Synthesis and spectroscopic characterization of indomethacin-Cd(II), Ce(III), and Th(IV) complexes: IR, 1H NMR, thermal, and biological studies

Article abstract of DOI:10.1134/S1070363213120463

Solid complexes have been prepared and characterized by IR, UV-Vis, elemental analysis, and ¹H NMR. Indomethacin forms complexes with Cd(II), Ce(III), and Th(IV) ions in molar ratios (ligand: metal) (2: 1), (3: 1), and (4: 1), respectively. The IR spectra of the complexes suggest that the Indomethacin behaves as a monobasic monodentate ligand coordinated to the metal ions via the deprotonated carboxylate group. Prepared complexes exhibit higher antimicrobial activity against several microorganisms, compared to free ligand.

Full text of DOI:10.1134/S1070363213120463

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 12, pp. 2479–2487. © Pleiades Publishing, Ltd., 2013.
Synthesis and Spectroscopic Characterization
of Indomethacin–Cd(II), Ce(III), and Th(IV) Complexes:
IR, 1H NMR, Thermal, and Biological Studies1
Moamen S. Refata,b, Gehad G. Mohamedc, Mohamed Y. S. Ibrahimd,
Hamada M. A. Killad, and Hammad Fetoohd
a Department of Chemistry, Faculty of Science, Port Said, Port Said University, Egypt
e-mail: msrefat@yahoo.com
b Department of Chemistry, Faculty of Science, Taif University, 888 Taif, Kingdom Saudi Arabia
c Department of Chemistry, Faculty of Science, Cairo University, Egypt
d Department of Chemistry, Faculty of Science, Zagazig University, Egypt
Received September 23, 2013
1
Abstract―Solid complexes have been prepared and characterized by IR, UV-Vis, elemental analysis, and H
NMR. Indomethacin forms complexes with Cd(II), Ce(III), and Th(IV) ions in molar ratios (ligand : metal)
(2 : 1), (3 : 1), and (4 : 1), respectively. The IR spectra of the complexes suggest that the Indomethacin behaves
as a monobasic monodentate ligand coordinated to the metal ions via the deprotonated carboxylate group.
Prepared complexes exhibit higher antimicrobial activity against several microorganisms, compared to free
ligand.
DOI: 10.1134/S1070363213120463
INTRODUCTION
bridging oxygen [19]. The crystal and molecular struc-
tures of the ternary copper–indomethacin complexes
were reported [20]. The interaction between indo-
methacin anions and heavy metal ions, such as Cd(II),
Zn(II) and Cu(II), was studied in aqueous solution by
polarographic techniques [21, 22]. Copper complex of
indomethacin was found to be more effective than the
parent drug against Staphylococcus aureus and
Escherichia coli bacteria [23]. The goal of this
research was to get a wider understanding of the struc-
tural and spectral properties as well as microbial acti-
vities of indomethacin-Cd(II), Ce(III), and Th(IV) com-
plexes. Metallo-indomethacinate complexes were invest-
tigated by a number of spectral and thermal techniques.
Indomethacin (Fig. 1) is one of the so called non-
steroid anti-inflammatory drug which used to treatment
fever, pain, stiffness, and swelling [1]. Indomethacin is
a good chelating agent because it contains carboxylic
group [2–4]. The metal carboxylates systems have an
important role in inorganic and bioinorganic chemistry
[5, 6]. There are many metal ions involved in various
biological processes as a component of several metal-
drug interactions [7–16]. It is a fact that metal
complexes may be more active than the parent free
ligand. Relatively small number of papers concerning
the association between indomethacin ligand and metal
ions can be found in the literature [17–23]. Complexes
of ruthenium ions and some of non-steroidal anti-
inflammatory drugs like ibuprofen, aspirin, naproxen
and indomethacin were synthesized and characterized
using various spectroscopic methods [17]. Two Sn(IV)
indomethacin complexes have been prepared and
structurally characterized by means of 119Sn Moes-
sbauer, vibrational, and NMR (1H and 13C) spectro-
scopy [18]. It was found that tin atoms are bridged by
bidentate carboxylate ligands and by a monoatomic
Cl
O
O
O
OH
1
Fig. 1. Indomethacin (IndoH).
