Synthesis, crystal structures, and antibacterial activities of Schiff base zinc(II) complexes [Zn(L1)2] and [Zn(L2) 2]1

Article abstract of DOI:10.1134/S1070328412010034

The reaction of cyclopentylamine with 2-hydroxy-1-naphthaldehyde and 5-nitrosalicylaldehyde, respectively, in methanol affords two new Schiff bases, 1-(cyclopentyliminomethyl)naphthalen-2-ol (HL¹) and 4-nitro-2-(cyclopentyliminomethyl)phenol (HL²). Two new zinc(II) complexes, [Zn(L¹)₂] (I) and [Zn(L²) ₂] (II), derived from the Schiff bases, have been prepared and characterized by single-crystal X-ray diffraction, FT-IR, and elemental analysis. Complex I crystallizes in the monoclinic space group P2₁/c with a = 17.834(4), b = 14.738(3), c = 9.868(2) A, β = 91.20(3)°, V = 2593.1(9) A³, Z = 4. Complex II crystallizes in the triclinic space group P1 with a = 10.206(1), b = 10.502(1), c = 12.554(1) A, a = 66.771(2)°, β = 78.133(2)°, y = 76.292(2)°, V = 1191.8(1) A³, Z = 2. The Zn atom in each complex is coordinated by two N and two O atoms from two Schiff base ligands, forming a tetrahedral geometry. The Schiff bases and the complexes were assayed for antibacterial activities. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070328412010034

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 2, pp. 121–125. © Pleiades Publishing, Ltd., 2012.
Synthesis, Crystal Structures, and Antibacterial Activities
of Schiff Base Zinc(II) Complexes [Zn(L1)2] and [Zn(L2)2]1
Y. N. Guo
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji, 721013 P.R. China
eꢀmail: ggyn1997@126.com
Received February 9, 2011
Abstract—The reaction of cyclopentylamine with 2ꢀhydroxyꢀ1ꢀnaphthaldehyde and 5ꢀnitrosalicylaldehyde,
respectively, in methanol affords two new Schiff bases, 1ꢀ(cyclopentyliminomethyl)naphthalenꢀ2ꢀol (HL1
)
and 4ꢀnitroꢀ2ꢀ(cyclopentyliminomethyl)phenol (HL2). Two new zinc(II) complexes, [Zn(L1)2] (
Zn(L2)2] (II), derived from the Schiff bases, have been prepared and characterized by singleꢀcrystal Xꢀray
diffraction, FTꢀIR, and elemental analysis. Complex crystallizes in the monoclinic space group 21/ with
= 17.834(4), = 14.738(3), = 9.868(2) = 91.20(3) = 4. Complex II crystallizes
= 2593.1(9) Å3
in the triclinic space group with = 10.206(1), = 10.502(1), = 12.554(1) = 66.771(2)
= 1191.8(1) Å3
= 2. The Zn atom in each complex is coordinated by two N
I) and
[
I
P
c
a
b
c
Å,
β
°,
V
, Z
P
a
b
c
Å,
α
°,
β
=
1
78.133(2)
°,
γ
= 76.292(2)
°,
V
, Z
and two O atoms from two Schiff base ligands, forming a tetrahedral geometry. The Schiff bases and the comꢀ
plexes were assayed for antibacterial activities.
DOI: 10.1134/S1070328412010034
1
INTRODUCTION
EXPERIMENTAL
Schiff bases in general have been reported to posꢀ
sess antimicrobial [1, 2] and antitumour activities
[3, 4]. Metal complexes with Schiff base ligands have
played an important role in the development of coorꢀ
dination chemistry due to their preparative accessibilꢀ
ity, structural variety, and biological properties [5–7].
Zinc is an essential element for all forms of life and is
present at the active site of various enzymes [8, 9]. The
diversity in the functions of zinc is attributed to its verꢀ
satile coordination chemistry. In this work, two new
Schiff bases, 1ꢀ(cyclopentyliminomethyl)naphthalenꢀ
Materials and measurements. 2ꢀHydroxyꢀ1ꢀnaphꢀ
thaldehyde, 5ꢀnitrosalicylaldehyde, and cyclopentyꢀ
lamine were purchased from Sigma. All other chemiꢀ
cals were commercial products and used without furꢀ
ther purification. C, H, and N elemental analyses were
performed on a Vario ELꢀIII analyzer. Infrared spectra
were recorded as KBr pellets on a Nicolet Avatar 360
spectrophotometer in the range 4000–400 cm–1
.
Molar conductivity was determined in methanol at
room temperature on a DDSꢀ11A conductometer.
2ꢀol
thyl)phenol (HL2), were prepared and two new zinc
complexes, [Zn(L1)2] ( and [Zn(L2)2] (II
, derived
( ) and 4ꢀnitroꢀ2ꢀ(cyclopentyliminomeꢀ
HL1
(
Zn(ClO4)2 is potentially explosive. Although no
problem has been encountered during the synthesis of
the complexes, it should be handled with proper care.
