Synthesis and antimicrobial activities of metal(II) complexes with 2,4-diiodo-6-phenyliminomethyl-phenol

Article abstract of DOI:10.1080/00958972.2010.507812

A bidentate ligand, 2,4-diiodo-6-phenyliminomethyl-phenol (HL) has been synthesized from 3,5-diiodosalicylaldehyde and phenylamine in ethanol. Five mononuclear complexes have been synthesized from 2,4-diiodo-6-phenyliminomethyl- phenol reaction with CuCl₂ 2H₂O, NiCl₂ 6H ₂O, CoCl₂ 6H₂O, MnCl2 4H₂O, and ZnCl₂ in ethanol or tetrahydrofuran (THF). The complexes were characterized by UV, infrared, ESI-MS, and elemental analyses. Complexes bis(2,4-diiodo-6-phenyliminomethyl-phenol)-copper(II) (1) and bis(2,4-diiodo-6-phenyliminomethyl-phenol)-zinc(II)-THF (5) were characterized by X-ray crystallography. Based on the crystal structure analysis of 1 and 5, coupled to their spectral similarity with other complexes prepared (2, 3, 4), we conclude that 2, 3, and 4 have similar structures to 1. The metal(II) in each complex is four-coordinate by two nitrogens and two oxygens from two ligands. All the complexes were assayed for antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter cloacae) activities by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method. Among the complexes tested, 1 showed the most favorable antimicrobial activity with minimum inhibitory concentrations of 3.125, 6.25, 6.25, 3.125, 3.125, 6.25 g mL-1 against B. subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae, respectively.

Full text of DOI:10.1080/00958972.2010.507812

This article was downloaded by: [University of Aberdeen]
On: 20 June 2013, At: 11:08
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis and antimicrobial activities of
metal(II) complexes with 2,4-diiodo-6-
phenyliminomethyl-phenol
Suo-Ping Xu a & Hai-Liang Zhu b
a School of Chemistry and Chemical Engineering, Xuzhou Normal
University, Xuzhou 221116, China
b School of Life Sciences, Nanjing University, Nanjing 210093,
China
Published online: 06 Aug 2010.
To cite this article: Suo-Ping Xu & Hai-Liang Zhu (2010): Synthesis and antimicrobial activities
of metal(II) complexes with 2,4-diiodo-6-phenyliminomethyl-phenol, Journal of Coordination
Chemistry, 63:18, 3291-3300
To link to this article: http://dx.doi.org/10.1080/00958972.2010.507812
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-
conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Journal of Coordination Chemistry
Vol. 63, No. 18, 20 September 2010, 3291–3300
Synthesis and antimicrobial activities of metal(II) complexes
with 2,4-diiodo-6-phenyliminomethyl-phenol
SUO-PING XUy and HAI-LIANG ZHU*z
ySchool of Chemistry and Chemical Engineering, Xuzhou Normal University,
Xuzhou 221116, China
zSchool of Life Sciences, Nanjing University, Nanjing 210093, China
(Received 13 December 2009; in final form 7 May 2010)
A bidentate ligand, 2,4-diiodo-6-phenyliminomethyl-phenol (HL) has been synthesized from
3,5-diiodosalicylaldehyde and phenylamine in ethanol. Five mononuclear complexes have been
synthesized from 2,4-diiodo-6-phenyliminomethyl-phenol reaction with CuCl2 ꢀ 2H2O,
NiCl2 ꢀ 6H2O, CoCl2 ꢀ 6H2O, MnCl2 ꢀ 4H2O, and ZnCl2 in ethanol or tetrahydrofuran (THF).
The complexes were characterized by UV, infrared, ESI-MS, and elemental analyses.
Complexes bis(2,4-diiodo-6-phenyliminomethyl-phenol)-copper(II) (1) and bis(2,4-diiodo-6-
phenyliminomethyl-phenol)-zinc(II)-THF (5) were characterized by X-ray crystallography.