The text was submitted by the authors in English.
2479

2480
MOAMEN S. REFAT et al.
Table 1. Elemental analyses and physical data of Indo-Cd(II), Ce(III), and Th(IV) complexes
C, %
H, %
N, %
M, %
calculated
Comp.
no.
MW (g/mol)
Λ, Ω–1 cm2 mol–1
found calculated found calculated found calculated found
880
1264.47
1784
51.05
53.93
50.83
51.80
54.09
51.12
4.28
3.67
4.36
4.09
4.03
4.15
2.99
2.85
2.66
3.18
3.32
3.13
12.43
11.55
13.35
12.77
11.08
13.00
8.60
13.00
18.00
I
II
III
EXPERIMENTAL
The pH of each solution was adjusted to 7–9 using 5%
alcoholic ammonia solution. The resulting solutions
were heated at 50°C for one hour and left to evaporate
slowly at room temperature overnight. Precipitates
obtained were filtered off, washed with hot water and
then dried at 60°C. Elemental analysis data for the
complexes are given in the Table 1.
All chemicals used were of the purest laboratory
grade (Merck). CdCl2·H2O, CeCl3·7H2O, Th(NO3)4·
5H2O, were used for the preparation of the
corresponding complexes. Indomethacin was received
from Egyptian international pharmaceutical industrial
company (EIPICO). CHN contents were determined
using a Perkin–Elmer CHN 2400 analyzer. Metal
content was found gravimetrically by converting the
compounds into corresponding oxides. Molar con-
ductivities of freshly prepared 1.0×10–3 mol/L DMSO
solutions of complexes were measured using Jenway
4010 conductivity meter. IR spectra were recorded on
a Bruker FTIR spectrophotometer (4000–400 cm–1) in
KBr pellets. UV-Vis spectra were recorded DMSO
solvent with concentration (1.0×10–3 M) for the free
Indo ligand and their complexes using Jenway 6405
spectrophotometer with 1 cm quartz cell, in the range
of 200–800 nm. Solid reflectance spectra were
performed on a Shimadzu 3101 pc spectrophotometer.
1H NMR spectra of the free Indo ligand and their
complexes were recorded on a Varian Gemini 200 MHz
spectrophotometer using DMSO-d6 as solvent and
TMS as an internal reference. Thermogravimetric
analysis (TG and DTG) was carried out in the
temperature range from 25 to 800°C in nitrogen
atmosphere on a Shimadzu TG 50H thermal analyzer.
The experimental conditions were: platinum crucible,
nitrogen atmosphere with a 30 mL/min flow rate,
heating rate 10°C/min. Hole well method was used for
the evaluation of antibacterial and antifungal activities
of synthesized compounds.
RESULTS AND DISCUSSION
Molar conductivities of metal chelates of IndoH.
The molar conductivity values for the Cd(II), Ce(III),
and Th(IV) complexes of IndoH in DMF solutions
(1.0×10–3 M) were found to be in the range of 8.60–
18.00 Ω–1 cm2 mol–1, suggesting them to be non-
electrolytes as shown in Table 1. The conductivity
measurements play an important role in detection the
place of counter ions inside or outside the coordination
sphere. This method testing the degree of ionization of
the complexes comparing to the free ligands, with the
higher molar conductance value corresponding to the
presence of counter ions outside the coordination
sphere and vice versa [24]. Under this prediction, it is
clear from the obtained data that all three Cd(II),
Ce(III), and Th(IV) complexes seem to be non-
electrolytes. Also the molar conductance values
indicate that the anions are absent or exhibited inside
the coordination sphere. The fact that Cl– ions were not
detected by addition of AgNO3 solution to the
solutions of the complexes in nitric acid matches well
this conclusion.
