Synthesis and spectroscopic studies of charge transfer complexes between chloranilic acid and some heterocyclic amines in ethanol

Article abstract of DOI:10.1016/j.molstruc.2009.03.025

Charge transfer (CT) complexes formed between 2-amino-4-methoxy-6-methyl-pyrimidine (AMMP), 2-amino-4,6-dimethyl-pyrimidine (ADMP), 3-amino-pyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-ami

Full text of DOI:10.1016/j.molstruc.2009.03.025

Journal of Molecular Structure 928 (2009) 158–170
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and spectroscopic studies of charge transfer complexes between
chloranilic acid and some heterocyclic amines in ethanol
b
a
Amirah S. AL-Attas a, , Moustafa M. Habeeb , Doaa S. AL-Raimi
*
a Chemistry Department, Girls College of Education, King Abdulaziz University, Jeddah, Saudi Arabia
b Chemistry Department, Faculty of Education, Alexandria University, Alexandria, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Charge transfer (CT) complexes formed between 2-amino-4-methoxy-6-methyl-pyrimidine (AMMP),
2-amino-4,6-dimethyl-pyrimidine (ADMP), 3-amino-pyrazole (AP), 3,5-dimethyl-pyrazole (DMP),
3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-methyl-1,3,4-thiadia-
Received 2 January 2009
Received in revised form 23 March 2009
Accepted 25 March 2009
Available online 5 April 2009
zole (AMTD) and 3-amino-5,6-dimethyl-1,2,4-triazine (ADMT) as electron donors with the
p-acceptor
chloranilic acid (CHA) were investigated spectrophotometrically in ethanol. Minimum–maximum absor-
bances method has been used for estimating the formation constants of the charge transfer reactions
(KCT). It has been found that KCT depends on the pKa of the studied donors. Job’s method of continuous
variation and photometric titration studies were used to detect the stoichiometric ratios of the formed
Keywords:
Spectra
CT-complexes
Amines
complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient (
e),
oscillator strength (f), dipole moment ( ), charge transfer energy (ECT), ionization potential (IP) and the
l
Chloranilic acid
dissociation energy (W) of the formed complexes were estimated, they reached acceptable values sug-
gesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and charac-
terized by elemental analyses, 1HNMR and FTIR spectroscopies where the formed complexes included
proton and electron transfer.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
tors are generally a route for the formation of ion pair adducts
[22–24].
In through last few decades, charge transfer complexes play an
essential role in the analysis of some drugs in pure form or phar-
maceutical preparation [1,2], solar energy storage [3] and surface
chemistry [4] as well as many biological fields [5], charge transfer
complexes are found to take part in many chemical reactions, like
addition, substitution and condensation [6–8]. These complexes
have great attention for non-linear optical materials and electrical
conductivities [9–12]. For their wide applications, extensive stud-
In connection with the study of CT-complexes and due to the
biological importance and industrial applications of the amino
heterocyclic donors, the present article included a continuation
on the CT complexes through studying and characterization of
charge transfer complexes of some amines of (pyrimidines, thia-
zoles, pyrazoles and triazines) as electron donors (Scheme 1) with
chloranilic acid as
constants (KCT), molar extinction coefficient (
(f), dipole moment ( ), energy (ECT), ionization potential (IP) and
p
-electron acceptor in ethanol. Formations
e), oscillator strength
ies on CT-complexes of
p
acceptors have been performed. Pyrim-
l
idines, thiazoles, pyrazoles and triazines are very important
heterocyclic compounds. They considered to be important not
only because they are on integral part of genetic materials viz.,
DNA and RNA as nucleotides and nucleosides also they have
important numerous biodynamic properties and biological activi-
ties such as bactericides, fungicides, vermicides and medicines
[13–19]. Charge transfer complexes of organic species are inten-
sively studied because of their special type of interaction, which
is accompanied by transfer of an electron from the donor to the
acceptor [20,21]. Also protonation of the donor from acidic accep-
dissociation energy (W) of the formed CT-complexes were esti-
mated and evaluated. The synthesis and characterization of the
solid CT-complexes are important aims of this work.
2. Experimental
2.1. Materials
All chemicals used were of analytical grade. Chloranilic acid
(98%) (CHA), ethanol absolute PA (99.5%) were obtained from
(BDH). 2-Amino-4-methoxy-6-methyl-pyrimidine (99%) (AMMP),
2-amino-4,6-dimethyl-pyrimidine (98%) (ADMP), 3-aminopyrazole
(98%) (AP), 3,5-dimethyl-pyrazole (98.5%) (DMP), 3-amino-5-
* Corresponding author. Tel.: +966 505677583; fax: +966 266732234.
E-mail address: amirh-alattas@hotmail.com (A.S. AL-Attas).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.03.025

