Synthesis and characterization of non-symmetric tetradentate complexes of Zn(II), Co(II), and Cu(II)

Article abstract of DOI:10.3906/kim-0811-31

The non-symmetrical tetradentate Schiff-base H₂L was obtained using the half-unit N-(1-hydroxy-2- acetophenone)-1-amino-2-phenyleneimine (HL) with ²-hydroxyl-1-naphthaldehyde. ZnL, CoL, and CuL complexes were prepared and characterized by ¹H-NMR, IR, electronic, and atomic absorption spectra. The single crystal X-ray structure of CuL was determined. Crystal data for CuL are triclinic space group P-1, a = 8.3933 (17) A, b = 11.197 (2) A, c = 13.381 (3) A, α = 95.29 (3) ° , β = 94.37 (3) ° , γ = 95.82 (3) °, and z = 2. TUeBITAK.

Full text of DOI:10.3906/kim-0811-31

Turk J Chem
34 (2010) , 263 – 268.
¨
˙
c
ꢀ TUBITAK
doi:10.3906/kim-0811-31
Synthesis and characterization of non-symmetric
tetradentate complexes of Zn(II), Co(II), and Cu(II)
Maryam LASHANIZADEGAN∗, Shima SERAJ
Department of Chemistry, Faculty of Science Alzahra University Vanak,
Tehran-IRAN e-mail: m lashani@alzahra.ac.ir
Received 24.11.2008
The non-symmetrical tetradentate Schiff-base H2 L was obtained using the half-unit N-(1-hydroxy-2-
acetophenone)-1-amino-2-phenyleneimine (HL) with 2-hydroxyl-1-naphthaldehyde. ZnL, CoL, and CuL
complexes were prepared and characterized by 1 H-NMR, IR, electronic, and atomic absorption spectra.
The single crystal X-ray structure of CuL was determined. Crystal data for CuL are triclinic space group
◦
◦
˚
˚
˚
P-1, a = 8.3933 (17) A, b = 11.197 (2) A, c = 13.381 (3) A, α = 95.29 (3) , β = 94.37 (3) , γ = 95.82
(3)◦ , and z = 2.
Introduction
Unsymmetrical Schiff bases derived from the condensation of diamine with ketones represent an important class
of chelating agents, the metal complexes of which have been studied widely in terms of catalysis,1 magnetic
properties,2 isomers,3 and reaction mechanisms.4 In this work the half-unit Schiff-base N-(2-hydroxyacetophenone)-
1-amino-2-phenyleneimine (HL) (Figure 1) was used as a precursor5 for the preparation of non-symmetrical
tetradentate Schiff-base ligand by simple condensation of its primary amino group with the carbonyl group of
2-hydroxy-1-naphthaldehyde (H2 L) (Figure 1). In this study, the structure of the half unit and ligand were
determined by 1 H- and 13 C-NMR spectra and elemental analysis.6 Their corresponding Zn(II), Co(II), and
Cu(II) complexes were synthesized and characterized. Single crystal X-ray analysis of CuL was carried out to
determine the coordination stereochemistry. A square planar structure was tentatively assigned to all of the
complexes.
∗Corresponding author
263

