Antioxidant, tautomerism and antibacterial studies of Fe(III)-1,2,4- triazole based complexes

Article abstract of DOI:10.1016/j.saa.2013.03.068

New Fe(III) complexes have been synthesized by the reactions of ferric nitrate with Schiff base derived from 3-substituted phenyl-4-amino-5-hydrazino- 1,2,4-triazole and indoline-2,3-dione. All these complexes are soluble in DMF and DMSO; low molar conductance values indicate that they are non-electrolytes. Elemental analyses suggest that the complexes have 1:1 stoichiometry of the type [FeL_n(H₂O)(OH)]xH₂O. Structural and spectroscopic properties have been studied on the basis of elemental analyses, infrared spectra, ¹H and ¹³H NMR spectra, electronic spectra, magnetic measurements and FAB mass spectra. FT-IR, ¹H and ¹³H NMR studies reveal that the ligand (L_n) exists in the tautomeric enol form in both the states with intramolecular hydrogen bonding. Magnetic moment and reflectance spectral studies reveal that an octahedral geometry has been assigned to all the prepared complexes. FRAP values indicate that all the compounds have a ferric reducing antioxidant power. The compounds 2 and 3 showed relatively high antioxidant activity while compound 1 and 4 shows poor antioxidant power. Also good antimicrobial activities of the complexes against Staphylococcus aureus, Bacillus subtilis, Serratia marcescens, Pseudomonas aeruginosa and Escherichia coli have been found compared to its free ligands.

Full text of DOI:10.1016/j.saa.2013.03.068

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Antioxidant, tautomerism and antibacterial studies of Fe(III)-1,2,4-triazole
based complexes
⇑
G.J. Kharadi
Department of Chemistry, Navjivan Science College, Gujarat University, Dahod 389 151, Gujarat, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
New Fe(III) complexes have been synthesized by 1,2,4-triazole based ligand complexes. FT-IR, 1H and 13
NMR studies reveal that the ligand (Ln) exists in the tautomeric enol form in both the states with intra-
molecular hydrogen bonding.
H
ꢀ
ꢀ
ꢀ
ꢀ
Structural characterization of Fe(III)-
1,2,4-triazole based complexes.
All the complexes were characterized
by spectroscopy techniques.
All the complexes were excellent
interpretation and discussion.
All the complexes show an effective
antibacterial activity.
a r t i c l e i n f o
a b s t r a c t
Article history:
New Fe(III) complexes have been synthesized by the reactions of ferric nitrate with Schiff base derived
from 3-substituted phenyl-4-amino-5-hydrazino-1,2,4-triazole and indoline-2,3-dione. All these com-
plexes are soluble in DMF and DMSO; low molar conductance values indicate that they are non-electro-
lytes. Elemental analyses suggest that the complexes have 1:1 stoichiometry of the type
[FeLn(H2O)(OH)]ꢁxH2O. Structural and spectroscopic properties have been studied on the basis of elemen-
tal analyses, infrared spectra, 1H and 13H NMR spectra, electronic spectra, magnetic measurements and
FAB mass spectra. FT-IR, 1H and 13H NMR studies reveal that the ligand (Ln) exists in the tautomeric enol
form in both the states with intramolecular hydrogen bonding. Magnetic moment and reflectance spectral
studies reveal that an octahedral geometry has been assigned to all the prepared complexes. FRAP values
indicate that all the compounds have a ferric reducing antioxidant power. The compounds 2 and 3 showed
relatively high antioxidant activity while compound 1 and 4 shows poor antioxidant power. Also good
antimicrobial activities of the complexes against Staphylococcus aureus, Bacillus subtilis, Serratia marces-
cens, Pseudomonas aeruginosa and Escherichia coli have been found compared to its free ligands.
Ó 2013 Elsevier B.V. All rights reserved.
Received 14 February 2013
Accepted 16 March 2013
Available online 25 March 2013
Keywords:
Fe(III) complexes
Antioxidant studies
Tautomerism studies
Antibacterial studies
Introduction
anticancer, anti-inflammatory and antibacterial properties [1–9].