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
159
H2N
N
N
N
H2N
N
O
2-amino-4,6-dimethyl-pyrimidine
ADMP
2-amino-4-methoxy-6-methyl-pyrimidine
AMMP
H
N
H
N
N
N
H2N
NH
N
NH 2
3-aminopyrazole
3,5-dimethyl-pyrazole
DMP
3-amino-5-methyl-pyrazole
AMP
AP
N
N
S
S
N
H2N
NH 2
2-amino-5-methyl-1,3,4-thiadiazole
AMTD
2-amino-4-methyl-thiazole
AMT
N
N
H2N
N
H
3-amino-5,6-dimethyl-1,2,4-triazine
ADMT
Scheme 1. Chemical Structures of donors.
methyl pyrazole (97%) (AMP), 2-amino-4-methyl-thiazole (98%)
(AMT), 2-amino-5-methyl-1,3,4-thiadiazole (97%) (AMTD) and
3-amino-5,6-dimethyl-1,2,4-triazine (98%) (ADMT) were pur-
chased from Acros organic. The heterocyclic donor amines and
chloranilic acid were used without further purification.
personal spectroscopy software version 3.7, connected to Shima-
dzu TCC-ZUOA temperature controller.
2.3.2. Infrared spectra
The infrared spectra of the prepared solid CT-complexes were
measured as KBr discs on Shimadzu FTIR-8400 S Fourier transform
infrared spectrophotometer (Japan).
2.2. Preparation of standard solutions of the donors and acceptor
Stock solutions of the donors (10ꢀ2 M) and CHA (5 ꢁ 10ꢀ3 M)
were freshly prepared before each series of measurements by dis-
solving precisely weighed amounts in the appropriate volume of
the solvent. The stock solutions of donors and acceptor were pro-
tected from light. Solutions for spectroscopic measurements were
made by mixing appropriate volumes of stock donors and CHA
solutions and pure solvent.
2.3.3. 1HNMR spectra
1HNMR spectra were obtained on Bruker 600 MHZ using TMS as
an internal reference and d6-DMSO as the solvent.
2.3.4. Elemental analyses
C, H and N contents were determined with the Micro Analyser,
Perkin Elmer 2400 (USA).
2.3. Instrumentation and physical measurements
2.3.5. Potentiometric titration
pH-metric titrations were performed using a Metrohm 744 pH
meter (Metrohm, Herisau, Switzerland). The combined glass elec-
trode was standardized using buffer solutions from Metrohm. All
titrations were carried out at room temperature.
2.3.1. Electronic absorption spectra
The electronic absorption spectra were recorded in the region
700–250 nm using UV–vis model Shimadzu UV-1601 with

160
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
2.4. Preparation of solid CT-complexes
2.5. Photometric titration
The solid CT-complexes between the donors and the acceptor
were prepared by mixing equimolar amounts of donor and accep-
tor in acetonitrile. The resulting color complex solutions were
allowed to evaporate slowly at room temperature where the solid
precipitated after reduction of the volume of the solvent. The
separated complexes were filtered off, washed several times with
acetonitrile, and then collected and dried; the analytical data of
the CT-complexes (C, H, N Content) along with some of the physi-
cal properties are listed in Table 1.
Photometric titrations at 528–530 nm for the reaction between
the studied donors and CHA in ethanol solvent were carried out as
follows; the concentration of CHA was kept constant at 5 ꢁ 10ꢀ4 M,
whereas that of the donors were changed over the wide range from
5 ꢁ 10ꢀ5 to 2 ꢁ 10ꢀ3 M. The donor–acceptor molar ratio (CD:CA)
obtained in this case varied from 0.25 to 4. The peak absorbances
appear in the spectra that were assigned to the formed CT-com-
plexes were measured and plotted as a function of the ratio (CD:CA)
according to the known method [25].
Table 1
Elemental analysis, stoichiometry, melting point, color of the CT-complexes of CHA with the donors.
Donor
Expected
C
Found
C
Stoichiometry
mp °C
Colour
H
N
H
N
AMTD
ADMT
DMP
AP
AMP
AM
33.32
39.62
43.26
36.98
39.20
37.13
41.38
43.37
2.16
3.00
3.28
2.40
2.94
2.48
3.16
3.31
12.96
16.81
9.18
14.83
13.72
8.66
33.35
40.23
43.34
37.54
39.52
37.60
41.42
43.58
2.11
2.91
3.08
2.92
2.38
2.33
2.87
2.18
12.29
17.62
9.06
15.04
13.80
8.91
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
208.3
185.0
210.0
205.0
186.0
209.0
216.8
205.7
Brown
Brown
Purple
Brown
Brown
Purple
Purple
Brown
AMMP
ADMP
12.07
12.65
12.14
12.84
Fig. 1. Effect of donor concentrations on the absorbance of CT-complexes with 5 ꢁ 10ꢀ4 M CHA at different temperatures in ethanol.

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
161
pKa ¼ pH þ log½BHþꢂ=½Bꢂ
2.6. Determination of pKa for donors
Twenty-five milliliter of 1 ꢁ 10ꢀ2 M from each of the donor (B)
solutions were transferred to the titration cell and titrated with
5 ꢁ 10ꢀ1 M HCl solution in presence of stream of dry nitrogen
gas. The pH value was recorded after through stirring following
each addition (0.05 ml) at room temperature. The pKa is estimated
from the following equation [26].
2.7. Determination of the formation constants of theCT-complexes (KCT
)
For the purpose of UV–vis spectral determination of the forma-
tion constants (KCT), we applied the minimum–maximum absor-
bances method according to the following procedure. One
Fig. 2. Jobs plot of CT-complexes of CHA with donors in ethanol.