I)
)
from the Schiff bases have been prepared and characꢀ
terized by singleꢀcrystal Xꢀray diffraction, FTꢀIR, and
elemental analysis. Their antibacterial activities
Synthesis of HL1.
2ꢀHydroxyꢀ1ꢀnaphthaldehyde
(1.72 g, 0.01 mol) dissolved in methanol (30 mL) was
added to cyclopentylamine (0.85 g, 0.01 mol) in methꢀ
anol (30 mL). The reaction mixture was heated to
against Bacillus subtilis, Staphylococcus aureus,
Escherichia coli, and Pseudomonas fluorescens were
evaluated.
50 C for 1 h and then cooled to room temperature folꢀ
°
lowed by concentrating the resulting mixture to a yelꢀ
low solid product. The yield was 2.33 g (97%).
O2N
For C16H17NO
N
N
anal. calcd., %:
Found, %:
C, 80.3;
C, 80.1;
H, 7.2;
H, 7.3;
N, 5.8.
N, 5.9.
OH
OH
(HL2)
(HL1)
Synthesis of HL2 was carried out according to a
similar procedure as that for HL1 with 5ꢀnitrosalicylaꢀ
1
The article is published in the original.
121

122
GUO
ldehyde instead of 2ꢀhydroxyꢀ1ꢀnaphthaldehyde. The chlorate in methanol in acordance to reactions (1)
yield was 2.29 g (98%).
and (2):
For C12H14N2O3
anal. calcd., %:
Found, %:
C, 61.5;
C, 61.3;
H, 6.0;
H, 6.1;
N, 12.0.
N, 11.9.
N
Methanol
HL1 + Zn(ClO4)
(1)
Zn
O
O
2
Synthesis of I. Zn(ClO4)2 6H2O (0.19 g, 0.5 mmol)
⋅
in methanol (20 mL) was added dropwise to HL1
(0.24 g, 1 mmol) in methanol (20 mL), and the resultꢀ
ant colorless reaction mixture was stirred at room temꢀ
perature for 1 h to give a clear solution. Colorless sinꢀ
gle crystals were obtained by slow evaporation of the
solution in air. The yield was 0.17 g (63%).
N
O2N
N
Zn
For 32H32N2O2Zn
(2)
O
O
Methanol
HL2 + Zn(ClO4)
anal. calcd., %:
Found, %:
C, 70.9;
C, 71.2;
H, 6.0;
H, 5.8;
N, 5.2.
N, 5.1.
2
N
NO2
Synthesis of II. The colorless single crystals of
complex II were synthesized according to a similar
Both the Schiff bases and the zinc complexes are
stable in air at room temperature, and soluble in comꢀ
mon polar organic solvents, such as DMSO, DMF,
methanol, ethanol, and acetonitrile. The molar conꢀ
ductance values of the complexes measured in methaꢀ
procedure as that for I
with HL2 instead of HL1. The
yield was 0.20 g (77%).
For 24H26N4O6Zn
nol at concentrations of 10–3 M at 298 K are in the
anal. calcd., %:
Found, %:
C, 54.2;
C, 54.5;
H, 4.9;
H, 4.9;
N, 10.5.
N, 10.3.
–1
range 15–21
Ω
cm2 mol–1, indicating that they are
nonelectrolytes.
The IR spectra of the Schiff bases showed weak
bands due to the phenolic groups in the region 3180–
3215 cm–1 due to the vibrations. The bands of the pheꢀ
nolic group are absent in the IR spectra of the zinc
complexes, indicating the deprotonation of the pheꢀ
nolic groups. The intense bands at 1280 cm–1 assigned
to phenolic C–O linkage shifting toward a higher wave
number of 1302–1310 cm–1 confirmed the involveꢀ
ment of the deprotonated phenolic groups in bond
formation with the zinc atoms. The strong bands in the
Schiff bases around 1645 cm–1 region underwent a
negative shift of about 20 cm–3 in the complexes, conꢀ
firming the coordination of the azomethine N atoms
to the zinc atoms. The weak absorption bands at about
450 and 418 cm–1 are assigned to the Zn–N and Zn–
O bonds, respectively.
Xꢀray structure determination. Crystal structure
determination of the two complexes were carried out
on a Bruker APEX II CCD area diffractometer
equipped with graphiteꢀmonochromatized Mo
K
( =
λ
α
0.71073 Å) radiation. The structures were solved by
direct methods and refined on F2 by fullꢀmatrix leastꢀ
squares methods using SHELXꢀ97 [10]. All the nonꢀ
hydrogen atoms were refined anisotropically. Hydroꢀ
gen atoms were included at geometrically calculated
positions and refined using a riding model. The crystal
data, experimental details, refinement results, and details
of structure determinations are shown in Table 1.
