Synthesis, spectroscopic characterization and antimicrobial activity of mono-, bi- and tri-nuclear metal complexes of a new Schiff base ligand

Article abstract of DOI:10.1016/j.molstruc.2010.06.034

Condensation of o-acetoacetylphenol and 1,2-diaminopropane in 1:1 molar ratio under condition of high dilution yielded the mono-condensed dibasic Schiff base ligand with a N₂O₂ donors. The mono-condensed ligand has been used for furt

Full text of DOI:10.1016/j.molstruc.2010.06.034

Journal of Molecular Structure 980 (2010) 39–50
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization and antimicrobial activity
of mono-, bi- and tri-nuclear metal complexes of a new Schiff base ligand
a
Magdy Shebl a, , Saied M.E. Khalil , Saleh A. Ahmed b,c, Hesham A.A. Medien b
*
a Chemistry Department, Faculty of Education, Ain Shams University, Roxy, Cairo 11341, Egypt
b Chemistry Department, Faculty of Science, Taibah University, 30002 Al-Madena Al-Mounnawara, Saudi Arabia
c Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 May 2010
Received in revised form 25 June 2010
Accepted 25 June 2010
Available online 6 July 2010
Condensation of o-acetoacetylphenol and 1,2-diaminopropane in 1:1 molar ratio under condition of high
dilution yielded the mono-condensed dibasic Schiff base ligand with a N2O2 donors. The mono-con-
densed ligand has been used for further condensation with 2-hydroxy-5-nitrobenzaldehyde to obtain
the new asymmetrical dicompartmental Schiff base ligand, H3L, with N2O3 donors. The structure of the
ligand was elucidated by analytical and spectroscopic tools (IR, 1H and 13C NMR spectra) which indicated
that the coordinating sites are oxygen atoms of the phenolic OH groups, nitrogen atoms of the azome-
thine groups and the oxygen atom of the ketonic group. Reactions of the ligand with metal salts yielded
mono- and homo-bi-nuclear complexes formulated as [M(HL)], where M@Co(II), Ni(II) and Cu(II),
Keywords:
Schiff base ligands
Mononuclear complexes
Binuclear complexes
Trinuclear complexes
Heteronuclear complexes
Antimicrobial activity
[Fe(H2L)Cl2(H2O)]ꢀ2½H2O,
[Fe2(HL)(ox)Cl3(H2O)2]ꢀ5H2O,
[UO2(H2L)(OAc)(H2O)2],
[VO(H3L)(SO4)(-
H2O)]ꢀH2O, [M2(L)Cl(H2O)2]ꢀ½H2O, where M@Co(II) and Ni(II) and [Cu(H2L)Cl]. The mononuclear Ni(II)
complex, [Ni(HL)], was used to synthesize homo- and hetero-bi- and tri-nuclear complexes with the
molecular formulae [Ni2(L)Cl(H2O)2], [Ni2(L)2FeCl(H2O)]ꢀH2O and [Ni2(HL)2CoCl2]. The structures of the
complexes were characterized by various techniques such as elemental and thermal analyses, IR, 1H
and 13C NMR, mass and electronic spectra as well as conductivity and magnetic moment measurements.
Square-planar and octahedral geometries are suggested for the Cu(II), Co(II) and Ni(II) complexes, octa-
hedral geometry for the Fe(III) and VO2+ complexes while uranium(VI) ion is octa-coordinated in its com-
plex. The Schiff base and its metal complexes were evaluated for antimicrobial activity against Gram
positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli) and fungi (Candida albi-
cans and Aspergillus flavus). The ligand and some of its complexes were found to be biologically active.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
larly wide attention of scientists. The term ‘‘compartmental’’ was
introduced to indicate a ligand containing two adjacent, but dis-
Schiff base ligands are considered privileged ligands, because
they are easily prepared by a simple one-pot condensation of alde-
hydes and primary amines in an alcohol solvent. Metal complexes
of these bases have numerous applications including antibacterial,
antifungal [1–6] and antiviral activities [7,8] as well as other bio-
logical applications [9–12]. Several applications have been related
for these complexes in chemical analysis [13], absorption and
transport of oxygen [14], in pesticides [15] and heterogeneous
and homogeneous catalysis for oxidation and polymerization of or-
ganic compounds [16–19]. The term ‘‘dinucleating ligands’’ was
first introduced in 1970 by Robson [20] to describe the class of
polydentate chelating ligands which able to bind simultaneously
two metal ions. Among many different types of dinucleating li-
gands, the phenol-based compartmental ligands attracted particu-
similar coordinating sites [21]. Particular interest in this type of li-
gands resulted from the recent recognition of the asymmetric
nature of a number of bimetallic biosites [22,23].
Thus, in the present work, a new asymmetric dicompartmental
Schiff base ligand, H3L, which contains N2O3 coordinating sites was
synthesized. Using this dicompartmental ligand, mono-, homo-
and hetero-bi- and tri-nuclear complexes were synthesized and
characterized. Indeed, the biological activity of the ligand and its
complexes was screened against selected kinds of bacteria and
fungi.
2. Experimental
2.1. Reagents and materials
CuCl2ꢀ2H2O, NiCl2ꢀ6H2O, CoCl2ꢀ6H2O, FeCl3ꢀ6H2O, Cu(OAc)2ꢀH2O,
Ni(OAc)2ꢀ4H2O, Co(OAc)2ꢀ4H2O, UO2(OAc)2ꢀ2H2O, VOSO4ꢀH2O,
* Corresponding author. Tel.: +20 233120546.
