Synthesis and spectroscopic studies of some cadmium(II) and mercury(II) complexes of an asymmetrical bidentate Schiff base ligand

Article abstract of DOI:10.1016/j.saa.2009.02.023

Synthesis and spectroscopic studies on four-coordinate complexes of cadmium(II) and mercury(II) halides with a new asymmetrical bidentate Schiff base ligand of N,N′-bis[α-methylcinamaldehydene]propane-1,2-diamine(L) are described. The ligand and its compl

Full text of DOI:10.1016/j.saa.2009.02.023

Spectrochimica Acta Part A 73 (2009) 231–237
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and spectroscopic studies of some cadmium(II) and mercury(II)
complexes of an asymmetrical bidentate Schiff base ligand
Morteza Montazerozohori∗, Shiva Joohari, Sayed Alireza Musavi
Department of Chemistry, Yasouj University, Daneshjoo Street, Yasouj 75918-74831, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis and spectroscopic studies on four-coordinate complexes of cadmium(II) and mercury(II) halides
with a new asymmetrical bidentate Schiff base ligand of N,Nꢀ-bis[␣-methylcinamaldehydene]propane-
1,2-diamine(L) are described. The ligand and its complexes were characterized by elemental analysis,
molar conductance, UV–visible spectra, FT-IR spectra, MS, 1H NMR and 13 C NMR spectra. The complexes
Received 30 August 2008
Received in revised form 19 January 2009
Accepted 4 February 2009
are non-electrolytes in DMF. The electronic spectra of the complexes were recorded in DMF solution.
Keywords:
Schiff base
Cadmium(II)
Mercury(II)
Spectroscopic
Asymmetrical
FT-IR
13
1H and
C NMR spectra been studied in CDCl3. The molar conductance as well as spectral properties
indicated the complexes do not dissociate in DMF and retain their coordination. FT-IR and NMR spectra of
the complexes exhibit downfield as well as upfield shifts of the free ligand resonances that show change
in geometry during the coordination. The suggested structure of the complexes is pseudo-tetrahedral.
Molecular structures of the complexes have been optimized by MM+ calculations that supported pseudo-
tetrahedral geometry around the metal (II) ions.
NMR
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
cal and electronic properties [15–17]. Recently group XII metal
complexes, which contain a stable d10 electronic configuration,
There is a continuing interest in the chemistry of Schiff
bases and their complexes because of their ability as biologically
active substances, liquid crystals, dyes, luminophores and poly-
mer stabilizers [1–3]. New applications such as antidepressants,
antimicrobial, antitumor, antiphlogogistic, nematocide, and other
medicinal agents have been reported based on these compounds
[4–5]. These compounds have played a major role in the develop-
ment of the inorganic coordination chemistry providing the effects
of steric interactions on coordination geometries. Numerous Schiff
base ligands are often used as polydentate ligands in coordination
chemistry by regarding their metal binding ability. Schiff base metal
complexes have good ability to reversibly bind oxygen in epox-
idation reactions [6], biological properties [7,8], catalytic role in
hydrogenation of olefins [9,10] and photochromic properties [11].
Schiff bases can be used to obtain optical materials and
conducting polymers [12,13]. Thus, new optical and organic con-
ducting materials can be produced by these compounds. The
compounds, containing Schiff bases seem to be suitable candidates
for further chemical modifications and may be optical communica-
tion and optical devices [14]. Schiff base containing amphiphiles
in polymeric films have been shown to have interesting opti-
have received a lot of attention in the fields of inorganic chem-
istry, biochemistry and environmental chemistry [18–26]. Also
d10 complexes with polydentate ligands have been considerably
investigated as potential luminescent materials [27–29]. The cin-
namaldehyde derivatives have been found to undergo a variety of
different photoprocesses including cis–trans isomerization, there-
fore photoprocesses studies of the titled compounds including
␣-methylcinnamaldehyde can be noteworthy on the photoisomer-
ization reactions which occur in photobiological processes such
as vision and damage in living systems [30,31]. There is sub-
stantial interest in the coordination chemistry of cadmium and
mercury because of the toxic environmental effect of them. There-
fore mobilization and immobilization of them in the environment,
in organisms, and in some chemical processes have been found
to depend significantly on the complexation of these metal ions
by coordination with nitrogen donor ligands [32]. On the other
hand, from the view of coordination chemistry of XII metals, the
report on synthesis and spectroscopic studies of new bidentate
Schiff base complexes of cadmium(II) and mercury(II) that are
scarce in the literature seems to be notable for inorganic chemist.
