Synthesis and spectral characterization of mercury(II) complexes with the bidentate Schiff base ligand N,N′-bis(2,3-dimethoxybenzylidene)-1,2- diaminoethane: The crystal structures of [Hg((23-MeO-ba)2en)I 2] and [Hg((23-MeO-ba)2en)Br2]

Article abstract of DOI:10.1016/j.poly.2011.08.024

Three mercury(II) complexes, [Hg((23-MeO-ba)₂en)X₂] (X = I (1), Br (2) and Cl(3)), and the ligand (23-MeO-ba)₂en ((23-MeO-ba)₂en = N,N′-bis(2,3-dimethoxybenzylidene)-1,2- diaminoethane) have been synthesized and characterized by elemental analyses, FT-IR and ¹H NMR spectroscopy. The crystal and molecular structures of 1 and 2 were determined by X-ray crystallography from single-crystal data. The metal-to-ligand ratio was found to be 1:1. The mercury(II) center in 1 and 2 has a distorted tetrahedral geometry with HgN₂I₂ and HgN₂Br₂ chromophores, respectively. The Schiff base ligand (23-MeO-ba)₂en acts as a chelating ligand, coordinating via the two nitrogen atoms to the mercury(II) center, and it adopts an E,E conformation. The coordination sphere of the mercury(II) center in 1 and 2 is completed by the two I and Br atoms, respectively. In complex 1 an inter-molecular non-classical hydrogen bond of the type C-H...O was found, while in complex 2 inter- and intra-molecular non-classical hydrogen bonds of the type C-H...X (X = O and Br) were found. The ¹H NMR spectra of the complexes exhibit downfield as well as upfield shifts of the free ligand resonances, reflecting changes in the ligand's geometry during its coordination.

Full text of DOI:10.1016/j.poly.2011.08.024

Polyhedron 30 (2011) 2790–2794
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and spectral characterization of mercury(II) complexes with the bidentate
Schiff base ligand N,N0-bis(2,3-dimethoxybenzylidene)-1,2-diaminoethane: The
crystal structures of [Hg((23-MeO-ba)2en)I2] and [Hg((23-MeO-ba)2en)Br2]
b
b
c
c
Aliakbar Dehno Khalaji a, , Gholamhossein Grivani , Morteza Rezaei , Karla Fejfarova , Michal Dusek
⇑
a Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran
b School of Chemistry, Damghan University, P.O. Box 36715-364, Damghan, Iran
c Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague 8, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Three mercury(II) complexes, [Hg((23-MeO-ba)2en)X2] (X = I (1), Br (2) and Cl(3)), and the ligand (23-MeO-
ba)2en ((23-MeO-ba)2en = N,N0-bis(2,3-dimethoxybenzylidene)-1,2-diaminoethane) have been synthe-
sized and characterized by elemental analyses, FT-IR and 1H NMR spectroscopy. The crystal and molecular
structures of 1 and 2 were determined by X-ray crystallography from single-crystal data. The metal-to-
ligand ratio was found to be 1:1. The mercury(II) center in 1 and 2 has a distorted tetrahedral geometry with
HgN2I2 and HgN2Br2 chromophores, respectively. The Schiff base ligand (23-MeO-ba)2en acts as a chelating
ligand, coordinating via the two nitrogen atoms to the mercury(II) center, and it adopts an E,E conformation.
The coordination sphere of the mercury(II) center in 1 and 2 is completed by the two I and Br atoms, respec-
tively. In complex 1an inter-molecular non-classical hydrogen bond of thetype C–Hꢀ ꢀ ꢀO was found, while in
complex 2 inter- and intra-molecular non-classical hydrogen bonds of the type C–Hꢀ ꢀ ꢀX (X = O and Br) were
found. The 1H NMR spectra of the complexes exhibit downfield as well as upfield shifts of the free ligand res-
onances, reflecting changes in the ligand’s geometry during its coordination.
