Synthesis, crystal structures, and antimicrobial activities of zinc complexes derived from methyl substituted 2-(Pyridin-2-yliminomethyl)phenols

Article abstract of DOI:10.3109/10799890903555640

A new mononuclear zinc(II) complex [ZnL1(MPA)I] (1) (HL1 = 2-[(4-methylpyridin-2-ylimino)methyl]phenol, MPA = 4-methylpyridin-2-ylamine), and a new centrosymmetric dinuclear zinc(II) complex [Zn₂L2 ₂I₂] (2) (HL2 = 2-[(5-me

Full text of DOI:10.3109/10799890903555640

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Synthesis, Crystal Structures, and Antimicrobial
Activities of Zinc Complexes Derived from Methyl
Substituted 2-(Pyridin-2-yliminomethyl)phenols
San-Jun Peng a , Liu-Bin Song a , Jin-Heng Ning a & Zhong-Liang Xiao a
a College of Chemistry and Biological Engineering , Changsha University of Science and
Technology , Hunan, Changsha, P. R. China
Published online: 16 Feb 2010.
To cite this article: San-Jun Peng , Liu-Bin Song , Jin-Heng Ning & Zhong-Liang Xiao (2010) Synthesis, Crystal Structures,
and Antimicrobial Activities of Zinc Complexes Derived from Methyl Substituted 2-(Pyridin-2-yliminomethyl)phenols,
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:2, 105-108
To link to this article: http://dx.doi.org/10.3109/10799890903555640
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:105–108, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.3109/10799890903555640
Synthesis, Crystal Structures, and Antimicrobial Activities
of Zinc Complexes Derived from Methyl Substituted
2-(Pyridin-2-yliminomethyl)phenols
San-Jun Peng, Liu-Bin Song, Jin-Heng Ning, and Zhong-Liang Xiao
College of Chemistry and Biological Engineering, Changsha University of Science and Technology,
Hunan, Changsha, P. R. China
A new mononuclear zinc(II) complex [ZnL1(MPA)I] (1)
N
(HL1 = 2-[(4-methylpyridin-2-ylimino)methyl]phenol, MPA = 4-
N
N
methylpyridin-2-ylamine), and a new centrosymmetric dinuclear
zinc(II) complex [Zn2L22I2] (2) (HL2 = 2-[(5-methylpyridin-2-
ylimino)methyl]phenol), have been synthesized and structurally
characterized by elemental analysis and X-ray diffraction. In 1,
the Zn atom is four-coordinate in a tetrahedral coordination, while
those in 2 are five-coordinate in severely distorted square pyrami-
dal coordinations. The complexes, as well as the two Schiff bases,
have been screened and evaluated for their antimicrobial activities.
OH
N
OH
HL1
HL2
EXPERIMENTAL
Keywords antimicrobial, crystal structure, schiff base, X-ray crys-
Materials and Methods
tallography, zinc complex
All chemicals and reagents were obtained from commercial
sources and used as received. Elemental analyses (C, H, N) were
performed on a Perkin-Elmer 240C elemental analyzer.
INTRODUCTION
Schiff bases are very easily synthesized by the conden-
sation reaction of aldehydes with primary amines.[1−3] Zinc
complexes derived from Schiff base ligands have been stud-
HL1 and HL2 were synthesized by the reaction of equimolar
quantities of salicylaldehyde with 4-methylpyridin-2-ylamine
and 5-methylpyridin-2-ylamine, respectively, in methanol, as
ied extensively due to their interesting structures and wide that described in the literature.[9] The Schiff bases were used
applications.[4−6] Recently, we have reported a few Schiff
base zinc complexes with halide ligands;[7,8] however, the
Schiff base zinc(II) complexes containing the iodide lig-
ands have seldom been reported so far. As a continuation
of our work on such complexes, we report herein the syn-
thesis, crystal structures and antimicrobial activities of two
new zinc complexes [ZnL1(MPA)I] (1) and [Zn2L22I2] (2)
(HL1 = 2-[(4-methylpyridin-2-ylimino)methyl]phenol, MPA
= 4-methylpyridin-2-ylamine, HL2 = 2-[(5-methylpyridin-2-
ylimino)methyl]phenol).
without purification.
Synthesis of the Complex 1
A methanol solution (2 mL) of ZnI2 (30.8 mg, 0.1 mmol)
was added dropwise to a methanol solution (10 mL) of freshly
produced HL1 (21.2 mg, 0.1 mmol) that might contain small
amount of starting materials. The mixture was stirred at room
temperature for 30 min and filtered. Colorless block crystals
were formed when slow evaporation of the filtrate in air for a few
days. Yield: 32.7 mg (64%). Anal. calcd. for C19H19IN4OZn:
C, 44.6; H, 3.7; N, 10.9%. Found: C, 44.3; H, 3.8; N, 11.1%.
Received 6 October 2009; accepted 3 November 2009.
This work was financially supported by Hunan Provincial Scientific
Program of China (2008FJ3010), Natural Science Foundation of Hu-
nan Province of China (07JJ6023), Hunan Provincial Natural Science
Foundation of China (06JJ20083), and National Program on Key Basic
Research Project of China (2007CB613600).
Address correspondence to Dr. San-Jun Peng, College of Chem-
istry and Biological Engineering, Changsha, 410014, China. E-mail:
sanjunpeng@163.com
Synthesis of the Complex 2
Complex 2 was prepared by a similar method as that for 1,
with HL1 replaced by HL2. Colorless block crystals of 2 were
formed after a few days. Yield: 35.0 mg (87%). Anal. calcd. for
C26H22I2N4O2Zn2: C, 38.7; H, 2.7; N, 6.9%. Found: C, 38.4; H,
2.9; N, 6.7%.
105

