Synthesis, spectroscopic characterization and crystal structure of novel NNNN-donor μ-bis(bidentate) tetraaza acyclic Schiff base ligands

Article abstract of DOI:10.1016/j.saa.2012.08.064

Novel NNNN-donor μ-bis(bidentate) tetraaza acyclic Schiff base ligands with different substituents (CF₃, N(CH₃)₂ or OH groups) were synthesized by the condensation reaction of triethylenetetramine with 4-substituted benzaldehydes. Triethylenetetramine tris(4- trifluoromethylbenzylidene) (TTFMB), triethylenetetramine tris(4- dimethylaminobenzylidene) (TTDMB) and triethylenetetramine tris(2,4- dihydroxybenzylidene) (TTDHB) were formed as N₄ donor ligands. The formation of a five-membered imidazolidine ring from the ethylenediamine backbone as a spacer-cumbridging unit gives rise to a new type of imidazolidine ligand. The structure of the TTFMB and TTDMB were determined by single crystal X-ray crystallography. The synthesized ligands have been characterized on the basis of the results of cyclic voltammetry (CV) and spectroscopic studies viz. FT-IR spectroscopy (FT-IR), mass spectroscopy (MS) and UV-Vis spectroscopy (UV-Vis).

Full text of DOI:10.1016/j.saa.2012.08.064

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopic characterization and crystal structure of novel
NNNN-donor
l-bis(bidentate) tetraaza acyclic Schiff base ligands
a
b
Mohammad Hossein Habibi a, , Elahe Shojaee , Gary S. Nichol
⇑
a Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Islamic Republic of Iran
b X-ray Crystallography, Department of Chemistry and Biochemistry, The University of Arizona, USA
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Three new tetraaza N4 acyclic Schiff bases with three pendant arms are prepared. The X-ray structure
(TTFMB and TTDMB), UV–Vis, CV, FT-IR and MS of the Schiff bases have been determined.
"
"
"
Three new tetraaza acyclic Schiff
bases were prepared.
Spectroscopic characterization and
crystal structure were determined.
Five-membered ring spacer as a
novel type of imidazolidine ligand is
formed.
"
A novel spacer-cumbridging unit is
formed.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 July 2012
Received in revised form 10 August 2012
Accepted 21 August 2012
Available online 1 September 2012
Novel NNNN-donor l-bis(bidentate) tetraaza acyclic Schiff base ligands with different substituents (CF3,
N(CH3)2 or OH groups) were synthesized by the condensation reaction of triethylenetetramine with 4-
substituted benzaldehydes. Triethylenetetramine tris(4-trifluoromethylbenzylidene) (TTFMB), triethyl-
enetetramine tris(4-dimethylaminobenzylidene) (TTDMB) and triethylenetetramine tris(2,4-dihydroxyb-
enzylidene) (TTDHB) were formed as N4 donor ligands. The formation of a five-membered imidazolidine
ring from the ethylenediamine backbone as a spacer-cumbridging unit gives rise to a new type of imidaz-
olidine ligand. The structure of the TTFMB and TTDMB were determined by single crystal X-ray crystal-
lography. The synthesized ligands have been characterized on the basis of the results of cyclic
voltammetry (CV) and spectroscopic studies viz. FT-IR spectroscopy (FT-IR), mass spectroscopy (MS)
and UV–Vis spectroscopy (UV–Vis).
Keywords:
Tetraaza acyclic
Imidazolidine ring
4-Substituted benzaldehydes
Pendant arms
Ó 2012 Elsevier B.V. All rights reserved.
Crystal structure
Introduction
ing species [4,5]. In studies of Schiff bases, the emphasis has been
mainly on macrocyclic ligands, macrocycles with one open side, or
Schiff bases ligands with multidentate N donors have received
sporadic attention for many year, but tetraaza acyclic ligands are
still rare [1–3]. Schiff bases have been studied extensively since
it is recognized that many complexes of this type with NxOy donor
sets may serve as models for biologically important metal-contain-
polypodal ligands [6–8]. Among various products from the conden-
sation of aromatic aldehydes with tetramine containing both pri-
mary and secondary amino groups is a binucleating Schiff base
with an in-built spacer imidazolidine ring, which can take up
two same or different metal ions [9–11]. The use of multidentate
ligands has been receiving considerable attention in recent years
following the identification of similar catalytically active biosites
in living systems [12–14]. Recently we reported X-ray structural
⇑
Corresponding author. Tel.: +98 311 7932707; fax: +98 311 6689732.