Received 8 June 2011
Accepted 7 August 2011
Available online 31 August 2011
Keywords:
Mercury(II) complexes
Schiff base
Spectroscopy
X-ray crystallography
Tetrahedral
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
zylidene)-1,2-diaminoethane ligand (Scheme 1). For [Hg((23-MeO-
ba)2en)I2] (1) and [Hg((23-MeO-ba)2en)Br2] (2), crystal structures
Schiff base ligands have been connected with the progress of
coordination chemistry since the late 19th century. They have
played a major role in the development of complexes, providing
the effects of steric interactions on coordination geometries [1–7].
Schiff base transition metal complexes have good ability to revers-
ibly bind oxygen in epoxidation reactions, interesting biological
properties, a catalytic role in the hydrogenation of olefins and
remarkable photochromic properties [8–13]. Recent interest in the
coordination chemistry of the group XII metals, with a stable d10
electron configuration, has concentrated on complexes of Zn and
Cd with bidentate Schiff base ligands [1–3,14–25]. There is also a
substantial interest in the coordination chemistry of mercury(II) be-
cause of its toxic environmental effects. In a continuation of our
studies on fourfold coordinated complexes of the group XII metals
with bidentate Schiff base ligands [15,26,27], we describe herein
the synthesis and spectral characterization of three mercury(II)
complexes, [Hg((23-MeO-ba)2en)X2] (X = I (1), Br (2) and Cl(3))
where (23-MeO-ba)2en represents the N,N0-bis(2,3-dimethoxyben-
are presented.
2. Experimental
2.1. Materials and methods
All organic solvents were commercially available and were used
as received without further purification. The 2,3-dimethoxybenzal-
dehyde, ethane-1,2-diamine, HgI2, HgBr2 and HgCl2 were pur-
chased from Merck Chemical Company. Fourier Transform
Infrared spectra were recorded as a KBr disk on a FT-IR Perkin–El-
mer spectrophotometer. Elemental analyses were carried out using
a Heraeus CHN-O-Rapid analyzer. 1H NMR spectra were measured
on a BRUKER DRX-500 AVANCE spectrometer at 500 MHz for the
Schiff-base ligands and its complexes. All chemical shifts are re-
ported in d units downfield from TMS.
2.2. Preparation of (23-MeO-ba)2en
⇑
(23-MeO-ba)2en was prepared by condensation of 2,3-dime-
thoxybenzaldehyde with ethane-1,2-diamine following methods
Corresponding author. Tel./fax: +98 171 4427050.
E-mail addresses: alidkhalaji@yahoo.com, ad.khalaji@gu.ac.ir (A.D. Khalaji).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.024

A.D. Khalaji et al. / Polyhedron 30 (2011) 2790–2794
2791
H 1
H 1
H 2
MeO
O
+
H 3
CH3OH
MeO
OMe
N
N
MeO
H2N
NH2
MeO
H 7
OMe
H 4
HgX2
N
H 5
H 6
MeO
OMe
N
X
Hg
MeO
OMe
X
Scheme 1. Synthesis of the mercury(II) complexes [Hg((23-MeO-ba)2en)X2], X = I (1), Br (2) and Cl(3). Hydrogen atoms important for discussion of NMR spectra are indicated.
Table 1
Table 2
Crystallographic data and structure refinement for 1 and 2.
Selected bond distances (Å) and angles (°) of 1 and 2.
