Preparation, X-Ray Structures, and Cytotoxic Property of Mononuclear Schiff Base Zinc Complexes [Zn(SalPr) 2] and [ZnI 2(SalPt) 2]

Article abstract of DOI:10.1080/15533174.2013.770763

Schiff bases obtained from 5-chlorosalicylaldehyde with cyclopropylamine, and 4-methoxysalicylaldehyde with cyclopentylamine, were used as ligands for Zn(II) resulting in two mononuclear zinc complexes, [Zn(SalPr)2] and [ZnI2(SalPt)2], where SalPr is 4-ch

Full text of DOI:10.1080/15533174.2013.770763

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Preparation, X-Ray Structures, and Cytotoxic Property
of Mononuclear Schiff Base Zinc Complexes [Zn(SalPr)2]
and [ZnI2(SalPt)2]
Nong Wang a b , Lixuan Chen a , Lijuan Yang a & Yumei Wan a
a School of Chemical and Biological Engineering , Lanzhou Jiaotong University , Lanzhou , P.
R. China
b Engineering and Technology Center of Gansu Province for Botanical Pesticides , Lanzhou
Jiaotong University , Lanzhou , P. R. China
Accepted author version posted online: 16 Sep 2013.Published online: 21 Oct 2013.
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To cite this article: Nong Wang , Lixuan Chen , Lijuan Yang & Yumei Wan (2014) Preparation, X-Ray Structures, and Cytotoxic
Property of Mononuclear Schiff Base Zinc Complexes [Zn(SalPr)2] and [ZnI2(SalPt)2], Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry, 44:2, 315-319, DOI: 10.1080/15533174.2013.770763
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 44:315–319, 2014
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.770763
Preparation, X-Ray Structures, and Cytotoxic Property
of Mononuclear Schiff Base Zinc Complexes [Zn(SalPr)2]
and [ZnI2(SalPt)2]
Nong Wang,1,2 Lixuan Chen,1 Lijuan Yang,1 and Yumei Wan1
1School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, P. R. China
2Engineering and Technology Center of Gansu Province for Botanical Pesticides, Lanzhou Jiaotong
University, Lanzhou, P. R. China
as NaOH, NaHCO3, NH3·H2O, and Et3N for the preparation
of Schiff base complexes are also not uncommon.[10–12] This
can facilitate the coordination processes. However, the addi-
tion of acids to the reaction systems of Schiff base compounds
has rarely been reported. We report here the preparation, X-
ray structures and cytotoxic property of two new mononuclear
zinc complexes, [Zn(SalPr)2] and [ZnI2(SalPt)2], where SalPr
is 4-chloro-2-(cyclopropyliminomethyl)phenolate and SalPt is
2-(cyclopentyliminiummethyl)-5-methoxyphenolate.
Schiff bases obtained from 5-chlorosalicylaldehyde with cy-
clopropylamine, and 4-methoxysalicylaldehyde with cyclopenty-
lamine, were used as ligands for Zn(II) resulting in two mononu-
clear zinc complexes, [Zn(SalPr)2] and [ZnI2(SalPt)2], where SalPr
is 4-chloro-2-(cyclopropyliminomethyl)phenolate and SalPt is
2-(cyclopentyliminiummethyl)-5-methoxyphenolate. The detailed
structures of the complexes were determined by single crystal X-
ray crystallography. Coordination sphere of Zn(II) atoms in both
complexes are slightly distorted tetrahedron. The cytotoxic prop-
erty of the complexes was evaluated.
EXPERIMENTAL
Keywords aromatic Schiff base ligand, cytotoxic property, mononu-
clear zinc complex, salicylaldimine derivatives, X-ray
structures
Materials and Measurements
All chemicals and reagents were commercially available and
used without further purification. The Schiff base ligands were
obtained by the reaction of 5-chlorosalicylaldehyde with cyclo-
propylamine, and 4-methoxysalicylaldehyde with cyclopenty-
lamine, according to the literature method.[13] C, H, and N
elemental analyses were performed on a Perkin-Elmer 240C
elemental analyzer. The X-ray diffraction was carried out on a
Bruker SMART 1000 CCD area diffractometer at 298(2) K.
INTRODUCTION
Salicylaldimine derivatives are among the most widely stud-
ied ligands in coordination chemistry.[1–3] Their structures are
often considered as representative models for the active sites of
biologically important metal-containing enzymes.[4–6] Coordi-
nation number of zinc in the catalytic sites is often lower than six,
although water molecule or hydroxide ion is bound to the metal
as an additional ligand. The reaction of the neutral phenol-imine
form of the salicylaldimine ligands with suitable metal starting
material is a simple and direct means of preparing metal sali-
cylaldiminato complexes.[7–9] In these complexes, the hydrogen
atoms of the hydroxyl groups of the free Schiff bases are readily
replaced by metal atoms. Besides, the addition of bases such
Synthesis of the Complex [Zn(SalPr)2]
The Schiff base HSalPr (2.5 mmol) was dissolved in 20 cm3
of EtOH, mixed with Zn(OAc)2·2H2O (2.5 mmol) in EtOH at
60◦C and stirred for 2 h. The obtained colorless precipitates have
been isolated, washed with diethyl ether, and air dried. Yield:
73%. Anal. Calcd. for C20H18Cl2N2O2Zn: C, 52.8; H, 4.0; N,
6.2. Found: C, 53.0; H, 3.9; N, 6.1%. IR (KBr, cm–1): 1608
(CH N). Single crystals suitable for X-ray diffraction were
obtained by slow evaporation of methanol solution containing
the complex at room temperature.
Received 17 January 2013; accepted 24 January 2013.
This work was supported by the Science and Technology Sup-
port Projects of Gansu Province (Grant No. 1204NKCA107), the
Engineering and Technology Center Projects of Gansu (Grant No.
1106NTGA013), and ‘Qing Lan’ Talent Engineering Funds of Lanzhou
Jiaotong University.
Address correspondence to Nong Wang, School of Chemical
and Biological Engineering, Lanzhou Jiaotong University, Lanzhou
730070, P. R. China. E-mail: wangnong05@163.com
Synthesis of the Complex [ZnI2(SalPt)2]
The Schiff base HSalPt (2.5 mmol) was dissolved in 20 cm3
of EtOH, mixed with Zn(OAc)2·2H2O (2.5 mmol) and HI
(2.5 mmol) in EtOH at 60◦C and stirred for 2 h. The obtained col-
orless precipitates have been isolated, washed with diethyl ether
and air dried. Yield: 65%. Anal. Calcd. for C26H34I2N2O4Zn:
315

