Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity

Article abstract of DOI:10.1016/j.saa.2012.11.006

New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and character

Full text of DOI:10.1016/j.saa.2012.11.006

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base
ligands: Synthesis, characterization, properties and biological activity
b
a
c
Mustafa Sßahin a, , Nuriye Koçak , Damla Erdenay , Ug˘ur Arslan
⇑
a Selcuk University, Faculty of Science, Department of Chemistry, 42075 Konya, Turkey
b Necmettin Erbakan University, Faculty of Education, Department of Science Education, 42090 Konya, Turkey
c Selcuk University, Selcuklu Medical Faculty, Department of Clinical Microbiology, Konya, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
Asymmetrical tridentate Schiff base
ligands and metal complexes were
synthesized.
Compounds were characterized by
using FT-IR, NMR, UV–Vis, XRD, ESR,
studies.
The biological activities of the Schiff
bases and metal complexes are
reported.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2012
Received in revised form 26 October 2012
Accepted 5 November 2012
Available online 15 November 2012
New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-
methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base
ligands and their metal complexes were synthesised and characterized by using FT-IR, 1H NMR, 13C
NMR, UV–Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the
ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus
ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC
25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done
using the broth microdilution methods. In general, it has been determined that the studied compounds
have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn
derivatives of HL1A and ZnL2A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Asymmetrical Schiff base
Metal complexes
XRD
ESR
Antibacterial
Introduction
ions in natural systems are asymmetrical [3]. Asymmetric
Schiff-base ligands have many advantages over their symmetrical
Schiff base ligands are considered privileged ligands, because
they are easily prepared by a simple one-pot condensation of ac-
tive carbonyl groups and primary amines in an alcohol solvent
[1,2]. The coordination chemistry of transition metal complexes
of asymmetrical Schiff base ligands has attracted much attention
in recent years due the fact that the ligands around central metal
counterparts in the composition and geometry of transition metal
complexes and properties [4]. Asymmetric Schiff base compounds
have been widely studied in connection with catalysis of many
reactions [5] due to the versatility of their steric and electronic
properties [6] and are promising materials for optoelectronic appli-
cations [7] and models of relevance for biologically important spe-
cies [8,9] and their industrial applications [10].
In this study, we describe the synthesis and characterization of
the Zn(II), Ni(II), Cu(II) and Pb(II) complexes with two asymmetric
⇑
Corresponding author. Tel.: +90 332 2233885; fax: +90 332 2412499.
E-mail address: musahin40@gmail.com (M. Sßahin).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.006

M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
401
ligands as well as the fluorescence behavior of metal complexes.
We also focus on the study of the chelating properties of such li-
gands based on elemental analyses and spectral methods (FT-IR,
1H NMR, 13C NMR, ESR, UV–Vis). The biological activities of the
asymmetric Schiff bases and their metal complexes are reported
and compared with a reference standard antibiotic drug.
7.75 (d, J 7.5 Hz, 1H, HAr), 7.82 (d, J 9.0 Hz, 1H, HAr), 8.16 (d, J
8.5 Hz, 1H, HAr) 9.42 (s, 1H, CH@N), 15.32 (s, 1H, OH).
13C NMR (400 MHz, CDCl3) HL1: d 165.39, 157.04, 140.36,
135.516, 134.25, 132.84, 129.29, 128.01, 127.62, 123.56, 120.48,
119.26, 119.06, 118.99, 118.78, 116.03, 109.63.
13C NMR (400 MHz, CDCl3) HL2: d 21.25, 109.60, 116.69, 118.44,
119.26, 119.91, 120.56, 123.50, 127.58, 127.91, 129.29, 131.72,
132.82, 135.31, 138.13, 140.19, 155.09, 165.42.
Experimental
General procedure for synthesis of asymmetrical Schiff base ligands
(HL1A and HL2A)
Chemicals and apparatus
Asymmetrical Schiff base ligands HL1A and HL2A, were synthe-
sized in a similar method. A solution of HL1 (1 mmol, 0.262 g) and
HL2 (1 mmol, 0.276 g) in 30 mL chloroform/methanol (2/3, v/v)
was added dropwise to a solution 9-anthracenecarboxaldehyde
(1 mmol, 0.206 g) in 30 mL chloroform/methanol (2/3, v/v). Stirring
was continued for 3 h at room temperature during which a yellow
and orange solid compound separated. It was filtered, washed with
methanol, recrystallized from dichloromethane/methanol and
dried in vacuum.
1,2-Phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hy-
droxy-1-napthaldehyde, 9-anthracenecarboxaldehyde, ethyl alco-
hol, metal salt (Zn(OAc)2ꢀ2H2O, Ni(OAc)2ꢀ4H2O, Cu(OAc)2ꢀH2O and
Pb(OAc)2) and other chemicals used in this study were obtained Flu-
ka, Sigma–Aldrich and Merck Companies. All aqueous solutions
were prepared with deionized water which is purified with Milli-
pore Milli-Q Plus water purification system.
