Synthesis, spectroscopic and thermal studies of charge-transfer molecular complexes formed in the reaction of 1,4-bis (3-aminopropyl) piperazine with σ- And π acceptors

Article abstract of DOI:10.1016/j.molstruc.2012.01.002

In the present study, solid charge-transfer (CT) molecular complexes formed in the reaction of the electron donor 1,4-bis (3-aminopropyl) piperazine (APPIP) with the σ-electron acceptor iodine and π-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetra

Full text of DOI:10.1016/j.molstruc.2012.01.002

Journal of Molecular Structure 1011 (2012) 172–180
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic and thermal studies of charge-transfer molecular
complexes formed in the reaction of 1,4-bis (3-aminopropyl) piperazine
with
r- and p acceptors
b
b
Siham Y. AlQaradawi a, , Adel Mostafa , Hassan S. Bazzi
⇑
a Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha, Qatar
b Department of Chemistry, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, solid charge-transfer (CT) molecular complexes formed in the reaction of the elec-
Received 26 November 2011
Received in revised form 1 January 2012
Accepted 2 January 2012
tron donor 1,4-bis (3-aminopropyl) piperazine (APPIP) with the
r-electron acceptor iodine and p-accep-
tors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ), and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been investigated
spectrophotometrically in chloroform at 25 °C. These were characterized through electronic and infrared
spectra as well as elemental and thermal analysis. The obtained results showed that the formed solid CT-
Available online 9 January 2012
Keywords:
1,4-Bis (3-aminopropyl) piperazine
Iodine
TBCHD
Charge-transfer
Spectra
complexes have the formulas [(APPIP) I]+ Iꢀ, [(APPIP)(TCNQ)], [(APPIP)2(TCNE)3], [(APPIP)(DDQ)] and
3
[(APPIP)(TBCHD)] in full agreement with the known reaction stoichiometries in solution as well as the
elemental measurements. The formation constant KCT, molar extinction coefficient
change
G0, CT energy ECT and the ionization potential Ip have been calculated for the CT complexes
[(APPIP) I]+ Iꢀ3 , [(APPIP)(TCNQ)], [(APPIP)(DDQ)] and [(APPIP)(TBCHD)].
eCT, free energy
D
Thermal analysis
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
electronics, optical devices and others [19]. These interactions play
in biological systems very important roles [20]; beside that CT-
complexes act as intermediate in a wide variety of reactions
involving nucleophiles and electron deficient molecules. In the pa-
per herein, we report the formation of five new CT-complexes pro-
duced from the reaction of 1,4-bis (3-aminopropyl) piperazine
The piperazines are a broad class of chemical compounds, many
with important pharmacological properties which contain a core
piperazine functional group. Piperazines are also used in the man-
ufacture of plastics, resins, pesticides and brake fluid. The charge-
transfer (CT) complexes formed in the reactions of
r
- and
p
-elec-
with the p-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ),
tron acceptors with organic electron donors have a great attention
for non-linear optical materials and electrical conductivities and
owing to their significant physical and chemical properties [1–4].
The chemical and physical properties of charge-transfer (CT) com-
tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone
(TBCHD) and
r-acceptor iodine in CHCl3 as the solvent. The aim
of this work is to make an assessment of the correct nature and
stoichiometry of each of the resulting new CT-complexes formed
with each acceptor.
plexes formed in the reactions of p- and r-electron acceptors with
different donors like amines, polysulfur, crown ethers bases and
oxygen–nitrogen mixed bases have been the subjects of many
studies both in solution and in solid state [5–14]. The formation
of a particular polyiodide species depends strongly on the nature
of the donor base and in some cases on the method of preparation
2. Experimental
Reagent grade chemicals were used in this study and purchased
from Sigma–Aldrich, USA, and used as received. The electronic
absorption spectra of the CHCl3 solutions of the solid CT-complexes
formed in the reactions of the donor 1,4-bis (3-aminopropyl) piper-
azine (APPIP) and the acceptors iodine, 7,7,8,8-tetracyanoquinodi-
methane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,
6-dicyano-1,4-benzoquinone (DDQ), and 2,4,4,6-tetrabromo-2,
5-cyclohexadienone (TBCHD) as well as the reaction products were
checked in the region 1200–250 nm using a lambda 950 Perkin El-
mer UV–Vis–NIR spectrometer with quartz cell of 1.0 cm path
[15–18]. The p-electron acceptors 7,7,8,8-tetracyanoquinodimeth-
ane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
and tetracyanoethylene (TCNE) are known to form stable colored
CT-complexes with many donor bases. The increased interest in
the study of charge-transfer interactions stems from the various
applications that CT-complexes can have. These include solar cells,
⇑
Corresponding author. Tel.: +974 55507904; fax: +974 44838650.
