Spectroscopic and physical measurements on charge-transfer complexes: Interactions between norfloxacin and ciprofloxacin drugs with picric acid and 3,5-dinitrobenzoic acid acceptors

Article abstract of DOI:10.1016/j.molstruc.2011.01.049

Charge-transfer complexes formed between norfloxacin (nor) or ciprofloxacin (cip) drugs as donors with picric acid (PA) and/or 3,5-dinitrobenzoic acid (DNB) as π-acceptors have been studied spectrophotometrically in methanol solvent at room temperature. T

Full text of DOI:10.1016/j.molstruc.2011.01.049

Journal of Molecular Structure 990 (2011) 217–226
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectroscopic and physical measurements on charge-transfer complexes:
Interactions between norfloxacin and ciprofloxacin drugs with picric acid
and 3,5-dinitrobenzoic acid acceptors
c
d
Moamen S. Refat a,b, , A. Elfalaky , Eman Elesh
⇑
a Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
b Department of Chemistry, Faculty of Science, Taif University, 888 Taif, Saudi Arabia
c Department of Physics, Faculty of Science, Zagazig University, Zagazig, Egypt
d Department of Physics, Faculty of Science, Port Said University, Port Said, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Charge-transfer complexes formed between norfloxacin (nor) or ciprofloxacin (cip) drugs as donors with
Received 2 December 2010
Received in revised form 22 January 2011
Accepted 24 January 2011
Available online 31 January 2011
picric acid (PA) and/or 3,5-dinitrobenzoic acid (DNB) as p-acceptors have been studied spectrophotomet-
rically in methanol solvent at room temperature. The results indicated the formation of CT-complexes
with molar ratio1:1 between donor and acceptor at maximum CT-bands. In the terms of formation con-
stant (KCT), molar extinction coefficient (
dipole moment ( ), resonance energy (RN) and ionization potential (ID) were estimated. IR, H NMR, UV–
eCT), standard free energy (D
Go), oscillator strength (f), transition
l
Keywords:
Norfloxacin
Ciprofloxacin
Charge-transfer complexes
TG/DTG
Vis techniques, elemental analyses (CHN) and TG–DTG investigations were used to characterize the
structural of charge-transfer complexes. It indicates that the CT interaction was associated with a proton
migration from each acceptor to nor or cip donors which followed by appearing intermolecular hydrogen
bond. In addition, X-ray investigation was carried out to scrutinize the crystal structure of the resulted
CT-complexes.
Picric acid
3,5-Dinitrobenzoic zcid
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Ciprofloxacin and norfloxacin (Formula 1) are considerably a
second generation class of a synthetic fluoroquinolone [18].
Charge-transfer complexes were known to take part in many
chemical reactions like addition, substitution and condensation
[1,2]. These complexes have great attention for non-linear optical
materials and electrical conductivities [3–6]. Electron donor–
acceptor (EDA) interaction is also important in the field of drug–
receptor binding mechanism [7], in solar energy storage [8] and
in surface chemistry [9] as well as in many biological fields [10].
The charge-transfer reactions of (nor) and (cip) with picric acid
and/or 3,5-dinitrobenzoic acid have not yet been reported in the
literature, therefore the aim of our present study was directed to
investigate these reactions. Results of the elemental analyses for
the norfloxacin and ciprofloxacin charge-transfer complexes are
listed in Table 1. From this table, it can be seen that the found val-
ues are in a good agreement with the calculated ones, and the com-
position of the CT-complexes are matched with the molar ratios
presented from the photometric titration occurs between (nor) or
(cip) and picric acid and/or 3,5-dinitrobenzoic acid acceptors.
These complexes are insoluble in cold and hot water, but easily sol-
uble in dimethyl formamide (DMF) and dimethylsulfoxide, d6
(DMSO).
On the other hand, the EDA reactions of certain
successfully been utilized in pharmaceutical analysis [11]. For such
wide applications extensive studies on CT-complexes of -accep-
p-acceptors have
p
tors have been performed [12]. Charge-transfer complexes of
organic species are intensively studied because of their special type
of interaction, which is accompanied by transfer of an electron
from the donor to the acceptor [13,14]. Also, protonation of the
donor from acidic acceptors are generally root for the formation
of ion pair adducts [15–17].