In continuation of our studies on four coordinated complexes
[33–36], in the present paper we report the synthesis, physical
and spectral characterisation of a new asymmetrical bidentate
Schiff base ligand of N,Nꢀ-bis[˛-methylcinamaldehydene]propane-
1,2-diamine(L) and its cadmium(II) and mercury(II) complexes with
general formula of MLX2 (M = Cd(II) and Hg(II); X = Cl−, Br− and I−).
∗
Corresponding author. Tel.: +98 7412223048; fax: +98 7412223048.
E-mail addresses: mmzohory@yahoo.com, mmzohori@mail.yu.ac.ir
(M. Montazerozohori).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.02.023

232
M. Montazerozohori et al. / Spectrochimica Acta Part A 73 (2009) 231–237
Table 1
Analytical and physical data of the Schiff base ligand (L) and its cadmium(II) and mercury(II) complexes.
Compound
Mol. wt. (calcd.)
Color
M.p. (◦C)
Yield (%)
Found (Calcd.) (%)
C
ꢀM (cm2 −1 mol−1
ꢁ )
H
N
L
330.47
513.78
602.68
696.69
601.96
690.86
784.86
Light Yellow
White
White
White
White
Viscose oil
240
230
210
149
72
75
84
76
78
79
77
83.75 (83.59)
53.88 (53.77)
46.01 (45.84)
39.72 (39.65)
45.95 (45.89)
40.09 (39.99)
35.11 (35.20)
7.71 (7.93)
5.21 (5.10)
4.41 (4.35)
3.64 (3.76)
4.43 (4.35)
3.88 (3.79)
3.42 (3.34)
8.32 (8.48)
5.35 (5.45)
5.56 (5.65)
4.11 (4.02)
4.54 (4.65)
4.01 (4.05)
3.48 (3.57)
2.08
21.15
22.14
23.74
13.77
14.22
14.66
CdLCl2
CdLBr2
CdLI2
HgLCl2
HgLBr2
HgLI2
White
White
155
140
2. Experimental
3. Results and discussion
2.1. Materials and methods
3.1. Physical data
(E)-␣-methyl-cinnamaldehyde,
1,2-propanediamine,
cad-
The analytical and physical data of the Schiff base ligand and
its complexes are given in Tables 1 and 2. The analytical data show
that the metal halides to ligand ratio are 1:1 in all the complexes.
All of the isolated complexes are soluble in organic solvents such as
chloroform, dichloromethane, dimethylformamide and dimethyl-
sulfoxide and insoluble in alcohols. The melting points of the
complexes were at 140–240 ◦C. The complexes can be presented
by the general formula of CdLX2 and HgLX2 (X = Cl−, Br− and I−)
as shown in Fig. 1. The low molar conductivities of 10−3 M solu-
tions of all complexes in DMF solvent at room temperature were
in the range of 13.77–23.74 cm2 ꢁ−1 mol−1 which shows them to
be non-electrolytes so that the complexes are not dissociated in
DMF solution and the anions are also coordinated to the metal ion
[37,38].
mium(II) and mercury(II) halides and other chemicals were
purchased from either Aldrich, Merck or BDH Chemicals. All the
chemicals used were of Analytical grade. Solvents were purified
and dried before use according to the standard method. FT-IR spec-
tra in KBr pellets were recorded on a JASCO FT/IR-680 spectrometer
in the 4000–400 cm−1 range. Electronic spectra were recorded in
DMF solutions on a JASCO-V570 model spectrometer with quartz
cells of 0.5 cm path length. 1H and 13C NMR spectra were obtained
using a Brucker DPX FT-NMR spectrometer at 500 MHz with the
samples dissolved in CDCl3 or CDCl3/DMSO-d6 mixture using
TMS as internal standard. MS (m/z) of the ligand was recorded on
Shimadzu model GC–MS QP5050. Carbon, hydrogen and nitrogen
of dried samples were performed using an elemental analyzer.
