Synthesis, spectroscopic, thermal and structural investigations of charge-transfer complexes of 4,4′-trimethylenedipiperidine with chloranil, TBCHD, DDQ, TCNQ and iodine

Article abstract of DOI:10.1016/j.molstruc.2009.05.056

The charge-transfer interactions between the electron donor 4,4′-trimethylenedipiperidine (TMDP) and the acceptors 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Full text of DOI:10.1016/j.molstruc.2009.05.056

Journal of Molecular Structure 933 (2009) 1–7
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic, thermal and structural investigations
of charge-transfer complexes of 4,40-trimethylenedipiperidine
with chloranil, TBCHD, DDQ, TCNQ and iodine
Lamis Shahada a, Adel Mostafa b, El-Metwally Nour a, Hassan S. Bazzi b,
*
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
The charge-transfer interactions between the electron donor 4,40-trimethylenedipiperidine (TMDP) and
the acceptors 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,4,4,6-tetrabromo-2,5-cyclohexadie-
none (TBCHD), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,70,8,80-tetracyanoquinodimethane
(TCNQ) and iodine have been studied spectrophotometrically in CHCI3 solutions. The formed solid
charge-transfer complexes were also isolated and characterized through infrared spectra as well as ther-
mal and elemental analysis. The stoichiometry of the complexes was found to be 1:1 in the case of TMDP–
chloranil and TMDP–TBCHD systems and 1:2 in the case of TMDP–DDQ and TMDP–TCNQ systems and 1:3
in the case of TMDP–iodine system. Taking this into consideration along with infrared spectra and ther-
mal and elemental analysis, the formed CT-complexes have the formulas [(TMDP)(chloranil)],
[(TMDP)(TBCHD)], [(TMDP)(DDQ)2] [(TMDP)(TCNQ)2] and [(TMDP)I]+ꢀI5ꢁ, respectively.
Article history:
Received 15 January 2009
Received in revised form 14 May 2009
Accepted 14 May 2009
Available online 6 June 2009
Keywords:
4,40-Trimethylenedipiperidine
Chloranil
TBCHD
DDQ
Ó 2009 Elsevier B.V. All rights reserved.
TCNQ
Iodine
1. Introduction
electron-donating piperidine rings readily available to undergo
charge-transfer complexation with electron acceptors.
During the last three decades, a large number of studies have
been reported on charge transfer (CT) complexes between n-do-
In this paper herein, we report the formation of novel CT-com-
plexes formed in the reaction of TMDP with the electron acceptors
2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,4,4,6-tetrab-
romo-2,5-cyclohexadienone (TBCHD), 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ), 7,70,8,80-tetracyanoquinodimethane
(TCNQ) and iodine using CHCl3 as a solvent. The obtained results
enabled us to investigate the stoichiometries, bonding and struc-
tures inherent in these formed new CT-complexes.
nors and
r- and p-acceptors in solid state and in solution [1–7].
This is owing to their significant physical and chemical properties.
For example, CT-complexes have been recognized as an important
phenomenon in drug–receptor binding mechanism and in many
biological processes [8,9]. Charge-transfer complexes also find
important applications in the fields of electronics, solar cells, opti-
cal devices and electrical conductivities [10,11].
In previous studies [6,7,12–14] we have demonstrated that the
formation and stoichiometries of CT-complexes between various
nitrogen containing donors and n- and p-acceptors depend mainly
on the number of the donor nitrogen atoms, the type of acceptor as
well as the symmetry and structure of both sides.