316
N. WANG ET AL.
TABLE 1
Crystal data and structure refinement for the complexes
[Zn(SalPr)2]
[ZnI2(SalPt)2]
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C20H18Cl2N2O2Zn
454.63
298(2)
0.71073
Orthorhombic
Pbca
C26H34I2N2O4Zn
757.72
298(2)
0.71073
Monoclinic
P21/n
a (Å)
b (Å)
13.234(2)
13.235(3)
22.729(2)
15.602(1)
9.962(1)
20.616(2)
107.124(4)
c (Å)
β (◦)
Volume (Å3)
3981.0(11)
3062.2(4)
Z
8
1.517
1.519
4
Calculated density (Mg/m3)
Absorption coefficient (mm–1)
F(000)
1.644
2.849
1488
1856
Crystal size (mm)
θ range for data collection (◦)
Index ranges
0.12 × 0.08 × 0.07
0.32 × 0.30 × 0.30
2.3 – 23.7
2.7 – 23.5
–13 < h < 15, –15 < k < 11,
–26 < l < 26
14954/3096
full-matrix least-squares on F2
3096/0/244
–19 < h < 18, –9 < k < 12, –25
< l < 25
Reflections collected/unique (Rint)
Refinement method
16278/5805
full-matrix least-squares on F2
5805/0/318
Data/restraints/parameters
Goodness-of-fit on F2
0.758
1.001
Final R indices [I > 2σ(I)]
R indices (all data)
0.0397
0.0547
0.221, –0.292
0.0570
0.1526
0.816, –0.569
Largest differential peak and hole (e Å–3)
C, 41.2; H, 4.5; N, 3.7. Found: C, 41.1; H, 4.6; N, 3.7%. IR RESULTS AND DISCUSSION
(KBr, cm–1): 3411 (NH), 1596 (CH = NH). Single crystals suit-
Synthesis
able for X-ray diffraction were obtained by slow evaporation of
Both Schiff bases are readily prepared by the condensation
reactions of salicylaldehyde derivatives with organic amines.
methanol solution containing the complex at room temperature.
TABLE 2
X-Ray Crystallography
Selected bond lengths (Å) and angles (◦) for the complexes
Suitable single crystals of the complexes were mounted on
the top of glass fibers. Graphite-monochromatized Mo-Kα ra-
diation (λ = 0.71073 Å) and the ω scan technique were used
to collect the diffraction data. Absorption correction was ap-
plied using SADABS.[14] The crystal structures were solved
with direct method and refined with a full-matrix least-squares
technique using SHELXTL.[15] Anisotropic thermal parame-
ters were applied to all non-hydrogen atoms. Hydrogen atoms
were generated geometrically. The crystallographic data and
the details of the data collection and refinement for the com-
plexes are listed in Table 1. Selected bond lengths and angles
are given in Table 2. Crystallographic data for the complexes
have been deposited with the Cambridge Crystallographic Data
Centre (CCDC 918053 and 918054).
[Zn(SalPr)2]
Zn(1)-O(1)
Zn(1)-N(1)
1.909(3)
2.025(3)
Zn(1)-O(2)
Zn(1)-N(2)
1.926(3)
1.994(3)
O(1)-Zn(1)-O(2) 114.61(11) O(1)-Zn(1)-N(2) 115.20(11)
O(2)-Zn(1)-N(2) 96.73(11) O(1)-Zn(1)-N(1) 97.82(13)
O(2)-Zn(1)-N(1) 112.71(13) N(2)-Zn(1)-N(1) 120.88(12)
[ZnI2(SalPt)2]
Zn(1)-O(1)
Zn(1)-I(1)
1.958(6)
2.5789(12)
Zn(1)-O(3)
Zn(1)-I(2)
1.956(6)
2.5944(12)
O(3)-Zn(1)-O(1) 102.5(3) O(3)-Zn(1)-I(1) 104.2(2)
O(1)-Zn(1)-I(1)
O(1)-Zn(1)-I(2)
115.3(2) O(3)-Zn(1)-I(2) 113.98(19)
102.4(2) I(1)-Zn(1)-I(2) 117.67(4)