The melting points (◦C) of the complexes were recorded on BUCHI
melting point B-545 instrument. Conductivity measurements of
the ligand and their complexes were made on freshly prepared
10−3 M solutions in DMF at room temperature with a Metrohm 712
conductometer with a dip-type conductivity cell made of platinum
black.
3.2. FT-IR spectra
The most characteristic absorptions of the bidentate Schiff base
ligand and its complexes are summarized in Table 2. The corre-
sponding cadmium(II) and mercury(II) complexes exhibit ligand
absorptions at different frequencies indicating the coordination of
the ligand.
Characteristic absorption frequencies of the starting mate-
rial including aldehyde and 1,2-propanediamine at 1680 and
3100–3300 cm−1 were not observed in the FT-IR spectrum of the
ligand at all. The ligand stretching frequencies at 3054, 3024, (2964,
2925) and 2858 cm−1 assigned to C–H of aromatic, olefinic, aliphatic
and iminic groups respectively are shifted to lower energy after
its coordination to metal ions. The band due to the imine group
ꢂC N mode of free ligand at 1626 cm−1 [6–11,18–20,26] is shifted
by 17–20 cm−1 to lower frequencies in the spectra of the complexes
indicating coordination through the iminic nitrogen of the Schiff
base. This observed red shift of iminic frequencies after coordina-
tion can be attributed to the ␲-back bonding of metal to ligand
2.2. Preparation of
N,Nꢀ-bis[(E)-˛-methylcinamaldehydene]propane-1,2-diamine(L)
To a solution of (E)-␣-methyl-cinnamaldehyde (0.584 g, 4 mmol)
in absolute methanol (10 mL) was added
a solution of 1,2-
propanediamine, (0.15 g, 2 mmol) in absolute methanol (10 mL) and
severely stirred for 3–4 h. After completion of the reaction, the sol-
vent of light yellow solution was reduced in vacuo using rotary
evaporator to give the Schiff base ligand as the yellowish-white
viscose oil. For purification, the oil obtained, was washed twice
with n-hexane as non-solvent, and dried under vacuum to obtain
the ligand with good purity with yield of 72% (0.48 g). The Schiff
base is soluble in dichloromethane, chloroform, acetone, dimethyl-
sulfoxide, dimethylformamide while is less soluble in alcohols and
non-soluble in n-hexane and n-heptane.
2.3. Preparation of MLX2 (M = Cd(II) and Hg(II); X = Cl−, Br− and
I−) complexes
The cadmium (II) and mercury(II) complexes were prepared by
stepwise addition and stirring of the ligand (0.5 mmol) in methanol
(15 mL) to the respective 0.5 mmol of cadmium(II) or mercury(II)
halides in methanol (15 mL) for 1–3 h. The white complexes, MLX2
so obtained were filtered off, washed with ethanol twice and
dried under vacuum. The precipitates were recrystallized from
dichloromethane (or chloroform)/ethanol mixture and dried at
80–100 ◦C under vacuum and were kept in a desiccator over silica-
gel. The yields are as in Table 1.
Fig. 1. The structure of MLX2 (M = Cd(II) and Hg(II); X = Cl−, Br− and I−).