4,40-Trimethylenedipiperidine, or TMDP, (also known as 1,3-
bis(4-piperidyl)propane) is an important organic compound used
in the polymer industry [15,16]. TMDP is commonly used as a
crosslinking agent, and in producing pressure sensitive adhesive
tapes and products. TMDP is also employed in the synthesis of
hyperbranched copolymers [17]. In addition, TMDP has two
2. Experimental
2.1. Materials and measurements
All chemicals were purchased from Sigma–Aldrich, USA, and
used as received. The electronic absorption of the reactants,
4,40-trimethylenedipiperidine (TMDP), 2,3,5,6-tetrachloro-1,4-
benzoquinone (chloranil), 2,4,4,6-tetrabromo-2,5-cyclohexadie-
none (TBCHD), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ),
* Corresponding author. Tel.: +974 423 0018; fax: +974 423 0060.
E-mail address: bazzi@tamu.edu (H.S. Bazzi).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.05.056

2
L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
7,70,8,80-tetracyanoquinodimethane (TCNQ) and iodine as well as
the reaction products were recorded in the region 1100–240 nm
using a lambda 950 Perkin-Elmer UV–vis spectrometer with a quartz
cell of 1.0 cm path length and elemental analysis was done using
model 2400 Perkin-Elmer C,H,N,S/O elemental analyzer.
Photometric titration measurements were performed for the
reactions between the donor TMDP and each of the acceptors
iodine, chloranil, TBCHD, DDQ and TCNQ in CHCl3 at 25 °C in order
to determine the reaction stoichiometries according to the litera-
ture method [18,19]. The measurements were conducted under
the conditions of fixed donor TMDP concentration while those of
the acceptors I2, chloranil, TBCHD, DDQ, or TCNQ 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 absorbancies 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.
Fig. 1. Electronic absorption spectra of 4,40-trimethylenedipiperidine–iodine reac-
tion in CHCl3. (A) [TMDP] = 1 ꢂ 10ꢁ3 M; (B) [I2] = 1 ꢂ 10ꢁ3 M; (C) [C] 1:3 TMDP–I2
mixture, [TMDP] = [I2] = 1 ꢂ 10ꢁ3 M. The band of diluted solution of TMDP/iodine
CT-complex (inset).
The infrared spectra of the reactants and the formed CT-com-
plexes (KBr pellets) were recorded on a spectrum one Perkin-Elmer
FTIR spectrophotometer.
Thermogravimetric (TG) and differential thermogravimetric
(DTG) analysis were carried out for all reactants and CT-com-
plexes; using a Perkin-Elmer model pyris 6 TGA computerized
thermal analysis system. The rate of heating of the sample was
kept at 10 °C minꢁ1 under nitrogen flow at 20 ml minꢁ1. Copper
sulfate pentahydrate was used as a calibration standard.
2.2. Preparation of the solid CT-complexes
The five solid CT-complexes formed in the reaction of 4,40-trim-
ethylenedipiperidine (TMDP) with each of I2, chloranil, TBCHD,
DDQ and TCNQ were prepared by the addition of a saturated solu-
tion of the donor (60 ml) to a saturated solution of each acceptor I2,
chloranil, TBCHD, DDQ and TCNQ (80 ml) in CHCl3.
The resulting precipitate in each case was filtered off, washed
with minimum amounts of CHCl3 and dried in vacuum over P2O5.
The complexes were characterized spectrophotometrically (FTIR
and UV–vis), thermogravimetric analysis and elemental analysis;
(theoretical values are shown in brackets):
Fig. 2. Electronic absorption spectra of 4,40-trimethylenedipiperidine–acceptors
reactions in CHCl3. (A) [(TMDP)(TCNQ)2], (B) [(TMDP)(DDQ)2], (C) [(TMDP)(TBCHD)]
and (D) [(TMDP)(chloranil)]; TMDP = TCNQ = DDQ = TBCHD = chloranil = 1 ꢂ
10ꢁ3 M.