106
S.-J. PENG ET AL.
TABLE 1
Crystal data for the complexes 1 and 2
TABLE 2
◦
˚
Selected bond lengths (A) and bond angles ( ) for the
complexes 1 and 2
Complex
1
2
1
Formula
FW
C19H19IN4OZn
511.6
Colorless/block Colorless/block
C26H22I2N4O2Zn2
807.0
Zn1 O1
Zn1 N1
O1 Zn1 N1
1.988(3) Zn1 N3
2.021(4) Zn1 I1
91.72(14) O1 Zn1 I1
2.029(4)
Crystal color/shape
2.5623(9)
112.76(11)
120.10(11)
107.02(11)
Crystal size/(mm3)
0.20 × 0.18 ×
0.20 × 0.17 ×
0.17
0.15
O1 Zn1 N3 107.48(14) N1 Zn1 I1
N1 Zn1 N3 116.46(15) N3 Zn1 I1
Crystal system
Space group
Monoclinic
P21/c
10.625(2)
21.716(3)
8.454(2)
90
94.74(3)
90
1943.9(7)
4
Triclinic
P –1
2
˚
a (A)
7.840(2)
8.741(2)
10.514(2)
84.557(3)
80.605(3)
72.598(3)
677.5(2)
1
Zn1 O1
2.082(4) Zn1 N2
1.975(4) Zn1 I1
2.003(5)
2.518(5)
2.5413(10)
Zn1 O1i
˚
b (A)
˚
c (A)
Zn1 N1
α (/◦)
β (/◦)
O1i Zn1 N1 125.8(2)
O1 Zn1 N2 140.51(18)
O1i Zn1 O1
N1 Zn1 O1
81.41(19) O1i Zn1 I1 113.94(14)
γ (/◦)
86.29(19) N1 Zn1 I1
119.55(15)
112.17(14)
100.89(13)
3
˚
V (A )
O1i Zn1 N2 104.85(19) O1 Zn1 I1
Z
N1 Zn1 N2
58.0(2)
N2 Zn1 I1
T (K)
298(2)
2.867
1.748
298(2)
4.079
1.978
2757
1893
Symmetry code: (i) 1 −x, −y, 2 −z.
µ (mm−1) (Mo Kα)
Dc (g cm−3
Unique reflections
Independent reflections 2930
Parameters
Restraints
)
respectively. Other H atoms were generated geometrically. The
crystallographic data as well as details of the data collection
and refinement for the complexes are listed in Table 1. Selected
bond lengths and angles are given in Table 2.
4373
243
3
164
0
F(000)
Index range (h, k, l)
944
388
RESULTS AND DISCUSSION
−13/13, −27/28, −9/9, −10/10,
−10/10 −13/13
0.598 0.496
0.641
Structure Description of the Complexes
Tmin
Tmax
Figures 1 and 2 give perspective views of the complexes 1
and 2 together with the atomic labeling systems. Complex 1 is a
mononuclear zinc(II) compound, while complex 2 is a phenolic
O-bridged centrosymmetric dinuclear zinc(II) compound.
The Zn atom in 1 is four coordinated by one O and one
N atoms of HL1, one pyridine N atom of a MPA, and one I
atom, forming a distorted tetrahedral coordination. The Zn I
bond is much longer than the other three bonds. The dihedral
angle between the HL1 and MPA planes is 73.3(2)◦, which can
decrease the steric effects between them. Except for the linkage
of the Zn1 atom between the HL1 and MPA molecules, there
exists an intramolecular N4 H4B· · ·O1 hydrogen bond. The
0.580
1.049
0.0510, 0.0934
0.0827, 0.1039
ꢀ
Goodness of fit on F2 1.029
R1, wR2 [I ≥ 2σ (I)]a 0.0490, 0.0948
R1, wR2 (all data)a
0.0818, 0.1064
ꢀ
ꢀ
aR1
w(Fo2)2]1/2
=
||Fo| − |Fc||/ |Fo|, wR2 = [ w(Fo2 − Fc2)2/
ꢀ
.
DATA COLLECTION, STRUCTURAL DETERMINATION,
AND REFINEMENT
Crystal Structure Determination
Single crystals of both complexes were selected and mounted molecules are further linked through intermolecular N H· · ·O
on the top of glass fibers. The data were collected on a Bruker hydrogen bonds, forming chains running along the c axis, as
SMART 1000 CCD area diffractometer at 298(2) K. Graphite- shown in Figure 3.
˚
monochromatized Mo Kα radiation (λ = 0.71073 A) and the
The inversion center of complex 2 lies at the midpoint of the
ω scan technique were used to collect the data sets. Absorp- two Zn atoms. Each Zn atom is five-coordinate in a distorted
tion corrections were applied using SADABS.[10] The crys- square pyramidal geometry, with one imine N, one pyridine N,
tal structures were solved with direct methods and refined and two phenolic O atoms from two Schiff base ligands defining
with a full-matrix least-squares technique using SHELXTL the base plane, and with one I atom occupying the apical posi-
package.[11] Anisotropic thermal parameters were applied to all tion. The square pyramidal coordination is distorted, which can
non-hydrogen atoms. The two amino H atoms in 1 were located be found from the coordinate bond angles. The N1 Zn1 N2
from a difference Fourier map and refined isotropically, with and O1 Zn1 O1i (symmetry code: i) 1 x, −y, 2 −z) bond
N H and H· · ·H distances restrained to 0.90(1) and 1.43(2) A, angles largely deviate from the ideal values of 90◦ for a square
˚