M. Montazerozohori et al. / Spectrochimica Acta Part A 73 (2009) 231–237
233
[37,38]. It seems with increasing of softness and polarizability of
coordinated halides from Cl− to I−, the ␲-back donation of metal
center and therefore the red shift of iminic frequency is smoothly
increased. The absorption at 1358 cm−1 of the spectrum of the lig-
and may be assigned to C–N stretching mode that is red shifted to
1347–1349 cm−1 after its coordination. The ligand C C stretching
vibrations at 1490 and 1447 cm−1, the bending vibration of methyl
groups at 1385 cm−1 and very strong out of plane (oop) bending
vibrations of the aromatic C–H and C–C at 752 and 698 cm−1 [39,40]
are nearly unchanged after coordination. In the spectra of the com-
plexes, the absorption at 458–490 and 417–460 cm−1 regions that
are absent in the spectrum of the ligand may be due to symmetrical
and asymmetrical vibration modes of M–N [37,38,41] supporting
the coordination of two iminic nitrogens. Finally three anions of
chloride, bromide and iodide have almost affected other vibration
modes especially on M–N of the complexes differently indicating
the coordination of these various halides in size in inner sphere
coordination as well as the bidentate ligand.
3.3. Electronic spectra
The electronic spectral data of the compounds, which were mea-
sured in DMF, are given in Table 2. In the spectrum of the ligand, the
bands at 276 and 282 (shoulder) are attributed to the ␲–␲* tran-
sition of the ethylenic and aromatic rings of the (PhCH CH(Me)–)
moieties and absorption at 290 nm (shoulder) may be due to the
␲–␲* transitions of the imine group which is mainly localized
within the iminic chromophore. During the formation of the com-
plexes, these bands are appeared as a broad band at 276 nm or
blue shifted band at 268 nm, suggesting the coordination of the
iminic nitrogens to the metal ions. The electronic spectra of d10
-
elements generally consists ligand to metal charge transfer that in
our complexes were not separately observed (probably overlapped
with internal transition of the ligand) [42]. The suggested structure
of d10-four coordinated complexes based our evidences and with
considering our previous report on this type of ligands [33–36] is
pseudo-tetrahedral as drawn in Fig. 1.
3.4. Mass spectra investigation
The mass spectrum of the ligand in Fig. 2 presents the peak
corresponding to the molecular ion 329(M+−1) lends support to
the formula shown in Fig. 1 and also indicates stability of ligand
molecules in gas phase. A probable fragmentation diagram of the
ligands is proposed in Fig. 3. Other fragments are in agreement with
the molecular structure of the ligand.
3.5. 1H and 13 C NMR spectra
The 1H and 13C NMR spectra were recorded using CDCl3 as sol-
vent at 500 MHz and their data were summarized in Tables 3 and 4.
The NMR spectra of the ligand and its Cd(II) and Hg(II) complexes
show well-resolved signals as expected (Fig. 4: 1H and 13C NMR
spectra of the ligand, CdLI2 and HgLI2) and strongly support the
geometry of the compounds. The 1H NMR spectrum of the ligand
ꢀ
includes the iminic protons (He and He ) resonances at 8.02 and
7.97 ppm [42]. These signals are red shifted to 8.35–8.20 ppm in its
complexes with respect to TMS, suggesting well coordination of the
iminic nitrogens to metal ions.
As shown in 1H NMR data in Table 3 and discussion in Section 3.2
herein again with increasing of softness and polarizability of coor-
dinated halides from Cl− to I−, the ␲-back donation of metal center
and therefore iminic protons is more shielded. The aromatic and
olefinic protons of the ligands appeared at 7.40–7.32 and 6.81–6.80
are shifted to weaker fields in its complexes. It is interesting that
the protons, Ha, Hb and Hc of the ligand are more completely sepa-

234
M. Montazerozohori et al. / Spectrochimica Acta Part A 73 (2009) 231–237
Fig. 2. MS spectrum of N,Nꢀ-bis[(E)-␣-methylcinamaldehydene]propane-1,2-diamine(L).
Fig. 3. A part of the probable fragmentation diagram of the ligand based on mass spectrum.
Table 3
1H NMR chemical shifts of ligand and its cadmium(II) and mercury(II) complexes in ppm in CDCl3 (supplementary materials).
