Spectroscopic evaluation of manganese(II) complexes derived from semicarbazones and thiosemicarbazones

Article abstract of DOI:10.1016/j.saa.2004.08.028

Manganese(II) complexes having the general composition Mn(L) ₂X₂ [where L = isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone

Full text of DOI:10.1016/j.saa.2004.08.028

Spectrochimica Acta Part A 61 (2005) 2549–2554
Spectroscopic evaluation of manganese(II) complexes derived
from semicarbazones and thiosemicarbazones
Sulekh Chandra∗, Lokesh Kumar Gupta
Department of Chemistry, Zakir Husain College (University of Delhi), JLN-Marg, NewDelhi 110002, India
Received 7 July 2004; accepted 31 August 2004
Abstract
Manganese(II) complexes having the general composition Mn(L)2X2 [where L = isopropyl methyl ketone semicarbazone (LLA), isopropyl
methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD)
and X = Cl−, 1/2SO42−] have been synthesized. All the complexes were characterized by elemental analyses, molar conductance, magnetic
moment susceptibility, EI-mass, 1H NMR, IR, EPR and electronic spectral studies. All the complexes show magnetic moments corresponding
to five unpaired electrons. The possible geometries of the complexes were assigned on the basis of EPR, electronic and infrared spectral
studies.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Thiosemicarbazones; Semicarbazones; Spectroscopic; Manganese(II)
1. Introduction
LLC and LLD (Fig. 1) and their complexes with man-
ganese(II).
Complexes of thiosemicarbazones with transition metal
have received attention because of their biological activ-
ity including antitumer, antibacterial, fungicidal and anti-
carcinogenic properties [1–6].
2. Physical measurements
Manganese and its compounds are widely used in analyti-
cal chemistry, metallurgical processes and paint and pigments
industry. The complexes of manganese(II) play an excellent
role in catalytic property [7–10]. Manganese metal has a well-
established importance in the field of biology and medicine.
A lot of articles are available on the physiology and biochem-
istry of manganese [11]. Ruminants manganese is present in
the serum of blood as manganese(III) ␤-globulin and in ery-
throcytes as manganese porphyrin ring.
The C, H and N were analyzed on a Carlo-Erba 1106 ele-
mental analyzer; the nitrogen contents of the complexes were
determined using Kjeldahl’s method. Molar conductance was
measured on an ELICO (CM82T) conductivity bridge. Mag-
netic susceptibility was measured at room temperature on a
Gouy balance using CuSO4·5H2O as a callibrant. Electron
impact mass spectra were recorded on JEOL, JMS, DX-303
1
mass spectrometer. H NMR spectra were recorded on Hi-
tachi FT-NMR, model R-600 spectrometer using CDCl3 as
solvent. Chemical shifts are given in ppm relative to tetram-
ethylsilane. IR spectra (KBr) were recorded on a FTIR Spec-
trum BX-II spectrophotometer. The electronic spectra were
recorded in DMSO on Shimadzu UV mini-1240 spectropho-
tometer. EPR spectra of the complexes were recorded as poly-
crystalline sample and in the DMSO solution, at room tem-
perature on E4-EPR spectrometer using the DPPH as the g-
marker.
The current paper is focused on the spectral charac-
terization of the newly synthesized ligands LLA, LLB,
∗
Corresponding author.
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
lokesh kg@rediffmail.com (L.K. Gupta).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.08.028

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2549–2554
3.1. Infra red spectra of the ligands
Infrared spectra of the ligands show bands in the region
∼1628 and 1575 cm−1 which may be assigned to the sym-
metric or asymmetric [ν(C N)] vibrations. A strong band
in the region ∼770–782 cm−1 in thiosemicarbazones and
∼1692–1709 cm−1 in semicarbazones is due to the [ν(C S)]
and [ν(C O)] groups, respectively. On complex formation,
the position of these bands is shifted toward lower frequency
as compared the metal free ligand, this indicates that the co-
ordination takes place through the nitrogen, oxygen, and sul-
fur atoms of (C N), (C O) and (C S) groups [13], respec-
tively. Thus, it has been concluded that the semicarbazones
and thiosemicarbazones act as bidentate chelating agent
[7].