E-mail address: siham@qu.edu.qa (S.Y. AlQaradawi).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.01.002

S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
173
of each of the donors to a saturated solution (85 ml) of each of
the acceptors. The mixture in each case was stirred for about
10–15 min. The mixing of reactants was associated with a strong
change in color. The resulting precipitate in each case was filtered
immediately and washed several times with minimum amounts of
CHCl3 and dried under vacuum. The complexes were characterized
using spectroscopic techniques (FTIR and UV–Vis) and by elemen-
tal analysis (theoretical values are shown in brackets):
[(APPIP) I]+ Iꢀ3 dark brown complex (M/W: 707.94 g); C, 16.89%
(16.95%) H, 3.36% (3.39%); N, 7.89% (7.91%); [(APPIP)(TCNQ)] dark
green complex (M/W: 404.51 g); C, 65.31% (65.26%); H, 6.96%
(6.92%); N, 27.65% (27.69%); [(APPIP)(TCNE)] yellow complex (M/
W: 784.91 g); C, 58.15% (58.1%); H, 6.18% (6.11%); N, 35.63%
(35.67%). [(APPIP)(DDQ)] reddish pink complex (M/W: 427.33 g);
C, 50.51% (50.55%); H, 5.66% (5.62%); N, 19.69% (19.66%) and [(AP-
PIP)(TBCHD)] apricot complex (M/W: 610.02 g); C, 31.51%
(31.47%); H, 4.29% (4.26%); N, 9.21% (9.18%).
3. Results and discussion
3.1. UV–Vis absorption spectra
The UV/vis absorption spectra of 1 ꢁ 10ꢀ3 M solution of the do-
nor 1,4-bis (3-aminopropyl) piperazine (APPIP) with acceptors io-
dine (1 ꢁ 10ꢀ3 M), 7,7,8,8-tetracyanoquinodimethane (TCNQ)
(3 ꢁ 10ꢀ3 M), tetracyanoethylene (TCNE) (5 ꢁ 10ꢀ3 M), 2,3-di-
chloro-5,6-dicyano-p-benzoquinone (DDQ) (3 ꢁ 10ꢀ3 M), and
2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) (5 ꢁ 10ꢀ3 M)
solutions along with those of the formed CT-complexes in CHCl3
are shown in Figs. 1–5, respectively. Once the donor and acceptor
solutions were mixed, strong change in color was observed and
was associated with the appearance of new absorption bands in re-
gions where neither donor nor acceptors have any absorption. This
is a clear indication of the formation of CT-complexes. These CT
absorptions appeared at 367 and 296 nm for (APPIP)–iodine mix-
ture, 860, 758 and 633 nm for (APPIP)–(TCNQ) mixture, 426 and
404 nm for (APPIP)–(TCNE) mixture, 742, 488 nm for (APPIP)–
(DDQ) mixture and at 513 nm for (APPIP)–(TBCHD) mixture. Table
1 shows the spectroscopic data of the resulting CT-complexes.
Photometric titration measurements were performed to deter-
mine the course of the reaction in CHCl3 between the donor and
each of the acceptors. These measurements were based on the
absorption bands of the formed CT-complexes.
O
CN
NC
O
C
N
Br
Cl
Cl
N
C
N
NC
NC
Br
C
N
C
O
Br
Br
NC
CN
TCNE
TCNQ
DDQ
TBCHID
length. Elemental analysis was done using a Perkin Elmer CHNSO
elemental analyzer model 2400 series II. The infrared spectra of
the reactants, APPIP, TCNQ, TCNE, DDQ and TBCHD (iodine has no
infrared activity) and the obtained CT-complexes (KBr pellets) were
recorded on a spectrum one Perkin Elmer FTIR spectrometer while
thermogravimetric analysis (TG & DTG) were performed using Per-
kin Elmer computerized thermal analyzer model Pyris 6 TGA under
Strong change in color is observed upon mixing of CHCl3 solu-
tion of iodine with the donor 1,4-bis (2-aminopropyl) piperazine
flow of nitrogen gas (20 ml minꢀ1) with heating rate of 10 °C minꢀ1
.
Photometric titration measurements were performed for the
reactions between the donor APPIP and each of the acceptors io-
dine, TCNQ, TCNE, DDQ and TBCHD in CHCl3 at 25 °C in order to
determine the reaction stoichiometries according to a literature
method [5,21]. The measurements were conducted under the con-
ditions of fixed donor APPIP concentrations while those of the
acceptors I2, TCNQ, TCNE, DDQ, and TBCHD were changed over a
wide range, to produce in each case reaction solutions where the
molar ratio of donor:acceptor varies from 1:0.25 to 1:4. The peak
absorbencies of the formed CT complexes were measured for all
solutions in each case and plotted as a function of the acceptor
to donor molar ratio. The infrared spectra of the reactants and
the formed CT complexes (KBr pellets) were recorded on a spec-
trum one Perkin–Elmer FTIR spectrophotometer.
The five solid CT-complexes formed in the reaction of APPIP
with each of I2, TCNQ, TCNE, DDQ and TBCHD were isolated in
CHCl3 by the drop wise addition of a saturated solution (70 ml)
Fig. 1. Electronic absorption spectra of 1,4-bis (3-aminopropyl) piperazine (APPIP)–
I
2 reaction in CHCl3. (A) [APPIP] = 1 ꢁ 10ꢀ3 M; (B) [I2] = 1 ꢁ 10ꢀ3 M; (C) 1:2 APPIP–I2
mixture, [APPIP] = [I2] = 1 ꢁ 10ꢀ3 M.