Synthesis and characterization of non-symmetric..., M. LASHANIZADEGAN, S. SERAJ
Experimental
IR spectra were recorded using a Bruker Tensor 27 spectrometer. Visible spectra and atomic absorption were
obtained using a Unicam 8700 series UV/Vis and Philips Pu 9100 spectrometer, respectively. 1 H and 13 C
spectra were obtained on a Bruker FTAC-80 (80 MHz) spectrometer using TMS as internal standard.
OH
HO
N
OH
N
NH2
N
H3C
H3C
HL
H2L
O
N
O
M
N
H3C
M= Cu, Zn, Co
Figure 1. Structure of HL, H2 L, and ML.
Preparation of the Half-Unit HL. It was prepared by a previously described method.6
Preparation of the Ligand H2 L. To a solution of HL (0.23 g, 1 mmol) and 2-hydroxy-1-naphthaldehyde
(0.17 g, 1 mmol) in methanol (20 mL) at room temperature were added a few drops of piperidine. The mixture
was then stirred for 30 min at room temperature and the solid product formed was collected by filtration,
washed with methanol and further purified by crystallization from methanol-chloroform (1:3) and dried at 50
◦ C, yield, 0.28 g (75%), mp 160-163 ◦ C.
Preparation of the Complexes CuL and ZnL. A mixture of the ligand H2 L (0.38 g, 1 mmol) in
CH2 Cl2 (10 mL) and a MeOH solution (10 mL) of the desired metal acetate salt (1 mmol) was stirred for 30
min at room temperature. The resulting precipitate was separated by filtration and washed with methanol and
air dried. CuL yield g (80%), mp 280 ◦ C (decomp.). ZnL yield 0.32 g (73%), mp 245 ◦ C (decomp.).
Preparation of the Complex CoL. A mixture of the ligand H2 L (0.38 g, 1 mmol) in CH2 Cl2 (10
mL) and a MeOH solution (10 mL) of cobalt acetate (0.25 g, 1 mmol) was stirred for 1 h at room temperature.
The resulting red precipitate was separated by filtration and washed with methanol and air dried. The yield
was 0.25 g (57%), mp 245 ◦ C (decomp.).
X-ray crystallography
Single crystals were mounted with oil on a quartz fiber and transferred into a cold nitrogen stream on a Siemens
SMART (Siemens, 1994) 3-circle system with a CCD area detector. The crystal was held at 220 (2) K with the
264

Synthesis and characterization of non-symmetric..., M. LASHANIZADEGAN, S. SERAJ
Oxford Crysosystem Cryostream cooler (Cosier & Glazer, 1986). The structures were solved by direct methods
using SHELXS (Sheldrick, 1990) (TREF) with light atoms found by Fourier methods.
Results and discussion
A Schiff-base ligand (H2 L) was prepared by a stepwise reaction procedure.7 The 1:1 condensation prod-
ucts of o-hydroxyacetopheone and phenylenediamine were prepared under refluxing conditions (Figure 1).
Then one equivalent of 2-hydroxy-1-naphthaldehyde in the presence of piperidine at room temperature was
reacted with the 1:1 condensation product to produce the unsymmetrical tetradentate ligand composed of o-
hydroxyacetopheone, phenylenediamine, and 2-hydroxy-1-naphthaldehyde (1:1:1) (Figure 1). Reaction of ligand
with zinc(II), cobalt(II), and copper(II) acetate gave the complexes ZnL, CoL, and CuL, respectively. Atomic
absorption spectroscopy of the complexes is consistent with the 1:1 ratio of ligand to metal ion. Details of the
single compound are as follows.
Brown plate-like crystals of CuL suitable for X-ray analysis (0.24, 0.12, 0.06 mm) were obtained by
recrystallization from chloroform/ethanol (3:1). The resolution of the structure is correct as confirmed by the
acceptable R (F) (0.0633) and goodness-of-fit (0.912) value.
IR Spectra
The IR spectrum for the ligand shows a broad and intense band at 1615 cm−1 , which is assignable to the
stretching vibration of the C=N bond.8,9 The absorption values of the C==N vibration at 1603, 1606, and
1600 cm−1 for ZnL, CoL, and CuL, respectively, are lower by about 9-15 cm−1 than those for the free ligand,
which indicates the coordination of azomethine nitrogen atom to metal ions in the complexes.7
Electronic spectra
The d-d spectra of the CuL consist of a broad band (Table 1). This position is consistent with the square-
planar structure of similar tetradentate Schiff-base ligands with o-phenylenediamine as diamine bridge.10 For
the CoL, d-d transition appears below 600 nm, which is characteristic of a square-planar or distorted square-
planar structure.11 The electronic spectra for ZnL are similar to those of the ligand and show very little shift in
the position of the absorption maxima.12 The high-energy band in the ligand at 331 nm and in the complexes
at 260-400 nm may be assigned to intra-ligand or charge-transfer transition.
Table 1. Electronic spectra bands.
Complex
H2L
Bands nm, (log ε)
473(sh), 329(), 234(4.5)
CoL
560(sh), 477(sh), 348(sh)
484(sh), 399 (sh) 329(sh), 237(4.2)
616(2.9), 424(4.1), 350(4)
ZnL
CuL
ε = Mol−1L cm−1 In CH2Cl2
265

