Coordination chemistry of rare earth metal complexes with coumarin-based imines: Ecofriendly synthesis, characterization, antimicrobial, DNA cleavage, pesticidal, and nematicidal activity evaluations

Article abstract of DOI:10.1080/00958972.2011.649265

Coordination and biocidal aspects of lanthanide(III) complexes with 3-formyl-4-chlorocoumarin hydrazinecarbothioamide (L¹H) and 3-formyl-4-chlorocoumarin hydrazinecarboxamide (L²H) are described with the support of elemental analyses, molecular weight, melting point, and molar conductance determinations along with the IR, ¹H NMR, EPR, UV spectral, and X-ray powder diffraction studies. The spectral data suggest that the ligands are monobasic bidentate, coordinating through nitrogen and sulfur/oxygen. The isolated products are colored solids, soluble in DMSO, DMF, and methanol. All the complexes are monomeric, as indicated by their molecular weight determinations. Conductivity measurements in dry DMF show them to be non-electrolytes. The antimicrobial, DNA cleavage, pesticidal, and nematicidal activities were examined and are discussed. Copyright

Full text of DOI:10.1080/00958972.2011.649265

This article was downloaded by: [York University Libraries]
On: 12 August 2014, At: 05:48
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Coordination chemistry of rare earth
metal complexes with coumarin-
based imines: ecofriendly synthesis,
characterization, antimicrobial, DNA
cleavage, pesticidal, and nematicidal
activity evaluations
a
a
a
Puja Kapoor , R.V. Singh & Nighat Fahmi
a
Department of Chemistry , University of Rajasthan , Jaipur ,
Rajasthan , India
Published online: 20 Jan 2012.
To cite this article: Puja Kapoor , R.V. Singh & Nighat Fahmi (2012) Coordination chemistry of
rare earth metal complexes with coumarin-based imines: ecofriendly synthesis, characterization,
antimicrobial, DNA cleavage, pesticidal, and nematicidal activity evaluations, Journal of
Coordination Chemistry, 65:2, 262-277, DOI: 10.1080/00958972.2011.649265
To link to this article: http://dx.doi.org/10.1080/00958972.2011.649265
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry
Vol. 65, No. 2, 20 January 2012, 262–277
Coordination chemistry of rare earth metal complexes with
coumarin-based imines: ecofriendly synthesis, characterization,
antimicrobial, DNA cleavage, pesticidal, and nematicidal
activity evaluations
PUJA KAPOOR, R.V. SINGH and NIGHAT FAHMI*
Department of Chemistry, University of Rajasthan, Jaipur, Rajasthan, India
(
Received 20 April 2011; in final form 28 November 2011)
Coordination and biocidal aspects of lanthanide(III) complexes with 3-formyl-4-chlorocou-
marin hydrazinecarbothioamide (L H) and 3-formyl-4-chlorocoumarin hydrazinecarboxamide
1
2
L H) are described with the support of elemental analyses, molecular weight, melting point,
(
1
and molar conductance determinations along with the IR, H NMR, EPR, UV spectral, and
X-ray powder diffraction studies. The spectral data suggest that the ligands are monobasic
bidentate, coordinating through nitrogen and sulfur/oxygen. The isolated products are colored
solids, soluble in DMSO, DMF, and methanol. All the complexes are monomeric, as indicated
by their molecular weight determinations. Conductivity measurements in dry DMF show them
to be non-electrolytes. The antimicrobial, DNA cleavage, pesticidal, and nematicidal activities
were examined and are discussed.
Keywords: 3-Formyl-4-chlorocoumarin
hydrazinecarbothioamide;
3-Formyl-4-
chlorocoumarin hydrazinecarboxamide; DNA cleavage activity; Pesticidal and nematicidal
activities
1. Introduction
The expanding development in the chemistry of coordination compounds is due to their
applications in agriculture and medicine. Coordination complexes of sulfur and nitrogen
donors have been widely investigated and show novel structural features [1], unusual
spectral and catalytic properties [2], and relevance to biological systems [3]. Schiff
base metal complexes act as active nematicidal agents [4]. Metal complexes of
thiosemicarbazones and semicarbazones have aroused interest in industrial and
biological applications [5]. Schiff bases derived from coumarin and its metal complexes
exhibit antibacterial, antifungal, anticoagulation, and plant growth regulating activi-
ties [6–8]. 4-Hydroxycoumarin derivatives exhibit an inclination for complexation [9–14]
with transition and rare earth complexes of hydroxycoumarin derivatives of increasing
interest in bioinorganic and coordination chemistry. Applications of trivalent lanthanide
complexes as contrast agents for Nuclear Magnetic Resonance (NMR) imaging [15],
*
Corresponding author. Email: nighat.fahmi@gmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.649265