E-mail address: magdy_shebl@hotmail.com (M. Shebl).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.06.034

40
M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
LiOHꢀH2O, oxalic acid, ethylacetate, sodium metal, o-hydroxyaceto-
phenone, 1,2-diaminopropane and 2-hydroxy-5-nitrobenzalde-
hyde were either BDH or Merck chemicals. o-Acetoacetylphenol
was prepared following the literature procedure [24]. Organic sol-
vents were spectroscopic grade and used without further
purification.
for the ligand and its metal complexes are listed in Table 1.
Scheme 1 represents the synthetic outline of the asymmetric Schiff
base ligand.
2.3. Syntheses of the metal complexes
A general method has been used for the preparation of all com-
2.2. Synthesis of the ligand
plexes. A hot 20 mL ethanolic solution of the metal salt of VO2+
,
Fe(III), Co(II), Ni(II), Cu(II) and UO22þ was gradually added to a chlo-
roform solution of the ligand (30 mL) in 1:1 or 1:2 molar ratio and
the solution was heated under reflux for 3 h on a water bath during
which the solid complex precipitated. The precipitate was filtered
off, washed with ethanol then diethyl ether and finally air-dried. In
case of VO2+ complex, water was added to ensure complete disso-
lution of VOSO4ꢀH2O. The uranyl complex was prepared in metha-
nol. The following detailed preparations are given as examples and
the other complexes were obtained similarly.
2.2.1. Synthesis of o-acetoacetylphenol
o-Acetoacetylphenol was prepared as cited in the literature
[24].
2.2.2. Synthesis of [(E)-3-(1-aminopropan-2-ylimino)-1-(2-
hydroxyphenyl)butan-1-one] (H.U.)
A solution of o-acetoacetylphenol, 15 g (84.3 mmol) in 250 mL
chloroform was added dropwise to a solution of 1,2-diaminopro-
pane, 6.24 g (84.3 mmol) in 150 mL chloroform. After complete
addition, the solution was stirred for an additional 18 h and chlo-
roform was removed under reduced pressure, yielding the half-
unit ligand as a viscous liquid which solidifies to form yellow pre-
cipitate upon addition of heptane. The yellow solid was filtered off,
washed with least amount of chloroform and air-dried. Yield:
16.5 g, 83.7%, m.p. 78 °C.
2.3.1. [Co(HL)], 6
Cobalt(II) acetate tetrahydrate, Co(OAc)2ꢀ4H2O (0.39 g,
1.57 mmol) in ethanol (20 mL) was added gradually with constant
stirring to the solution of the ligand, H3L, (0.6 g, 1.57 mmol) in
chloroform (25 mL). The reaction mixture was heated under reflux
for 3 h. The precipitate was filtered off, washed with ethanol then
ether and finally air-dried. Yield: 0.5 g (72.5%).
2.2.3. Synthesis of the asymmetric Schiff base ligand
The new Schiff base (E)-3-(1-((E)-2-hydroxy-5-nitrobenzylide-
neamino)propan-2-ylimino)-1-(2-hydroxyphenyl)butan-1-one
(H3L) was prepared by condensation of (E)-3-(1-aminopropan-2-
ylimino)-1-(2-hydroxyphenyl)butan-1-one dissolved in CHCl3
with 2-hydroxy-5-nitrobenzaldehyde. A yellow solid product is
formed upon cooling the solution slowly to room temperature
and the precipitate was filtered off, washed with chloroform then
diethyl ether and finally air-dried. The analytical and physical data
2.3.2. [Fe2(H2L)(ox)Cl3(H2O)2]ꢀ5H2O, 5
Lithium hydroxide monohydrate, LiOHꢀH2O (0.197 g, 4.7 mmol)
in methanol (10 mL) was added gradually with constant stirring to
the solution of the ligand, H3L, (0.6 g, 1.57 mmol) in chloroform
(25 mL). Oxalic acid (0.197 g, 1.57 mmol) in ethanol (15 mL) was
added gradually to the above mixture then iron(III) chloride hexa-
hydrate, FeCl3ꢀ6H2O (0.85 g, 3.15 mmol) in ethanol (20 mL) was
added and the reaction mixture was heated under reflux for 3 h.
Table 1
Analytical and physical data for the Schiff base, H3L, ligand and its metal complexes.
No. Reactions
Complexes M.F. [F.W.]
Color
Yield M.P.
Elemental analysis, % Found/(Calc.)
(%)
(°C)
C
H
N
Cl (S)
–
M
–
1
2
H.U.
