A new Cu-Zn heteronuclear schiff base complex: Synthesis, structure, and antimicrobial activity

Article abstract of DOI:10.1080/15533174.2012.750342

A new Cu-Zn heteronuclear complex, [CuZnCl₂L], where L is the dianionic form of N,N-bis(salicylidene)propane-1,2-diamine, has been prepared and characterized by elemental analyses, IR, and single-crystal X-ray crystallographic determination. The crystal of the complex is monoclinic: space group P₂₁/c, a = 12.195(5), b = 8.009(3), c = 18.082(7) A, β = 93.745(6)°, V = 1762.3(12) A³, Z = 4. The Cu atom is coordinated by two phenolate O and two imine N atoms of the Schiff base ligand, forming a square planar geometry. The Zn atom is coordinated by two phenolate O atoms of the Schiff base ligand and two Cl atoms, forming a tetrahedral geometry. The effect of the Schiff base ligand and the complex on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans was studied. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Full text of DOI:10.1080/15533174.2012.750342

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A New Cu–Zn Heteronuclear Schiff Base Complex:
Synthesis, Structure, and Antimicrobial Activity
Qing-Bin Li a , Ling-Wei Xue a , Wei-Chun Yang a & Gan-Qing Zhao a
a College of Chemistry and Chemical Engineering , Pingdingshan University , Pingdingshan
Henan , P. R. China
Accepted author version posted online: 25 Jan 2013.Published online: 04 Apr 2013.
To cite this article: Qing-Bin Li , Ling-Wei Xue , Wei-Chun Yang & Gan-Qing Zhao (2013) A New Cu–Zn Heteronuclear Schiff
Base Complex: Synthesis, Structure, and Antimicrobial Activity, Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, 43:7, 822-825, DOI: 10.1080/15533174.2012.750342
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:822–825, 2013
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.750342
A New Cu–Zn Heteronuclear Schiff Base Complex:
Synthesis, Structure, and Antimicrobial Activity
Qing-Bin Li, Ling-Wei Xue, Wei-Chun Yang, and Gan-Qing Zhao
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan Henan,
P. R. China
two metal centers usually reside in chemically distinct bind-
ing environments. Differences in the ligand types as well as
in the coordination numbers and geometries can contribute to
the formation of dinuclear complexes. Common examples of
dinuclear metalloenzymes are the purple acid phosphatases and
Cu–Zn superoxide dismutase. As an extension of the work on
the structures and antimicrobial activities of Schiff base com-
plexes, in the present paper, a new Cu–Zn heteronuclear com-
plex, [CuZnCl2L], derived from the tetradentate Schiff base lig-
and N,N’-bis(salicylidene)propane-1,2-diamine (H2L; Scheme
1) has been prepared, structurally characterized, and investi-
gated for its antimicrobial activity.
A new Cu–Zn heteronuclear complex, [CuZnCl2L], where L is
the dianionic form of N,N’-bis(salicylidene)propane-1,2-diamine,
has been prepared and characterized by elemental analyses, IR,
and single-crystal X-ray crystallographic determination. The crys-
tal of the complex is monoclinic: space group P21/c, a = 12.195(5),
b = 8.009(3), c = 18.082(7) Å, β = 93.745(6)◦, V = 1762.3(12) Å3,
Z = 4. The Cu atom is coordinated by two phenolate O and two
imine N atoms of the Schiff base ligand, forming a square planar
geometry. The Zn atom is coordinated by two phenolate O atoms of
the Schiff base ligand and two Cl atoms, forming a tetrahedral ge-
ometry. The effect of the Schiff base ligand and the complex on the
antimicrobial activity against Staphylococcus aureus, Escherichia
coli, and Candida albicans was studied.
Supplemental materials are available for this article. Go to the
publisher’s online edition of Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry to view the supplemen-
tal file.
N
N
OH
HO
Keywords antimicrobial, Cu-Zn complex, crystal structure, hete-
ronuclear complex, Schiff base
H2L
INTRODUCTION
SCH. 1. The Schiff base ligand H2L.
Schiff bases are a kind of versatile ligands that have widely
been used in coordination chemistry.[1–3] In recent years, metal
complexes of Schiff bases have attracted considerable attention
due to their remarkable biological activity, such as antifungal,
antibacterial, and antitumor.[4–6] It has been shown that the Schiff
base complexes derived from salicylaldehyde and its derivatives
with primary amines, bearing the N2O, N2S, NO2, or NSO donor
sets, have interesting biological activity.[6–8] Among the Schiff
base complexes, the heteronuclear species have attracted par-
ticular interest due to their special properties.[9–11] For homo-
and heterodinuclear active sites found in metalloenzymes, the
EXPERIMENTAL
Material and Methods
All organic chemicals were purchased from Fluka (Switzer-
land). The metal salts and solvents with analytical grade were
obtained commercially. Elemental (C, H, and N) analyses
were made on a Perkin-Elmer Model 240B automatic analyzer
(USA). IR spectra were recorded on an IR-408 Shimadzu 568
spectrophotometer (Japan). X-ray diffraction was carried out on
a Bruker SMART 1000 CCD area diffractometer (Germany).
Synthesis of H2L
Received 12 June 2012; accepted 13 November 2012.
This research was supported by the National Sciences Foundation
of China (Nos. 20676057 and 20877036) and Top-Class Foundation of
Pingdingshan University (No. 2008010).
Address correspondence to Ling-Wei Xue, College of Chemistry
and Chemical Engineering, Pingdingshan University, Pingdingshan
Henan 467000, P. R. China. E-mail: pdsuchemistry@163.com
Salicylaldehyde (0.245 g, 2.0 mmol) was dissolved in
methanol (30 mL), to which was added with stirring a methanol
solution (10 mL) of propane-1,2-diamine (0.074 g, 1.0 mmol).
The mixture was stirred for 1 h at reflux, and most of the sol-
vents were removed by distillation, yielding yellow precipita-
tion. The product was isolated by filtration and recrystallized
822