Infrared spectra of IndoH and its Cd(II),
Ce(III), and Th(IV) complexes. The IR data for
IndoH and its complexes are listed in Table 2 and
shown in Fig. 2 (as example, for Ce(III) complex II).
The IR spectra of the complexes are compared with
those of the free ligand in order to determine the
coordination sites that may involved in chelation.
There are some guide peaks in the spectra of the
ligand, which are useful in achieving this goal. The
position and/or the intensities of these peaks are
expected to change upon chelation. These guide peaks
Synthesis of Indo complexes. Target complexes
were prepared using a ligand : salt molar ratio 1 : 2,
1 : 3, and 1 : 4 for Cd(II), Ce(III), and Th(IV)
complexes, respectively. A solution of 0.5 mmol,
0.33 mmol and 0.25 mmol of appropriate salt (for Cd(II),
Ce(III), and Th(IV) complexes, respectively), in 10 mL
of distilled water was added to a solution of 1.0 mmol
of Indomethacin in 20 mL of methanol under stirring.
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SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION
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Table 2. IR frequencies (4000–400 cm–1) of IndoH and its Cd(II), Ce(III), and Th(IV) complexes
ν(C=O)
(–COOH)
ν(C=O)
(amide)
ν(M–O)
(COO)
ν(M–O)
(H2O)
Comp. no.
νas(COO)
νs(COO)
Δ
IndoH
1590 sh
1590 s
1454 sh
1474 m
1471 s
136
116
118
117
1716 sh
1685 sh
1680 sh
1681 sh
1682 sh
–
–
–
–
–
477 s
522 s
599 s
547 s
I
1589 m
1588 m
478 w, 432 s
478 s, 433 w
II
III
1471 sh
Table 3. 1H NMR spectral data of IndoH and its Cd(II) complex
δ, ppm of hydrogen
Compound
2H; CH2
2.10
3H; CH3
3H; CH3O
4.10
5H; ArH
H; COOH
11.00
IndoH
3.50
3.49
6.15–7.15
Cd(II) complex
2.18
3.73
6.65–7.64
–
are listed in Table 2. No significant spectral changes
are observed for IndoH after its coordination with the
metal ions, expect for the frequencies related to the
carboxylic (–COOH) groups [25]. The absence of the
ν(O–H) and ν(C=O) absorption bands of the parent
acid [3300 cm–1 and 1716 cm–1 of ν(O–H) and ν(C=O)
bands for IndoH, respectively] in the IR spectra of the
complexes is indicative of carboxylate group binding.
The difference of bands of the prepared complexes;
νas(COO) and νs(COO), is characterized for the
carboxylate ligation. The νas(COO) and νs(COO) bands
of Indo complexes are found at 1590–1588 and 1474–
1471 cm–1, respectively. The values for Δ[νas(COO) –
νs(COO)] are in the range of 116–118 cm–1, indicating
that the coordination mode of the carboxylate ligand
with the metal ion cores is monodentate [25–28].
Indomethacin complexes exhibited bands at the range
of 3405–3444 cm–1, attributed to the presence of
coordinated and lattice water molecules [27]. The
multiple weak bands at 478–432 cm–1 and the medium
small bands at 599–522 cm–1 of the complexes are
assigned to the ν(M–O)COO and ν(M–O)S, respectively,
where s is the oxygen bonded solvent (H2O) [25, 27,
28].
through the carboxylate group by the absence of the
COOH signal in Cd(II) complex and the aromatic
singals decreased in intensities, indicating that the
magnetic environment of the aromatic ring has
changed significantly with coordination. The signals
observed at 2.48–2.50 and 3.36 ppm in case of Cd(II)
complex, are assigned to the coordinated and uncoor-
dinated water molecules. The results of elemental
1
analyses, infrared and H NMR spectral data are in
agreement with each other to support the proposed
structure of IndoH metal complexes.
