Synthesis, spectroscopic and thermal studies of zinc(II) complexes with the symmetrical bidentate schiff-base ligand (2,3-MeO-ba)2en: Crystal structure of Zn((2,3-MeO-ba)2en)I2

Article abstract of DOI:10.1007/s10870-011-0207-3

Two zinc(II) complexes [ZnI₂((2,3-MeO-ba)₂en)] (1) and [ZnCl₂((2,3-MeO-ba)₂en)] (2), with the symmetrical bidentate Schiff-base ligand (2,3-MeO-ba)₂en [N,N′-bis(2,3- dimethoxybenzylidene)-1,2-diaminoe

Full text of DOI:10.1007/s10870-011-0207-3

J Chem Crystallogr (2012) 42:83–88
DOI 10.1007/s10870-011-0207-3
ORIGINAL PAPER
Synthesis, Spectroscopic and Thermal Studies of Zinc(II)
Complexes with the Symmetrical Bidentate Schiff-Base Ligand
(2,3-MeO-ba)2en: Crystal Structure of Zn((2,3-MeO-ba)2en)I2
•
Aliakbar Dehno Khalaji Gholamhossein Grivani
•
•
Samaneh Jalali Akerdi Helen Stoeckli-Evans
•
Debasis Das
Received: 29 January 2011 / Accepted: 17 November 2011 / Published online: 1 December 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Two zinc(II) complexes [ZnI2((2,3-MeO-ba)2en)]
(1) and [ZnCl2((2,3-MeO-ba)2en)] (2), with the symmetri-
cal bidentate Schiff-base ligand (2,3-MeO-ba)2en
[N,N0-bis(2,3-dimethoxybenzylidene)-1,2-diaminoethane]
have been synthesized and characterized by elemental
Introduction
The coordination chemistry of transition metals containing
the bidentate Schiff-base ligands has been of interest for
many years [1–5]. The preparation of new Schiff-base
ligands is perhaps the interesting step in the development
of coordination chemistry of transition metals [6–10].
These ligands have played a special role as chelating
ligands in transition metal complexes due to their stability
[1–10]. These complexes are an important class of coor-
dination chemistry not only because they have interesting
properties and geometry, but also they have found impor-
tant applications in catalysis [11, 12].
1
analyses (CHN), FT-IR and H-NMR spectroscopy. The
thermal behaviors of these complexes were studied using
thermogravimetry in order to evaluate their thermal sta-
bility and thermal decomposition pathways. The crystal
structure of [ZnI2((2,3-MeO-ba)2en)] (1) was determined
from single-crystal X-ray diffraction. The coordination
polyhedron about the zinc(II) center in the complex 1 is
best described as a distorted tetrahedron.
Although the coordination chemistry of symmetric
bidentate Schiff-base ligands with copper(I) has been
extensively studied [6–12], there is few data on zinc(II)
complexes with these ligands [13–17]. In a continuation of
our work on the preparation of zinc(II) complexes with
bidentate Schiff-base ligands [18–20], here we report the
synthesis and characterization of two zinc(II) complexes
[ZnI2((2,3-MeO-ba)2en)] (1) and [ZnCl2((2,3-MeO-ba)2en)]
(2), with the symmetrical bidentate Schiff-base ligand
Keywords Schiff-base; zinc(II) complexes ꢀ
Spectroscopy; single-crystal ꢀ Thermal
A. D. Khalaji (&)
Department of Chemistry, Faculty of Science,
Golestan University, Gorgan, Iran
e-mail: alidkhalaji@yahoo.com; ad.khalaji@gu.ac.ir
(2,3-MeO-ba)2en
[N,N0-bis(2,3-dimethoxybenzylidene)-
1,2-diaminoethane] (Scheme 1).