Several compounds containing 1,2,4-triazole ring are well known
Triazoles and their derivatives are found to be associated with
various biological activities, such as anticonvulsant, antifungal,
for drug synthesis [1]. 1,2,4-triazole containing amino group is also
important for obtaining various Schiff base with well known
⇑
Tel.: +91 2673 250346.
E-mail addresses: gaurangkharadi@yahoo.com, drkharadi84@gmail.com
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.03.068

312
G.J. Kharadi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
antimicrobial properties [10–17]. Although many studies have
investigated the antioxidant properties of resveratrol [18], there
have been only a few reports of antioxidant and antiproliferative
effects of hydroxyl-substituted Schiff bases.
Synthesis of ligands [31]
Synthesis of 3-(substituted phenyl)-4-amino-5-hydrazino-1,2,4-
triazole
Fe(III) complexes of Schiff bases are playing an important role in
the development of coordination chemistry, which is evident in
number of publications, including physicochemistry studies [19]
and biological aspects [20–24]. Iron is one of the most important
trace elements in the human body [25]. Increased iron availability
in serum or tissues is associated with an increased risk of several
tumors and may promote carcinogenesis [26]. Moreover, heredi-
tary hemochromatosis is characterized by excess iron that causes
tissue damage and fibrosis with irreversible damage to various
organs [27]. Iron homeostasis is an important factor involved in
neuroinflammation and progression of Alzheimer’s disease [28].
In this study, Schiff base ligands and their Fe(III) complexes
were synthesized and characterized by the analytical and spectro-
scopic methods. Antioxidant properties of the hydroxyl substituted
Schiff base ligands were investigated. The antimicrobial activities
of the ligands and their metal complexes were studied using the
bacteria and yeast. The redox properties of the compounds were
investigated by cyclic voltammetry. Thermal properties of the
metal complexes were investigated in the 20–800 °C temperature
range.
A mixture of 3-(substituted phenyl)-4-amino-5-mercapto-
1,2,4-triazole and N2H4ꢁH2O in ethanol was boiled under reflux
for 4–5 h on a water bath. The reaction mixture was cooled at room
temperature, within an hour the compound separated from the
clear solution. It was filtered, washed and recrystallized in ethanol.
Synthesis of Schiff bases
A
mixture of 3-(substituted phenyl)-4-amino-5-hydrazino-
1,2,4-triazole and indoline-2,3-dione in 1:2 M ratio in an alcoholic
medium containing a few drops of conc. HCl was refluxed for 5–
6 h. The product separated on evaporation of the alcohol was
recystallized in ethanol.
General procedure for the synthesis of complexes
A general procedure was followed to synthesize these complexes.
The procedure involves the addition of the appropriate ligand
(0.04 mol) to an aqueous ethanolic solution of Fe(NO3)3ꢁ9H2O
(0.04 mol) and sodium acetate (0.08 mol). The mixture was refluxed
for 10–11 h on a water bath. Reddish brown or orange precipitate
obtained was filtered, washed with ethanol and hot water and dried
in vacuo at room temperature. The complexes were obtained as
powdered material.
Materials and methods
The details of the reactions along with the analytical data of the
product are given in Table 1. The general reaction scheme is given
in Fig. 1.
Materials
The solvents were purchased from Merck and used without fur-
ther purification. Ferric nitrate was purchased from Aldrich. The li-
gands were prepared as reported in literature [29]. Luria broth was
purchased from Hi-media Laboratories Pvt. Ltd., India.
Minimum inhibitory concentration value
An antibacterial activity assay was performed on Staphylococcus
aureus, Bacillus subtilis, Serratia marcescens, Pseudomonas aerugin-
osa and Escherichia coli. The antibacterial activity for the test com-
pounds was tested to determine the bacteriostatic concentration,
i.e. minimum inhibitory concentration (MIC) in terms micromoles.