Fig. 1. Structure of the ligands.
3.2. 1H NMR spectra of the ligands
3. Results and discussion
1H NMR spectra of the ligands in DMSO show the signals
[14] as follows (chemical shift in ppm):
The molar conductance for these complexes has been de-
termined in dimethylformamide (DMF). The results were in
agreement for the nonelectrolytic nature for all the chloride
complexes and 1:1 electrolyte for sulphate complexes [12]
(Table 2). On the basis of the above data, the [Mn(L)2Cl2]
formula may be suggested for the chloro complexes, and
[Mn(L)]SO4 forsulphatecomplexesTable1[whereL = LLA,
LLB, LLC and LLD].
3.2.1. Ligand (LLA)
δ 1.82 ppm (t) (3H, H3C C ), δ 8.58 ppm (s) (1H,
HN CO), δ 3.45 ppm (d) (2H, H2N CO), δ 1.18 (t), δ 2.48
(sextet), δ 4.41 ppm (d) (C3H7 C).
Table 1
Physical and elemental analysis data of the complexes
Complex
MW found
(calculated)
Colour
M.p.a (◦C) Yield (%) Elemental analysis data found (calculated, %)
Mn
C
H
N
(LLA) C6H13N3O
(LLB) C6H13N3S
(LLC) C9H12N4O
(LLD) C9H12N4S
[Mn(LLA)2Cl2] MnC12H26N6O2Cl2 (412)
[Mn(LLA)2]SO4 MnC12H26N6O6S (437)
[Mn(LLB)2Cl2] MnC12H26N6S2Cl2 (444)
[Mn(LLB)2]SO4 MnC12H26N6O4S3 (469)
[Mn(LLC)2Cl2] MnC18H24N8O2Cl2 (510)
144 (143)
161 (159)
192 (192)
209 (208)
Off white
Dirty white 220
Cream
Off white
Light brown 271
Brown 260
Pale brown 291
Brown
Brown
Rust brown 253
Dull brown 260
Brown
229
68
78
70
73
69
66
72
71
70
63
65
69
–
–
–
–
50.32 (50.35) 9.21 (9.09) 29.22 (29.37)
45.17 (45.28) 8.03 (8.18) 26.57 (26.41)
56.38 (56.25) 6.36 (6.25) 29.03 (29.17)
52.01 (51.92) 5.92 (5.77) 26.83 (26.92)
204
210
13.28 (13.35) 35.07 (34.95) 6.22 (6.31) 20.30 (20.39)
12.50 (12.59) 32.88 (32.95) 6.03 (5.95) 19.13 (19.22)
12.54 (12.39) 32.58 (32.43) 5.81 (5.86) 18.99 (18.92)
11.61 (11.73) 30.83 (30.70) 5.40 (5.54) 18.00 (17.91)
10.93 (10.78) 42.43 (42.35) 4.62 (4.71) 22.05 (21.96)
10.41 (10.28) 40.29 (40.37) 4.40 (4.49) 21.02 (20.93)
10.06 (10.15) 39.97 (39.85) 4.37 (4.43) 20.74 (20.66)
285
266
[Mn(LLC)2]SO4 MnC18H24N8O6S
[Mn(LLD)2Cl2] MnC18H24N8S2Cl2 (542)
[Mn(LLD)2]SO4 MnC18H24N8O4S3 (566)
(535)
259
9.81 (9.72)
38.05 (38.16) 4.16 (4.24) 19.70 (19.79)
a
Decomposition temperature.
Table 2
Molar conductance, magnetic moment and electronic spectral data
Complex
Molar conductancea (ꢀ−1 cm2 mol−1
)
aµeff. (B.M.)