G. Grivani ꢀ S. J. Akerdi
School of Chemistry, Damghan University, Damghan,
P. O. Box 36715-364, Iran
Experimental
H. Stoeckli-Evans
Institute of Physics, University of Neuchatel,
Materials and General Methods
ˆ
Rue Emile-Argand 11,
CH-2009 Neuchatel, Switzerland
All reagents and solvents for synthesis and analysis were
commercially available and used as received without
further purifications. Infrared spectra were recorded using
KBr disks on a FT-IR Perkin-Elmer spectrophotometer.
Elemental analyses were carried out using a Heraeus
D. Das
Department of Chemistry,
The University of Burdwan, Burdwan,
West Bengal, India
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J Chem Crystallogr (2012) 42:83–88
Scheme 1 Synthesis and
chemical structures of Zn(II)
complexes
MeO
O
+
MeO
OMe
N
N
CH3OH
2
-
H2O2
H2N
NH2
MeO
MeO
OMe
ZnX2
N
compound
[ZnI2((2,3-MeO-ba)2en)] (1)
[ZnCl2((2,3-MeO-ba)2en)] (2)
X
I
MeO
N
OMe
Cl
Zn
MeO
OMe
X
X
Table 1 Crystallographic data and structure refinement for
[ZnI2((2,3-MeO-ba)2en)] (1)
CHN-O-Rapid analyzer, and results agreed with calculated
1
values. H-NMR spectra were measured on a BRUKER
DRX-500 AVANCE spectrometer at 500 MHz for the
Schiff-base ligands and their complexes. All chemical
shifts are reported in d units downfield from TMS.
Thermogravimetric analyses were done on a Perkin Elmer
TGA/DTA lab system l (Technology by SII) in nitrogen
atmosphere with a heating rate of 20 °C/min from
35–700 °C.
Empirical formula
Formula weight
Crystal system, space group
T (K)
C20H24N2O4ZnI2
675.58
Monoclinic, C2/c
173
˚
a (A)
˚
29.384 (3) A
˚
b (A)
˚
7.2220 (4) A
˚
c (A)
˚
12.2890 (9) A
b (deg)
113.724 (6)
3
V (A )
3
˚
˚
2,387.5 (3) A
Preparation of (2,3-MeO-ba)2en Ligand
Z
4
l (mm-1
)
3.64 mm-1
0.098, 0.171
10554
A
solution of 2,3-dimethoxybenzaldehyde (3.30 g,
Tmin, Tmax
0.02 mol) in 25 mL methanol was heated and stirred for
15 min. To this stirring solution, a solution of ethylene-
diamine (0.6 g, 0.01 mol) in 15 mL methanol was added
dropwise with constant stirring. The mixture was heated
at about 50 °C for 1.5 hours and then allowed to cool
overnight at 273 K. The resulting crude solid was col-
lected by filtration and dried at room temperature. Crys-
tals were grown by the slow evaporation technique at
room temperature in 25 mL methanol as a solvent for
5 days. At the period of super saturation, tiny crystals
were nucleated. They were allowed to grow to a maxi-
mum possible dimension and then filtered. Yield: 3.28 g,
92%. Colorless crystals. Anal. Calc. for C20H24N2O4: C,
67.39; H, 6.78; N, 7.86%. Found: C, 67.35; H, 6.69; N,
7.79%. IR (KBr pellet, cm-1): 2,830 (s, CH=N),
2,842–3,010 (m, C–H aromatic and aliphatic), 1,654 (s,
C=N), 1595, 1496, 1460, 1416 (s, C=C aromatic). 1H-
NMR (CDCl3, d(ppm)): 3.76 (s, 6H), 3.84 (s, 6H), 3.99
(s, 4H), 6.91 (dd, 2H), 7.02 (t, j = 7.95, 2H), 7.51 (dd,
2H), 8.64 (s, 2H).
Measured reflections
Independent reflections
Reflection with I [ 2r(I)
Rint
2262
1775
0.09
S
1.04
R[F2 [ 2r(F2)]
wR(F2)
0.042
0.094
Parameters
135
-3
)
˚
Dqmax, Dqmin (eA
Crystal size (mm3)
0.72, -0.60
0.03 9 0.40 9 0.45
was stirred for 10 min in air at room temperature and was
then left at 273 K for several days without disturbance.