E-mail addresses: habibi@chem.ui.ac.ir, habibi284@gmail.com (M.H. Habibi).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.064

M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
397
Fig. 1. Structure of the three new tetraaza acyclic ligands TTDMB, TTFMB and TTDHMB.
Table 1
Crystal data and structure refinement for TTDMB and TTFMB.
Chemical formula
C33H45N7, TTDMB
C30H27F9N4, TTFMB
Formula weight
Temperature (K)
Radiation, wavelength (Å)
Crystal system, space group
a (Å)
539.76
150(2)
614.56
150(2)
Mo Ka, 0.71073
Triclinic, Pc
5.7301(5)
Mo K
a, 0.71073
Monoclinic, P21/c
9.9799(13)
b (Å)
30.568(3)
10.9123(9)
c (Å)
19.951(3)
22.7746(18)
a
(°)
90
90
b (°)
92.888
90.157
c
(°)
90
90
1424.1(2)
V (Å3)
6078.7(13)
Z
8
2
Dcalc (g cmꢀ3
)
1.180
1.433
Crystal colour and size (mm)
Colourless, 0.19 ꢁ 0.08 ꢁ 0.08
Colourless, 0.64 ꢁ 0.11 ꢁ 0.06
l
(mmꢀ1
)
0.072
0.127
632
F(000)
2336
h Range
2.7–20.1
2.6–23.0
Index ranges
ꢀ9 < h < 9, ꢀ28 < k < 28, ꢀ18 < l < 18
ꢀ6 < h < 6, ꢀ12 < k < 12, ꢀ25 < l < 25
Reflections collected
Independent reflections [Rint]
17925
18164
5358[0.0569]
3553
2066[0.0447]
1975
Reflections with F2 > 2
r
Absorption correction
Numerical
Numerical
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.9867 and 0.9943
5358/0/734
0.995
R1 = 0.0433, wR2 = 0.0921
R1 = 0.0828, wR2 = 0.1079
0.15, 0.15
0.9235 and 0.9919
2066/2/390
1.064
R1 = 0.0345, wR2 = 0.0859
R1 = 0.0370, wR2 = 0.0884
0.27, 0.20
Final R indices [F2 > 2
R indices (all data)
r]
Largest difference peak, hole (eÅꢀ3
)
characterization of one tetramine held by an imidazolidine ring
[15]. In order to broaden our perspective on potentially tetraaza
acyclic ligands, we have prepared the new tetraaza acyclic Schiff
bases shown in Fig. 1. These ligands potentially act as tetradentate
(NNNN) ligand but may act as bidentate ligands [16,17]. When the
polyamines contain both primary and secondary amino groups,

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M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
of various substituent of imidazolines ring as pendant arms and
spacer on structure and physico-chemical properties of the multid-
entate ligands, derivatives of benzaldehyde with CF3, N(CH3)2 or
OH groups were used in the synthesis of three new tetraaza acyclic
Schiff bases. The relationship between the electronic properties
and reactivity of these novel N4-donor
l-bis(bidentate) tetraaza
acyclic Schiff base ligands mimic some naturally occurring acyclic
compounds [20,21]. These properties continue to endorse great
interest in their design and preparation. Among the ligands em-
ployed for drug design, imidazolidine nucleus serves as an impor-
tant pharmacophore in drug discovery [22,23]. Imidazolidines are
very useful subunits for the development of molecules of pharma-
ceutical or biological interest. There are reports on tetraaza Schiff
base ligands [11,16]. To the best of our knowledge there is no re-
port on NNNN-donor
l-bis(bidentate) tetraaza acyclic Schiff base
ligands with CF3, N(CH3)2 or OH groups substituents. Considering
all these specifics, spectroscopic properties and electrochemical
activity of N4-donor l-bis(bidentate) tetraaza acyclic Schiff base li-
gands, with interesting physical and spectroscopic properties, have
become our main significance.