CU–ZN HETERONUCLEAR SCHIFF BASE COMPLEX
823
SAINT[12] and corrected for absorption using SADABS.[13]
Multiscan absorption corrections were applied with ψ scans.[14]
The structure was solved by direct methods using the SHELXS-
97 program and refined by full-matrix least-squares techniques
on F2 using anisotropic displacement parameters.[15] Hydrogen
atoms were placed at the calculated positions. Idealized H atoms
were refined with isotropic displacement parameters set to 1.2
(1.5 for methyl group) times the equivalent isotropic U values
of the parent carbon atoms. The crystallographic data for the
complex are listed in Table 1.
TABLE 1
Crystal and structure refinement data for the complex
Empirical formula
C17H16Cl2CuN2O2Zn
Color; habit
Formula weight
Temperature (K)
Crystal size (mm)
Radiation (λ, Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
Blue; block
480.1
298(2)
0.27 × 0.23 × 0.22
MoKα (0.71073)
Monoclinic
P21/c
RESULTS AND DISCUSSION
12.195(5)
8.009(3)
18.082(7)
93.745(6)
1762.3(12)
4
1.810
964
2.884
2.7–24.5
–15 ≤ h ≤ 15, –10 ≤
k ≤ 9, –23 ≤ l ≤ 22
12244
3814
1469/227
6
0.0737, 0.1661
0.2025, 0.2162
0.921
The Cu-Zn heteronuclear complex was readily synthesized
by the reaction of equimolar quantities of the Schiff base, copper
perchlorate, and zinc chloride at ambient temperature. The crys-
tals of the complex are very stable at room temperature in the
solid state and are soluble in common organic solvents, such as
methanol, ethanol, chloroform, and acetonitrile. The results of
elemental analyses are in accord with the composition suggested
for the Schiff base and the complex.
b (Å)
c (Å)
β (◦)
V (Å3)
Z
Density (g cm−3
)
F(000)
Absorption coefficient (mm−1
θ range for data collection (◦)
Index ranges (h, k, l)
)
Infrared Spectra
In the IR spectrum of the Schiff base ligand, the weak ab-
sorption centered at 3420 cm−1 attributed to the phenol groups
are absent in the spectrum of the complex, indicating the co-
ordination of the Schiff base to the metal atoms through the
deprotonated form. The strong band observed at 1629 cm−1 in
the spectrum of the complex is assigned to the azomethine group
vibration.
Reflections collected
Independent reflections
Data/parameters
Restraints
Final R indices [I > 2σ(I)]
R indices (all data)
Goodness-of-fit on F2
ꢀρmax, ꢀρmin, e Å−3
Crystal Structure Description of the Complex
The molecular structure of the complex is shown in Figure 1.
Selected bond distances and angles are listed in Table 2. The
0.948, –0.982
from ethanol. The yield was 78%. Elemental analysis: Found
(%): C, 72.1; H, 6.5; N, 10.0. Anal. Calcd. (%) C17H18N2O2: C,
72.3; H, 6.4; N, 9.9.
Synthesis of the Complex [CuZnCl2L]
The Schiff base H2L (0.140 g, 0.5 mmol) was dissolved in
methanol (30 mL), to which was added with stirring a methanol
solution (15 mL) of Cu(ClO4)2·7H2O (0.195 g, 0.5 mmol) and
ZnCl2 (0.069 g, 0.5 mmol). The mixture was stirred for 1 h at
ambient temperature to give a blue solution. Blue block-shaped
single crystals suitable for X-ray diffraction were formed by
slow evaporation of the solution in air for several days. The
yield was 38% (based on H2L). Elemental analysis: Found (%):
C, 42.4; H, 3.4; N, 5.7. Anal. Calcd. (%) C17H16Cl2CuN2O2Zn:
C, 42.5; H, 3.4; N, 5.8.
X-Ray Diffraction
Data were collected from a selected crystal mounted on
FIG. 1. Perspective view of the complex with 30% probability thermal ellip-
a glass fiber. The data for the complex was processed with soids.