[(TMDP)I]+ꢀIꢁ5 dark brown complex (M/W: 971.79 g): C, 15.97%
(16.05%); H, 2.61% (2.7%); N, 2.89% (2.9%); [(TMDP)(chloranil)] dark
brown complex (M/W: 456.24 g): C, 50.1% (49.97%); H, 5.78%
(5.7%); N, 6.16% (6.14%); [(TMDP)(TBCHD)] dark brown complex
(M/W: 620.06 g): C, 36.83% (36.80%); H, 4.56% (4.5%); N, 4.48%
(4.5%) [(TMDP)(DDQ)2] dark reddish brown complex (M/W:
664.38 g): C, 52.42% (52.38%); H, 3.97% (3.91%); N, 12.58% (12.64%)
and [(TMDP)(TCNQ)2] light yellow complex (M/W: 618.74 g): C
71.84% (71.8%); H, 5.56% (5.5%); N, 22.56% (22.6%).
chloranil, 536 and 447 for TBCHD, 732 and 497 nm for DDQ and at
581 and 617 nm for TCNQ products, respectively.
Photometric titration measurements for the five reactions in
CHCl3 were performed and shown in Figs. 3–7. Interestingly, the
measurements show that the donor–acceptor molar ratio is vari-
able depending on the type of acceptor. These molar ratios were
found to be 1:1 in the case of TMDP–chloranil and TMDP–TBCHD
and 1:2 in the case of TMDP–DDQ and TMDP–TCNQ and 1:3 in
the case of TMDP–I2 system. Based on this fact, the structures of
the five new formed CT-complexes were formulated to be
3. Results and discussion
3.1. Electronic absorption spectra
[(TMDP)(Chloranil)],
[(TMDP)(TBCHD)],
[(TMDP)(DDQ)2],
Strong change in colors was observed upon mixing of CHCl3
solutions of the donor 4,40-trimethylenedipiperidine (TMDP) with
each of the acceptors iodine, chloranil, TBCHD, DDQ and TCNQ.
The new colors are dark brown for TMDP–I2, TMDP–chloranil and
TMDP–TBCHD, dark reddish brown for TMDP–DDQ and light yellow
for TMDP–TCNQ reaction mixtures. These changes in colors repre-
sent strong evidence of the charge-transfer interactions between
the donor and each of the acceptors. The electronic absorption spec-
tra of the reactants in each case along with those of the complexes
formed between the donor TMDP and each of I2, chloranil, TBCHD,
DDQ and TCNQ are shown in Figs. 1 and 2. Strong absorption bands
due to the formed products appeared at 375, 270 for I2, 574 nm for
[(TMDP)(TCNQ)2] and [(TMDP)(I2)3]. These structures and stoichi-
ometries agree quite well with the elemental analysis of the
formed solid CT-complexes. It should be indicated here, that, the
absorption of the iodine complex shows two new strong absorp-
tions at 375 and 270 nm. Neither free iodine nor TMDP show these
absorptions Fig. 1 and Table 1. These two absorptions of formed
CT-complex of iodine at 375 and 270 are well known [6,19] to be
characteristic for the poly iodide ion of the type Iꢁ5 . Accordingly,
the formed CT-complex of iodine is identified as [(TMDP)I]+ꢀI5ꢁ. Sim-
ꢁ
ilar pentaiodide species such as [(TODACOD)I]+ꢀI5ꢁ ((TODACOD) is
5
1,4,10,13-tetraoxo-7,16-diazacyclooctadecane) are well known in
the literature [19]. The formation of [(TMDP)I]+ꢀI5ꢁ could be

L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
3
Fig. 3. Photometric titration curve for TMDP–I2 reaction in CHCl3 based on the
375 nm absorption.
Fig. 6. Photometric titration curve for TMDP–TCNQ reaction in CHCl3 based on the
581 and 617 nm absorptions.
Fig. 4. Photometric titration curve for TMDP–chloranil reaction in CHCl3 based on
the 574 nm absorption.
Fig. 7. Photometric titration curve for TMDP–DDQ reaction in CHCl3 based on the
497 and 732 nm absorptions.
Table 1
Spectroscopic data for CHCl3 solutions for CT-complexes of TMDP and acceptors I2,
chloranil, TBCHD, DDQ and TCNQ.