In view of the above biological consequence and in continuation
of our previous work [24–26], we here demonstrate a new strategy
to introduce imidazolidine rings as subunits in tetraaza acyclic li-
gands employing novel precursors. The synthesis, spectroscopic
studies, crystal structure and electrochemical properties of three
new tetraaza acyclic Schiff bases with imidazolidine ring, spacer
and two pendant arms from condensation of substituted benzalde-
hydes and triethylenetetramine (trien) are reported. The structures
Fig. 2. ORTEP drawing of TTFMB ligand, 2-(40-trifluoromethylphenyl)-l,3-bis[30-
aza-40-(400-trifluoromethylphenyl)-prop-40-en-10-yl]-1,3-imidazolinelne
50% probability displacement ellipsoids and the atom-numbering scheme.
showing
either Schiff bases, imidazolines or Schiff bases containing addi-
tional imidazoline rings are obtained [18,19]. To study the effects
Fig. 3. ORTEP drawing of TTDMB ligand, 2-(40-dimethylaminophenyl)-l,3-bis[30-aza-40-(400-dimethylaminophenyl)-prop-40-en-10-yl]-1,3-imidazolinelne showing 50%
probability displacement ellipsoids and the atom-numbering scheme.

M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
399
Table 2
Selected bond lengths (Å) for C33H45N7 and C30H27F9N4.
Table 3
Selected bond angle (°) for C33H45N7 and C30H27F9N4.
Ligand
C33H45N7
C30H27F9N4
Bond angles
C33H45N7
C30H27F9N4
Bond lengths
N(1)–C(1)
N(1)–C(2)
N(1)–C(12)
N(2)–C(1)
N(2)–C(3)
C(1)–N(1)–C(2)
103.1(3)
112.5(3)
113.5(3)
108.0(2)
114.9(3)
116.0(3)
117.9(3)
118.5(3)
114.3(3)
115.8(4)
119.5(3)
121.7(3)
117.8(3)
118.5(3)
120.6(3)
119.8(3)
118.7(3)
104.0(3)
111.9(3)
113.2(3)
108.0(3)
115.1(3)
114.9(3)
118.1(4)
120.8(4)
114.8(4)
117.1(3)
121.1(3)
120.7(4)
118.0(3)
116.0(4)
120.4(3)
120.1(4)
118.8(3)
C(1)–N(1)–C(2)
C(1)–N(1)–C(11)
C(2)–N(1)–C(11)
C(1)–N(2)–C(3)
C(1)–N(2)–C(21)
C(3)–N(2)–C(21)
C(12)–N(3)–C(13)
C(22)–N(4)–C(23)
108.1(3)
114.3(3)
115.2(4)
105.0(3)
112.5(3)
112.8(4)
116.4(4)
118.8(4)
1.472(4)
1.462(4)
1.457(4)
1.463(4)
1.468(4)
1.449(4)
1.394(4)
1.455(4)
1.457(4)
1.466(4)
1.266(4)
1.382(4)
1.447(5)
1.436(5)
1.455(4)
1.271(4)
1.375(4)
1.433(4)
1.450(4)
1.486(4)
1.467(4)
1.453(4)
1.448(4)
1.457(4)
1.458(4)
1.399(5)
1.444(5)
1.446(5)
1.465(4)
1.268(4)
1.381(4)
1.430(5)
1.435(5)
1.480(5)
1.246(5)
1.372(4)
1.436(5)
1.457(5)
N(1)–C(1)
N(1)–C(2)
N(1)–C(11)
N(2)–C(1)
N(2)–C(3)
N(2)–C(21)
N(3)–C(12)
N(3)–C(13)
N(4)–C(22)
N(4)–C(23)
1.466(6)
1.478(6)
1.447(6)
1.455(6)
1.480(6)
1.464(6)
1.453(6)
1.264(6)
1.462(7)
1.259(7)
C(1)–N(1)–C(12)
C(2)–N(1)–C(12)
C(1)–N(2)–C(3)
C(1)–N(2)–C(23)
C(3)–N(2)–C(23)
C(7)–N(3)–C(10)
C(7)–N(3)–C(11)
C(10)–N(3)–C(11)
C(13)–N(4)–C(14)
C(18)–N(5)–C(21)
C(18)–N(5)–C(22)
C(21)–N(5)–C(22)
C(24)–N(6)–C(25)
C(29)–N(7)–C(32)
C(29)–N(7)–C(33)
C(32)–N(7)–C(33)
C(51)–N(51)–C(52)
C(51)–N(51)–C(62)
C(52)–N(51)–C(62)
C(51)–N(52)–C(53)
C(51)–N(52)–C(73)
C(53)–N(52)–C(73)
C(57)–N(53)–C(60)
C(57)–N(53)–C(61)
C(60)–N(53)–C(61)
C(63)–N(54)–C(64)
C(68)–N(55)–C(71)
C(68)–N(55)–C(72)
C(71)–N(55)–C(72)
C(74)–N(56)–C(75)
C(79)–N(57)–C(82)
C(79)–N(57)–C(83)
C(82)–N(57)–C(83)
N(2)–C(23)
N(3)–C(7)
N(3)–C(10)
N(3)–C(11)
N(4)–C(13)
N(4)–C(14)
N(5)–C(18)
N(5)–C(21)
N(5)–C(22)
N(6)–C(24)
N(6)–C(25)
N(7)–C(29)
N(7)–C(32)
N(7)–C(33)
N(51)–C(51)
N(51)–C(52)
N(51)–C(62)
