Synthesis, characterization and biological activity of ferrocene-based Schiff base ligands and their metal (II) complexes

Article abstract of DOI:10.1016/j.saa.2012.03.049

Metal (II) complexes derived from S-benzyl-N-(1-ferrocenyl-3-(4- methylbenzene)acrylketone) dithiocarbazate; HL¹, S-benzyl-N-(1- ferrocenyl-3-(4-chlorobenzene)acrylketone)dithiocarbazate; HL², all the compounds were characterized using various spectroscopic techniques. The molar conductance data revealed that the chelates were non-electrolytes. IR spectra showed that the Schiff bases were coordinated to the metal ions in a bidentate manner with N, S donor sites. The ligands and their metal complexes have been screened for in vitro antibacterial, antifungal properties. The result of these studies have revealed that zinc (II) complexes 6 and 13 of both the ligands and copper (II) complexes 9 of the HL² were observed to be the most active against all bacterial strains, antifungal activity was overall enhanced after complexation of the ligands.

Full text of DOI:10.1016/j.saa.2012.03.049

Spectrochimica Acta Part A 100 (2013) 131–137
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and biological activity of ferrocene-based Schiff base
ligands and their metal (II) complexes
Yu-Ting Liu∗, Gui-Dan Lian, Da-Wei Yin, Bao-Jun Su
Key Laboratory of Auxiliary Chemistry & Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science & Technology, Xi’an, Shaanxi 710021, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal (II) complexes derived from S-benzyl-N-(1-ferrocenyl-3-(4-methylbenzene)acrylketone) dithio-
carbazate; HL1, S-benzyl-N-(1-ferrocenyl-3-(4-chlorobenzene)acrylketone)dithiocarbazate; HL2, all the
compounds were characterized using various spectroscopic techniques. The molar conductance data
revealed that the chelates were non-electrolytes. IR spectra showed that the Schiff bases were coordi-
nated to the metal ions in a bidentate manner with N, S donor sites. The ligands and their metal complexes
have been screened for in vitro antibacterial, antifungal properties. The result of these studies have
revealed that zinc (II) complexes 6 and 13 of both the ligands and copper (II) complexes 9 of the HL2 were
observed to be the most active against all bacterial strains, antifungal activity was overall enhanced after
complexation of the ligands.
Received 13 December 2011
Received in revised form 28 January 2012
Accepted 7 March 2012
Keywords:
Synthesis
Schiff bases
Antibacterial activity
Antifungal activity
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
basis of these observations and as part of our program in the search
for new antibacterial and antifungal bioorganometallics, we have
There are only a few groups of compounds that have captured
the attention of chemists so intensively as ferrocenes. Since the
discovery of this sandwich complex in 1951 [1,2], a plethora of
its derivatives has been synthesized and characterized following
classical methods of organic chemistry. In the last two decades,
ferrocene has shown great promise in the area of medicinal
organometallic chemistry [3–8]. Based on its unique properties
such as stability, aromaticity, low toxicity and redox activity,
the ferrocene core is an attractive pharmacophore for drug
design [9,10]. Schiff bases represent an important class of organic
compounds and have often been used as chelating ligands in
coordination chemistry [11,12]. Schiff bases with donors (N, S, etc.)
have structure similarities with neutral biological systems and due
to presence of imines group are utilized in elucidating the mech-
anism of transformation of rasemination reaction in biological
system [13–16]. Thiosemicarbazide and its derivatives as ligands
with potential sulfur and nitrogen bands are interesting and have
gained special attention not only the structural chemistry of their
multifunctional coordination modes but also of their importance
in medicinal and pharmaceutical field. They show biological activ-
ities including antibacterial antifungal [17,18], antidiabetic [19],
antitumor [20], antiproliferative [21], anticancer [22], herbicidal
[23], anticorrosion and antiinflammatory activities [24,25]. On the
designed and synthesized a new series of ferrocene-based Schiff
base ligands by the condensation of 1-ferrocenyl-3-(4-methyl ben-
zene)acrylketone, 1-ferrocenyl-3-(4-chlorobenzene)acrylketone,
respectively with S-benzyl dithiocarbazate, and its metal com-
plexes to gain more information about spectral properties and
antimicrobial activities.
2. Experimental
2.1. Materials and reagents
All chemicals were commercially available, all the solvents were
dried before use by the literature methods [26] and moisture was
excluded from the glass apparatus using CaCl2 drying tubes. S-
benzyl dithiocarbazate was synthesized according to the literature
method [27]. The ferrocene-based chalcones were prepared as
reported [28,29].