1
2
1
Hg1–I1
2.6556(4)
2.6556(4)
2.398(4)
N1–C1
N1–C2
C1–C1i
1.473(7)
1.262(8)
1.509(9)
Empirical formula
C
20H24N2O4HgI2
C20H24N2O4HgBr2
716.8
monoclinic
P21/c
Hg1–I1i
Formula weight
Crystal system
Space group
T (K)
a (Å)
b (Å)
810.8
monoclinic
C2/c
Hg1–N1
Hg1–N1i
2.398(4)
I1–Hg1–I1i
I1–Hg1–N1
I1–Hg1–N1i
Hg1–N1–C2
N1–C1–C1i
C1–N1–C2
134.547(14)
112.64(9)
103.45(9)
131.6(3)
109.7(4)
117.9(4)
I1i–Hg1–N1
I1i–Hg1–N1i
N1–Hg1–N1i
Hg1–N1–C1
N1–C2–C3
103.45(9)
112.64(9)
73.90(16)
108.9(3)
124.7(4)
120
150
29.4352(15)
7.1690(3)
12.3260(5)
110.896(5)
2430.0(2)
4
8.9
0.228
0.537
18 033
3115
132
2370
29.34
0.042
1.06
0.028
0.081
0.94
15.1569(3)
15.6692(2)
9.8671(2)
105.957(2)
2253.11(7)
4
10.43
0.121
0.581
32 584
4604
262
3845
26.4
0.043
1.20
0.021
0.048
0.72
c (Å)
b (°)
V (Å3)
2
Z
l
(mmꢁ1
)
Hg1–Br1
Hg1–N1
Hg1–Br2
Hg1–N2
2.5067(4)
2.351(2)
2.5050(4)
2.410(2)
N1–C2
1.265(4)
1.510(5)
1.464(4)
1.271(4)
C1–C11
N2–C11
N2–C12
Tmin
Tmax
Measured reflections
Independent reflections
Parameters
Reflection with I > 3
hmax (°)
N1–C1
1.464(4)
Br1–Hg1–Br2
Br1–Hg1–N1
Br2–Hg1–N1
N1–Hg1–N2
Br1–Hg1–N2
Br2–Hg1–N2
Hg1–N1–C1
Hg1–N1–C2
126.629(12)
111.22(6)
111.89(7)
75.95(8)
110.63(7)
119.12(6)
107.73(17)
133.5(2)
Hg1–N2–C11
Hg1–N2–C12
N1–C1–C11
N1–C2–C3
104.18(16)
138.6(2)
110.1(3)
124.6(3)
117.9(3)
110.0(3)
126.4(3)
117.2(2)
r(I)
Rint
C1–N1–C2
S
R[F2 > 2
wR(F2)
r
(F2)]
N2–C11–C1
N2–C12–C13
C11–N2–C12
D
D
qmax (e Åꢁ3
)
)
qmin (e Åꢁ3
ꢁ0.56
ꢁ0.39
Symmetry codes: (i) ꢁx + 1, y, ꢁz + ½.
Crystal size (mm)
0.28 ꢂ 0.23 ꢂ 0.10
0.40 ꢂ 0.16 ꢂ 0.07
described in [28].
A solution of 2,3-dimethoxybenzaldehyde
(3.30 g, 0.02 mol) in 25 ml methanol was heated for 15 min at
50 °C and then stirred for about 15 min. To this stirring solution,
a solution of ethane-1,2-diamine (0.6 g, 0.01 mol) in 15 ml metha-
nol was added dropwise under constant stirring. The mixture was
heated at about 50 °C for 1.5 h and then allowed to cool overnight
at 273 K. The resulting crude solid was collected by filtration and
dried at room temperature. Crystals were grown by the slow evap-
oration technique at room temperature in 25 ml methanol as a sol-
vent over 5 days. At the period of super saturation, tiny crystals
were nucleated. They were allowed to grow to the maximum pos-
sible dimensions and then filtered. Yield: 3.03 g, 85%. Colorless
crystals. Anal. Calc. for C20H24N2O4: C, 67.42; H, 6.74; N, 7.86.
Found: C, 67.35; H, 6.69; N, 7.79%. IR (KBr pellet, cmꢁ1): 2830–
3010 (m, C–H aromatic and aliphatic), 1639 (s, C@N). 1H NMR
(CDCl3, d (ppm)): 3.76 (s, 6H3), 3.84 (s, 6H4), 3.99 (s, 4H1), 6.91
(dd, 2H7), 7.02 (t, 2H6), 7.51 (dd, 2H5), 8.64 (s, 2H2).
0.2 mmol) in 10 ml of methanol. The mixture was stirred for
10 min in air at room temperature and then left at room tempera-
ture for several days without disturbance, yielding suitable crystals
of 1. They were filtered off and washed with Et2O. Yield: 75%. Col-
orless crystals. Anal. Calc. for C20H24N2O4HgI2: C, 29.63; H, 2.98; N,
3.45. Found: C, 29.44; H, 2.8; N, 3.49%. IR (KBr pellet, cmꢁ1): 2840–
3002 (m, C–H aromatic and aliphatic), 1651 (s, C@N). 1H NMR
(CDCl3, d (ppm)): 3.66 (s, 6H3), 3.79 (s, 6H4), 3.88 (s, 4H1), 7.05 (t,
2H6), 7.10 (dd, 2H7), 7.39 (dd, 2H5), 8.54 (s, 2H2).