Based on the crystal structure analysis of 1 and 5, coupled to their spectral similarity with other
complexes prepared (2, 3, 4), we conclude that 2, 3, and 4 have similar structures to 1. The
metal(II) in each complex is four-coordinate by two nitrogens and two oxygens from two
ligands. All the complexes were assayed for antibacterial (Bacillus subtilis, Staphylococcus
aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter
cloacae) activities by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide)
method. Among the complexes tested, 1 showed the most favorable antimicrobial activity with
minimum inhibitory concentrations of 3.125, 6.25, 6.25, 3.125, 3.125, 6.25 mg mLꢁ1 against
B. subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae, respectively.
Keywords: 3,5-Diiodosalicylaldehyde; Phenylamine; Metal complexes; Antibacterial activity
1. Introduction
Salicylaldehyde Schiff-base metal complexes have a wide range of antibacterial activity
[1–6] with many studies of the synthesis, characterization, and structure-activity
relationships (SAR) of Schiff bases [7–10]. Salicylaldehyde derivatives, with one or
more halogens in the aromatic ring, showed antibacterial and antifungal activities [11].
Schiff-base ligands play important roles in the development of coordination chemistry
related to catalysis and enzymatic reactions, magnetism, and molecular architecture,
and also exhibit biological activities [12–15]. In this article, five new mononuclear
complexes have been synthesized from the condensation of 3,5-diiodosalicylaldehyde
with phenylamine and different metal ions. All the complexes were assayed for
*Corresponding author. Email: zhul@nju.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.507812

3292
S.-P. Xu and H.-L. Zhu
I
I
NH2
O
N
ethanol
+
OH
OH
I
I
I
I
N
I
N
ethanol
O
2
+
M
MCl
O
2
OH
I
N
I
I
M= Cu, Ni, Co, Mn
I
I
N
I
N
THF
O
2
+
Zn
ZnCl2
O
OH
I
I
N
I
O
Scheme 1. Syntheses of the complexes.
antibacterial activities against three Gram-positive bacterial strains (Bacillus subtilis,
Staphylococcus aureus, and Streptococcus faecalis) and three Gram-negative bacterial
strains (Escherichia coli, Pseudomonas aeruginosa, and Enterobacter cloacae) by the
MTT method. The results gain more understanding of the antimicrobial activity of
metal(II) complexes with 3,5-diiodosalicylalidene Schiff bases.
2. Experimental section
2.1. Chemistry
Reaction of 2,4-diiodo-6-phenyliminomethyl-phenol (HL) with CuCl2 ꢀ 2H2O,
NiCl2 ꢀ 6H2O, CoCl2 ꢀ 6H2O, MnCl2 ꢀ 4H2O in ethanol solvent, and ZnCl2 in tetrahy-
drofuran (THF) led to the formation of five new mononuclear complexes (scheme 1).
All the complexes gave satisfactory chemical analyses (ꢂ0.4%). UV, infrared (IR)
spectroscopy, and ESI-MS spectra were consistent with the assigned structures. The
crystal structures of 1 and 5 were determined using SMART 1000 CCD diffractometer
instrument. Single crystals of 1 and 5 with dimensions 0.43 mm ꢃ 0.39 mm ꢃ 0.16 mm
and 0.45 mm ꢃ 0.43 mm ꢃ 0.18 mm were chosen for X-ray diffraction. The data were
˚
collected with graphite-monochromated Mo-Kꢀ radiation (ꢁ ¼ 071073 A) using !-2ꢂ
scan technique. Complex 1 is a green prism crystal. A total of 13,225 reflections were
collected and 4779 were independent (Rint ¼ 0.0893), of which 3314 observed reflections

2,4-Diiodo-6-phenyliminomethyl-phenol
Table 1. Crystallographic and experimental data for 1 and 5.
3293
1
5
Empirical formula
Formula weight
Crystal system
Space group
C26H16I4N2O2Cu
959.55
Monoclinic
P2(1)/c
C30H24I2N2O3Zn
1033.48
Monoclinic
C2/c
ꢄ
˚
Unit cell dimensions (A,
)
a
b
c
ꢀ
ꢄ
ꢅ
21.559(2)
15.06190(17)
8.479(8)
90
97.7910(10)
90
2728.1(5), 4
298(2)
2.336
5.354
1772
22.287(2)
11.6994(13)
26.065(3)
90
104.930(2)
90
6566.7(12), 8
298(2)
2.091
4.541
3872
3
˚
Volume (A ), Z
Temperature (K)
Density (g cmꢁ3
)
m (mmꢁ1
F(000)
)
Max. and min. transmission
Data/restraints/parameters
ꢂ range (ꢄ)
0.4813 and 0.2067
4779/0/316
1.65–25.02
ꢁ16 ꢅ h ꢅ 25;
ꢁ17 ꢅ k ꢅ 17;
ꢁ10 ꢅ l ꢅ 9
13225/4779
0.0893
0.4953 and 0.2344
5774/0/361
1.62–25.02
ꢁ17 ꢅ h ꢅ 26;
ꢁ13 ꢅ k ꢅ 13;
ꢁ29 ꢅ l ꢅ 31
16180/5774
0.0442
Index ranges (h, k, l)
Reflections collected/unique
Rint
R (I42ꢃ(I))
wR (I42ꢃ(I))
(Dꢆ)max and (Dꢆ)min (e A
0.0519
0.1278
1.011 and ꢁ1.871
0.0547
0.1316
1.573 and ꢁ1.345
ꢁ3
˚
)
P
P
P
2
2
1=2
R ¼ jjFoj ꢁ Fcj= jFoj, wR ¼ ½ ½wðFo2 ꢁ Fc2Þ ꢆ=½wðFo2Þ ꢆꢆ
:
had I42ꢃ(I ). Complex 5 is a brown prism crystal. A total of 16,180 reflections were
collected and 5774 were independent (Rint ¼ 0.0442), of which 3685 were observed with
I42ꢃ(I ). The structures were solved using direct methods and refined by full-matrix
least-squares. All non-hydrogen atoms were assigned anisotropic displacement param-
eters in the refinement. All hydrogens were added at calculated positions and refined
using a riding model. The structures were refined on F2 using SHELXTL-97 [16].
