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Patel et al RJLBPCS 2019 www.rjlbpcs.com Life Science Informatics Publications
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Original Research Article DOI: 10.26479/2019.0503.01
RARE EARTH METAL COMPLEXES WITH SCHIFF BASE LIGAND:
SYNTHESIS, CHARACTERIZATION AND BIOCHEMICAL EVALUATION
Hitesh Patel1*, L. S. Bhutadiya1, Jabali J.Vora2, Toral H. Yadav1
1. Chemistry Department Sheth M. N. Science College, Patan, Gujarat, India.
2. Department of Chemistry, Hem. North Gujarat University, Patan, Gujarat, India.
ABSTRACT: The lanthanide ions are having the distinctive qualities like lanthanide contraction,
magnetic properties, etc. The product of lanthanide ions with N-salicylaldehyde-anthranilic acid
(NSAA) ligand to form coordination compounds is an important area of current research. N-
salicylaldehyde-anthranilic acid (NSAA) has massive biological importance like anti-Alzheimer
and antiulcer activity[1-3]. Synthesized complexes were characterized by IR spectroscopy,
elemental analysis, TGA, mass spectrometry, electronic spectra, magnetic susceptibility, and molar
conductance. On the basis of analytical data, the stoichiometry of metal to ligand in complexes is
found as 1:2 combination of metal and Schiff base ligand. The bioactivity of the prepared complexes
has been examined with antibacterial activity.
KEYWORDS: complexes of lanthanide ions, Schiff base, antibacterial activity, catalysis.
Corresponding Author: Hitesh Patel*
Chemistry Department Sheth M. N. Science College, Patan, Gujarat, India.
1.INTRODUCTION
The chemistry of Schiff base is in an important zone of research with increasing interest due to their
simple formation, versatility, the diverse range of medicinal application of their metal complexes
e.g. anticancer, as anti-bactericidal agents, antiviral agent and other biological properties. Also, they
find uses in polymers and dyes, agriculture [4-6]. A Schiff base is a nitrogen analogue of an aldehyde
or ketone in which the C=O group is replaced by C=N-R group. It is normally formation by
condensation of an aldehyde or ketone with primary amine [7-8]. The inner transition metals and
transition metals are known to form Schiff base complexes [9]. The lanthanide elements recently
found to possess a wide range of coordination numbers and geometries [10]. Rare earth’s
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coordination compounds are most crucial in cancer diagnosis and cure. It may be due to the
paramagnetic properties of lanthanides and their complexes. These compounds are generally used
in medicine as a difference media for MRI [11-12].
2. MATERIALS AND METHODS
All the chemicals used for whole work were of analyticalgrade. Salicylaldehyde, anthranilic
acid, ethanol were used for preparation of Schiff base. 0.3M perchloric acid, 0.1M perchlorate
were prepared from 70% perchloric acid and M(III) ions in aqueous solution.
Synthesis of Schiff base ligand
N-salicylaldehydeanthranilic acid was synthesized by adding equal volumes of 0.04 mol ethanolic
solution of salicylaldehyde to a solution of 0.04 mol ethanolic solution of anthranilic acid and the
mixture was stirred for 3hrs. The solution was concentered and orange coloured Schiff base of N-
salicylaldehyde-anthranilic acid was generated. The precipitated Schiff base was filtered and
recrystallized twice from alcohol, M.P 205 0C.
Table 01: physical data of ligand
Figure 01: Ligand structure(NSAA)
Preparation of Complexes
The formation of complexes was carried out by the mixing of 60 ml of 0.1M metal perchlorate
solution and 60 ml 0.1M ligand solution in 50% ethanol-water. The mole ratio of ligand and metal
was (1:1). The reaction mixture was refluxed for 2 to 3 hrs at 90-100 0C. Then after some time the
mixture was cooled and complex slowly precipitated. The pH of the above solution was raised up
to 5.5 using 0.1M NaOH solution and the precipitated complex was filtered and washed with hot
alcohol and dried at room temperature.