162
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
milliliter (CTA) of freshly prepared stock solution (5 ꢁ 10ꢀ3 M) was
transferred into a series of 10 ml calibrated flasks. To each of these
were added different concentrations of the freshly stock donor
solution (1 ꢁ 10ꢀ2 M) and diluted to the mark with ethanol. The
least concentration of the added amine led to the minimum absor-
bance of the complex (Amin). The concentration of the donor is in-
creased gradually and the absorbance is recorded at the absorption
band of the CT-complexes (Amix) until we got the highest constant
absorbance (Amax). The CT-formation constants (KCT) were esti-
mated as given by the following equation:
Amix ꢀ Amin
Amax ¼ Amix
þ
ð1Þ
KCT ꢁ Camine
where Amax: Maximum absorbance of the complex. Amin: Minimum
absorbance of the complex. Amix: Complexes absorbance values be-
tween Amax and Amin. Camine: Concentration of the added amine in
mol Lꢀ1
.
The set of equilibrium constants were averaged [27].
3. Results and discussion
3.1. Effect of CHA concentration
The effect of reagent concentration was studied by following
the absorbance of the CT-complexes between varied amounts of
5 ꢁ 10ꢀ3 M CHA with 1 ml of 2 ꢁ 10ꢀ3 M from each of the donors
in 10 mL calibrated flasks and diluted to the mark with ethanol.
It has been found that maximum constant absorbances of the CT-
complexes were obtained with 1 mL of 5 ꢁ 10ꢀ3 M CHA.
3.2. Effect of reaction time and temperature
Reaction time and temperature was determined by following
the absorbance of the formed purple color of CT-complex develop-
ment upon mixing 1 mL of 5 ꢁ 10ꢀ3 M CHA solution with various
concentrations from each of the donors in 10 mL calibrated flasks
and diluted to the mark with ethanol. It has been found that the
purple color is formed instantly at room temperature and the CT-
complexes were stable within 2 h.
The effect of temperature on the formed complexes was stud-
ied, where the formed complexes were stable up to 40 °C as shown
in Fig. 1.
Fig. 3. Molar ratio plots for CT-complexes of CHA with donors in ethanol.
3.3. Stoichiometric ratios of the formed CT-complexes
The composition of the formed CT-complexes were determined
by applying Job’s method of continuous variations [28] and photo-
metric titrations. Fig. 2 represents the continuous variation method
curves according to Job’s Method, the maximum absorbance was
recorded at 0.5 mol fraction indicating 1:1 CT-complex formation
(donor:acceptor). Fig. 3 represents the photometric titrations
where two straight lines were produced intercepting at 1:1 ratio
(donor:acceptor).
(CHA)], [(ADMP) (CHA)], [(AP) (CHA)] and [(ADMT) (CHA)], at
529 nm for the complexes [(AMTD) (CHA)], [(AMP) (CHA)] and
[(AMT) (CHA)] and at 528 nm for the complex [(DMP) (CHA)],
respectively.
The electronic spectra were scanned against the same electron
acceptor concentration as in the working solution to eliminate
the possible overlap that may arise between CT-complex band
and that of the acceptor.
3.4. Spectral characteristics of the CT-complexes
3.5. Mechanism of the CT reaction
The electronic absorption spectra of the CT-complexes be-
tween the donors and acceptor were carried out in ethanol sol-
vent, illustrative examples of the electronic spectra are shown in
Fig. 4. once the donor and acceptor solutions are mixed, strong
change in color was observed and associated with the appear-
ance of a new symmetrical long wave length absorption band
The new, low energy absorptions observed in ethanol solu-
tions containing both a donor and acceptor have been described
by Mulliken [29] as charge CT transitions involving the excita-
tion of an electron on the donor to an empty orbital on the
acceptor. As indicated in Scheme 2, the origin of the bands of
EDA complex is understood to result from promotion of an elec-
attributing to the
These bands were located at 530 nm for the complexes [(AMMT)
p–
p* transition of the formed CT-complexes.
tron from filled
p-donor orbital to the LUMO of CHA producing a