[Zn(SalPr)2] AND [ZnI2(SalPt)2]
317
FIG. 1. The atom numbering scheme for [Zn(SalPr)2], with the thermal ellipsoids plotted at 30% probability.
Complex [Zn(SalPr)2] was prepared by the reaction of HSalPr compound. The Zn atom, coordinated by two phenolate O and
with zinc acetate in ethanol. But for complex [ZnI2(SalPt)2], two imino N atoms from two monoanionic Schiff base ligands,
it was prepared by the reaction of SalPt with zinc acetate in is in a tetrahedral coordination. The tetrahedral coordination
the presence of HI in ethanol. The protonation of the iminium of the complex is distorted, as evidenced by the bond lengths
hydrogen in complex [ZnI2(SalPt)2] results from the reaction and angles. The average Zn–O bond lengths of 1.92 Å and
of the strong acid HI with the imine group of SalPt ligand, the average Zn–N bond lengths of 2.00 Å are in good agree-
generating a zwitterion ligand.
ment with those observed in related zinc complexes.[16,17] The
The synthetic procedure of the complex is described as fol- bond angles about the Zn atom range from 96.7(1) to 120.9(1)◦.
lowing:
The dihedral angles between the least-squares planes of C(1)-
C(6) and C(8)-C(10), C(11)-C(16) and C(18)-C(20), and C(1)-
C(16) and C(11)-C(16) are 70.2(5)◦, 91.0(5)◦, and 92.3(6)◦,
respectively.
Structure Description of the Complex [Zn(SalPr)2]
The molecular structure of the complex [Zn(SalPr)2] is
shown in Figure 1. The complex is a mononuclear zinc
FIG. 2. The atom numbering scheme for [ZnI2(SalPt)2], with the thermal ellipsoids plotted at 30% probability. Intramolecular N–H···O hydrogen bonds are
presented as thin dashed lines.