3. RESULTS AND DISCUSSION
Analysis and Physical Measurement
M.P. and TLC (Solvent toluene: methanol 7:3) were taken in usual method. TLC indicated single
spot so confirming the complex formation. The UV visible spectrum measured by Shimadzu UV-
1800 UV-VIS spectrophotometer (double beam) in the range of 200 nm to 800 nm using DMF
solvent. Elemental analysis was performed with a ThermoFinnigan FLASH EA 1112 Series CHN
analyzer. The metal percentage was determined with EDTA back titration method. Magnetic
susceptibility was determined by Gouy’s method with utilizing Hg[Co(NCS)4] as a calibrant on
About NSAA ligand
Mol. Formula: C14H11NO3
Formula Wt.: 241.242 g/mol
Color: Orange
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Polytronic electromagnet HEM-100. The FTIR of all compounds were obtained in the range of
4000-400 cm-1using KBr pellets on a Shimadzu IR Affinity 1 S spectrophotometer. T.G.A/D.S.C
measured by Perkin-Elmer Diamond Thermogravimetric/Differential Thermal Analyzer.
The molar conductance value suggested non-electrolytic nature. Although, a high degree of
dissociation of complexes was inferred from molar conductance values.
Results of Physical Measurements
Table02: Analytical Data and Some Physical Properties of the Ligand and Metal Complexes
Complex Colour
Formul
a weight
Gm/mol
M.P.
(C)
Magn
Sus.
(BM)
R.F
value
Molar
Conductance
S cm2 mol-1
Elemental Analysis
Found
(calc) %
C H N M
Ligand
NSAA
Orange 241.24 205 - 0.61 -
68.07
(69.70)
4.765
(4.59)
5.79
(5.80)
-
La-
NSAA
Light
orange
691 >300
Dia
Magn
etic
0.57 23.67
49.30
(48.71)
3.98
(3.94)
4.09
(4.06)
19.44
(20.12)
Ce-
NSAA
Red
Orange
709
>300 2.39 0.53 27.45
50.94
(47.39)
4.06
(4.12)
4.39
(3.95)
18.21
(19.74)
Pr- NSAA
Yellow
Orange
729 >300 3.46 0.50 37.61
47.33
(46.17)
3.78
(4.29)
3.84
(3.85)
18.31
(19.34)
Infrared Spectroscopy
The IR spectra of the Schiff base and Ln(III) complexes are given in table 03. The IR spectra of
Ln(III) complexes show the ligand characteristic bands with the proper shifts due to complex
formation and spectra of all complexes are discussed as below. The IR band at 1618 cm-1 of the free
Schiff base ligand is present due to the azomethine group in complexation This band is shifted to
lower wave number in complexes. In NSAA the signal at 3470 cm-1 was from the stretching
vibration of phenolic –OH [13]group but in metal complexes the phenolic –OH frequency vanishes,
it confirmed that the oxygen atom of phenolic group is making complexes with metals. In NSAA
carboxylic group showed 2954 cm-1,1686 cm-1,1292 cm-1bands for respectively –OH group, C=O
group and C-O group [14-15]. In complexation, all of these signals are shifted to lower wave number.
The stretching vibration bands of 3475 to 3579 cm-1 assigned for coordinated H2O in La-NSAA to
Pr-NSAA respectively. Some new frequencies emerge in metal complexes in the favour of M-N and
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M-O, for La-NSAA it shows at 622.90, 577.55 cm-1, for Ce-NSAA 623.01, 575, 553.57 cm-1, for
Pr-NSAA 626.87, 559.36 cm-1 [16-17].
Table 03: IR spectra of ligand and complexes
Compound
ν(̶ C=N)
Str.
(cm-1)
Phenolic
vH2O
(cm-1)
COOH
ν(M ̶ O)
(cm-1)
ν(M ̶ N)
(cm-1)
ν(O ̶ H)
Str.
(cm-1)
ν(C ̶ O)
Str.
(cm-1)
ν(O ̶ H)
Str.
(cm-1)
ν(C=O)
Str.
(cm-1)
ν(C ̶ O)
Str.
