A novel Schiff base bearing dopamine groups with tripodal structure. Synthesis and its salen/salophen-bridged Fe/Cr(III) capped complexes

Article abstract of DOI:10.1016/j.molstruc.2012.09.008

This work presents the synthesis of a novel Schiff base and its complexation properties with Fe(III) and Cr(III). A Schiff base bearing dopamine (TRDPA) was synthesized using dopamine hydrochloride and 1,3,5-tris (formylphenoxymethyl)benzene in methanol media. The prepared TRDPA was then reacted with four new trinuclear Fe(III) and Cr(III) complexes involving tetradenta Schiff bases N,N-bis(salicylidene)ethylenediamine-(salenH ₂) or bis(salicylidene)-o-phenylenediamine-(salophenH₂). The structures of these compounds were characterized through ¹H NMR, ¹³C NMR, FT-IR, thermal analysis (TG), elemental analysis, and magnetic susceptibility measurements. The complexes were also characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by a catechol group.

Full text of DOI:10.1016/j.molstruc.2012.09.008

Journal of Molecular Structure 1034 (2013) 69–74
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A novel Schiff base bearing dopamine groups with tripodal structure. Synthesis
and its salen/salophen-bridged Fe/Cr(III) capped complexes
⇑
Ozcan Kocyigit
Selcuk University, Department of Chemistry, 42031 Konya, Turkey
h i g h l i g h t s
"
"
"
"
"
A novel Schiff base bearing dopamine groups with tripodal structure have been synthesized.
The Fe/Cr(III)-salen/salophen complexes of this Schiff base have been prepared.
These complexes are the examples of trinuclear complexes.
The magnetic data for the complexes show well agreement with the d3 and d5 metal ion in an octahedral structure.
All of the complexes were characterized by means of magnetic susceptibility and other techniques.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 August 2012
Received in revised form 3 September 2012
Accepted 4 September 2012
Available online 12 September 2012
This work presents the synthesis of a novel Schiff base and its complexation properties with Fe(III) and
Cr(III). A Schiff base bearing dopamine (TRDPA) was synthesized using dopamine hydrochloride and
1,3,5-tris (formylphenoxymethyl)benzene in methanol media. The prepared TRDPA was then reacted
with four new trinuclear Fe(III) and Cr(III) complexes involving tetradenta Schiff bases N,N-bis(salicylid-
ene)ethylenediamine-(salenH2) or bis(salicylidene)-o-phenylenediamine-(salophenH2). The structures of
these compounds were characterized through 1H NMR, 13C NMR, FT-IR, thermal analysis (TG), elemental
analysis, and magnetic susceptibility measurements. The complexes were also characterized as low-spin
distorted octahedral Fe(III) and Cr(III) bridged by a catechol group.
Keywords:
Complexation
Trisaldehyde
Schiff base
Dopamine
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
as well as in liquid-crystal technology and mechanistic investiga-
tions of drugs used in pharmacology, biochemistry and physiology
The investigation of metal organic complexes is one of the most
active areas of material science and chemical research. Major ad-
vances have been made with these materials due to their interest-
ing properties and potential uses various applications, e.g.,
electrical conductivity, magnetism, host–guest chemistry, ion ex-
change, catalysis, nonlinear optics, etc. [1–3]. Many recent investi-
gations have aimed to synthesize new Schiff bases and their metal
complexes.
Schiff base ligands are considered ‘‘privileged ligands’’ because
they are easily prepared by a simple one-pot condensation of an
aldehyde and primary amines. The Schiff base ligands with nitro-
gen, oxygen and sulfur donor atoms in their structures act as good
chelating agents for transition and non-transition metal ions [4,5].
Transition metal complexes of Schiff bases are becoming increas-
ingly important in the pharmaceutical, dye, and plastic industries
[6,7]. Schiff bases are a class of chelators capable of forming coor-
dinate bonds with many metal ions through both azomethine and
phenolic groups [8–11]. Condensation of salicylaldehyde or salicyl-
aldehyde derivatives with 1,2-diamines leads to the formation of
one extremely important class of ligands, generally known as
‘‘Salens’’ (accordingly with o-phenylenediamine, Salophen).