The MIC value was determined by broth dilution technique [32]. A
preculture of bacteria was grown in LB (Luria broth) overnight at
the most favorable temperature of each species. This culture was
used as a control to examine if the growth of bacteria tested was
Instruments
Elemental analysis (C, H, N) was performed using a 2400-II CHN
analyzer (PerkinElmer, USA). Analyses of metal ions was carried
out by dissolution of the solid complexes in hot concentrated nitric
acid, further diluting with distilled water and filtered to remove
the precipitated organic ligands. The remaining solution was neu-
tralized with ammonia solution and the metal ions were titrated
against EDTA. The melting point of all compounds was measured
using the open capillary tube method. FT-IR spectra (400–
4000 cmꢂ1) were recorded with a Spectrum GX-PerkinElmer spec-
trophotometer using KBr pellets. 1H NMR and 13C-NMR spectra of
ligands were recorded on a model Advance 400 Bruker FT-NMR
instrument using tetramethylsilane as internal standard and
DMSO-d6 as solvent. The fast atom bombardment (FAB) mass spec-
trum of the complexes was recorded at SAIF, CDRI, Lucknow with a
JEOL SX-102/DA-6000 mass spectrometer at room temperature
using argon/xenon as the FAB gas. Electronic spectra (200–
1200 nm) were collected using a LAMBDA 19 UV–visible/near-
infrared spectrophotometer.
Thermal stability and decomposition of the complexes were
determined by TG and DTG using a model 5000/2960 SDT (TA
Instruments, USA). The experiments were performed in N2 atmo-
sphere at a heating rate of 20 °C minꢂ1 in the temperature range
20–800 °C. Sample sizes ranging in mass from 3 to 8 mg were
heated in an Al2O3 crucible. Magnetic susceptibility measurements
were obtained by Gouy’s method using mercury tetrathiocyanato
cobaltate(II) as a calibrant (w = 16.44 ꢃ 10ꢂ6 c.g.s. units at 20 °C).
Diamagnetic corrections were made using Pascal’s constant [30].
normal. In a similar second culture, 20 ll of the bacteria as well
as the tested compound at the desired concentration were added
and monitored for bacterial growth by measuring turbidity of the
culture after 18 h. If a certain concentration of a compound inhib-
ited bacterial growth, half of the concentration of the compound
was tested. This procedure was carried out up to the concentration
which inhibited the growth of bacteria. The lowest concentration
that inhibited bacterial growth was considered the MIC value. All
equipments and culture media were sterilized [33].
Antioxidant studies
Ferric reducing antioxidant power (FRAP) was measured by a
modified method of Benzie and Strain [34]. The antioxidant poten-
tials of the compounds were estimated as their power to reduce
the TPTZ-Fe(III) complex to TPTZ-Fe(II) complex (FRAP assay),
which is simple, fast, and reproducible. FRAP working solution
was prepared by mixing a 25.0 mL, 10 mM TPTZ solution in
40 mM HCl, 20 mM FeCl3.6H2O and 25 mL, 0.3 M acetate buffer
at pH 3.6. A mixture of 40.0 mL, 0.5 mM sample solution and
1.2 mL FRAP reagent was incubated at 37 °C for 15 min. Absor-
bance of intensive blue color [Fe(II)-TPTZ] complex was measured
at 593 nm. The ascorbic acid was used as a standard antioxidant
compound. The results are expressed as ascorbic equivalent

G.J. Kharadi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
313
Table 1
Physical properties and analytical data of Fe(III) complexes of 3-(substituted phenyl)-4-amino-5-hydrazino-1,2,4-triazole Schiff bases.
Compound
Color
Molecular weight found (Cal.)
% Analysis found (Cal.)