2.2. Instruments
The melting points were determined in an open glass capillary
and were uncorrected. C, H, N, S analyses were performed with a
Fisons EA 1108 (CHNS-O) elemental analyzer. Molecular weights
were determined by the Rast Camphor method. IR spectra were
recorded on a Nicolet FT-IR-170SX instrument (KBr discs) in the
4000–250 cm−1 region. 1H and 13C NMR spectra were recorded on
a Varian Gemini 400 spectrometer, using DMSO-d6 as the solvent
and TMS as the internal standard, chemical shifts are expressed
∗
Corresponding author. Tel.: +86 029 86168828; fax: +86 029 86168828.
E-mail addresses: lyt@sust.edu.cn (Y.-T. Liu), Lianguidan1986@163.com
(G.-D. Lian).
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.03.049

132
Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
Fig. 2. Tautomerism of the ligands.
Fig. 1. Structures of HL1 and HL2 ligands.
Gram-negative (Escherichia coli ATCC 25922 and Pseudomonas
aeruginosa ATCC 43288) bacterial strains by the agar-well diffu-
sion method [30,31]. The wells (6 mm in diameter) were dug in
the media with the help of a sterile metallic borer with centers at
least 24 mm. Bacterial inocula containing approximately 104–106
colonyforming units (cfu/mL) were spread on the surface of the
nutrient agar with the help of a sterile cotton swab. The recom-
mended concentration of the test sample (50 ␮g/␮L in DMSO) was
introduced in the respective wells. Other wells supplemented with
DMSO and reference antibacterial drug, Tetracycline, served as neg-
ative and positive controls, respectively. The plates were incubated
at 37 ◦C for 24 h. Activity was determined by measuring the diam-
eter (mm) of zones showing complete inhibition. In order to clarify
any participating role of DMSO in the biological screening, separate
studies were carried out with the solutions alone of DMSO and they
showed no activity against any bacterial strains.
in (ppm). The spectrophotometric measurements in solution were
carried out using automated spectrophotometer UV–vis Perkin-
Elmer Model Lambda 20 ranged from 200 to 1100 nm. The molar
conductance of the complexes was measured for 1.00 × 10−3 M
DMSO solutions at 25 1 ◦C using a systronic conductivity bridge
type 305.
2.3. Synthesis of the ligands
The ligands HL1, HL2 (Fig. 1) were synthesized by the
condensation of S-benzyl dithiocarbazate (10 mmol) with the
ferrocene-based chalcones (10 mmol) in 1:1 molar ratio using abso-
lute ethanol (30 mL) as the reaction medium and were then, it was
refluxed for 5–8 h. The progress of the reaction was monitored by
TLC and on completion the resulting mixture was concentrated
under reduced pressure. The crude mixture was purified by silica-
gel column chromatography using benzene as solvent systems
which lead to pure the ferrocene-based Schiff base ligands HL1, HL2
(Scheme 1 and Table 1). The parent ligands exist in the tautomeric
forms (Fig. 2).
2.5.2. Antifungal activity (in vitro)
Antifungal activity of all the compounds was studied against two
fungal strains (Aspergillus niger ATCC 9092 and Aspergillus fumigatus
ATCC 46645) and cultured on malt medium, the broth media were
incubated for approximately 48 h, with subsequent filtering of the
culture through a thin layer of sterile Sintered Glass G2 to remove
mycelia fragments before the solution containing the spores was
used for inoculation. For preparation of plates and inoculation,
1.0 mL of inocula were added to 50 mL of agar media (50 ◦C) and
mixed. The agar was poured into 120 mm petri dishes and allowed
to cool to room temperature. Wells (6 mm in diameter) were cut
in the agar plates using a proper sterile tube. Then, fill wells were
filled up to the surface of agar with 0.1 mL of the test compounds
dissolved in DMSO (200 ␮mol/mL). The plates were left on a leveled
surface, and incubated at 30 ◦C for 48 h. The results were recorded
as the diameter of the inhibition zones and compared with standard
drugs Nistatine.
2.4. Synthesis of the metal complexes
To metal (II) salt was added to the calculated amount of the
ligands (1 mmol) in 1:2 molar ratio in dry ethylether (20 mL),
ethanol (10 mL) mixture as solvent in an oxygen-free argon atmo-
sphere. The resulting mixture was stirred under reflux for 8–10 h
whereupon the complexes precipitated. They were collected by fil-
tration, washed several times with ethanol–ethylether mixture to
remove any traces of unreacted starting materials, then washed
with ethanol and dried in a vacuum desiccator over fused CaCl2,
which leads to target metal (II) complexes (Fig. 3). The purity of
the compounds was checked by TLC. The analytical data for C, H, N
and S were repeated twice. The details of the analytical data of the
product are given in Table 1.