Compounds
L
Proposed assignment of the protons
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.02 (s, 1He), 7.97 (s, 1He ), 7.40 (m, 8H(2Hh, 2Hh , 2Hi, 2Hi )), 7.32 (t, 2Hjj , J = 5.80 Hz and J = 5.15 Hz), 6.81 (s, 1Hf), 6.80 (s, 1Hf ), 3.86 (dd, 1Ha, J = 10.56 Hz
ꢀ
and J = 4.63 Hz), 3.69 (sextet, 1Hc, J = 6.10 Hz), 3.66 (dd, 1Hb, J = 10.59 Hz and J = 7.33 Hz), 2.18 (s, 3Hg), 2.17 (s, 3Hg ) and 1.36 (d, 3Hd, J = 6.14 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
CdLCl2
CdLBr2
CdLI2
8.33 (t, 1He, J = 19.22 Hz), 8.29 (t, 1He , J = 18.97 Hz), 7.46 (m, 8H(2Hh, 2Hh , 2Hi, 2Hi )), 7.42 (m, 2Hjj ), 7.19 (s, 1Hf), 7.18 (s, 1Hf ), 4.29 (bd, 1Ha, J = 12.97 Hz),
ꢀ
4.07 (nine, 1Hc, J = 3.41 Hz), 3.64 (dd, 1Hb, J = 13.30 Hz and J = 1.81 Hz), 2.61 (d, 3Hg, J = 1.07 Hz), 2.60 (d, 3Hg , J = 1.18 Hz) and 1.46 (d, 3Hd, J = 6.84 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.32 (t, 1He, J = 19.22 Hz), 8.28 (t, 1He , J = 18.97 Hz), 7.46 (m, 8H(2Hh, 2Hh , 2Hi, 2Hi )), 7.42 (t, 2Hjj , J = 5.28 Hz and J = 4.5 Hz), 7.19 (s, 1Hf), 7.18 (s, 1Hf ), 4.27
ꢀ
(bd, 1Ha, J = 13.32 Hz), 4.08 (nine, 1Hc, J = 3.41 Hz)), 3.65 (dd, 1Hb, J = 13.40 Hz and J = 1.72 Hz) 2.60 (s, 3Hg), 2.59 (s, 3Hg ) and 1.43 (d, 3Hd, J = 6.81 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.30 (t, 1He, J = 17.05 Hz), 8.25 (t, 1He , J = 16.57 Hz), 7.46 (m, 8H(2Hh, 2Hh , 2Hi, 2Hi )), 7.42 (m, 2Hjj ), 7.19 (bs, 2Hff ), 4.32 (bd, 1Ha, J = 13.34 Hz), 4.09 (nine,
ꢀ
1Hc, J = 3.15 Hz)), 3.61 (dd, 1Hb, J = 13.41 Hz and J = 1.86 Hz), 2.63 (s, 3Hg), 2.61 (s, 3Hg ) and 1.46 (d, 3Hd, J = 6.81 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
HgLCl2
HgLBr2
HgLI2
8.35 (s, 1He), 8.29 (s, 1He ), 7.46 (m, 8H (4Hhh , 4Hii )), 7.40 (m, 2Hjj ), 7.11 (bs, 2Hff ), 4.28 (bd, 1Ha, J = 12.90 Hz), 3.99 (nine, 1Hc, J = 3.42 Hz), 3.59 (dd, 1Hb,
ꢀ
J = 13.07 Hz and J = 2.42 Hz), 2.51 (bs, 6Hgg ) and 1.38 (d, 3Hd, J = 8.81 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.33 (s, 1He), 8.27 (s, 1He ), 7.46 (m, 8H (4Hhh , 4Hii )), 7.40 (m, 2Hjj ), 7.11 (bs, 2Hff ), 4.30 (bd, 1Ha, J = 12.96 Hz), 4.00 (nine, 1Hc, J = 3.36 Hz), 3.56 (dd, 1Hb,
ꢀ
J = 13.10 Hz and J = 2.56 Hz), 2.52 (d, 3Hg, J = 1.07), 2.51 (s, 3Hg ) and 1.40 (d, 3Hd, J = 6.77 Hz).