Salen-type and Salophen-type ligands with N and O donor atoms
are important since their metal complexes find widespread appli-
cations as homogeneous and heterogeneous catalysts in various or-
ganic transformation reactions [12]. The bridged complexes of
salen–salophen are especially attractive, according to recent stud-
ies in inorganic chemistry [13,14].
Tripodal ligands have also long been used in both coordination
and bioinorganic chemistry [15,16]; typical examples include the
tripodal ligands, tripyridylalkylamine, triazine, and polypyridyl-
amine [17,18].
We report here that a tris aldehyde and its Schiff base derivative
have been synthesized to become a new template. The reaction of
⇑
Tel.: +90 3322232796; fax: +90 3322230106.
E-mail address: kocyigit76@gmail.com
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.008

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O. Kocyigit / Journal of Molecular Structure 1034 (2013) 69–74
trimeric 1,3,5-tris(bromomethyl)benzene (C9H9Br3) with 3 equiv of
4-hydroxybenzaldehyde in acetonitrile media has given the de-
sired tris aldehyde in a single step, coded as TRIPOD. Tris aldehyde
[20,21] was then converted to a novel Schiff base (TRDPA) with
dopamine. It may be useful to stress at this point that the new
products mentioned above are the main results of this work.
amount of triethylamine were added dropwise to the above solu-
tion. The mixture was refluxed for 36 h. The reaction mixture
was then allowed to cool to room temperature, and filtered. The
precipitate was washed with cool ethanol. Yield: 80%, FT-IR
(KBr): 1665 cmÀ1 (C@N), 3373 cmÀ1 (OH), 1H NMR (DMSO): d
2.80 (m, 6H, CH2CHN), 3.00 (m, 6H, PhCH2), 4.93 (s, 3H, ArOH),
5.11 (br s, 9H, CH2O, ArOH), 6.00 (s, 3H, ArH), 6.48 (s, 3H, ArH),
6.92–7.01 (m, 9H, ArH), 7.15-7.18 (m, 6H, ArH), 7.50 (m, 6H,
CHN, ArH). 13C NMR (DMSO): d 162.50, 155,68, 154,94, 144,21,
135,67, 131,27, 128,60, 126,89, 117.87, 115.92, 111.77, 110.54,
108.35, 73.22, 63.93, 42.50.
2. Experimental
2.1. Materials and methods
All starting materials and reagents used were of standard
analytical grade from Fluka, Merck, and Aldrich, and used with-
out further purification. [{Fe(salen)2}O], [{Fe(salophen)2}O],
[{Cr(salen)2}O] and Cr(salophen)2}O] were prepared according to
previously published methods [22,23]. Melting points were mea-
sured using a Buchi B-540 melting point apparatus. 1H and 13C
NMR spectra were recorded at room temperature on a Varian
400 MHz spectrometer in CDCl3. Thermal analysis (TG) was carried
out with a Seteram thermogravimetric analyzer. The sample
weight was 15–17 mg. Analysis was performed from room temper-
ature to 900 °C at a heating rate of 10 °C/min in an argon atmo-
sphere with a gas flow rate of 20 mL/min. Elemental analyses of
the ligand and its complexes were carried out on a Hewlett-
Packard 185 analyzer. FT-IR spectra were recorded using a Perkin
Elmer Spectrum 100. Magnetic susceptibilities of metal complexes
were determined using a Sheerwood Scientific MX Gouy magnetic
susceptibility apparatus, and carried out using the Gouy method
with Hg[Co(SCN)4] as a calibrant. The effective magnetic moments,
2.2.2. Preparation of [TRDPA-{Fe(III)(Salen/Salophen) (3,4)}] and
[TRDPA-{Cr(III)(Salen/Salophen) (5,6)}] complexes
A solution of TRDPA (1.72 g, 2 mmol) and [{Fe/Cr(salen)}2O] or
[{Fe/Cr(salophen)}2O] (3.1 mmol) in 80 mL of absolute ethanol
was refluxed for 4 h. The mixture was allowed to cool to room tem-
perature. The precipitate obtained was filtered and dried under
vacuum. The elemental analysis results, magnetic and physical
properties of the synthesized complexes are given in Table 1.