Single crystals suitable for X-ray crystallography of 1 were
obtained by slow evaporation of solvent. They were filtered
off and washed with Et2O. Yield: 0.12 g, 89%. Colorless
crystals. Anal. Calc. for C20H24N2O4ZnI2: C, 35.55; H,
3.58; N, 4.15%. Found: C, 35.45; H, 3.36; N, 4.18%. IR
(KBr pellet, cm-1): 2,833 (s, CH=N), 2,864–3,033 (m,
C–H aromatic and aliphatic), 1651 (s, C=N), 1582, 1487,
Preparation of [ZnI2((2,3-MeO-ba)2en)] (1)
1
To a stirring solution of the (2,3-MeO-ba)2en ligand
(0.071 g, 0.2 mmol, in 5 mL chloroform) was added ZnI2
(0.064 g, 0.2 mmol) in 10 mL methanol and the mixture
1464, 1429 (s, C=C aromatic). H-NMR (CDCl3, d(ppm)):
3.64 (s, 6H), 3.78 (s, 6H), 3.87 (s, 4H), 7.02–7.09 (m, 4H),
7.37 (dd, 2H), 8.49 (s, 2H).
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J Chem Crystallogr (2012) 42:83–88
85
Fig. 1 1H-NMR spectrum of 1
(a) and 2 (b) in DMSO-d6 at
298 K
Fig. 2 The molecular structure
of 1 with the atom-numbering
schemes. Atomic displacement
parameters are shown at 50%
probability level
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J Chem Crystallogr (2012) 42:83–88
˚
Table 2 Selected bond distances (A) and angles (°) of 1
Table 4 Inter-molecular hydrogen bond geometry for 1
˚
Bond distance (A)
D–HꢀꢀꢀA
D–H
HꢀꢀꢀA
DꢀꢀꢀA
D–HꢀꢀꢀA
I1–Zn1
2.5454(6)
2.069(5)
2.069(5)
1.391(7)
1.427(10)
1.363(8)
1.429(10)
1.476(8)
1.247(11)
C9–H9CꢀꢀꢀO2ii
0.98
0.98
2.57
2.53
3.438(10)
3.472(10)
148
161
Zn1–N1
Zn1–N1i
C10–H10AꢀꢀꢀO1iii
Symmetry codes: ii -x - 1/2, -y - 1/2, -z; iii -x - 1/2, y ? 1/2,
-z ? 1/2
O1–C4
O1–C9
O2–C5
1
(s, C=N), 1583, 1483, 1458, 1444 (s, C=C aromatic). H-
O2–C10
N1–C1
NMR (CDCl3, d(ppm)): 3.64 (s, 6H), 3.78 (s, 6H), 3.87 (s,
4H), 7.02–7.09 (m, 4H), 7.38 (dd, 2H), 8.50 (s, 2H).