leff (B.M)
C
H
N
Fe(III)
L1/C24H16N8O2
L2/C24H15ClN8O2
L3/ C24H15ClN8O2
L4/C24H15N9O4
[FeL1(H2O)(OH)]ꢁ2H2O/C24H17FeN8O4
[FeL2(H2O)(OH)]ꢁH2O/C24H16ClFeN8O4
[FeL3(H2O)(OH)]ꢁH2O/C24H16ClFeN8O4
[FeL4(H2O)(OH)]ꢁ2H2O/C24H16FeN9O6
Light yellow
Yellow
Yellow
Light yellow
Reddish brown
Orange
Reddish brown
Dull orange
448.08 (448.14)
482.79 (482.88)
482.82 (482.88)
493.38 (493.43)
573.23 (573.32)
589.65 (589.75)
589.69 (589.75)
618.28 (618.32)
64.22(64.28)
59.59(59.70)
59.61(59.70)
59.38(58.42)
50.21(50.28)
48.76(48.88)
48.78(48.88)
46.58(46.62)
3.55(3.60)
3.09(3.13)
3.01(3.13)
3.04(3.06)
3.55(3.69)
3.01(3.08)
2.97(3.08)
3.19(3.26)
24.89(24.99)
23.17(23.21)
23.14(23.21)
25.19(25.55)
19.30(19.54)
18.96(19.00)
18.99(19.00)
20.20(20.39)
–
–
–
–
–
–
–
–
5.98
6.05
5.95
5.99
9.72(9.74)
9.45(9.47)
9.42(9.47)
9.02(9.03)
Fig. 1. Synthesis and structure of the ligand.
(mmol/100 g of dried compound). All the tests were run in tripli-
cate and are expressed as the mean and standard deviation (SD).
disappears in their corresponding Fe(III) complexes indicating the
coordination of phenolic oxygen to Fe(III) metal ion through depro-
tonation. This is further supported by shift in phenolic ˆ(CAO) band
from 1285 cmꢂ1 (in the free ligand) to 1380–1310 cmꢂ1 in the
complexes. The coordination through phenolic oxygen further
confirmed by the appearance of band at 448–472 cmꢂ1 assignable
[40] to ˆ(FeAO). The presence of coordinated water in the com-
plexes [41] is indicated by a broad band in the region 3400 cmꢂ1
and two weaker bands in the region 810–750 and 730–700 cmꢂ1
due to ˆ(AOH) rocking and wagging mode of vibrations, respec-
tively [42]. In the far-IR region, two new band at 448–472 and
418–420 cmꢂ1 in the complexes are assigned to ˆ(FeAO) and
ˆ(FeAN) respectively.
Results and discussion
Chemistry
The structural investigation of all the prepared ligands (Ln) was
done using elemental analyses, IR, 1H and 13C NMR spectroscopy.
The complexes were prepared by reacting ferric nitrate with vari-
able ligands (L1ꢂL4) in a 1:1 ratio. The analytical and physical data
of the complexes are given in Table 1. The following chemical reac-
tion describes the formation of the complexes:
FeðNO3Þ3 ꢁ9H2OLn !½FeLnðH2OÞðOHÞꢄꢁxH2Oþð7ꢂmÞH2Oþ3HNO3
ðWhere n¼1&4;x¼2;n¼2&3;x¼1Þ
Tautomerism studies of ligands
The molecular structures of the ligands are such that they can
exist in six tautomeric forms as shown in Fig. 2. Detailed solution
and solid-state studies of this ligand were carried out to establish
their geometry. The IR spectra provide valuable information
regarding the Schiff base ligands appear to exist in both band
(solution spectra) at 2600 cmꢂ1, due to intramolecular H-bonded
OH group. The spectra of Schiff bases show a medium band at
3175 cmꢂ1 due to ˆ(NAH) which remains almost at the same posi-
tion in complex indicating the noninvolvement NAH group in bond
formation. 1H NMR chemical shift for the OH group was observed
at d 12.83 ppm. This signal disappeared when a D2O exchange
experiment carried out. It can be assigned either to OH of ligand
group, in either case it is strongly deshielded because of hydrogen
bonding with the other oxygen atom. It may be noted that the
integration of this signal perfectly matches with one proton and
there is no other fragments of this signal, which suggests that only
All the complexes are insoluble in water, ethanol, methanol, chloro-
form, acetonitrile, CCl4 and hexane; while soluble in DMF and
DMSO, so it is difficult to grow single crystals for X-ray Diffraction
analysis.
IR spectra
The important infrared spectral bands and their tentative
assignments for the synthesized ligand and its complexes were re-
corded as KBr disks and are discussed (Table 2).