3. Results and discussion
We will describe the synthesis of a novel tripodal Schiff base
bearing dopamine (TRDPA) and its complexation properties with
[{Fe/Cr(salen)}2O] and [{Fe/Cr(salophen)}2O]. The synthesis of
TRDPA depicted in Fig. 1 was carried out as follows: Firstly, TRIPOD
(1) was synthesized using 1,3,5-trisbromomethylbenzene and 4-
hydroxybenzaldehyde in the presence of K2CO3 according to the
literature [19]. Then, the tripodal Schiff base (TRDPA, 2) was syn-
thesized using TRIPOD (1) and dopamine hydrochloride and a
catalytic amount of triethylamine in methanol (Fig. 1). The synthe-
sized compounds were characterized with 1H NMR, 13C NMR,
FT-IR, and elemental analysis. The 1H NMR spectra of TRDPA (2)
is depicted in Fig. 2. As can be seen in Fig. 2, the synthesis of TRDPA
(2) with new a Schiff base was confirmed by the disappearance of
aldehyde protons (9.89 ppm) in TRIPOD and the appearance of the
imine protons belong to a TRDPA compound (CH@N) at 7.50 ppm.
TRDPA prepared in this way has been obtained in nearly quantita-
tive yield and high purity. Synthetic strategy for preparing
Tripodal–Trinuclear uses a complex as a ‘‘ligand’’ that contains a
potential donor group capable of coordinating to another ligand.
[{Fe(salen)}2O] and [{Fe(salophen)}2O] have been chosen as ‘‘ligand
complex’’ because they can coordinate to another ligand [24].
These complexes are the first examples of tripodal–trinuclear
complexes bridged by catechol groups to the iron and chromium
l
eff, per metal atom was calculated from the expression:
leff = 2.84.
(vM)
1/2, where vM is the molar susceptibility.
2.2. Synthesis
1,3,5-Tris(formylphenoxymethyl)benzene (1,TRIPOD) as start-
ing material was obtained from the reaction of trimeric 1,3,5-
tris(bromomethyl)benzene (C9H9Br3) with 3 equiv of 4-hydroxy-
benzaldehyde, in our previous study [19]. For compound 1, 1H
NMR (CDCl3): d = 5.20 (s, 6H, ArACH2AO), 7.07 (d, 6H, ArAH,
J = 8.8 Hz), 7.50 (s, 3H, ArAH), 7.84 (d, 6H, ArAH, J = 8.8 Hz), and
9.89 (s, 3H, CHO).
2.2.1. Schiff base containing dopamine (2, TRDPA)
The suspension of 1,3,5-Tris(formylphenoxymethyl)benzene
(TRIPOD) (0.48 g, 1 mmol) and K2CO3 (1.55 g, 9 mmol) in methanol
(20 mL) was refluxed for 1 h. Next, a solution of dopamine hydro-
chloride (0.59 g, 3.1 mmol) in methanol (30 mL) and a catalytic
centers (Figs.
3
and 4). All compounds are stable at room
Table 1
Elemental analysis, magnetic and physical properties of the compounds.