318
N. WANG ET AL.
Cl
N
Cl
N
O
Zn
+
O
Zn(OAc)2
OH
N
Cl
NH
I
MeO
O
I
N
+
Zn(OAc)2
+
HI
Zn
O
OMe
MeO
OH
NH
TABLE 3
Structure Description of the Complex [ZnI2(SalPt)2]
Cytotoxic results of the complex (IC50, μM)
The molecular structure of the complex [ZnI2(SalPt)2] is
shown in Figure 2. The complex is a mononuclear zinc com-
pound. The Zn atom, coordinated by two phenolate O atoms
from two monoanionic Schiff base ligands and two I atoms,
is in a tetrahedral coordination. The Schiff base ligands are
in their phenolate-iminium (zwitterion) form. Only the pheno-
late oxygen atom of the potentially bidentate Schiff base ligand
binds to the Zn atom. There form intramolecular N–H···O hy-
drogen bonds in the complex. Noticeably, the imine nitrogen
is non-coordinating and protonated. The structure is similar to
the previously reported structures of zinc complexes.[18,19] The
coordination mode of the monodentate zwitterions Schiff bases
SalPt is in obvious contrast to that of the SalPr ligands in com-
plex [Zn(SalPr)2]. The tetrahedral coordination of the complex
is distorted, as evidenced by the bond lengths and angles. The
average Zn–O bond lengths of 1.96 Å are much longer than
those in complex [Zn(SalPr)2]. The average Zn–I bond lengths
of 2.59 Å are in good agreement with those observed in re-
lated zinc complexes bearing Zn–I bonds.[20] The bond angles
about the Zn atom range from 102.4(2) to 117.7(1)◦. The dihe-
dral angles between the least-squares planes of C(1)-C(6) and
C(14)-C(19) is 95.6(3)◦.
Hela HepG2 BGC 95-D CNE L-02 NIH 3T3
[Zn(SalPr)2] >50 25
25 >50 12.5 >50 >50
[ZnI2(SalPt)2] >50 >50 25 >50 25 >50 >50
bromide], and the O.D. values were measured by ELX800 (uni-
versal microplate reader, BIO-TEK Instruments, Inc.) under
490 nm wavelength. Each test was performed in triplicate. The
IC50 values are listed in Table 3. It can be seen that both com-
plexes show moderate cytotoxic property to the carcinoma cells
BGC and CNE, but no or very weak property to the carcinoma
cells Hela and 95-D, and the normal cells L-02 and NIH 3T3. For
the carcinoma cell HepG2, complex [Zn(SalPr)2] has moderate
property, while complex [ZnI2(SalPt)2] has no or very weak
property.
CONCLUSIONS
Zinc(II) ions reacted with HSalPr and SalPt (in the presence
of HI) to form two new mononuclear zinc complexes. Structure
determination of the complexes by X-ray analysis shows that the
Zn atoms are in distorted tetrahedral coordination. The addition
of acid such as HI can lead to the protonation of the imine
group of the Schiff base ligand. Cytotoxic assay indicates the
complexes have moderate property to some carcinoma cells.
Cytotoxic Tests
Five human solid carcinoma cell lines, Hela (cervix adeno-
carcinoma), HepG2 (hepatocellular carcinoma), BGC (gastric
carcinoma), 95-D (lung carcinoma), CNE (rhinocarcinoma),
and two normal cell lines, NIH 3T3 (mouse normal fibrob-
last) and L-02 (human normal liver cell), were obtained from
Hubei Cancer Hospital. These cells were subcultured in me-
dia RMPI 1640 (GIBCO-BRL product) with 10% fetal bovine
serum (Hyclone product), at 37◦C with 5% cells mL–1 and
were planted in a 96-well tissue culture plate, and then were
exposed to the test compounds with concentration ranging
from 2.5 to 100 μg mL–1 for 48 h. The cells were pigmented
by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
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