[C13H18N2O2] [234.30]
[C20H21N3O5] [383.41]
Yellow
Yellow
83.8
77.0
60.0
77.0
51.7
72.5
70.0
83.5
66.7
80.0
75.0
78 66.7
7.5
12.1
(66.64) (7.74) (11.96)
137 62.7 5.5 11.1
(62.65) (5.52) (10.96)
>342 41.0 4.1 7.3
(41.24) (4.33) (7.21)
>342 42.1 4.6 7.3
(41.98) (4.76) (7.34)
>342 32.2 4.0 5.3
(32.44) (4.21) (5.16)
>342 54.5 4.4 9.5
(54.56) (4.35) (9.54)
308 54.5 4.3 9.3
(54.58) (4.35) (9.55)
>342 53.8 4.4 9.3
(53.99) (4.30) (9.44)
>342 41.5 4.2 7.2
(41.51) (4.01) (7.26)
>342 41.3 3.9 7.4
(41.54) (4.01) (7.27)
>342 49.8 4.3 8.7
(49.90) (4.19) (8.73)
>342 47.5 4.0 8.4
(47.78) (4.01) (8.36)
>342 47.5 3.8 8.4
(47.57) (3.79) (8.32)
>342 42.3 3.7 7.4
(42.20) (3.90) (7.38)
144 35.1 3.5 5.8
(35.35) (3.64) (5.62)
H3L
–
–
3
H3L + VOSO4ꢀH2O
H3L + FeCl3ꢀ6H2O
[VO(H3L)(SO4)(H2O)]ꢀH2O
Pale
brown
Deep
brown
Reddish
brown
Bick red
5.5
8.7 (8.75)
9.7 (9.76)
13.7 (13.71)
13.3 (13.38)
13.4 (13.34)
14.2 (14.28)
20.5 (20.37)
20.3 (20.30)
13.0 (13.20)
[C20H25N3O12SV] [582.44]
[Fe(H2L)Cl2(H2O)]ꢀ2½H2O
(5.51)
12.5
(12.39)
12.8
(13.06)
–
4
[C20H27N3O8½Cl2Fe] [572.21]
[Fe2(HL)(ox)Cl3(H2O)2]ꢀ5H2O
[C22H34N3O16Cl3Fe2] [814.58]
[Co(HL)] [C20H19N3O5Co] [440.32]
5
H3L + Oxalic
acid + LiOHꢀH2O + FeCl3ꢀ6H2O
6
H3L + Co(OAc)2ꢀ4H2O
7
H3L + Ni(OAc)2ꢀ4H2O
[Ni(HL)] [C20H19N3O5Ni] [440.10]
[Cu(HL)] [C20H19N3O5Cu] [444.94]
Red
–
–
8
H3L + Cu(OAc)2ꢀH2O
Pale
violet
Brown
9
H3L + CoCl2ꢀ6H2O + LiOHꢀH2O
H3L + NiCl2ꢀ6H2O + LiOHꢀH2O
H3L + CuCl2ꢀ2H2O + LiOHꢀH2O
[Co2(L)Cl(H2O)2]ꢀ½H2O
[C20H23N3O7½ClCo2] [578.74]
[Ni2(L)Cl(H2O)2]ꢀ½H2O
[C20H23N3O7½ClNi2] [578.29]
[Cu(H2L)Cl] [C20H20N3O5ClCu]
[481.40]
6.2
(6.13)
6.3
(6.13)
7.4
(7.36)
3.6
(3.53)
6.8
(7.02)
6.2
(6.23)
–
10
11
12
13
14
15
Pale
brown
Brown
[Ni(HL)] + FeCl3ꢀ6H2O + LiOHꢀH2O [Ni2(L)2FeCl(H2O)]ꢀH2O
[C40H40N6O12ClNi2Fe] [1005.52]
[Ni(HL)] + CoCl2ꢀ6H2O + LiOHꢀH2O [Ni2(HL)2CoCl2]
[C40H38N6O10Cl2Ni2Co] [1010.04]
Brownish 82.0
red
Reddish
brown
Ni;11.5 (11.68),
Fe; 5.4 (5.55)
Ni;11.7 (11.63),
Co; 5.6 (5.83)
20.5 (20.63)
69.5
71.0
81.0
[Ni(HL)] + NiCl2ꢀ6H2O + LiOHꢀH2O [Ni2(L)Cl(H2O)2] [C20H22N3O7ClNi2] Brown
[569.29]
[UO2(H2L)(OAc)(H2O)2]
[C22H27N3O11U] [747.50]
H3L + UO2(OAc)2ꢀ2H2O
Orange
31.4 (31.84)

M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
41
2.4. Analytical and physical measurements
CH3
CH3
Electronic spectra were recorded as solutions in DMF on a Jasco
UV–Vis spectrophotometer model V-550 UV–Vis. IR spectra were
recorded using KBr disks on a FT-IR 1650 Shimadzu Spectrometer.
1H and 13C NMR spectra were carried out in DMSO-d6 at room tem-
perature using TMS as internal standard on a Brucker 400 MHz
spectrophotometer. Magnetic susceptibilities of the complexes
were measured by the Gouy method at room temperature using
a model MK1 Johnson Matthey, Alpha Products, magnetic suscep-
tibility balance. Effective magnetic moments were calculated using
+
H2N
NH2
OH
O
O
the relation
leff. = 2.828(v
mT)1/2 B.M. where vm is the molar sus-
CH3
ceptibility corrected using Pascal’s constants for diamagnetism of
all atoms in the compounds. Molar conductivities of 10ꢁ3 M solu-
tions of the solid complexes in DMF were measured on the Corning
conductivity meter NY 14831 model 441. The TG–DTG measure-
ments were carried out on a Shimadzu thermogravimetric analyzer
in dry nitrogen atmosphere and a heating rate of 20 °C/min using
the TA-50 WS1 program. Mass spectra were recorded at 70 eV
and 300 °C on a GC MS-QP 100 Ex 5988 mass spectrometer. Anal-
yses of the metals followed decomposition of their complexes with
concentrated nitric acid. The resultant solution was diluted with
bidistilled water and filtered. The solution was then neutralized
with aqueous ammonia solution and the metal ions titrated with
EDTA. The uranium content of the UO22þ complex was determined
by igniting a definite quantity of the complex at ꢂ1000 °C and
weighing the residue as U2O3. Microanalyses of carbon, hydrogen,
nitrogen, chlorine and sulfur were carried out at the Microanalyt-
ical Center, Cairo University, Giza, Egypt. The antimicrobial activity
was studied using the disk diffusion method [25] at the Microana-
lytical Center, Cairo University, Giza, Egypt.