2.5. Biological activity study
2.5.3. Minimum inhibitory concentration (MIC)
Compounds containing high antimicrobial activity (≥20 mm)
were selected for minimum inhibitory concentration (MIC) stud-
ies. The minimum inhibitory concentration was determined using
the disc diffusion technique by preparing discs containing 10, 25, 50
and 100 ␮g/mL of the compounds and applying the protocol [32].
2.5.1. Antibacterial activity (in vitro)
The synthesized ferrocene-based Schiff bases (HL1) and (HL2)
and their metal (II) complexes were screened in vitro for their
antibacterial activity against two Gram-positive (Staphylococcus
aureus ATCC 9144 and Bacillus cereus ATCC 11778) and two
Scheme 1. Preparation of HL1 and HL2 Schiff base ligands.

Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
133
Table 1
Elemental analysis, molar conductivity, molar weight and melting point of the ligands and its metal (II) complexes.
Comp. no.
Compounds, molar
weight, mol. formula
Color (%yield)
M.P. (◦C)
Found (calcd.) %
ꢀm
(ꢁ−1 mol−1 cm2)
C
H
N
S
HL1
1
HL1, [511]
Red
135–137
176
65.73
(65.87)
60.22
(60.39)
60.01
(60.13)
60.29
(60.38)
55.07
(55.15)
57.53
(57.61)
59.97
(60.03)
53.23
(53.28)
61.13
(61.08)
55.99
(55.98)
55.83
(55.75)
56.03
(55.97)
51.54
(51.45)
53.59
(53.50)
55.73
(55.66)
49.75
5.21
(5.13)
4.98
(4.89)
4.95
(4.87)
4.99
(4.89)
4.17
(4.13)
4.75
(4.66)
4.93
(4.86)
4.42
(4.31)
4.24
(4.37)
4.08
(4.18)
4.04
(4.16)
4.09
(4.18)
3.39
(3.52)
3.88
(3.99)
4.03
(4.15)
3.53
5.61
(5.49)
5.17
(5.03)
5.13
(5.01)
5.09
(5.03)
4.67
(4.60)
4.91
(4.80)
5.13
(5.00)
4.51
(4.44)
5.21
(5.28)
4.79
(4.84)
4.73
(4.82)
4.75
(4.84)
4.33
(4.45)
4.56
(4.62)
4.72
(4.81)
4.21
12.49
(12.56)
11.43
(11.52)
11.31
(11.47)
11.40
(11.52)
10.41
(10.52)
10.83
(10.99)
11.36
(11.45)
10.09
(10.16)
12.01
(12.08)
11.00
(11.07)
10.98
(11.03)
11.01
(11.07)
10.03
(10.18)
10.47
(10.58)
10.96
(11.01)
9.67
–
C28H26FeN2S2
(63.6)
Brown
(66.7)
Brown
(71.5)
Red
(65.4)
Dark red
(69.3)
Dark
(70.2)
Brown
(73.4)
Dark
(70.9)
Brown
(71.3)
Dark
(70.9)
Brown
(75.1)
Red
(68.3)
Dark
(69.8)
Dark
(71.6)
Dark
[Ni(L1)2]·2H2O, [1112]
7.83
9.87
6.85
6.06
7.83
8.75
6.97
–
C56H54NiFe2N4S4O2
2
[Cu(L1)2]·2H2O, [1117]
C56H54CuFe2N4S4O2
[Co(L1)2]·2H2O, [1113]
C56H54CoFe2N4S4O2
[Hg(L1)2], [1218]
163
3
161
4
158
C
56H50HgFe2N4S4
5
[Cd(L1)2]·2H2O, [1166]
183
C56H54CdFe2N4S4O2
6
[Zn(L1)2]·2H2O, [1120]
C56H54ZnFe2N4S4O2
[Pb(L1)2]·2H2O, [1261]
C56H54PbFe2N4S4O2
HL2, [531]
187
7
169
HL2
8
120–122
183
C27
H23FeN2S2CI
[Ni(L2)2]·2H2O, [1157]
C54H48NiFe2N4S4CI2O2
[Cu(L2)2]·2H2O, [1162]
C54H48CuFe2N4S4CI2O2
[Co(L2)2]·2H2O, [1158]
C54H48CoFe2N4S4CI2O2
[Hg(L2)2], [1259]
7.65
9.28
6.91
6.53
8.09
7.73
6.59
9
170
10
11
12
13
14
159
178
C
54H44HgFe2N4S4CI2
[Cd(L2)2]·2H2O, [1211]
203
C
54H48CdFe2N4S4CI2O2
[Zn(L2)2]·2H2O, [1164]
C54H48ZnFe2N4S4CI2O2
[Pb(L2)2]·2H2O, [1305]
175
(74.7)
Brown
(70)
155
C54
H48PbFe2N4S4CI2O2
(49.62)
(3.70)
(4.29)
(9.81)
Fig. 3. Structure of the metal complexes.