Elemental analyses (C, H, N) were performed using a LECO CHNS
932 (Inonu University, Malatya, Turkey) elemental analyzer. The
FT-IR spectra were recorded in the 4000–400 cmꢁ1 region, on a
Perkin Elmer Spectrum 100/ATR Sampling Accessory. The 1H
NMR and 13C NMR spectra were recorded on a Varian 400 MHz
spectrometer. Melting points were measured using a Buchi SMP-
20 melting point apparatus. Magnetic susceptibilities of metal
complex were determined using a Sheerwood Scientific MX Gouy
magnetic susceptibility apparatus and magnetic measurements
were carried out at room temperature (25 °C) using the Gouy
method with Hg[Co(SCN)4] as calibrant and diamagnetic correc-
tions were calculated from Pascal’s constants [11]. The effective
1H NMR (400 MHz, CDCl3) HL1A: d 6.95 (d, J 9.4 Hz, 1H, HAr),
7.16 (d, J 9.26 Hz, 1H, HAr), 7.20–7.23 (m, 2H, HAr), 7.38–7.39 (m,
2H, HAr), 7.46–7.52 (m, 4H, HAr) 7.66–7.84 (m, 4H, HAr), 8.04 (d, J
9.4 Hz, 2H, HAr), 8.57 (s, 1H, CH = N), 9.00 (d, J 9.0 Hz, 2H, HAr),
9.45 (d, J 12.0 Hz, 1H HAr), 9.82(s, 1H, CHANH), 11.53 (s, 1H,
CH@N), 15.06 (s, 1H, OH), 15.39 (s, 1H, CHANH).
1H NMR (400 MHz, CDCl3) HL2A: d 2.50 (s, 3H, CH3), 6.64 (s, 1H,
HAr), 6.93 (d, J 9.0 Hz, 1H, HAr), 7.16–7.20 (m, 2H, HAr), 7.28–7.32
(m, 1H, HAr), 7.48–7.56 (m, 4H, HAr), 7.64–7.72 (m, 2H, HAr),
7.76–7.80 (m, 2H, HAr), 8.03 (d, J 8.6 Hz, 2H, HAr), 8.57 (s, 1H,
CH = N), 8.99 (d, J 9.2 Hz, 2H, HAr), 9.39–9.47 (m, 1H, HAr), 9.80(d,
J 7.0 Hz, 1H, CHANH), 11.53 (s, 1H, CH@N), 15.09 (s, 1H, OH),
15.43(bs, 1H, CHANH).
magnetic moments,
the equation:
l
eff, per metal atom were calculated from
p
l
eff = 2.84 XMT BM, where XM is the molar suscepti-
bility. These synthesized materials were dried in vacuum drying
ovens marked as Vacucell 22. Ground state absorptions for the li-
gand and the complexes were made with a Perkin–Elmer Lambda
25 (UV–Vis) spectrophotometer. Perkin–Elmer LS55 Floresance
Spectrometer model was used for the steady state fluorescence
measurements of the complexes and Schiff base ligand at room
temperature (25 °C). The solutions of the ligand and complexes
were prepared in methanol medium. The XRD powder pattern
was recorded on a Bruker D.8 advance diffractometer, Sample
was scanned between 10° and 100° (2h) at 25 °C. ESR spectra of
Cu(II) complexes were recorded on a JEOL JESFA-300 X-band ESR
spectrometer with 100 kHz field modulation.
13C NMR (400 MHz, CDCl3) HL1A: d 173.66, 160.90, 168.96,
156.06, 153.93, 137.92, 137.28, 136.62, 133.56, 133.16, 131.69,
131.30, 131.09, 129.36, 129.19, 129.08, 128.03, 127.91, 127.73,
127.37, 127.26, 126.94, 125.47, 124.87, 123.58, 123.28, 122.06,
119.73, 119.60, 119.08, 118.99, 118.75, 108.85.
13C NMR (400 MHz, CDCl3) HL2A: d 173.48, 160.66, 153.67,
145.00, 137.38, 137.08, 135.23, 133.58, 131.47, 131.31, 131.08,
131.05, 129.14, 129.07, 127.86, 127.81, 127.69, 127.65, 127.54,
126.83, 125.46, 124.94, 124.90, 123.95, 123.64, 123.21, 123.12,
120.26, 120.08, 119.59, 119.35, 118.99, 118.70, 108.72, 21.26.
General procedure for synthesis of Zn(II), Ni(II), Cu(II) and Pb(II)
complexes
Synthesis
The Zn(II), Ni(II), Cu(II) and Pb(II) complexes were synthesised
by refluxing a methanolic solution of asymmetrical Schiff base li-
gands and M(II) acetate hydrate. The reaction was continued for
2 h during which a precipitate separated. It was filtered, washed
with methanol and dried in vacuum.
Synthesis of the tridentate Schiff base ligands (HL1 and HL2)
2-Hydroxy-1-napthaldehyde (1 mmol, 0.172 g) was dissolved in
30 mL mixture of chloroform/ethanol (2/3, v/v). The solution of
2-hydroxy-1-napthaldehyde was added to a solution of 1,2-phe-
nylendiamine (1.2 mmol, 0.130 g) and 4-methyl-1,2-phenylenedi-
amine(1 mmol, 0.122 g) dissolved in 20 mL ethanol. After
complete addition, the solution was stirred at ꢁ5 °C for 4 h. After
stirring the solvent was removed by rotary evaporation under re-
duced pressure. The resulting orange or dark yellow solid was col-
lected, washed with water and then recrystallized from methanol
and dried in vacuum.