Magnetic measurements of Ce(III) and Th(IV)
complexes II and III. The magnetic moment value of
the Th(IV) complex (III) was calculated from the
1H NMR spectra of IndoH and its Cd(II)
1
complex. H NMR spectra of IndoH and its Cd(II)
1
complex are shown in Table 3 and Fig. 3; H NMR
data for free IndoH are: δ = 11.00 [H, COOH], 2.10
[2H, CH2], 3.50 [3H, CH3], 4.10 [3H, CH3O], 6.15–
7.15 [H, Ar–H]. H NMR data for [Cd(Indo)2(H2O)2]·
H2O solid complex are in agreement with coordination
Wavenumber, cm–1
1
Fig. 2. FT–IR Spectrum of Ce(III) complex II.
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MOAMEN S. REFAT et al.
δ, ppm
Fig. 3. 1H NMR spectrum of Cd(II) complex I.
measured magnetic susceptibility after employing
diamagnetic correction and revealed its diamagnetic
nature as expected for thorium metal with 5F°
configuration [29]. The magnetic moment of Ce(III)
complex II lies at 2.58 BM and the magnetic moments
values, μeff of the Ce(III) complexes are in the range
2.34–2.57 BM, being consistent with mono nuclear
complexes and free from antiferromagnetism. The
Ce(III) complex has a coordination number six and
exists in octahedral geometry [30].
hetero cyclic moiety and benzene ring. The second
band observed at 350 nm is attributed to n→π* elec-
tronic transition. In the spectra of the metal complexes,
Electronic absorption spectra of Indo complexes.
The formation of metal complexes was also confirmed
by UV-Vis spectra. Fig. 4 shows as example the
electronic absorption spectra of the Th(IV) complex
III in 200–600 nm range. It can be seen that free
IndoH has two distinct absorption bands. The first one
at 275 nm may be attributed to π→π* transition of the
240
400
600
800
Wavelength, nm
Wavelength, nm
Fig. 4. Electronic absorption spectrum of Th(IV) complex III.
Fig. 5. Solid reflectance spectrum of Ce(III) complex II.
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SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION
TGA, %
2483
DTGA, mg/min
Temperature, °C
Fig. 7. TG/DTG curve of Cd(II) complex I.
Figs. 7 and 8. The weight losses for each chelate were
calculated within the corresponding temperature ranges.
[Cd(Indo)2(H2O)2]·H2O (I). The thermal decom-
position of [Cd(Indo)2(H2O)2]·H2O complex occurs in
three steps (Fig. 7). The first degradation step takes
place in the range of 40–165°C and corresponds to the
elimination of H2O molecule with an observed weight
loss of 2.83% (calculated 2.05%). The second step
happens in the range of 165–420°C, assigned to the
loss of 2 water molecules and C21H15ClNO5 fragment
with a weight loss of 49.22 (calculated 49.15%). The
third decomposition step within the temperature range
420–640°C was accompanied by mass loss of 33.93%
(calculated 34.15%), which is assigned to the loss of
C17H15ClNO2. The CdO is the final product remaining
stable till 800°C. On the corresponding DTG curve,
four peaks are observed. The first maximum is at 145°C
and the second, third and fourth at 325, 369, and 594°C,
respectively.
Wavelength, nm
Fig. 6. Solid reflectance spectrum of Th(IV) complex III.
the two bands are bathochromically affected (Red-
shifted), obviously suggesting the ligand has changed
to the Zwitterionic form. The results clearly indicate
that the ligand coordinate to metal ions via depro-
tonated carboxylate that in accordance with the results
of the FTIR and 1H NMR spectra.
