Synthesis, X-ray crystal structure, electrochemical and antibacterial activity of a silver(I) complex with α-bromo-cinnamaldehyde salicylhydrazone

Article abstract of DOI:10.1007/s11243-010-9356-z

The mononuclear silver(I) complex [AgL(HL)· DMF] (I) (HL = C ₆H₁₃O₂N₂Br) has been prepared and characterized by physicochemical and spectroscopic methods, single crystal X-ray diffraction, cyclic voltammetry, and antibacterial activity tests. The complex crystallized in the triclinic system, and each Ag(I) is six-coordinate with a distorted octahedral geometry. The ligands chelate the metal center with N, O, and Br atoms from two different Schiff base ligands. O- H···O intermolecular hydrogen bonds connect adjacent complex molecules to form zigzag one-dimensional linear chains along the b axis. Cyclic voltammetry showed that the complex displays an irreversible reduction process at -0.41 V. The data from antibacterial activity tests indicate that the complex inhibits the growth of Staphyloccus aureus and Bacillus subtilis Cohn. Springer Science+Business Media B.V. 2010.

Full text of DOI:10.1007/s11243-010-9356-z

Transition Met Chem (2010) 35:507–511
DOI 10.1007/s11243-010-9356-z
Synthesis, X-ray crystal structure, electrochemical
and antibacterial activity of a silver(I) complex
with a-bromo-cinnamaldehyde salicylhydrazone
Jun An Liu
Guo Qing Gan
•
Qing Li
•
•
Ming Ming Wang
Zhi Dong Lin
•
Hui Wang
•
Yang Qu
•
Received: 18 January 2010 / Accepted: 23 March 2010 / Published online: 4 May 2010
Ó Springer Science+Business Media B.V. 2010
Abstract The mononuclear silver(I) complex [AgL(HL)ꢀ
DMF] (I) (HL = C H O N Br) has been prepared and
antimicrobial activity and other desirable properties of
silver complexes can be changed by varying the number
and type of ligands coordinated to the silver atom.
6
13 2 2
characterized by physicochemical and spectroscopic
methods, single crystal X-ray diffraction, cyclic voltam-
metry, and antibacterial activity tests. The complex
crystallized in the triclinic system, and each Ag(I) is
six-coordinate with a distorted octahedral geometry. The
ligands chelate the metal center with N, O, and Br atoms
from two different Schiff base ligands. O–HꢀꢀꢀO intermo-
lecular hydrogen bonds connect adjacent complex mole-
cules to form zigzag one-dimensional linear chains along
the b axis. Cyclic voltammetry showed that the complex
displays an irreversible reduction process at -0.41 V. The
data from antibacterial activity tests indicate that the
complex inhibits the growth of Staphyloccus aureus and
Bacillus subtilis Cohn.
Hydrazones are a versatile class of ligands, which have
been studied for a long time as potential muitfunctional
ligands with multidentate coordination modes. The bio-
logical activities of metal–hydrazone complexes have
attracted considerable attention. For example, salicylalde-
hyde benzoylhydrazone (H SBHz) appears to be an
2
unusually potent inhibitor of DNA synthesis and cell
growth in a variety of human and rodent cancer cell lines
[2, 3]. Therefore, studies of such metal complexes are
important to explore the possible new development of
drugs.
In this study, we report the preparation and character-
ization of a new silver(I) complex with a Schiff base,
namely a-bromo-cinnamaldehyde salicylhydrazone (HL)
and describe the IR, electrochemical studies, X-ray crystal
structures, and antibacterial activities of this complex.
Introduction
Silver salts and complexes have been widely used in var-
ious antibiotic applications including water purification,
wound management, eye drops, anti-infective coatings
for medical devices, and burn treatment [1–4]. The
Experimental
Salicylhydrazine, AgSCN, and a-Bromo-cinnamaldehyde
were used without further purification. All the solvents
were dried by standard methods before use.