Determination of antibacterial activities
The minimal inhibitory concentration (MIC) were determined
by broth microdilution methods according to CLSI (Clinical and
Laboratory Standarts Instıtute) guidelines (2009) in MHB (Becton
Dickinson, Sparks, MD) with an inoculum of approximately
5 ꢂ 105 colony-forming units (CFU)/mL (37). The invitro antibacte-
rial activity of the complexes was evaluated against standart
strains; Staphylococcus aureus ATCC (American Type Culture
Collection) 29213, S. aureus ATCC 25923, Streptococcus mutans
RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC
25922, Pseudomonas aeruginosa ATCC 27853. The antibacterial
activity was performed in Mueller–Hinton broth (MHB) (Becton
Dickinson, Sparks, MD). All the synthesized complexes were
1H NMR (400 MHz, CDCl3) HL1: d 6.80–6.87 (m, 2H, HAr), 7.10–
7.19 (m, 3H, HAr), 7.36 (t, J 7.5 Hz, 1H, HAr), 7.53 (t, J 7.7 Hz, 1H,
HAr), 7.76 (d, J 7.9 Hz 1H, HAr), 7.83 (d, J 9.0 Hz, 1H, HAr), 8.16 (d,
J 8.5 Hz, 1H, HAr) 9.42 (s, 1H, CH@N), 15.32 (s, 1H, OH).
1H NMR (400 MHz, CDCl3) HL2: d 2.31 (s, 3H, CH3), 6.64 (s, 1H,
HAr), 6.74 (d, J 7.9 Hz, 1H, HAr), 7.08 (d, J 7.9 Hz, 1H, HAr), 7.16 (d, J
9.0 Hz, 1H, HAr), 7.33–7.38 (m, 1H, HAr), 7.50–7.55 (m, 1H, HAr),

402
M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
weighed (10.24 mg) and dissolved in DMSO (10 mL) to prepare the
stock solutions. The serial dilution from 256 to 0.25
g mLꢁ1 were
made in a 96-wells plate. To each well 100 L of a bacterial suspen-
l
l
sion, obtained from a 24 h culture, containing ꢃ5 ꢂ 105 colony-
forming units (CFU)/mL was added. The plate was incubated at
35 °C for 24 h. The data were reported as MICs, the lowest concen-
tration of antibiotic and complexes inhibiting visible growth after
24 h of incubation at 35 °C. For quality control of the method amp-
icilline (IE Ulugay, Turkey) and Gentamicine (IE Ulugay, Turkey)
and were tested as antimicrobial agent. These experiments were
carried out in duplicate.
Results and discussion
Elemental analysis
The elemental analysis (Table 1) is in good agreement with that
calculated for the proposed formula.
IR characteristics
The FT-IR spectra of Schiff bases (HL1, HL2, HL1A and HL2A)
shows Fig. 3a and b. The IR spectra of the HL1 and HL2 ligands ex-
hibit sharp medium intensity bands at 3321 and 3468 cmꢁ1, which
are assigned to the NH2 functional group. These bands disappeared
in the spectrum of HL1A and HL2A ligands [12]. For the ligands, the
strong bands observed in the 1601–1621 cmꢁ1 range are assigned
to azomethine group vibration. These bands are slightly shifted to
lower frequencies in the complexes, and this change in the frequen-
cies indicates that the imine nitrogen atom is coordinated to the
metal ions [13,14]. The IR spectra of the metal complexes of the
Schiff base ligands were compared with those of the Schiff bases
themselves in order to determine the coordination sites that may
be involved in chelation (Table 2). The medium intensity bands ob-
served for HL1A and HL2A ligands in the 1306–1286 cmꢁ1 range can
be attributed to phenolic group vibration. These bands are observed
for the complexes at lower frequencies relative to the free ligands,
suggesting involvement of the oxygen atom of the CAO moiety in
coordination [15]. The strong broad bands of HL1A and HL2A, with-
Fig. 1. 1H NMR (400 MHz, CDCl3) spectrum of HL1 and HL2.
in the range 2752–3569 cmꢁ1 show the presence of (OAHꢀ ꢀ ꢀN)
intramolecular hydrogen bonding due to phenolic OH groups of
the phenol–imine forms [16]. In the spectra of the complexes, the
occurrence of bands at 417–440 cmꢁ1 (MAO) and 525–546 cmꢁ1
(MAN) provides evidence for the bonding of oxygen and nitrogen
to the central metal ion [17]. The general structural formula of the
ligands and their metal complexes is shown in Scheme 1.
Electronic spectra
The electronic spectra of ligands and complexes are measured
in CH3CN/CH2Cl2, respectively, and presented in Table 2. Ligands
and complexes exhibit similar UV spectra. In the UV spectrum of
Table 1
Analytical and physical data of ligands and its metal complexes.