[Ce(Indo)3(H2O)3] (II). The thermal decomposi-
tion of [Ce(Indo)3(H2O)3] complex occurs completely
The diffused reflectance spectrum of Ce(III) com-
plex II, shown in Fig. 5 demonstrates two detectable
absorption bands at 32258 and 38760 cm–1 which may
be related to metal-ligand charge transfer (MLCT)
excitations and corresponding to the octahedral geo-
metry of the Ce(III) complex [29]. The solid
reflectance spectrum of Th(IV) complex III, shown in
Fig. 6 was recorded in the UV-Vis region. There are
three detectable transitions at 39682, 32573, and
28248 cm–1 and ascribed to π→π*, n→π* and the
charge transfer transition from the ligand to the metal,
respectively [30].
TGA, %
DTGA, mg/min
Temperature, °C
Thermal analysis of Cd(II), Ce(III), and Th(IV)
complexes. The data are listed in Table 4 and shown in
Fig. 8. TG/DTG curve of Th(IV) complex III.
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MOAMEN S. REFAT et al.
Table 4. Thermal data for Indo complexes
Comp. TG range,
DTGmax
°C
,
Mass loss, %
found (calculated)
Total mass
left
na
Assignment
Residue
CdO
no.
°C
40–165
165–420
420–640
145
325, 369
594
1
1
1
2.83 (2.05)
49.22 (49.15)
33.93 (34.15)
Loss of H2O.
Loss of 2H2O and C21H15ClNO5.
14.02 (14.65) Loss of C17H15ClNO2.
I
225–670
459
1
67.56 (67.97)
32.44 (32.03) Loss of 3H2O, C37H45N3Cl3 and 1/2 O21 1/2Ce2O3+20C
II
20–80
215–365
365–545
36
353
502
1
1
1
13.97 (13.96)
17.50 (17.55)
37.91 (38.23)
Loss of 5H2O, Cl2 and 2CO2.
Loss of 2H2O and C18H15NO2.
30.62 (30.26) Loss of C33H45Cl2N3O8.
ThO2+23C
III
a (n) is number of decomposition steps.
Table 5. Kinetic parameters using the Coats–Redfern (CR) and Horowitz–Metzger (HM) equations for Indo complexes
Parameter
r
E*, J mol−1
A, s–1
ΔS*, J mol−1 K−1 ΔH*, J mol−1 ΔG* J mol−1
Comp. no. Stage Method
4
1
3
CR
HM
0.9959
0.9987
I
1.47×105
1.75×105
1.59×105
1.69×105
2.93×105
3.10×105
7.10×106
2.82×108
1.68×109
1.15×1010
9.27×1017
1.21×1019
–1.23×102
–9.20×101
–7.58×101
–5.98×101
–9.11×101
–1.12×102
1.40×105
1.68×105
1.53×105
1.63×105
2.86×105
3.03×105
2.46×105
2.47×105
2.08×105
2.07×105
2.16×105
2.16×105
CR
HM
0.9983
0.9950
II
III
CR
HM
0.9963
0.9965
in one step. This step proceeds at 225–670°C and
corresponds to the loss of 3H2O, C37H45N3Cl3 and
1/2O2 molecules, representing a weight loss of 67.56%
(calculated 67.97%). The final residue at the end of
this stage is 1/2Ce2O3 and 20C. From the correspond-
ing DTG curve, only one peak is seen at 459°C.
Kinetic studies for Cd(II), Ce(III), and Th(IV)
complexes of IndoH. In the present investigation, the
general thermal behaviour of the Indo complexes in
terms of stability ranges, peak temperatures and values
of kinetic parameters [31, 32], are listed in Table 5 and
shown in Figs. 9a (HM equation) and 9b (CR equation).
The thermodynamic data obtained with the two
methods are in harmony with each other. The
activation energies values of the Indo complexes
reflect the thermal stability of the studied complexes.