Rare earth coumarin complexes
263
stains for fluorescence imaging [16], responsive luminescent systems [17], catalysts for
specific cleavage of RNA hydrolysis [18], or as active agents in cancer radiotherapy [19]
have prompted considerable interest in lanthanide coordination chemistry [20]. This
study deals with synthesis, characterization, and biological evaluation of lanthanide(III)
complexes of coumarin-based ligands. Emphasis has been put on biological evaluation of
the complexes.
2. Experimental
All the chemicals were of reagent grade, and the solvents of analytical grade were
distilled from appropriate drying agents immediately prior to use. 4-Hydroxycoumarin,
samarium(III), and neodymium(III) salts were purchased from Alfa Aesar.
Gadolinium(III) salt was procured from Sigma Aldrich. The metal chlorides used
were in hydrated form. Molecular weight determinations were carried out by the Rast
Camphor method [21]. Sulfur, chlorine, and nitrogen were estimated by Messenger’s
[
22], Volhard’s and Kjeldahl’s [22] methods, respectively. Metal contents were estimated
complexometrically with EDTA using Erichrome Black T as an indicator. Melting
points were determined by using capillaries in an electrical melting point apparatus. The
ꢀ3
ꢀ3
conductivity values measured on 10 mol dm solution in DMF at room temperature
on a Century Digital Conductivity Meter model CC601. Magnetic moment measure-
ments were taken on a model 155 vibrating sample magnetometer. Infrared (IR) spectra
of the ligands and their complexes were recorded on a Nicolet Magna FTIR-550
1
spectrophotometer as KBr pellets. H NMR spectra were recorded on a JEOL-AL-300
FT NMR spectrometer in DMSO-d using TMS as the internal standard. Electron
6
Paramagnetic Resonance (EPR) spectra of the complexes were monitored on a Varian
Make E Line Century X-band EPR spectrometer (Model E-112). The electronic spectra
were recorded on a Varian–Cary/5E spectrophotometer.
2
2
.1. Preparation of the ligands
.1.1. Synthesis of 3-formyl-4-chlorocoumarin. 3-Formyl-4-chlorocoumarin is
prepared as described [23]. Phosphorus oxychloride (10 mL) was added dropwise to a
ꢁ
solution of DMF (20 mL) keeping the temperature below 50 C. Solution of
4
-hydroxycoumarin (4.0 g) in DMF (10 mL) was then gradually added to the mixture
ꢁ
with constant stirring and temperature was maintened below 5 C. The reaction mixture
was then allowed to stand at room temperature for 2 h and heated on a steam bath for
1
with sodium carbonate. A solid product was immediately formed and was crystallized
h. After cooling, the reaction mixture was poured onto crushed ice and neutralized
ꢁ
from ethanol to give a yellow solid, m.p. 115 C, yield 3.2 g; 80%.
2
.1.2. Microwave-assisted synthesis. The ligands were prepared by the condensation
of 3-formyl-4-chlorocoumarin (2.68 g, 0.01 mol) with thiosemicarbazide (1.55 g,
.01 mol) or semicarbazide hydrochloride (1.90 g, 0.01 mol) in the presence of sodium
acetate. The reaction mixture was irradiated using 2–3 mL solvent. The reactions were
0

2
64
P. Kapoor et al.
Table 1. Analytical data and physical properties of the ligands and their complexes.
Found (Calcd) (%)
Melting
Mol. Wt.
Found
(Calcd)
ꢀ
eff
(B.M)
ꢁ
Compound
Color
Yellow
point ( C)
N
Cl
S
Ln
1
2
3
4
5
6
7
8
127
133
14.72
14.92)
15.56
15.82)
11.96
12.11)
11.95
12.05)
11.45
11.97)
12.54
12.70)
12.52
12.75)
12.45
12.54)
12.04
(12.58)
13.02
11.12
(11.38)
–
–
–
–
278.15
(281.71)
261.32
(
(
(
(
(
(
(
(
White
–
(13.35)
10.04
(10.22)
10.16
(10.71)
9.85
(10.10)
10.63
(10.72)
10.74
(10.76)
10.48
(10.58)
(265.65)
1031.430
(1040.419)
1034.251
(1046.539)
1037.269
(1053.429)
976.655
(992.224)
965.573
(998.344)
993.021
(1005.234)
Wine red
Brown
205(d)
218
9.08
(9.24)
9.85
(10.20)
9.11
13.15
(13.86)
14.03
(14.37)
14.33
(14.93)
14.02
(14.54)
15.05
3.62
1.63
7.98
3.51
1.52
7.90
Orange
Green
225
(9.13)
–
195(d)
228(d)
237
Cream
–
–
(15.21)
156.15
(15.64)
Light green
O
O
O
O
O
O
X
EtOH
X
POCl 3 /DMF
+
H2N
–
H O
N
N
NH2
2
N
NH2
CHO
H
X=O/S
H
OH
Cl
H
Cl
Figure 1. Synthetic scheme of the ligands.
completed in 5–6 min. After completion, the reaction was cooled to afford a solid
product, which was recrystallized in alcohol, characterized and analyzed before use.
Elemental analyses (N and S) were conducted using the methods mentioned above and
their results were found to be in good agreement with the calculated values (table 1).
The systematic scheme for preparation of the ligands is shown in figure 1.
2
.1.3. Conventional thermal method. For comparison, the above ligands were also
synthesized by thermal methods. In this method, instead of a few drops of ethanol,
00 mL of ethanol was used to dissolve the starting materials of the ligands and the
1
contents were refluxed for 3.5–4 h. The residue formed was separated out, filtered off,
washed with water, recrystallized from ethanol, and finally dried in vacuum over fused
calcium chloride. A comparison between the thermal method and microwave method is
given in table 2.
2
.2. Synthesis of the sodium salt of the ligands
Sodium metal and the ligand were dissolved in minimum of methanol separately.
Ultimately, these two solutions had been dissolved to prepare sodium salt of the ligand.
In this process the sodium metal first reacts with methanol and forms sodium methoxide.