174
S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
Fig. 5. Electronic absorption spectra of 1,4-bis (3-aminopropyl) piperazine (APPIP)–
TBCHD reaction in CHCl3. (A) [APPIP] = 1 ꢁ 10ꢀ3 M; (B) [TBCHD] = 5 ꢁ 10ꢀ3 M; (C)
1: APPIP–TBCHD mixture, [APPIP] = 1 ꢁ 10ꢀ3 M and [TBCHD] = 5 ꢁ 10ꢀ3 M.
Fig. 2. Electronic absorption spectra of 1,4-bis (3-aminopropyl) piperazine (APPIP)–
TCNQ reaction in CHCl3. (A) [APPIP] = 1 ꢁ 10ꢀ3 M; (B) [TCNQ] = 3 ꢁ 10ꢀ3 M; (C) 1:1
APPIP–TCNQ mixture, [APPIP] = 1 ꢁ 10ꢀ3 M and [TCNQ] = 3 ꢁ 10ꢀ3 M.
Table 1
Spectroscopic data for the CHCl3 solutions of solid CT-complexes of APPIP with the
acceptors I2, TCNQ, TCNE, DDQ and TBCHD.
Complex
Color
Absorptiona
(nm)
Stoichiometry
(donor:acceptor)
[(APPIP) I]+ Iꢀ3
Dark
brown
Dark
367s, 296s
1:2
1:1
[(APPIP)(TCNQ)]
860m, 758w,
633sh
green
[(APPIP)2(TCNE)3] Yellow
426s, 404m
742h, 488s
1:1½
1:1
[(APPIP)(DDQ)]
Reddish
pink
[(APPIP)(TBCHD)] Apricot
513h
1:1
a
The reactants APPIP, Iodine, TCNQ, TCNE, DDQ and TBCHD have no measurable
absorptions in the region of study with used concentrations; m, medium; s, strong;
sh, shoulder; h, hump.
Fig. 3. Electronic absorption spectra of 1,4-bis (3-aminopropyl) piperazine (APPIP)–
TCNE reaction in CHCl3. (A) [APPIP] = 1 ꢁ 10ꢀ3 M; (B) [TCNE] = 5 ꢁ 10ꢀ3 M; (C) 1:1½
APPIP–TCNE mixture, [APPIP] = 1 ꢁ 10ꢀ3 M and [TCNE] = 5 ꢁ 10ꢀ3 M.
Fig. 6. Photometric titration curves for 1,4-bis (3-aminopropyl) piperazine (APPIP)–
I2 reaction in CHCl3 measured at 367 and 296 nm.
Fig. 4. Electronic absorption spectra of 1,4-bis (3-aminopropyl) piperazine (APPIP)–
DDQ reaction in CHCl3. (A) [APPIP] = 1 ꢁ 10ꢀ3 M; (B) [DDQ] = 3 ꢁ 10ꢀ3 M; (C) 1:1
APPIP–DDQ mixture, [APPIP] = 1 ꢁ 10ꢀ3 M and [DDQ] = 3 ꢁ 10ꢀ3 M.
Strong absorption bands, due to the formed product, appeared
at 365 and 290 nm for APPIP–I2. Photometric titration measure-
ments for the reaction in CHCl3 were performed. The molar ratio
was found to be 1:2, as shown in Fig. 6. This reaction stoichiometry
was supported by the obtained elemental analysis of the formed
solid products. However, the two absorption bands of the formed
iodine complex around 367 and 296 nm in Fig. 1, are known to
be characteristics of the formation of the polyiodide ion of the type
Iꢀ3 [22]. The reactions should be as in the following steps.
(APPIP), as the solution turned into an intense dark brown color.
This color, that is not associated with either of the reactants, indi-
cates the existence of charge-transfer interactions between iodine
and the donor. The electronic absorption spectra of the reactants
along with the CT-complex formed with iodine/APPIP are shown
in Fig. 1.

S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
175
(i) ðAPPIPÞ þ I2 ! ½ðAPPIPÞꢂ ꢃ I2
ꢄ
Formation of the inner complex,
(ii) ½ðAPPIPÞꢂ ꢃ I2 ! ½ðAPPIPÞIꢂþ ꢃ Iꢀ
ꢄ
Formaþtion of the triiodide CT-complex,
(iii) ½ðAPPIPÞIꢂ Iꢀ þ I2 ! ½ðAPPIPÞIꢂþIꢀ3
The structure of the formed CT-complex should be [(APPIP) I]+
Iꢀ3 and the formation of iodide intermediate [(APPIP) I]+ꢃIꢀ is char-
acterized by its known absorption [23] at 245 nm and the forma-
tion of [(APPIP) I]+ I3ꢀ could be understood considering the
previous three reaction steps.
Interestingly, the donor–acceptor molar ratio was found to be
the same for TCNQ, DDQ and TBCHD and different for TCNE. The
APPIP:acceptor ratios were found to be 1:1 for the TCNQ, DDQ
and TBCHD complexes and 1:1½ for TCNE complex as shown in
Figs. 6–10. These obtained reaction stoichiometries are in very
good agreement with the obtained elemental analysis for the solid
CT-complexes.