2.4. Preparation of [Hg((23-MeO-ba)2en)Br2] (2)
This complex was prepared in a similar manner to 1 using HgBr2.
Yield: 68%. Colorless crystals. Anal. Calc. for C20H24N2O4HgBr2: C,
33.51; H, 3.37; N, 3.90. Found: C, 33.48; H, 3.31; N, 3.85%. IR (KBr pel-
let, cmꢁ1): 2832–3012 (m, C–H aromatic and aliphatic), 1631 (s,
C@N). 1H NMR (CDCl3, d (ppm)): 3.67 (s, 6H3), 3.80 (s, 6H4), 3.89 (s,
4H1), 7.06 (t, 2H6), 7.11 (dd, 2H7), 7.40 (dd, 2H5), 8.58 (s, 2H2).
2.3. Preparation of [Hg((23-MeO-ba)2en)I2] (1)
To a stirring solution of the (23-MeO-ba)2en ligand (0.071 g,
0.2 mmol) in 5 ml of chloroform was added HgI2 (0.091 g,

2792
A.D. Khalaji et al. / Polyhedron 30 (2011) 2790–2794
Fig. 1. The molecular structure of 1, showing 50% probability displacement ellipsoids and the atom-numbering.
Fig. 2. The molecular structure of 2, showing 50% probability displacement ellipsoids and the atom-numbering. The dashed line indicates a non-classical C–Hꢀ ꢀ ꢀBr hydrogen
bond.
ference Fourier maps and could be refined to a reasonable geometry.
According to common practice they were nevertheless kept in ideal
positions during the refinement. The isotropic atomic displacement
parameters of the hydrogen atoms were evaluated as 1.2Ueq of the
parent atom. Crystallographic data and details of the data collection
and structure solution and refinements are listed in Table 1. Se-
lected bond lengths and angles of 1 and 2 are listed in Table 2.
Table 3
Inter-molecular non-classical hydrogen bond in complex 1.
0
0
0
D–Hꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA (°)
D–H (ÅA)
Hꢀ ꢀ ꢀA (ÅA)
Dꢀ ꢀ ꢀA (AÅ)
3.496(7)
C10–H10bꢀ ꢀ ꢀO1
0.96
2.55
168
2.5. Preparation of [Hg((23-MeO-ba)2en)Cl2] (3)
3. Results and discussion
This complex was prepared in a similar manner to 1 using HgCl2.
Yield: 68%. Colorless micro-crystals. Anal. Calc. for
3.1. Synthesis
C
20H24N2O4HgCl2: C, 38.25; H, 3.85; N, 4.46. Found: C, 37.83; H,
The Schiff-base ligand (23-MeO-ba)2en was prepared by con-
densation of ethylenediamine with 2,3-dimethoxybenzaldehyde
following the method in [28]. The reaction of HgX2 with (23-
MeO-ba)2en in a methanol–chloroform solvent mixture at room
temperature resulted in monomeric mercury(II) complexes, as
shown in Scheme 1.
3.64; N, 4.43%. IR (KBr pellet, cmꢁ1): 2836 (s, CH@N), 2862–3037
(m, C–H aromatic and aliphatic), 1631 (s, C@N). 1H NMR (CDCl3, d
(ppm)): 3.66 (s, 6H3), 3.79 (s, 6H4), 3.89 (s, 4H1), 7.06 (t, 2H6), 7.11
(dd, 2H7), 7.40 (dd, 2H5), 8.57 (s, 2H2).