CT-complex
Color
Absorptionsa (nm)
[(TMDP)(chloranil)]
[(TMDP)(TBCHD)]
[(TMDP)(DDQ)2]
[(TMDP)(TCNQ)2]
[(TMDP)I]+ꢀIꢁ5
Dark brown
Dark brown
Dark reddish brown
Light yellow
Dark brown
574s
536m, 447s
732s, 497m
581 vs. 617s
375s, 270vs
a
The reactants TMDP, chloranil, TBCHD, DDQ, TCNQ and iodine have no mea-
surable absorptions in the region of study with used concentrations: m, medium; s,
strong; v, very.
Fig. 5. Photometric titration curve for TMDP–TBCHD reaction in CHCl3 based on the
447 and 536 nm absorptions.
(iii) (TMDP)I]+ꢀIꢁ + I2 ? [(TMDP)I]+ꢀIꢁ3
(iv) [(TMDP)I]+ꢀI3ꢁ + I2 ? [(TMDP)I]+ꢀIꢁ5
understood considering the four reaction steps, the first involves the
formation of the outer complex;
As mentioned earlier in the text, the addition of solution of the
donor TMDP to iodine solution, the absorption of iodine band
(i) (TMDP) + I2 ? (TMDP)ꢀI2
around 515 nm which is attributed to the 4p
? 10 r* electronic
transition in free iodine [20] was hypsochromically shifted due to
its complexation with the added donor, TMDP and the blue shifted
iodine bands located around 375 and 270 nm. The observed blue
shift in the free iodine band and its split into two bands is obvi-
ously due to the perturbation of the 10 r* molecular orbital of
Followed by the formation of the inner complex,
(ii) (TMDP)ꢀI2 ? (TMDP)I]+ꢀIꢁ which combines with one iodine
molecule to form Iꢁ3 and this reacts with the third iodine mol-
ecule to give the final pentaiodide , Iꢁ5 complex.

4
L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
iodine due to the CT-interaction with the donor. The split of the
iodine band around 515 nm into two absorptions around 375 and
270 nm is related to allowed transition in the formed pentaiodide,
Iꢁ5 ion. It should be indicated here that the formed Iꢁ5 ion in the CT-
complex [(TMDP)I]+ꢀI5ꢁ may be of the type (I3)(I2) or it may exist as
one unit with either linear or bent structures [6]. In order to clarify
this point, more measurements and studies are needed including the
far-infrared and Raman spectra in the region (50–200) cmꢁ1 along
with carrying out normal coordinate analysis which is not the scope
of this study and could be performed in future investigation.
It is of interest to see that reaction stoichiometries of TMDP
with each of the acceptors under investigation vary from 1:1 to
1:3 depending on the type of donor, Table 1. For the
p-acceptors,
the stoichiometry value is 1:1 in the case of chloranil and TBCHD
while it is 1:2 in the case of DDQ and TCNQ.
Fig. 9. The plot of (C0a ꢂ Cd01=A) values against (Ca0 þ C0d1=A) values for the
[(TMDP)(TBCHD)] reaction in CHCl3 at 447 nm.