(cm-1)
Ligand 1618
3470
1246 - 2954
1686
1292 - -
La-NSAA 1613.8 -
1228
3475 2947 1633 1277.70 577.55 622.90
Ce- NSAA 1614.42 - 1232.51 3500 2837
1660
1276 575,
553.57 623.01
Pr-NSAA 1597 - 1232 3579 2951 1608 1276 559.36 626.87
Mass Spectra
Table 04: Mass spectra of ligand and complexes
Compound Possible Fragments m/z value
Calculated Found
NSAA
C14H11NO3
C13H10NO
C7H5NO2
241.24
196.22
135.12
241.8
195.9
136.8
La-NSAA
C28H21N2O7La
C14H13NO5La
C7H5NO2
636.38
414.16
135.12
637.3
412.1
136.26
Ce-NSAA C7H7NO2Ce
C7H5NO2
277.25
135.12
282.1
136.06
Pr-NSAA C14H19NO8Pr
C7H5NO2
470.21
135.12
468.2
137.10
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Figure 02: ligand mass spectra
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Figure 03: La-NSAA Mass spectrum
Figure 04: Ce-NSAA Mass spectrum
Figure 05: Pr-NSAA Mass spectrum
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Magnetic Moments
Gouy’s method used for measurement of the magnetic moments. At room temperature magnetic
moment for solid complexes of La3+, Ce3+, Pr3+, respectively 0 BM, 2.39 BM, 3.46 BM. This
suggests that 0,1 and 2 unpair electron for La(III), Ce(III) and Pr(III) ions respectively, considering
spin-orbit coupling [18-20].
Electronic Spectral Study
Lanthanum (III) hаѕnо significant absorption in thе visible region, duеtоthе absence оf 4f orbital
electrons. The absorption spectra of lanthanide complexes show presence due to laporte forbidden
f-f transitions. 4f orbitals of lanthanide metals are deep-seated therefore not exposed to surrounding
ligands. Ce(III) exhibits broad bands due to L→Mcharge transfer transitions [21-22].
Table 05: Electronic spectra of ligand and complexes
Compounds Λmax Cm-1 Band assignments
NSAA
332.5
263
204
30075.18
38022.81
49019.60
n→π*
π→π*
π→π*
La-NSAA
333
281.5
258
230
211
30030.03
35523.97
38759.68
43478.26
47281.32
Ligand and C.T.
transitions
Ce-NSAA 330
245
30303.03
40816.32
2F5/2→2D3/2
2F5/2 →5D5/2
Pr-NSAA 327.5
219.5
30534.35
45558.08
3H4→3P2
3H4→1S0
Figure 06: Electronic spectra of ligand and complexes
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Thermal analysis
It is observed that at 150 0Ctemperature in La-NSAA complex 50.23 gm weight loss per mole
occurred, which implies that two H2O molecules of crystallization with La-NSAA is present and at
250 0C temperature 35.56 gm weight loss per mole occurred which implies that two H2O molecules
coordinate with La-NSAA. Thermogravimetric analysis for 1 mole of Ce-NSAA at 150 0C
temperature 20.35 gm weight loss per mole occurred which implies there is one water molecule of
crystallization and at 250 0C temperature 79.40 gm weight loss per mole occurred which implies
that four H2O molecules coordinate with Ce-NSAA. For Pr-NSAA at 150 0C 41.9 gm weight loss
per mole occurred which implies that two H2O molecules of crystallization and at 250 0C
temperature 63.42 gm weight loss per mole occurred which implies that three H2O molecules
coordinate with Pr-NSAA. Nikolaev et al thought-about water eliminated below 150°C as lattice
water and higher than 150°C as coordinated water to the metal ions [23-24].
Table 06: Thermogravimetric Analysis
Complexes RT-150 0C
Water of crystallization
150 0C-250 0C
Water of coordination
% Loss Loss of
Weight
Water
molecules % Loss
Loss of
Weight
Water
molecules
La-NSAA 7.27 50.23 2 5.02 35.56 2
Ce-NSAA 2.80 20.35 1 11.2 79.40 4
Pr-NSAA 5.9 41.9 2 8.92 63.42 3
RT= Room Temperature
Figure 07: TGA of complexes
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Based upon TGA the results complexes coordination number
Table 07: Complexes and Coordination Numbers*
Complexes
Coordination number
of metal in the suggested
structures
Usual coordination number *
of metal ion
La-NSAA 08 4,8-11
Ce-NSAA 10 9,10,12
Pr-NSAA 09 6,9,12
*See reference no [25-26]
As the above results of physicochemical analyses, their probable structures are shown in figures
below.