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
163
0.5
0.4
0.3
0.2
0.1
0.0
0.30
A
B
10
0.25
0.20
0.15
0.10
0.05
10
1
1
0.00
400
500
600
700
400
500
600
700
Wavelength(nm.)
Wavelength(nm.)
0.5
0.5
0.4
0.3
0.2
0.1
C
D
10
0.4
0.3
0.2
0.1
0.0
10
1
1
0.0
400
500
600
700
400
500
600
700
800
Wavelength(nm.)
Wavelength(nm.)
Fig. 4. Electronic spectra of the CT-complexes formation between [5 ꢁ 10ꢀ4 M] CHA in ethanol in presence of various concentrations of (A) AMP (1) 1 ꢁ 10ꢀ4 ꢀ (10)
1.5 ꢁ 10ꢀ3 M, (B) ADMP (1) 1 ꢁ 10ꢀ4 ꢀ (10) 1.5 ꢁ 10ꢀ3 M, (C) DMP (1) 1 ꢁ 10ꢀ4 ꢀ (10) 1 ꢁ 10ꢀ3 M and (D) AMMP (1) 1 ꢁ 10ꢀ4 ꢀ (10) 1 ꢁ 10ꢀ3 M.
pair of radical ions. Hence one concludes that the observed new
low energy absorption bands are presumably attributed to the
radical anion of chloranilic acid (Scheme 3).The energy associ-
ated with each transition will depend on the relative energies
of the initial and electronic state [30].
3.6. Formation constants of the charge transfer reaction (KCT)
Based on the electronic spectra of the formed complexes at var-
ious concentrations of the donors, KCT were estimated by using the
minimum–maximum absorbances method, the results are
collected in Tables 2 and 3. Generally, KCT recorded higher values
suggesting the formation of stable CT-complexes. It has been found
that KCT of the formed CT-complexes depend on the pKa values of
the electron donors where a direct proportionality between KCT
and pKa values was found except for the CHA–ADMP complex
(Fig. 5). It seems that the symmetry of ADMP donor led to the for-
mation of a bifurcated hydrogen bonding interaction between the
carbonyl and hydroxyl groups of chloranilic acid with the amino
group and the ring nitrogen of ADMP. This hydrogen bonding re-
duces the electron density of the
p-system of ADMP leading to a
lower KCT value [31]. This situation will be further confirmed by
FTIR measurements in Section 3.9. The higher value of KCT for
CHA–AMMP charge transfer complex is certainly attributed to
the presence of the strongly electron donating methoxy group
and the absence of the bifurcated hydrogen bonding beside the
higher pKa value of AMMP.
The oscillator strength (f) which is a dimensionless quantity
used to express the transition probability of the CT band [32]
Scheme 2. Charge-transfer transition from HOMOs of the donor compounds and
LUMOs of the acceptor compounds.

164
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
O
O
H2N
N
Cl
CH3
H2N
N
HO
Cl
Cl
HO
Cl
CH3
N
N
OH
OH
OCH3
OCH3
O
O
AMMP
CHA
CHA
AMMP
Slow Polar Solvent
O
H2N
N
HO
Cl
Cl
CH3
N
OH
OCH3
O
AMMP
CHA
Radical Ions
Inner - sphere complex
Scheme 3. The molecular structure of compound and charge-transfer transition between CHA and donors.
tion peak of the CT-complex, respectively. As clearly observed from
Table 4, the donors with higher pKa values recorded higher oscillator
and the transition dipole moment (l) of the CT-complexes [33].
The following expressions [34] are commonly used to calculate
strengths (f) and higher dipole moments (l) which could be attrib-
these two and the results are compiled in Table 4.
uted to the higher concentration of the produced chloranilic acid rad-
ical anion. The complex CHA–ADMP reached small values of both (f)
f ¼ 4:32 ꢁ 10ꢀ9
½
emax
D
m1=2ꢂ;
ð2Þ
ð3Þ
1=2
l
¼ 0:0958½emax
D
m1=2
=
mmax
ꢂ
and (
both (f) and (
l
) in concordant with its lower KCT value. The small values of
) for the lower pKa donors confirmed the formation
l
where
D
m
isthe halfbandwidthat halfabsorbance,
e
max and
m
max are
½
of a lower concentration of chloranilic acid radical anion.
the extinction coefficient and wave number at the maximum absorp-
Table 2
Minimum, maximum and mixture concentrations (M) of the added donors at 25 °C.
Donor
Cmin ꢁ 10ꢀ4
Cmax ꢁ 10ꢀ4
Cmix ꢁ 10ꢀ4
AMTD
ADMT
DMP
AP
AMP
ADMP
AMT
1.00
1.00
1.00
1.00
1.00
1.00
0.50
1.00
20
15
10
13
15
15
7
2.00
2.00
1.50
1.50
1.50
2.00
1.00
1.50
3.00
3.00
2.00
2.00
2.00
3.00
1.50
2.00
5.00
4.00
3.00
2.50
2.50
4.00
2.00
2.50
7.00
5.00
4.00
3.00
3.00
5.00
2.50
3.00
10.00
6.00
5.00
4.00
3.50
6.00
3.00
3.50
11.00
8.00
7.00
5.00
4.00
8.00
3.50
4.00
15
10
8
7
5
10
4
5
17
13
9
10
7
13
5
7
AMMP
10
Table 3
Minimum–maximum absorbance’s data and CT-formation constants at 25 °C.
KCT (L molꢀ1) ꢁ 10
3
Donor
pKa
Amin
Amax
Amix
AMTD kmax = 529 nm
ADMT kmax = 530 nm
DMP kmax = 528 nm
AP kmax = 530 nm
AMP kmax = 529 nm
ADMP kmax = 530 nm
AMT kmax = 529 nm
AMMP kmax = 529 nm
3.56
3.94
4.28
4.30
4.64
5.11
5.62
5.71
0.042
0.055
0.014
0.078
0.079
0.023
0.051
0.089
0.204
0.308
0.124
0.366
0.418
0.251
0.408
0.401
0.061
0.101
0.023
0.115
0.126
0.023
0.051
0.122
0.073
0.123
0.031
0.149
0.169
0.049
0.085
0.165
0.095
0.150
0.055
0.180
0.200
0.074
0.130
0.212
0.116
0.156
0.062
0.197
0.238
0.085
0.176
0.236
0.143
0.152
0.219
0.101
0.278
0.302
0.141
0.264
0.304
0.172
0.186
0.262
0.116
0.343
0.384
0.197
0.325
0.370
1.83
1.99
4.14
4.17
4.51
2.63
4.65
4.91
0.190
0.092
0.245
0.282
0.125
0.215
0.276
0.246
0.110
0.315
0.335
0.172
0.298
0.342