The crystals used for diffraction showed no decomposition during data collection. The
crystal data and refinement data are listed in table 1. Selected bond lengths and angles
are given in table 2.
The 3,5-diiodosalicylalidene was synthesized with salicylaldehyde, KI, and KIO3 [17];
other chemicals (reagent grade) used were commercially available. UV spectra were
recorded on a U-3000 spectrophotometer. IR spectra were recorded on a Nexus 870
FT-IR. ESI-MS spectra were recorded on a Mariner System 5304 Mass spectrometer.
Elemental analyses were performed on a CHN-O-Rapid instrument and were
within ꢂ 0.4% of the theoretical values. Melting points were measured on a Boetius
micromelting point apparatus.
Quantities (4 mmol) of 3,5-diiodo-salicylaldehyde and phenylamine with 2 mmol
CuCl2 ꢀ 2H2O, NiCl2 ꢀ 6H2O, CoCl2 ꢀ 6H2O, MnCl2 ꢀ 4H2O were dissolved in ethanol
(12 mL) (2 mmol ZnCl2 was dissolved in 10 mL THF) and stirred at room temperature
for 30 min to give a clear solution. After standing for approximately 7–10 days,

3294
S.-P. Xu and H.-L. Zhu
ꢄ
˚
Table 2. Selected bond lengths (A) and angles ( ) of 1 and 5.
Bond
Distance
Bond
Distance
Bond
Distance
1
Cu(1)–O(2)
Cu(1)–N(1)
I(3)–C(17)
N(1)–C(8)
O(1)–C(3)
1.893(6)
2.001(7)
2.103(9)
1.435(11)
1.290(10)
Cu(1)–O(1)
I(1)–C(4)
I(4)–C(19)
N(2)–C(14)
O(2)–C(16)
1.922(6)
2.093(8)
2.088(8)
1.297(10)
1.288(10)
Cu(1)–N(2)
I(2)–C(6)
N(1)–C(1)
N(2)–C(21)
1.966(7)
2.106(8)
1.290(11)
1.459(10)
5
Zn(2)–O(2)
Zn(2)–N(2)
I(3)–C(17)
N(1)–C(8)
O(1)–C(3)
O(3)–C(30)
1.903(7)
2.010(7)
2.112(11)
1.448(12)
1.291(10)
1.45(3)
Zn(2)–O(1)
I(1)–C(4)
I(4)–C(19)
N(2)–C(14)
O(2)–C(16)
1.919(6)
2.091(9)
2.109(11)
1.298(13)
1.291(10)
Zn(2)–N(1)
I(2)–C(6)
N(1)–C(1)
N(2)–C(21)
O(3)–C(27)
2.004(7)
2.105(10)
1.294(11)
1.422(13)
1.42(3)
Bond
Angle(ꢄ)
Bond
Angle(ꢄ)
Bond
Angle(ꢄ)
1
O(2)–Cu(1)–O(1)
O(2)–Cu(1)–N(1)
C(1)–N(1)–C(8)
C(14)–N(2)–C(21)
C(3)–O(1)–Cu(1)
O(1)–C(3)–C(2)
C(3)–C(4)–I(1)
C(13)–C(8)–N(1)
O(2)–C(16)–C(15)
C(16)–C(17)–I(3)
C(26)–C(21)–N(2)
158.7(3)
91.7(3)
O(2)–Cu(1)–N(2)
O(1)–Cu(1)–N(1)