The ligands show one medium intensity band at 1605 cmꢂ1
assignable [35] to ˆ(C@N) which shifts to 1575 cmꢂ1 in the com-
plexes. This shift indicates the coordination of azomethine nitro-
gen to metal ion [36–39]. Schiff bases show broad band
2640 cmꢂ1 due to intermolecular H-bonded OH group. This band

314
G.J. Kharadi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
Table 2
The importance infra red frequencies in (cmꢂ1) of Fe(III) complexes of 3-(substituted phenyl)-4-amino-5-hydrazino-1,2,4- triazole Schiff bases.
Complex
IR frequency (cmꢂ1
)
ˆ(OAH)
ˆ(NAH)
ˆ(C@N)
ˆ(C@C)
Phenolic ˆ(CAO)
ˆ(FeAO)
ˆ(FeAN)
[FeL1(H2O)(OH)]ꢁ2H2O
[FeL2(H2O)(OH)]ꢁH2O
[FeL3(H2O)(OH)]ꢁH2O
[FeL4(H2O)(OH)]ꢁ2H2O
3410
3414
3320
3425
3165
3150
3152
3150
1575
1560
1580
1558
1555
1560
1595
1520
1355
1320
1323
1350
449
472
448
449
420
418
419
420
Fig. 2. Possible tautomers of the ligand.
one tautomeric form of the ligand exists in solution under the
experimental conditions. Any temperature dependent experiments
have not been carried out. Comparing with the solid state study,
we prefer to assign this signal to OH of the of the ligand; however,
assignment of this peak to OH of the Schiff base-ring cannot be
ruled out provided solid state structural evidence is not considered
[43]. On the basis of 13C signal for the carbonyl carbon of the Schiff
base ligand-ring is observed at 166 ppm [44] clearly correspond to
ketone form (Fig. 2D0). These values are very close to those already
reported by other authors [45] showing that the lignds form
(Fig. 2A and A0) can be excluded. The presence of ethanone form
of the ligand (Fig. 2C) is not likely because this form requires an
additional signal set (approximately at 195.0–204.5 ppm) [46] in
13C NMR spectra, clearly correspond to a ketone form of the ligand,
which was not observed. The presence of a CH form (C) is not likely
because it is known that proton transfer between ligand and OH is
usually slow [45,47]. Consequently, in DMSO-d6 solution, the
ligand exist mainly as hydroxyethylidene form (Fig. 2D0) with
intramolecular hydrogen bond, in agreement with other reports
[45,48–50].
ligands (Ln) were carried out in a polar solvent such as DMSO-d6 at
room temperature and the data are given in the experimental sec-
tion. A broad singlet corresponding to one proton for all the Schiff
base ligands (Ln) is observed in the range d 12.42–12.40 ppm. This
signal disappeared when a D2O exchange experiment was carried
out. It can be assigned either to OH or NH, in either case it is
strongly deshielded because of hydrogen bonding with the other
atom (N/O) (Fig. 1). It shows the enolic nature of ligand and
broadness of singlet due to fast exchange interaction of proton
via keto-enol tautomerism with nitrogen of the azomethine group
[51]. It may be noted that the integration of this signal perfectly
matches with one proton and there is no other fragment(s) of this
signal, which suggests that only one tautomeric form of the Schiff
base ligands exist in solution under the experimental conditions.
We have not done any temperature dependent experiments.
Comparing with the solid state study, we prefer to assign this sig-
nal to OH; however, assignment of this peak to NH cannot be ruled
out provided solid state structural evidence is not considered.
Schiff base derived from indoline-2,3-dione of type (L1–L4) exhi-
bit signals at 12.40 and 5.5 ppm due to NH and hydrazine proton.
Multiplet is observed at 7.00–7.75 ppm due to aromatic protons in
the Schiff base. The 13C NMR spectra of these ligands were recorded
in DMSO-d6. Schiff bases derived from Indoline-2,3-dione (L1) show
signals at d 166 and 156.7 aromatic (AC@N). Aromatic ring protons
signals at d 150, 131.2, 130.6, 130.2, 129.4, 127.5, 126.6, 122.