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
165
Fig. 5. Correlation between KCT and pKa of donors.
The standard free energy changes of complexation (DG°) were
also calculated from the formation constant (KCT) using the follow-
ing equation [35].
D
Gꢃ ¼ ꢀ2:303RT log KCT
ð4Þ
The dissociation energy (W), can be calculated from the
corresponding CT energy ECT, ionization potential of the donor
(IP) and electron affinity of the acceptor (EA) using the relation-
ship [36]:
ECT ¼ IP ꢀ EA ꢀ W
ð5Þ
The energy of the
p
–
p* interaction (ECT) is calculated using the
following equation [37a]:
ECT ¼ 1243:667=kCT nm
ð6Þ
where kCT is the wavelength of the CT band of the complexes. The
ECT values calculated from Eq. (6) are listed in Table 4.
The ionization potential values of the donors are calculated by
using the Eq. (7):
IP ¼ a þ bðhmmax
Þ
ð7Þ
where h max is the
m
p–p
* transition energy in electron volts eV, a and
b are 5.11 and 0.701 [38], 4.39 and 0.857 [39] or 5.156 and 0.778
[40], respectively. The mean value calculated by these methods
and the values of (W) are collected in Table 4.The electron affinity
(EA) of CHA is 1.1 eV [37b].
Returning to Table 4 one observes that the ionization potential
of the donors are constant confirming that the same molecular
orbital of the donors
p overlaps with the same p
* of the acceptors.
On the other hand, the constancy of the ionization potential indi-
cated that Ip has a limited effect on the stability of the formed com-
plexes. The calculated values of the dissociation energy (W) of the
charge transfer excited states of the studied complexes are con-
stant suggesting that the investigated complexes are reasonably
Table 4
Energy, ionization potential, dissociation energy, oscillator strength, dipole moment
and free energy of CT-complex formation in ethanol.
Donor
pKa
ECT
(eV)
IP (eV)
W (eV)
D
G°
f ꢁ 100
l
(k J molꢀ1
)
(Debye)
AMTD
ADMT
DMP
AP
AMP
ADMP
AMT
3.56
3.94
4.28
4.30
4.64
5.11
5.62
5.71
2.35
2.35
2.36
2.35
2.35
2.35
2.35
2.35
6.72
6.72
6.76
6.72
6.72
6.72
6.72
6.72
3.27
3.27
3.26
3.27
3.27
3.27
3.27
3.27
4.48
4.53
5.05
4.97
5.02
4.69
5.93
5.07
6
1
8
2.67
3.43
2.93
4.69
4.43
3.38
4.31
5.27
2
17
10
17
25
AMMP