Selected bond lengths and bond angles are listed in
Table 2.
Supplementary material for structures
been deposited with the Cambridge Crystallographic
Data Centre (nos. 812144 for and 812145 for II
I and II has
The crystal structures of I and II with the atomic
I
;
numbering scheme are presented in Figs. 1 and 2,
respectively. Both compounds are structurally similar
mononuclear zinc(II) complexes. The Zn atom in
each complex is fourꢀcoordinated by two imino
N atoms and two phenolic O atoms from two Schiff
base ligands, forming a tetrahedral geometry. The
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
RESULTS AND DISCUSSION
The Schiff bases HL1 and HL2 were prepared in bond lengths of Zn–O and Zn–N in both complexes
excellent yields (over 95%) in absolute methanol. The are comparable to each other and also comparable to
compounds are yellow solids and stable in air at room those in similar Schiff base zinc(II) complexes [11–
temperature. The elemental analyses are in good 13]. The angles subtended at the Zn atoms are in the
agreement with the chemical formulas proposed for range 93.9(2)
the compounds. The two zinc(II) complexes were preꢀ for II, indicating that tetrahedral coordinations are
pared by the reaction of the Schiff bases with zinc perꢀ distorted. The cyclopentyl rings in the complexes
°
–122.2(2)
°
for
I
and 96.8(1)
°
–120.0(1)
°
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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SYNTHESIS, CRYSTAL STRUCTURES, AND ANTIBACTERIAL ACTIVITIES
123
Table 1. Crystallographic data and structure refinement for the complexes
I
and II
Value
Parameter
I
II
Formula weight
Temperature, K
Scan mode
541.97
298(2)
531.86
298(2)
Multiꢀscan
Monoclinic
Multiꢀscan
Triclinic
Crystal system
Space group
P
21/
c
P
1
Unit cell dimensions:
a
, Å
, Å
17.834(4)
14.738(3)
9.868(2)
90
10.206(1)
10.502(1)
12.554(1)
66.771(2)
78.133(2)
76.292(2)
1191.84(8)
2
b
c
, Å
, deg
, deg
, deg
α
β
91.20(3)
90
γ
V
Z
, Å3
2593.1(9)
4
ρcalcd, g cm–3
, mm–1
1.388
1.482
μ
0.980
1.078
F(000)
1136
552
Crystal size, mm3
0.17
1.79–25.50
19, –16 17, –11
×
0.15
×
0.15
0.32
1.78–27.00
12, –13 13, –10
×
0.30
×
0.30
θ
Range for data collection, deg
Indices
h
,
k
,
l
–21
≤
h
≤
≤
k
≤
≤
l
≤
11 –12
≤
h
≤
≤
k
≤
≤
l ≤ 16
Reflections collected
Observed reflections (
12206
2952
7367
4070
I
> 2σ
(I
))
Max and min transmission
Data/restraints/parameters
Goodnessꢀofꢀfit on F2
0.8511 and 0.8669
4515/12/334
1.027
0.7241 and 0.7380
5089/0/316
1.024
Final R1
,
wR2 indices (
I
> 2σ(
I))
0.0848, 0.2070
0.1233, 0.2370
0.41/–0.54
0.0408, 0.1013
0.0543, 0.1095
0.46/–0.37
R1,
wR2 indices (all data)
Å–3
Δρmax/Δρmin, e
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124
GUO
Table 2. Selected bond lengths and bond angles for the Table 3. Antibacterial activity of the tested material
complex and II (MIC,
g mL–1
I
μ
)
Bacillus Staphylococꢀ Escheriꢀ Pseudomonas
subtilis cus aureus chia coli fluorescens
Bond
d
, Å
Bond
d, Å
Compound
I
HL1
HL2
25
25
50
75
>100
25
Zn(1)–O(1)
Zn(1)–N(1)
1.912(4) Zn(1)–O(2)
1.968(5) Zn(1)–N(2)
II
1.897(5)
1.996(5)
12.5
25
25
I
6.25
12.5
12.5
II
1.56
0.78
3.13
3.13
6.25
>100
50
Penicillin
>100
Zn(1)–O(1)
Zn(1)–N(1)
1.910(2) Zn(1)–O(2)
2.015(2) Zn(1)–N(2)
1.911(2)
2.011(2)
All the synthesized compounds were screened for
antibacterial activity against Bacillus subtilis Staphyꢀ
lococcus aureus Escherichia coli, and Pseudomonas
Angle
ω
, deg
Angle
ω
, deg
,
I
,
fluorescens by the MTT (3ꢀ(4,5ꢀdimethylthiazolꢀ2ꢀ
yl)ꢀ2,5ꢀdiphenyltetrazolium bromide) method. The
minimum inhibitory concentrations (MICs) of the
compounds against these bacteria are presented in
Table 3. Penicillin was used as a reference. The results
revealed that most of the synthesized compounds
exhibited significant antibacterial activity. The Schiff
bases HL1 and HL2 showed stronger antibacterial
activity against Escherichia coli and Pseudomonas fluꢀ
orescens but weaker antibacterial activity against
Bacillus subtilis and Staphylococcus aureus than Peniꢀ
cillin. The zinc complexes showed relatively stronger
activities against all the bacteria than the Schiff base
ligands. It is notable that complex II has the low MIC
values against Bacillus subtilis and Staphylococcus
aureus, which deserves further study.