OH
O
N
CH3
H2N
CHO
OH
O2N
2.5. Antimicrobial activity
CH3
The standardized disk–agar diffusion method [25] was followed
to determine the activity of the synthesized compounds against
the sensitive organisms Staphylococcus aureus as Gram positive
bacteria, Escherichia coli as Gram negative bacteria and the fungi
Candida albicans and Aspergillus flavus. Tetracycline was used as a
standard reference in the case of bacteria while Amphotricine B
was used as a standard antifungal reference.
OH
O
N
CH3
The tested compounds were dissolved in dimethylsulfoxide
[(DMSO) which has no inhibition activity] to get concentration of
2 mg/mL. The test was performed on medium potato dextrose agar
(PDA) which contains infusion of 200 g potatoes, 6 g dextrose and
15 g agar [26]. Uniform size filter paper disks (three disks per com-
N
OH
CH
pound) were impregnated by equal volume (10 lL) from the spe-
cific concentration of dissolved test compounds and carefully
placed on incubated agar surface. After incubation for 36 h at
27 °C in the case of bacteria and for 48 h at 24 °C in the case of fun-
gi, inhibition of the organisms which evidenced by clear zone sur-
round each disk was measured and used to calculate mean of
inhibition zones.
NO2
Scheme 1. Synthetic outline of the asymmetric Schiff base, H3L, ligand.
The precipitate was filtered off, washed with ethanol then ether
and finally air-dried. Yield: 0.66 g (51.7%).
3. Results and discussion
2.3.3. Heterotrinuclear complex [Ni2(HL)2CoCl2], 13
Cobalt(II) chloride hexahydrate, CoCl2ꢀ6H2O (0.27 g, 1.13 mmol)
in ethanol (20 mL) was added gradually with constant stirring to
the hot mixture of the mononuclear Ni(II) complex, [Ni(HL)]ꢀH2O,
(0.5 g, 1.13 mmol) in chloroform (30 mL) and LiOH (0.048 g,
1.13 mmol) in methanol (5 mL). The reaction mixture was heated
under reflux for 10 h. The reddish brown precipitate was filtered
off, washed several times with ethanol then ether and finally air-
dried. Yield was 0.8 g (69.5%). The complex [Ni2(L)2FeCl(H2O)]ꢀH2O
was prepared by a similar method.
3.1. The ligand
The 1:1 condensation of o-acetoacetylphenol and 1,2-diamino-
propane yielded (E)-3-(1-aminopropan-2-ylimino)-1-(2-hydroxy-
phenyl)butan-1-one (H.U.). Condensation of the formed
compound with 2-hydroxy-5-nitrobenzaldehyde yielded the new
Schiff base ligand, H3L. The IR spectrum of (H.U.) showed bands
at 3382 and 3305 cmꢁ1 that may be assigned to masym and msym of
the ANH2 group, respectively. The two bands observed at 1600

42
M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
120
131.3
188.4
128.9
119
a
CH3
24
90.6
CH3
127.7
167
172
b
CH3
21.6
CH3
OH
OH
O
HN
f
O
N
49
c
53.6
d
e
H2N
H2N
I
II
Scheme 2. Tautomeric structures of (H.U.).
Table 2
a
Characteristic IR spectral data (cmꢁ1
)
of the Schiff base, H3L, ligand and its metal complexes.
IR spectra (cmꢁ1
OH
No. Compound
)
m
m
C@N
m
C¤O +
m
mC¤N
m
CAO,
m
H2O,
Other bands
(Phenolic + H2O)
C¤C
phenolic
coordinate
1
H.U.
3420 m, b
1600 s
1543 m
1519 s
1519 s
1330 m
–
3382 m, 3305 m, sharp;
group)
mNH2 (amino
2
3
4
5
6
7
8
9
10
11
12
13
14
15
H3L
3450 m, b
3450 m, b
3440 m, b
1627 s
1645 s
1627 s
1635 s
1562 m
1554 m
1554 m
1558 m
1338 m
–
[VO(H3L)(SO4)(H2O)]ꢀH2O
1500 m 1311 m
802 m, 756 m 1107 s, 1060 b;
806 s, 756 m
802 m, 756 w 1670 m;
mSO4, 984 m; mV@O
[Fe(H2L)Cl2(H2O)]ꢀ2½H2O
1508 s
1504 s
1496 s
1473 s
1508 s
1496 s
1508 s
1508 s
1508 s
1303 m
1303 s
1319 s
1319 m
1303 m
1319 s
1315 s
1315 s
1315 s
[Fe2(HL)(ox)Cl3(H2O)2]ꢀ5H2O 3449 m, b
m
COO, oxalate
[Co(HL)]
[Ni(HL)]
[Cu(HL)]
3444 w
3445 w
1600 m 1558 m
1600 s
1619 s
1604 s
1604 m 1550 m
1643 s
1601 s
1600 m 1554 w
1600 s
1627 s
1554 m
1550 s
1550 s
3450 m, b
3452 s, b
3421 m, b
3463 m, b
3440 s, b
3444 m, b
3444 s, b
3440 vs, b
[Co2(L)Cl(H2O)2]ꢀ½H2O
[Ni2(L)Cl(H2O)2]ꢀ½H2O
[Cu(H2L)Cl]
[Ni2(L)2FeCl(H2O)]ꢀH2O
[Ni2(HL)2CoCl2]
[Ni2(L)Cl(H2O)2]
[UO2(H2L)(OAc)(H2O)2]
803 m, 752 w
804 m, 752 w
3290 w;
1554 m
1554 m
m
NH
833 m, 748 w
1508 m 1315 s
1508 m 1315 s
1485 s
1554 m
1554 s
833 m, 748 m
802 m, 759 m 1535 s, 1400 m;
O@U@O
1315 s
mCOO, acetate, 906 vs;
m
a
vs: very strong; s: strong; m: medium; w: weak; b: broad.