1H NMR and 13C NMR spectra of the ligands
The proton magnetic resonance spectra of these ligands have
been recorded (Table 3). The 1H NMR studies of all the Schiff base

G.J. Kharadi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
315
Table 3
1H NMR and 13C NMR Spectral band (ppm) of Fe(III) complexes of 3-(substituted phenyl)-4-amino-5-hydrazino-1,2,4- triazole Schiff base.
Compound
1H NMR
13C NMR
ANH(s) Aromatic ring (M)
AC@N Aromatic ring
[FeL1(H2O)(OH)]ꢁ2H2O 12.40
7.51 (1H, H-5 of indol ring-1), 7.58 (1H, H-50 of indol ring-2),
7.60–7.98 (9H, m, ArAH), 8.30 (2H, d, J = 7.8, phenyl ring (H-2 156.7
166.3,
150.2(C-7a and C-7a0(of indol ring-1 and 2)), 131.2,
130.6, 130.2, 129.4, 127.5, 126.6(ArAC), 122(C-3a and
and 6))
3a0 of indol ring 1 and 2)
[FeL2(H2O)(OH)]ꢁH2O
[FeL3(H2O)(OH)]ꢁH2O
12.42
12.41
7.55(1H, H-5 of indol ring-1), 7.61(1H, H-50 of indol ring-2),
166.1,
150.3(C-7a and C-7a0 (of indol ring-1 and 2)), 138.7,
7.65–7.94 (8H, m, ArAH), 8.21(1H, d, J = 8.0, phenyl ring H-3), 156.1
8.35 (1H, d, J = 7.4, phenyl ring 6)
7.65(1H, H-5 of indol ring-1), 7.71(1H, H-50 of indol ring-2),
132.5, 130.3, 130.0, 129.4, 128.9, 127.3(ArAC), 126.7(C-
3a and 3a0 of indol ring 1 and 2)
166.2,
151.2(C-7a and C-7a0 (of indol ring-1 and 2)), 135.2,
130.2, 129.5, 128.9, 128.7(ArAC), 122.0(C-3a and 3a0 of
indol ring 1 and 2)
7.78–8.23(8H, m, ArAH), 8.45((2H, d, J = 7.8, phenyl ring (H-2 156.2
and 6))
[FeL4(H2O)(OH)]ꢁ2H2O 12.40
7.70(1H, H-5 of indol ring-1), 7.74(1H, H-50 of indol ring-2),
166.3,
149.5(C-7a and C-7a0 (of indol ring-1 and 2)), 147.9,
130.2, 127.7, 126.6, 124.8(ArAC), 122.3(C-3a and 3a0 of
indol ring 1 and 2)
7.77–8.05(8H, m, ArAH), 8.10((2H, d, J = 8.0, phenyl ring (H-2 156.4
and 6))
Table 4
FAB-mass spectra
Minimum inhibitory concentration date of the compounds (
lM).
Compounds
S.
B.
subtilis
S.
P.
E.
In the mass spectra of [Fe(L1)(H2O)(OH)]ꢁ2H2O, the peak at m/
z = 537 stands for the molecular ion peak of complex (without
water of crystallization). The proposed fragmentation pattern of
[Fe(L1)(H2O)(OH)], obtained using m-nitro benzyl alcohol as
matrix. Peaks at 136, 137, 154, 289 and 307 m/z value were due
to the usage of matrix. Peaks at 537, 358 and 539 in spectra were
assigned to (M), (M + 1) and (M + 2) of the complex molecule figure
in Supplementary data.