C(1)–N(1)–Cu(1)
C(14)–N(2)–Cu(1)
C(16)–O(2)–Cu(1)
O(1)–C(3)–C(4)
C(7)–C(6)–I(2)
C(9)–C(8)–N(1)
O(2)–C(16)–C(17)
C(18)–C(19)–I(4)
C(22)–C(21)–N(2)
91.6(3)
92.6(3)
O(1)–Cu(1)–N(2)
N(2)–Cu(1)–N(1)
C(8)–N(1)–Cu(1)
C(21)–N(2)–Cu(1)
N(1)–C(1)–C(2)
C(5)–C(4)–I(1)
92.4(3)
157.4(3)
120.9(6)
118.9(5)
126.7(8)
119.7(6)
118.9(6)
125.6(8)
119.9(6)
122.4(7)
115.7(7)
116.6(7)
127.0(5)
124.2(7)
117.8(6)
121.6(9)
125.2(8)
116.9(6)
116.6(8)
123.4(6)
124.4(6)
127.4(5)
120.4(7)
120.3(6)
119.0(9)
120.0(8)
118.3(6)
122.9(8)
C(5)–C(6)–I(2)
N(2)–C(14)–C(15)
C(18)–C(17)–I(3)
C(20)–C(19)–I(4)
5
O(2)–Zn(2)–O(1)
O(2)–Zn(2)–N(2)
C(1)–N(1)–C(8)
C(14)–N(2)–C(21)
C(3)–O(1)–Zn(2)
N(1)–C(1)–C(2)
C(5)–C(4)–I(1)
C(7)–C(6)–I(2)
N(2)–C(14)–C(15)
C(22)–C(21)–N(2)
116.1(3)
97.7(3)
O(2)–Zn(2)–N(1)
O(1)–Zn(2)–N(2)
C(1)–N(1)–Zn(2)
C(14)–N(2)–Zn(2)
C(16)–O(2)–Zn(2)
O(1)–C(3)–C(4)
C(3)–C(4)–I(1)
C(13)–C(8)–N(1)
C(20)–C(19)–I(4)
C(26)–C(21)–N(2)
112.5(3)
113.6(3)
118.9(6)
118.2(7)
125.5(7)
119.9(8)
117.7(6)
118.1(8)
119.7(9)
116.8(9)
O(1)–Zn(2)–N(1)
N(1)–Zn(2)–N(2)
C(8)–N(1)–Zn(2)
C(21)–N(2)–Zn(2)
C(27)–O(3)–C(30)
O(1)–C(3)–C(2)
C(5)–C(6)–I(2)
97.3(3)
120.8(3)
121.0(6)
122.1(6)
111(2)
124.4(8)
119.0(8)
122.7(9)
119.9(10)
120.1(7)
119.6(8)
125.1(6)
129.0(8)
118.1(7)
119.3(7)
129.3(9)
125.0(10)
C(9)–C(8)–N(1)
C(18)–C(19)–I(4)
the precipitates were separated by filtration, washed with methanol three times, and
dried in a vacuum desiccator containing anhydrous CaCl2.
2.1.1. 2,4-Diiodo-6-phenyliminomethyl-phenol (HL). Nacarat pole crystal, yield 92%,
m.p.: 145–147ꢄC, UV (ꢁ nm): 435.4; 256.5. 1H NMR [300 MHz, CDCl3] (ꢇ ppm): 14.688
(s, 1H); 8.456 (s, 1H); 8.107 (d, J ¼ 2.1 Hz, 1H); 7.671 (d, J ¼ 2.1 Hz, 1H); 7.433
(d, J ¼ 7.8 Hz, 2H); 7.303 (d, J ¼ 1.8 Hz, 1H); 7.267 (d, J ¼ 7.8 Hz, 2H). Selected IR data
(cmꢁ1, KBr): 3133.4(s); 1621.6(s); 1580.9(s); 1439.3(s); 1349.0(m); 1279.4(m); 1198.0(m);
1150.2(s); 855.5(m); 764.6(m); 738.3(m). ESI-MS: 449.9 (C13H10I2NOþ, [M þ H]þ).
Anal. Calcd for C13H9I2NO (%): C, 34.77; H, 2.02; N, 3.12; Found (%): C, 34.65;
H, 1.96; N, 3.08.