and 1330 cmꢁ1 can be assigned to
m
(C@N) (tautomer II, Scheme 2)
bonded phenolic protons. Signals for the methine protons of the
azomethine group, AN@C(H)A, and NH protons were observed at
7.3 and 10.95 ppm, respectively. The aromatic protons were ob-
served in the range of 7.6–6.8 ppm. Assignment of the 13C NMR
spectral data of the H3L ligand, Fig. 2, is based on 13C shifts in sim-
ilar Schiff base ligands [27]. The chemical shifts for carbons of
ANACH2CH2ANA were recorded between 48.3 and 61.2 ppm
while carbons of (@CANH) and (AN@C(H)A) groups were observed
between 165.6 and 161.4 ppm. The signals observed at 188.7,
167.2 and 173.2 ppm are assigned to (C@O) and the two (CAO)
phenolic carbons, respectively. Methyl groups were observed be-
tween 19.4 and 18.5 ppm. Based on IR and NMR spectral data, it
was concluded that the half-unit (H.U.) and H3L ligands exist as
tautomer II in solid state and tautomer I in solutions.
and
data of the Schiff base ligand with that of (H.U.) (Table 2) showed
the disappearance of (NH2), confirming the formation of the Schiff
base ligand. The IR spectrum of the Schiff base ligand showed
bands at 1627 and 1338 cmꢁ1 that may be assigned to
(C@N)
and (CAO) phenolic, respectively. Finally, the IR spectra of (H.U.)
and the ligand displayed bands in the ranges of 3420–3450 and
1543–1562 cmꢁ1 that may be due to
(OAH) phenolic and
(C¤O) + (C¤C) groups, respectively.
The 1H NMR spectrum of (H.U.), Fig. S1 (Supplementary mate-
m(CAO) phenolic, respectively. Comparison of the IR spectral
m
m
m
m
m
m
rial) showed a singlet peak at 10.9 ppm which may be assigned
to the proton of the ANH group (f), Scheme 2. The triplet peak ap-
peared at 5.8 ppm may be assigned to ANH2 protons (e). The mul-
tiplet peak at 2.1 ppm corresponding to the protons, c and d,
Scheme 2. The peaks at 1.0 and 1.8 ppm may be assigned to the
protons of methyl groups (a and b). The observed signals at 7.2–
7.8 ppm may be attributed to the aromatic protons (m, 4ArAH).
13C NMR spectrum of (H.U.), Fig. S1 (Supplementary material)
exhibited signals at 188.4, 172 and 167 ppm corresponding to
the carbon of ketonic (C@O), (@CANH) and phenolic (CAOH)
groups, respectively. Also, the spectrum showed peaks at 131–
119 ppm corresponding to carbons of the phenyl ring.
Mass spectra of (H.U.) and Schiff base ligand (Fig. 3) showed the
molecular ion peaks at m/e 234 and 383, confirming their formula
weights (F.W. 234.30 and 383.41), respectively.
3.2. Metal complexes
The Schiff base ligand, H3L, possesses two compartments and
thus able to bind more than one cation because the bridging ability
of their oxygen atoms and their conformational flexibility. Reac-
tions of the ligand with VO2+, Fe(III), Co(II), Ni(II), Cu(II) and
UO22þ, in the molar ratio 1:1 or 1:2 (L:M) in presence and absence
1H NMR spectral data of H3L dissolved in DMSO-d6, Fig. 1, exhib-
ited two peaks at 14.3 and 13.5 ppm, which are due to hydrogen-

M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
43
5.83
H
3.6
CH3
3.5
CH3
OH
3.6
O
HN
10.95
14.3
3.91
13.5
OH
N
CH 7.3
NO2
Fig. 1. 1H NMR spectrum of the Schiff base ligand and its assignment.
of LiOHꢀH2O as a deprotonating agent yielded mono- and bi-nucle-
ar complexes. Also, the mononuclear Ni(II) complex, [Ni(HL)], has
been used as a further ligand towards Fe(III), Co(II) and Ni(II) ions
to produce homo- and hetero-bi- and tri-nuclear complexes.
frequenciesincaseof complexes6–10and 12–14, indicatingthepar-
ticipation of the azomethine group in chelation [32,33]. However, in
complexes 3–5, 11 and 15, no shift of the
where metal ions are coordinated to the outer O2O compartment of
the ligand. The band assigned to (C¤O) + (C¤C) was shifted to
m(C@N) band was observed
m
m
3.2.1. IR spectra
lower frequencies in all complexes, suggesting the participation of
the carbonyl oxygen in chelation. The VO2+ complex 3 showed new
bands at 1107 and 1060 cmꢁ1 which may be assigned to the coordi-
nated sulphate group in a monodentate fashion [34]. Also, the com-
The IR spectral data of the metal complexes are listed in Table 2.
Comparison of the IR spectra of the metal complexes with that of the
free ligand revealed that all complexes showed broad bands in the
range 3421–3463 cmꢁ1 which can be assigned to the stretching fre-
plex displayed a strong band at 984 cmꢁ1, assignable to
m(V@O)
quency of the phenolic AOH groups of the ligand,
m
(OH), coordinated
moiety [35,36], consistent with a six-coordination geometry which
is completed by coordinating sulphate and water molecules, Fig. 4.