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.26 (s, 1He), 8.20 (s, 1He ), 7.46 (m, 8H (4Hhh , 4Hii )), 7.39 (septet, 2Hjj , J = 3.82 Hz), 7.08 (bs, 2Hff ), 4.32 (bd, 1Ha, J = 12.83 Hz), 3.98 (nine, 1Hc, J = 3.33 Hz),
ꢀ
3.52 (dd, 1Hb, J = 12.96 Hz and J = 3.01 Hz), 2.49 (s, 3Hg), 2.48 (s, 3Hg ) and 1.42 (d, 3Hd, J = 6.76 Hz).

M. Montazerozohori et al. / Spectrochimica Acta Part A 73 (2009) 231–237
235
Table 4
13 C NMR chemical shifts of the ligand and its cadmium(II) and mercury(II) complexes in ppm in CDCl3.
Compounds Proposed assignment of the carbons
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C(1 ,1)
C(2 ,2)
C(3 ,3)
C(4 ,4)
C(5 ,5)
C(6 ,6)
C(7 ,7)
C(8 ,8)
C(9 ,9)
C(10)
L
137.10
130.28
130.26
129.77
130.13
130.14
129.19, 129.14
137.14
130.26
130.29
129.79, 128.72 137.36, 137.27
139.48, 139.23 128.10, 128.01
148.69, 148.63 129.89, 129.17
148.59, 148.53 129.79, 129.07 15.77, 15.69
148.39, 148.32 129.75, 129.05 17.41, 17.26
13.85, 13.68 167.94, 165.95 68.10, 66.68 20.96
CdLCl2
CdLBr2
CdLI2
HgLCl2
HgLBr2
HgLI2
134.01
134.02
135.30
135.32
15.27, 15.11
174.86, 173.08 66.12, 65.51 20.44
174.86, 173.08 66.13, 65.52 20.84
130.32, 130.30 134.24, 134.22 135.37
130.16
130.16
130.15, 130.13
174.67, 173.09
172.63, 170.83 66.83, 65.95 20.36
129.30, 128.97 15.85, 15.83 172.46, 170.78 66.84, 66.28 20.47
135.95, 135.93 145.44, 145.36 128.95, 128.93 16.86, 16.73 171.78, 170.26 66.85, 66.83 20.63
66.08, 66.03 21.02
134.58, 134.52 135.74, 135.70
134.80, 134.73 135.80, 135.76
135.25, 135.15
146.56
146.33
129.35, 128.99 15.12, 15.09
Fig. 4. 1H NMR (A–C) and 13 C NMR (D–F) of the ligand, CdLI2 and HgLI2.

236
M. Montazerozohori et al. / Spectrochimica Acta Part A 73 (2009) 231–237
Table 5
Data for selected bond lengths and bond angles of MLX2 complexes.