N1–C2
Bond angle (°)
I1–Zn1–N1
I1–Zn1–I1i
I1–Zn1–N1i
I1i–Zn1–N1
N1–Zn1–N1i
I1i–Zn1–N1i
C4–O1–C9
C5–O2–C10
Zn1–N1–C1
Zn1–N1–C2
C1–N1–C2
N1–C1–C1i
N1–C2–C3
O1–C4–C3
O1–C4–C5
O2–C5–C4
O2–C5–C6
108.62(14)
120.61(3)
114.80(13)
114.80(13)
83.6(2)
X-Ray Crystallography for 1
Single crystals suitable for X-ray crystallography of 1 was
obtained as colorless plates by slow evaporation of solvent at
273 K {Crystal size: 0.03 9 0.40 9 0.45 mm3}. The
intensity data were collected at 173 K (-100 °C) on a Stoe
Mark II-Image Plate Diffraction System [21] equipped with
a two-circle goniometer and using MoKa graphite mono-
chromated radiation (k = 0.71073 A). Image plate distance
130 mm, x rotation scans 0–180° at /0°, and 0–62.0° at /
90°, step Dx = 1.3°, exposures of 7 min per image, 2h range
108.62(14)
115.7(5)
117.6(5)
108.0(5)
134.9(4)
116.0(5)
108.0(5)
124.9(5)
118.3(5)
119.9(6)
116.5(5)
125.5(6)
˚
˚
1.76–52.59°, dmin – dmax = 2,3.107–0.802 A. The structure
was solved by direct methods using the programme SHEL-
XS-97 [22]. The refinement and all further calculations were
carried out using SHELXL-97 [22]. The H-atoms were
included in calculated positions and treated as riding atoms
using SHELXL default parameters. The non-H atoms were
refined anisotropically, using weighted full-matrix least-
squares on F2. An empirical absorption correction was
applied using the MULscanABS routine in PLATON [23].
The molecule has crystallographic C2 symmetry, with the
zinc(II) atom sitting on the 2-fold rotation axis. Crystallo-
graphic data and details of the data collection and structure
solution and refinements are listed in Table 1.
i: x, y, -z ? 1/2
Table 3 Selected torsion angles (°) of 1
Torsion angles
C2–N1–C1–C1i
C1–N1–C2–C3
N1–C2–C3–C8
N1–C2–C3–C4
C2–C3–C4–C5
C2–C3–C8–C7
128.8(6)
178.4(5)
-33.8(9)
149.5(6)
178.0(6)
-177.6(6)
Results and Discussion
Synthesis
i: -x, y, -z ? 1/2
The Schiff-base N,N0-bis(2,3-dimethoxybenzylidene)-1,2-
diaminoethane, (2,3-MeO-ba)2en, was synthesized by the
mixing of ethylenediamine and 2,3-dimethoxybenzalde-
hyde. The reaction of ZnX2 and (2,3-MeO-ba)2en in meth-
nol-chloroform solvent mixture at room temperature results
in monomeric zinc(II) complexes as shown in Scheme 1.
The Schiff-base ligand is soluble in a range of common
organic solvents such as methanol, ethanol, chloroform,
dichloromethane, acetone, acetonitrile, dimethylformamide
and dimethylsulfoxide, but insoluble in water. The
Preparation of [ZnCl2((2,3-MeO-ba)2en)] (2)
This complex was prepared by a procedure similar to 1 using
0.2 mmol (0.027 g) of ZnCl2 dissolved in in 10 mL metha-
nol. Yield: 0.074 g, 86%. Colorless crystals. Anal. Calc. for
C20H24N2O4ZnCl2: C, 48.75; H, 4.91; N, 5.69%. Found: C,
48.48; H, 4.73; N, 5.67%. IR (KBr pellet, cm-1): 2,834 (s,
CH=N), 2853–3039 (m, C–H aromatic and aliphatic), 1636
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J Chem Crystallogr (2012) 42:83–88
87
Fig. 3 Non-classical C–HꢀꢀꢀI
and C–HꢀꢀꢀO hydrogen bonds in
complex 1 (dashed lines)
complexes are only soluble in coordinate solvents such as
dimethylformamide and dimethylsulfoxide, but insoluble in
a range of common organic solvent such as methanol, etha-
nol, chloroform, dichloromethane, acetone, acetonitrile and
water.
Spectral Studies
The most characteristic absorptions of the bidentate Schiff-
base ligand (2,3-MeO-ba)2en and its zinc(II) complexes are
presented in the experimental section. The complexes
exhibit ligand absorption at different frequencies indicating
the coordination of the ligands [13–18]. The t(C=N)
band which appears at 1,654 cm-1 in the free ligand, (2,3-
MeO-ba)2en, shift to lower frequency, 1,651 cm-1 (1) and
1,636 cm-1 (2), upon complexation [13–18].