2,4-Diiodo-6-phenyliminomethyl-phenol
3295
2.1.2. Bis(2,4-diiodo-6-phenyliminomethyl-phenol)-copper(II) (1). Green prism crystal,
yield 86%, m.p.: 243–245ꢄC. UV (ꢁ nm): 406.5; 255.5. Selected IR data (cmꢁ1, KBr):
3059.8(m); 1611.8(s); 1581.4(s); 1439.6(s); 1349.9(m); 1150.5(s); 855.5(m); 764.8(m);
738.5(m); 692.0(m); 658.8(m). ESI-MS: 960.56 (C26H17I4N2O2Cuþ, [M þ H]þ). Anal.
Calcd for C26H16I4N2O2Cu (%): C, 32.54; H, 1.68; N, 2.92; Cu, 6.62. Found (%):
C, 32.75; H, 1.69; N, 2.87; Cu, 6.58.
2.1.3. Bis(2,4-diiodo-6-phenyliminomethyl-phenol)-nickel(II) (2). Glaucous pole crꢁys1-
tal, yield 82%, m.p.: 281–286ꢄC. UV (ꢁ nm): 410.5; 256.5. Selected IR data (cm
,
KBr): 3060.0(m); 1611.9(s); 1581.5(s); 1439.7(s); 1350.0(m); 1280.4(m); 1198.5(m);
1150.5(s); 855.7(m); 764.8(m); 738.6(m); 692.2(m); 658.9(m). ESI-MS: 955.72
(C26H17I4N2O2Niþ, [M þ H]þ). Anal. Calcd for C26H16I4N2O2Ni (%): C, 32.71;
H, 1.69; N, 2.93; Ni, 6.15. Found (%): C, 32.63; H, 1.65; N, 3.04; Ni, 6.20.
2.1.4. Bis(2,4-diiodo-6-phenyliminomethyl-phenol)-cobalt(II) (3). Brown pole crystal,
yield 75%, m.p.: 145–147ꢄC. UV (ꢁ nm): 413.7; 256.5. Selected IR data (cmꢁ1, KBr):
3060.2(m); 1611.9(s); 1581.4(s); 1439.8(s); 1350.0(m); 1280.2(m); 1150.6(s); 855.7(m);
765.0(m); 738.7(m); 692.3(m); 659.0(m). ESI-MS: 955.97 (C26H17I4N2O2Coþ,
[M þ H]þ). Anal. Calcd for C26H16I4N2O2Co (%): C, 32.70; H, 1.69; N, 2.93; Co,
6.17. Found (%): C, 32.75; H, 1.66; N, 2.88; Co, 6.14.
2.1.5. Bis(2,4-diiodo-6-phenyliminomethyl-phenol)-manganese(II) (4). Brown pole crꢁys1-
tal, yield 70%, m.p.: 151–154ꢄC. UV (ꢁ nm): 412.0; 257.5. Selected IR data (cm
,
KBr): 3060.4(m); 1611.8(s); 1581.3(s); 1439.5(s); 1349.8(m); 1280.1(m); 1198.5(m);
1150.4(s); 855.5(m); 764.8(m); 738.4(m); 692.0(m); 658.8(m). ESI-MS: 951.97
(C26H17I4N2O2Mnþ, [M þ H]þ). Anal. Calcd for C26H16I4N3O2Mn (%): C, 32.84;
H, 1.70; N, 2.95; Mn, 5.78. Found (%): C, 32.88; H, 1.69; N, 2.89; Mn, 5.75.
2.1.6. Bis(2,4-diiodo-6-phenyliminomethyl-phenol)-zinc(II) tetrahydrofuran (5). Brown
prism crystal, yield 78%, m.p.: 287–289ꢄC. UV (ꢁ nm): 413.0; 257.0. Selected IR data
(cmꢁ1, KBr): 3059.7(m); 1602.5(s); 1578.4(s); 1489.6(s); 1426.6(s); 1404.2(s); 1289.7(m);
1228.6(m); 1188.5(m); 1145.1(s); 1116.4(m); 870.2(m); 829.3(m); 762.9(m); 747.8(m);
688.7(m); 674.4(m). ESI-MS: 1034.48 (C30H25I4N2O3Znþ, [M þ H]þ). Anal. Calcd for
C30H24I4N2O3Zn (%): C, 34.86; H, 2.34; N, 2.71; Zn, 6.38. Found (%): C, 34.85;
H, 2.32; N, 2.75; Zn, 6.36.