2. Experimental
Norfloxacin and ciprofloxacin were of analytical reagent grade
(Merck reagent). The picric and 3,5-dinitrobenzoic acids acceptors
were supplied from Aldrich. Stock solutions of norfloxacin, cipro-
floxacin, picric acid or 3,5-dinitrobenzoic acid were freshly
prepared and spectroscopic grade that used as received.
⇑
Corresponding author at: Department of Chemistry, Faculty of Science, Port Said
University, Port Said, Egypt.
E-mail address: msrefat@yahoo.com (M.S. Refat).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.01.049

218
M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
O
O
O
N+ O-
F
CO2H
(A)
N+ O-
HO
O
O
N
N
N+
HN
C2H5
-O
N+
O
HO
N+ O-
(B)
O
N
-O
O
picric acid
3,5 dinitrobenzoic acid
F
CO2H
(A)
Formula 2. Structures of: (A) 3,5-dinitrobenzoic acid and (B) picric acid.
N
2.3.2. Electronic spectra
The electronic spectra of the donors, acceptors 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.
HN
(B)
Formula 1. (A) Norfloxacin (nor) and (B) ciprofloxacin (cip).
2.3.3. Infrared spectra
2.1. Nor-PA and nor-DNB complexes
IR measurements (KBr discs) of the solid donors, acceptor and
CT-complexes were carried out on a Bruker FT-IR spectrophotom-
eter (400–4000 cmꢀ1).
The solid CT-complexes of (nor) with acceptors (PA and DNB,
Formula 2) were prepared by mixing 1 mmol of (nor) donor in
10 mL methanol with 1 mmol of each acceptor in the same solvent
with stirring for about 6 h. The solutions were allowed to evapo-
rate slowly at room temperature, the solids precipitates filtered
off and washed several times with little amounts of the same sol-
vent and dried under vacuum over anhydrous calcium chloride.
The charge-transfer complexes: [(nor)(PA)] (yellow) formed with
2.3.4. 1H NMR spectra
1H NMR spectra were obtained on a Varian Gemini 200 MHz
spectrometer. 1H NMR data are expressed in parts per million
(ppm), referenced internally to the residual proton impurity in
DMSO solvent.
empirical formula as
C22H21FN6O10 with molecular weight
548.40 g/mol and [(nor)(DNB)] (buff) formed with empirical for-
mula as C23H22FN5O9 with molecular weight 531.42 g/mol.
2.3.5. Thermal analysis
The thermal analyses TGA, and DTG were carried under nitro-
gen atmosphere with a heating rate of 10 °C/min using a Shimadzu
TGA-50H thermal analyzers.
2.2. Preparation of cip-PA acid charge-transfer complex
The cip-PA CT complex with the general formula [(cip)(PA)] was
isolated by mixing (0.331 g, 1.0 mmol) of (cip) donor in 10 mL meth-
anol, a solution of PA was added (0.229 g, 1.0 mmol) in the same sol-
vent with continuously stirring for about 5 h at room temperature
and the solution was allowed to evaporate slowly at room temper-
ature. A pale yellow powder was formed, washed several times with
little amounts of methanol and dried under vacuum over anhydrous
calcium chloride. The empirical formula of the [(cip)(PA)] complex
is C23H21FN6O10 with molecular weight 560.45 g/mol.
3. Results and discussion
3.1. X-ray examination
For investigating the crystal structure of the obtained com-
plexes; samples in powder form were X-ray examined, the diffrac-
tion patterns were displayed. According to the obtained patterns,
the samples were in a polycrystalline form. CMPR program has
been applied to index the diffraction pattern of the investigated
materials [19], since there are no available structural data. It has
been recognized that the structure of nor/PA, cip/PA and nor/DNB
systems are well designated by monoclinic system. In Table 2,
the corresponding lattice parameters, volume and X-ray data of
[(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-complexes are given
where the volume is equal aꢁbꢁc sin b [20].
2.3. Instrumentation and physical measurements
2.3.1. Crystal structure
Structural investigations were performed utilizing X-ray dif-
fraction, PHILIPS X-Pert Diffractometer with Ni filter and Cu K
a
radiation (k = 1.5419).
Table 1
Elemental analysis CHN and physical parameters data of the [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-complexes.
Complexes
Mwt
C%
H%
N%
Physical data
m ( s)
Found
Calc.
Found
Calc.
Found
Calc.