Rare earth coumarin complexes
265
Table 2. Comparison between microwave and thermal method.
Yield (%)
Solvent (mL)
Time
Sl.
No.
Thermal
(h)
Microwave
(min)
Compound
Thermal
Microwave
Thermal
Microwave
1
L H
1
2
3
4
5
6
7
8
85
84
70
72
74
73
78
75
92
90
82
86
82
85
84
83
100
100
35
40
45
40
35
45
3
2
3
4
3.5
4
13
14
14.5
13.5
15
5
6
8
5
6
5
5.5
6
2
L H
1
Nd(L )
3
3
3
3
3
3
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
2
2
2
2
2
2
O
O
O
O
O
O
1
Sm(L )
1
Gd(L )
2
2
Nd(L )
3.5
2.5
3
2
Sm(L )
2
Gd(L )
16
This sodium methoxide in the next step reacts with the ligand and replaces acidic proton
from the enolic form of the ligand with the sodium metal and forms sodium salt of the
particular ligand.
2
2
.3. Preparation of the metal complexes
.3.1. Microwave-assisted synthesis. In microwave-assisted synthesis, the complexes
were prepared by irradiating the reaction mixture of LnCl ꢂ 6H O (0.01 mol) and the
3
2
respective sodium salt of the ligands (0.03 mol) in 1 : 3 molar ratios. The products were
recovered and dissolved in a few mL of dry methanol, where the precipitate of sodium
chloride formed during the course of the reaction was removed by filtration and the
filtrate was concentrated under reduced pressure. The resulting compounds were
washed and recrystallized with cyclohexane.
2
.3.2. Thermal method. These complexes were also synthesized by thermal methods
where instead of 5–8 min, reactions were completed in 13–16 h, and the yield of the
products was also less than that obtained by the microwave-assisted synthesis. In this
method, LnCl ꢂ 6H O (0.01 mol) was added with sodium salt of the ligands (0.03 mol)
3
2
in 1 : 3 molar ratios. The resulting mixture was heated under reflux for 13–16 h, the
sodium chloride formed during the course of the reaction was removed by filtration and
the solvent was removed under reduced pressure. The product was dried in vacuum. The
complexes were washed with dry n-hexane and recrystallized with cyclohexane.
2
2
2
.4. Pharmacology
.4.1. Anti-microbial studies
.4.1.1. Antifungal activity. The antifungal activities were evaluated against Candida
albicans, Aspergillus niger, and Fusarium oxysporum using Czapek’s agar medium [24]
having the following composition: glucose 20 g, starch 20 g, agar–agar 20 g, and distilled

2
66
P. Kapoor et al.
water 1000 mL. The requisite amount of the compounds was added to this medium after
being dissolved in methanol so as to obtain three different concentrations (50, 100, and
200 ppm). The medium then was poured into Petri plates, and the spores of fungi were
placed on the medium with the help of an inoculum needle. These Petri plates were
wrapped in polyethene bags containing a few drops of alcohol and were placed in an
ꢁ
incubator at 30 ꢃ 2 C. The controls were also run, and three replicates were used in
each case. The antifungal activity of a common standard flucanazole was also recorded
using the same procedure as above at the same concentrations and solvent. The linear
growth of the fungus was recorded by measuring the diameter of the fungal colony after
9
6 h, and the percentage inhibition was calculated by the following equation:
% Inhibition ¼ ðC ꢀ T Þ100=C
where C and T are the diameters of the fungal colony in the control and the test plates,
respectively.
2.4.1.2. Antibacterial activity. Antibacterial activity was tested against E. coli,
P. aeruginosa, B. subtilis, and S. aureus using the paper disc plate method [24]. Each
compound was dissolved in methanol and solutions of the concentrations (500 and
000 ppm) were prepared separately. Paper discs of Whatman filter paper (No. 42) of
1
uniform diameter (2 cm) were cut and sterilized in an autoclave. The paper discs soaked
in the desired concentration of the complex solutions were placed aseptically in the Petri
dishes containing nutrient agar media (agar 20 g þ beef extract 3 g þ peptone 5 g) seeded
with E. coli and P. aeruginosa bacteria separately. The Petri dishes were incubated at
ꢁ
3
7 C and the inhibition zones were recorded after 24 h of incubation. The antibacterial
activity of a common standard antibiotic Ciprofloxacin was also recorded using the
same procedure as above at the same concentrations and solvent.
2.4.1.3. Determination of minimum inhibitory concentration. Minimum Inhibitory
Concentration (MIC) is the lowest concentration of test agent that inhibited visible
ꢁ
growth of bacteria after 18 h incubation at 37 C. The determination of the MIC
involves a semi quantitative test procedure which gives an approximation to the least
concentration of an antimicrobial needed to prevent microbial growth. The MIC was
determined by liquid dilution method [25]. Stock solutions of Ln(III) complexes with
ꢀ
1
1
0–50 mg mL
were prepared with aqueous methanol. Inoculum of the overnight
culture was prepared. In a series of tubes, 1 mL each of metal complex solutions with
different concentrations was taken and 0.4 mL of the inoculum was added to each tube.
Further, 3.5 mL of the sterile water was added to each of the test tubes. These test tubes
were incubated for 24 h and observed for the presence of turbidity. The absorbance of
the suspension of the inoculum was observed with a spectrophotometer at 555 nm. The
end result of the test was the minimum concentration of antimicrobial (test materials)
which gave a clear solution, i.e., no visual growth [26, 27].
2
.4.2. Pesticidal activity. Adult red flour beetles Tribolium castaneum were used for
the experiment. Rearing of insects was maintained at the storage section of Division of
Entomology, Agricultural Research Institute, Durgapura, Jaipur, in a laboratory for
bioassay. All compounds were weighed and dissolved in methanol to prepare 500, 200,
and 100 ppm solutions. One mL of each concentration of various compounds was