C, H, and N microanalyses were obtained on a Perkin–
Elmer Elemental analyzer. FTIR spectra were recorded
-1
J. A. Liu ꢀ Q. Li ꢀ M. M. Wang ꢀ H. Wang ꢀ
G. Q. Gan ꢀ Y. Qu (&)
using KBr discs (4,000–400 cm ) on a Bruker Tensor 27
Biochemical Institute, Department of Applied Chemistry,
College of Science, Huazhong Agricultural University,
instrument. Cyclic voltammograms were obtained using
-
3
430070 Wuhan, Hubei, People’s Republic of China
e-mail: doctor-qu@126.com
1 9 10 M solutions of the complex in DMF using a
CHI660B instrument. A three-electrode system was used,
composed of a glassy carbon working electrode, a platinum
wire auxiliary electrode, and a saturated calomel electrode
(SCE) for reference.
Z. D. Lin
School of Materials Science and Engineering, Wuhan Institute of
Technology, 430073 Wuhan, Hubei, People’s Republic of China
123

5
08
Transition Met Chem (2010) 35:507–511
-1 -1
,663 cm (s, vC=N), 1,598 cm (s, vC=O), 1,248 cm
-
1
1
acetic acid
+
CHO
Br2
(m, vPh–O).
CHO
Br
X-ray structure determination
Scheme 1 Synthesis of a-bromo-cinnamaldehyde
Preparation of a-bromo-cinnamaldehyde
X-ray diffraction data were collected on a Bruker Smart
˚
Apex CCD diffractometer (k = 0.71073 A) at 298 K. The
intensity data were corrected for Lorentz and polarization
effects, and empirical absorption corrections were also
applied. The structure was solved by direct methods [5] and
refined by full-matrix least-squares with anisotropic tem-
perature factors for the non-hydrogen atoms. All atoms
except all hydrogen atoms were refined anisotropically.
The hydrogen atoms were located using the HYDROGEN
program and added to the structure factor calculation but
their positions were not refined. Further details are given in
Table 1.
Bromine (16 g, 0.2 mol) was added dropwise to a stirred
solution of cinnamaldehyde (13.2 g, 0.1 mol) in acetic acid
(40 mL) below 5 °C. After the completion of addition,
anhydrous potassium carbonate (1 g) was added in batches.
The resulting solution was vigorously stirred at 80 °C for
1
.5 h, and then added to 100 mL of distilled water. The
precipitate obtained was filtered off, and washed several
times with distilled water, then the precipitate was re-
crystallized in ethanol and dried at room temperature to get
the pure compound in 75% yield. m. p. 72 °C (Scheme 1).
Biological activity
Preparation of a-bromo-cinnamaldehyde
salicylhydrazone(HL)
Antibacterial activity of HL and the complex was exam-
ined by agar diffusion method [6]. The minimum inhibitory
concentration of HL and complex was ascertained using
different bacteria. The concentration of the drug solution
was maintained at 200 ug/mL in DMF. One day prior to the
test, the bacteria were inoculated in a nutrient broth
A solution of a-bromo-cinnamaldehyde (2.1 g, 10 mmol) in
ethanol (50 mL) was mixed with salicyloylhydrazine
(
2.3 g, 15 mmol) and refluxed for 2 h [4]. After completion
of the reaction, the solvent was evaporated to 20 mL, the
crude brown solid crude was filtered off, recrystallized from
ethanol, then dried in vacuo to give the pure compound
(
inoculation medium) and kept in an incubator at 37 °C for
8 h.
The bacteria were cultured in nutrient agar medium.
4
(
yield 75–80%). m. p. 185 °C. IR spectra (KBr, 4,000–
Whatmann filter paper discs (diameter 9.0 mm, the solvent
-
1
-1
00 cm selected). 3,031 cm (s, vO–H), 1,631 cm
-1
4
used was DMF) were sterilized by dry heat at 140 °C for
-1
-1
s, vC=N), 1,601 cm (s, vC = O) 1,234 cm (m, vPh–O)
(
1
h and saturated with the solution of test compound
-
(
Scheme 2).