ACTIVITIES OF ZINC COMPLEXES
107
FIG. 1. The structure of 1 showing the atom-numbering scheme. Displace-
ment ellipsoids are drawn at the 30% probability level. Intramolecular hydrogen
bond is drawn as a dashed line.
pyramidal geometry, and are caused by the strain created by the
four-membered chelate rings Zn1-N1-C8-N2 and Zn1-O1-Zn1i-
O1i. The Zn1 N2 bond is much longer than those of the other
bonds in the base plane, indicating the coordination between
them is very weak. Each Schiff base ligand is nearly coplanar
with the dihedral angle of 3.1(2)◦ between the benzene and the
pyridine rings. The dihedral angle between the perfectly planar
Zn1 O1 Zn1i O1i and the least-squares plane of the Schiff
base ligand is 44.6(2)◦. The distance between the two Zn atoms
FIG. 3. The molecular packing of 1, viewed along the a axis. Intermolecular
hydrogen bonds are shown as dashed lines.
along the a axis, with no obvious short contacts, as shown in
Figure 4.
The corresponding bond lengths in the two complexes are
comparable to each other, and also comparable to the similar
Schiff base zinc complexes with I atoms.[12]
˚
is 3.076(2) A. In the crystal structure of 2, molecules are stack
IR Spectra
The IR spectra of HL1, HL2, and the two complexes provide
information about the metal-ligand bonding. The assignments
are based on the typical group frequencies. The middle and
broad bands centered at about 3420–3450 cm−1 in the two Schiff
bases are due to the phenolic OH groups, which are absent in the
two complexes. The strong absorption bands at 1627 cm−1 in
the spectra of both Schiff bases are assigned to the azomethine
groups, ν(C=N). The bands are shifted to lower wave numbers
in the two complexes (1613 cm−1 for 1 and 1615 cm−1 for 2),
which may be attributed to the coordination of the nitrogen atom
of the azomethine group to the Zn atoms. The middle absorption
bands at about 1200 cm−1 in the spectra of the Schiff bases are
assigned to the phenolic groups, ν(Ar O). The bands are also
shifted to lower wave numbers in the two complexes (1187 cm−1
for 1 and 1172 cm−1 for 2), indicating the coordination of the
phenolic O to the Zn atoms.
FIG. 2. The structure of 2 showing the atom-numbering scheme. Displace-
ment ellipsoids are drawn at the 30% probability level. Atoms labeled with the
suffix A or unlabeled are at the symmetry position (– x, y, 1/2 – z).