166
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
Table 6
Precision and accuracy of the formed CT-complexes in ethanol.
ꢄtnꢀ1S
g mlꢀ1
)
Amount found (
l
g mlꢀ1
)
Rec. (%)
X
SD
RSD
2.26
jX ꢀ
0.23
lj
Confidence limits
100.23 3.60
p
ffiffi
Donor
AMMP
Amount taken (
l
n
25.05
32.01
41.75
45.92
25.73
32.39
41.61
44.75
102.72
101.19
99.56
100.23
2.26
3.60
97.45
AP
10.80
18.28
29.08
10.72
18.96
30.43
99.26
105.31
104.64
103.07
99.160
101.11
3.32
0.33
0.51
3.22
0.33
0.50
3.07
0.84
1.11
8.25
0.82
0.81
103.07 8.25
99.16 0.82
101.11 0.81
ADMT
DMP
31.04
55.86
65.79
30.67
55.43
65.43
98.81
99.23
99.45
24.03
33.65
40.38
46.14
24.13
34.13
41.00
46.63
100.42
101.43
101.54
101.06
AMTD
AMP
46.06
56.42
69.09
45.22
56.33
69.66
98.18
99.84
100.83
99.620
99.910
1.34
1.17
1.35
1.17
0.38
0.09
3.33
2.91
99.62 3.33
99.91 2.91
17.48
27.19
31.08
17.30
27.77
31.46
98.97
99.53
101.22
t = 3.182 for n = 4 at 95% confidence level.
t = 4.303 for n = 3 at 95% confidence level.
SD, standard deviation.
RSD, relative standard deviation.
strong and stable under the studies conditions with higher reso-
nance stabilization energy [41].
formed CT-complexes are predominantly of
the planarity of the donors molecules [43].
p
–
p* type based on
As clearly observed in Table 4 the negative values of the free en-
ergy (D
G°) suggested the simultaneous production of the CT-com-
3.9.2. FTIR spectra
plexes. This is also supported by the small values of the CT energy
(2.3 eV).
The formation of CT-complexes during the reaction of the do-
nors with chloranilic acid is strongly supported by observing the
main infrared bands of the donor and acceptor in the product spec-
tra. However, the bands of the donor and acceptors in the com-
plexes spectra reveal small shifts in intensities compared with
those of the free donors and acceptor. This should be attributed
to the expected symmetry and electronic structure change upon
the formation of CT-complexes.
Chloranilic acid is a strong electron acceptor to form stable CT-
complexes with the donors. Beside this function CHA is a strong
acid (pK1 = 1.07 and pK2 = 2.24) [44], hence a proton transfer from
CHA to the donors is expected.
3.7. Quantification parameters
The quantification parameters of the formed CT-complexes are
compiled in Tables 5 and 6 where good ranges of different donors
concentration obeyed Beer’s law were found under the optimum
conditions. The limit of detection and limit of quantification
recorded small values confirming the validity of the method for do-
nors determination. On the other hand, the regression equation
predicted small values of slope, intercept and good correlation
coefficient (r) near 0.99 suggesting a very good linear relationship.
Comparison of the infrared spectral bands of the free donors
and acceptor with the corresponding ones appearing in the
IR spectra of the CT-complexes (Figs. 6 and 7) revealed the
following:
3.8. Precision and accuracy of the method
The accuracy of the method was established by performing
three and four analyses on solution containing three and four dif-
ferent amounts within the Beer’s law limits of each donor. The %
recovery recorded values near 100% confirming the accuracy of
the method. Moreover the standard deviation recorded small val-
ues suggesting the higher precision of the method. Comparison
1. The carbonyl C@O stretching vibration appearing at 1662 cmꢀ1
in the IR spectrum of (CHA) is shifted to 1643, 1637, 1620
1635,1629 and 1620 cmꢀ1 in the FTIR spectra of the CT-com-
plexes of CHA with AP,AMT,ADMT, DMP AMTD and AMP,
respectively.
of (the difference between the determined value and the true
2. The m
C–C1 vibrations appearing at (854, 839, 752 cmꢀ1) in the IR
ꢄtnꢀ1S
value) with the indeterminate error
was carried out and the
spectrum of CHA are shifted to (840, 769, 719 cmꢀ1), (839, 761,
717 cmꢀ1), (840, 827, 781 cmꢀ1), (790, 779, 721 cmꢀ1), (839,
752, 705 cmꢀ1) and (783, 759, 644 cmꢀ1) in the FTIR spectra
of the CT-complexes of CHA with AP, AMT, ADMT, DMP, AMTD
and AMP, respectively.
p
ffiffi
results were compiled in Table 6 [42]. nIt was found that (Xꢀ ꢀ
l)
p
are less than tS/ n indicating that no significant difference
between the mean and the true values.
3.9. Characterization of the solid CT-complexes
3. The asymmetric and symmetric stretching vibrations of the
amino group mas (NH2), ms (NH2) appearing at (3439,
3300 cmꢀ1) and (3255, 3091 cmꢀ1) in the IR spectra of the
donors (AMT, AMTD) are not affected on complexation with
CHA suggesting that they are not participating in hydrogen
3.9.1. Elemental analyses
The chemical analysis (Table 1) data of the isolated color solid
CT-complexes indicated the formation of 1:1 CT-complexes. The

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
167
70
60
50
40
30
20
10
0
%T
A
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
60
52.5
45
%T
B
37.5
30
22.5
15
7.5
0
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
52.5
45
%T
C
37.5
30
22.5
15
7.5
0
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
60
52.5
45
%T
D
37.5
30
22.5
15
7.5
0
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
60
50
40
30
20
10
0
%T
E
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
52.5
45
%T
F
37.5
30
22.5
15
7.5
0
4000
3500
3000
2500
2000
1750
1500
1250
1000
750
500
FTIR Measurement
1/cm
Fig. 6. FTIR spectra of CT-complexes of CHA and donors [(A) AMT, (B) ADMT, (C) AMP, (D) DMP, (E) AP, (F) AMTD] in the range 4000–400 cmꢀ1
.