OH2OH2
O OH
N
O-
O O-
N
O-
La3+
OH2 2
Figure 08: Possible STRUCTURE of La-NSAA complex
Figure 09: Possible STRUCTURE of Ce-NSAA complex
OH2
OH2
OH2
OH2
O OH
N
O-
O O-
N
O-
Ce3+
OH2
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Figure 10: Possible STRUCTURE of Pr-NSAA complex
Catalysis of an organic reaction
A mixture of furan (1.5 ml) and maleic acid (2.32 gm) in water (15 ml) was stirred for 3 hours at
room temperature the solid colorless compound synthesized, was filtered and washed with water,
dried and recrystallized with MeOH. M.P 138-140oC. yield 2.67 gm (72.7 %). This is a standard
organic reaction [27-28] which on carrying out for 3hrs and results in in72.7 % yield. The same
reaction was carried out for 2 hrs. The 2.07 gm (56.49 %) yield found.the same reaction was carried
out using 1mol % catalytic amount of complexes, % yield and % increases in yield of the reaction
are indicated in table no.08.
Figure 11: Dies-Alder reaction
Table 08:% Yield of Organic reaction
Temperature
Time
% yield
Standard
reaction
% yield
with
ligand
La-NSAA
% yield
with
ligand
Ce-NSAA
% yield
with
ligand
Pr-NSAA
% yield
increase
with La-
NSAA
% yield
increase
with Ce-
NSAA
% yield
increase
with Pr-
NSAA
Room temp.
(25 0C)
2 hrs.
56.25% 58.42% 61.68% 62.77% 3.86% 9.66% 11.59%
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Kinetics study
Table 09:Reaction rate with Ln-NSAA and without Ln-NSAA
Reaction KBrO3 + KI + HCl K2S2O8 + KI H2O2 + KI+H2SO4
k without metal
complex 2.28 x 10-4 3.00 x 10-5 3.91 x 10-4
k with La-NSAA 4.99 x 10-4 3.56 x 10-5 3.84 x 10-4
k with Ce-NSAA 3.05 x 10-4 3.15 x 10-5 5.75 x 10-4
k with Pr-NSAA 4.18 x 10-4 3.05 x 10-5 3.00 x 10-4
% Increase in
reaction rate at 305 k
temp. La-NSAA
119.0 % 18.7 % -1.9 %
% Increase in
reaction rate at 305 k
temp. Ce-NSAA
33.8 % 5.0 % 47.0 %
% Increase in
reaction rate at 305 k
temp. Pr-NSAA
83.3 % 1.7 % -23.4 %
Where, k indicates the rate of reaction, Negative sign indicates decrease in reaction rate
The catalytic study shows that metal complexes of La, Ce and Pr were found to increase the rate of
reaction between potassium bromate and potassium iodide while the complex of La exhibited the
good enhancement in the reaction rate between the reaction of potassium persulphate and potassium
iodide. In the reaction between hydrogen peroxide and potassium iodide, Ce-complex was found to
increase the reaction rate while other two complexes were found to reduce the rate of reaction.
Overall the La-complex was able to act as a good catalyst and impressively catalyzed the redox
reaction of potassium bromate and potassium persulphate with potassium iodide respectively and
between the reaction of hydrogen peroxide and potassium iodide, Ce-complex was found as a good
catalyst compared with Pr and La complexes.
Activation energy determination by Broido method
Broido method can be applied to TGA data to estimate activation energy as well as other kinetic
parameters [29-30]. The equation of Broido method is as follows:
𝑙𝑛𝑙𝑛 (1
𝑦) = − (
𝐸𝑎
𝑅) (
1
𝑇) + 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
Where, y denotes the fraction of number of initial molecules not yet decomposed. Slope of plot
lnln(1/y) vs. 1000/K related with activation energy as follow:
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Activation energy (Ea) = -2.303 x R x slope
Where, R = gas constant
Activation energy evaluated for thermal decomposition of complexes are shown in table :10
Table 10: Activation energy of complexes
Complexes Temp. range Activation energy
La-NSAA 43°C to 128°C 74.05 kJ·mol-1
Ce-NSAA 57°C to 127°C 28.50kJ·mol-1
Pr-NSAA 36°C to 96°C 93.61kJ·mol-1
Figure 12: Graph of ln[ln(1/y)] vs 1000/T for complexes
The activation energy of thermal degradation of La-NSAA, Ce-NSAA, and Pr-NSAA were found
to be 74.05 kJ mol-1, 28.50 kJ mol-1, and 93.61 kJ mol-1respectively.