Fig. 9. Photometric titration curve for 1,4-bis (3-aminopropyl) piperazine (APPIP)–
DDQ reaction in CHCl3 measured at 488 nm.
Accordingly, the formed CT-complexes are formulated as [(AP-
PIP) I]+ Iꢀ3 , [(APPIP)(TCNQ)], [(APPIP)2(TCNE)3], [(APPIP)(DDQ)]
and [(APPIP)(TBCHD)] with colors dark brown, dark green, yellow,
reddish pink and apricot, respectively.
This variation in reaction stoichiometries (donor:acceptor)
could be associated with the molecular steric hindrance of the
acceptor which is expected to be higher in the case of TCNQ,
DDQ and TBCHD lowering the donor:acceptor ratio compared with
that of TCNE where the ratio is 1:1½. This finding agrees quite well
with the fact that TCNE always form CT-complexes with higher ra-
Fig. 10. Photometric titration curve for 1,4-bis (3-aminopropyl) piperazine
(APPIP)–TBCHD reaction in CHCl3 measured at 513 nm.
tios compared with the aromatic acceptors. [24,25]. It is of interest
to note that the CT-electronic transition in the five complexes has
different band structure and occurs at different wavelength values
as clarified above. The formation constant (KCT) and molar extinc-
tion coefficient (eCT) values for the formed CT-complexes of the do-
nor 1,4-bis (3-aminopropyl) piperazine (APPIP) with iodine, TCNQ,
DDQ and TBCHD in CHCl3 at 25 °C were calculated.
The 1:1 modified Benesi–Hildebrand Eq. (1) [26] was used to
calculate the values of the formation constant, KCT (L molꢀ1), and
the molar extinction coefficient eCT (L molꢀ1 cmꢀ1), for the com-
plexes [(APPIP)(TCNQ)], [(APPIP)(DDQ)] and [(APPIP)(TBCHD)].
Fig. 7. Photometric titration curves for 1,4-bis (3-aminopropyl) piperazine (APPIP)–
TCNQ reaction in CHCl3 measured at 860, 758 and 633 nm.
A0D0‘
A
1
A0 þ D0
¼
þ
ð1Þ
ke
e
The corresponding spectral parameters for the complex [(APPIP)
I]+ Iꢀ3 , was calculated using the known [27] Eq. (2) of 1:2
complexes:
2
ðA0Þ D0‘
1
A0ðA0 þ 4D0Þ
¼
þ
ð2Þ
A
ke
e
where A0 and D0 are the initial concentrations of the acceptors and
donors, respectively, while A is the absorbance at the mentioned CT
bands and ‘ is the cell path length (1 cm).
The data obtained throughout this calculation are given in
Table 2.
Plotting the values of A0D0‘/A against (A0 + D0) values of Eq. (1)
Fig. 8. Photometric titration curves for 1,4-bis (3-aminopropyl) piperazine (APPIP)–
TCNE reaction in CHCl3 measured at 426 and 404 nm.
and plotting values of (A0)2D0‘/A versus A0 (A0 + 4D0) values of Eq.

176
S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
Table 2
Spectrophotometric and free energy change results of CT-complexes of [(APPIP) I]+ I3ꢀ
[(APPIP)(TCNQ)], [(APPIP)(DDQ)] and [(APPIP)(TBCHD)] in CHCl3.
,
Complex
KCT
kmax
(nm)
ꢀ
D
G0
(cal molꢀ1
ECT
(eV)
eCT
(L molꢀ1
)
)
(L molꢀ1 cmꢀ1
)
[(APPIP) I]+ Iꢀ3
33.0 ꢁ 103 296
6.160 ꢁ 103 4.20 0.434 ꢁ 103
5.622 ꢁ 103 1.45 0.438 ꢁ 103
4.327 ꢁ 103 2.55 0.700 ꢁ 103
3.001 ꢁ 103 2.42 0.237 ꢁ 103
[(APPIP)(TCNQ)] 13.28 ꢁ 103 860
[(APPIP)(DDQ)]
1.49 ꢁ 103 488
[(APPIP)(TBCHD)] 0.16 ꢁ 103 513
Fig. 11. The plots of A0 (A0 + 4D0) values against [(A0)2D0‘/A] values of the charge-
transfer complex [(APPIP) I]+ I3ꢀ at 296 and 367 nm.
Fig. 13. Benesi–Hildebrand plots for the CT-complexes: (A) [(APPIP)(DDQ)] at
488 nm and (B) [(APPIP)(TBCHD)] at 513 nm.
has four strong withdrawing cyano groups in conjugation with an
aromatic ring which causes high delocalization leads to a great in-
crease in the Lewis acidity of the acceptor, (TCNQ), and hence the
higher value of KCT for [(APPIP)(TCNQ)] CT-complex compared with
those of the other used acceptors except that of iodine. This cer-
tainly, allows stronger electron donation from APPIP base to the
two acceptors DDQ and TCNQ compared with that with TBCHD.
