Synthesis, characterization, spectral and antimicrobial studies of some trivalent Ln(III) metal complexes with ligands containing 'N' and 'O' donor atoms

Article abstract of DOI:10.14233/ajchem.2015.17144

Ten new coloured solid complexes of type [ML₂X₂], Where M=La(III), Pr(III), Nd(III), Sm(III) & Dy(III), 'L' = Ligand i.e., N-(3-methylthiocarbamyl-5-oxo-2-pyrazolin-4-ylene-N′-(4′-antipyrine)hydrazine (HATP) and N-(3-methyl-1-thiocar

Full text of DOI:10.14233/ajchem.2015.17144

Asian Journal of Chemistry; Vol. 27, No. 3 (2015), 860-864
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17144
Synthesis, Characterization, Spectral and Antimicrobial Studies of Some Trivalent
Ln(III) Metal Complexes with Ligands Containing ‘N’ and ‘O’ Donor Atoms
*
RAJESH KUMAR MISHRA and B.G. THAKUR
Department of Chemistry, C.M. Science College, Lalit Narayan Mithila University, Darbhanga-846 004, India
*Corresponding author: E-mail: mishrarajesh366@gmail.com
Received: 30 January 2014;
Accepted: 26 April 2014;
Published online: 19 January 2015;
AJC-16685
Ten new coloured solid complexes of type [ML2X2], Where M=La(III), Pr(III), Nd(III), Sm(III) & Dy(III), ‘L’= Ligand i.e., N-(3-methyl-
thiocarbamyl-5-oxo-2-pyrazolin-4-ylene-N'-(4'-antipyrine)hydrazine (HATP) and N-(3-methyl-1-thiocarbamyl-5-oxo-2-pyrazolin-4-ylene)-
N'-(4'-benzothiazole)hydrazine (HBTP) and ‘X’=H2O have been synthesized and characterized by their elemental analysis, molar
conductance values, magnetic susceptibilities, UV, IR and NMR spectral studies. Elemental analysis confirms 1:2 stoichiometry of the
synthesized complexes. Spectral studies confirms that the ligand ‘HATP’ and ‘HBTP’ acts as tetradentate and tridentate, respectively and
coordinates to central metal ion by ‘N’and ‘O’donor atoms. Complexes are ten and eight coordinated. Further the ligands and synthesized
complexes have been screened for their antibacterial activity against some Gram-positive and Gram-negative bacteria.
Keywords: Synthesis, Ln(III), Metal complexes.
But the literature survey revealed that the complexation
of ligands under our study with trivalent lanthanides have not
been studied so far. In view of this, we report here the synthesis,
characterization and antibacterial screening of a few complexes
of N-(3-methyl-thiocarbamyl-5-oxo-2-pyrazolin-4-ylene-N'-
(4'-antipyrine)hydrazine (HATP) and N-(3-Methyl-1-thio-
carbamyl-5-oxo-2-pyrazolin-4-ylene)-N'-(4'-benzothiazole)-
hydrazine (HBTP) with some trivalent lanthanide metal ions.
INTRODUCTION
Hydrazones of pyrazolone derivatives are of much interest
due to their high chelating ability and applications in analytical
chemistry1,2. Such ligands and their derivatives are an active
moiety in the class of non-steroidal, antiinflammatory agents
used in the treatment of arthritis and other musculoskeletal and
joint disorders. The pyrazolone derivatives shows remarkable
antibacterial, antioxidant and analgesic activity3. Also, azo
hydrazone tautomerism of aryl azo derivatives of β-dicarbonyls,
naphthols and 2-pyrazolin-5-ones has provided controversy and
interest both in the past4,5. These have varied ligational behaviour
towards different metal ions and have created specific structural
features in their metal complexes6. A large number of ligands
containing ‘N’ and ‘O’ donor atoms coordinate with rare earth
metals forming stable complexes have been reported7-16. Synthesis
and characterization of nickel(II) and copper(II) complexes with
3-(p-chlorobenzyl)-4-(p-hydroxy-m-methoxybenzylidenamino)-
1H-1,2,4-triazole-5-one17 and synthesis, characterization and
DNA-binding of cobalt(II) complex with 3-benzyl-4-(p-hydroxy-
m-methoxybenzylidenamino)-1H-1,2,4-triazole-5-one18 have
been reported. Synthesis, characterization and biocidal activities
of mixed ligand complexes of dioxomolybdenum(VI) derived
from sulpha drugs and 4-benzoyl-3-methyl-1-phenyl-2-
pyrazoline-5-one19 and structural and spectroscopic aspects of
2,3-butanedionemonoxime monohydrazone have also been
reported20.