Rare earth coumarin complexes
267
directly poured in each petri plate (90 mm) with the help of a micropipette. Petri plates
with test solution were rotated vigorously to prepare uniform film and allowed to dry
for 3–5 min.
A thin layer was prepared in the petri dishes (10 cm in diameter) using solution after
drying at room temperature. Thirty insects were released in treated Petri dishes. These
ꢁ
were kept in an incubator at a fixed temperature (30 ꢃ 0.5 C). Along with a control,
experiment was replicated thrice. The mortality of these beetles was observed after 96 h.
A simple microscope was used to check natural movement of the pests. The mortality
percentage was calculated by using Abbott’s formula [28]:
P ꢀ P
o
c
Pt ¼
ꢄ 100
1
00 ꢀ Pc
where P ¼ corrected mortality (%), P ¼ observed mortality (%), and P ¼ controlled
t
o
c
mortality (%).
2
.4.3. Nematicidal activity. Nematicidal activity was carried out on Meloidogyne
incognita. Nematode M. incognita is known to attack more than 3000 host plants [29].
The yields of okra, tomato, and brinjal typically suffer 90.9%, 46.2%, and 2.3% losses,
respectively, due to M. incognita. Meloidogyne incognita produces galls on the roots of
many host plants and is responsible for 44.87% yield loss in brinjal. The root-knot
nematode produces galls on the roots of many vegetables, pulses, some fruit crops,
tobacco, and ornamental crops and causes severe losses.
Clean M. incognita eggs were obtained by the reported method [30]. Egg masses were
separated from heavily infected brinjal roots and washed under running water. After
cutting the roots, 1% of sodium hypochlorite solution was added, shaken, and then
sieved through 150 and 400 sieves. Then the eggs of nematode were counted. A total of
1
50 eggs of nematode M. incognita were used per replicate sample and each treatment
ꢁ
was replicated three times. The experiment was conducted at 30 ꢃ 2 C. The eggs were
treated with complexes dissolved in 25, 50, and 100 ppm for 24 h and observations in
relation to hatching of eggs were noted. The nematicidal activity was calculated using
the following formula:
HT
NAð%Þ ¼
ꢄ 100
HC
where N is the nematicidal activity, H is the amount of hatching in the control and
A
C
H is the amount of hatching in the test plate.
T
2
.4.4. DNA cleavage analysis
2
organism was prepared, then autoclaved for 15 min at 121 C and 15 lb pressure. The
.4.4.1. Preparation of culture media. Nutrient broth used for the growth of the
ꢁ
ꢁ
autoclaved media were inoculated with the seed culture and incubated at 37 C for 24 h
on a shaker with 180 rpm.
2.4.4.2. Isolation of DNA. DNA was isolated using the following procedure [31].
Fresh bacterial culture (1.5 mL) was centrifuged to obtain the pellet. The pellet was

2
68
P. Kapoor et al.
ꢀ
1
dissolved in 0.5 mL of lysis buffer (100 mmol L tris pH 8.0, 50 mmol L EDTA,
5
ꢀ1
ꢀ1
ꢁ
0 mmol L lysozyme). 0.5 mL saturated phenol was added and incubated at 55 C for
0 min, then centrifuged at 10,000 rpm for 10 min. To the supernatant, equal volume of
chloroform : isoamyl alcohol (24 : 1) and 1/20th volume of 3 mol L sodium acetate
pH 4.8) was added and again centrifuged at 10,000 rpm for 10 min; 3 volumes of chilled
absolute alcohol were added to the supernatant. The precipitated DNA was separated
1
ꢀ1
(
ꢀ
1
by centrifugation. The pellet was dried and dissolved in TAE buffer (100 mmol L tris
ꢀ
1
pH 8.0 adjusted with glacial acetic acid, 10 mmol L EDTA) and stored in cold.
2.4.4.3. Treatment of DNA with the samples. The compounds (500 ppm) were added
ꢁ
separately to the DNA sample and mixtures were incubated at 37 C for 2 h.
2
.4.4.4. Agarose gel electrophoresis. Following the treatment of DNA samples,
electrophoresis of the samples was done according to the following procedure [31].
00 mg of agarose was weighed and dissolved in 25 mL of TAE buffer (4.84 g Tris base,
2
ꢀ
1
ꢁ
pH 8.0, 0.5 mol L EDTA/1 L) by boiling. When the gel attained ꢅ55 C, it was poured
into the gel cassette fitted with comb. The gel was solidified. The comb was removed
carefully and the gel was placed in the electrophoresis chamber flooded with TAE
buffer. 20 mL of DNA sample (mixed with bromophenol blue dye in 1 : 1 ratio) was
loaded carefully into the wells, along with control and constant 50 V of electricity was
passed for 30 min. The gel was removed, carefully stained with ethidium bromide
ꢀ
1
solution (10 mg mL ) for 10–15 min, and the bands were observed under UV
transilluminator (UVP, Germany).
3
. Results and discussion
The reactions of hydrated lanthanide chlorides with monobasic bidentate ligands have
been shown by the following general equation:
MeOH Â
Ã
LnCl3 ꢂ xH2O þ 3LNa ꢀ! LnðLÞ ꢂ nH2O þ 3NaCl þ ðx ꢀ 3ÞH2O
3
where LNa is the sodium salt of the ligand, Ln ¼ Nd, Sm, and Gd, n ¼ 3 and x ¼ 6. The
newly synthesized complexes have been obtained as colored solids with solubility in
ꢀ3
ꢀ1
methanol, DMSO, and DMF. The molar conductance values of 10 mol L solutions
ꢀ
1
2
ꢀ1
of metal complexes are 10–15 Ohm cm mol in dry DMF, indicating their non-
electrolytic behavior. The complexes are monomers as revealed by their molecular
weight determinations.
3
.1. IR spectra
Absorption frequencies of the ligands and their metal complexes show that both ligands
are monobasic bidentate, coordinating through thiol sulfur/ketone oxygen, and
azomethine nitrogen. IR spectra of the free ligands show a medium intensity band
ꢀ1
at 3150–3240 cm
due to ꢁNH, which is absent in spectra of the complexes.
The bands due to ꢁ(C¼O) and ꢁ(C¼S) in the spectra of the ligands are observed

