Zinc(II) and nickel(II) complexes derived from 2-bromo-6-[(2- Isopropylaminoethylimino)methyl]phenol: Synthesis, structures, and antimicrobial activity

Article abstract of DOI:10.1134/S1070328414040022

The Schiff base 2-bromo-6-[(2-isopropylaminoethylimino)methyl]phenol (HL), derived from 3-bromosalicylaldehyde with N-isopropylethane-1,2-diamine, and its zinc(II) and nickel(II) complexes [Zn(HL)₂(NCS)₂] (I) and [Ni(HL)₂(N₃)₂)] · 0.25H₂O (II) have been prepared and characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination. The crystal of I is orthorhombic: space group Pbca, a = 13.6928(9), b = 9.7203(6), c = 22.926(1) A, V = 3051.4(3) A^{3, Z} = 4. The crystal of II is triclinic: space group P1, a} = 8.0212(7), b = 12.744(1), c = 15.590(2) A, α = 104.802(3)°, β = 90.561(3)°, γ = 103.130(3)°, V = 1496.6(2) A^{3, Z} = 1. The zwitterionic Schiff base ligands coordinate to the metal atoms through phenolate O, imine N, and amine N atoms. Each metal atom in the complexes is in octahedral coordination. The effect of these complexes on the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied.

Full text of DOI:10.1134/S1070328414040022

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 5, pp. 284–288. © Pleiades Publishing, Ltd., 2014.
Zinc(II) and Nickel(II) Complexes Derived
from 2ꢀBromoꢀ6ꢀ[(2ꢀIsopropylaminoethylimino)methyl]phenol:
Synthesis, Structures, and Antimicrobial Activity1
G. P. Chenga, L. W. Xuea, *, and C. X. Zhangb
a College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan, Henan, 467000 P.R. China
b Coal Chemical Industry Branch of Shenhua Ningxia Coal Group, Yinchuan, Ningxia, 750411 P.R. China
*eꢀmail: pdsuchemistry@163.com
Received June 26, 2013
Abstract
3ꢀbromosalicylaldehyde with
[Zn(HL)2(NCS)2] ( ) and [Ni(HL)2(N3)2)]
tal analyses, IR, and single crystal Xꢀray crystallographic determination. The crystal of
space group Pbca = 13.6928(9), = 9.7203(6), = 22.926(1) = 4. The crystal of II
= 3051.4(3) Å3
is triclinic: space group = 8.0212(7), = 12.744(1), = 15.590(2) = 104.802(3) = 90.561(3)
= 103.130(3) = 1. The zwitterionic Schiff base ligands coordinate to the
= 1496.6(2) Å3
metal atoms through phenolate O, imine N, and amine N atoms. Each metal atom in the complexes is in
octahedral coordination. The effect of these complexes on the antimicrobial activity against Staphylococcus
aureus Escherichia coli, and Candida albicans were studied.
—
The Schiff base 2ꢀbromoꢀ6ꢀ[(2ꢀisopropylaminoethylimino)methyl]phenol (HL), derived from
ꢀisopropylethaneꢀ1,2ꢀdiamine, and its zinc(II) and nickel(II) complexes
0.25H2O (II) have been prepared and characterized by elemenꢀ
is orthorhombic:
N
I
·
I
,
a
b
c
Å,
V
, Z
−
P
1,
a
b
c
Å,
α
°,
β
°,
γ
°,
V
, Z
,
DOI: 10.1134/S1070328414040022
1
INTRODUCTION
EXPERIMENTAL
Schiff bases have long been considered as a kind of
Material and methods. 3ꢀBromosalicylaldehyde
and Nꢀisopropylethaneꢀ1,2ꢀdiamine were purchased
from Fluka. Other reagents and solvents were analytiꢀ
cal grade and used without further purification. Eleꢀ
mental (C, H, and N) analyses were made on a Perkinꢀ
Elmer Model 240B automatic analyser. Zinc and nickꢀ
el analyses were carried out by EDTA titration. Infraꢀ
red (IR) spectra were recorded on an IRꢀ408 Shimadꢀ
zu 568 spectrophotometer. Xꢀray diffraction was carꢀ
ried out on a Bruker SMART 1000 CCD area
diffractometer.
interesting ligands in coordination chemistry [1–3].
In recent years, metal complexes of Schiff bases have
attracted dramatically attention due to their versatile
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 [7–10]. Recent research indicates
that the halideꢀsubstituent groups in aromatic rings
of Schiff bases can severely increase the antimicrobiꢀ
al activity [11]. To the best of our knowledge, no
complexes have been reported with the bromoꢀsubꢀ
stituted Schiff base 2ꢀbromoꢀ6ꢀ[(2ꢀisopropylaminoꢀ
ethylimino)methyl]phenol (HL):
Synthesis of HL. The Schiff base ligand HL was
prepared by the condensation of equimolar quantities
of 3ꢀbromosalicylaldehyde (0.201 g, 1 mmol) with
N
ꢀisopropylethaneꢀ1,2ꢀdiamine (0.102 g, 1 mmol) in
methanol (30 mL) at ambient temperature for 1 h.