EXPERIMENTAL
Thiosemicarbazide and 2-aminobenzothiazole were
purchased from Loba. 4-Aminoantipyrine were purchased
from Fluka.All other chemicals, solvents were purchased from
CDH and metal salts (99.97 % purity) used were of AR grade
and were purchased from Indian Rare Earth Udyog Mandal,
Kerala, India.
Synthesis of N-(3-methyl-thiocarbamyl-5-oxo-2-
pyrazolin-4-ylene-N'-(4'-antipyrine)hydrazine (HATP): 3-
Methyl-1-thiocarbamyl-2-pyrazolin-5-one (MTP) has been
prepared by as in literature21. 4-Aminoantipyrine (20 g,
0.1 mol) was diazotized and the diazonium salt solution was
added slowly with stirring to an ice-cold alkaline solution of
(0.1 mol 15.70 g) MTP. This mixture was kept in an ice-bath
for 1 h with occasional stirring.Bright red crystals of HATP
separated. It was filtered under suction, washed with ether and
then recrystallized from ethanol. The purity of the compound

Vol. 27, No. 3 (2015)
Synthesis and Antimicrobial Studies of Some Trivalent Ln(III) metal Complexes 861
was checked by TLC using silica gel plate and its elemental
analysis. Its m.pt. was found to be 210 °C.
the courtesy of CDRI and Deptt. of Chemistry, IIT Delhi. 1H
NMR spectra were recorded on Perkin Elmer 90 MHz NMR
spectrometer from CDRI Lucknow.
Biological evaluation: The bacterial activity of HATP
and HBTP and their Ln(III) metal complexes were tested
against Gram-positive bacteria Staphylococcus aureus and
Gram-negative bacteria Pseudomonas aeruginosa, E. coli and
Klebsiella pneumonia by disc-diffusion method using Agar
Nutrient as medium and ofloxacin as control23.
DMSO was used as solvent for making test solutions of
all the compounds studied. The paper disc (6 mm) containing
the compound (100 µg/disc) was placed on the surface of the
nutrient agar plate previously spread with 0.1 mL of sterilized
culture of micro-organism. These were incubated at 37 °C for
2 days. The diameter of inhibition zone around the paper disc
was measured (Table-2).
Synthesis of N-(3-methyl-1-thiocarbamyl-5-oxo-2-
pyrazolin-4-ylene)-N'-(4'-benzothiazole)hydrazine (HBTP):
0.1 mol, 20 g of 2-aminobenzothizaole was diazotized and
diazonium salt solution was added slowly with stirring to an
ice-cold alkaline solution of MTP (15.70 g, 0.1 mol). The mix-
ture was kept in ice for 40 min, fine yellowish brown crystals
of HBTP separated out. It was filtered under suction washed
with ether and then recrystallized from ethanol. The purity
was checked by TLC and its elemental analysis. Its melting
point was 195 °C.
Synthesis of complexes: Complexes were prepared by
refluxing aqueous ethanolic solution of corresponding metal
salts (0.1 mol) and ligands (0.12 mol) in ethanol for 1 h on a
water thermostat. On cooling the coloured solid complexes
separated. These were filtered and washed with ethanol to
remove excess ligand if any and then with benzene. It was
now dried over P4O10.