Compound
Formula
Color
leff (BM)
m.p (°C)
Yield (%)
Found (Calcd.) (%)
C
N
H
M
1
2
3
4
5
6
C
C
C
C
C
C
30H24O16
Cream
–
155
85
80
70
75
65
75
74.99
(74.95)
73.31
(73.20)
66.70
(66.24)
66.73
(66.66)
68.82
(68.68)
69.23
–
–
5.03
(5.02)
5.89
(5.80)
5.12
(4.91)
5.05
(4.94)
4.69
(4.55)
4.72
–
–
–
–
54H51N3O9
Brown
–
205
4.82
(4.74)
6.99
(6.82)
7.03
(6.86)
6.47
(6.32)
6.51
(6.36)
102H90N9O15Fe3
102H90N9O15Cr3
114H90N9O15Fe3
114H90N9O15Cr3
Red Brown
Dark Green
Brown
1.51
3.62
1.73
3.55
312a
310a
305a
360a
9.29
(9.06)
8.60
(8.49)
8.60
(8.40)
8.15
(8.08)
Dark green
(69.08)
(4.58)
a
Decomposition.

O. Kocyigit / Journal of Molecular Structure 1034 (2013) 69–74
71
OH
HO
N
O
CHO
O
Metanol,triethylamine, reflux
NH2. HCl
HO
HO
+
pH = 5.0
O
O
O
O
OHC
N
CHO
N
HO
HO
OH
HO
TRIPOD (1)
TRDPA (2)
Fig. 1. Synthesis of a novel Schiff base containing dopamine (TRDPA).
Fig. 2. The 1H NMR spectra of TRIPOD (a) and TRDPA (b).
temperature in the solid state. The results of the elemental
analyses presented in Table 1 are in a close agreement with the
structures suggested for the ligand and its complexes. In addition,
the prepared salen and salophen capped complexes were charac-
terized through elemental analysis, thermal analysis, magnetic
susceptibility and FT-IR techniques.
The magnetic moments of the complexes presented in Table 1
were measured at room temperature. On the basis of spectral evi-
dence, the Fe(III) and Cr(III) complexes have trinuclear structures
in which the Fe(III) and Cr(III) cations have an approximately octa-
hedral structure. The magnetic behaviour of Fe(III) and Cr(III) com-
plexes is in accord with proposed trinuclear structures. The
magnetic moments of the trinuclear complexes indicate paramag-
netic properties with magnetic susceptibility values per atom of
1.51, 1.73, 3.62 and 3.55 B.M., respectively. The [{Fe(salen)}2O],
[{Fe(salophen)}2O], [{Cr(salen)}2O] and [{Cr(salophen)}2O] con-
taining compounds appear to be represented by the electronic
structures of t2g5eg0 and t2g3eg0. The magnetic data for the
[{Fe(salen)}2O], [{Fe(salophen)}2O], [{Cr(salen)}2O] and [{Cr(salo-
phen)}2O] tripodal complexes demonstrate strong agreement with
the d5 and d3 metal ion in an octahedral structure. This finding is
supported by the results of the elemental analyses also suggesting
that these trinuclear complexes have an octahedral structure
[19,22,23].
A FT-IR spectrum is one of the most suitable techniques to give
enough information to elucidate the nature of bonding of the li-
gand to the metal ion. The FT-IR spectra of the free ligand and me-
tal complexes were carried out in the range 4000–400 cmÀ1. The
characteristic FT-IR bands for compound 2 (TRDPA) and its Fe/
Cr(III)-salen/salophen complexes (3, 4, 5 and 6) are given in Table 2.

72
O. Kocyigit / Journal of Molecular Structure 1034 (2013) 69–74
N
N
N
N
O
O
Fe
Fe
H
O
O
H
O
O
O
O
N
N
O
O
O
O
O
O
N
N
N
N
H
O
H
O
O
O
H
N
H
O
N
O
O
O
O
Fe
O
O
O
O
Fe
O
O
N
O
N
Fe
Fe
N
N
N
N
3
4
R
N
N
O
M
O
O
+
TRDPA (2)
O
O
M
R
N
N
N
N
N
Cr
O
O
O
N
O
H
Cr
O
H
O
O
O
N
N
O
O
O
O
H
O
O
O
N
N
N
O
Cr
O
N
O
N
N
H
O
H
O
O
O
N
N
O
O
Cr
O
H
O
O
O
Cr
O
N
O
5
N
Cr
6
N
N
Fig. 3. Synthetic routes for complexation between TRDPA and Fe(III)–Cr(III).