2.6. Crystallography data collection and refinement
The solubility of the Schiff base ligand (23-MeO-ba)2en and its
mercury(II) complexes were determined by adding the solvent to
a known amount of compound until complete dissolution. It was
found that the Schiff base ligand is moderately soluble in metha-
nol, ethanol and acetonitrile, insoluble in water and completely
soluble in chloroform, dichloromethane, DMF and DMSO, while
the mercury(II) complexes are only soluble in coordinating sol-
vents such as DMF and DMSO, but are insoluble in a range of com-
mon organic solvents such as methanol, ethanol, chloroform,
dichloromethane, acetone, acetonitrile and water. In order to con-
firm the chemical composition of the synthesized compounds, CHN
analysis was carried out on the recrystallized compounds. The re-
sults of the analysis are presented in Section 2.
Single crystal of dimensions 0.28 ꢂ 0.23 ꢂ 0.10 mm of 1, and
0.40 ꢂ 0.16 ꢂ 0.07 mm of 2 were chosen for the X-ray diffraction
study. Crystallographic measurements were done at 120 K for 1
and 150 K for 2 with a four circle CCD Gemini diffractometer of Ox-
ford diffraction, Ltd., using graphite-monochromated Mo Ka radia-
tion (k = 0.71069 Å), with a Mo-enhance fiber optics collimator
and Atlas CCD detector. The crystal structures were solved by direct
methods with the program SIR2002 [29] and refined with the
JANA2006 program package [30] by the full-matrix least-squares
technique on F2. The molecular structure plots were prepared by
ORTEP III [31]. Hydrogen atoms were mostly discernible in the dif-

A.D. Khalaji et al. / Polyhedron 30 (2011) 2790–2794
2793
3.2. 1H NMR spectra
3.4. Crystal and molecular structures of 1 and 2
The 1H NMR spectra of the (23-MeO-ba)2en ligand and its
mercury(II) complexes were recorded using CDCl3 and DMSO,
respectively. The 1H NMR spectra suggest that both the free li-
gand and the complexes have symmetrical structures. All methy-
lene and methoxy protons (H1, H3 and H4) appear as singlets in
the region 3.6–4.0 ppm. The signals appearing in the region
6.91–7.51 ppm have been assigned to the hydrogens atoms of
the aromatic rings (H5, H6 and H7) of the free Schiff base ligand.
The H7 protons exhibit a downfield shift relative to the free ligand
and show no significant differences by changing the anion. We
have found non-classical hydrogen bonds of the type C–Hꢀ ꢀ ꢀBr be-
tween the H7 and Br atoms in complex 2. The azomethine group
(H2) in the Schiff base ligand (23-MeO-ba)2en shows up at
8.64 ppm as a single signal [28]. In the complexes, the signal re-
lated to this group is shifted to a higher region [8.54 (1), 8.58 (2)
and 8.57 (3)]. This shift shows that the nitrogen atom of the azo-
methine group is coordinated to the mercury(II) ion.
The molecular structures of [Hg((23-MeO-ba)2en)I2] (1) and
[Hg((23-MeO-ba)2en)Br2] (2) with the atom-numbering schemes
are presented in Figs. 1 and 2, respectively. Selected bond distances
and angles are given in Table 2. In both structures, the mercury(II)
center is coordinated by the bidentate Schiff-base ligand (23-MeO-
ba)2en and two halide ions. Our results show that 1 and 2 are
isostructural. The structures of these complexes are quite different
from the mercury(II) complex Hg3I6(en)2 reported by Grdenic et al.
[32] and the mercury(II) complexes [HgBr2en]n and [HgI2en]n
reported by Matkovic-Calogovic and Sikirica [33]. The mercury(II)
complex Hg3I6(en)2 [32] was prepared by the reaction of ethane-
1,2-diamine with mercury(II) iodide in an aqueous solution of
potassium iodide, while the polymeric mercury(II) complexes
[HgBr2en]n and [HgI2en]n [33] were prepared by the reaction of
ethane-1,2-diamine with mercury(II) iodide in methanol solution.
In this paper, we prepared the Schiff base ligand (23-MeO-ba)2en
from the reaction of ethane-1,2-diamine with 2,3-dimethoxybenz-
aldehyde, and the complexes 1 and 2 were prepared from the reac-
tion of this ligand with mercury(II) halide in mixture of chloroform
and methanol (1:2).