RESULTS AND DISCUSSION
The complexes are non-hygroscopic, almost coloured
stable solids and are soluble in DMSO and DMF. They decom-
pose above 300 °C. The molar conductance values show their
non-electrolytic nature. IR spectra of the ligands shows a band
at 1660 cm–1 assignable to ν(C=O) of thiocarbamyl pyrazo-
lone24. The band at 1640 cm–1 in the spectra of HATP is due to
ν(C=O) at antipyrine25. The bands at 1620 and at 1585 cm–1
can be due to C=N mode of HATP and HBTP, respectively26.
A weak band at 3100 cm–1 can be assigned to stretching frequency
of intramolecularly hydrogen bonded NH in HATP and the
band at 3175 cm–1 in the spectrum of HBTP is due to NH of
hydrazone part27. The ν(NH2) and ν(C=N) appeared at 3360
cm–1 and 1160 cm–1, respectively28. The –N=C=S ring stretching
frequency in HBTP is observed at 2020 cm–1.
Metal contents were estimated by usual procedure after
digesting the complexes with conc. H2SO4. Chloride in the
complex was estimated byVolhards method22. Nitrogen content
was determined using elemental analyzer Heraeus Carlo Erba-
1108 at CDRI Lucknow. Magnetic moments of the complexes
were determined in Gouy Balance Calibrated using [HgCo(NCS)4]
at room temperature in Inorganic Research Laboratory. P.G.
Deptt. Of Chemistry, L.N.M.U. Darbhanga. Molar conduc-
tance of the complexes was measured by digital conductance
meter systronics model 304. Analytical data, decomposition
temperature, conductance, colour and µeff values are listed in
Table-1.
IR spectra of the ligand and complexes were recorded on
a Perkin-Elmer IR spectrometer using KBr Pellet method by
TABLE-1
ANALYTICAL DATA OF LIGAND AND METAL COMPLEXES
Λm (ohm-1
Elemental analysis (%): Obs. (calcd.)
S.
No.
Compound /
Colour
m.w. obs.
(calcd.)
Decomp.
temp. (°)
µeff
(BM)
cm2 mol-1)
C
H
N
S
Ln
–
1
2
3
4
5
6
7
8
9
HATP
Bright Red
[La(HATP)2(H2O)2]
Light Blue
[Pr(HATP)2(H2O)2]
Blue
[Nd(HATP)2(H2O)2]
Light Blue
[Sm(HATP)2(H2O)2]
Blue
[Dy(HATP)2(H2O)2]
Bluish White
HBTP
371.02
(371.00)
915.13
(915.00)
917.45
(917.00)
920.38
(920.00)
926.47
(926.00)
938.27
(938.00)
333.12
(333.00)
839.64
(839.00)
841.07
(841.00)
844.45
(844.00)
850.23
51.77
(51.75)
42.00
(41.96)
41.89
(41.87)
41.77
(41.73)
41.52
(41.46)
40.95
(40.93)
47.00
(46.84)
37.20
(37.18)
37.11
(37.09)
37.02
(36.96)
36.78
4.62
(4.58)
3.97
26.45
(26.41)
21.48
8.64
(8.62)
7.01
–
–
–
15.24
(15.19)
15.42
(15.37)
15.72
(15.65)
16.25
(16.19)
17.35
(17.27)
–
342
338
355
346
370
–
10.5
14.3
12.2
14.5
16.2
–
Dia
(3.93)
(21.42)
(6.99)
3.94
(3.92)
3.97
21.43
(21.37)
21.35
7.02
(6.97)
6.99
3.67
3.60
1.66
11.31
–
(3.91)
(21.30)
(6.95)
3.95
(3.88)
3.87
21.19
(21.16)
20.94
7.00
(6.91)
6.84
(3.83)
3.94
(3.90)
3.39
(3.33)
3.37
(3.32)
3.35
(3.31)
3.32
(20.89)
25.27
(25.22)
20.08
(20.02)
20.00
(19.97)
19.98
(19.90)
19.83
(6.82)
19.26
(19.21)
15.28
(15.25)
15.24
(15.21)
15.19
(15.16)
15.09
(15.05)
14.92
(14.84)
Yellowish Brown
[La(HBTP)2(H2O)2]
Light Yellowish Brown
[Pr(HBTP)2(H2O)2]
Yellowish Brown
16.64
(16.56)
16.84
(16.76)
17.09
(17.06)
17.67
(17.64)
18.83
(18.79)
332
339
348
337
328
10.2
13.7
12.3
15.1
16.7
Dia.