N(52)–C(51)
N(52)–C(53)
N(52)–C(73)
N(53)–C(57)
N(53)–C(60)
N(53)–C(61)
N(54)–C(63)
N(54)–C(64)
N(55)–C(68)
N(55)–C(71)
N(55)–C(72)
N(56)–C(74)
N(56)–C(75)
N(57)–C(79)
N(57)–C(82)
N(57)–C(83)
of TTTFMB and TTDMB were characterized using single crystal X-
ray crystallography. UV–Vis, FT-IR, mass spectroscopy and electro-
chemical properties of the TTFMB, TTDHB and TTDMB (Fig. 1) were
studied.
Experimental
Materials and methods
Triethylenetetramine hydrate (trien), 4-dimethylaminobenzal-
dehyde, 4-trifluoromethyl-benzaldehyde and 2,4-dihydroxybenz-
aldehyde, were purchased from Aldrich or Alfa and were used
without further purification. Infrared spectra were recorded as
KBr disks in the range 4000–400 cmꢀ1 on a Bruker FT-IR (Tensor
27) spectrophotometer. Mass spectra were obtained with Platform
II from Micromass. UV/Vis spectra were recorded on a Varian Cary
500 Scan spectrophotometer. Cyclic voltammograms (CV) were re-
corded by using a SAMA Research Analyzer M-500. Three elec-
trodes were utilized in this system, a glassy carbon working
electrode, a platinum disk auxiliary electrode and Ag/Ag+ as refer-
ence electrode. The glassy carbon working electrode (Metrohm
6.1204.110) with 2.0 0.1 mm diameter was manually cleaned
with 1 lm alumina polish prior to each scan. Tetrabutylammonium
tetrafluoroborate (n-Bu)4NBF4, was used as supporting electrolyte.
All electrochemical potentials were calibrated vs. internal Fc+/o
(E0 = 0.40 V vs. SCE) couple under the same conditions.
Fig. 4. Dihedral angle of TTFMB showing 45.72° angles between pendant arms and
the spacer.
and TTDMB were mounted on a MiTeGen mout with Paratone oil
and cooled to ꢀ150 °C in a stream of nitrogen gas. Data collection
were performed on a Bruker Kappa APEXII DUO diffractometer
with graphite-monochromated Mo K
a radiation (k = 0.71073 Å).
The data were integrated using SAINT [27] software and absorption
corrections were applied using program SADABS [28]. The structures
were solved by direct methods and refined by full-matrix least-
Single crystals suitable for X-ray diffraction were obtained as
described in the Experimental Section. Single crystals of TTFMB

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M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
synthesized as described in the experimental section and gave a
good overall yield for one pot synthesis of 72–90%. Starting from
the 4-substituted benzaldehydes and triethylenetetramine (trien)
the desired Schiff bases containing imidazolidine rings TTFMB,
TTDMB and TTDHB were produced (Fig. 1). Final purification was
achieved by recrystallization.
2-(40-Dimethylaminophenyl)-l,3-bis[30-aza-40-(400-dimethylamino-
phenyl)-prop-40-en-10-yl]-1,3-imidazolinelne (TTDMB)
A solution of 0.75 mmol of trien in 2.5 mL of ethanol was added
to a stirred solution of 3 mmol of 4-dimethylaminobenzaldehyde
in 2.5 mL ethanol for 3 h at 30 °C. The product was filtered out,
washed with cold ethanol and subsequently dried over anhydrous
CaCl2 in a desiccators yielding 75%, mp 167 °C. Recrystallization
from ethanol afforded X-ray quality crystals. Mass spectrum (EI):
539 (M+ = TTDMB+). Infrared spectrum (cmꢀ1, KBr disk): 1638 (s,
C@N), 1176 (s, C–N). UV–Vis (kmax/nm): 270, 305.