Compound
m.p. (°C)
Color
Yield (%)
Calculated (Found) (%)
leff (BM)
C
H
N
M
–
HL1
169
Dark yellow
Orange
88
78
68
70
70
65
82
85
75
78
80
73
77.84
(77.78)
85.31
5.38
(5.40)
4.92
10.68
(10.57)
6.22
–
C
17H14N2O
HL1A
32H22 N2O
ZnL1A
34H24N2O3Zn
NiL1A
34H24N2O3Ni
CuL1A
34H24N2O3Cu
PbL1A
34H24N2O3Pb
HL2
199
–
C
(85.27)
71.15
(71.10)
71.99
(71.92)
71.38
(71.33)
57.05
(57.00)
78.24
(78.17)
85.32
(85.36)
71.49
(71.45)
72.32
(4.90)
4.21
(4.18)
4.26
(4.18)
4.23
(4.26)
3.38
(3.35)
5.84
(5.87)
5.21
(5.20)
4.46
(4.40)
4.51
(6.24)
4.88
(4.91)
4.94
(5.00)
4.90
(4.85)
3.91
(3.95)
10.14
(10.08)
6.03
(5.97)
4.76
(4.80)
4.82
(4.72)
4.78
>300
>300
>300
>300
175
Orange
11.40
(11.32)
10.35
(10.27)
11.11
(11.08)
28.95
(28.90)
–
Dia
Dia
C
Light brown
Dark brown
Orange
C
C
1.93
Dia
C
Orange
–
C
18H16 N2O
HL2A
198
Yellow
–
–
C
33H24 N2O
ZnL2A
35H26N2O3Zn
NiL2A
35H26N2O3Ni
CuL2A
35H26N2O3Cu
PbL2A
35H26N2O3Pb
>300
>300
>300
>300
Dark yellow
Brown
11.12
(11.07)
10.10
(10.05)
10.84
(10.78)
28.39
Dia
Dia
1.85
Dia
C
C
(72.30)
71.72
(71.65)
57.60
(4.45)
4.47
(4.42)
3.59
Dark brown
Dark yellow
C
(4.68)
3.84
(3.90)
C
(57.50)
(3.55)
(28.35)

M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
403
Magnetic properties
Magnetic measurements were recorded at room temperature.
The effective magnetic moment ( eff) values of the complexes are
l
given in Table 1. The magnetic moment of the copper(II) complexes
was observed in the range of 1.85–1.93 BM which corresponds to a
single unpaired electron with a very slight orbital contribution
[15]. The observed room-temperature magnetic moment value
for the Ni(II), Zn(II) and Pb(II) complexes showed them to be dia-
magnetic [21,22].
1H NMR spectra
The 1H NMR spectrum of compound HL1 showed two multiplet
(5H), two triplet (2H) and three doublet (3H) for aromatic protons,
one singlet (1H) for the imino proton and one singlet (1H) for hy-
droxyl proton of compound HL1. The tautomeric species of the
2-hydroxy Schiff bases in solution was determined by 1H NMR
spectroscopy. In CDCl3, the 1H NMR data for compounds HL1 and
HL2 (Fig. 1) show the existence of only phenol–imine tautomers,
while both keto–amine and phenolimine forms have been ob-
served for compound HL1A and HL2A.
Fig. 2. 1H NMR (400 MHz, CDCl3) spectrum of HL1A and HL2A.
This means that the 1H NMR spectra of naphthalimine
derivatives (HL1A and HL2A) show that both phenol–imine and
keto–amine forms are in equilibria. For instance, signals were
observed at 9.82 and 15.39 ppm for compound HL1A, and at 9.80
and 15.43 ppm for compound HL2A respectively, for the protons
of HCANH and HCANH (Fig. 2). On the other hand, for compounds
HL1 and HL2, two signals each appearing as a singlet at 9.42 and
15.32 ppm can be ascribed to HC@N and ArOH indicating that
the tautomeric equilibrium in these compounds favors the phe-
nol–imine form in CDCl3 (Scheme 2) [23–25]. The relative ratios
of keto–amine/phenol–imine tautomers are estimated from the
spectra of HL1A and HL2A as 82/18 and 70/30, respectively. The
keto–amine form is the predominant tautomer in the solution [26].
Fluorescence spectral studies
Absorption spectra of ligands (5 ꢂ 10ꢁ5 M for fluorescence mea-
surements and 1 ꢂ 10ꢁ4
M for absorption measurements) in
CH3CN/CH2Cl2 solutions containing 10 mol equiv of the appropri-
ate metal salt were measured using a 1 cm absorption cell. Fluores-
cence spectra of the same solutions were measured with a 1 cm
quartz cell. The excitation wavelength was 300 nm for compounds
HL1A and HL2A. Fluorescence spectra of HL1A (5 ꢂ 10ꢁ5 M) in the
absence and presence of different metal salts (5 ꢂ 10ꢁ4 M) was re-
corded in an acetonitrile/dichloromethane (1:1) solvent system.
The excitation wavelength was 300 nm Fluorescence spectra of
HL2A (5 ꢂ 10ꢁ5 M) in the absence and presence of different metal
salts (5 ꢂ 10ꢁ4 M) was recorded in an acetonitrile/dichlorometh-
ane (1:1) solvent system. The excitation wavelength was 300 nm.