1
(concentration: 250 lg mL ). These discs were air-dried
at room temperature to remove any residual solvent, which
Synthesis of [AgL(HL)ꢀDMF]
might interfere with the determination.
To a boiling solution of AgSCN (0.017 g, 0.1 mmol) in
DMF (30 mL), a solution of a-bromo-cinnamaldehyde
salicylhydrazone HL (0.069 g, 0.2 mmol) in DMF (30 mL)
was added slowly with constant stirring and the mixture
was boiled under reflux for 4 h. The resulting brown
solution was cooled to room temperature and allowed to
stand for 1 week, during which brown crystals were
formed. The crystals were filtered off, washed with
cold ethanol (5 mL), and dried in air. m. p. 260 °C IR
Results and discussion
Crystal structure
The principle structure features for [AgL(HL)ꢀDMF] are
illustrated in Fig. 1. Figure 2 shows the one-dimensional
chain propagated along the b axis and packing plots of the
unit cell. Selected bond lengths and angles are listed in
Table 2. The hydrogen bonds are indicated in Table 3.
-
1
-1
(
KBr, 4,000–400 cm
selected): 3,450 cm (s, vO–H),
Scheme 2 Synthesis of Schiff
base (HL) ligand
OH
O
Br
Br
OHC
CH
N
NH
O
C2H5 OH
+
HN NH2
HO
1
23

Transition Met Chem (2010) 35:507–511
509
Table 1 Crystallographic data
for [AgL(HL)ꢀDMF]
Formula weight
Temperature/K
870.35
Empirical formula
3
Volume (A ), Z
3
Calculated density (calculated) (Mg/m )
35 2 5 5
C H32AgBr N O
˚
298(2)
1734.9(3), 2
1.666
˚
Wave length (A)
0.71073
868
F(000)
˚
a (A)
H range for data collection (°)
a (°)
b (°)
c (°)
Data/restraints/parameters
1.7*25
9.7532(9)
13.0507(11)
15.2568(13)
2.933
72.934(2)
76.475(2)
71.023(2)
6048/0/435
˚
b (A)
˚
c (A)
Absorption coefficient
Space group
P - 1
Final R indices [I [ 2r(I)]
R
1
= 0.1378,
2
wR = 0.1412
Crystal system
Triclinic
0.912
R indices (all data)
R
1
= 0.0633,
wR = 0.1153
1.244, -0.657
2
2
-3
)
˚
Largest diff. peak and hole (eA
Goodness-of-fit on F
˚
Table 2 Selected bond lengths (A) and angles (°)
Ag(1)–N(2)
2.337(5)
2.445(5)
Ag(1)–N(4)
Ag(1)–O(2)
2.357(5)
2.449(6)
Ag(1)–O(4)
Ag(1)–Br(1)
3.0707(12) Ag(1)–Br(2)
3.109(12)
170.6(2)
N(2)–Ag(1)–O(4)
N(2)–Ag(1)–O(2)
O(4)–Ag(1)–O(2)
120.01(17) N(2)–Ag(1)–N(4)
69.2(2)
N(4)–Ag(1)–O(4)
69.26(18)
109.72(18)
68.52(18)
94.55(13)
113.55(19) N(4)–Ag(1)–O(2)
N(4)–Ag(1)–Br(1) 110.53(14) N(2)–Ag(1)–Br(1)
O(2)–Ag(1)–Br(1) 136.94(11) O(4)–Ag(1)–Br(1)
˚
Table 3 Hydrogen bonds for the title compound (A and °)
Fig. 1 Molecular structure of the complex, showing the atom-
numbering scheme. Displacement ellipsoids are drawn at the 30%
probability level. H atoms are omitted for clarity
D–HꢀꢀꢀA
d(D–H)
d(HꢀꢀꢀA)
d(DꢀꢀꢀA)
\(DHA)
N1–H1AꢀꢀꢀO1
N3–H3ꢀꢀꢀO3
O3–H3BꢀꢀꢀO1
0.86
0.86
0.82
1.82
1.88
1.65
2.548(8)
2.580(7)
2.465(6)
141.5
137.1
173.4
A relatively high coordination number of 6 is achieved
by Ag, involving two tridentate Schiff base ligands, as
shown in Fig. 1. The silver(I) coordination sphere is
AgO N Br and the concomitant geometry is distorted
2
2
2
octahedral, with the bond angles around silver ranging