The 1H-NMR spectra of zinc(II) complexes were
recorded using DMSO-d6 are shown in Fig. 1a and b,
1
respectively. The H-NMR spectra of the Schiff-base and
its zinc(II) complexes suggest that the ligand has sym-
metrical structure in free and in the complexes. The com-
plexes exhibit similar signals to the free ligand, indicating
the coordination of the ligand to the metal ions [13–18]. All
methylene and methoxy protons appear as a singlet in the
region 3.6–4.0 ppm. In the region of 6.60–7.65 ppm were
assigned chemical schifts for hydrogen of symmetrical
aromatic ring of ligands. The 1H-NMR spectra of the
Schiff-base ligands and their complexes show a singlet in
the region 8.37–8.65 ppm, which has been assigned to the
azomethine (HC=N) proton.
Fig. 4 TG graph of 1 (a) and 2 (b)
Structure of 1, show the zinc(II) is coordinated by the
bidentate Schiff-base ligand (2,3-MeO-ba)2en and two
iodine ions. While a tetrahedral geometry might be expec-
ted for a four coordinated zinc(II) center, the geometry
around the zinc(II) ion in 1 is distorted by the restricting bite
of chelate angle N1–Zn1–N1i 83.60(2)°of the Schiff-base
ligands. This angle is in the range of 82–89° found for
ethylenediamine chelate compounds [13–18], and much
less than 109.5°. On the contrary the I1–Zn1–I1i angle has
opened up to 120.61(3)°. The N–Zn–I angles are also dis-
torted from the tetrahedral values (Table 2).
Crystal and Molecular Structure of 1
The molecular structure of [ZnI2(2,3-MeO-ba)2en] (1) with
the atom-numbering schemes is presented in Fig. 2.
Selected bond distances and angles are given in Table 3.
˚
The average Zn–N bond lengths of 2.069 A and Zn–I
˚
bond lengths of 2.545 A agree well with the same distances
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J Chem Crystallogr (2012) 42:83–88
in other tetrahedral zinc(II) complexes [19, 20]. The
geometry about the zinc(II) center in these complexes is
also approximately tetrahedral, with distortion indicated by
the unequal metal–ligand bond distances and angles. In
order to obtain a low structure preference energy for other
complexes with d10 ions, then a distorted tetrahedral
structure can be inferred for other zinc(II) complexes
[13–20]. The Schiff-base ligand (2,3-MeO-ba)2en adopts
a Z,Z configuration in this complex [18–20]. The value
for the dihedral angles C1–N1–C2–C3 is 178.4(5)° and
C2–C3–C8–C7 is -177.6(6)°, indicating an almost planar
configuration of this moiety for the complexes studied here
(Table 3) [18–20].
the complexes) are well characterized by different spec-
troscopic techniques and microanalytical data. The struc-
ture of 1 has been confirmed by X-ray crystallographic
analysis. Thermal stability and decomposition pattern of
the Zn(II) complexes are described elaborately.
Acknowledgments We acknowledge Golestan University (GU) and
Damghan University (DU) for partial support of this work, The
ˆ
University of Burdwan (UB) for TG and University of Neuchatel
(UN) for X-ray analysis.
References
1. Drew MGB, De S, Datta D (2009) Inorg Chim Acta 362:2487
2. Das S, Sarkar BN, Bhar K, Chattopadhyay S, Fun HK, Mitra P,
Ghosh BK (2010) Inorg Chem Commun 13:353
3. Dolaz M, McKee V, Urus S, Demir N, Sabik AE, Golcu A,
Tumer N (2010) Spectrochim Acta A76:174
4. Morshedi M, Amirnasr M, Triki S, Khalaji AD (2009) Inorg
Chim Acta 362:1637
The geometry of hydrogen bonds in 1 is given in
Table 4. Complex 1, exhibits a different hydrogen bonding
pattern built up from non-classical C–HꢀꢀꢀO hydrogen
bonds in the crystal structure (Fig. 3).