Synthesis and characterization of non-symmetric..., M. LASHANIZADEGAN, S. SERAJ
1 H-NMR spectrum
The 1 H-NMR spectrum of H2 L gives direct evidence of the formation of an unsymmetrical tetradentate ligand.
As anticipated, the spectrum consists of 1 methyl at δ 2.3, 1 azomethine hydrogen at δ 9.3, 2 hydroxy hydrogens
at δ 14.2 and 14.9, and aromatic protons at δ 6.8-8.1 signals. On the formation of ZnL complex the signals of
the methyl group are shifted to δ 2.56 and of the azomethine hydrogen to δ 9.62, and the signals of the OH
groups disappear.
Figure 2. ORTEP drawing of CuL with the atom numbering scheme.
Structure of the complex CuL
Figure 2 show ORTEP drawing of the complex CuL. The present X-ray analyses verified the structure of
copper(II) complexes with unsymmetrical tetradentate ligand composed of the condensation products of o-
hydroxyacetophenone, phenylenediamine, and 2-hydroxy-1-naphthaldehyde in the mole ratio 1:1:1. The crystal
structure analysis of this compound reveals the tetradentate ligand in which 2 nitrogen and 2 oxygen atoms are
coordinated to the copper atom. The copper(II) ion shows a slightly distorted square-planar structure. The
˚
Cu-O and Cu-N distances (Table 2) are close to the limits of ranges 1.87-1.91 and 1.92-1.95 A for Cu-O and Cu-
N distances, respectively, normally observed in N2 O2 square-planar copper(II) complexes.13 The asymmetric
266

Synthesis and characterization of non-symmetric..., M. LASHANIZADEGAN, S. SERAJ
unit included 2 molecules of chloroform, 1 with half occupancy. The crystal and experimental data are presented
in Table 3.
◦
˚
Table 2. Selected bond lengths (A) and bond angles ( ) for CuL.
Cu1-O11
Cu1-N12
1.873(3)
1.926(4)
Cu1-O12
Cu1-N11
N11-C107
1.915(3)
1.950(4)
1.326(6)
C101-O11
1.311(6)
O11-Cu1-O12
O12-Cu1-N12
88.33 (15)
93.25 (16)
O11-Cu1-N12 176.20(16)
O11-Cu1-N11 94.00 (17)
O12-Cu1-N11 174.36 (16) N12-Cu1-N11
84.74 (17)
122.6(3)
128.0(3)
112.8 (3)
C101-O11-Cu1
C108-N11-Cu1
C114-N12-Cu1
124.8(3)
110.7(3)
125.0 (3)
C107-N11-Cu1
C124-O12-Cu1
C113-N12-Cu1
Table 3. Experimental data for the X-ray diffraction of CuL.
3
˚
Formula weight
Molecular weight
Crystal system
Space group
C26.50H19.50Cl4.50N2CuO2
621.01
V (A )
1241.0 (4)
2
Z
Triclinic
(mm−1
Dc(g/cm3)
F (000)
)
1.394
P-1
1.662
˚
a (A)
˚
b (A )
˚
c (A )
8.3933 (17)
11.197 (2)
13.381 (3)
95.29(3)
628
min, min/θ◦
1.53 to 28.50
2655
Total reflection
α
β
γ
Independent reflections 5480 (Rint = 0.0401)
Goodness of fit on F2
0.912
94.37 (3)
95.82 (3)
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