Also, complex 5 showed a new band at 1670 cmꢁ1 that can be as-
signed to the bidentate oxalate group. Finally, complex 15 showed
or uncoordinated water molecules associated with the complexes
which are confirmed by elemental and thermal analyses. Also, the
presence of coordinated water molecules in the complexes is sup-
ported by the two bands in the ranges 802–833 and 748–759 cmꢁ1
which are due to (H2O) rocking and wagging mode of vibrations,
new bands characteristic for m m
asym(COOꢁ) and sym(COOꢁ) of acetate
ion at 1535 and 1400 cmꢁ1. The higher difference (135 cmꢁ1) be-
tween the two bands indicates the monodentate nature of the ace-
tate group [37,38]. Also, the complex displayed a new band at
respectively [28]. The
m(CAO) phenolic of the free ligand at
1338 cmꢁ1 was shifted to lower frequencies in all complexes, sug-
gesting its participation in chelation [29–31]. The strong band at
906 cmꢁ1, which may be assigned to the
the uranyl ion is linear [28].
m3(UO2), suggesting that
1627 cmꢁ1 assigned to
m(C@N) in the free ligand was shifted to lower

44
M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
120.3
130.5
188.7
120.3
133.3
115.2
19.4
90.9
CH3
167.2
165.6
18.5
CH3
OH
O
HN
48.3
61.2
N
OH
173.2
115.8
161.4
CH
127.8
120.8
128.6
136.5
NO2
Fig. 2. 13C NMR spectrum of the Schiff base ligand and its assignment.
Fig. 3. Mass spectra of (H.U.) (A), H3L ligand (B) and complex 7 (C).
3.2.2. Conductivity measurements
listed in Table 3. The values show that all complexes have non-
electrolytic nature. The relatively high molar conductance values
of some complexes (4, 5, 12 and 13) may be due to the replacement
The molar conductance values of the complexes in DMF (10ꢁ3
M
solutions) were measured at room temperature and the results are

M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
45
CH3
CH3
CH3
OH
O
O
HN
O
HN
CH3
V
Fe
O
Cl
OH2
OH2
.H2O
.2.5H2O
O3SO
Cl
N
N
OH
OH
CH
CH
NO2
NO2
4
3
CH3
CH3
CH3
CH3
OH
CH3
CH3
O
N
N
O
O
O
HN
O
HN
O
U
O
M
Cu
H2O
OH2
Cl
CH3COO
N
N
O
OH
OH
CH
CH
CH
NO2
NO2
NO2
15
11
M
Complex
Co
Ni
Cu
6
7
8
Fig. 4. Suggested structures of the mononuclear complexes.
of the coordinated chloride ions by solvent molecules, a phenome-
non usually encountered in complexes containing chloride ions
[39].
the spin only value for VO2+ complexes when the orbital contribu-
tion is quenched.
The electronic spectra of the Fe(III) complexes, 4 and 5 showed
bands in the range of 495–510 nm, within the range reported for
octahedral complexes [42]. The magnetic moments of the com-
plexes (Table 3) are compatible with those reported for octahedral
iron(III) complexes [43,44]. The octahedral geometry of the iron(III)
complexes is achieved by chloride, oxalate ions and water mole-
cules (Figs. 4 and 5) as evidenced by elemental analyses, IR and
conductivity measurements.
The electronic spectrum of the Co(II) complex 6, [Co(HL)],
showed two bands at 575 and 450 nm which may be assigned to
2A1g ? 2B2g and 2A1g ? 2Eg transitions, respectively, for Co(II) in
a square-planar geometry [45,46] (Fig. 4). This is supported by
3.2.3. Electronic, mass, 1H and 13C NMR spectra and magnetic
measurements
3.2.3.1. Mono- and bi-nuclear complexes. Most of the mononuclear
VO2+ complexes with square-pyramidal coordination are green
while the polynuclear linear chain octahedral structures
(V@OAV@OA) are usually orange [40].
The electronic spectrum of the VO2+ complex 3 showed absorp-
tion bands at 580 nm (Table 3) that can be assigned to the
2B2 ? 2B1
Its magnetic moment (
(m
2) transition in an octahedral geometry [41] (Fig. 4).
eff.) is 1.8 B.M., which is in the range of
l

46
M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
Table 3
Electronic spectra, magnetic moments and molar conductivity data of the metal complexes of the Schiff base, H3L, ligand.
No.
Compounds
Electronic spectral bandsa (nm)
Magnetic moments (B.M.)
Conductanced Ohmꢁ1 cm2 molꢁ1
b
c
lcompl.
leff.
3
4
5
6
7
[VO(H3L)(SO4)(H2O)]ꢀH2O
[Fe(H2L)Cl2(H2O)]ꢀ2½H2O
[Fe2(HL)(ox)Cl3(H2O)2]ꢀ5H2O
[Co(HL)]
[Ni(HL)]
[Cu(HL)]
[Co2(L)Cl(H2O)2]ꢀ½H2O
[Ni2(L)Cl(H2O)2]ꢀ½H2O
[Cu(H2L)Cl]
580 (0.13)
510 (0.15)
495 (0.17)
575 (0.02), 450 (0.03)
528 (0.08), 440 (0.1)
577 (0.12)
650 (0.03), 550 (0.02)
548 (0.07)
–
–
7.93
–
–
1.80
5.85
5.60
2.55
8
37
40
5
7
8
20
21
22
33
30
12
9
Diamagnetic
8
9
–
1.8
3.70
–
2.04
–
–
–
–
5.2
3.2
–
5.95
5.50
2.90
–
10
11
12
13
14
15
572 (0.14)
[Ni2(L)2FeCl(H2O)]ꢀH2O
565 (0.12), 520 (0.09)
585 (0.08), 525 (0.1)
620 (0.14), 515 (0.12)
510 (0.32), 440 (0.34)
[Ni2(HL)2CoCl2]
[Ni2(L)Cl(H2O)2]
[UO2(H2L)(OAc)(H2O)2]
a
b
c
Values of emax are in parentheses and multiplied by 10ꢁ4 (L molꢁ1cmꢁ1).
lcompl. is the magnetic moment of all cations in the complex.
leff. is the magnetic moment of the complex.
d
Solutions in DMF (10ꢁ3 M).
