)] > [(o-TOL)(CA)].
[18] M.S. Refat, L.A. El-Zayat, Okan Zafer Yes¸ ilel, Polyhedron 27 (2) (2008) 475.
[19] M.S. Refat, H.A. Ahmed, I. Grabchev, L.A. El-Zayat, Spectrochim. Acta 70 (4)
(2008) 907.
[20] M.S. Refat, L.A. El-Zayat, Okan Zafer Yes¸ ilel, Spectrochim. Acta Part A 75 (2010)
745.
[21] D.A. Skoog, Principle of Instrumental Analysis, 3rd edn., Saunders College Pub-
lishing, New York, USA, 1985 (Chapter 7).
From the kinetic and thermodynamic data resulted from the
TGA curves and tabulated in Table 3, the following outcome can be
discussed as follows:
[22] A. El-Kourashy, Spectrochim. Acta 37A (1981) 399.
[23] H. Tsubomura, R.P. Lang, J. Am. Chem. Soc. 86 (1964) 3930.
[24] S.M. Teleb, M.S. Refat, Spectrochim. Acta Part A 60 (7) (2004) 1579.
[25] E.M. Nour, S.M. Teleb, M.A.F. El-Mosallamy, M.S. Refat, South Afr. J. Chem. 56
(2003) 10.
[26] R. Rathone, S.V. Lindeman, J.K. Kochi, J. Am. Chem. Soc. 119 (1997) 9393.
[27] G. Aloisi, S. Pignataro, J. Chem. Soc. Faraday Trans. 69 (1972) 534.
[28] G. Briegleb, Z. Angew. Chem. 72 (1960) 401;
1 The higher values of activation energies of the o-TOL complexes
led to thermal stability of the studied complexes.
2 The correlation coefficients of the Arrhenius plots of the thermal
decomposition steps were found to lie in the range 0.98–0.99,
showing a good fit with linear function.
3 It is clear that the thermal decomposition process of all o-TOL
complexes is non-spontaneous, i.e., the complexes are thermally
stable.
G. Briegleb, Z. Angew. Chem. 76 (1964) 326.
[29] G. Briegleb, J. Czekalla, Z. Physikchem. (Frankfurt) 24 (1960) 237.
[30] A.N. Martin, J. Swarbrick, A. Cammarata, Physical Pharmacy, 3rd ed., Lee and
Febiger, Philadelphia, PA, 1969, 344 pp.
[31] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Chapman & Hall, Lon-
don, 1975.
[32] A.W. Coats, J.P. Redfern, Nature (London) 201 (1964) 68.
[33] H.H. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464.
[34] N. Sharma, Archana, M. Thakur, S.S. Bhatt, S.C. Chaudhry, J. Chem. Sci. 119 (4)
(2007) 311.
References
[1] J.R. Peregrina, A. Sánchez-Azqueta, B. Herguedas, M. Martínez-Júlvez, Biochim.
Biophys. Acta (BBA): Bioenerg. 1797 (9) (2010) 1638.