168
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
Fig. 7. FTIR spectra of CHA and donors [(A) AMMP and (B) ADMP] in the range 4000–400 cmꢀ1
.
bonding with OH of CHA. On the other hand, these vibrations
are shifted to (3286, 3350 cmꢀ1) and (3331 and 3130 cmꢀ1),
respectively, confirming the formation of CT-complexes.
8. The FTIR spectrum of CHA–ADMP CT-complex is shown in
Fig. 7B where a broad band at 3157 and a shoulder at
3200 cmꢀ1 attributing to the asymmetric and symmetric
stretching vibrations of the amino group are recorded. The
disturbance of the amino group reflects the sensitivity of this
group towards hydrogen bonding interaction. The recorded
4. The IR Spectra of the formed CT complexes showed
m
(NH+)
bands at 2750 and 2997 cmꢀ1 for AP and AMP donor complexes
with CHA confirming the formation of hydrogen bonded proton
transfer complexes between OH of CHA and the ring nitrogen.
5. The IR Spectrum of CHA–ADMT CT complex showed a broad
band at 2889 cmꢀ1 is presumably attributed to
m
(NH+) and
confirming the migration of CHA phenolic proton to the ring
band at 3136 cmꢀ1 for
m
(NH3+) confirming the migration of
nitrogen through intermolecular hydrogen bonding. The m
CHA proton to the amino group of ADMT through intermolecu-
lar hydrogen bonding.
(C@O) was recorded at 1657 cmꢀ1 compared with 1667 and
1662 cmꢀ1 for CHA–AMMP and CHA, respectively. The situa-
tion confirms the formation of bifurcated hydrogen bonding
6. The FTIR spectrum of AMTD–CHA complex (Fig. 6F) showed that
this complex is a critical hydrogen bonded one (50% proton
transfer O. . .H. . .N) [45]. It showed a number of anomalies such
as the appearance of continuous absorption band extending
from 4000 to 400 cmꢀ1 [46] and the appearance of a strong
Evan hall at 790 cmꢀ1 resulting from the coupling between
the ring skeletal and protonic vibrations [47]. Another feature
in Fig. 6F is the appearance of new vibrational bands at 515,
538, 567, 590 cmꢀ1, respectively. These bands are presumably
attributed to the formation of NHN hydrogen bonding beside
OHN one in AMTD–CHA complex [48].
7. The FTIR Spectra of the CT-complexes between CHA and
AMMP and ADMP are presented in Fig. 7. Fig. 7A showed
the FTIR spectrum of CHA–AMMP complex where the sym-
metric and asymmetric stretching vibrations of the amino
group mas (NH2), ms (NH2) are recorded at 3196 and
3347 cmꢀ1 compared with 3205 and 3326 for AMMP donor.
in this complex. The formation of such bond reduces the
p
electron density of ADMP and led to a lower value of KCT as
discussed previously. The formed CT-complex between CHA
and ADMP is further confirmed by the appearance of
m (CACl)
at 784 and 676 cmꢀ1, respectively.
3.9.3. 1HNMR spectra
The proton transfer process from CHA to the donors was fur-
ther confirmed by measuring the 1HNMR spectra of the reac-
tants and the formed complexes in DMSO-d6. It has been
found that, the phenolic proton of CHA is assigned at
9.15 ppm. The 1HNMR signal of CHA disappeared in the com-
plexes of AP, AMP, ADMT, ADMP and AMMP with CHA. Instead
a new peaks are observed at 5.89, 5.78, 6.7 and 6.3 ppm for the
complexes of AP, AMP, ADMP and AMMP, respectively, attribut-
ing to NH+ proton. This situation confirmed the transfer of the
phenolic proton of CHA to the ring nitrogen of these donors in
concordance with the FTIR results. Concerning the complex
The
m
(C@O) is recorded at 1667 cmꢀ1 compared with
1662 cmꢀ1 for CHA. The shift of the amino and carbonyl
vibrations in the complex compared with those for the donor
and acceptor confirmed the formation of CT-complex between
CHA and AMMP. An important finding in Fig. 7A is the
CHA–ADMT,
a signal at 4.62 ppm is recorded attributing to
+
three protons NH3 and confirming the proton transfer from
CHA to the amino group nitrogen. The 1HNMR spectra of the
CT-complexes between the donors DMP, AMT and CHA included
the peaks of the phenolic proton of CHA at 8.98 and 9.12 ppm,
respectively. These results confirmed the absence of proton
transfer in these complexes.
appearance of
m
(NH+) at 2670 cmꢀ1 asserting the migration
of CHA phenolic proton to the ring nitrogen through intermo-
lecular hydrogen bonding. The CT-complex formation
between CHA and AMMP is further confirmed by the appear-
ance of
m .
(C-Cl) at 839 cmꢀ1