CH3
CH3
OH2
M
O
O
HN
O
CH3
O
N
CH3
Cl
O
O
O
M
Fe
OH2
Fe Cl
.0.5H2O
.5H2O
HO
Cl
OH2
N
Cl
N
O
O
OH2
CH
CH
NO2
NO2
M
Complex
5
Co
Ni
9
10
Fig. 5. Suggested structures of the binuclear complexes.
the magnetic moment (
l
eff.) of the complex (2.55 B.M.) which indi-
showed the first mass peak at m/e 439 which agrees well with
the molecular ion peak for [Ni(HL)], confirming its structure. On
the other hand, the electronic spectrum of the Ni(II) complex 10
cates a square-planar configuration. On the other hand, the elec-
tronic spectrum of the Co(II) complex 9, [Co2(L)Cl(H2O)2]ꢀ½H2O,
(Table 3) showed two bands at 550 and 650 nm that may be as-
signed to the 4T1g(F) ? 4T1g(P) and 4T1g(F) ? 4A2g(F) transitions,
respectively, of the octahedral geometry [47]. The lower magnetic
moment of the complex (3.70 B.M.) suggests the presence of both
square-planar and octahedral geometries around the Co(II) ions
[48,49] (Fig. 5).
The electronic spectrum of the Ni(II) complex 7 showed a band
at 528 nm that may be assigned to the 1A1g ? 1A2g transition, indi-
cating a square-planar environment around the nickel(II) ion [50]
(Fig. 4) which is confirmed by the diamagnetic properties of the
complex. The mass spectrum of the nickel(II) complex 7 (Fig. 3),
showed
a band at 548 nm, which can be assigned to the
3A2g(F) ? 3T1g(F) transition indicating an octahedral nickel(II) com-
plex [51]. The magnetic moment of complex 10 is 3.2 B.M., which
suggests the presence of octahedral and diamagnetic square-planar
geometries together [52,53] (Fig. 5).
The electronic spectra of the Cu(II) complexes 8 and 11 showed
bands in the range 572–577 nm that may be assigned to the
2B1g ? 2A1g transition in a square-planar geometry [54] (Fig. 4).
The magnetic moment (leff.) for complexes 8 and 11 are 1.80 and
2.04 B.M., respectively which is consistent with one unpaired elec-
tron (d9) [55]. The higher leff. value of complex 11 indicates that

M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
47
Fig. 6. 1H and 13C NMR spectra of the UO22þ complex (15).
the complex is slightly distorted towards tetrahedral symmetry
[56].
cates changes in the charge redistribution in the whole molecule
induced by the complexation. The spectrum exhibited a sharp sig-
nal corresponding to the azomethine carbon (C@N) at 161.4 ppm
as observed in the ligand, indicating the non-participation of the
group in complexation which is consistent with the IR spectral data
(Table 2).
The electronic spectrum of the uranyl complex 15 showed two
bands at 440 and 510 nm. The higher energy band is attributed to
electronic transitions from apical oxygen atoms to f orbitals of the
uranium(VI) ion and the lower energy band is due to charge trans-
fer transition from equatorial ligand to the uranium(VI) ion [57].
Comparing of the 1H NMR spectrum of the uranyl complex,
[UO2(H2L)(OAc)(H2O)2], Fig. 6, with that of the free ligand revealed
the following:
3.2.3.2. Heteronuclear complexes. Since the complex [Ni(HL)] (7) has
di-l-phenoxy oxygen bridges which act as O2O coordinating sites,
it can be used as a chelating agent towards metal cations [Fe(III),
Co(II) and Ni(II)]. Also, the complex ligand (7) has diamagnetic
properties, so any magnetic moments of the homo- and hetero-nu-
clear complexes were altered by the introduction of metal cations.
The reactions of the complex ligand [Ni(HL)], 7, with
FeCl3ꢀ6H2O, CoCl2ꢀ6H2O and NiCl2ꢀ6H2O in the molar ratio 1:1 in
the presence of LiOHꢀH2O yielded trinuclear complexes, [Ni2(L)2-
FeCl(H2O)]ꢀH2O, 12 and [Ni2(HL)2CoCl2], 13 and binuclear Ni(II)
complex, [Ni2(L)Cl(H2O)2], 14, Fig. 7. It was found that Ni(II) com-
plex, 14, is similar to 10.
The electronic spectrum of the homobinuclear complex
[Ni2(L)Cl(H2O)2], 14 showed two absorption bands at 620 and
515 nm. The band at 620 nm is due to the 3A2g(F) ? 3T1g(F) transi-
tion, indicating an octahedral nickel(II) of O2O sites while the band
at 515 nm is assigned to the 1A1g ? 1A2g transition, indicating a
1. The disappearance of one signal of the phenolic OH group
(d = 14.3) referring to its involvement in coordinating with ura-
nyl cation after deprotonation [58–60], while the signal of the
other phenolic OH (d = 13.5 ppm) and NH (d = 10.95 ppm)
groups are unchanged, confirming the suggested structure of
the complex (Fig. 4).
2. The signals due to the aromatic ring showed fine structure and
appear as four separate signals at d = 6.53, 6.67, 7.14 and
7.6 ppm. The absence of OH protons (coordinated H2O) may
be due to their replacement by DMSO-d6 molecules [61].