3.59
3.48
1.59
10.99
10 [Nd(HBTP)2(H2O)2]
Deep Yellowish Brown
11 [Sm(HBTP)2(H2O)2]
Yellowish Brown
12 [Dy(HBTP)2(H2O)2]
Pale Yellow
(850.00)
862.74
(862.00)
(36.70)
36.25
(36.19)
(3.29)
3.27
(3.24)
(19.76)
19.52
(19.48)

862 Mishra et al.
Asian J. Chem.
TABLE-2
NMR and IR spectra of ligands reveals that coupling of
4-diazoantipyrine and 2-diazobenzothiazole with 3-methyl-
1-thiocarbamyl-2-pyrazolin-5-one at its 4th position has
ANTIBACTERIAL ACTIVITIES OF THE LIGANDS
AND COMPLEXES (ZONE FORMATION IN mm)
resulted in the production of a hydrazone via rearrangement30,31
.
Pseudomonas
aeruginosa
S.
aureus
Compound
E. coli
Klebs.
In the IR spectra of HATP metal complexes we find a
shift in the ν(N-H) mode of NH2 to 3300 from 3360 cm–1, it
reveals the coordination of N-atom of NH2. Also, stretching
frequencies of C=O and C=N bonds are lowered by 40-60
cm–1. So, in addition of coordination via NH2, both carbonyl
oxygen atoms and azomethine nitrogen atoms are coordinated
to the metal ions. Thus HATP acts as tetradentate of N2O2 type
ligands. Similar negative shift in the frequencies of ν(C=O),
ν(C=N) and ν(N-H) of NH2 is found in the spectra of HBTP
metal(III) complexes revealing the coordination through
carbonyl oxygen, azomethine nitrogen and amino nitrogen
atoms, so that HBTP acts as ONN donor ligand. The bands
around 3500-3300 cm–1 and 830-800 cm–1, found in both i.e.,
HATP and HBTP metal(III) complexes indicate the presence
of coordinated water molecule. Presence of coordinated water
molecule is further confirmed by TG analysis32. The presence
of additional non-ligands band in the spectra of the all metal
complexes around 560-520 cm–1 and 450-400 cm–1 are assign-
able to M-N and M-O stretching frequencies33.
Control (Ofloxacin)
HATP
20
18
30
31
28
38
22
–
32
30
35
37
26
22
10
32
35
34
33
25
18
34
33
28
33
28
16
10
23
24
32
34
31
–
28
37
36
–
18
–
[La(HATP)2(H2O)2]
[Pr(HATP)2(H2O)2]
[Nd(HATP)2(H2O)2]
[Sm(HATP)2(H2O)2]
[Dy(HATP)2(H2O)2]
HBTP
[La (HBTP)2(H2O)2]
[Pr(HBTP)2(H2O)2]
[Nd(HBTP)2(H2O)2]
[Sm(HBTP)2(H2O)2]
[Dy(HBTP)2(H2O)2]
20
30
29
37
35
16
32
28
34
25
29
32
The 1H NMR spectra of ligands are recorded in DMSO.
δs and peaks are observed at 7.3-7.7 δ and 7-7.9 δ. These are
assigned to aromatic C-H of the ligands HATP showed low
field signal for the hydrazone proton at 13.3 δ29. This low field
shift is due to intramolecular hydrogen bonding. The hydra-
zone proton of HBTP appears at 8.7 δ. The signals at 2.1
δ-(6H), 2.5 δ(3H) and 3.0 δ(2H) may be due to two identical
C-CH3, N-CH3 and NH2 protons, respectively.
Electronic spectral data for the solution of Ln(III)-pyrazo-
lone complexes investigated in CH3CN are reported in Table-3.