Then the methanol was evaporated by distillation,
yielding yellow gummy product of the Schiff base.
H
N
N
For C12H17N2OBr
OH
Br
anal. calcd., %:
Found, %:
C, 50.5;
C, 50.7;
H, 6.0;
H, 6.1;
N, 9.8.
N, 9.7.
(HL)
In the present paper, the preparation, characterizaꢀ
tion and antimicrobial activity of new zinc(II) and
nickel(II) complexes derived from the Schiff base
ligand are reported.
Synthesis of the complex [Zn(HL)2(NCS)2] (I).
The Schiff base HL (0.285 g, 1.0 mmol) was dissolved
by methanol (20 mL), to which was added with stirring
1
a methanol solution (20 mL) of Zn(CH3COO) ⋅ 2H2O
The article is published in the original.
284

ZINC(II) AND NICKEL(II) COMPLEXES
285
(0.219 g, 1.0 mmol). The mixture was stirred for 1 h at
RESULTS AND DISCUSSION
ambient temperature to give a colorless solution. Colꢀ
orless blockꢀshaped single crystals suitable for Xꢀray
diffraction were formed by slow evaporation of the soꢀ
lution in air for several days. The yield was 38% (based
on HL).
The Schiff base HL was prepared by the condensaꢀ
tion of equimolar quantities of 3ꢀbromosalicylaldeꢀ
hyde with Nꢀisopropylethaneꢀ1,2ꢀdiamine in methaꢀ
nol at ambient temperature [10]. The Schiff base preꢀ
pared in this way is formed in nearly quantitative yield
and of high purity. The complexes were readily syntheꢀ
sized by reaction of the Schiff base and metal salts in
methanol at ambient temperature. All the compounds
are very stable at room temperature in the solid state
and soluble in common organic solvents, such as
methanol, ethanol, chloroform, and acetonitrile. The
results of the elemental analyses are in accord with the
composition suggested for the ligand and the comꢀ
plexes.
For C26H34Br2N6O2S2Zn
anal. calcd., %: C, 41.5; H, 4.6; N, 11.2; Zn, 8.7.
Found, %:
C, 41.4; H, 4.5; N, 11.0; Zn, 8.9.
Selected IR data (
ν
(C=N).
ν
, cm–1): 2062 s,
(NCS), 1622 s
ν
Synthesis of the complex [Ni(HL)2(N3)2)]
·
For the IR spectra of both complexes, the strong
bands observed at 1622 cm–1 for and 1630 cm–1 for II
I
0.25H2O (II). The Schiff base HL (0.285 g, 1.0 mmol)
was dissolved by methanol (20 mL), to which was addꢀ
are assigned to the azomethine group vibrations. The
and 2040 cm–1 for II
are assigned to the stretching vibrations of the thiocyꢀ
anate and azide ligands, respectively.
The molecular structures of complexes
ed with stirring a methanol solution (20 mL) of intense bands at 2062 cm–1 for
I
Ni(CH3COO) ⋅ 4H2O (0.249 g, 1.0 mmol). The mixꢀ
ture was stirred for 1 h at ambient temperature to give
a green solution. Green blockꢀshaped single crystals
suitable for Xꢀray diffraction were formed by slow
evaporation of the solution in air for several days. The
yield was 53% (based on HL).
I
and II are
shown in figure. Selected bond distances and angles
are listed in Table 2. The complexes are structurally
similar centrosymmetric mononuclear compounds,
with the metal atoms lying on the inversion centers.
Complex I has only one complex molecule, while the
For C48H69Br4N20Ni2O4.5
asymmetric unit of complex II contains two complex
molecules and one quarter disordered water molecule.
Each metal atom in the complexes is coordinated by
two phenolate O and two imine N atoms from two
zwitterionic Schiff base ligands, defining the equatoriꢀ
al plane, and by two N atoms from two pseudohalide
anal. calcd., %: C, 40.2; H, 4.8; N, 19.5; Ni, 8.2.
Found, %:
C, 40.1; H, 4.9; N, 19.6; Zn, 8.3.
Selected IR data (
ν
(C=N).
ν
, cm–1): 2040 s
(N3), 1630 s
ν
ligands (NCS for I and N3 for II), occupying the two
axial positions, generating an octahedral geometry.