Selected data
CdCl2
CdLBr2
CdLI2
HgCl2
HgBr2
HgI2
Bond length (Å)
M–N(1)
2.1408
2.1435
2.1456
2.1550
2.1541
2.1533
M–N(2)
M–X(1)
M–X(2)
2.1431
2.4652
2.4650
2.1455
2.6179
2.6176
2.1436
2.8073
2.8077
2.1535
2.4774
2.4779
2.1528
2.6298
2.6299
2.1542
2.8201
2.8199
Bond angle (◦)
N(2)–M–N(1)
N(2)–M–X(1)
N(2)–M–X(2)
N(1)–M–X(1)
N(1)–M–X(2)
X(1)–M–X(2)
84.4661
111.4560
114.7600
114.4330
111.6750
116.0850
84.3566
112.1890
114.1930
113.8050
112.6970
115.7180
84.3719
112.2720
114.0670
113.733
112.6900
115.7980
84.0701
84.3098
109.891
110.5450
116.0210
116.1480
115.4120
84.3385
110.3670
109.6210
116.2200
116.2820
115.4060
114.3240
112.1540
112.7380
113.8770
115.7290
Torsion angle (◦)
N(2)–C(1)–C(2)–N(1)
−45.5478
−47.6533
−47.5893
−47.9243
−47.5966
−47.6094
rated in its cadmium and mercury complexes. In the spectrum of the
ligand, Ha is observed at 3.86 ppm as doublet of doublet due to cou-
pling with the Hc and Hb respectively. Hb is appeared similar to Ha
at 3.66 ppm as doublet of doublet due to its couplings with Ha and
Hc respectively. But in all complexes Ha is shown as broad doublet
but Hb is stayed doublet of doublet and the signals of both protons
are shifted to weak fields after coordination. The signal of the Hc of
the ligand is appeared as clear sextet because of its coupling with
Hd and then with Ha and Hb with coupling constant of 6.10 Hz. But
this signal is observed as multiplet (nine) in all complexes. Hd of the
ligand is seen as a doublet at 1.36 ppm due to coupling with Hc that
Edihedral, Eelectrostatic, for the optimized structures of the complexes,
CdLCl2, CdLBr2, CdLI2, HgLCl2, HgLBr2 and HgLI2 are 56.15, 57.52,
57.53, 57.90, 44.47 and 44.35 kcal/mol respectively. The molecular
mechanics geometry optimization as well as other evidences sup-
ports pseudo-tetrahedral geometry of the metal complexes. The
optimized molecular structure of CdLCl2 as a typical complex is
given in Fig. 5. The selected bond length and bond angles of the
complexes are represented in Table 5, that are comparable with
pseudo-tetrahedral geometry.
4. Conclusion
ꢀ
shifted to 1.38–1.46 ppm in the complexes. Hg and Hg signals of the
ligand at 2.17–2.18 ppm, are appeared at weaker fields after coordi-
nation. The 13C NMR spectrum of the ligand shows the two iminic
carbons C(8ꢀ,8) resonances as functional groups signals at 167.94,
and 165.95 ppm [42] because of its asymmetrical structure. These
peaks are shifted to 170.26–174.86 ppm in its complexes, suggest-
ing well coordination of the iminic nitrogens to metal ion. Among
the other signals, C(3ꢀ,3), C(5ꢀ,5), C(6ꢀ,6) and C(7ꢀ,7) are deshielded
but C(1ꢀ,1), C(2ꢀ,2), C(4ꢀ,4), C(9ꢀ,9) and C(10) shielded after coordina-
tion. These changes in 13C NMR chemical shifts are due to balancing
of the probable resonances during the long conjugation of the lig-
and with ␲-back bonding of metal to ligand after coordination. Full
detailed assignments of the 1H NMR and 13C NMR spectra based on
structure of Fig. 1 are given in Tables 3 and 4.
In this paper we report the synthesis and full spectroscopic char-
acterization of newly synthesized asymmetrical bidentate Schiff
base ligand and some its cadmium(II) and mercury(II) complexes.
The physical and spectral data as well as molecular modeling
studies using molecular mechanics geometry optimization suggest
coordination of the ligand and halides in pseudo-tetrahedral geom-
etry for all complexes. These complexes will be a new series of four
coordinated complexes of group XII along with other reported com-
plexes. Due to asymmetrical structure of the ligand and complexes,
these complexes can display different properties in compared with
similar complexes with symmetrical ligands.
Acknowledgement
3.6. Molecular structures and analysis of bonding modes
Partial support of this research by Yasouj University is acknowl-
edged. Also thanks to Azad University of Yasouj for some
cooperations in this research.
In order to ascertain the structural preferences and coordi-
nation behaviors of bidentate Schiff base ligand to metal ions,
molecular mechanics (MM+) calculations on the MLX2 complexes
were performed. We have optimized the molecular structures of
the complexes. Energy minimization was repeated several times
to find the global minimum. The energy minimization value (E)
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