TABLE-3
ELECTRONIC SPECTRAL DATA ALONG WITH BAND ASSIGNMENTS (kk)
Bands of Ln3+-
aqua ions (kk)
Bands of
complex (kk)
Calculated bonding parameter
B1/2
Complex
Band assignments
(1-β)
β
δ (%)
η
3H4 → 3P2
→ 3P1
22.5
21.7
20.4
21.9
21.1
19.8
0.0267
0.0277
0.0295
0.0302
0.0146
0.0197
0.0258
0.0400
0.0539
0.0142
0.0120
0.0147
0.0192
0.0165
0.0204
0.0271
0.0359
0.0411
0.0248
0.0536
0.0185
0.0111
0.0204
0.0371
0.0525
0.9733
0.9723
0.9705
0.9698
0.9854
0.9803
0.9742
0.9600
0.9461
0.0817
0.0832
0.0858
0.0868
0.0604
0.0701
0.0803
0.1000
0.1160
2.7432
2.8489
3.0396
3.1140
1.4816
2.0095
2.6983
4.1666
5.6970
0.0136
0.0141
0.0151
0.0155
0.0074
0.0099
0.0131
0.0207
0.0281
0.0072
0.0061
0.0074
0.0097
0.0083
0.0104
0.0138
0.0185
0.0212
0.0126
0.0279
0.0093
0.0056
0.0104
0.0191
0.0274
[Pr(HATP)2(H2O)2]
→ 3P0
→ 1D2
16.6
16.1
4I9/2 → 4G9/2
→ 4G5/2,2G7/2
→ 4F9/2
19.27
17.32
14.38
13.76
12.81
33.85
28.764
26.56
22.43
12.18
22.62
23.69
22.3
18.99
16.98
14.01
13.21
12.12
33.37
28.42
26.17
22.00
11.98
22.16
23.05
21.5
[Nd(HATP)2(H2O)2]
→ 2S3/2,4F7/2
→ 4F5/2,4H9/2
6H5/2 → 7F5/2
→ 4H7/2
0.9858
0.9880
0.9853
0.9808
0.0595
0.0547
0.0606
0.0692
1.4404
1.2145
1.4919
1.9575
[Sm(HATP)2(H2O)2]
[Dy(HATP)2(H2O)2]
[Pr(HBTP)2(H2O)2]
→ 4I7/2
→ 4I15/2
6H15/2 → 6F5/2
→ 4I15/2
0.9835
0.9796
0.9729
0.9641
0.9589
0.9752
0.9464
0.0642
0.0714
0.0823
0.0947
0.1013
0.0787
0.1157
1.6776
2.0824
2.7854
3.7236
4.2861
2.5430
5.6635
→ 4G11/2
3H4 → 3P2
→ 3P1
21.9
20.2
16.8
21.0
19.7
15.9
→ 3P0
→ 1D2
4I9/2 → 4G9/2
→ 4G5/2,2G7/2
→ 4F9/2
19.48
17.24
14.26
13.50
12.78
33.67
28.54
26.42
22.01
11.90
22.75
23.28
19.12
17.05
13.97
13.00
12.11
33.12
28.11
26.09
21.87
11.13
22.29
22.99
0.9815
0.9889
0.9796
0.9629
0.9475
0.0680
0.0526
0.0714
0.0963
0.1145
1.8848
1.1224
2.0824
3.8529
5.5408
[Nd(HBTP)2(H2O)2]
→ 2S3/2,4F7/2
→ 4F5/2,4H9/2
6H5/2 → 7F5/2
→ 4H7/2
0.0164
0.0151
0.0125
0.0064
0.0648
0.0203
0.0125
0.9836
0.9849
0.9875
0.9936
0.9352
0.9797
0.9875
0.0640
0.0614
0.0559
0.0400
0.1272
0.0712
0.0559
1.6673
1.5331
1.2675
0.6441
6.9289
2.0720
1.2658
0.0083
0.0076
0.0063
0.0033
0.0341
0.0104
0.0063
[Sm(HBTP)2(H2O)2]
[Dy(HBTP)2(H2O)2]
→ 4I7/2
→ 4I15/2
6H15/2 → 6F5/2
→ 4I15/2
→ 4G11/2

Vol. 27, No. 3 (2015)
Synthesis and Antimicrobial Studies of Some Trivalent Ln(III) metal Complexes 863
For comparison, the spectral data for the corresponding aqueous
salt solution are also given in Table-3. Lanthanum(III) has no
significant absorption in the UV-visible region. The absorption
bands of Pr3+, Nd3+, Sm3+ and Dy3+ in the visible and near
infrared region appear due to transitions from ground levels
3H4, 4I9/2, 6H5/2 and 6H15/2, respectively to the excited J-levels of
4f n-configuration34 of Ln(III) central metal ions. Some red shift
or, nephlauxetic effect is observed. This red shift proves a
higher degree of covalency in the complexes than that existing
in their aquo salts35. The various spectral parameters like
nephlauxetic ratio (i.e., β), covalence factor (i.e., b1/2), metal-
ligand covalency % i.e., Sinhas parameter (δ %) and covalency
angular overlap parameter (η) have been calculated.