The Schiff base ligand acts as a zwitterionic tridentate
ligand, forming one sixꢀmembered chelate ring with
the metal center. The amino group of the Schiff base
ligand is protonated, which form a hydrogen bond
with the phenolate O atom of adjacent Schiff base
ligand. The two axial bonds are much longer than the
basal bonds, which is caused by the Jahn–Teller efꢀ
fects. The bond distances subtended at the metal atꢀ
oms are comparable to those observed in similar
zinc(II) and nickel(II) complexes with Schiff bases
[16–20].
Qualitative determination of antimicrobial activity
was done using the disk diffusion method [21, 22]. The
results are summarized in Table 3. A comparative
study of minimum inhibitory concentration (MIC)
values of the Schiff base and the complexes indicate
that the two complexes have more effective activity
than the free Schiff base. Generally, this is caused by
the greater lipophilic nature of the complexes than the
ligand. Such increased activity of the metal chelates
can be explained on the basis of chelating theory [23].
On chelating, the polarity of the metal atoms will be
reduced to a greater extent due to the overlap of the
Xꢀray diffraction. Data were collected from selectꢀ
ed crystals mounted on glass fibers. The data for the
two complexes were processed with SAINT [12] and
corrected for absorption using SADABS [13]. Multiꢀ
scan absorption corrections were applied with ψꢀscans
[14]. The structures were solved by direct methods usꢀ
ing the program SHELXSꢀ97 and refined by fullꢀmaꢀ
trix leastꢀsquares techniques on F2 using anisotropic
displacement parameters [15]. The amino hydrogen
atoms in
and refined isotropically, with N–H and H···H disꢀ
tances restrained to 0.90(1) and 1.43(2) , respectiveꢀ
I were located from a difference Fourier map
Å
ly. The remaining hydrogen atoms were placed at the calꢀ
culated positions. Idealized H atoms were refined with
isotropic displacement parameters set to 1.2 (1.5 for meꢀ
thyl groups) times the equivalent isotropic
U values of
the parent carbon and nitrogen atoms. The crystalloꢀ
graphic data for the complexes are listed Table 1.
Supplementary material has been deposited with
the Cambridge Crystallographic Data Centre
(nos. 945894 (I) and 945895 (II); deposit@
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
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286
CHENG et al.
Table 1. Crystallographic data and experimental details for I and II
Value
Parameter
I
II
Habit; color
Block; colorless
751.9
Block; green
1435.2
Formula weight
Temperature, K
Crystal size, mm
298(2)
298(2)
0.17
Mo
×
0.17
×
0.13
0.23
×
0.23
×
0.20
Radiation,
λ
, Å
K
(0.71073)
Mo
K (0.71073)
α
α
Crystal system
Orthorhombic
Triclinic
Space group
Pbca
P1
Unit cell dimensions:
a
, Å
, Å
13.6928(9)
9.7203(6)
22.926(1)
90
8.0212(7)
b
12.744(1)
15.590(2)
104.802(3)
90.561(3)
103.130(3)
1496.6(2)
1
c
, Å
, deg
, deg
, deg
α
β
90
γ
90
V
Z
, Å3
3051.4(3)
4
ρcalcd, g cm–3
(000)
Absorption coefficient, mm–1
Range for data collection, deg
Index ranges,
1.637
1.584
F
1520
725
3.595
3.358
θ
2.32–25.75
1.87–25.50
h
,
k
,
l
–16
≤
h
≤
16, –10
≤
k
≤
11, –24
≤
l
≤
27 –9
≤
h
≤
8, –15
≤
k
≤
14, –18
≤
l ≤ 18
Reflections collected
28392
14431
Independent reflections (Rint
)
2920 (0.0521)
2232
5544 (0.0356)
4071
Reflections with (
Data/parameters
Restraints
I
> 2σ(I))
2920/186
3
5544/365
6
Goodnessꢀofꢀfit on F 2
Final indices, ( > 2
indices (all data)
Largest difference peak and hole,
1.035
1.044
R
I
σ(I
))
R
1 = 0.0708, wR2 = 0.1525
1 = 0.0945, wR2 = 0.1677
1.277, –1.153
R
R
1 = 0.0448, wR2 = 0.1149
1 = 0.0713, wR2 = 0.1306
1.153, –0.702
R
R
e
Å–3
ligand orbital and partial sharing of positive charge of free Schiff base HL. For Staphylococcus aureus and
the metal atoms with donor atoms. Further, it increasꢀ Escherichia coli, the activities of the complexes are
es the delocalization of pꢀelectrons over the whole somewhat less than the control drug Tetracycline. But
chelate ring and enhances the lipophilicity of the comꢀ for Candida albicans, the complexes have stronger acꢀ
plexes. This increased lipophilicity enhances the penꢀ tivities than Tetracycline. Further work needs to be
etration of the complexes into lipid membrane and carried out to investigate the structureꢀactivity relaꢀ
blocks the metal binding sites on enzymes of microꢀ tionship.
organisms.