Kc and eC are 9.68 ꢂ 102 L molꢁ1 and 14.97 ꢂ 105 L molꢁ1 cmꢁ1 for
ꢀ
[(TMDP)(chloranil)] and 0.384 ꢂ 102 L molꢁ1 and 8.24 ꢂ 102 L
molꢁ1 cmꢁ1 for the second complex [(TMDP)(TBCHD)]. The high
ꢀ
values of eC are characteristic for CT-complexes. The obtained data
shows that the [(TMDP)(chloranil)] has a much higher value of Kc
compared with that of [(TMDP)(TBCHD)]. This demonstrates a
much higher stability of chloranil complex compared with that of
TBCHD. This could be related to many factors, first the steric hinder-
ance which is relatively high in the case of TBCHD due to the larger
substituent Br atomic size compared with that of chlorine in chlora-
nil. This will weaken the interaction between TMDP and TBCHD
compared with that of chloranil. Second, the aromatic ring in
TBCHD has lower electron accepting ability compared with to
chloranil, related to the lower electron withdrawing process of
the substituent Br in TBCHD compared with Cl in chloranil. This cer-
tainly allows stronger electron donation from TMDP base to chlora-
nil compared with that with TBCHD. An unsuccessful attempt was
These pronounced variations of CT-interaction stoichiometries are
relatively complicated issue to be sorted out. It is definitely con-
nected to many factors such as the donor molecular symmetry,
the type of electron withdrawing groups or atoms Cl, Br, O@ or
CN as well as the steric hindrance between reactants. All of these
factors are expected to play an important role in the electron dona-
tion process from the nitrogen electron pairs of the donor TMDP and
the aromatic ring of each acceptor. Including the I2 in such a com-
parison is invalid, since I2 is an n-electron donor.
To know more regarding the properties of the two CT-com-
plexes [(TMDP)(chloranil)] and [(TMDP)(TBCHD) where the reac-
tion stoichiometries are 1:1, the formation constant, Kc, and the
ꢀ
absorptivity, eC for each complex were calculated using the modi-
ꢀ
made to calculate the corresponding values of Kc and eC for both
fied Benesi–Hildebrand equation [21] for the 1:1 reaction;
the 1:2 and 1:3 complexes [(TMDP)(DDQ)2], [(TMDP)(TCNQ)2] and
[(TMDP)I]+ꢀIꢁ5 . The 1:2 and 1:3 stoichiometric ratios have many
complicated terms to deal with and our future work will focus on
finding these values.
ꢀ
ꢀ
½A0ꢃ½D0ꢃ=A ¼ 1=Kcec þ ½ðA0Þ þ ðD0Þꢃ=ec
where A is the absorbance of the CT-transition of [(TMDP)(chlora-
nil)] at 574 nm and of [(TMDP)(TBCHD)] at 447 nm. [A0] and [D0]
are the initial concentrations of the acceptor and the donor, respec-
tively. Straight lines are obtained from the plot in each case, com-
plex, of [A0][D0]/A vs. [A0] + [D0] confirming our conclusion of the
formation of 1:1 complexes, Figs. 8 and 9. The obtained values of
3.2. Infrared absorption spectra
Infrared spectra of the electron donor TMDP and its CT-com-
plexes [(TMDP)(chloranil)], [(TMDP)(TBCHD)], [(TMDP)(DDQ)2],
[(TMDP)(TCNQ)2] and [(TMDP)I]+ꢀI5ꢁ are shown in Fig. 10 and their
infrared band assignments are given in Table 2. In the spectra of
the CT-complexes main bands of both the donor and the acceptors
are observed. This is a clear indication of the formation of the CT-
interactions. Interestingly, both m(CAH) and m(NAH) of the free base
TMDP show some changes in both band intensities, band number
and wavenumber values upon complexation, Table 2.
The
2231 cmꢁ1, respectively and at 2230, 2170, 2131 and 2203 cmꢁ1
upon complexation. The split of the (CN) into three bands in the
m(C„N) for the free TCNQ and DDQ occur at 2220 and
m
case of [(TMDP)(TCNQ)2] could be related to that the reaction prod-
uct has more than one TCNQ in addition to other reasons such as
symmetry and dipole moments changes in the complexed TCNQ
compared with the free molecule.
Similar changes are observed for the
m
(C@C) vibrations for all
(C@C)
free acceptors chloranil, TBCHD, DDQ and TCNQ where
m
are at 1569, 1553, 1553 and 1539 cmꢁ1, respectively, correspond
to1563, 1593, 1547 and 1538 cmꢁ1 upon complexation. These
Fig. 8. The plot of (C0a ꢂ Cd01=A) values against (Ca0 þ C0d1=A) values for the
[(TMDP)(chloranil)] reaction in CHCl3 at 574 nm.