K
l
mp (°C)
[(nor)(PA)]
[(cip)(PA)]
[(nor)(DNB)]
548.40
560.45
531.42
47.81
48.87
51.38
48.14
49.25
51.94
3.80
3.66
4.02
3.83
3.75
4.14
15.10
14.78
13.08
15.32
14.99
13.17
32
28
31
ꢂ300
ꢂ300
ꢂ300

M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
219
Table 2
The corresponding lattice parameters a, b, c, a, b, c, volume v and X-ray data of the nor-PA, cip-PA and nor-DNB complexes.
Name of sample
NOR-PA complex
System
a (Å)
b (Å)
c (Å)
a
b
c
v
(Å3)
h
k
l
2h
d-obs
d-calc
Monoclinic
8.432763
6.24722
8.279976
90
100
90
429.52
0
1
1
0
0
1
1
2
1
1
1
1
0
3
1
2
3
2
2
4
0
1
0
1
1
2
0
2
3
3
0
1
2
3
4
1
3
1
0
6.51
9.118
9.81
6.25
6.272
4.421
4.26
3.988
3.043
3.021
2.925
2.46
ꢀ1
4.471
4.156
3.99
3.029
3.007
2.923
2.47
2
ꢀ2
2
1
1
2
10.218
13.471
13.571
13.964
16.54
20.28
20.67
20.79
21.172
23.03
23.605
24.03
25.69
26.46
27.7
0
2.018
1.98
2.012
1.971
1.96
ꢀ1
4
1.969
1.9344
1.7801
1.7364
1.7078
1.5977
1.5518
1.481
1.461
4
1
1.934
1.773
1.737
1.707
1.598
1.553
1.483
1.462
ꢀ4
0
3
3
ꢀ5
2
28.1
Cip-PA complex
Cip-PA complex
Monoclinic
Monoclinic
9.309277
9.309277
9.014438
9.014438
7.103755
7.103755
90
90
91.1896
91.1896
90
90
596
596
1
0
1
ꢀ1
ꢀ2
ꢀ3
0
1
2
0
2
1
0
1
0
2
1
1
4.37
9.34
9.39
9.012
4.16
3.347
2.958
2.727
4.519
10.05
12.212
13.78
14.95
9.012
4.052
3.3416
2.965
2.730
2
2
0
0
3
1
1
3
3
2
4
4
5
1
2
2
1
0
1
3
0
2
2
2
2
1
4
17.26
17.31
2.376
2.306
2.2228
2.156
2.1345
2.0391
1.8415
1.8323
1.8010
1.7547
1.6138
1.526
2.373
2.358
ꢀ3
ꢀ4
3
4
2
18.393
18. 97
19.168
20.073
22.253
22.361
22.76
23.368
25.442
26.931
27.297
2.2218
2.1556
2.1335
2.0165
1.8374
1.8211
1.799
1.754
1.6125
1.523
4
3
ꢀ4
2
3
ꢀ3
3
1.5060
1.505
NOR-DNB complex
Monoclinic
11.186452
5.438887
10.621446
90
104.591026
90
625.39
0
1
0
0
0
0
0
0
0
0
1
1
0
0
2
1
2
3
2
4
4
4
4
3
2
7.48
7.849
9.36
5.446
5.172
4.3553
4.305
3.4178
2.692
2.5713
2.3981
2.369
2.322
2.2261
2.2051
5.62
ꢀ1
5.175
4.418
4.398
3.536
2.688
2.573
2.395
2.377
2.326
2.224
2.199
2
ꢀ2
0
9.49
11.930
15.169
15.88
17.04
17.25
17.60
18.37
18.55
ꢀ4
0
ꢀ3
1
0
ꢀ4
ꢀ5
NOR-DNB complex
11.186452
5.438887
10.621446
90
104.591026
90
625.39
0
0
1
2
0
1
0
3
2
5
5
2
4
2
1
1
3
19.91
20.83
21.416
21.76
23.57
24.03
24.501
24.851
2.059
1.964
1.9118
1.882
1.739
1.7055
1.674
1.652
2.059
1.974
1.93
1.886
1.743
1.706
1.64
ꢀ2
ꢀ4
3
5
6
2
ꢀ5
1.629
3.2. Microstructure analysis
the complexes were formed by adding X ml of 5.0 ꢃ 10ꢀ4
M
(acceptor = PA and/or DNB) (X = 0.25, 0.50, 0.75, 1.00, 1.50, 2.00,
2.50 and 3.00 ml) to 1.00 ml of 5.0 ꢃ 10ꢀ4 M of nor and/or cip as
donors. The volume of the mixtures in each case was completed
to 10 ml with the respected solvent. In the reaction mixture the
The calculation of the crystallite size of nor/PA, cip/PA and nor/
DNB complexes were performed by using simulation program [21].