The thermograms and the calculated thermal
parameters for the complexes show that the stability of
these complexes depends on the nature of the central
metal ion. It can be seen from the curves that the
thermal stability of Th(IV) complex is higher than that
for the corresponding Ce(III) and Cd(II) complexes
with the same ligand. The thermal stability of the metal
complexes was found to increase periodically with
increase in atomic number of the metal and the larger
value of charge/radius ratio [33].
[Th(Indo)4(H2O)2]·5H2O (III). The [Th(Indo)4(H2O)2]·
5H2O complex decomposes in three steps
(Fig. 8). The first step occurs at 20–80°C and
corresponds to the loss of 5H2O, Cl2 and 2CO2
molecules and representing a weight loss of 13.97%
(calculated 13.96%). The second step occurs within the
temperature range of 215–365°C, corresponding to the
loss of 2H2O and C18H15NO2 fragment. Observed
weight loss associated with this stage is 17.50%
(calculated 17.55%). The third step takes place within
the temperature range 365–545°C and can be assigned
to the loss of C33H45Cl2N3O8 molecule as CO, CO2,
NO, …, etc., gases and the mass loss due to this step
was 37.91% (calculated 38.23%). The final residue at
the end of this stage is ThO2 and 23C. From the
corresponding DTG curve, three peaks are noted. The
first maximum is at 36°C, second and third peaks are
found at 353 and 502°C, respectively.
The correlation coefficients of the Arrhenius plots
of the thermal decomposition steps were found to lie in
the range 0.9950 to 0.9987, showing a good fit with
linear function. It is clear that the thermal
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SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION
2485
(b)
(a)
0.00123 0.00126 0.00129 0.00132 0.00135 0.00138
–60
–40
–20
0
20
40
1000/T, K–1
θ, K
Fig. 9. Kinetic data curves for Th(IV) complex III. (a) HM equation and (b) CR equation.
Fig. 10. Biological activity of Indo complexes.
decomposition process of all Indo complexes is non-
spontaneous, i.e., the complexes are thermally stable.
have high activity against bacteria, especially Gram+
and two kinds of fungi, where the Th(IV) complex is
more active than the Ce(III) and Cd(II) complexes
against Aspergllus niger. The data are shown in
Fig. 10.
Microbiological investigation of IndoH com-
plexes. Obtained complexes were tested for anti-
bacterial activities against Gram– (E. coli and
Pseudomonas aeruginosa), Gram+ (Bacillus subtilis
and Bacillus cereus) and antifungal such as Aspergillus
niger and Aspergillus flavus organisms. Commercial
DMSO was used to dissolve the tested samples.
Concentration of each solution was 1.0×10–3 mol/L.
The antimicrobial activity was estimated based on the
size of inhibition zone. The complexes were found to
Structure of IndoH complexes. The structures of
the complexes of Indo with Cd(II), Ce(III), and Th(IV)
ions have been confirmed by the elemental analyses,
IR, molar conductance, UV-Vis and thermal analysis
data. Thus, from the IR spectra, it is concluded that
IndoH behaves as a monobasic monodentate ligand
coordinated to the metal ions via the deprotonated
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2486
MOAMEN S. REFAT et al.
Fig. 11. Structure of Th(IV) complex III.
9. Nolan, K.B. and Soudi, A.A., Inorg. Chim. Acta, 1995,
vol. 230, p. 209.
10. Muller, J.G. and Burrows, C.J., Inorg. Chim. Acta,
1998, vol. 275, p. 314.
11. Underhill, A.E., Bougourd, S.A., Flugge, M.L., Gale, S.E.,
and Gomm, P.S., J. Inorg. Biochem., 1993, vol. 52,
p. 139.
carboxylate O atom. From the molar conductance data,
it is found that the complexes are non-electrolytes.
Because of the above observations, tetrahedral and
octahedral geometries are suggested for the
investigated complexes. As an example, the proposed
structure of Th(IV) complex III is shown in Fig. 11.
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