The tetrahedral geometry might be expected for the fourfold
coordinated mercury(II) atom in 1 and 2 from the restricted bite
of the Schiff-base ligand (23-MeO-ba)2en, with a N–Hg–N chelate
angles of 73.90(16)° in 1 and 75.95(8)° in 2. This angle is smaller
than the range of 82–89° found for ethane-1,2-diamine chelate
3.3. FT-IR spectra
The FT-IR spectra of the free ligand (23-MeO-ba)2en exhibits the
characteristic band of the azomethine group (–C@N–), which ap-
pears at 1638 cmꢁ1 [28]. This band is shifted in the complexes to-
wards higher frequency in 1 and lower frequencies in 2 and 3
because of the coordination of the nitrogen atoms to the mer-
cury(II) ion, and appears at 1651 (1), 1630 (2) and 1632 cmꢁ1 (3).
The ligand’s stretching vibrations at about 2830–3015 cmꢁ1, as-
signed to the C–H azomethine, aromatic and aliphatic hydrogens,
are shifted to higher frequency in 1 and lower frequencies in 2
and 3.
compounds [15]. This angle is fixed0 by the size of the ligand
0
(Nꢀ ꢀ ꢀN = 2.883(2) ÅA in 1 and 2.930(4) ÅA in 2). On the contrary the
X–Hg–X bond angles have opened up to 134.547(14)° in 1 and
126.629(12)° in 2. The N–Hg–X bond angles are also distorted from
the tetrahedral values (see Table 2).
The average Hg–N bond lengths of 2.398 Å in 1 and 2.38 Å in 2
and Hg–X bond lengths of 2.66 Å in 1 and 2.51 Å in 2 agree well
with the corresponding distances in other tetrahedral mercury(II)
complexes [20–22], which also have distorted tetrahedral geome-
Fig. 3. Non-classical C10–H10bꢀ ꢀ ꢀO1 hydrogen bond in complex 1 (dashed line).
Fig. 4. Inter- and intra-molecular non-classical C–Hꢀ ꢀ ꢀX (X = O, Br) hydrogen bonds in complex 2 (dashed lines).

2794
A.D. Khalaji et al. / Polyhedron 30 (2011) 2790–2794
Table 4
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Intra- and inter-molecular non-classical hydrogen bonds in complex 2.
0
0
0
D–Hꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA (°)
D–H (ÅA)
Hꢀ ꢀ ꢀA (ÅA)
Dꢀ ꢀ ꢀA (AÅ)
C8–H8ꢀ ꢀ ꢀBr2
0.96
0.96
0.96
0.96
3.09
2.97
2.41
2.73
4.048(3)
3.875(4)
3.326(4)
3.652(4)
174.04
158.65
158.73
162.26
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tries about the mercury(II) center with unequal metal–ligand bond
distances and angles. The Schiff-base ligand (23-MeO-ba)2en
adopts a E,E configuration in these complexes. The value for the
torsion angle C1–N1–C2–C3 is 178.6(4)° in 1 and ꢁ178.9(3)° in 2
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complex 1, its molecules are eventually linked together via an
inter-molecular non-classical C10–H10bꢀ ꢀ ꢀO1 hydrogen bond
(Table 3 and Fig. 3).
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non-classical hydrogen bonds of the type C–Hꢀ ꢀ ꢀX (X = O, Br)
(Fig. 4 and Table 4). The intra-molecular hydrogen bonds are
formed between aromatic H-atoms of the bidentate Schiff base
ligand and the coordinated bromine atom (Figs. 2 and 4). The
[Hg((23-MeO-ba)2en)Br2] (2) molecules are eventually linked
together via inter-molecular non-classical hydrogen bonds formed
between aromatic and aliphatic H-atoms of the ligand and the
bromine atoms (Fig. 4).
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Acknowledgements
We acknowledge Golestan University (GU) and Damghan Uni-
versity (DU) for partial support of this work, the institutional re-
search plan No. AVOZ10100521 of the Institute of Physics and
the project P204/11/0809 of the Grant Agency of the Czech
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Appendix A. Supplementary data
CCDC 821624 and 821625 contain the supplementary crystallo-
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