Fig. 1 represents the output of the winfit program from which the
crystallite size was deduced to be 2258 Å, 1302 Å and 2260 Å,
respectively, for nor/PA, cip/PA and nor/DNB.
concentration of (nor and/or cip) was kept fixed at 0.50 ꢃ 10ꢀ4
M
in the MeOH solvent, while, the concentration of PA and/or DNB
was varied over the range of 0.125–1.500 ꢃ 10ꢀ4 M. These concen-
trations produce donor: acceptor ratios extending along the range
from 1:0.25 to 1:3.00. Spectra of the electronic absorption of the
1:1 ratio in MeOH together with the reactants donors (nor and
cip) and acceptors (PA and DNB) are shown in Fig. 2.
3.3. Electronic absorption spectra of nor/PA, cip/PA and nor/DNB system
The electronic absorption spectra of nor/PA, cip/PA and nor/DNB
systems were measured in MeOH solvent. In case of MeOH solvent

220
M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
Fig. 1. The output of the winfit program of (a) [(Nor)(PA)], (b) [(Cip)(PA)] and (c) [(Nor)(DNB)] complexes.
the detected bands at 300, 278 and 297 nm due to the [(nor)(PA)],
[(cip)(PA)] and [(nor)(DNB)] CT-complexes. In Eq. (1), K and repre-
The new characteristic absorption bands, which are not present
e
in the spectra of the reactants free acceptors (PA and DNB) and do-
nors (nor and cip), were refereed in the spectra. These bands at
about 300, 278 and 297 nm are assigned to be due to the [(nor)
(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-complexes formed charge
transfer interactions. Photometric titration curves based on these
characterized absorption bands are given in Fig. 3. The photometric
titration curves were obtained according to the well known meth-
ods by plotting of the absorbance against the X ml added of the PA
sent the equilibrium constant and extinction coefficient respec-
tively. When the Coa ꢄ Cdo/A values for each system are plotted
against the corresponding (Coa þ Cod) values straight lines were ob-
tained with a slope of 1/e and intercept of 1/Ke as shown in Fig. 4
for the reactions in MeOH. The oscillator strength f was obtained
from the approximate formula [24].
f ¼ ð4:319 ꢃ 10ꢀ9
Þemax
ꢄ
m
1=2 . . .
ð2Þ
and/or DNB as
p-acceptors [22]. In these curves the equivalent
points clearly indicate that the formed CT-complexes between
(nor and/or cip) and (PA and/or DNB) are 1:1. The formation of
1:1 complexes were strongly supported by elemental analysis,
mid infrared, 1H NMR, and thermal analysis TG/DTG. Calculations,
based upon the modified Benesi–Hildebrand (1:1) equation, were
executed for [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-com-
plexes as follow [23].
where m1/2 is the band-width at half-intensity in cmꢀ1. The oscilla-
tor strength values together with the corresponding dielectric con-
stants, D, of the solvent used are given in Table 3. Regarding Table 3,
several facts may be considered. The CT-complexes of nor and cip
have a high values of both K and e. Such high value of (K) reflects
the high stability of nor and cip complexes as a result of the ex-
pected high donation of nor and cip.
CoaCodl
A
1
Coa þ Cod
The transition dipole moments (
l) of nor and cip CT-complexes,
¼
þ
:
ð1Þ
Table 3, have been calculated from the following equation [25]:
K
e
e
where Coa and Cod are the initial concentrations of the acceptors and
l
¼ 0:0958½emaxm1=2
=mmax
ꢅ
1=2 . . .
ð3Þ
the donors, respectively. l is a path length and A is the absorbance of

M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
221
Fig. 2. Spectra of electronic absorption of: (a) nor-PA, (b) cip-PA and (c) nor-DNB reactions in MeOH.
0.90
0.75
0.60
0.45
0.30
0.15
0.69
0.66
0.63
0.60
0
1
2
3
4
ml added of DNB
0
1
2
3
4
ml added of PA
Fig. 3c. Photometric titration curve for the nor-DNB system in MeOH at 297 nm.