Calculation reveals that the value of δ % and (1-β) in all
the synthesized Ln(III) complexes comes out to be positive
throughout which indicates strong coordinate covalent bonding
in all the complexes.
Thermal studies of the metal-complexes were carried
under static air condition. The thermogram of HBTP metal(II)
complexes indicate two clear cut stages, first corresponding
to the dehydration of the coordinated water molecule and
second to the decomposition process37.
A comparison of the diameters of inhibition zone of
compounds investigated shows that all the Ln(III) complexes
exhibit higher antibacterial activity against Pseudomonas and
Klebsiella than even the control ofloxacin at the same
concentration and identical conditions. The complexes are
more antibacterial than the respective ligands against all the
bacteria studied.
Conclusion
On the basis of above discussion coordination number
ten for Ln(III)-HATP and eight for Ln(III)-HBTP complexes
has been suggested. The proposed structure of complexes may
be as shown in Fig. 1.
Unlike the d-electrons of the transition metal ions, the
f-electrons of the lanthanide ions are almost unaffected by the
chemical environment and the energy levels are the same as
in the free ion due to very effective shielding by the overlying
5s2 and 5p6 shells. The magnetic moment values of the comp-
lexes showed that only La(III) complex is diamagnetic while
the rest are paramagnetic, showing close agreement with the
calculated values except for the Sm(III), indicating an insigni-
ficant participation of the 4f-electrons in the bonding. The
relatively high value obtained in the case of samarium(III)
complex may be due to small J-J separation, which leads to
the thermal population of the higher energy levels and show
susceptibilities due to first order Zeemann effect36.
ACKNOWLEDGEMENTS
The authors express their sincere gratitude to Prof. S. Jha,
University P.G. Department of Chemistry, L.N.M. University,
Darbhanga, India for providing valuable suggestions. Prof.
L.K. Mishra, Department of Chemistry, Science College, Patna
University, Patna, India is also gratefully acknowledged for
providing valuable suggestions. Courtesy of CDRI Lucknow
and Deptt. Of Chemistry, IIT Delhi for carrying out elemental
and spectral analysis is highly acknowledged. One of the
authors, B.G. Thakur, is thankful to UGC, New Delhi, India
for providing Major Research Project Under XIth Plan.
C
H3
H
N
C
H3
C
C
H3
H3
N
N
N
H
N
N
N
N
O
C
N
O
H3
N
C
N
O
S
C
S
S
N
H
N
H
H2O
Ln
H2O
Ln
OH2
OH2
N
H
N
H
S
C
S
C
O
S
N
N
O
N
N
C
H3
N
N
O
N
C
H3
N
N
N
C
H3
H
C
H3
N
H
C
H3
(I)[Ln(HATP)2(H2O)2]
Where, Ln=Nd(III), Sm(III) & Dy(III)
(II)
[Ln(HBTP)2(H2O)2]
Where, Ln=Nd(III), Sm(III) & Dy(III)
Fig. 1.

864 Mishra et al.
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