Also, the comparison of the 13C NMR spectrum of the UO22þ com-
plex, Fig. 6, and its ligand leads to a similar conclusion and indi-

48
M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
H3C
CH3
OH2
CH3
O
O
N
O
H3C
N
O
Ni
Fe
Cl
Ni
.H2O
N
O
N
O
HC
CH
NO2
NO2
12
CH3
H3C
Cl
Co
Cl
OH
CH3
O
OH
N
H3C
N
O
O
Ni
Ni
N
N
O
HC
CH
NO2
NO2
13
CH3
OH2
Ni
CH3
O
O
N
Ni
Cl
N
O
OH2
CH
NO2
14
Fig. 7. Suggested structures of the hetero- and homo-nuclear complexes.
square-planar environment around the inner nickel(II) ion of N2O2
sites. The magnetic moment of complex 14 is 2.9 B.M. which is in
good agreement with the presence of the outer Ni(II) ion in octahe-
dral geometry.

M. Shebl et al. / Journal of Molecular Structure 980 (2010) 39–50
49
Table 4
Antimicrobial activity of the Schiff base ligand and its metal complexes.
No.
Sample
Meana of zone diameter, nearest whole mm
Escherichia coli
Staphylococcus aureus
Candida albicans
Aspergillus flavus
Control DMSO
0.0
32
–
0.0
34
–
0.0
–
21
0
0.0
–
Tetracycline (Antibacterial agent)
Amphotricine B (Antifungal agent)
H.U.
17
15
20
0.0
0.0
0.0
0.0
0.0
0.0
13
14
0.0
0.0
14
15
0.0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
14
21
12
14
13
20
0.0
0.0
14
18
17
11
20
15
14
14
23
18
16
20
20
14
0.0
23
18
21
13
21
20
15
H3L
12
0.0
0.0
0.0
0.0
0.0
0.0
16
0.0
0.0
0.0
16
0.0
0.0
[VO(H3L)SO4(H2O)]ꢀH2O
[Fe(H2L)Cl2(H2O)]ꢀ2½H2O
[Fe2(HL)(ox)Cl3(H2O)2]ꢀ5H2O
[Co(HL)]
[Ni(HL)]
[Cu(HL)]
[Co2(L)Cl(H2O)2]ꢀ½H2O
[Ni2(L)Cl(H2O)2]ꢀ½H2O
[Cu(H2L)Cl]
[Ni2(L)2FeCl(H2O)]ꢀH2O
[Ni2(HL)2CoCl2]
[Ni2(L)Cl(H2O)2]
[UO2(H2L)(OAc)(H2O)2]
a
Calculated from three values.
The electronic spectra of the heterotrinuclear complexes 12 and
9 and 13 had the highest inhibition against S. aureus. Some of the
metal complexes had inhibition against C. albicans and A. flavus.
Complexes 9 and 13 had inhibition against C. albicans higher than
its ligand. Also, complexes 9, 10, 13 and 14 had inhibition against A.
flavus. Generally, it was found that the highest antimicrobial activ-
ity is obtained in Co(II)-containing complexes regardless of their
structures (mono-, bi- or tri-nuclear complexes).
13 (Table 3) showed two bands in the ranges of 565–585 and 520–
525 nm. The first band of each complex is attributed to a d–d tran-
sition of both Fe(III) and Co(II) ions in octahedral geometries
[30,44]. The second band is due to a d–d transition of Ni(II) in
square-planar geometry and similar to that of the complex ligand
[Ni(HL)]. The magnetic moments of the heterotrinuclear complexes
[Ni2(L)2FeCl(H2O)]ꢀH2O, 12 and [Ni2(HL)2CoCl2], 13 are 5.95 and 5.5
B.M., respectively, which is consistent with the presence of both
Fe(III) and Co(II) ions in high spin octahedral geometries.
4. Conclusion
In this work, the synthesis and characterization of a new asym-
metric Schiff base ligand were reported. Mono-, homo- and hetero-
bi- and tri-nuclear complexes were synthesized and characterized
using spectroscopic methods, molar conductivity, magnetic mea-
surements and thermal analysis. The Schiff base ligand behaved
as versatile chelating agent exhibiting variable denticity towards
metal ions depending on the pH of the reaction medium and the
metal ion. The Schiff base ligand and its complexes showed antimi-
crobial activity against selected kinds of bacteria and fungi.
3.2.4. Thermal analysis
Thermal gravimetric analyses for some selected complexes
were obtained to give information concerning the thermal stability
of the complex and decide whether the water molecules are in the
inner or outer coordination sphere of the central metal ion. The re-
sults of thermal analyses showed good agreement with the theo-
retical formula as suggested from the elemental analyses.
The TG and DTG curves of [Co(HL)], [Ni(HL)], [Cu(HL)] and
[Cu(H2L)Cl] showed the absence of hydrated or coordinated water
molecules. Thermal decomposition of the anhydrous products
takes place at different temperatures, 338.3, 357.6, 348.4 and
340 °C, respectively. The thermogram of the UO22þ complex (15),
represents four decomposition steps. The first step of decomposi-
tion at 167.5 °C corresponds to the loss of two coordinated water
and acetate molecules with a weight loss of 12.2% (calcd. 12.7%),
confirming the suggested formula of the complex. The remaining
steps of decomposition within the temperature range 168–600 °C
correspond to the removal of H3L ligand as gases. The overall
weight losses amount to 66.59% (calcd. 64%). The percentage of
uranium can be determined as U2O3 and was 30% (calcd. 31.8%).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.06.034.
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