Thus, a new Schiff base ligand 2ꢀbromoꢀ6ꢀ[(2ꢀisoꢀ
From Table 3, it can be seen that in general the zinc propylaminoethylimino)methyl]phenol and its zinc(II)
complex
activities against Staphylococcus aureus
I
shows greater antibacterial and antifungi and nickel(II) complexes were prepared and characꢀ
Escherichia terized. The crystal structures of both complexes were
,
coli, and Candida albicans when compared to the confirmed by Xꢀray single crystal structure determinaꢀ
nickel complex II. And, it is obvious that both comꢀ tion. The metal atoms in the complexes are in octaheꢀ
plexes have more effective activities than the dral coordination. The antimicrobial test shows that
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ZINC(II) AND NICKEL(II) COMPLEXES
287
(a)
(b)
C(5)
C(5)
C(4)
C(3)
C(6)
C(6)
C(4)
C(3)
C(2)
C(1)
C(7)
Br(1)
C(7)
N(1)
C(1)
N(1)
C(9)
C(8)
C(2)
O(1)
Br(1)
C(8)
S(1)
C(11)
C(10)
C(9)
N(2)
O(1)
N(3)
Ni(1)
C(11)
N(2)
N(3)
N(4)
C(13)
Zn(1)
N(5)
C(12)
C(10)
C(12)
Perspective view of the complexes
lines.
I (a) and II (b) with 30% probability thermal ellipsoids. Hydrogen bonds are drawn as dashed
Table 2. Selected bond distances (Å) and angles (deg) for
Bond , Å
I
and II*
d
Bond
d, Å
I
Zn(1)–O(1)
2.024(4)
Zn(1)–N(1)
2.071(5)
Zn(1)–N(3)
2.518(10)
II
Ni(1)–O(1)
Ni(1)–N(3)
Ni(2)–N(6)
2.043(3)
2.131(4)
2.093(4)
Ni(1)–N(1)
Ni(2)–O(2)
Ni(2)–N(8)
2.077(3)
2.049(3)
2.151(4)
Angle
ω
, deg
Angle
ω
, deg
I
O(1)Zn(1)O(1)#1
O(1)Zn(1)N(1)
O(1)Zn(1)N(3)#1
O(1)Zn(1)N(3)
N(3)Zn(1)N(3)#1
180
88.62(18)
O(1)Zn(1)N(1)#1
N(1)Zn(1)N(1)#1
N(1)Zn(1)N(3)#1
N(1)Zn(1)N(3)
91.38(18)
180
89.1(2)
90.9(2)
94.2(2)
85.8(2)
180
II
O(1)Ni(1)O(1)#2
O(1)Ni(1)N(1)
O(1)Ni(1)N(3)#2
O(1)Ni(1)N(3)
N(3)Ni(1)N(3)#2
O(2)Ni(2)N(6)#3
N(6)Ni(2)N(6)#3
N(6)Ni(2)N(8)#3
N(6)Ni(2)N(8)
180
87.99(12)
O(1)Ni(1)N(1)#2
N(1)Ni(1)N(1)#2
N(1)Ni(1)N(3)
N(1)Ni(1)N(3)
O(2)Ni(2)O(2)#3
O(2)Ni(2)N(6)
O(2)Ni(2)N(8)#3
O(2)Ni(2)N(8)
N(8)Ni(2)N(8)#3
92.01(12)
180
89.90(14)
90.10(14)
93.05(14)
86.95(14)
180
91.52(13)
180
180
88.48(13)
89.67(16)
90.33(16)
91.42(16)
88.58(16)
180
#1
#2
#3
* Symmetry codes: 2 –
x, 1 –
y, 1 –
z;
–x, 1 –
y, 1 –
z;
2 –
x, 1 –
y, 2 –
z.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 5
2014

288
CHENG et al.
g/mL) for the antimicrobial activiꢀ 7. Yuan, C.X., Lu, L.P., Gao, X.L., et al., J. Bio. Inorg.
Table 3. MIC values (
ties of the tested compounds
μ
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Staphylococcus Escherichia
Candida
albicans
Compound
HL
aureus
coli
64
2
256
8
>1024
32
I
II
8
16
64
Tetracycline
0.32
2.12
>1024
12. Bruker, SMART and SAINT
Integration Software, Madison (WI, USA): Bruker Anꢀ
alytical Xꢀray Instruments Inc., 1997.
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, Area Detector Control and
both complexes have effective activities against Staꢀ
phylococcus aureus
bicans.
,
,
ö
ö
ACKNOWLEDGMENTS
,
A
,
This research was supported by the National Sciꢀ
ences Foundation of China (nos. 20676057 and
20877036) and Topꢀclass foundation of Pingdingshan
University (no. 2008010).
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