from 69.2(2)° to 136.94(11)°. The a-bromo-cinnamalde-
hyde and salicyloylhydrazine moieties in the ligands are in
one plane forming an extensive delocalized system. The
Schiff base ligands coordinate silver(I) through the car-
bonyl O, Br, and hydrazine N atoms. All the Ag–N bond
Fig. 2 Packing diagram of [AgL(HL)ꢀDMF] (I), Hydrogen bonds are
indicated by broken lines
˚
distances [2.337(5)–2.357(5) A] are within expected ran-
ges [7, 8]. It is interesting to note that the title compound
˚
has two long Ag–Br bonds, 3.0707(12) and 3.109(12) A,
The X-ray structure determination shows that the com-
plex crystallized as a triclinic crystal in a P - 1 space
group with two molecules per unit cell. The complex is an
electronically neutral silver complex. The smallest repeat
unit for the complex comprises one silver atom, two
a-bromo-cinnamaldehyde salicylhydrazone ligands (one of
which is deprotonated), and one lattice DMF molecule.
which are longer than previously reported (Ag–Br
˚
2.7–3.0 A) [9, 10], but clearly shorter than the sum of the
˚
van der Waals radii of silver and bromine (3.21 A) [11].
The complex forms infinite one-dimensional supramo-
lecular chains along the b axis in the crystals, supported by
two intramolecular hydrogen bonds involving N3–H3ꢀꢀꢀO3,
123

5
10
Transition Met Chem (2010) 35:507–511
-
1
Table 4 UV–Vis spectroscopic data of HL and the complex
2
/nm /nm k /nm
the absence of the PhO–H stretching at 3,031 cm in the
spectrum of the complex [14].
k
1
k
2
The UV–Vis solution spectra of the free Schiff base and
[
AgL(HL)ꢀDMF]
HL
221
225
246
253
358
334
[
AgL(HL)ꢀDMF] are summarized in Table 4. The band
centered at 225 nm in the uncoordinated Schiff base is
attributed to p–p* transitions, probably from the aro-
ylhydrazone moiety [17]. This band hardly changes upon
coordination to silver. A band at 246 nm in the complex
spectrum attributed to phenyl p–p* transition is 7 nm blue-
shifted compared to the free ligand. This fact suggests
P-conjugation is decreased in coordination, in agreement
with the study. Finally, the shoulder near 358 nm in
[
AgL(HL)ꢀDMF] is attributed to MLCT d-P transitions
from the Ag to the hydrazone ligand [15] (Table 4).
Cyclic voltammetry
Electrochemical studies of the complex were performed on
a CHI660B electrochemical system in N,N-dimethylform-
amide medium, with tetrabutylammonium bromide as
supporting electrolyte, a platinum wire as counter electrode
and a glassy carbon electrode as working electrode at a
scan rate of 50 mV/s. The complex shows a weak reductive
peak at -0.41 V, as expected, assigned to reduction of
Ag(I) to Ag(0) by comparing with the cyclic voltammo-
gram of free Schiff base in DMF solution. (The cyclic
voltammograms of free HL show no peak between -0.6
and 0.6 V). The complex exhibits an irreversible reduction
process at the -0.41 V, as shown in Fig. 3.
Fig. 3 Cyclic voltammogram of [AgL(HL)ꢀDMF]
and N1–H1AꢀꢀꢀO1, and intermolecular hydrogen bond
O3–H3BꢀꢀꢀO1 as shown in Table 3.