Rare earth coumarin complexes
269
ꢀ
1
at 1715 and 1080 cm , respectively. Bands for ꢁ(C–S) and ꢁ(CꢀO) in spectra of the
1
complexes support the involvement of sulfur and oxygen in coordination. For L H and
2
ꢀ1
L H, the most significant band at 1630–1635 cm assigned to ꢁ(C¼N) shifts to lower
frequency in the complexes, suggesting the coordination of azomethine nitrogen. There
are no changes in the ꢁsym (3340–3490) and ꢁasym (3350–3500) of NH , indicating
2
ꢀ
1
non-involvement of this group in chelation. The band at 1735 cm due to (>C¼O)
remains unchanged in the complexes, indicating that the lactone oxygen is not involved in
ꢀ
1
coordination. The complexes exhibit new bands at 510–550 and 360–420/580–620 cm
which may be attributed to the different vibrational modes of ꢁ(M–N) and ꢁ(M–S)/
(M–O), respectively, and support the coordination of the azomethine nitrogen and
ꢁ
bonding of the thiol sulfur/ketone oxygen.
1
.2. H NMR spectra
3
1
The H NMR spectra of both ligands were recorded in DMSO-d . Signal at ꢂ 2.83–
6
2
The free ligands show multiplets at ꢂ 6.45–8.20 ppm attributable to aromatic protons.
.85 ppm is observed for ꢀNH and the signal of ꢀNH is observed at ꢂ 9.90–9.62 ppm.
2
3
.3. Electronic spectra
The electronic spectra of the ligands and their complexes were recorded in distilled
1
2
DMSO. The spectra of L H and L H show a broad band at 365–375 nm which can be
assigned to n–ꢃ* transitions of the azomethine group which undergoes a blue shift in
the complexes due to polarization within the >C¼N chromophore caused by the metal–
ligand interaction. Two bands at 275–285 nm and 295–310 nm due to ꢃ–ꢃ* transitions
in the ligands remain at the same positions in spectra of the metal complexes.
4
Absorptions of Nd(III) and Sm(III) are due to transitions from the ground levels, I9/2,
6
and H to the excited ‘‘J’’ levels of 4f configuration. The nephelauxetic parameter (ꢄ)
5
/2
1
32], bonding parameter (b ) [33], Sinha’s covalency parameter (ꢂ) [34], and angular
/2
[
covalency (ꢅ) for the Nd(III) and Sm(III) complexes are presented in table 3. Sinha’s
parameter (ꢂ) suggests the degree of covalency and is obtained by the equation
ꢂ ¼ ð1 ꢀ ꢄ Þ=ꢄ ꢂ 100
av
av
Table 3. Electronic spectral data of lanthanide complexes.
V
Ln ion complexes
max of
Vmax of
þ3
ꢀ
1
ꢀ1
1/2
b
Complex
Assignment
(cm
)
(cm
)
ꢄ
1 ꢀ ꢄ
ꢂ
ꢅ
1
Sm(L )
[
3
] ꢂ 3H
2
O
6H5/2 –4I13/2
21,455
25,830
26,525
28,735
21,272
25,650
26,320
28,565
0.9915 0.0085 0.0652 0.8572 0.0926
0.9930 0.0070 0.0592 0.7049 0.0840
0.9923 0.0077 0.0620 0.7760 0.0881
0.9941 0.0059 0.0543 0.5935 0.0770
–
–
–
4F9/2
4I9/2
6P3/2
2
Nd(L H)
[
3
] ꢂ 3H
2
O
4I9/2 –4G5/2, 2G7/2
16,822
19,813
21,915
16,660
19,630
21,740
0.9904 0.0096 0.0693 0.9693 0.0985
0.9908 0.0092 0.0678 0.9285 0.0964
0.9920 0.0080 0.0632 0.8064 0.0897
–
–
2G9/2
4G11/2

2
70
P. Kapoor et al.
where ꢄav is the average value of the ratio of ꢁcomplex/ꢁmetal ion. The magnitude of the
1
/2
bonding parameters (b ) suggests the degree of involvement of 4f orbitals in metal–
ligand bonding and is related to nephelauxetic ratio (ꢄ) by the equation
1
=2
1=2
b
¼ ½ð1 ꢀ ꢄ Þ=2ꢆ
av
1=2
1=2
av
Angular covalency ðꢅÞ ¼ ð1 ꢀ ꢄavÞ =ꢄ
According to Karraker [35], the shape and intensity of these transitions indicate the
geometry of the complex. In the present complexes, nephelauxetic ratio (ꢄ) being
1
/2
less than one and positive values of b
and ꢂ indicate slight covalent bonding
between metal and ligand. On comparison of the spectra with that of the known
compounds [36, 37], it is concluded that the coordination number of the present
complexes is six.
3
.4. Magnetic studies
Magnetic moment data are summarized in table 1. The paramagnetic behavior of the
lanthanide complexes is consistent with the presence of unpaired electrons. The
magnetic susceptibility measurements of the complexes show little deviation from the
Van Vleck values, indicating nonparticipation of the 4f electrons in bonding. However,
in the case of Sm(III) complexes, the agreement between calculated and experimental
values is not good [36].
3.5. EPR spectra
EPR spectra of some of the synthesized compounds were recorded (both at RT and
LNT) and similar g values of 1.98 have been observed, nearly equal to the free electron
value (g ¼ 2.00277). Similar line widths at both temperatures indicate spin–lattice and
spin–spin relaxation processes contribute equally to line width.
3.6. X-ray powder diffraction spectra
2
Lattice dynamics of the finely powdered product, [Nd(L ) ꢂ 3(H O)], have been deduced
3
2
on the basis of X-ray powder diffraction studies. The observed interplanar spacing values
˚
‘d’ in A) have been measured from the diffractogram of the compound and the Miller
(
indices h, k, and l have been assigned to each d value and 2ꢆ angles are reported. The
results show that the compound belongs to ‘‘Monoclinic’’ crystal system having unit cell
parameters a ¼ 11.260, b ¼ 12.458, c ¼ 14.890, maximum deviation of 2ꢆ ¼ 0.046 and
ꢇ ¼ 90, ꢄ ¼ 103.58, ꢈ ¼ 90 at the wavelength ¼ 1.54178 (table 4 and figure 2).
3
.7. Mass spectra
1
The mass spectrum of Sm(L ) ꢂ 3H O (2) was studied as a representative case. Peaks of
3
2
appreciable intensity were observed at m/z values 1046.2581, 992.2909, and 261.3233
1
(
1
figure S1, Supplementary material). The molecular ion peak for Sm(L ) ꢂ 3H O at m/z
3
2
046.2581 is in good agreement with its molecular weight, which suggests the monomeric