Accordingly the donation from APPIP to acceptors are in the order
of I2 > TCNQ > DDQ > TBCHD. An unsuccessful attempt was made
to calculate the corresponding values of KCT and eCT for the 1:1½
complex [(APPIP)2(TCNE)3]. The 1:1½ stoichiometric ratio has
many complicated terms to deal with and we might in the future
overcome this problem and publish these results.
Fig. 12. Benesi–Hildebrand plots for the CT-complex [(APPIP)(TCNQ)] at 860, 756
and 633 nm.
The free energy change
D
G0 (cal molꢀ1) values of the complexes
[(APPIP) I]+ Iꢀ3 , [(APPIP)(TCNQ)], [(APPIP)(DDQ)] and [(AP-
PIP)(TBCHD)] were calculated from Gibbs free energy of formation
according to Eq. (3) [28,29]:
(2), straight lines were obtained with a slop of 1/eCT and intercept
of (1/KCT
In general these complexes show high values of both the forma-
tion constant (KCT) and the molar extinction coefficient ( CT). These
eCT) as shown in Figs. 11–13.
G0 ¼ ꢀRT ln KCT
ð3Þ
e
D
high values of KCT confirm the expected high stabilities of the
formed CT-complexes as a result of the expected high donation
of 1, 4-bis (3-aminopropyl) piperazine (APPIP) which contains four
donor nitrogen atoms.
The formation constants are strongly dependent on the nature
of the used acceptors including the type of electron withdrawing
substituent to it such as cyano and halogen groups. The obtained
data show that the CT-complex [(APPIP)(TBCHDꢀ)] has much lower
value of KCT compared with that of [(APPIP) I]+ I3 , [(APPIP)(TCNQ)]
and [(APPIP)(DDQ)]. The value of formation constant of [(AP-
PIP)(TCNQ)] is higher than that of [(APPIP)(DDQ)] and this can be
understood on the basis of the differences in the electronic struc-
ture of the acceptors TCNQ, DDQ and TBCHD, while TCNQ acceptor
where
D
G0 is the free energy of the charge transfer complexes; R
the gas constant (1.987 cal molꢀ1 °C); T the temperature in Kelvin
degrees; KCT the formation constant of donor–acceptor complexes
(L molꢀ1). The
The obtained results of
process is exothermic in nature and spontaneous. The results of
D
G0 values of the complexes are given in Table 2.
D
G0 reveal that the CT-complexes formation
D
G0
are generally more negative as the formation constants of the CT-
complexes increase. As the bond between the components becomes
stronger and thus the components are subjected to more physical
strain or loss of freedom, the values of
The more negative the value for
G0, the farther to the right the
reaction will proceed in order to achieve equilibrium.
D
G0 become more negative.
D

S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
177
PIP)(TBCHD)]. The ECT values calculated from Eq. (4) are listed in
Table 2. These results (KCT
G0 and ECT) are clarifying that
The charge transfer energy ECT of the formed solid CT-com-
plexes is calculated using the following Eq. (4) [30,31]:
,
eCT, D
the obtained solid CT-complexes formed in the reaction of the do-
nor APPIP and the acceptors iodine, TCNQ, DDQ and TBCHD have
1243:667
ECT
¼
ð4Þ
kCT
high CT energy and formation constants KCT
.
The ionization potential of the free donor was determined from
the CT energies of the CT band of its complexes. In case of the
where kCT is the wavelength of the band of the studied CT-com-
plexes [(APPIP) I]+ I3ꢀ, [(APPIP)(TCNQ)] [(APPIP)(DDQ)] and [(AP-
Fig. 14. Infrared absorption spectra of: (A) 1,4-bis (3-aminopropyl) piperazine (APPIP), (B) [(APPIP)(TCNQ)], (C) [(APPIP)2(TCNE)3], (D) [(APPIP)(DDQ), (E) [(APPIP)(TBCHD]
and (F) [(APPIP) I]+I3ꢀ
.
Table 3
Infrared wavenumbers(a) (cmꢀ1
)
and tentative band assignments for 1,4-bis (3-aminopropyl) piperazine (APPIP), and CT-complexes [(APPIP)(TCNQ)], [(APPIP)(DDQ)],
[(APPIP)(TBCHD)] [(APPIP)2(TCNE)3] and [(APPIP)I] I3.