λmax (cm−1
)
ε (L mole−1 cm−1
)
[Mn(LLA)2Cl2]
[Mn(LLA)2]SO4
[Mn(LLB)2Cl2]
[Mn(LLB)2]SO4
[Mn(LLC)2Cl2]
[Mn(LLC)2]SO4
[Mn(LLD)2Cl2]
[Mn(LLD)2]SO4
07
114
06
118
07
105
11
119
5.89
17890, 21846, 28872, 35936
22692, 27920, 36900
17750, 22354, 29108, 36293
21981, 28076, 36992
18258, 21982, 29320, 36182
23108, 27851, 36805
17912, 22416, 28766, 36377
22464, 27948, 37364
34, 39, 68, 125
36, 63, 139
34, 40, 69, 122
34, 66, 140
35, 40, 71, 126
36, 65, 139
34, 39, 69, 123
35, 65, 141
5.96
5.90
5.99
5.93
5.98
5.92
5.97
a
Error limit, 3%.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2549–2554
2551
Fig. 2. Electron impact mass spectra of the ligands.
3.2.2. Ligand (LLB)
99 and 127 amu may be due to different fragments. The in-
tensity of these peaks gives an idea of the stability of these
fragments.
δ 1.84 ppm (t) (3H, H3C C ), δ 8.65 ppm (s) (1H,
HN CS), δ 3.59 ppm (d) (2H, H2N CS), δ 1.15 (t), δ 2.50
(sextet), δ 4.44 ppm (d) (C3H7 C).
3.3.2. Ligand (LLB)
3.2.3. Ligand (LLC)
Under the EI mass spectral study, it gives a final peak at
158 amu confirms the proposed formula (C6H13N3S calcu-
lated atomic mass, 159 amu) and other peaks at 15, 44, 60, 77,
89, 127 and 143 amu may be attributed to different fragments.
δ 1.80 ppm (t) (3H, H3C C ), δ 8.57 ppm (s) (1H,
HN CO), δ 3.45 ppm (d) (2H, H2N CO), δ 7.11 ppm (m)
(4H, Ph ), δ 3.80 ppm (d) (2H, Ph NH2).
3.2.4. Ligand (LLD)
δ 1.78 ppm (t) (3H, H3C C ), δ 8.63 ppm (s) (1H,
HN CS), δ 3.55 ppm (d) (2H, H2N CS), δ 7.10 ppm (m)
(4H, Ph ), δ 3.86 ppm (d) (2H, Ph NH2).
3.3.3. Ligand (LLC)
The presence of EI mass spectral peak at 193 amu confirms
the proposed formula (C9H12N4O calculated atomic mass,
192 amu). A set of peaks observed in the range 16, 44, 59, 77,
92, 104, 119 and 134 amu are assigned to various fragments.
3.3. Electron impact mass spectra of the ligands
EI mass spectra of the ligands (Fig. 2) confirm the pro-
posed formula [15] by showing the following peaks.
3.3.4. Ligand (LLD)
Presence of a peak at 208 amu support to the proposed
formula (C9H12N4S calculated atomic mass 208 amu). The
peaks due to the various fragments appears at 15, 60, 78, 92,
105, 134, 192 and 208 amu.
3.3.1. Ligand (LLA)
Appearance of final peak at 144 amu (C6H13N3O calcu-
lated atomic mass 143 amu) and other peaks at 15, 43, 78,

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2549–2554
Fig. 4. Electronic spectra of the complexes.
(ε = 63–66 L mole−1 cm−1
)
and
36 805–37 364 cm−1
(ε = 139–141 L mole−1 cm−1), which may be assigned
Fig. 3. IR spectral band of uncoordinated sulphate group in
[Mn(LLB)2]SO4.
6
4
6
4
to the transitions: A1g → T2g (4G), A1g → T2g (4D),
6A1g → A2g (4F), respectively [20]. These bands are char-
4
3.4. Chloride complexes [Mn(L)2Cl2]
acteristic for four coordinate tetrahedral Mn(II) complexes
(Fig. 5).