Spectroscopic properties
The IR spectra of the complex were analyzed in compari-
son with that of the free Schiff base in the region 4,000–
-
1
00 cm . The IR spectrum of the free hydrazone shows
4
-
1
typical bands at approximately 1,631 and 1,601 cm
,
In vitro antimicrobial activity
which can be assigned to v(C=O) and v(C=N), respectively
[
-
1
12, 13]. The broad band present at 2,943–3,240 cm is
The in vitro antibacterial and antifungal activities of both
the free Schiff base and [AgL(HL)ꢀDMF] were tested
against the bacteria, Staphyloccus aureus, Bacillus subtilis
Cohn), Diplococcus pneumoniae (Gram-positive), Esche-
rischia coli (Gram-negative), Salmonella enterica, and the
fungi, Candida, Hansenula anomala. The obtained results
are summarized in Table 5.
due to the stretches of NH or OH. The absorption band of
v(C=N) in the complex is significantly shifted to higher
-
1
frequency, at 1,663 cm . The reason for this hypsochro-
mic shift may be due to stretching of the C=N bond when
the ligand chelates the silver center with the nitrogen atom
of C=N. These data suggest that the free Schiff base takes
the enol form. The shift of v(C=O) in the complex toward
An inhibition zone diameter over 9 mm indicates that
the tested compounds are active against the relevant
microorganism. The antimicrobial activity test results show
that both HL and the complex possess significant inhibition
activity against S. aureus and B. subtilis, and moderate
inhibition against the yeast-like C. albicans. The complex
exhibited distinctly higher biological activity against
-
1
lower wave number at 1,598 cm may be attributed to
-
complexation of the atom. A band at 1,234 cm in the
1
hydrazone has been assigned to the Ph–O stretch, it is
-
1
shifted to 1,248 cm after coordination, which may be
due to deprotonation of one ligand, in order to keep charge
balance with the silver ion. This also can be supported by
Table 5 Antibacterial activity of [AgL(HL)ꢀDMF] and HL (ring of antibacterial diameter mm)
Test organism
E. coli
S. aureus
D. pneumoniae
C. albicans
S. enterica
B. Subtilis
H. anomala
HL
9
9
14
18
9
9
12
13
9
9
16
22
10
10
AgL(HL)DMF
1
23

Transition Met Chem (2010) 35:507–511
511
S. aureus and B. subtilis compared with HL, which also is
consistent with our earlier reports [16]. Compared to the
free ligand such an increased biological activity can be
3. Pickart L, Goodwin WH, Burgua W, Murphy TB, Johnson DK
(
1983) Biochem Pharmacol 32:3868
. Mostafa MM, Khattab MA, Ibrahim KM (1983) Polyhedron
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5. Sheldrick GM (1990) Acta Crystallogr A46:467
4
2
0
explained on the basis of Tweedy s chelation theory [17].
6
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Taylor R (1989) J Chem Soc Dalton Trans S1–S83
. Keeffe MO, Brese NE (1991) J Am Chem Soc 113:3226
Supplementary material
CCDC 749181 contains the supplementary crystallographic
data for [AgL(HL)ꢀDMF]. The data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: (t44) 1223–
9. Laube T, Weidenhaupt A, Hunziker R (1991) J Am Chem Soc
13:2561
0. Charbonnier F, Faure R, Loiseleur H (1978) Acta Cryst B
4:3598
11. Bondi AJ (1964) Phys Chem 68:441
12. Nakamoto K (1986) Infrared and Raman spectra of inorganic and
coordination compounds. Willy, New York
3. Navaneetham NS, Kalyanasundaram R, Soundararajan S (1985)
Inorg Chim Acta 110:169
4. Chitrapriya N, Mahalingam V, Natarajan K (2008) Polyhedron
1
1
3
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36–033 or E-mail: deposit@ccdc.cam.ac.uk).
1
Acknowledgments The authors acknowledge financial support
from National Natural Science Foundation of China, (grant
1
2
7:1573
2
0702016).
1
1
1
5. Vogler A, Kunkel H (2000) Coord Chem Rev 200–202:991
6. Xie AG, Qu Y, Wang MM (2009) J Coord Chem 62:2268
7. Tweedy BG (1964) Phytopathology 55:910
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123