The studies were carried out by exciting the solutions at 300 nm
and recording the fluorescence spectra in the range of 350–
570 nm. When excited at 300 nm in the same solvent system the
fluorescence spectrum exhibited two main bands in the visible re-
gion with kmax values of 430 and 510 nm (Figs. 5a and 5b). Binding
Fig. 3. FT-IR spectrum of HL1, HL1A, HL2 and HL2A.
properties of HL1A and HL2A toward metal ions (Zn2+, Cu2+, Pb2+
,
Ni2+) in acetonitrile/dichloromethane were investigated. Upon
addition of Cu2+ ion to the solution of HL1A and HL2A, the fluores-
cence intensity of HL1A and HL2A at 430 nm increases [27]. How-
ever, when similar titrations were carried out with other metal
ions, such as Zn2+, Pb2+, and Ni2+, only a minimal enhancement
or minimal quenching was observed at 510 nm. The reason for
the increase in the emission intensity of the 430 nm band, attrib-
uted to naphthalene–Schiff base emission, is most likely a preven-
tion of the rapid AC@N bond isomerisation upon Cu2+ binding that
ligands HL1A and HL2A (Figs. 4a and 4b), three anterior peaks oc-
cur at 256 and 268 nm, attributed to the p–
pꢄ of phenyl ring tran-
sitions, and a peak attributed to the azomethine group transition is
observed at 319 and 340 nm [4,18]. The third band at >400 nm in-
volves n ? pꢄ transitions of the C@O group [19]. In the spectra of
the complexes, the bands of the azomethine chromophore bands
are shifted to lower frequencies or lost, indicating that the imine
nitrogen atom is involved in coordination to the metal ion [15,20].

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M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
Table 2
Characteristic IR bands (cmꢁ1) of the ligands and their Zn(II), Ni(II), Cu(II) and Pb(II) complexes.
Compound
m
(OAH)
m
(NH2)
m
(CH@N)
m
(C@C)
m
(CAO)
m
(MAO)
m
(MAN)
kmax (nm)
HL1
–
3376, 3468
–
–
–
–
–
1611
1621
1615
1612
1609
1617
1601
1613
1600
1605
1610
1607
1492–1557
1480–1536
1460–1574
1456–1533
1465–1543
1453–1537
1492–1538
1486–1542
1488–1539
1456–1531
1476–1535
1461–1539
1252
1286
1275
1270
1280
1279
1310
1306
1295
1298
1288
1290
–
–
–
–
HL1A
ZnL1A
NiL1A
CuL1A
PbL1A
HL2
HL2A
ZnL2A
NiL2A
CuL2A
PbL2A
3562, 2755
–
–
–
–
–
268, 329, 383
260, 413
260, 321, 407,475
–
417
439
425
434
–
525
539
546
540
–
262, 417
3321, 3392
3569,2752
–
–
–
–
–
–
–
258, 340, 395, 475
258, 413
260, 332, 408, 475
256, 335
–
–
–
–
438
440
429
435
530
543
546
535
418
R
R
N
O
OH
R
O
N
NH
2
N
OH
OH
H N
NH
2
2
M(II)
R
R= H (HL1 and HL1A)
N
N
R= CH3 (HL2 and HL2A)
M= Zn(II), Ni(II), Cu(II), Pb(II)
M
OAc
O
Scheme 1. Chemical structures of the Schiff base ligands and its Zn(II), Ni(II), Cu(II) and Pb(II) complexes.
Fig. 4a. Electronic spectrum (CH3CN/CH2Cl2) of HL1A and Zn(II), Ni(II), Cu(II) and
Fig. 4b. Electronic spectrum (CH3CN/CH2Cl2) of HL2A and Zn(II), Ni(II), Cu(II) and
Pb(II) complex.
Pb(II) complexes.

M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
405
(a)
(b)
Scheme 2. Tautomeric forms of the ligands of HL1A (a) and HL2A (b).
otherwise leads to non-radiative decay of the excited state [28,29].
We believe this Cu2+ quenching effect also significantly reduces the
enhancement of naphthalene fluorescence at 430 nm. In other
words, the enhancement brought about from the prevention of
C@N isomerisation is cancelled somewhat by a simultaneous
quenching effect by Cu2+ on naphthalene emission. We were un-
able to further probe the binding event between HL1A and HL2A
and Cu2+ by NMR due to the paramagnetic nature of Cu2+ [30].
3.7. Powder X-ray diffraction
X-ray diffraction patterns of the ligands and their metal com-
plexes were recorded in the 2h = 0–100° range and ligands and
their metal complexes are shown in Figs. 6a and 6b. The ligands
of HL1A and HL2A show sharp peaks. This shows that these ligands
are crystalline in nature. Cu(II) complexes of HL1A did not show
sharp peaks, indicating their amorphous nature, but Zn(II), Ni(II)
and Pb(II) complexes of HL1A show peaks. This shows that these
Zn(II), Ni(II) and Pb(II) complexes are crystalline in nature [20]
Pb(II) complexes of HL2A did not show sharp peaks, indicating
their amorphous nature, but Zn(II), Ni(II) and Cu(II) complexes of
HL2A show peaks. This shows that these Zn(II), Ni(II) and Cu(II)
complexes are crystalline in nature. The structures of the com-
plexes could not be determined because single crystals were not
obtained. Each complex has specific d values, which can be used
in for its characterization [4,31,32].