L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
5
Fig. 10. Infrared absorption spectra of (A) 4,40-trimethylenedipiperidine (TMDP); (B) [(TMDP)(DDQ)2]; (C) [(TMDP)(TCNQ)2]; (D) [(TMDP)(chloranil)]; (E) [(TMDP)(TBCHD)]
and (F) [(TMDP)I]ꢀI5.
changes could be related to both electronic and symmetry changes
upon complexation.
decompositions and structures of the formed solid CT-complexes.
Figs. 11(A)–(C) and 12(D) and (E) show the thermograms of
[(TMDP)(chloranil)], [(TMDP)(TBCHD)], [(TMDP)(DDQ)2], [(TMDP)
3.3. Thermal analysis measurements
(TCNQ)2] and [(TMDP)I]ꢀI5, respectively. Table
3 shows the
thermogravimetric data for all complexes.
Thermogravimetric (TG) and differential thermogravimetric
(DTG) analysis were carried out in order to confirm the
The data supports the calculated formulas and structures of the
formed CT-complexes. The degradations steps and their associated
Table 2
Infrared wavenumbersa (cmꢁ1
)
and tentative band assignments for 4,40-trimethylenedipiperidine (TMDP), and CT-complexes. [(TMDP)(TCNQ)2], [(TMDP)(DDQ)2],
[(TMDP)(TBCHD)] [(TMDP)(chloranil)] and [(TMDP)I]ꢀI5.
TMDP
[(TMDP)(TCNQ)2)] [(TMDP)(DDQ)2] [(TMDP)(TBCHD)] [(TMDP)(chloranil)]
[(TMDP)I]ꢀI5
Assignments
3401s,br
3190s, 2912s
2840s
3402s,br
3192w
2922s, 2842sm
2230w
3439s,br
3022w
3429s,br
3435m,br
3184s
2917s, 2884w, 2840m
3434s,br
3132w
3104m, 2911m
m
m
m
m
m
m
m
(H2O); KBr
(NAH); TMDP
(CAH); TMDP, TNCQ
(C„N); TCNQ and DDQ
(C@O); DDQ, TBCHD chloranil, TBCHD
(C@C); TCNQ, DDQ, TBCHD and chloranil
(CH2); TMDP
2926sm, 2850m 2923sm, 2847m
2203sm
1623s
1547sm
1450sm
1626s
1593w, 1548s
1423s
1386s, 1302wm
1241m, 1163w
1648s
1563sm
1454w, 1446sm
1394w, 1365w
1268m, 1151w
1538sm
1470s, 1421s
1444s, 1428s
1393w, 1375wm 1377w, 1339w
1222w, 1150w 1245w, 1190w
1449sm
1399sm, 1284m
1278w, 1171w
1385w, 1375w
1220w, 1199w
Free and complexed TMDP
m
m
m
(CAN); TMDP
(CAC); TMDP, chloranil; characteristic band
(CACl); chloranil
1131w, 1098wm 1117w, 1092wm 1149w, 1073w
1141wm, 1076wm 1151wm, 1099w, 1113w 1104wm, 1057wm
731m
a
m, medium; s, strong; w, weak; br, broad; m, stretching; d, bending.

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L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
Table 3
Thermal dataa for the CT-complexes.
Complex
Reaction
stoichiometry
donor:acceptor
DTG
Max.
(°C)
TG % mass
loss found/
cal.
Lost
species
[(TMDP)(chloranil)] 1:1
193
390
TMDP
11
/ 47
35
454
678
Chloranil
45
/ 54
9
[(TMDP)(TBCHD)]
1:1
1:2
125
246
TMDP
15
/33.87
18
394
548
666
TBCHD
50
7
8
/ 66.13
[(TMDP)(DDQ)2]
380
454
704
31/31.6
TMDP
Two
43
/ 68.34 molecules
24
of DDQ
[(TMDP)(TCNQ)2]
1:2
1:3
107
225
28/33.9
71/66.1
TMDP
TCNQ
[(TMDP)I]ꢀI5
199
387
595
52/52.2
34/26
14/21.8
2I2
I+ꢀIꢁ
TMDP
a
Thermal measurements were carried out under N2 flow at 20 ml minꢁ1
.