O. Kocyigit / Journal of Molecular Structure 1034 (2013) 69–74
73
CHO
R
N
N
M
O
O
O
and
O
O
M
O
O
OHC
N
N
R
CHO
OH
H2N
OH
+
Fig. 4. Proposed models of Tripodal Oxy-Schiff base ligand and Tripodal–Trinuclear complexes.
bands in complexes 3, 4, 5 and 6 shift from 1665 to 1655, 1648,
1668, and 1661 cmÀ1, respectively. The phenolic OH bands in com-
plexes 3, 4, 5 and 6 also shift from 3373 to 3380, 3358, 3340, and
3395 cmÀ1, respectively. Phenolic CAO stretching vibrations at
1272, 1272, 1273 and 1271 cm-1 have also been observed at the
FT-IR spectra of 3, 4, 5 and 6, respectively, whereas they had been
observed at 1281 cmÀ1 for 2. It has been interpreted that a down-
ward shifts of 8–10 cmÀ1 for phenolic CAO stretching vibration in
the complexes indicates coordination through the oxygen atoms.
In the FT-IR analysis of the complexes (3, 4, 5 and 6), the bands
in the 554–535 and 467–475 cmÀ1 range can be attributed to the
MAN and MAO stretching modes [5].
Table 2
Characteristic FT-IR bands (cmÀ1) of ligand and its complexes.
Compounds C@N
OAH
3373 b 1125 s
1655 m 3380 b
1648 m 3358 b 1108 m
1668 m 3340 b 1121 m 1571 m 2930 w
1661 m 3395 b 1101 m 1525 m 2933 w
CAN
CACar
CAHaliph
CAOph
2
3
4
5
6
1665 s
1570 m
2936 w
1281 s
1129 m 1565 m 2928 w
1546 m 2924 w
1272 m
1272 m
1273 m
1271 m
s, strong; m, medium; w, weak; b, broad.
For exemplary, the FT-IR spectra of 2 and complex 6 were also de-
picted in Fig. 5. The FT-IR spectra of the complexes have different
absorption peaks, compared with that of the ligand. As can be seen
in Table 2, the imine C@N and phenolic OH stretching vibrations
for 2 were observed at 1665 and 3373 cm-1, respectively. In the
complexes, however, these bands are shifted to lower or higher fre-
quencies, indicating that the nitrogen and oxygen atoms of com-
pound 2 are coordinated to the ligand complexes [25]. The C@N
The thermal stability of prepared complex 4 was evaluated by
thermal gravimetric analysis (TG) and recorded in an argon
atmosphere from 40 °C to 900 °C. It was found that complex 4
undergoes a four-step thermal degradation (Fig. 6). The first step
(40–150 °C) is due to the loss of moisture. The decompositions
within the 250–575 °C and 575–750 °C temperature ranges are
due to the loss of coordinated water, N2, C2H4, salen groups, and
C6H6 from the main structure. Although the total weight lost was
Fig. 5. FT-IR spectra of TRDPA (2) and TRDPA-Cr(III)/Salophen (6).

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O. Kocyigit / Journal of Molecular Structure 1034 (2013) 69–74
Fig. 6. TG and dTG curve of complex 4.
theoretically calculated to be 73.71%, it was observed experimen-
tally to be 75.55%.
References
[1] D. Gatteschi, O. Kahn, J. Miller (Eds.), Molecular Magnetic Materials, Nato ASI
Series E198, Kluwer, Dordrecht, The Netherlands, 1991.
[2] O.M. Yaghi, G. Li, H. Li, Nature 378 (1995) 703.
[3] C.T. Chen, K.S. Suslick, Coord. Chem. Rev. 128 (1993) 293.
[4] M. Asadi, Z. Asadi, S. Torabi, N. Lotfi, Spectrochim. Acta. A 94 (2012) 372.