2.2. Antimicrobial activity
The antibacterial activities of the synthesized complexes were tested against B. subtilis,
S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae using MTT medium. The
minimum inhibitory concentrations (MICs) of the complexes were determined by a
colorimetric method using the dye MTT [18]. A stock solution of the synthesized
complex (50 mg mLꢁ1) in DMSO was prepared and graded quantities of the test
complexes were incorporated in a specified quantity of sterilized liquid medium.
A specified quantity of the medium containing the complex was poured into

3296
S.-P. Xu and H.-L. Zhu
Table 3. MICs of the synthetic complexes.
Microorganisms MICs (mg mLꢁ1
)
Gram positive
Gram negative
Compound
B. subtilis
S. aureus
S. faecalis
P. aeruginosa
E. coli
E. cloacae
1
2
3
4
3.125
12.5
6.25
12.5
6.25
3.125
1.562
0.39
6.25
12.5
12. 5
12.5
25
25
1.562
1.562
6.25
6.25
12.5
25
12.5
6.25
1.562
3.125
3.125
6.25
6.25
12.5
6.25
3.125
6.25
3.125
3.125
6.25
6.25
25
12.5
3.125
6.25
3.125
6.25
12.5
12.5
12.5
12.5
6.25
3.125
1.562
5
HL
Penicillin
Kanamycin
microtitration plates. Suspension of the microorganism was prepared to contain
approximately 105 cfu mLꢁ1 and applied to microtitration plates with serially diluted
complexes in DMSO to be tested and incubated at 37ꢄC for 24 h for bacterial
suspensions. After the MICs were visually determined on each of the microtitration
plates, 50 mL of phosphate buffered saline (PBS 0.01 mol Lꢁ1
,
pH 7.4:
Na2HPO4 ꢀ 12H2O 2.9 g, KH2PO4 0.2 g, NaCl 8.0 g, KCl 0.2 g, distilled water
1000 mL) containing 2 mg mLꢁ1 of MTT was added to each well. Incubation was
continued at room temperature for 4–5 h. The content of each well was removed and
100 mL of isopropanol containing 5% 1 mol Lꢁ1 HCl was added to extract the dye.
After 12 h of incubation at room temperature, the optical density (OD) was measured
with a microplate reader at 570 nm. The observed MICs are presented in table 3.
3. Results and discussion
Complexes 1–4, C26H16I4N3O2M (M ¼ Cu, Ni, Co, Mn) were prepared from
2,4-diiodo-6-phenyliminomethyl-phenol (C13H9I2NO) in ethanol, as described in
Section 2, in moderate yields (70–86%). Complex 5, C30H24I4N2O3Zn, was prepared
from 2,4-diiodo-6-phenyliminomethyl-phenol in THF. The IR spectra of the complexes
(KBr pellets) display an intense absorption at ca 1602–1612 cmꢁ1 attributable to
ꢈ
(C¼N)imine. This band shifts ca 10–19 cmꢁ1 to lower wavenumbers compared to the
ca 1622 cmꢁ1 attributable to ꢈ(C¼O)imine. The UV spectra of the complexes display
intense absorptions at 255–257 nm (ꢉ ! ꢉ*) and 406–414 nm (n!ꢉ*).
The molecular structure of 1 crystallizes in monoclinic space group P2(1)/c.
A perspective view of the crystal structure and packing diagram of 1 are shown in
figures 1 and 2, respectively. The Cu(II) adopts a distorted square plane coordinated by
two nitrogens and two oxygens from L. The Cu(1)–O(1), Cu(1)–N(1), Cu(1)–O(2), and
˚
Cu(1)–N(2) bond lengths are 1.922(6), 2.001(7), 1.893(6), and 1.966(7) A, respectively.
The dihedral angle between Cu(1)/O(1)/N(1) and Cu(1)/O(2)/N(2) planes is 149.3ꢄ.
The dihedral angle between Cu(1)/O(1)/N(1) and C(1)/C(2)/C(3) planes is
14.3ꢄ. The dihedral angle between Cu(1)/O(2)/N(2) and C(16)/C(15)/C(14) planes

2,4-Diiodo-6-phenyliminomethyl-phenol
3297
Figure 1. Crystal structures of 1 and 5 showing 30% probability displacement ellipsoids (arbitrary spheres
for hydrogens).