Magnetic moment of the Mn(II) chloride com-
plexes recorded at room temperature lies in the range
5.89–5.93 B.M. corresponding to high spin configuration cor-
responding to five unpaired electrons [16].
AnEPRspectraisreadilydetectedevenforlargezero-field
splitting, because d5 is an odd electron system whose ground
state is a Kramer’s doublet and whose degeneracy is only
completely removed by a magnetic field. The broad signal
in the polycrystalline EPR spectra of Mn(II) complexes is at-
tributed to forbidden transitions, where M = 1 (M = electron
spin quantum number). The broadening of spectra is due to
immobilization of Mn(II) ion in the ligand results because
the rotational motion of Mn(II) is highly restricted. Another
origin of line broadening is due to spin relaxation, which
is temperature dependent. All the Mn(II) complexes, under
study, shows isotropic EPR spectra (Fig. 6), when recorded as
polycrystalline sample. In DMF solution, Mn(II) complexes
give EPR spectra containing the six lines, arising due to the
hyperfine interaction between the unpaired electron with the
55Mn nuclear (1 = 5/2). The nuclear magnetic quantum num-
ber M1, corresponding to these lines are −5/2, −3/2, −1/2,
+1/2, +3/2 and +5/2 from low to the high field. The g-tensor
values have been calculated by the Kneubuhl method and the
results are shown in Table 3.
In the high spin octahedrally coordinated Mn(II) com-
plexes, the lowest configuration (t2g)3(eg)2 gives rise to
6
the ground state A1g. Since this is the only sextet level
present, all the absorption bands must, therefore, be spin
forbidden transitions. As a consequence of the sharp-
ness of the bands, it is possible to obtain very accurate
measurements of electronic transition energies with d5
complexes. Such spectra, therefore, provide a very adequate
test for the spectroscopic theory. The electronic spectra of
the complexes (Table 2) show four weak intensity bands
in the range 17 750–18 258 (ε = 34–35 L mole−1 cm−1),
21 826–22 416 (ε = 39–40 L mole−1 cm−1), 28 766–29 320
(ε = 68–71 L mole−1 cm−1
)
and
35 936–36 377 cm−1
(ε = 122–126 L mole−1 cm−1). These bands may be as-
6
4
6
4
4
signed to: A1g → T1g (4G), A1g → Eg, A1g (4G)
6
4
6
4
(10B + 5C), A1g → Eg (4D) (17B + 5C) and A1g → T1g
(4P) (7B + 7C), respectively [17,18].
The parameters B and C were calculated from the second
and third transitions because these transitions are free from
the crystal field splitting and depend on B and C parameters
[16]. The values of Dq were obtained with the help of curve,
transition energies versus Dq, as given by the Orgel [21] using
3.5. Sulphate complexes [Mn(L)2]SO4
Room temperature magnetic moment of the Mn(II) sul-
phate complexes lie in the range 5.96–5.99 B.M., these values
are in tune with a high spin configuration.
Table 3
The infrared spectra of the sulphate complexes (Fig. 3)
show IR bands in the region of ∼1408–1426(s) and
∼615–622 cm−1 characteristic for the uncoordinated sul-
phate group [19].
The molar conductance measurements of the sulphate
complexes recorded at room temperature in DMF solution
were in the tune of 1:1 electrolyte [12]. The electronic
spectra of the complexes (Fig. 4) recorded at room tem-
perature in DMF solution show three bands in the range
21 981–23 108 (ε = 34–36 L mole−1 cm−1), 27 851–28 076
EPR spectral data of the complexes
Complex
Temperature
giso
A0
[Mn(LLA)2Cl2]
[Mn(LLA)2]SO4
[Mn(LLB)2Cl2]
[Mn(LLB)2]SO4
[Mn(LLC)2Cl2]
[Mn(LLC)2]SO4
[Mn(LLD)2Cl2]
[Mn(LLD)2]SO4
R.T.