824
Q.-B. LI ET AL.
TABLE 2
Coordinate bond distances (Å) and angles (◦) for the complex
Bond distances
Cu1-O1
Cu1-N1
Zn1-O1
1.905(6)
1.914(9)
2.031(7)
2.198(3)
Cu1-O2
Cu1-N2
Zn1-O2
Zn1-Cl2
1.907(7)
1.887(8)
2.030(6)
2.196(3)
Zn1-Cl1
Bond angles
N2-Cu1-O1
O1-Cu1-O2
O1-Cu1-N1
O2-Zn1-O1
O1-Zn1-Cl2
O1-Zn1-Cl1
176.5(4)
83.3(3)
94.7(3)
77.2(3)
115.1(2)
111.5(2)
N2-Cu1-O2
N2-Cu1-N1
O2-Cu1-N1
O2-Zn1-Cl2
O2-Zn1-Cl1
Cl2-Zn1-Cl1
94.1(3)
88.0(4)
176.0(3)
116.6(2)
111.0(2)
118.51(12)
complex is a Cu–Zn heterodinuclear compound, with the dis-
tance between the Cu and Zn atoms of 3.004(1) Å, which is
comparable to those observed in similar Cu–Zn heterodinuclear
complexes with Schiff bases.[16–18] The coordination around the
Cu atom is distorted square planar involving two O and two N
atoms from the Schiff base ligand. The Cu1–N1 bond is a little
longer than the Cu1–N2 bond. The irregularity of the square-
planar coordination is mainly due to the different bond angles
around the Cu atom. Although the O1–Cu1–N1 [94.7(3)◦] and
O2–Cu1–N2 [94.1(3)◦] bond angles are close to each other,
the O1–Cu1–O2 [83.3(3)◦] and N1–Cu1–N2 [88.0(4)◦] bond
angles are clearly different. This is caused by the steric limita-
tions in the ethanediamine chelate ring as well as in the bridg-
ing plane. The Cu atom is located at a distance of 0.010(1) Å
from the coordination plane defined by the atoms N1, O1, O2,
and N2.
The second metal atom, zinc, in the molecule has a dis-
torted tetrahedral environment, and is coordinated by the two
O atoms of the Schiff base ligand and the two Cl atoms. The
two O atoms also constitute the bridge between the Cu and
Zn atoms. The bond angles around the Zn atom range from
77.2(3)◦ (O1–Zn1–O2) to 118.5(1)◦ (Cl1–Zn1–Cl2), which in-
dicates a serious deviation from the ideal tetrahedral angle. The
two Zn–O and the Zn–Cl distances are mutually equal within
the experimental error.
TABLE 3
Minimum inhibitory concentration values (μg/mL) for the
antimicrobial activities of the tested compounds
FIG. 2. The C−H···Cl hydrogen bonds linked dimeric structure of the
complex.
Staphylococcus
aureus
Escherichia
coli
Candida
albicans
The bridging plane (Cu1, O1, Zn1, O2) is not completely
planar. The distances of the two metal atoms, Cu and Zn, from
the respective best plane are 0.054(1) and 0.048(1) Å, while the
corresponding distances for O1 and O2 have equal values of
H2L
[CuZnCl2L]
Tetracycline
64
4
0.32
512
32
2.12
>1024
256
>1024

CU–ZN HETERONUCLEAR SCHIFF BASE COMPLEX
825
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0.051(2) Å. The dihedral angle between the two benzene rings
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In the crystal structure, adjacent two complex molecules are
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Antimicrobial Activity
Qualitative determination of antimicrobial activity was done
using the disk diffusion method.[19,20] The results are summa-
rized in Table 3. A comparative study of minimum inhibitory
concentration values of the Schiff base and the complex indi-
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Generally, this is caused by the greater lipophilic nature of the
complex than the ligand. Such increased activity of the metal
chelates can be explained on the basis of chelating theory.[21] On
chelating, the polarity of the metal atoms will be reduced to a
greater extent due to the overlap of the ligand orbital and partial
sharing of positive charge of the metal atoms with donor atoms.
Further, it increases the delocalization of p electrons over the
whole chelate ring and enhances the lipophilicity of the com-
plexes. This increased lipophilicity enhances the penetration of
the complexes into the lipid membrane and blocks the metal
binding sites on enzymes of microorganisms.
From Table 3 it is obvious that the complex shows greater
antibacterial and antifungi activities against Staphylococcus au-
reus, Escherichia coli, and Candida albicans than the free Schiff
base. For Staphylococcus aureus and Escherichia coli, the activ-
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A new Cu–Zn heterodinuclear complex with the Schiff base
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cessfully prepared. The crystal structure of the complex was
determined by single-crystal X-ray determination. The antimi-
crobial test shows that complex has potential activity against
Staphylococcus aureus, Escherichia coli, and Candida albicans.
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Cambridge Crystallographic Data Centre, 12 Union Road,
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