Fig. 5. Dihedral angle of TTDMB showing 69.19° angles between pendant arms and
the spacer.
squares using SHELTXL [29]. Experimental and refinement parame-
ters are summarized in Table 1. In both cases diffraction was weak
and required long exposure times to measure the data; for TTFMB
data were recorded to a resolution of 0.9 Å and for TTDMB to 1 Å. In
TTFMB, Friedel pairs were merged during final refinement, due to
lack of significant anomalous dispersion data. Probable disorder
of fluorine atoms in TTFMB was not modeled, in order to support
the poor data-to-paramater ratio. TTFMB was refined as a pseudo-
merohedral twin, with twin law 100/0ꢀ10/00ꢀ1 and an
18.38(18)% contribution from the minor twin component.
2-(40-Trifluoromethylphenyl)-l,3-bis[30-aza-40-(400-trifluoromethyl-
phenyl)-prop-40-en-10-yl]-1,3-imidazolinelne (TTFMB)
This was synthesized by the procedure outlined above for
TTDMB using trien (0.75 mmol) and 4-trifluoromethylbenzalde-
hyde (3 mmol).
Recrystallization from ethanol afforded X-ray quality crystals.
The yield was 72%; mp 110 °C. Mass spectrum (EI): 614 (M+ -
= TTFMB+). Infrared spectrum (cmꢀ1, KBr disk): 1650 (s, C@N),
1328 (s, C–F). UV–Vis (kmax/nm): 297.
Synthesis
2-(20,40-Dihydroxyphenyl)-l,3-bis[30-aza-40-(200,400-dihydroxy-phenyl)-
prop-40-en-10-yl]-1,3-imidazolinelne (TTDHMB)
A solution of 0.75 mmol of trien in 2.5 mL of ethanol was added
to a solution of 3 mmol of 2,4-dihydroxybenzaldehyde in 2.5 mL of
In a one-pot reaction the ligand was prepared by the condensa-
tion of 1 equivalent of trien and 3 equivalents of 4-substituted
benzaldehyde (Fig. 1). The desired 4-substituted benzylidene was
Fig. 6. Mass spectra of TTDMB ligand, 2-(40-dimethylaminophenyl)-l,3-bis[30-aza-40-(400-dimethylaminophenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.

M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
401
Fig. 7. Mass spectra of TTFMB ligand, 2-(40-trifluoromethylphenyl)-l,3-bis[30-aza-40-(400-trifluoromethylphenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.
ethanol. An orange precipitate was formed in 7 days. The product
was isolated by filtration, washed with cold ethanol and dried at
room temperature for a yield of 90%, mp 300 °C. Mass spectrum
(EI): 509 (M+ = TTDHMB+). Infrared spectrum (cmꢀ1, KBr disk):
1636 (s, C@N), 1360 (s, C–O), 3425 (m, O-H).UV–Vis (kmax/nm):
280, 310, 380.
Z = 2; those of TTDMB (C33H45N7) are monoclinic, P21/c,
a = 9.9799(13) Å, b = 30.568(3) Å, c = 19.951(3) Å, b = 92.888(2)°,
Z = 8. ORTEP views of the TTFMB and TTDHMB are shown in Figs.
2 and 3 respectively. Experimental details are reported in Table
1, selected bond lengths in Table 2 and bond angles in Table 3
The structure of TTDMB contains two crystallographically unique
molecules in the asymmetric unit; molecule A (defined by atoms
N1 to C33) and molecule B (defined by atoms N51 to C83. In both
TTFMB and TTDMB, all of the angles and distances are in the range
of those expected for this kind of Schiff base [31], and each adopts a
conformation which is determined by the formation of a five-
membered imidazolinic ring. The N3–C13 and N4–C23 distances
of 1.264(6) Å and 1.259(9) Å in TTFMB, and N4–C14 [N54–C64]
and N6–C25 [N56–C75] distances of 1.226(4) Å [1.268(4) Å] and
1.271(4) Å [1.246(5) Å] in TTDMB correspond to an N@C double
bond. Figs. 4 and 5 show the dihedral angle of TTFMB and TTDMB
with 45.72° and 69.19° angle between pendant arms and the
spacer respectively. More electron withdrawing substituent, CF3
of phenyl group will weaken the magnitude of electron density,
at least around the nearest primary amine, thereby reducing the
distances between pendant arms and the spacer while the mre
electron donating substituent, N(CH3)2 of phenyl group will en-
hance the distances between pendant arms and the spacer.