Fig. 3a. Photometric titration curve for the nor-PA system in MeOH at 300 nm.
100
80
60
40
20
0
0.95
0.90
0.85
0.80
0.75
0.70
0.65
60
90
120 150 180 210
-6
o
o
0.0 0.5 1.0 1.5 2.0 2.5 3.0
ml added of PA
(C + C ) X 10
a
d
Fig. 4a. The plot of (Cod þ Cao) values against (Cdo ꢄ Coa=A) values for the nor-PA system
Fig. 3b. Photometric titration curve for the cip-PA system in MeOH at 278 nm.
in MeOH at 300 nm.

222
M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
obviously is a contributing factor to the stability constant of the
30
25
20
15
10
5
complexes (a ground state property). The values of RN for the
[(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] of the studied complexes
were reported in Table 3. The standard free energy change of com-
plexation (
the following equation [19].
D
Go) was calculated from the association constants by
D
Go ¼ ꢀ2:303RT logKCT . . .
ð7Þ
where
DG
o is the free energy change of the complexes (kJ molꢀ1), R
is the gas constant (8.314 J molꢀ1 K), T is the temperature in Kelvin
and KCT is the association constant of the complexes (l molꢀ1) in
respective solvent at room temperature. The calculated values are
represented in Table 3.
0
30
45
60
75
90
-6
105
o
o
(C + C ) X 10
a
d
Fig. 4b. The plot of (Cod þ Cao) values against (Cdo ꢄ Coa=A) values for the cip-PA system
in MeOH at 278 nm.
3.4. Infrared spectra
3.4.1. [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-complexes
25
20
15
10
5
The infrared spectra of the free donors (nor and cip) and accep-
tors (PA and DNB) as well as the formed CT complexes [(nor)(PA)],
[(cip)(PA)] and [(nor)(DNB)] were discussed and their band assign-
ments were reported in Table 4. The presence of a new IR spectral
bands in the spectra of CT-complexes are confirmed the conclusion
that a deformation of the electronic environment of nor and cip oc-
curred by accepting proton from PA or DNB. The IR spectra of the
three CT-complexes of PA and DNB were characterized by the pres-
ence of detected new bands in the region ꢂ2300 to ꢂ2800 cmꢀ1
,
which are absent in the spectra of the free donors and acceptors.
These bands are attributed to the stretching vibrations of a hydro-
gen bonding [28]. These bands build up according to the proton-
ation of the +NH of the piperazine group of nor and cip donors
via the transfer of one protons from the acidic center of PA and
0
30
45
60
o
75
o
90
-6
105
(C +C ) 10
d
a
+
Fig. 4c. The plot of (Cod þ Cao) values against (Cdo ꢄ Cao=A) values for the nor-DNB
DNB acceptors to the basic center on the donor NH group. There-
system in MeOH at 297 nm.
fore an intermolecular hydrogen bond occurs, in PA or DNB accep-
tor, between the OH group and the basic center nitrogen atom in
case of nor or cip. Such assumption is strongly supported by the
existence of an absorbance bands at (1622 and 1557 cmꢀ1),
(1620 and 1562 cmꢀ1) and (1618 and 1531 cmꢀ1) for [(nor)(PA)],
[(cip)(PA)] and [(nor)(DNB)] complexes, respectively, due to +NH2
deformation and all absorbed bands ꢂ800 cmꢀ1 are attributed to
NH2 rock. The formation of +NH2 is also supported by disappear
or decrease in the stretching vibrations of OH and COOH groups
for PA and DNB, respectively.
The complexes [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] are
slightly soluble in CH3OH. The molar conductance values at
1.0 ꢃ 10ꢀ3 concentration indicated that these complexes have a
small limit of conductivity. The data of conductivity confirms that
these complexes have a positive charge (+NH2) and negative charge
(Oꢀ of acidic in PA and DNB) resulted from CT transition. The low
conductivity values for the three CT-complexes may be due to
intermolecular hydrogen bond formation.