APPIP
[(APPIP)(TCNQ) ]
[(APPIP)(DDQ) ]
3416s,br
[(APPIP)(TBCHD) ] [(APPIP)2(TCNE)3] [(APPIP) I] I3
Assignments
3582w
3360m
3284m
3431s,br
3357w, 3192m,
3044m
3434s,br
3437s,br
3429s,br
m
m
(H2O); KBr
(NAH); APPIP
3247w, 3164w, 3016w 3227s, 3082s
3258w, 3000w
3164w, 3104w, 3029s
2936s, 2874m,
2808s
2942m, 2819m
2951s, 2826s
2208sm
2941s, 2840s
1658sm
2945m, 2820m
2236w, 2219sm,
2928w, 2835s
m
m
(CAH); APPIP
2225m, 2128s,
2174s
(C„N); TCNQ, TCNE and DDQ
1623w
1596s
2193s, 2163s
1579s
m
m
(C@O); DDQ, TBCHD
(C@C); TCNQ, DDQ,
1598s
1596w, 1569w
TBCHD, TCNE
(CH2); APPIP
Free and complexed APPIP
1462sm, 1372sm,
1349sm
1271sm,
1464m, 1448w
1380w, 1323s
1273m, 1232m
1193sm
1466m, 1451w
1347w, 1318s
1284w, 1265m
1169w
1478sm, 1451w
389m, 1356m
1274m, 1254w
1161s
1464sm, 1442m
1335sm, 1314m
1281m, 1256w
1158m
1466s, 1431s
1347sm, 1325sm
1259m, 1243m
1155s
m
m
m
(CAN); APPIP
(CAC); APPIP
1157s
1173m
1154sm
1115m
1130m
1098s
611sm
m
(CACl); DDQ
(a)
m, medium; s, strong; w, weak; br, broad; m, stretching

178
S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
acceptors iodine, DDQ, TCNQ and TBCHD the relationship becomes
the following [27–29]:
the spectra of the free reactants, the donor 1,4-bis(3-aminopropyl)
piperazine and the acceptors TCNQ, DDQ, TCNE and TBCHD (iodine
has no infrared activity). Interestingly, the spectra of the reaction
products contain the main infrared bands for both the reactants
in each case. This strongly supports the formation of the donor–
acceptor CT-complexes. However, the absorptions of APPIP and
acceptors in the formed products show some changes in band
intensities and in some cases small shifts in the frequency wave-
number values. These changes could be understood on the basis
of the expected symmetry and electronic structure modifications
in both donor and acceptor units in the formed products compared
1:5
Ip ꢀ 5:2
ECT ¼ Ip ꢀ 5:2 þ
ð5Þ
where Ip is the ionization potential and ECT is the charge transfer
energy of the formed solid CT-complexes. The obtained values of
Ip are 7.3, 5.9, 7.2 and 6.4 eV for the CT-complexes [APPIP)I]+ I3ꢀ,
[(APPIP)(TCNQ)], [(APPIP)(DDQ)] and [(APPIP)(TBCHD)], respec-
tively. It has been reported that the ionization potential of the elec-
tron donor may be correlated with the charge transfer transition
energy of the complex [32].
with those of the free molecules. The
m(NAH) vibrations of the free
1,4-bis (3-aminopropyl) piperazine are 3360 and 3284 cmꢀ1. Three
absorptions for m(NAH) are observed in [(APPIP)(TCNQ)] at 3357,
3.2. Infrared spectra
3192 and 3044 cmꢀ1, in [(APPIP)(DDQ) ] at 3247, 3164 and
3016 cmꢀ1, in the [(APPIP) I]+ I3ꢀ at 3164, 3104, and 3029 cmꢀ1
while in [(APPIP)(TBCHD)] two absorption are observed at 3227
The obtained infrared spectra of the donor 1,4-bis (3-aminopro-
pyl) piperazine (APPIP) along with those of the formed complexes
and 3082 cmꢀ1 and in [(APPIP)2(TCNE)3] at 3258 and 3000 cmꢀ1
.
[(APPIP)I]+ Iꢀ, [(APPIP)(TCNQ)], [(APPIP)(DDQ)], [(APPIP)2(TCNE)3]
3
The outlined changes in m(NAH) upon complexation clearly sup-
port the involvement of the nitrogen atom of the amino group in the
donor APPIP through the CT-interaction process. It might also to
and [(APPIP)(TBCHD)] are shown in Fig. 14 and the infrared band
assignments are given in Table 3. These assignments are based
on the comparison of the spectra of the formed products with
105
100
DTG
105
100
DTG
90
90
80
70
60
50
40
30
80
70
60
50
40
30
20
20
TG
TG
10
10
0
(A)
(B)
0
30
200
400
600
800
950
30
100
200
300
400
500
Temperature (oC)
Temperature (oC)
105
100
105
100
DTG
90
90
80
70
60
80
70
60
50
40
30
DTG
50
40
30
20
10
0
20
TG
TG
10
0
(C)
(D)
30
200
400
600
800
900
30
200
400
600
800
950
Temperature (oC)
Temperature (o C)
Fig. 15. (A–D) Thermograms of the CT-complexes; (A) [(APPIP) I]ꢃI3, (B) [(APPIP)(TCNQ)], (C) [(APPIP)(TBCHD)] and (D) [(APPIP)(DDQ)].

S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
179
Table 4
The second CT-complex [(APPIP)(TCNQ)] is shown in Fig. 14 (B)
at 163, 269, 313 °C correspond to the loss of the donor APPIP with
total weight loss of 47.9% (49.5% calculated). The acceptor TCNQ
has been decomposed at 648 and 723 °C with total weight loss of
48.7% (50.5% calculated).
Thermal data for the CT-complexes [(APPIP) I]+ I3ꢀ, [(APPIP)(TCNQ)], [(APPIP)(DDQ)],
[(APPIP)(TBCHD)] and [(APPIP)2(TCNE)3].