O(1)Zn(1)O(2) 120.0(1) O(1)Zn(1)N(2) 113.3(1)
O(2)Zn(1)N(2) 96.9(1) O(1)Zn(1)N(1) 96.8(1)
O(2)Zn(1)N(1) 112.3(1) N(2)Zn(1)N(1) 119.0(1)
II
O(2)Zn(1)O(1) 121.6(2) O(2)Zn(1)N(1) 111.9(2)
O(1)Zn(1)N(1)
93.9(2) O(2)Zn(1)N(2) 95.5(2)
O(1)Zn(1)N(2) 113.8(2) N(1)Zn(1)N(2) 122.2(2)
adopt enveloped conformation with the C(12) and
C(28) atoms in
I and are displaced by 0.390(8) and
0.453(8) Å, respectively, from the leastꢀsquares planes
defined by the remaining four C atoms. The C(8) and
C(20) atoms in II are displaced by 0.424(3) and
0.556(3) Å, respectively, from the leastꢀsquares planes
defined by the remaining four C atoms.
Thus, two new Schiff bases derived from cycloꢀ
pentylamine with 2ꢀhydroxyꢀ1ꢀnaphthaldehyde and
5ꢀnitrosalicylaldehyde, respectively, have been syntheꢀ
C(30)
C(29)
C(31)
C(28)
N(2)
C(27)
C(25)
C(26)
C(10)
C(9)
C(24)
C(23)
C(32)
C(7)
C(8)
C(17)
O(1)
C(1)
C(22)
C(21)
Zn(1)
C(2)
C(3)
C(6)
C(18)
O(2)
C(16)
N(1)
C(20)
C(19)
C(4)
C(5)
C(11)
C(12)
C(15)
C(14)
C(13)
Fig. 1. ORTEP plots (30% probability level) for
I.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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SYNTHESIS, CRYSTAL STRUCTURES, AND ANTIBACTERIAL ACTIVITIES
125
C(9)
C(10)
C(8)
O(4)
C(7)
N(1)
C(6)
C(5)
C(11)
C(14)
C(1)
C(12)
O(2)
N(3)
C(15)
C(16)
Zn(1)
C(2)
O(3)
C(4)
C(3)
N(4)
O(5)
O(1)
C(24)
O(6)
C(17)
C(18)
C(13)
N(2)
C(19)
C(23)
C(20)
C(21)
C(22)
Fig. 2. ORTEP plots (30% probability level) for II
.
3. Ren, S.J., Wang, R., Komatsu, K., et al., J. Med.
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4. Kamel, M.M., Ali, H.I., Anwar, M.M., et al., Eur.
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sized. Reaction of the Schiff bases with zinc acetate
led to the formation of two new mononuclear comꢀ
plexes. The Schiff bases and the zinc complexes were
assayed for antibacterial activities by MTT method.
The complex II has the low MIC values against Bacilꢀ
lus subtilis and Staphylococcus aureus, which deserves
further study.
7. Shi, D.ꢀH. and You, Z.ꢀL., Russ. J. Coord. Chem., 2010,
ACKNOWLEDGMENTS
vol. 36, no. 7, p. 535.
8. Salter, M.H., Reibenspies, J.H., Jones, S.B., et al.,
The author acknowledges the financial support
from research project of the Phytochemistry Key Labꢀ
oratory of Shaanxi Province (grant no. 2010JS069)
and the Key Project Foundation of Baoji University of
Arts and Sciences (grant no. ZK0917).
Inorg. Chem., 2005, vol. 44, no. 8, p. 2791.
9. Wang, S.ꢀF., Tian, G.ꢀR., Zhang, W.ꢀZ., et al., Bioorg.
Med. Chem. Lett., 2009, vol. 19, no. 17, p. 5009.
10. Sheldrick, G.M., SHELXTL, Version 5.1, Software Refꢀ
erence Manual, Madison (WI, USA): Bruker AXS Inc.,
1997.
11. Shi, L., Fang, R.ꢀQ., Xue, J.ꢀY., et al., Aust. J. Chem.
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No. 2
2012