R.T.
R.T.
R.T.
R.T.
R.T.
R.T.
R.T.
1.9656
1.9992
1.9986
2.0014
2.0739
2.0080
2.0152
1.9998
109.5760
102.5000
121.6667
119.6667
112.1678
105.0000
105.9832
106.4854

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2549–2554
2553
Fig. 5.
the energy due to the transition 6A1g → T1g (4G). Parame-
4
4. Experimental
ters B and C are linear combinations of certain coulombs
and exchange integral and are generally treated empirical pa-
rameters obtained from the spectra of the free ions. Slater
Condon-shortly repulsion parameters F2 and F4 are related
to Racah parameters B and C as: B = F2–5F4 and C = 35F4,
The electron–electron repulsion in the complexes is more
than in the free ion, resulting in an increased distance be-
tween electrons, and thus, affects the size of the orbital. On
increasing delocalization, the value of β decreases up to less
than one in the complexes. The value of β can be calcu-
lated from the Nephelauxetic parameter for the ligand (hx)
and the Nephelauxetic parameter for the metal ion (km) as
(1 − β) = hxX km. The value of the parameter hx for Mn(II)
complexes have been calculated by using the co-valency con-
tribution of Mn(II), while for the calculation of β, we used the
All the chemicals used were of AnalaR grade, and pro-
cured from Sigma Aldrich and Fluka. Metal salts were pur-
chased from E. Merck and were used as received.
4.1. Preparation of ligands
All the ligands were prepared by the methods reported
earlier [24] by coupling of semicarbazide hydrochloride and
thiosemicarbazide, respectively, with corresponding ketones.
4.2. Preparation of complexes
A general method has been adopted for the synthesis of
the Mn(II) complexes. A hot (∼45 ◦C) aqueous ethanolic so-
lution (20 mL, 1:1 v/v) of the hydrated metal salts (0.05 mole)
and a hot ethanolic solution (20 mL) of the respective ligand
(0.1 mole) were mixed with constant stirring. The mixture
was refluxed for about 5 h at a temperature of ∼75 ◦C. On
cooling the contents to a temperature of ∼5 ◦C, the com-
numerical value of B for Mn(II) free ion which is 786 cm−1
.
The observed values for parameter β and hx suggest that the
complexes, reported here, have appreciable ionic character
[22,23]. The calculated values of the ligand field parameters
are given in Table 4.
Table 4
Ligand field parameters of the complexes
Complex
Dq (cm−1
)
B (cm−1
)
β
C (cm−1
)
F4
F2
ν2/ν1
hx
[Mn(LLA)2Cl2]
[Mn(LLA)2]SO4
[Mn(LLB)2Cl2]
[Mn(LLB)2]SO4
[Mn(LLC)2Cl2]
[Mn(LLC)2]SO4
[Mn(LLD)2Cl2]
[Mn(LLD)2]SO4
1789
2269
1775
2198
1826
2311
1791
2246
1003.71
1282.86
964.86
1273.71
1048.29
1279.14
907.14
0.64
0.82
0.61
0.81
0.67
0.81
0.58
0.86
2361.78
3018.28
2541.08
3067.78
2299.82
3011.92
2668.92
2899.32
67.48
86.24
72.60
87.65
65.71
86.05
76.26
82.84
1341.11
1714.06
1327.86
1711.96
1376.84
1709.39
1288.44
1759.34
1.22
1.23
1.26
1.28
1.20
1.21
1.25
1.24
5.14
2.57
5.57
2.71
4.71
2.71
6.00
2.00
1345.14

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2549–2554
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Acknowledgements
The authors are thankful to the University Grant Commis-
sion, New Delhi, for financial assistance and the principal,
Zakir Husain College, for providing research facilities. We
also express our sincere thanks to RSIC, IIT Mumbai, for
recording EPR spectra.