Rare earth coumarin complexes
271
2
Table 4. X-ray powder diffraction data of Nd(L )
3
ꢂ 3H
2
O.
h
k
l
2ꢆ (Exp.)
2ꢆ (Calcd)
2ꢆ (Diff.)
d (Exp.)
d (Calcd)
Intensity (Exp.)
2
0
0
3
3
3
0
1
6
4
1
8
3
5
2
5
7
1
27.324
31.752
45.436
53.606
56.540
66.120
27.363
31.734
45.443
53.595
56.560
66.150
ꢀ0.039
0.018
3.26383
2.81807
1.99612
1.70958
1.62762
1.41314
3.25926
2.81963
1.99581
1.70991
1.62709
1.41258
51.46
206.92
171.08
16.34
72.95
45.82
ꢀ0.007
0.011
ꢀ0.020
ꢀ0.030
2
Figure 2. X-ray powder diffraction of Nd(L )
3
ꢂ 3H
2
O.
nature of the complex and confirms the proposed formula. The peak at m/z 992.2909
1
indicates that the molecular ion gives a fragment ion [Sm(L ) ] by losing three water
3
þ
molecules. This fragment ion undergoes demetallation to form [L þ H] , resulting in a
peak at m/z 261.3233. The mass spectra of all the complexes are summarized in table 5.
4
4
. Pharmacology
.1. Antimicrobial assay
The ligands and their metal complexes were evaluated for antimicrobial activity against
four bacteria, E. coli, P. aeruginosa, B. subtilis, and S. aureus, and three fungi,
C. albicans, A. niger, and F. oxysporum. The results, summarized in tables 6 and 7, are
compared with those of the standard drug ciprofloxacin for bacteria and flucanazole for
fungi. The results show that the complexes are more active than their parent ligands
against the same microorganisms and as the concentration increases the activity

2
72
Table 5. Mass spectra of the complexes.
Molecular ion peak [ML
P. Kapoor et al.
þ
þ
3
]
3
ꢂ 3H
2
O]
ML
3
ꢂ 3H
2
O–3H
2
O ! [ML
Name of the
compound
Observed
Calculated
Observed
Calculated
1
Nd(L )
3
3
3
3
3
3
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
ꢂ 3H
2
O
2
O
2
O
2
O
2
O
2
O
1040.1514
1046.2581
1053.3458
992.1225
998.2958
1005.0456
1040.4186
1046.5386
1053.4286
992.2236
998.3436
1005.2336
986.1896
992.2909
999.1592
938.0598
944.1916
951.0398
986.3742
992.4942
999.3842
938.1792
944.2992
951.1892
1
Sm(L )
1
Gd(L )
2
Nd(L )
2
Sm(L )
2
Gd(L )
Table 6. Antifungal screening data for the ligands and their corresponding metal complexes.
Antifungal activity) Percentage inhibition after 96 h (conc. in ppm)
F. oxysporum C. albicans A. niger
(
Compound
100
200
100
200
100
200
1
2
3
4
5
6
7
39 ꢃ 0.4
32 ꢃ 1.1
79 ꢃ 1.4
71 ꢃ 0.4
84 ꢃ 0.6
50 ꢃ 0.2
53 ꢃ 0.6
69 ꢃ 0.2
100 ꢃ 1.1
43 ꢃ 0.7
40 ꢃ 1.1
83 ꢃ 0.2
77 ꢃ 1.1
89 ꢃ 0.5
65 ꢃ 0.2
63 ꢃ 0.2
73 ꢃ 0.5
100 ꢃ 0.8
42 ꢃ 0.3
34 ꢃ 0.4
78 ꢃ 0.7
61 ꢃ 0.6
69 ꢃ 0.7
59 ꢃ 0.7
60 ꢃ 0.4
60 ꢃ 0.2
100 ꢃ 0.5
47 ꢃ 0.5
44 ꢃ 0.3
80 ꢃ 0.6
67 ꢃ 0.6
77 ꢃ 0.5
65 ꢃ 0.2
78 ꢃ 0.4
65 ꢃ 0.2
100 ꢃ 1.1
45 ꢃ 0.3
38 ꢃ 0.3
72 ꢃ 1.4
50 ꢃ 0.4
63 ꢃ 1.4
55 ꢃ 0.6
50 ꢃ 0.7
54 ꢃ 0.4
100 ꢃ 0.9
48 ꢃ 0.5
42 ꢃ 0.2
75 ꢃ 0.4
57 ꢃ 1.1
68 ꢃ 0.2
61 ꢃ 0.5
64 ꢃ 0.3
59 ꢃ 1.4
100 ꢃ 0.6
8
Flucanazole
also increases. Chelation theory [38] accounts for the increased activity of the metal
complexes. The enhanced activity could also be due to inherent properties of the metal
ion in precipitating or denaturing proteins. Since enzymes are proteins, it would be
expected that the heavy metal would inactivate these catalysts [39]. The mode of action
of antimicrobials may involve various targets in microorganisms, e.g., interference with
cell wall synthesis, damage to the cytoplasmic membrane, causing an alteration of the
cell permeability or a disorganization of the lipoproteins leading to cell death.
Antimicrobials can bind to ribosome and may interfere with peptide chain formation in
microorganisms or with the transcription mechanisms. At lower concentration,
inhibition is less severe because the activities of the organisms will be slowed down,
while at higher concentration, more enzymes will become inhibited leading to a quicker
death of the organisms [40]. Revankar et al. [41] and Alghool [42] have reported similar
results. Revankar et al. synthesized Co(II), Ni(II), and Cu(II) complexes of Schiff base
derived from the condensation of 2,6-diaminopyridine and 3-acetylcoumarin and
screened them for their antimicrobial activity, and observed that all the complexes were
more active against bacteria and fungi. Alghool screened Cu(II), Co(II), Ni(II), Cd(II),
and Zn(II) complexes of 6-(2-phenyldiazenyl)-7-hydroxy-4-methyl coumarin (PAHC)
for antibacterial activity and found that all the complexes show better activity than the
ligand but less activity than the standard drug.