108
S.-J. PENG ET AL.
the large steric effects of the four-membered chelated rings. The
antimicrobial tests indicate that both complexes show remark-
able activities against the bacteria.
Supplementary Data
Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre with the Cambridge Crystallographic
Data Centre (The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK; e-mail: deposit@ccdc.cam.ac.uk;
website: http://www.ccdc.cam.ac.uk; fax: +44 1223 336033)
and are available free of charge on request, quoting the Deposi-
tion No. CCDC 729551 & 729552.
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lidene)2,6-pyridinediamine. Struct. Chem. 2000, 11, 361–365.
¨
3. Unver, H., Zengin, D.M., Gu¨ven, K. Intramolecular hydrogen bond-
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naphthalenone. J. Chem. Crystallogr. 2000, 30, 359–364.
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Met.-Org. Nano-Met. Chem. 2009, 39, 165–174.
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complex with an axial substituent in the diamine backbone: Stereoselective
recognition of amino alcohols. J. Am. Chem. Soc. 2005, 127, 16776–16777.
7. Peng, S.-J., Ping, W.-J., Song, L.-B. Crystal structure of dibromo(N-ethyl-
Nꢀ-pyridinylmethyleneethane-1,2-diamino)zinc(II), ZnBr2(C10H15N3). Z.
Kristallogr. NCS 2007, 222, 425–426.
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m1149.
Antimicrobial Activities
The antimicrobial activities of the complexes were estimated
by minimum inhibitory concentration (MIC: µg mL−1), accord-
ing to the literature method.[13]
The anitimicrobial activities of the complexes and the corre-
sponding Schiff bases are listed in Table 3, as estimated by MIC.
Antimicrobial activities of the free Schiff bases, HL1 and HL2,
were estimated as >100 µg mL−1 for B. subtilis and S. aureus,
but show weak activities against E. coli and P. aeruginosa. The
two complexes show stronger activities agaist all the bacteria
than the two Schiff bases. The activities of complex 1 are a little
superior than those of 2, which might be caused by the amino
groups in the complex, which readily forms intermolecular hy-
drogen bonds.
9. Zakrzewski, G., Sacconi, L. Four-, five and six-coordinated nickel(II)
and cobalt(II) complexes of Schiff bases derived from pyridine-2-
carboxaldehyde and N,N-substituted ethylenediamines. Inorg. Chem. 1968,
7, 1034–1036.
10. Sheldrick, G.M. SADABS. Program for Empirical Absorption Correction
of Area Detector, University of Go¨ttingen, Germany, 1996.
CONCLUSIONS
In the above study, two new zinc(II) complexes with Schiff
bases HL1 and HL2 are discussed. X-ray crystallography indi-
cates that the Schiff bases coordinate to the Zn atoms through
the phenolic O and imine N atoms. The pyridine N atoms of the
Schiff bases are not or weak coordinate to the Zn atoms due to
11. Sheldrick, G.M. SHELXTL, Version 6.10, Software Reference Manual,
Bruker Instrumentation, Madison, Wisconsin, USA, 2000.
12. Drew, M.G.B., Hollis, S.
A potentially seven-co-ordinate complex
that is only five-co-ordinate;crystal and molecular structure of di-
iodo(6,7,8,9-tetrahydro-16,22-di-methyl-5,10-dithia-15,23,24-triaza-17,
21-methenodibenzo[a,i]cyclonona-decene-NN’N”)zinc(II). J. Chem. Soc.,
Dalton Trans. 1978, 511–515.
TABLE 3
Antimicrobial activities (MIC: µg mL−1
)
E. coli
B. subtilis
S. aureus
P. aeruginosa
13. Nomiya, K., Takahashi, S., Noguchi, R., Nemoto, S., Takayama, T., Oda,
M. Synthesis and characterization of water-soluble silver(I) complexes with
l-Histidine (H2his) and (S)-(-)-2-pyrrolidone-5-carboxylic acid (H2pyrrld)
showing a wide spectrum of effective antibacterial and antifungal ac-
tivities. Crystal structures of chiral helical polymers [Ag(Hhis)]n and
{[Ag(Hpyrrld)]2}n in the solid state. Inorg. Chem. 2000, 39, 3301–3311.
HL1
HL2
1
52.3
61.2
8.5
> 100
> 100
15.8
> 100
> 100
13.2
37.2
35.0
4.5
2
11.2
27.6
19.0
8.7