Fig. 5a. Fluorescence spectrum (CH3CN/CH2Cl2, kexc = 300 nm) of HL1A and Zn(II),
Ni(II), Cu(II) and Pb(II)complexes: (a) Cu, (b) Zn, (c) Ni, (d) Pb and (e) HL1A.
Electron spin resonance spectra of Cu(II) complexes
ESR spectra of Cu(II) complexes measurement have been re-
corded on powder samples at 25 °C temperature and 1 mW micro-
wave power. The g value of the paramagnetic complexes are
calculated by considering the g value of the standard sample
Mn2+. ESR studies of paramagnetic transition-metal ions yield a
great deal of information about the magnetic properties of the
paramagnetic center. The copper(II) ion, with a 3d9 configuration,
has an effective spin of S = 1/2 and is associated with a spin angular
momentum, ms = 1/2, leading to a doubly degenerate spin state
in the absence of a magnetic field. In a magnetic field the degener-
acy is lifted between these states and the energy difference be-
Fig. 5b. Fluorescence spectrum (CH3CN/CH2Cl2, kexc = 300 nm) of HL2A and Zn(II),
Ni(II), Cu(II) and Pb(II)complexes: (A) Cu, (B) Ni, (C) Pb, (D) Zn and (E) HL2A.
tween them is given by E = hm = gbB, where h is Planck’s constant,

406
M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
Fig. 6a. X-ray powder diffraction patterns (2h = 0–100°) of HL1A and its metal complexes.
m
is the frequency, g is the Lande splitting factor (equal to 2.0023
exchange interaction is indicated in the solid complex [47]. By
using the g values given in Table 3 the geometric parameter calcu-
lated as G > 4 for each complexes, so the exchange interaction is
negligible.
for a free electron), b is the Bohr magneton and B is the magnetic
field [33–38]. The hyperfine splitting are due to the interaction of
the electron spin with copper nuclear spin (63,65Cu, I = 3/2). The g
values provide valuable information on the electronic ground state
of the copper(II) ion. The spectrum of copper complexes recorded
at 25 °C, shown in Figs. 7a and 7b, reveals three sets of resonance
at low, mid and high field corresponding to gzz, gxx and gyy indicat-
ing rhombic distortion in the geometry. From the determined ESR
parameters for the complexes, which are shown in Table 3, it can
be seen that gzz > gxx > gyy. When R = (gxx ꢁ gyy)/(gzz ꢁ gxx) is less
than unity, hence, the unpaired electron is dominantly in the
Biological activity
The free ligand and its metal complexes were screened for their
antibacterial activity. The results (Table 4) indicate that the ligand
does not have any significant activity, while some complexes
showed more activity against some bacteria under identical exper-
imental conditions. The antibacterial activities of the compounds
towards Gram-positive bacteria ( S. aureus, S. mutans, E. faecalis)
have been analyzed, and MIC values have been determined to be
dx2 state, and for R greater than unity it is in the d3z2
state
2
ꢁr2
ꢁy
[39]. The observed R values for Cu2+ are 0.278 and 0.343 for CuL1A,
in the range of 32–256 l
g mLꢁ1. It has been determined that the
analyzed HL1A and HL2A compounds have the same antibacterial
CuL2A, respectively) which are less than unity, so the ground state
of the electron is dx2
[40–45]. Also the gzz values of complexes
ꢁy2
are less than 2.3 which is in agreement with the covalent character
of MAL bonds [46]. The geometric parameter G, a measure of the
exchange interaction between the copper centers, is calculated
for each species using the equation: G = (g// ꢁ 2.0023)/
(g\ ꢁ 2.0023) where g// = gzz and g\ = (gxx + gyy)/2. If G > 4, ex-
change interaction is negligible and if it is less than 4, considerable
values for Gram-positive bacteria. The lowest MIC value
(32 l
g mLꢁ1) with Gram-positive bacteria has been observed for
ZnL1A ve HL2A Zn derivatives. It has been determined that ZnL1A
and ZnL2A derivatives effect S. mutans and S. aureus strains at the
same MIC ratios. The ZnL2A derivative also has the lowest MIC va-
lue (32 l
g mLꢁ1) for E. faecalis among the other compounds. Thus,

M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
407
Fig. 6b. X-ray powder diffraction patterns (2h = 0–100°) of HL2A and its metal complexes.
Fig. 7a. ESR spectra of CuL1A.