A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
169
Cl
NH2
O
Cl
O
NH2
O
HN
HN
HN
HN
HO
O
HO
O
Cl
Cl
O
CHA-AP
CHA-AMP
Cl
N
NH2
N
Cl
OH
O
N
H
OH
S
O
O
HO
O
HO
Cl
Cl
CHA-DMP
CHA-AMT
N
Cl
N
O
Cl
O
H
N
O
S
N
N
H3
N
H
O
HO
HO
NH2
O
O
Cl
Cl
CHA-ADMT
CHA-AMTD
Cl
O
NH2
NH
OH
Cl
O
N
HN
O
O
H
N
O
Cl
N
O
HO
O
Cl
H
CHA-AMMP
CHA-ADMP
Scheme 4. Structures of the formed CT-complexes of CHA with donors.
[12] B. Chakraborty, A.S. Mukherjee, B.K. Seal, Spectrochim. Acta A 57 (2001)
223.
[13] D.J. Brown, S.F. Mason, The Pyrimidines, Interscience Publishers, John Wiley
and Sons, New York, 1962.
[14] C.B. Brouillette, C.T. Chang, M.P. Mertes, J. Med. Chem. 22 (1979) 1541.
[15] E. De Dlercq, J. Descamps, G. Huang, P. Torrence, Mol. Pharmacol. 14 (1978)
422.
[16] P.V. Danenberg, Biochim. Biophys. Acta 497 (1977) 73.
[17] A.D. Da Silva, A.S. Machado, C. Tempete, M. Rebort-Gero, Eur. J. Med. Chem.
Chim. Ther. 29 (1994) 1149.
[18] S.M. Sondhi, M. Johar, S. Rajvanshi, S.G. Dastidar, R. Shukla, R. Raghubir, J.W.
Lown, Aust. J. Chem. 54 (2001) 169.
[19] M. Kidwi, S. Saxena, S. Rastogi, R. Venkataraman, Curr. Med.Chem. Ant. Infect.
2 (2004) 269.
[20] S.K. Das, G. Krishnamoorthy, S.K. Dofra, Can. J. Chem. 78 (2000) 191.
[21] G.J. Ones, J.A. Jimenez, Tetrahydon Lett. 40 (1999) 8551.
[22] G. Smilh, R.C. Bott, A.D. Rae, A.C. Willis, Aust. J. Chem. 53 (2000) 531.
[23] G. Smilh, D.E. Lynch, K.A. Byriel, C.H. Kennard, J. Chem. Crystallogr. 27 (1997)
307.
[24] G. Smilh, D.E. Lynch, R.C. Bott, Aust. J. Chem. 51 (1998) 159.
[25] D.A. Skoog, Principle of Instrumental Analysis, third ed., Saunders College
Publishing, New York, 1985 (Chapter 7).
Generally, one concludes that the molecular complexes be-
tween CHA and the donors are formed through electron and proton
transfer except for DMP and AMT complexes. The suggested struc-
tures of the formed complexes are gathered in Scheme 4.
References
[1] S. Sadeghi, E. Karimi, Chem. Pharm. Bull. 54 (2006) 1107.
[2] I.A. Darwish, Anal. Chim. Acta 549 (2005) 212.
[3] H. Kusama, H. Sugihara, J. Photochem. Photobiol. A Chem. 181 (2006) 268.
[4] S.M. Andrade, S.M.B. Costa, R. Pansu, J. Collidal. Interf. Sci. 226 (2000) 260.
[5] K. Bradley, M. Briman, A. Satr, G. Gruner, Nano Lett. 4 (2004) 253.
[6] E.M. Koswer, Porg. Phys. Org. Chem. 3 (1965) 81.
[7] F.P. Fla, J. Palour, R. Valero, C.D. Hall, JCS Perkin Trans. 2 (1991) (1925).
[8] T. Roy, K. Dutta, M.K. Nayek, A.K. Mukherjee, M. Baneriee, B.K. Seal, JCS Perkin
Trans. 2 (2000) 531.
[9] F. Yakuphanoglu, M. Arslan, Opt. Mater. 27 (2004) 29.
[10] F. Yakuphanoglu, M. Arslan, Solid State Comm. 132 (2004) 229.
[11] F. Yakuphanoglu, M. Arslan, M. Kucukislamoglu, M. Zengin, Sol. Energy 79
(2005) 96.

170
A.S. AL-Attas et al. / Journal of Molecular Structure 928 (2009) 158–170
[26] Adrien Albert, E.P. Serjeant, Ionization Constants of Acids and Bases, Methuen
and Co Ltd., London, John Wiley and Sons Inc., New York, 1962 (Chapter 2).
[27] E.D. Berman, R. Thomas, P. Stahi, R. Scott, Can. J. Chem. 65 (1987) 1954.
[28] P. Job, Ann. Chim. Phys. 9 (1928) 113.
[37] a G. Briegleb, Z. Angew. Chem. 72 (1960) 401;
b G. Briegleb, Z. Angew. Chem. 76 (1964) 326.
[38] R.C. Weast, Hand Book of Chemistry and Physics, fifteenth ed., CRC Press,
1969–1970.
[29] R.S. Mulliken, J. Am. Chem. Soc. 74 (1952) 811.
[30] G.J. Haderski, Z. Chen, R.B. Krafccik, J. Mansovi, R.J. Baker, R.L. Towns, J. Phys.
Chem. B 104 (2000) 2242.
[31] T. Kitamura, A. Hikita, H. Ishikawa, A. Fujimoto, Spectrochim. Acta A 62 (2005)
1157.
[39] A.F. Mosten, J. Chem. Phys. 24 (1956) 602.
[40] R.S. Becker, F.W. Worth, J. Am. Chem. Soc. 84 (1962) 4263.
[41] M. Pandeeswaran, K.P. Elango, Spectrochim. Acta A 65 (2006) 1148.
[42] J.C. Miller, J.N. Miller, Statistics for Analytical Chemistry, second ed., Ellis
Horwood Limited, 1988.
[32] A.B.P. Leve, Inorganic Electronic Spectroscopy, second ed., Elsevier,
Amsterdam, 1985. p. 161.
[33] E.M. Voigt, C. Reid, J. Am. Chem. Soc. 86 (1964) 3930.
[34] R. Rathone, S.V. Linderman, J.K. Kochi, J. Am. Chem. Soc. 119 (1997)
9393.
[43] S. Akyuz, T. Akyuz, J. Mol. Struct. 551 (2003) 205.
[44] M. El-Sayed, S. Agrawl, Talanta 29 (1982) 535.
[45] M.M. Habeeb, Pol. J. Chem. 69 (1995) 1428.
[46] J. Kalenik, I. Majerz, L. Sobczyk, E. Grech, M.M. Habeeb, J. Chem. Soc. Faraday
Trans. I 85 (1989) 3187.
[35] W.B. Person, J. Am. Chem. Soc. 84 (1962) 536.
[36] H.M. McConnel, J.J. Ham, J.R. Platt, J. Chem. Phys. 21 (1964) 66.
[47] E. Grech, J. Kalenik, Z. Malarski, J. Chem. Soc. Faraday Trans. 79 (1983) 2005.
[48] M.M. Habeeb, Appl. Spectrosc. Rev. 32 (1997) 103.