aureus
marcescens aeruginosa coil
Fe(NO3)3ꢁ9H2O
Ciprofloxacin
Norfloxacin
Enrofloxacin
Pefloxacin
Levofloxacin
Sparfloxacin
Ligand 1 (A1)
Ligand 2 (A2)
Ligand 3 (A3)
Ligand 4 (A4)
[FeL1(H2O)(OH)]ꢁ2H2O
(1)
1.8
1.6
2.5
1.9
2.1
1.7
1.3
500
575
775
650
2.7
1.7
1.1
2.5
3.9
2.4
2.2
2.0
525
550
725
650
2.7
1.7
1.6
4.1
1.7
5.1
1.7
1.5
575
525
700
675
2.7
1.5
1.4
3.8
1.4
5.7
1.7
1.5
525
575
750
700
2.3
1.2
1.4
2.8
1.4
2.7
1.0
1.3
550
550
725
625
2.8
Thermal studies of [Fe(L1)(H2O)(OH)]ꢁ2H2O complex
Thermal behavior of the complex ware studied by TG. The
thermal decomposition occurs in four steps. According to the mass
losses, all the compounds decompose progressively by the follow-
ing degradation pattern for the complex. Thermal decomposition
started by a dehydration process and was accompanied by endo-
thermic effect between 80 and 130 °C due to loss of two lattice
water molecules in the first step. The observed mass loss was
6.08%, which was nearly equal to the theoretical value 6.45%. The
loss of 2 mol lattice water molecules was first order. In the second
step, exothermic decomposition between 180 and 230 °C corre-
sponds to loss of one water and one hydroxyl molecules. The
observed mass loss was 5.45%, which was nearly equal to the the-
oretical value of 5.75%. The next step was exothermic, associated
with elimination of coordinated ligand, respectively. As tempera-
ture 400–600 °C increases the intermediate complexes convert to
CuO residue of fragments. The observed mass loss for the third
stages was 46.88%, respectively. The final solid product of decom-
position was CuO, accompanied by a broad exothermic effect at
600 °C [52,53].
[FeL2(H2O)(OH)]ꢁH2O
2.8
3.3
3.1
2.7
3.2
3.1
2.9
3.3
3.2
2.4
2.9
2.4
2.9
3.5
2.9
(2)
[FeL3(H2O)(OH)]ꢁH2O
(3)
[FeL4(H2O)(OH)]ꢁ2H2O
(4)
metal ions upon chelation. Chelation reduces the polarity of the
metal ion, mainly because of the partial sharing of its positive
charge with the donor groups and possibly the p-electron delocal-
ization within the whole chelate ring system thus formed during
coordination. This process of chelation increases the lipophilic nat-
ure of the central metal atom, which in turn favors its permeation
through the lipoid layer of the membrane, increasing the hydro-
phobic character and liposolubility of the molecule in crossing
the cell membrane of the microorganism, and hence enhances
the biological utilization ratio and activity of the testing drugs/
compounds.
Antibacterial screening
The results of the minimum inhibitory concentration (MIC), ex-
pressed in micromoles, are presented in Table 4. All compounds
exhibited good activity compare to reference drugs. The complexes
showed better antimicrobial activity than the free ligands and
ciprofloxacin. The higher antimicrobial activity can be mainly
attributed to the existence of the quinolone in the complexes.
The antibacterial activity of all the complexes is even higher than
the antibacterial activity of complexes, which were previously re-
ported by our group [54]. It has also been suggested [55,56] that
the ligands with nitrogen donor systems might inhibit enzyme
production, since the enzymes that require these groups for their
activity appear to be especially susceptible to deactivation by the
Electronic spectra and magnetic moments
The information regarding geometry of the complexes was
obtained from their electronic spectral data and magnetic moment
values. The diffused reflectance spectra of the complexes
[FeLn(H2O)(OH)]ꢁxH2O exhibited two bands at about ꢅ20,
000 cm–1
,
assigned to the 6A1g ? 4T2g transitions, and at
ꢅ32,500 cmꢂ1, assigned to MLCT in the d5-system of the Fe(III)
atom. The Fe(III) complexes exhibited magnetic moment of 5.90–
6.01 B.M. From the electronic spectra and magnetic measurement
data of Fe(III) complexes, an octahedral geometry around the cen-
tral metal ion is suggested [57–59].

316
G.J. Kharadi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 311–316
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Compounds
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FRAP value (mmol/100 g)
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[FeL1(H2O)(OH)]ꢁ2H2O (1)
[FeL2(H2O)(OH)]ꢁH2O (2)
[FeL3(H2O)(OH)]ꢁH2O (3)
[FeL4(H2O)(OH)]ꢁ2H2O (4)
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.03.068.
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