Electrochemical studies
The cyclic voltammograms of the three new tetraaza acyclic
Schiff bases were conducted at 25 °C under an argon atmosphere
using DMF solutions containing 0.05 mol dmꢀ3, (n-Bu)4NBF4 as
supporting electrolyte and complex concentrations of about
3 ꢂ 10ꢀ3 mol dmꢀ3
.
Results and discussion
Three new tetraaza acyclic Schiff bases TTFMB, TTDHB and
TTDMB used in this work belongs to a new class of l-bis(bidentate)
type with substituted five-membered imidazolidine spacer. The
synthesis and characterization of three tribenzylidinetriethylen-
etetramine ligands, TTFMB, TTDHB and TTDMB are described in
this work. The ligand with bis imine groups separated by a flexible
semi rigid imidazolidine ring can behave as a good bis(bidentate)-
N,N donor. This type of ligands is also favourable for the formation
of an infinite self-assembly which is not achieved with other ligand
system [30].
Spectroscopic studies
Mass spectrometry
The electron impact mass spectrum of the three new tetraaza
acyclic ligands confirms the proposed formula by showing peaks
(m/z) at 539 (M+ = TTDMB+), 614 (M+ = TTFMB+), 509 (M+ -
= TTDHMB+) which indicates the formation of the desired imidaz-
olidino N4 Schiff base ligand. The EI mass spectrums of the
X-ray diffraction studies
Crystals of TTTFMB (C30H27F9N4) are monoclinic, space group Pc,
a = 5.7301(5) Å, b = 10.9123(9) Å, c = 22.7746(18) Å, b = 90.157(5)°,

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M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
Fig. 8. Mass spectra of TTDHMB ligand, 2-(20,40-dihydroxyphenyl)-l,3-bis[30-aza-40-(200,400-dihydroxy-phenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.
Fig. 9. FT-IR spectra of TTDMB ligand, 2-(40-dimethylaminophenyl)-l,3-bis[30-aza-
40-(400-dimethylaminophenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.
Fig. 10. FT-IR spectra of TTFMB ligand, 2-(40-trifluoromethylphenyl)-l,3-bis[30-aza-
40-(400-trifluoromethylphenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.
ligands are shown in Figs. 6–8 respectively. The molecular peaks of
the cations are observed with the same isotopic distribution as the
theoretical ones.
(TTDHMB) which is shifted from the TTDMB, TTDHMB, TTFMB. In
the IR spectrum of the ligands the absence of band in the region
3400 cmꢀ1 (corresponding to free primary diamine) suggests that
complete condensation of amino group with keto group [32].
Appearance of a new strong absorption band at 1639–1650 cmꢀ1
range attributable to the characteristic stretching frequencies of
FT-IR spectra
IR spectra of the three new tetraaza acyclic ligands TTDMB,
TTFMB and TTDHMB are shown in Fig. 9–11 respectively. IR spectra
of the ligands show strong C@N stretching frequency of the imine
functions at 1650 cmꢀ1 (TTDMB), 1636 cmꢀ1 (TTFMB), 1638 cmꢀ1
the imino linkage t(C@N). The absorption in IR spectrum of (L) in
the range of 730–770 cmꢀ1 is due to the presence of phenyl group.
The electron withdrawing effect of substituent of phenyl group will

M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
403
Fig. 13a. Cyclic voltammogram of TTDMB in DMF solution stored for 48 h at 293 K.
Fig. 11. FT-IR spectra of TTDHMB ligand, 2-(20,40-dihydroxyphenyl)-l,3-bis[30-aza-
40-(200,400-dihydroxy-phenyl)-prop-40-en-10-yl]-1,3-imidazolinelne.
Scan rate: 100 mV/s. c = 3.0 ꢂ 10ꢀ3
.
Table 4
Electronic spectral data of the three new tetraaza acyclic ligands TTDMB, TTFMB and
TTDHMB in methanol.