Fig. 7b. ESR spectra of CuL2A.
coli and P. aeruginosa among Gram-negative bacteria. These values
are equal to the efficiency of ampicillin forP. aeruginosa. The lowest
MIC value for Gram-negative bacteria was obtained with the Pb
it is more efficient than the other compounds and their derivatives
for this bacteria. The MIC values (32–64
mutans and E. faecalis are lower than those of S. aureus strains
(128–256
g mLꢁ1) whether PbL1A and NiL1A or PbL2A and NiL2A
derivatives. The lowest MIC value (64
g mLꢁ1) was observed with
CuL2A among the copper derivatives in the S. mutans strain. HL1A
and HL2A compounds have same MIC values (128
g mLꢁ1) for E.
l
g mLꢁ1) obtained for S.
derivative of HL1A. The MIC value of PbL1A is 32 l
g mLꢁ1 for E. coli
l
and P. aeruginosa. The most efficient derivative of HL2A for these
l
bacteria is ZnL2A. The MIC value of ZnL2A has been found as
64 l
g mLꢁ1for E. coli and P. aeruginosa. However, ZnL2A is not seen
l

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M. Sßahin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 400–408
Table 3
ESR parameters of Cu(II) complexes of HL1A and HL2A.
Complex name
gzz
gxx
gyy
giso
Azz (mT)
Axx (mT)
Ayy (mT)
aiso (mT)
CuL1A
CuL2A
2.2232
2.2272
2.0611
2.0718
2.0160
2.0185
2.1001
2.1058
14.79
14.16
4.22
4.59
4.01
3.76
7.67
7.50
[3] S. Meghdadi, K. Mereite, V. Langer, A. Amiri, R. Sadeghi Erami, A.A. Massoud, M.
Amirnasr, Inorg. Chim. Acta 385 (2012) 31–38.
[4] A.D. Khalaji, S.M. Rad, G. Grivani, D. Das, J. Therm. Anal. Calorim. 103 (2011)
747–751.
[5] S.A.A. Latif, H.B. Hassib, Y.M. Issa, Spectrochim. Acta A 67 (2007) 950–957.
[6] S. Menati, R. Azadbakht, A. Kakanejadi, G. Bruno, H. Rudbari, In: Proceedings of
the 14th Int. Electron. Conf. Synth. Org. Chem., 1–30 November 2010, Sciforum
Elecronic Conferences Series, a046, 2010, pp. 1–9.
[7] K.L. Kuo, C.C. Huang, Y.C. Lin, Dalton Trans. (2008) 3889–3898.
[8] L.A. Saghatforoush, F. Chalabian, A. Aminkhani, G. Karimnezhad, S. Ershad, Eur.
J. Med. Chem. 44 (2009) 4490–4495.
[9] J. Lv, T. Liu, S. Cai, X. Wang, L. Liu, Y. Wang, J. Inorg. Biochem. 100 (2006) 1888–
1896.
[10] G.G. Mohamed, M.M. Omar, A.A. Ibrahim, Spectrochim. Acta A 75 (2010) 678–
685.
[11] A. Earnshaw, Introduction to Magnetochemistry, Academic Press, London,
1968. p. 4.
[12] A.H. Kianfar, L. Keramat, M. Dostani, M. Shamsipur, M. Roushani, F. Nikpour,
Spectrochim. Acta A 77 (2010) 424–429.
Table 4
Antibacterial activities of ligands and metal complexes as MICꢄ values/
l
g mLꢁ1
.
E. coli
ATCC
25922
P. aeruginosa S. aureus
ATCC 27853 ATCC
25923
S. aureus
ATCC
29213
S. mutans
RSHM 676
Ampicillin
Gentamicin
HL1A
NiL1A
PbL1A
ZnL1A
CuL1A
HL2A
NiL2A
2
1
128
64
32
128
128
128
128
128
64
128
0.25
128
64
32
64
128
128
128
128
64
0.125
0.25
256
256
128
64
128
256
256
128
64
2
1
1
4
256
256
128
64
128
256
256
128
64
128
64
64
32
128
128
128
64
32
64
PbL2A
ZnL2A
CuL2A
128
128
128
128
[13] A. Prakash, B.K. Singh, N. Bhojak, D. Adhikari, Spectrochim. Acta A 76 (2010)
356–362.
[14] D. M Boghaei, M. Behzad, Synth. React. Inorg., Met-Org, Nano-Met.Chem. 35
(2005) 261–267.
[15] A. Golcu, M. Tumer, H. Demirelli, R.A. Wheatley, Inorg. Chim. Acta 358 (2005)
1785–1797.
[16] O. Gungor, P. Gurkan, Spectrochim. Acta A 77 (2010) 304–311.
[17] I. Demir, M. Bayrakci, K. Mutlu, A.I. Pekacar, Acta Chim. Slov. 55 (2008) 120–
124.
[18] S. Knoblauch, R. Benedix, M. Ecke, T. Gelbrich, J. Sieler, F. Somoza, H. Hennig,
Eur. J. Inorg. Chem. 8 (1999) 1393–1403.
[19] S. Bilge, Z. Kilic, Z. Hayvali, T. Hokelek, S. Safran, J. Chem. Sci. 121 (2009) 989–
1001.
[20] M.S. Nair, R.S. Joseyphus, Spectrochim. Acta A 70 (2008) 749–753.
[21] S. Ilhan, H. Temel, I. Yilmaz, M. Sekerci, Polyhedron 26 (2007) 2795–2802.