Figure 2. The packing structure of 1 along the c-axis.
is 19.6ꢄ. The O(1)–Cu(1)–O(2) and N(1)–Cu(1)–N(2) bond angles are 158.7(3) and
157.4(3)ꢄ. These discrete monomers in 1 are stacked to furnish a 3-D supramolecular
network (figure 2). The molecular structure of 5 crystallizes in monoclinic space group
C2/c. A perspective view of the crystal structure and packing diagram of 5 are shown in
figures 1 and 3, respectively. The Zn(II) adopts a distorted tetrahedral geometry,
coordinated by two nitrogens and two oxygens from L. The Zn(2)–O(1), Zn(2)–N(1),
Zn(2)–O(2), and Zn(2)–N(2) bond lengths are 1.919(6), 2.004(7), 1.903(7), and
˚
2.010(7) A, respectively. The O(1)–Zn(2)–O(2), O(2)–Zn(2)–N(1), O(1)–Zn(2)–N(1),
O(2)–Zn(2)–N(2), O(1)–Zn(2)–N(2), and N(1)–Zn(2)–N(2) bond angles are 116.1(3)ꢄ,
112.5(3)ꢄ, 97.3(3)ꢄ, 97.7(3)ꢄ, 113.6(3)ꢄ, and 120.8(3)ꢄ. These discrete monomers in 5 are

3298
S.-P. Xu and H.-L. Zhu
Figure 3. The packing structure of 5 along the b-axis.
ꢄ
˚
Table 4. Hydrogen bonds for 5 [(A) and ( )].
Complex
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
d(D ꢀ ꢀ ꢀ A)
ff(DHA)
5
C(9)–H(9) ꢀ ꢀ ꢀ O(2)
0.93
2.48
3.341(3)
155
stacked to furnish a 3-D supramolecular network (figure 3) with intramolecular
hydrogen bonds (table 4).
The ways in which different metal(II) complexes react with bacteria vary due to the
difference in structures. Structural analyses of these complexes provide explanation for
structure–activity relationships, helpful in the design of better inhibitors. The biological
activity of a particular substance depends on a complex sum of individual properties
including complex structure, affinity for the target site, survival in the medium of
application, survival within the biological system, transport properties, and state of the
target organism [19]. In this study, we focus on the structure–activity relationships.
All the synthesized complexes were screened for antibacterial activity against three
Gram (þ) bacterial strains (B. subtilis, S. aureus, and S. faecalis) and three Gram (ꢁ)
bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by the MTT method. The MICs
of the complexes against the six bacteria are presented in table 3. Also included are the
activities of reference compounds penicillin (North China Pharmaceutical Co. Ltd,
D0211107, Hebei 050015, China) and kanamycin (Nanjing Zhuyan Biotechnology
Co. Ltd, Amresco 060D0504, Nanjing 210002, China). Complexes 1, 3, and 5 showed
higher activity against B. subtilis (MICs: 3.125–6.25 mg mLꢁ1) than 2 and 4
(MICs: 12.5 mg mLꢁ1). Complex 1 showed significant activity against S. aureus

2,4-Diiodo-6-phenyliminomethyl-phenol
3299
(MICs: 6.25 mg mLꢁ1). Complexes 1 and 2 showed higher activity against S. faecalis
(MICs: 6.25 mg mLꢁ1) than other complexes (MICs: 12.5–25 mg mLꢁ1). Complex 1
showed higher activity against P. aeruginosa (MICs: 3.125 mg mLꢁ1) and E. coli
(MICs: 3.125 mg mLꢁ1) while other complexes exhibited significant activity (MICs:
6.25–12.5 mg mLꢁ1). Complex 1 exhibited significant activity against E. cloacae
(MICs: 6.25 mg mLꢁ1) while other complexes exhibited significant activity (MICs:
12.5 mg mLꢁ1).
Complex 1 showed the most favorable antimicrobial activity with MICs of 3.125,
6.25, 6.25, 3.125, 3.125, 6.25 mg mLꢁ1 against B. subtilis, S. aureus, S. faecalis,
P. aeruginosa, E. coli, and E. cloacae, respectively. Complex 2 showed moderate
antimicrobial activity against S. faecalis, P. aeruginosa, and E. coli (MICs:
6.25 mg mLꢁ1). Complex 3 showed moderate antimicrobial activity against B. subtilis,
P. aeruginosa, and E. coli (MICs: 6.25 mg mLꢁ1). Complex 4 showed average
antimicrobial activity against B. subtilis, S. aureus, P. aeruginosa, and E. cloacae
(MICs: 12.5 mg mLꢁ1). Complex 5 showed moderate antimicrobial activity against
B. subtilis and P. aeruginosa (MICs: 6.25 mg mLꢁ1). HL showed high antimicrobial
activity against B. subtilis, S. faecalis, P. aeruginosa, E. coli, and E. cloacae (MICs:
3.125–6.25 mg mLꢁ1) while all the metal salts showed no antimicrobial activity with
MICs over 50 mg mLꢁ1 against the six tested bacterial strains (not presented in table 3).