3. Results and discussion
ions, using the following metal salts: NiCl2·6H2O (for complexes
1 and 8), CuCl2·2H2O (for 2 and 9), CoCl2·6H2O (for 3 and 10),
Hg(CH3COO)2 (for 4 and 11), Cd(CH3COO)2·2H2O (for 5 and 12),
Zn(CH3COO)2·2H2O (for 6 and 13), Pb(CH3COO)2·2H2O (for 7 and
14). The obtained complexes are stable in air; they are insoluble
in organic solvents such as methanol and ethanol, but soluble in
chloroform, DMF and DMSO. The molar conductance of the soluble
complexes in DMSO showed values indicating that all synthesized
metal complexes are nonelectrolytes. With the elemental analyses
data of the Schiff bases and their complexes are in agreement with
structures of the ligands and its metal (II) complexes.
The present Schiff bases HL1, HL2 were prepared by refluxing in
absolute ethanol (30 mL) an equimolar mixture of S-benzyl dithio-
carbazate with 1-ferrocenyl-3-(4-methylbenzene)acrylketone or
1-ferrocenyl-3-(4-chlorobenzene)acrylketone. The structures of
these formed Schiff bases were established by elemental analy-
ses, Fourier Transform Infrared (FT-IR), 1H, 13C NMR spectroscopy,
ultraviolet–visible (UV–vis) and molar conductance measure-
ments. These Schiff bases were further used for the complexation
reaction with Ni2+, Cu2+, Co2+, Hg2+, Cd 2+, Zn2+ and Pb2+ metal

134
Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
Table 2
Characteristic IR bands (4000–250cm−1) of the ligands and their metal (II) complexes.
Comp. no.
ꢂ(O H)
ꢂ(N H)
ꢂ(C N)
ꢂ(N N)
ı(N H)
ꢂ(C S)
ꢂ(C SM)
g (Fe-ring)
ꢂ(N M)
ꢂ(S M)
HL1
1
2
3
4
–
3409
3412
3405
–
3411
3417
3404
–
3411
3415
3409
–
3413
3420
3411
3163
1607
1596
1593
1597
1590
1594
1591
1591
1609
1597
1599
1598
1597
1599
1598
1598
971
960
963
961
960
961
959
962
971
962
964
963
961
963
960
964
1551
1067
–
1053
1050
1051
1052
1050
1051
1051
–
1055
1052
1052
1053
1051
1051
1053
481
482
482
483
481
482
483
483
482
482
483
482
481
481
481
483
–
471
477
473
473
472
476
474
–
467
469
465
466
467
469
467
–
365
366
364
365
367
361
363
–
362
363
361
362
363
359
361
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
5
6
7
HL2
8
3165
1553
1069
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
9
10
11
12
13
14
3.1. Infrared spectra
reported in Table 3. All assignments of the carbon atoms in the free
ligand (HL1) were found in their expected region [38,39] and are
well supported by their IR and 1H NMR spectra. Downfield shifting
of the azomethine carbon from 151.0 ppm in the free ligand (HL1) to
151.8–152.3 ppm in its metal complexes revealed coordination of
the azomethine to the metal atom. Similarly, the ligand shows the
thione carbon peak in the 191.6 ppm. While the thionic sulfur car-
bon of its metal complexes were observed 192.4–192.7 ppm. The
The IR spectra of the free Schiff base ligand as well as its metal
complexes are listed in Table 2, together with assignments for most
of the major peaks. In order to study the binding mode of the Schiff
base ligand to the metal ions in complexes, the IR spectrum of
the free Schiff base ligand was compared with the spectra of the
complexes. The IR spectra of the free Schiff base ligands showed
characteristic bands at 1067, 1069 cm−1 and 3163, 3165 cm−1. The
sharp band at 1067, 1069 cm−1 can be attributed to the ꢂ(C S)
group, while the characteristic band observed in the region of
3163, 3165 cm−1 may be due to the ꢂ(N H) group. These bands
indicate the thione nature of the ligands. However, as expected,
in the metal complexes a new band was observed in the region
1050–1055 cm−1 for ꢂ(C SM) with the disappearance of the band
ꢂ(C S). This is further confirmed by the appearance of band at
359–367 cm−1 assignable [33] to ꢂ(M S). The strong band observed
at 1607, 1609 cm−1 in the free Schiff base ligand is assigned to the
azomehtine group vibration. This band is shifted toward lower fre-
quencies by 8–17 cm−1 in the complexes, indicating coordination of
the imine nitrogen atom to the metal ion [34,35]. This is further sup-
ported by the appearance of band at 465–477 cm−1 assignable [36]
to ꢂ(M N). The free ligand exhibit a band at 481, 482 cm−1 assigned
to g (Fe-ring). In the metal complexes, no significant change was
observed, indicates its not participate in the coordination. The pres-
ence of coordinated water in the complexes [37] is indicated by a
broad band in the region 3400 cm−1. The above discussion indicates
that the nature of the free Schiff base is bidentate and shows the
coordination through N and S atoms to the metal.