The ionization potential (Ip) of the free (nor and cip) donors
were determined according to the CT band of complexes using
the following relationship [26,27]:
IpðeVÞ ¼ 5:76 þ 1:53 ꢃ 10ꢀ4mCT
The energy of the charge-transfer ECT of the [(nor)(PA)], [(cip)(PA)]
and [(nor)(DNB)] CT-complexes were calculated using the following
equation [25]:
ð4Þ
ECT ¼ ðhmCTÞ ¼ 1243:667=kCT ðnmÞ
The molar extinction coefficient of the complexes at the maximum
ð5Þ
of the CT absorption ( max) can be calculated as follows [19];
e
emax ¼ 7:7 ꢃ 10ꢀ4=½h
where kCT is the wavelength of the complexation band, RN is the res-
onance energy (RN), CT is the frequency of the CT peak and RN is the
mCT=½RNꢅ ꢀ 3:5ꢅ
ð6Þ
m
Accordingly, the hydrogen bonding between the donors and the
acceptors can be formulated as: (see Formula 3–5).
resonance energy of the complexes in the ground state, which,
Table 3
Spectrophotometric results in MeOH solvent at 25 °C.
kmax (nm)
ECT (eV)
K (l molꢀ1
)
emax (l molꢀ1 cmꢀ1
0.50 ꢃ 104
)
f ꢁ 103
2.00
l
ꢁ 103
Ip
D
RN
D
Go (25 °C) kJ molꢀ1
[(nor)(PA)]
300
4.14
12.00 ꢃ 104
5.00 ꢃ 104
4.00 ꢃ 104
13.00
38.00
32.00
9.04
10.04
10.93
33
33
33
0.141
0.617
0.672
28,981
26,812
26,259
[(cip)(PA)]
278
4.47
3.60 ꢃ 104
21.00
12.00
[(nor)(DNB)]
297
4.19
2.80 ꢃ 104

M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
223
3.5. 1H NMR spectra of [(nor)(PA)], [(cip)(PA)] and [(nor)DNB)] CT-
complexes
Table 4
Infrared frequenciesa (cmꢀ1) and tentative assignments for [(nor)(PA)], [(cip)(PA)] and
[(nor)(DNB)] complexes.
1H NMR spectra of (nor and cip) as free donors, (PA and DNB) as
[(nor)(PA)] [(cip)(PA)] [(nor)(DNB)] Assignments
a free acceptors and [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] com-
plexes in DMSO at room temperature were measured. The chemi-
cal shifts (ppm) of proton NMR for the detected peaks are assigned
and listed in Table 5. The results obtained from elemental analysis
and photometric titrations designate the same way with 1H NMR
spectra to suggest the mode of interaction between donor and
acceptor as follows:
3471 vw
3861
vw,br
3741 vw
3437 w,br
3744 vw
3423 s,br
m
(NAH) + m(OAH)
3442 w,br
3200 vw
3184 w
3072 m
2976 vw
2844 w
2762 w
2718 w
2471 m
2363 m
3147 vw
3062 w,br 3052 ms
3088 vw
m
(CAH) hydrogen bond
2926 w
2835 w
2752 w
2485 m
2361 ms
2972 m
2927 vw
2835 m
2715 w,br
2472 m
2368 vw
i. In case of [(nor)(PA)] and [(cip)(PA)] CT-complexes, the sig-
nal distinguishing proton of OH of PA acceptor at 8.90 ppm
was disappeared due to deprotonation from acceptor-to-
donor. Besides, the formation of new signals at 4.611 and
3.883 ppm for [(nor)(PA)] and [(cip)(PA)] CT-complexes,
respectively, due to the presence of +NH2. The located of sig-
nals at 15.274 ppm for [(nor)(PA)] and at 15.190 ppm for
[(cip)(PA)] were assigned to the proton of carboxylic group
of nor and cip, which confirms the non participation of
COOH in the complexation process.
ii. The mode of chelation concerning [(nor)(DNB)] complex was
sustained by the presence of signal at 4.60 ppm due to the
formation of +NH2 and absence of signal at 13.600 ppm
was assigned to proton of COOH. These results match to each
other according to the sharing of proton of carboxylic group
of (DNB) acceptor with NH of piperazine ring (cip, donor).