Rare earth coumarin complexes
273

2
74
P. Kapoor et al.
ꢀ1
Table 8. MIC (mg mL ) of the ligands and their corresponding complexes.
Compound
E. coli
P.aeruginosa
B.subtilis
S.aureus
C.albicans
F. oxysporum
A. niger
1
2
3
4
5
6
7
8
20
25
15
10
15
20
15
20
25
30
20
15
15
25
20
20
35
40
25
20
25
30
25
30
10
25
10
10
15
15
15
20
10
20
10
10
10
15
10
15
10
25
10
10
25
10
10
10
10
25
10
10
10
25
10
10
Figure 3. Pesticidal activity (% corrected mortality) for the ligands and their corresponding metal
complexes.
4.2. Minimum inhibitory concentration
MIC values calculated for the ligands and their lanthanide complexes are shown in
table 8. The ligands and their metal complexes were most active in inhibiting growth of
ꢀ
1
the tested organisms between 10–40 MIC (mg mL ) against selected bacteria and fungi.
The MIC values for Ciprofloxacin against E. coli and S. aureus are 0.009 and 0.016,
respectively, and for Flucanazole against C. Albicans, the value is 0.079 [43].
4
.3. Pesticidal and nematicidal activity
The results of pesticidal activity reveal that the ligands and their metal complexes
showed good pesticidal activity (figure 3). All the compounds are fairly active in killing
T. castaneum. An appreciable increase in the pesticidal activities in the case of metal
complexes compared to the uncomplexed ligands was observed. Sm(III) chelates were
most effective as evidenced from the comparative study of their percentage mortality
data with other metal chelates. Dawara and Singh [44] have also screened Bi(III) and

Rare earth coumarin complexes
275
Figure 4. Nematicidal activity for the ligands and their corresponding metal complexes.
Sb(III) complexes of 3-acetylcoumarin-based ligands for their antimicrobial as well as
pesticidal activity and observed that all complexes are active in inhibiting the growth of
microorganisms and pests.
The objective of nematode control is to improve growth and yield of plants, which can
be achieved through reduction of the nematode population in soil or in plants, or through
reduction of their damage. From the results of nematicidal activity, maximum hatching
was recorded in the control but in the eggs treated with the ligands as well as metal
complexes, low hatching was recorded. The results in figure 4 reveal that the activity
increases on complexation and chelation, i.e., the newly synthesized complexes have been
found to be more active in lowering the hatching of eggs than the parent ligand itself.
4
.4. DNA cleavage activity
DNA cleavage studies of both the synthesized ligands and corresponding lanthanide
metal complexes have been carried out against E. coli ATCC 35218 by agarose gel
electrophoresis. Gel electrophoresis works on the migration of DNA under the
influence of electric potential. Gel electrophoresis in control experiments clearly reveal
that the untreated DNA does not show any cleavage (figure S2 (Lane C),
Supplementary material), whereas all the metal complexes along with the ligand
exhibit cleavage activity on DNA. The difference in migration was observed in the
Lanes L, N1, N2, N3 of ligand and lanthanide complexes, respectively, compared to the
control DNA of E. coli (Lane C). N2 clearly showed the absence of the marker band,
thus providing proof for their DNA cleaving ability, whereas N1 and N3 displayed
partial cleavage. L is the least active among the four. The results indicate the important
role of coumarin-based ligand coordinated with metal ions in isolated DNA cleavage.
Kostova and Stefanova [45] have synthesized Sm(III) and Gd(III) metal complexes of
acenocumarol and screened them for their cytotoxic study. The Sm(III) and Gd(III)
complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and are
stronger inhibitors of tumor cell proliferation than the ligand. In this work, the
comparative data of DNA cleavage of lanthanide complexes showed that Sm(III)

2
76
P. Kapoor et al.
H N
2
N
N
H
R
R
X
H
X
N
Ln
NH2
3H O
2
N
X
N
N
R
H N
H
2
Ln = Nd, Sm and G, X = S/O, R =
O
O
Figure 5. Proposed structure of the synthesized metal complexes.
complex with thiosemicarbazone has the highest activity towards cleavage of DNA and
all the metal complexes exhibited better results than free ligand 3-formyl-4-
chlorocoumarin thiosemicarbazone.
5. Conclusion
Microwave irradiation is an efficient and environmentally-benign method to accom-
plish various syntheses in higher yields in shorter reaction periods. From analytical data
and spectral studies, the ligands coordinate in a monobasic bidentate manner and the
complexes possess octahedral geometry. The analytical and spectral studies suggest the
structure shown in figure 5. The ligand and metal complexes were active for pesticidal,
nematicidal, antibacterial, and antifungal activities. The compounds are more active
than the ligands but less active than Flucanazole and Ciprofloxacin as standard drugs.
The nematicidal activity shows that the metal complexes are more active in lowering the
hatching of eggs than the parent ligand. The DNA cleavage studies revealed that the
metal complexes showed good efficiency towards DNA cleavage.
Acknowledgments
The authors are thankful to UGC, New Delhi, India for financial assistance
through grant no. 34-324/08/(SR-I) and CSIR, New Delhi through grant no.
01(2307)/09/EMR-II.