spectra exhibit the
S CH2 carbon at 43.9 ppm, being near to the
coordination sites also showed downfield shifting by 0.1–0.3 ppm.
The results also indicate that the presences of number of carbons
agree well with the expected number of carbons.
3.3. UV–vis spectra
The UV–vis spectra of the ligand and its metal (II) complexes are
recorded in DMF solution in the wavelength range 200–1100 nm
and their corresponding data are given in Table 4. The UV–vis
spectra of the free ligand (HL1) showed three absorption bands in
the ultraviolet region (246–369 nm), the first high intensity bands
observed at ꢃmax = 246 nm. It follows from the literature that the
band at 246 nm is related to the ␲–␲* transitions of the benzene
rings [40]. The second absorption band at ꢃmax = 275 nm may cor-
respond to the ␲–␲* transition of the azomethine group C N while
the last band at ꢃmax = 369 nm may correspond to the n–␲* transi-
tions associated with the azomethine group. In the UV–vis spectra
of the metal complexes, the band of the high wavelength side
shows a bathochromic shifts relative to its free ligand. The absorp-
tion bands between 246 and 369 nm in free ligand change a bit in
intensity and remain essentially slightly changed for metal com-
plexes. The absorption shift and intensity change in the spectra
of the metal complexes most likely originate from the metalation
which increases the conjugation and delocalization of the whole
electronic system and results in the energy change of the ␲–␲*
and n–␲* transition of the conjugated chromophore [41,42]. The
results clearly indicate that the ligand coordinates to Ni(II), Cu(II),
Co(II), Hg(II), Cd(II), Zn(II) and Pb(II) ions, which are in accordance
with the results of the other spectral data. Furthermore, in the
case of the metal complexes, the absorption bands in the visible
region are observed at between 519 and 527 nm as a low inten-
sity bands. These bands are considered to arise from the forbidden
d–d transition, which is generally too weak. The nature of the
Ni(II), Cu(II), Co(II), Hg(II), Cd(II), Zn(II) and Pb(II) ions affects the
position of absorption band significantly [43]. According to mod-
ern molecular orbital theory [44], any factors that can influence
the electronic density of conjugated system must result in the
bathochromic or hypsochromic shift of absorption bands. Here, in
3.2. 1H NMR and 13C NMR spectra
1H NMR spectra of the free ligand (HL1) and their metal (II)
complexes were recorded in DMSO-d6. The 1H NMR spectral data
are reported in Table 3. All the protons due to ferrocene/aromatic
groups were found to be in their expected region [38,39]. The con-
clusions drawn from these studies provide further support to the
mode of bonding discussed in their IR spectra. The Schiff bases
exhibit signal due to the NH proton at 12.14 ppm. In its metal
complexes NH peak disappears. Other protons viz. CH2 protons
of S-benzyldithiocarbazate residue and ferrocene/aromatic pro-
tons resonate nearly at the same region as that of the free ligand.
The number of protons calculated from the integration curves, and
those obtained from the values of the expected CHNS analyses agree
well with each other (Table 1).
13C NMR spectra of the free ligand (HL1) and their metal (II) com-
plexes were recorded in DMSO-d6. The 13C NMR spectral data are

Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
135
Table 3
1H NMR and 13C NMR spectral data of the ligand (HL1) and its metal (II) complexes (DMSO-d6).