1721 vs
1622 vs
1698 s
1620 vs
1718 vs
1618 vs
m
m
(C@O): (COOH)
(C@O) + db(H2O) + ddef(NAH);
+NH2
1557 s
1562 m
1531 s
1488 s
Phenyl breathing modes
1476 vs
1325 s
1319 s
1262 s
1210 vw
1500 vs
1392 w
1346 vs
1262 vs
CH; deformation of ACH2A
db(CH2)
1263 s
m
(CAC)
1169 vw
1089 w
1026 mw
1160 w
1073 w
1030 m
1077 s
1028 w
m(CAO) + m(CAN) + m(CAC) + dr(CH2)
932 w
897 vw
857 vw
813 w
797 w
961 vw
939 vw
895 m
830 vw
815 vw
796 vw
929 s
CH-bend; phenyl
drock
+NH2
831 vw
819 vw
805 vw
;
3.6. Thermal analysis studies
The [(nor)(PA)] complex starts to decompose at ꢂ290 °C with
simultaneous decomposition. The TG/DTG profile of this complex
is shown in Fig. 5a. From TG curve, it appears that the sample
decomposes in two stages over the range 290–800 °C. The first
decomposition occurs between 284 and 304 °C with a mass loss
of 42.43% while the second decomposition starts at 305 °C and
ends at 800 °C with a 49.10% mass loss. Both decomposition stages
(which may be attributed to the loss of C18H21FN6O10), is in reason-
able agreement with the theoretical value of 91.25% over the whole
range of temperature.
749 ms
702 s
780 vw
746 vw
702 ms
722 vs
db(COOꢀ)
557 m
510 m
451 vw
545 w
471 vw
431 w
563 ms
521 ms
466 vw
425 vw
Ring deformation
d(ONO); PA
CNC deformation
m
, stretching; d, bending.
s = strong, w = weak, m = medium, sh = shoulder, v = very, br = broad;
a
O
O
N
F
HO
N
H
N
-O
O
N+
H
O
O
O
N+
O-
N+
O-
Formula 3. Structure of [(nor)(PA)] CT-complexes.

224
M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
O
O
F
HO
N
N
O
H
N+ O-
N
H
O
O
N+
O
-O
Formula 4. Structure of [(nor)(DNB)] CT-complexes.
O
O
F
HO
N
N
H
N
-O
O
N+
H
O
O
O
N+
N+
O-
O-
Formula 5. Structure of [(cip)(PA)] CT-complexes.
Table 5
1H NMR spectral data of free nor, [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] complexes.
nor
[(nor)(PA)]
[(cip)(PA)]
[(nor)(DNB)]
Assignments
1.13
2.0
1.442, 1.563
–
1.334
–
1.408
–
d H, ACH3
d H, ANH; piperazine
2.78, 3.10,
3.47
2.665, 3.433, 4.611
2.602, 2.665
2.670, 3.442, 3.549, 4.600
d H, ACH2; piperazine d H, ACH2;
ACH2CH3
3.412, 3.493, 3.673, 3.883
+NH2
5.93, 7.12,
8.01
15.00
7.239, 7.869, 8.587,
8.956
15.274
7.461, 7.622, 7.973, 8.586, 8.685,
8.857
15.215
7.237, 7.847, 7.913, 8.800, 8.877,
8.923
–
d H, ACH aromatic
d H, ACOOH
Regarding Fig. 5b, [(nor)(DNB)] CT-complex thermally decom-
poses in three successive steps within the temperature rang 25–
800 °C. The decomposition steps started clearly at 300 °C with
experimental weight loss of 14.25%, 28.39%, and 53.24%, respec-
tively, were attributed to the loss of C21H22FN5O9 organic moiety
with a final residual carbon.
metric analysis at 305 °C. The first stage ranges from 284 till
314 °C with a weight loss 44.50% and the second stage extend to
800 °C with 53.89% weight loss.
3.7. Kinetic studies
As indicated in Fig. 5c, the charge transfer of [(cip)(PA)] complex
decomposes in two stages with a sharp differential thermogravi-
Two major different methods were applied for the evaluation of
kinetic parameters as follow:

M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
225
Fig. 5a. TG–DTG curve of [(nor)(PA)] charge-transfer complex.
Fig. 5b. TG–DTG curve of [(cip)(PA)] charge-transfer complex.
Fig. 5c. TG–DTG curve of [(nor)(DNB)] charge-transfer complex.
straight line the slope of which is E, and Z can be deduced according
i. Horowitz and Metzger (HM) approximation method [29].
to the relation:
Consider the following relation [29]:
ꢀ
ꢁ
E
u
E
RTm
E
Z ¼
exp
. . .
ð9Þ
ln½ꢀ lnð1 ꢀ
aÞꢅ ¼
H
. . .