Complex
Reaction
DTG
max
TG % mass
loss found/
calculated
Lost species
stoichiometry
donor:acceptor (°C)
Fig. 14C shows the third complex [(APPIP)(TBCHD)] decomposes
in four temperatures at 165, 357, 421 and 749 °C. The temperatures
165 and 357 °C show total weight loss of 65.4% corresponds to the
loss of the donor with three bromine atoms [(APPIP)(Br)3] very
close to the calculated value of 67.3%. The decomposition tempera-
tures at 421 and 749 °C are associated with a total weight loss of
33.4% corresponds to the loss of the [C6H2BrO] equivalent to the
acceptor after losing three bromine atoms (in the decomposition
steps at 165 and 357 °C) in agreement with the calculated value
of 34.6%. Accordingly, a proposed mechanism for the thermal
decomposition of [(APPIP)(TBCHD)] as follows:
[(APPIP) I]+ Iꢀ3
1:2
331
424,
679
163,
269,
313
79.9/82.1
16.5/17.9
[(APPIP) I2]ꢃI+
[I]ꢀ
[(APPIP)(TCNQ)]
1:1
47.9/49.5
APPIP
648,723 48.7/50.5
TCNQ
APPIP
[(APPIP)(DDQ)]
1:1
195,
337,
419
575,
810
165,
357
421
749
49.6/46.9
48.7/53.1
68.4/72.2
DDQ
[(APPIP)(TBCHD)] 1:1
[(APPIP)2(TCNE)3] 1:1½
[(APPIP)(Br)3]
ꢅC
(i) ½ðAPPIPÞðC H Br OÞꢂ 165;357 ½ðAPPIPÞðBrÞ ꢂ þ ½C H BrOꢂ
ƒƒƒƒƒ!
16.8/15.7
11.9/12.1
Decomposed with broad
decomposition peak with
one maxima for a complete
loss of the whole compound
[BrO]
[C6H2]
6
2
4
ꢅC
6
2
3
(ii) ½C H BrOꢂ 421;749 ½BrOꢂ þ ½C H ꢂ
ƒƒƒƒƒ!
6
2
6
2
where the chemical structure of the acceptor TBCHD is C6H2Br4O.
The fourth complex [(APPIP)(DDQ)] is shown in Fig. 14 (D) at
195, 337 and 419 °C corresponds to the loss of the donor APPIP
with a weight loss of 49.6% close to the calculated value of 46.9%.
The acceptor has decomposed 575 and 810 °C with total weight
loss of 48.7% (53.1% calculated).
indicate here that
and DDQ show some changes particularly in terms of band wave-
number values upon complexation. The (C„N) vibration for free
TCNQ is observed at 2223 cmꢀ1 for free DDQ at 2230 cmꢀ1 and
m(C„N) vibrations of the acceptors TCNQ, TCNE
The fifth CT-complex [(APPIP)2(TCNE)3] decomposes with broad
decomposition peak with one maxima for a complete loss of the
whole compound.
m
for free TCNE a doublet is observed at 2196 and 2182 cmꢀ1
.
These vibrations occur at 2225, 2174 and 2128 cmꢀ1 in the
spectrum of [(APPIP)(TCNQ)], at 2208 cmꢀ1 for [(APPIP)(DDQ)]
and at 2236, 2219, 2193 and 2163 cmꢀ1 for [(APPIP)2(TCNE)3].
4. Conclusion
Charge-transfer interactions between the donor 1,4-bis (3-ami-
nopropyl) piperazine (APPIP) and the
r-acceptor iodine and the p-
3.3. Thermal analysis
acceptors TCNQ, TCNE, DDQ and TBCHD were studied in CHCl3 at
25 °C. We were able to show that the reaction stoichiometry is
the same (1:1) for the acceptors TCNQ, DDQ and TBCHD and is dif-
ferent for TCNE (1:1½) and iodine (1:2).
To confirm the proposed formula and structure for the obtained
CT-complexes, thermogravimetric (TG) and differential TG (DTG)
were carried out under a nitrogen gas flow (20 ml minꢀ1) within
The resulting CT-complexes were shown to have the formulas:
[(APPIP) I]+ I3ꢀ, [(APPIP)(TCNQ)], [(APPIP)2(TCNE)3], [(APPIP)(DDQ)]
and [(APPIP)(TBCHD)]. The obtained data show that the CT-com-
plex [(APPIP)(TBCHD)] has much lower value of KCT compared with
that of [(APPIP)I]+I3ꢀ, [(APPIP)(TCNQ)] and [(APPIP)(DDQ)] and indi-
cate that the nitrogen atom of the amino group in the donor 1,4-bis
(3-aminopropyl) piperazine (APPIP) is involved in the complexa-
tion with the acceptors. Further studies will focus on using differ-
ent acceptors and donors to further investigate the nature of such
complexations.
a temperature range 30–950 °C and heating rate 10 °C mlꢀ1
.
Fig. 15A–D shows the thermograms of [(APPIP) I]+ I3ꢀ, [(AP-
PIP)(TCNQ)], [(APPIP)(TBCHD)] and [(APPIP)(DDQ)], respectively.