Compounds
Proposed assignment of the protons (ppm)
1H NMR: ı = 2.34 (s, 3H, CH3), 4.37 (s, 5H, C5H5), 4.55 (s, 2H, S CH2), 4.67 (s, 2H, C5H4), 4.96 (s, 2H, C5H4), 6.64 (d,
1H, J = 15.4 Hz, CH=), 6.91 (d, 1H, J = 15.4 Hz, =CH), 6.95–7.76 (m, 9H, ArH), 12.14 (s, 1H, NH)
HL1
13C NMR: ı = 191.6 (ꢀC S), 151.0 (ꢀC
N
), 141.8, 130.1 ( CH CH ), 139.6, 138.1, 133.1, 129.3, 128.4, 127.1,
CH2 ), 23.1 ( CH3)
126.7, 119.8 (Aromatic ring), 79.3, 69.6, 69.6, 68.6 (Ferrocenyl carbons), 43.9 (
S
1
2
3
4
5
6
7
1H NMR: ı = 2.34 (s, 6H, CH3), 4.37 (s, 10H, C5H5), 4.57 (s, 4H, S CH2), 4.69 (s, 4H, C5H4), 4.96 (s, 4H, C5H4), 6.70
(d, 2H, J = 14.5 Hz, CH=), 6.95 (d, 2H, J = 14.5 Hz, =CH), 7.01–7.81 (m, 18H, ArH)
13C NMR: ı = 192.5 (ꢀC
S
), 151.9 (ꢀC
N
), 142.0, 130.6 ( CH CH ), 139.2, 138.3, 133.2, 129.3, 128.5, 127.3,
CH2 ), 23.1 ( CH3)
126.7, 119.9 (Aromatic ring), 79.2, 70.2, 69.7, 69.0 (Ferrocenyl carbons), 44.2 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.38 (s, 10H, C5H5), 4.57 (s, 4H, S CH2), 4.70 (s, 4H, C5H4), 5.00 (s, 4H, C5H4), 6.71
(d, 2H, J = 14.4 Hz, CH=), 6.98 (d, 2H, J = 14.4 Hz, =CH), 7.05–7.87 (m, 18H, ArH)
13C NMR: ı = 192.4 (ꢀC
S
), 151.8 (ꢀC
N
), 142.4, 131.3 ( CH CH ), 139.7, 138.3, 133.5, 129.5, 128.4, 127.2,
CH2 ), 23.1 ( CH3)
126.7, 119.9 (Aromatic ring), 79.7, 70.6, 70.5, 69.3 (Ferrocenyl carbons), 44.1 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.37(s, 10H, C5H5), 4.56 (s, 4H, S CH2), 4.67 (s, 4H, C5H4), 4.97 (s, 4H, C5H4), 6.73 (d,
2H, J = 14.5 Hz, CH=), 6.95 (d, 2H, J = 14.5 Hz, =CH), 7.02–7.79 (m, 18H, ArH)
13C NMR: ı = 192.5 (ꢀC
S
), 152.1 (ꢀC
N
), 142.3, 130.9 ( CH CH ), 139.5, 138.2, 133.2, 129.4, 128.6, 127.2,
CH2 ), 23.1 ( CH3)
126.8, 119.8 (Aromatic ring), 79.1, 69.7, 69.7, 68.8 (Ferrocenyl carbons), 44.2 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.38 (s, 10H, C5H5), 4.56 (s, 4H, S CH2), 4.69 (s, 4H, C5H4), 4.98 (s, 4H, C5H4), 6.71
(d, 2H, J = 14.4 Hz, CH=), 6.95 (d, 2H, J = 14.4 Hz, =CH), 7.00–7.79 (m, 18H, ArH)
13C NMR: ı = 192.7 (ꢀC
S
), 152.3 (ꢀC
N
), 142.3, 130.5 ( CH CH ), 139.7, 138.1, 133.3, 129.6, 128.5, 127.1,
CH2 ), 23.1 ( CH3)
126.8, 119.9 (Aromatic ring), 79.9, 70.5, 70.4, 69.0 (Ferrocenyl carbons), 44.1 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.37 (s, 10H, C5H5), 4.56 (s, 4H, S CH2), 4.69 (s, 4H, C5H4), 4.98 (s, 4H, C5H4), 6.72
(d, 2H, J = 14.6 Hz, CH=), 6.96 (d, 2H, J = 14.6 Hz, =CH), 7.01–7.93 (m, 18H, ArH)
13C NMR: ı = 192.4 (ꢀC
S
), 151.9 (ꢀC
N
), 142.0, 130.7 ( CH CH ), 139.2, 138.2, 133.2, 129.3, 128.4, 127.3,
CH2 ), 23.1 ( CH3)
126.7, 119.9 (Aromatic ring), 79.3, 70.2, 69.7, 69.0 (Ferrocenyl carbons), 44.0 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.37 (s, 10H, C5H5), 4.57 (s, 4H, S CH2), 4.68 (s, 4H, C5H4), 4.96 (s, 4H, C5H4), 6.70
(d, 2H, J = 14.5 Hz, CH=), 6.95 (d, 2H, J = 14.5 Hz, =CH), 7.03–7.81 (m, 18H, ArH)
13C NMR: ı = 192.5 (ꢀC
S
), 152.0 (ꢀC
N