[22] M. Aslantas, E. Kendi, N. Demir, A.E. Sabik, M. Tümer, M. Kertmen,
Spectrochim. Acta A 74 (2009) 617–624.
to be as efficient as PbL1A. It has been determined that ZnL2A has
the same MIC value (64
g mLꢁ1) as NiL1A. In general, when the
l
activities of the compounds were investigated, it was determined
that the compounds were not as efficient as gentamicin and MIC
values were found to be higher than this antibiotic. However,
MIC values lower than or equal to ampicillin for P. aeruginosa were
found. The MIC values of NiL1A, PbL1A, Zn L1A, and ZnL2A especially
were observed to be lower than that of ampicilin.
[23] M. Yildiz, Z. Kilic, T. Hokelek, J. Mol. Struct. 441 (1998) 1–10.
[24] Z. Popovic, V. Roje, G. Pavlovic, D.M. Calogovic, M. Rajic, I. Leban, Polyhedron
23 (2004) 1293–1302.
Conclusion
[25] H. Nazir, M. Yildiz, H. Yilmaz, M.N. Tahir, D. Ulku, J. Mol. Struct. 524 (2000)
241–250.
[26] D.T. Sawyer, W.R. Heineman, J.M. Beebe, Chemistry Experiment for
Instrumental Methods, Wiley, New York, 1984.
[27] S. Konar, A. Jana, K. Das, S. Ray, S. Chatterjee, J.A. Golen, A.L. Rheingold, S.K. Kar,
Polyhedron 30 (2011) 2801–2808.
[28] D. Ray, P.K. Bharadwaj, Inorg. Chem. 47 (2008) 2252–2254.
[29] J.S. Wu, W.M. Liu, X.Q. Zhuang, F. Wang, P.F. Wang, S.L. Tao, X. H Zhang, S.K.
Wu, S.T. Lee, Org. Lett. 9 (2007) 33–36.
[30] S. Narinder, K. Navneet, McC. Bridgeen, F.C. John, Tetrahedron Lett. 51 (2010)
3385–3387.
[31] R.S. Joseyphus, C.J. Dhanaraj, M.S. Nair, Transition Met. Chem. 31 (2006) 699–
702.
[32] R.S. Joseyphus, M.S. Nair, Mycobiology 36 (2008) 93–98.
[33] R. Kripal, S. Misra, J. Phys. Chem. Solids 65 (2003) 939–948.
[34] N.O. Gopal, K.V. Narasimbulu, J.L. Rao, Physica B 307 (2001) 117–124.
[35] B. Karabulut, R. Tapramaz, A. Bulut, Z. Naturforsch A 54 (1999) 256–260.
[36] P.A.A. Mary, S. Dhanuskodi, Spectrochim. Acta A 57 (2001) 2345–2353.
[37] E. Bozkurt, I. Kartal, B. Karabulut, O.Z. Yesilel, Appl. Magn. Reson. 26 (2004)
275–282.
[38] B. Karabulut, R. Tapramaz, A. Karadag, Appl. Magn. Reson. 35 (2008) 239–245.
[39] R.J. Dudley, B.J. Hathaway, J. Chem. Soc. Sec. A 12 (1970) 2799–2803.
[40] E.D. Maur, S.M. Dominiciano, J. Phys. Chem. Solids 60 (1999) 1849–1854.
[41] Y. Yerli, A. Karadag, F. Koksal, Appl. Magn. Reson. 23 (2002) 43–49.
[42] P. Chand, M. Umar, Phys. Status Solidi B 127 (1985) 179–186.
[43] P. Chand, G.C. Upreti, M. Uyar, R.J. Singh, Phys. Status Solidi B 131 (1985) 357.
[44] Z. Sroubek, K. Zdansky, J. Chem. Phys. 44 (1966) 3378.
[45] R. Biyik, R. Tapramaz, B. Karabulut, Z. Naturforsch 58a (2003) 499–502.
[46] D. Kivelson, R. Neiman, J. Chem. Phys. 35 (1961) 149–155.
[47] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 5 (1970) 143–207.
We have described the preparation, characterization and bio-
logical activities of a novel asymmetrical Schiff base ligands and
their Zn(II), Ni(II), Cu(II) and Pb(II) metal complexes. The structural
properties of ligands and their complexes were proposed based on
elemental analyses, FT-IR, UV–Vis, 1H NMR, ESR, fluorescence spec-
troscopy and XRD. The antibacterial data given for the compounds
presented in this paper allowed us to state that the some metal
complexes generally has a better activity than ligands and all the
compounds have mild antibacterial activity against selected kinds
of bacteria.
Acknowledgments
The authors thank the Selcuk University Research Foundation
and Necmettin Erbakan University Research Foundation for the
financial support of this study. We thank Dr. Ulku Sayin (Selcuk
University, Physics Department) for the ESR.
References
[1] M. Shebl, S.M.E. Khalil, S.A. Ahmed, H.A.A. Medien, J. Mol. Struct. 980 (2010)
39–50.
[2] S.K. Bharti, G. Nath, R. Tilak, S.K. Singh, Eur. J. Med. Chem. 45 (2010) 651–660.