Comparison of antibacterial potential of the metal complexes with the parent Schiff
base shows that 1 was more active than other metal complexes and the complexation of
Schiff base with copper enhances its antibacterial potential.
4. Conclusion
A new Schiff-base ligand derived from 3,5-diiodosalicylaldehyde and phenylamine has
been synthesized and reacted with different metal salts to form five new mononuclear
complexes. All the complexes were assayed for antibacterial activities against B. subtilis,
S. aureus, S. faecalis, E. coli, P. aeruginosa, and E. cloacae by the MTT method.
The complexes showed potent antibacterial activity against the six bacterial strains with
copper complex (1) showing the most favorable antibacterial activity.
Acknowledgments
The work was co-financed by grants (Projects 30772627) from National Natural Science
Foundation of China and (Projects 09KJD150005) from Province Natural Science
Foundation of Jiang Su.
References
[1] S.-P. Xu, P.-C. Lv, L. Shi, X.-L. Li, H.-L. Zhu. J. Coord. Chem., 62, 3198 (2009).
[2] A. Roth, E.T. Spielberg, W. Plass. Inorg. Chem., 46, 4362 (2007).

3300
S.-P. Xu and H.-L. Zhu
[3] L. Shi, H.-M. Ge, S.-H. Tan, H.-Q. Li, Y.-C. Song, H.-L. Zhu, R.-X. Tan. Eur. J. Med. Chem., 42, 558
(2007).
[4] L.-M. Wu, H.-B. Teng, X.-C. Feng, X.-B. Ke, Q.-F. Zhu, J.-T. Su, W.-J. Xu, X.-M. Hu. Cryst. Growth
Des., 7, 1337 (2007).
[5] S.-P. Xu, L. Shi, P.-C. Lv, R.-Q. Fang, H.-L. Zhu. J. Coord. Chem., 62, 2048 (2009).
[6] J.D. Ranford, J.J. Vittal, Y.M. Wang. Inorg. Chem., 37, 1226 (1998).
[7] E.F. Elslager, J. Battaglia, A.A. Phillips, L.M. Werbel. J. Med. Chem., 13, 587 (1970).
[8] P. Prusis, M. Dambrova, V. Andrianov, E. Rozhkov, V. Semenikhina, I. Piskunova, E. Ongwae,
T. Lundstedt, I. Kalvinsh, J.E.S. Wikberg. J. Med. Chem., 47, 3105 (2004).
[9] S. Ren, R. Wang, K. Komatsu, P.B. Krause, Y. Zyrianov, C.E. McKenna, C. Csipke, Z.A. Tokes,
E.J. Lien. J. Med. Chem., 45, 410 (2002).
[10] P.H. Wang, J.G. Keck, E.J. Lien, M.M.C. Lai. J. Med. Chem., 33, 608 (1990).
[11] L.C. Felton, J.H. Brewer. Science, 105, 409 (1947).
[12] A.D. Garnovskii, I.S. Vasilchenko, D.A. Garnovskii, B.I. Kharisov. J. Coord. Chem., 62, 151 (2009).
[13] M. Rajasekar, S. Sreedaran, R. Prabu, V. Narayanan, R. Jegadeesh, N. Raaman, A.K. Rahiman.
J. Coord. Chem., 63, 136 (2010).
[14] H. Naeimi, M. Moradian. J. Coord. Chem., 63, 156 (2010).
[15] V.B. Badwaik, R.D. Deshmukh, A.S. Aswar. J. Coord. Chem., 62, 2037 (2009).
[16] G.M. Sheldrick. SHELX-97. Program for X-ray Crystal Structure Solution and Refinement, Gottingen
¨
University, Germany (1997).
[17] S.-P. Xu, G.-Z. Zhu, R.-Q. Fang, X.-L. Li, H.-L. Zhu. Chin. J. Struct. Chem., 28, 87 (2009).
[18] Z.-C. Song, G.-Y. Ma, P.-C. Lv, H.-Q. Li, Z.-P. Xiao, H.-L. Zhu. Eur. J. Med. Chem., 44, 3903 (2009).
[19] E.M. Kosower, T. Miyadera. J. Med. Chem., 15, 307 (1972).