[5] A. Afkhami, T. Madrakian, H. Keypour, S. Soltanbeygi, F. Khajavi, M. Rezaeivala,
J. Mol. Struct. 985 (2011) 86.
[6] A. Chakraborty, P. Kumar, K. Ghosh, P. Roy, Eur. J. Pharmacol. 647 (2010) 1.
[7] M.S. Alam, J.H. Choi, D.U. Lee, Med. Chem. 20 (2012) 4103.
[8] O. Kocyigit, React. Inorg. Met.-Org. Chem. 4 (2) (2012) 196.
[9] R. Prabhakaran, A.M. Thilagavathi, R. Karvembu, V. Krishnan, H. Bertagnolli, K.
Natarajan, J. Inorg. Biochem. 98 (2004) 2131.
4. Conclusion
In the present study, a new Tripodal Oxy-Schiff base containing
dopamine was synthesized and its complexes were prepared. Syn-
thetic strategy for preparing Tripodal–Trinuclear uses a complex as
a ‘‘ligand’’ that contains a potential donor group capable of coordi-
nating to the other ligand. We have chosen [{Fe(salen/salophen)}2-
O] and [{Cr(salen/salophen)}2O] as ‘‘ligand complexes’’ because
they can coordinate to the other ligands. The prepared complexes
are examples of tripodal–trinuclear complexes bridged by catechol
groups to the iron and chromium centers. Their structures were
characterized by means of elemental analysis, 1H NMR, 13C NMR,
FT-IR spectroscopy, thermal analyses, and magnetic susceptibility
measurements. The magnetic data for the tripodal–trinuclear com-
plexes show strong agreement with the d5 and d3 metal ions in an
octahedral structure.
[10] K.P. Balasubramanian, R. Karvembu, R. Prabhakaran, V. Chinnusamy, K.
Natarajan, Spectrochim. Acta, Part A 68 (2007) 50.
[11] E. Guler, S. Ertul, A. Okudan, O. Kocyigit, Asian J. Chem. 20 (2008) 1533.
[12] B. Tamami, S. Ghasemi, Appl. Catal. A – Gen. 393 (2011) 242.
[13] A.R. Silva, C. Freire, B. Castro, New J. Chem. 28 (2004) 253.
[14] S.H. Wang, Y.T. Li, C.W. Yan, Pol. J. Chem. 80 (2006) 865.
[15] M. Etienne, Coord. Chem. Rev. 156 (1996) 201.
[16] F.S. Lisa, L.M. Withamb, K.J. Takeuchi, Coord. Chem. Rev. 174 (1998) 5.
[17] M. Schatz, M. Becker, F. Thaler, F. Hampe, S. Schindler, R.R. Jacobson, Z. Tyeklár,
N.N. Murthy, G. Phalguni, Q. Chen, J. Zubieta, K.D. Karlin, Inorg. Chem. 40
(2001) 2312.
[18] K. Jitsukawa, M. Harataa, H. Ariia, H. Sakuraib, H. Masudaa, Inorg. Chim. Acta
324 (2001) 108.
[19] O. Kocyigit, E. Guler, J. Incl. Phenom. Macrocycl. Chem. 67 (2010) 29.
[20] D.C. Tahmassebi, T. Sasaki, J. Org. Chem. 63 (1998) 728.
[21] D.C. Tahmassebi, T. Sasaki, J. Org. Chem. 59 (1994) 679.
[22] P. Kopel, Z. Sindelar, R. Klicka, Transition Met. Chem. 23 (1998) 139.
[23] M. Gembicky, R. Boca, F. Renz, Inorg. Chem. Commun. 3 (2000) 662.
[24] J.R. Dorfman, J.J. Girerd, E.D. Simhon, T.D.P. Stack, R.H. Holm, Inorg. Chem. 23
(1984) 4407.
Acknowledgement
We thank the Research Foundation of The Selcuk University
(BAP) for financial support of this work.
[25] O. Kocyigit, E. Guler, J. Incl. Phenom. Macrocycl. Chem. 67 (2010) 287.