Thermal Analysis
5. Morshedi M, Amirnasr M, Slawin AMZ, Woollins JD, Khalaji
AD (2009) Polyhedron 28:167
6. Pascu M, Clarkson GJ, Kariuki BM, Hannon MJ (2006) Dalton
Trans 22:2635
Thermogravimetric analyses of these complexes under N2
were examined and the TG graphs are shown in Fig. 4. The
title compounds [ZnI2(2,3-MeO-ba)2en] (1) and [ZnCl2(2,3-
MeO-ba)2en] (2) are stable up to 471 and 489 K, respec-
tively, and during further heating undergoes decomposition
in four stages. Complex 1 shows a weight loss of 19.89%
(&134.37 g) in the temperature range 471–492 K, corre-
sponding to the removal of one (Ch3O)2Ph group (Calcd.
20.27%), 9.61% (&64.92 g) in the temperature range
492–626 K, corresponding to the removal of two methoxy
groups (Calcd. 9.17%), 11.24% (&75.94 g) in the temper-
ature range 626–774 K, corresponding to the removal of one
Ph group (Calcd. 11.11%) and 19.84% (&134.03 g) in the
temperature range 774–1013 K, corresponding to the
removal of one C and I groups (Calcd. 20.57%). While,
complex 2 shows a weight loss of 9.82% (&48.46 g) in the
temperature range 489–515 K, corresponding to the removal
of four methyl groups (Calcd. 12.17%), 13.24% (&65.35 g)
in the temperature range 515–635 K, corresponding to the
removal of four oxygen atoms (Calcd. 12.98%), 20.35%
(&100.44 g) in the temperature range 635–876 K, corre-
sponding to the removal of one Ph–C group (Calcd. 17.86%)
and 17.47% (&86.23 g) in the temperature range
876–1013 K, corresponding to the removal of one Ph–C
group (Calcd. 17.86%).
7. Price JR, Lan Y, Brooker S (2007) Dalton Trans 18:1807
8. Zhou XH, Wu T, Li D (2006) Inorg Chim Acta 359:1442
9. Zhang G, Yang G, Ma JS (2006) J Chem Crystallogr 36:631
10. Dehghanpour S, Mahmoudi A, Hadjikhani R (2008) J Braz Chem
Soc 19:600
11. Ardizzoia GA, Brenna S, Castelli F, Galli S (2009) Inorg Chim
Acta 362:3507
12. Sawant SK, Gaikwad GA, Sawant VA, Yamgar BA, Chavan SS
(2009) Inorg Chem Commun 12:632
13. Dehghanpour S, Mahmoudi A (2007) Synth React Inorg Met-Org
Nano-Met Chem 37:35
14. Montazerozohori M, Joohari S, Musavi SA (2009) J Coord Chem
62:1285
15. Montazerozohori M, Musavi SA (2008) J Coord Chem 61:3934
16. Marjani K, Asgarian J, Mousavi M, Amani V (2009) Z Anorg
Allg Chem 635:1633
17. Prakash A, Singh BK, Bhojak N, Adhikari D (2010) Spectrochim
Acta A76:356
18. Khalaji AD, Weil M, Grivani G, Jalali Akerdi S (2010) Mon
Chem 141:539
19. Khalaji AD, Zhang Y, Mojdekanlou S (2008) Anal Sci 24:x131
20. Khalaji AD, Jian F, Xiao H, Mojdekanlou S (2008) Anal Sci
24:x91
21. Stoe Cie (2009) X-Area V1.52 & X-RED32 V1.48 Software. Stoe
& Cie GmbH, Darmstadt
22. Sheldrick GM (2008) Acta Cryst A64:112
23. Spek AL (2009) Acta Cryst D65:148
Conclusion
We have synthesized tetrahedral Zn(II) complex with Schif
base ligand (2,3-MeO-ba)2en. All compounds (ligand and
123