TTDMB
TTFMB
TTDHMB
280 nm (p– )
pꢁ
270 nm (
p
–
pꢁ
)
297 nm (
p–
pꢁ
)
(920 Mꢀ1 cmꢀ1
)
(1533 Mꢀ1 cmꢀ1
)
(800 Mꢀ1 cmꢀ1
)
305 (n–pꢁ
)
310, 380 nm (n–pꢁ
)
Fig. 13b. Cyclic voltammogram of TTFMB in DMF solution stored for 48 h at 293 K.
Scan rate: 100 mV/s. c = 3.0 ꢂ 10ꢀ3
.
Fig. 12. UV–Vis of (a) TTDMB, (b) TTFMB and (c) TTDHMB ligands.
weaken the magnitude of electron density, at least around the
nearest primary amine, thereby reducing the C@N stretching fre-
t
quency. The other effect of substituents is steric, as the rather
bulky pendant group will hinder the movement of reactants into
the site where reaction can take place. In models shown in Fig. 1,
some conformations of the phenyl group lead to steric blocking
being clearly significant. Both aspects are more severe at the pri-
mary amine closest to the phenyl group. X-ray crystal structure
evidence, strongly support this argument.
Electronic spectra
Electronic spectra for TTDMB, TTFMB and TTDHMB were col-
lected in methanol and molar absorptivity data are summarized
in Table 4 Generally, two absorbance maxima were observed in
Fig. 13c. Cyclic voltammogram of TTDHMB in DMF solution stored for 48 h at
293 K. Scan rate: 100 mV/s. c = 3.0 ꢂ 10ꢀ3
.

404
M.H. Habibi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 396–404
ranges of 270–297 nm and 305–380 nm. The electronic spectra of
TTDMB in methanol have a maxima at 270 nm (Fig. 12) which
can be related to the spin allowed
Appendix A. Supplementary material
p–
pꢁ azomethene intraligand
CCDC 826165 and 826166 contains the supplementary crystal-
lographic data for ligand. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK, fax: +44 1223 336 033, or e-mail:
deposit@ccdc.cam.ac.uk.
transition [33]. The band at 305 nm can be assigned to spin-al-
lowed n–pꢁ transition. The absorbance spectra of ligands TTFMB
and TTDHMB show maxima at 297 and 280 nm respectively which
are proposed to be ligand based p–
pꢁ transitions.
Electrochemistry
References
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formamide by cyclic voltammetry which are shown in Figs. 13a–c
respectively. The voltammetric profile (Fig. 13a) for TTDMB on first
scan displays one oxidation wave at 1.50 V while TTFMB (Fig. 13b)
shows no electron transfer oxidation. The voltammetric profile
(Fig. 13c) for TTDHMB shows two oxidation waves at 1.11,
1.78 V, which appears to be completely irreversible (i.e., these lack
corresponding return waves), while a separate, irreversible reduc-
tion at ꢀ1.84, ꢀ1.91 and ꢀ1.50 V vs. SCE (again without its corre-
sponding oxidation wave) is observed for one-electron transfer
respectively. The lack of corresponding return waves is attributed
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Three new tetraaza acyclic Schiff bases TTFMB, TTDHB and
TTDMB with imidazolidine ring have been prepared by the reaction
of 4-substituted benzaldehydes and triethylenetetramine (trien)
with imidazolidine ring. The effects of various substituents (CF3,
N(CH3)2 or OH groups) on structure and physico-chemical proper-
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can behave as a good N4 donor. The electron withdrawing effect of
substituent of phenyl group will weaken the magnitude of electron
density, at least around the nearest primary amine, thereby reduc-
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electron donating N(CH3)2 of phenyl group will enhance the dis-
tances between pendant arms and the spacer. The novel NNNN-do-
nor
l-bis(bidentate) tetraaza acyclic Schiff base ligands with
different substituents (CF3, N(CH3)2 or OH groups) exhibit absor-
bance maxima related to the intraligand transition. The electro-
chemical behaviour shows oxidation waves related to electron
transfer reaction by cyclic voltammetry. Based on these results
and straightforward synthesis, ligands are interesting candidates
for mimic biological electron-transport.
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The authors wish to thank the University of Isfahan for finan-
cially supporting this work. The diffractometer was purchased with
funding from NSF Grant CHE-0741837.