), 142.3, 131.4 ( CH CH ), 139.7, 138.3, 133.6, 129.3, 128.2, 127.3,
CH2 ), 23.1 ( CH3)
126.7, 119.9 (Aromatic ring), 79.7, 70.8, 70.0, 69.3 (Ferrocenyl carbons), 44.1 (
S
1H NMR: ı = 2.34 (s, 6H, CH3), 4.38 (s, 10H, C5H5), 4.56 (s, 4H, S CH2), 4.70 (s, 4H, C5H4), 4.97 (s, 4H, C5H4), 6.71
(d, 2H, J = 14.4 Hz, CH=), 6.95 (d, 2H, J = 14.4 Hz, =CH), 7.02–7.88 (m, 18H, ArH)
13C NMR: ı = 192.6 (ꢀC
S
), 152.2 (ꢀC
N
), 142.1, 131.0 ( CH CH ), 139.7, 138.5, 133.5, 129.6, 128.5, 127.1,
CH2 ), 23.1 ( CH3)
126.8, 119.7 (Aromatic ring), 79.7, 70.5, 69.9, 69.3 (Ferrocenyl carbons), 44.1 (
S
the case of the metal complexes with same ligand, the main reason
of bathochromic shifts is generally related with the electronegativ-
ity of the different metal ions [41].
3.5. Biological activity
3.5.1. Antibacterial activity (in vitro)
The synthesized ligands (HL1) and (HL2) and their metal (II)
complexes were tested against two Gram-positive (S. aureus and
B. cereus) bacterial strains and two Gram-negative (E. coli and P.
aeruginosa) (Table 5) according to literature protocol [30,31]. The
results were compared with those of the standard drug Tetracy-
cline. As it can be seen, the all compounds have shown a wide
range of activities—from weak active compounds, through mod-
erate active to the significant active ones. The compounds 6, 9, and
13 were shown to be significant activity against all bacterial strains.
Compounds HL1, HL2, 1, 3, 4, showed weak activity against S. aureus
3.4. Molar conductance measurements
The molar conductance values of the metal (II) complexes
under investigation were determined using 1 × 10−3 M DMSO
solution at 25 ◦C is listed in Table 1, are in the range of
6.53–9.87 ꢁ−1 mol−1 cm2. These values indicated that, all synthe-
sized metal complexes are nonelectrolytes. This is in accordance
with the fact that conductivity values for a nonelectrolytes are
below 50 ꢁ−1 mol−1 cm2 in DMSO solution [45,46].
Table 4
The UV–vis absorption bands (ꢃmax) and molar absorptivities (ε) of the ligands and its metal (II) complexes in DMF solution at 25 ◦C.
Comp. no.
ꢃmax (nm)
ε (×104 M−1 cm−1
)
HL1
1
2
3
4
246
247
248
246
247
249
248
246
251
254
255
252
253
256
255
251
275
283
294
280
289
293
297
282
276
284
295
282
290
295
297
284
369
381
387
383
384
386
390
381
372
383
388
385
385
386
389
385
–
519
526
521
521
524
527
521
–
522
526
519
523
524
530
521
1.56
1.89
2.03
1.89
1.93
1.87
1.91
1.73
1.73
1.83
1.97
1.86
1.92
1.95
1.89
1.97
2.47
2.67
2.91
2.31
2.54
2.36
2.42
2.56
2.69
2.72
2.83
2.65
2.67
2.69
2.71
2.83
0.23
0.93
1.01
0.79
0.89
0.8
0.85
0.87
0.45
0.97
1.02
0.95
0.93
1.03
0.96
0.92
–
0.31
0.37
0.29
0.34
0.35
0.36
0.26
–
0.39
0.43
0.37
0.38
0.41
0.39
0.41
5
6
7
HL2
8
9
10
11
12
13
14

136
Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
Table 5
Antibacterial and antifungal activity (concentration used 1 mg/mL of DMSO) of the
ligands and their metal (II) complexes [zone of inhibition (mm)].