ð8Þ
RT2m
RTm
where
a, is the fraction of the sample decomposed at time t and
where
u
is the linear heating rate. The order of reaction, n, can be
H
= T ꢀ Tm.A plot of ln [ꢀln (1 ꢀ )] against was found to be
a
H
calculated regarding the following relation:

226
M.S. Refat et al. / Journal of Molecular Structure 990 (2011) 217–226
Table 6
Kinetic parameters of [(nor)(PA)], [(cip)(PA)] and [(nor)(DNB)] CT-complexes.
Method
n
Parameter
r
E (kJ molꢀ1
)
Z (sꢀ1
)
D
S (J molꢀ1 Kꢀ1
)
D
H (kJ molꢀ1
)
D )
G (kJ molꢀ1
[(nor)(PA)]
HM
CR
1
1
470
456
4.82 ꢃ 1039
3.98 ꢃ 1023
ꢀ509
ꢀ501
471
423
163
154
0.9669
0.9666
[(cip)(PA)]
HM
CR
1
1
123
67.1
1.72 ꢃ 109
1.18 ꢃ 104
ꢀ73.6
ꢀ172
118
134
160
146
0.9992
0.9961
[(nor)(DNB)]
HM
CR
1
1
27.2
23.2
1.03
ꢀ250
ꢀ266
22.6
18.7
160
165
0.9966
0.9973
1.42 ꢃ 101
n = number of decomposition steps.
n ¼ 33:64758 ꢀ 182:295am þ 435:9073a2m ꢀ 551:157am3
þ 357:3703a4m ꢀ 93:4828a5m
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(2005) 96.
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223.
ð10Þ
[7] A. Korolkovas, Essentials of Medical Chem, second ed., Wiley, New York, 1998
(Chapter 3).
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733.
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[10] A.M. Slifkin, Charge-transfer Interaction of Biomolecules, Academic Press, New
York, 1971.
where am is the fraction of the substance decomposed at Tm.
ii. Coats and Redfern (CR) integral method [30].
For first-order reactions, the following equation of Coats–Red-
fern is fulfilled:
ꢂ
ꢃ
ꢀ
ꢁ
ꢀ ln ð1 ꢀ
a
Þ
ZR
E
RT
ln
¼ ln
ꢀ
. . .
ð11Þ
[11] F.M. Abou Attia, Farmaco 55 (2000) 659.
[12] K. Basavaiah, Farmaco 59 (2004) 315.
T2
u
E
ꢀ lnð1ꢀ
a
A plot of ln½
Þꢅ against 1/T was found to be linear. From the
[13] S.K. Das, G. Krishnamoorthy, S.K. Dofra, Can. J. Chem. 78 (2000) 191.
[14] G. Jones, J.A.C. Jimenez, Tetrahedron Lett. 40 (1999) 8551.
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307.
2
slope E was caTlculated and Z can be deduced from the intercept.
The enthalpy of activation,
DH, and the free enthalpy of activation,
D
G, can be calculated via the equations:
[18] http://www.faqs.org/rulings/rulings1999HQ545710.html.
[19] G. Briegleb, J. Czekalla, Z. Physikchem. (Frankfurt) 24 (1960) 237.
[20] B.D. Culity, X-ray Diffraction, Addison Wesley, London, 1959.
[21] Winfit 1.2.1, 1997, <http://xray.cz/ecm/cm/>.
[22] D.A. Skoog, Principle of Instrumental Analysis, third ed., Saunders College
Publishing, New York, USA, 1985 (Chapter 7).
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[24] H. Tsubomura, R.P. Lang, J. Am. Chem. Soc. 86 (1964) 3930.
[25] R. Rathone, S.V. Lindeman, J.K. Kochi, J. Am. Chem. Soc. 119 (1997) 9393.
[26] G. Aloisi, S. Pignataro, J. Chem. Soc. Faraday Trans. 69 (1972) 534.
[27] G. Briegleb, Z. Angew. Chem. 72 (1960) 401;
D
H ¼ E ꢀ RTm; G ¼ H ꢀ TmDS . . .
The evaluated kinetic parameters, using of the above two men-
D
D
ð12Þ
tioned methods by graphical means, are listed in Table 6. The sat-
isfactory value of correlation coefficient (r ꢂ 1) in all cases
indicates reasonable agreement between experimental data and
the values of kinetic parameters.
References
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[30] A.W. Coats, J.P. Redfern, Nature (London) 201 (1964) 68.
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