Rare earth coumarin complexes
277
References
[
[
[
[
[
[
[
[
[
1] C. Saxena, R.V. Singh. Phosphorus, Sulfur Silicon Relat. Elem., 97, 17 (1994).
2] G. Venkatachalam, S. Maheswaran, R. Ramesh. Indian J. Chem., 44(A), 705 (2005).
3] A.S.A. Zidan. Phosphorus, Sulfur Silicon Relat. Elem., 178, 567 (2003).
4] M. Jain, S. Maanju, R.V. Singh. Appl. Organomet. Chem., 18, 73 (2004).
5] P. Chaudhary, M. Swami, D.K. Sharma, R.V. Singh. Appl. Organomet. Chem., 23, 140 (2009).
6] A.P. Mishra, S.K. Sharma, A. Tanija, D.S. Seth. Proc. Natl. Acad. Sci. India, Sect. A, 68, 129 (1998).
7] A. Sajed, A.M. Abid. Phosphorus, Sulfur Silicon Relat. Elem., 170, 75 (2001).
8] K. Balakrishna, A.M. Isloor, S. Shenoy. Indian J. Heterocycl. Chem., 11, 159 (2001).
9] J. Joseph, B.H. Mehta. Russ. J. Coord. Chem., 33, 124 (2007).
[
10] P.B. Pansuriya, M.N. Patel, M.R. Chhasatia, P. Dhandhukia, V. Thakkar. J. Coord. Chem., 61, 3336
2008).
(
[
[
[
[
[
11] X. Chen, J. Wang, S. Sun, J. Fan. Bioorg. Med. Chem. Lett., 18, 109 (2008).
12] C. Liu, M. Wang, T. Zhang, H. Sun. Coord. Chem. Rev., 248, 147 (2004).
13] A. Sreedhara, A. Cowan. J. Biol. Inorg. Chem., 6, 337 (2001).
14] R.T. Kovacic, J.T. Welch, S.J. Franklin. J. Am. Chem. Soc., 125, 6656 (2003).
15] R.B. Lauffer. In MRI Clinical Magnetic Resonance Imaging, R.R. Edelman, M.B. Zlatkin,
J.R. Hesselink, W.B. Saunders (Eds), 2nd Edn, W. B. Saunders Company, Philadelphia (1996).
[
¨
16] Hemmila, T. Stahlberg, P. Mottram (Eds). Bioanalytical Applications of Labelling Technologies, Wallac
Oy, Turku (1994).
[17] D. Parker. Coord. Chem. Rev., 205, 109 (2000).
[18] T.C. Bruice, A. Tsubouchi, R.O. Dempcy, L.P. Olson. J. Am. Chem. Soc., 118, 9867 (1996).
[19] G.L. De Nardo, G.R. Mirik, L.A. Kroger, R.T. O’Donnel, C.F. Meares, S.L. De Nardo. J. Nucl. Med.,
37, 451 (1996).
[
[
20] D. Parker, R.S. Dickins, H. Puschmann, C. Crossland, J.A.K. Howard. Chem. Rev., 102, 1977 (2002).
21] A.I. Vogel. A Textbook of Organic Quantitative Analysis, 5th Edn, Pearson Education Ltd., Thames
PolytechniqueLondon (2004).
[
22] A.I. Vogel. A Textbook of Quantitative Chemical Analysis, 6th Edn, Pearson Education Ltd., Thames
Polytechnique, London (2006).
[
23] B.S. Furniss, A.J. Hannaford, P.W.G. Smith, A.R. Tatchell. Vogels’ Text Book of Practical Organic
Chemistry, 5th Edn, Longman Scientific & Technical, Harlow, UK (1994).
24] K. Sharma, R. Singh, N. Fahmi, R.V. Singh. Spectrochim. Acta, Part A, 75, 422 (2010).
25] K. Shanker, R. Rohini, V. Ravinder, P. Reddy, Y.P. Ho. Spectrochim. Acta, Part A, 73, 205 (2009).
26] P.M. Davidson, M.E. Parish. Food Technol., 43, 148 (1989).
[
[
[
[
[
[
[
[
[
27] C.H. Collins. Microbiological Methods, p. 296, Butterworths, London (1964).
28] M.M. Ali, M. Jesmin, S.M.A. Salam, J.A. Khanam, M.F. Islam, M.N. Islam. J. Sci. Res., 1, 641 (2009).
29] R.P. Parvatha, R.M. Khan. Curr. Nematolog., 2, 115 (1991).
30] M. Jain, S. Nehra, P.C. Trivedi, R.V. Singh. J. Phytolog. Res., 16, 5 (2003).
31] T.A. Brown. Mol. Biol. – A Practical Approach, 1, 51 (1990).
32] C.K. Jorgenson. In The Nephelauxetic Series, Progress in Inorganic Chemistry, F.A. Cotton (Ed.), Vol. 4,
p. 73, Interscience Publishers, Division of John Wiley, New York, NY (1962).
33] D.E. Henrie, G.R. Choppin. J. Chem. Phys., 49, 477 (1968).
[
[
[
[
[
[
[
[
[
[
[
34] S.P. Sinha. Spectrochim. Acta, Part A, 22, 57 (1966).
35] D.G. Karraker. Inorg. Chem., 6, 1863 (1967).
36] R. Singh, K. Sharma, R.V. Singh. J. Sulfur Chem., 31, 61 (2010).
37] P. Kapoor, N. Fahmi, R.V. Singh. Spectrochim. Acta, Part A, 83, 74 (2011).
38] S. Belwal, N. Fahmi, R.V. Singh. Appl. Organomet. Chem., 22, 615 (2008).
39] N. Fahmi, C. Saxena, R.V. Singh. Bull. Chem. Soc. Jpn., 69, 963 (1996).
40] Z.H. Abd El-Wahab, M.R. El-Sarrag. Spectrochim. Acta, Part A, 60, 271 (2004).
41] S. Budagumpi, U.N. Shetti, N.V. Kulkarni, V.K. Revankar. J. Coord. Chem., 62, 3961 (2009).
42] S. Alghool. J. Coord. Chem., 63, 3322 (2010).
43] R.S. Hunoor, B.R. Patil, D.S. Badiger, R.S. Vadavi, K.B. Gudasi, V.M. Chandrashekhar,
I.S. Muchchandi. Spectrochim. Acta, Part A, 77, 838 (2010).
44] L. Dawara, R.V. Singh. J. Coord. Chem., 64, 931 (2011).
[
[
45] I. Kostova, T. Stefanova. J. Coord. Chem., 62, 3187 (2009).