Comp. no.
Gram-positive
Gram-negative
Fungus
S. aureus B. cereus E. coli P. aeruginosa A. niger A. fumigatus
HL1
1
2
3
4
11
12
15
13
14
18
22
18
13
17
21
16
15
15
21
16
–
13
14
18
14
12
19
21
14
15
19
21
13
12
13
20
14
–
17
16
22
20
17
16
24
19
18
17
22
17
16
17
24
19
–
16
15
19
15
13
17
21
14
16
20
21
14
13
15
23
15
–
15
18
21
20
17
19
23
16
16
19
22
20
18
21
23
21
–
16
16
22
17
20
21
21
18
18
17
21
21
19
18
22
19
–
5
6
7
HL2
8
9
10
11
12
13
14
DMSO
Tetracycline 27
Nistatine
27
–
25
–
25
–
–
26
–
24
Fig. 4. Comparison of antibacterial activity of ligands (HL1) and their metal (II).
complexes 1–7.
–
<15, weak; 15–20, moderate; >20, significant.
while compounds 2, 5, 7, 8, 10, 11, 12 and 14 exhibited moderate
activity. Compounds HL2, 2, 5, 8 showed moderate activity against
B. cereus. Compounds 2, 3, 6, 9 and 13 showed significant activity
against E. coli while other compounds exhibited moderate activ-
ity. Compounds 4, 7, 10, and 11 showed moderate activity against
P. aeruginosa while compounds 6, 8, 9 and 13 exhibited significant
activity, the surplus compounds showed weak activity. The zinc (II)
complexes 6 and 13 of both the ligands and copper (II) complexes 9
of the HL2 were observed to be the most active against all bacterial
strains (Fig. 4).
3.5.2. Antifungal activity (in vitro)
The antifungal activity of the compounds was tested against A.
niger and A. fumigatus (Table 5). Majority of the synthesized com-
pounds showed good antifungal activity against different fungal
strains. Compounds 2, 6, 9, 10 and 13 showed excellent while all
other compounds showed moderate to excellent activities against
various fungal strains. The compounds 2, 3, 6, 9, 10, 12, 13 and
14 showed excellent antifungal activities against A. niger. Similarly
compounds 2, 4, 5, 6, 9, 10 and 13 against A. fumigatus, the sur-
plus compounds showed moderate activity. Antifungal activity is
overall enhanced after complexation of the ligands (Fig. 5).
Fig. 5. Comparison of antifungal activity of ligands (HL1) and their complexes 1–7.
3.5.3. Minimum inhibitory concentration (MIC) for antimicrobial
activity
and 22.17, respectively. These compounds were therefore, selected
for antimicrobial minimum inhibitory concentration (MIC) stud-
ies (Table 6). The MIC of these most active compounds was in the
range of 1.54 × 10−8 to 3.750 × 10−7 M while compound 6 proved
to be the most active one. It inhibited the growth of A. niger at
1.319 × 10−8 M.
All compounds have shown variable average inhibition activ-
ity against different strains in the range of 14.67 (57.14%) to
22.17 (86.36%). The data obtained after preliminary antimicro-
bial screening showed that compounds 6, 9 and 13 were the
most active and their average inhibition values were 21.33, 22
Table 6
Minimum inhibitory concentration (M/mL) of the selected compounds 6, 9 and 13 against bacteria and fungi.
Comp. no. In vitro antimicrobial activity minimum inhibitory concentration
Gram-positive
Gram-negative
Fungus
S. aureus
B. cereus
E. coli
P. aeruginosa
A. niger
A. fumigatus
6
9
13
–
3.671 × 10−7
1.653 × 10−7
3.316 × 10−8
1.897 × 10−8
3.750 × 10−7
3.171 × 10−8
–
1.319 × 10−8
1.541 × 10−8
1.713 × 10−8
1.523 × 10−8
2.019 × 10−7
1.973 × 10−8
1.375 × 10−7
–
–
1.769 × 10−8

Y.-T. Liu et al. / Spectrochimica Acta Part A 100 (2013) 131–137
137
4. Conclusions
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Acknowledgments
The authors are indebted to Prof. Yuting Liu for her constant
support and encouragement. The authors also thank Prof. Zhiwei
Zhang for having carried out all the antimicrobial activity tests. The
authors are thankful to Shaanxi University of Science & Technology
for Elemental, FT-IR, UV–vis, 13C NMR, 1H NMR spectroscopy and
molar conductance measurements.
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