The thermogravimetric data for these complexes are shown in Ta-
ble 4. The obtained data support the calculated formulas and struc-
tures of the formed CT-complexes. The degradations steps and
their associated temperatures vary from one complex to another
depending on the type of constituents as well as on the stoichiom-
etry in each case. Obviously, these two factors have pronounced ef-
fects on the type of bonding, relative complex stabilities and
geometries.
References
It is of interest to see that the triiodide complex [(APPIP) I] I3
shown in Fig. 14A decomposes in three degradation steps; at tem-
perature 331 °C corresponds to the decomposition of [(APPIP) I2] I+
with a weight loss of 79.9% very close to the calculated value of
82.1%. This step is followed by another two degradations at 424
and 679 °C correspond to the loss of [I]ꢀ species with a total weight
loss of 16.5% with about 1.4% deviation from the calculated value
(17.9%). This is an evident that the donor APPIP represents
28.29% of the complex, Table 4.
[1] R. Foster, Organic Charge Transfer Complexes, Academic Press, London, 1969.
pp. 51, 387.
[2] R.S. Mulliken, W.B. Person, Molecular Complexes,
Volume, Wiley, New York, 1969.
[3] K.K. Lahiri, K.K. Mazumdar, Spectrochim. Acta 46A (1990) 1137.
[4] R. Foster, J. Chem. Soc. 1075 (1960).
[5] H.S. Bazzi, A. Mostafa, S.Y. AlQaradawi, E.M. Nour, J. Mol. Struct. 842 (2007) 1.
[6] H.S. Bazzi, S.Y. AlQaradawi, A. Mostafa, E.M. Nour, J. Mol. Struct. 879 (2008) 60.
[7] A. Mostafa, H.S. Bazzi, J. Mol. Struct. 983 (2010) 126.
[8] A. Mostafa, H.S. Bazzi, Spectrochim. Acta Part A 79 (2011) 1613.
[9] S.Y. AlQaradawi, H.S. Bazzi, A. Mostafa, E.M. Nour, Spectrochim. Acta Part A 71
(2008) 1594.
A Lecture and Reprint
Accordingly, a proposed mechanism for the thermal decomposi-
tion of [(APPIP) I]+ I3ꢀ as follows:
[10] J. Casaszar, Acta Phys. Chim. 29 (1998) 34.
424, 679 °C:
[11] E.M. Nour, Spectrochim. Acta Part A 167 (2000) 56.
[12] A.S.N. Murthy, A.P. Bhardwaj, Spectrochim. Acta 39A (1983) 415.
[13] S.Y. AlQaradawi, E.M. Nour, Spectrosc. Lett. 37 (2004) 337.
[14] E.M. Nour, L.H. Chen, J. Laane, J. Raman Spectrosc. 467 (1986) 17.
[15] P.J. Trotter, P.A. White, Appl. Spectrosc. 32 (1978) 323.
331 ꢅC
(i) ½ðAPPIPÞIꢂþI3ꢀ
½ðAPPIPÞI ꢂIþ þ ½Iꢀꢂ
ƒƒƒƒƒ!
2
424;679 ꢅC
(ii) ½Iꢀꢂ
½Iꢀꢂ
ƒƒƒƒƒ!

180
S.Y. AlQaradawi et al. / Journal of Molecular Structure 1011 (2012) 172–180
[16] E.M. Nour, L.A. Shahada, Spectrochim. Acta 44A (1988) 1277.
[17] W. Kiefer, H.J. Bernstein, Chem. Phys. Lett. 16 (1972) 5.
[18] G.A. Bowmaker, R.J. Knappstein, J. Chem. Soc. Dalton (1977) 1928.
[19] S. Licht, Sol. Energy Mater. Sol. Cells 35 (1995) 305.
[20] H. Salem, J. Pharm. Biomed. Anal. 29 (2002) 527.
[21] D.A. Skoog, F.J. Holler, T.A. Nieman, Principle of Instrumental Analysis, 5th ed.,
vol. 347., Saunders College Publishing, New York, 1992.
[22] E.M. Nour, Spectrochim. Acta 47A (1991) 743.
[25] E.M. Nour, L.A. Shahada, A. Sadeek, S.M. Teleb, Spectrochem. Acta (A) 471
(1995) 51.
[26] R. Abu-Eittah, F. Al-Sugeir, Can. J. Chem. 54 (1976) 3705.
[27] A. El-Kourashy, Spectrochim. Acta A 37 (1981) 399.
[28] M. Arslan, H. Duymus, Spectrochim. Acta A 67 (2007) 573–577.
[29] A.A.A. Boraei, Spectrochim. Acta A 58 (9) (2002) 1895.
[30] G. Briegleb, Z. Angew. Chem. 72 (1960) 401.
[31] G. Briegleb, Z. Angew. Chem. 76 (1964) 326.
[23] M. Mizuno, J. Tanaka, I. Harda, J. Phys. Chem. 85 (1981) 1789.
[24] E.M. Nour, S.M. Metwally, M.A.F. ElMosallamy, Y. Gameel, Spectrosc. Lett. 115
(1999) 32.
[32] M. Pandeeswaran, K.P. Elango, Spectrochim. Acta A 65 (2006) 1148.