199 ꢄC
ð1Þ ½ðTMDPÞIꢃþ ꢀ I5ꢁ ! 2I2 þ ½ðTMDPÞIꢃþ ꢀ Iꢁ
ꢄ
387
ð2Þ ½ðTMDPÞIꢃþ ꢀ Iꢁ !CðTMDPÞ þ I2
The [(TMDP)(DDQ)2] complex decomposes at three tempera-
tures, at 380 °C corresponds exactly to the loss of the donor TMDP
with weight loss of 31% (31.6% calculated). The two DDQ molecules
are lost at two temperatures of 454 and 704 °C.
Fig. 11. TG and DTG diagrams of (A), [(TMDP)(chloranil)], (B) [(TMDP)(TBCHD)] and
[(TMDP)(DDQ)2].
temperatures vary from one complex to another depending on the
type of constituents as well as on the stoichiometries in each case.
Obviously, these two factors have pronounced effects on the type
of bonding, relative complex stabilities and geometries.
It is of interest to see that the pentaiodide complex [(TMDP)I]ꢀI5
decomposes in three degradation steps at 199 °C corresponds to
the loss of 2I2 with a weight loss of 52% in agreement with the cal-
culated value of 52.2%. This step is followed by another degrada-
tion at 387 °C corresponds to the loss of the third I2 species with
a weight loss of 34% with about 8% deviation from the calculated
value, Table 3. This could be related this degradation at 387 °C
might involve in part the donor TMDP. This is evident that the
TMDP represents 21.8% of the complex and is left with only 14%
to be completely lost at higher temperature 595 °C, Table 3 and
Fig. 12(E).
The loss of the third I2 molecule at higher temperature than that
of the first two complexes could be related to its ionic nature I+ꢀIꢁ.
Accordingly, the thermal decomposition of [(TMDP)I]+ꢀI5ꢁ is as
follows:
Fig. 12. TG and DTG diagrams of (D) [(TMDP)(TCNQ)2] and (E) [(TMDP)I]ꢀI5.

L. Shahada et al. / Journal of Molecular Structure 933 (2009) 1–7
7
With total weight loss of 67% very close to the calculated value
of 68.34%.
sponds to the loss of the acceptor TBCHD in agreement with the
calculated value of 66.13%.
The third complex [(TMDP)(TCNQ)2] shows main degradation
steps, Table 3, at 107 and 225 °C correspond to the loss of TMDP
donor and the two TCNQ molecules, respectively. The deviation
between the found and calculated values (ꢅ5%) could be related
to the decomposition interference between the two different
parts of the complex, TMDP and TCNQ. This is evident from the
fact that the decomposition band at 225 °C, Fig. 12(D) is of
asymmetric.
The fourth complex [(TMDP)(chloranil)] has four degradation
steps, the first two occur at 193 and 390 °C correspond to 46% of
weight loss in full agreement with the calculated value of
46.02%. The other two decomposition temperatures at 454 and
678 °C are related to the decomposition of the chloranil molecule.
The total weight loss of those steps is 54% in agreement with the
calculated value of 53.98%, Table 3.
References
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The thermograms of the last complex [(TMDP)(TBCHD)] are
shown in Fig. 11(B). These thermograms are relatively complicated.
It shows five decomposition steps at 125, 246, 394, 548 and 666 °C.
The first two at 125 and 246 °C show total weight loss of 33% cor-
responds to the loss of the donor TMDP very close to the calculated
value of 33.87%. The other decomposition temperatures at 394, 548
and 666 °C are associated with a total weight loss of 65% corre-
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