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Antibacterial activity
Table 11:Results of antibacterial activity of ligand and its metal complexes
Sr.
no
Bacterial species μg/ml NSAA La-
NSAA
Ce-
NSAA
Pr-
NSAA
Ciprofloxacin
1 B. subtilis
(G+)
100 μg/ml + + + + ++++
200 μg/ml + +++ ++ ++ ++++
300 μg/ml + +++ +++ +++ ++++
400 μg/ml ++ ++++ ++++ +++ ++++
2 Staphylococcus
Aureus
(G+)
100 μg/ml + ++ + + ++++
200 μg/ml + +++ + ++ ++++
300 μg/ml + ++++ ++ +++ ++++
400 μg/ml ++ ++++ ++ ++++ ++++
3 E. coli
(G-)
100 μg/ml - + - + ++++
200 μg/ml - ++ - ++ ++++
300 μg/ml + ++ + ++ ++++
400 μg/ml + +++ + +++ ++++
4 P. aeruginosa
(G-)
100 μg/ml - + - - ++++
200 μg/ml - ++ + + ++++
300 μg/ml + +++ + + ++++
400 μg/ml + ++++ ++ ++ ++++
++++ indicates 26 to 30 mm, +++ indicates 21 to 25 mm, ++ indicates 16 to 20 mm, + indicates 11
to 15 mm, – indicates no zone
The ligand is moderately active and the complexes are more active as antibacterial[31]. Ligand-
NSAA is more active against Gram’s positive bacteria as compared to Gram’s negative bacteria.
Mostly all the lanthanide complexes were found to exhibit antibacterial activities against four
bacterial species (two Gram’s positive and two Gram’s negative) with concentration ranging from
100 to 400 µg/mL as shown in the table 07. Gram’s positive Bacillus subtilis was the most affected
bacterial species followed by Staphylococcus aureus. The activity increases with increase in
concentration of complexes. The complex La- NSAA was the most effective inhibitor against all
the four bacteria followed by Ce-NSAA, Pr-NSAA.Ligand–NSAA at all its concentrations shows
inhibitory effect on Gram’s positive bacteria: Bacillus Subtilis and Staphylococcus Aureus, but at
100 and 200 µg/mL concentrations, it could not exhibit any inhibitory effect onGram’s negative
bacteria: Escherichia Coli and Pseudomonas Aeruginosa. At 400 µg/mL concentration, all the
complexes were less active compared to Ciprofloxacin. Ce- NSAA is the only one complex which
did not demonstrate any inhibitory effect againstEscherichia Coli at 100 and 200 µg/mL
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concentrations. Whereas at 100 µg/ml concentration, Ce- NSAA and Pr- NSAA both did not show
any inhibitory activity against Pseudomonas aeruginosa.In general, all the complexes were able
to inhibit Gram’s positive bacteria and not Gram’s negative one.
4. CONCLUSION
Inner Transition metal complexes of La(III), Ce(III) and Pr(III) with Schiff base derived from
anthranilic acid and salicylaldehyde have been synthesized from their corresponding
metal perchlorate and characterized. The structure of the Schiff base and metal
complexes are determined with the assistance of elemental analysis, IR, Uv-visible spectra,
mass spectrometry, molar conductance, magnetic moment and thermal analysis. The catalytic
effect of complexes on Dies-Alder reaction has been also studied. Kinetic study on three well-
known redox reactions, La-NSAA was found to increase the rate of reaction of potassium
bromate and potassium iodide. The activation energy for thermal decomposition was calculated
from TGA data by Broido method. The higher activation energy indicating complexes have
good thermal stability and ability to pass on energy consequently good catalysis ability. Schiff
base and every complex were screened for antibacterial activity against Bacillus subtilis,
Staphylococcus Aureus, Escherichia coli, Pseudomonas aeruginosa Victimization
ciprofloxacin antibiotic drug as standards. It had been shown that La, Ce and Pr complexes
show increased antimicrobial activity than Schiff base.
CONFLICT OF INTEREST
The authors have declared that they have no conflict of interest.
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