Synthesis, ESR, magnetic, and electronic spectral studies on manganese(II) complexes of semicarbazone and thiosemicarbazone

Article abstract of DOI:10.1081/SIM-100108260

Manganese(II) complexes of the general composition Mn(L)₂-X₂ (where L = p-methyl acetophenone semicarbazone (HL¹) and thiosemicarbazone (HL²) and X = Cl, Br, (1/2SO₄) have been synthesized. All of the

Full text of DOI:10.1081/SIM-100108260

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SYNTHESIS, ESR, MAGNETIC, AND ELECTRONIC
SPECTRAL STUDIES ON MANGANESE(II) COMPLEXES OF
SEMICARBAZONE AND THIOSEMICARBAZONE
Sulekh Chandra a , Gajendra Singh a , V. P. Tyagi b & Smriti Raizada b
a Department of Chemistry, Zakir Husain College, University of Delhi, J.L.N Marg, New Delhi,
110002, India
b Department of Chemistry, Mahanand Mission Harijan College, Ghaziabad, U.P., 201011,
India
Available online: 15 Feb 2007
To cite this article: Sulekh Chandra, Gajendra Singh, V. P. Tyagi & Smriti Raizada (2001): SYNTHESIS, ESR, MAGNETIC, AND
ELECTRONIC SPECTRAL STUDIES ON MANGANESE(II) COMPLEXES OF SEMICARBAZONE AND THIOSEMICARBAZONE, Synthesis and
Reactivity in Inorganic and Metal-Organic Chemistry, 31:10, 1759-1769
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(10), 1759–1769 (2001)
SYNTHESIS, ESR, MAGNETIC, AND
ELECTRONIC SPECTRAL STUDIES ON
MANGANESE(II) COMPLEXES OF
SEMICARBAZONE AND
THIOSEMICARBAZONE
Sulekh Chandra,1 Gajendra Singh,1 V. P. Tyagi,2,*
2
andSmriti Raizada
1Department of Chemistry, Zakir Husain College,
University of Delhi, J.L.N Marg,
NewDelhi 110002, India
E-mail: schandra_00@yahoo. com
2Department of Chemistry, Mahanand Mission Harijan
College, Ghaziabad (U.P.) 201011, India
E-mail: v_p_tyagi@hotmail.com;
smriti_raizada@hotmail.com
ABSTRACT
Manganese(II) complexes of the general composition Mn(L)2-
X2 (where L ¼ p-methyl acetophenone semicarbazone (HL1)
and thiosemicarbazone (HL2) and X ¼ Cl; Br; ð1=2 SO4) have
been synthesized. All of the complexes were characterized by
elemental analyses, magnetic moments, electronic and ESR
spectral studies. The complexes were found to have magnetic
moments corresponding to five unpaired electrons. Possible
geometries of the complexes were assigned on the basis of
electronic and ESR spectra.
*Corresponding author.
1759
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1760
CHANDRA ET AL.
INTRODUCTION
Metal complexes of thiosemicarbazones were found to possess pro-
nounced carcinostatic properties against a wide range of transplanted neo-
plasia176, while the oxygen analogues (semicarbazones) were found to be
inactive as carcinostatic agents. Such differences in antitumour activity can
be related to the different coordination sites, oxygen=sulfur of semi-
carbazones and thiosemicarbazones, respectively. In a series of papers7711
,
the synthetic and structural aspects of a number of transition metal com-
plexes of NS and NO donor ligands have been described.
The present work relates to the preparation and characterization of
manganese complexes with p-methylacetophenone semicarbazone (HL1)
and p-methylacetophenone thiosemicarbazone (HL2) (Fig. 1). Six co-
ordinated high spin octahedral complexes of the type Mn(ligand )2X2 (X ¼
Cl, Br, and 1=2 SO4) were obtained.
EXPERIMETNAL
Preparation of Complexes
Hot ethanolic solutions (50 mL) of manganese(II) halides (chloride or
bromide) or manganese(II) sulfate (0.05 mole) and the corresponding ligand
(0.1 mole) were mixed together and the solution was refluxed on a water
bath for about three hours. Upon cooling, the white to yellow complexes
Figure 1. Structure of ligands.

MANGANESE(II) COMPLEXES
1761
separated out. They were filtered, washed with 50% ethanol and dried over
P4O10 in a vacuum dessicator.
Physical Measurements
Magnetic susceptibility measurements were performed on a Cahn 2000
Faraday balance using Hg[Co(CNS)4], wg ¼ 16:44 Â 10À6 g=mL (at 28 ꢀC) as
the calibrating agent. Conductance measurements in nitrobenzene were
carried out on a Leeds Northup Model 4995 conductivity bridge. IR spectra
of the ligands and complexes were recorded in KBr on a Shimadzu IR 435
infrared spectrophotometer. The electronic spectra were recorded in DMF
on a Shimadzu UV Mini 1240 spectrophotometer. Microanalyses of C, H,
and N were performed at the Microanalytical Laboratory of Delhi Uni-
versity. ESR spectra were recorded in polycrystalline samples and in aqu-
eous solution on a Varian E4 ESR spectrometer. For the determination of
metal12,13, a known amount of the complex was decomposed by repeated
treatment with concentrated HNO3 and the residue was extracted with
concentrated HCl. From the acid solution manganese was precipitated with
diammonium hydrogen phosphate and weighed as Mn2P2O7.
RESULTS AND DISCUSSION
Magnetic Studies
All the complexes have the composition Mn(ligand)2X2 (X = Cl, Br,
and 1=2 SO4) (Table I). They showroom temperature magnetic moments of
5.90 to 6.02 B.M. (Table II) which is very close to the spin-only value (5.92
B.M.) predicted for five unpaired spins.
IR Spectra
The characteristic absorption of the carbonyl group in HL1 is ob-
served14 at 1680 cmÀ1. In the complexes this band shifted towards lower
wave numbers by ca. 25 cmÀ1. The amide II band in HL1 appears at
1618 cmÀ1 and in the complexes this band is also shifted towards lower wave
numbers by ca. 50 cmÀ1. This observation suggests that coordination takes
place through the vðC›OÞ oxygen. The strong band at 1580 cmÀ1 in HL1
contains apparently large contribution from vðC›NÞ. Coordination
through O increases the double bond character of the CN bond. In

1762
CHANDRA ET AL.
Table I. Elemental Analyses and Molar Conductance Data
Elemental Analyses,
% Found=(calc.)
Formula OÀ1 cmÀ1
Weight
%
Dec. p.
Complex
molÀ1
Yield ꢀC
Mn
C
H
N
MnðHL1Þ2Cl2
508.27
10.03
10.79 47.20 5.15 16.50 55
(10.81) (47.25) (5.12) (16.54)
8.25 35.90 3.85 12.56 62
(8.22) (35.93) (3.89) (12.58)
10.28 45.00 4.85 15.74 64
(10.30) (45.04) (4.88) (15.76)
10.20 44.42 4.80 15.58 58
(10.17) (44.45) (4.82) (15.56)
8.75 38.18 4.15 13.32 54
(8.73) (38.16) (4.13) (13.36)
180
210
195
201
215
C20H26Cl2MnN6O2
MnðHL1Þ2Br2
597.21
533.47
540.40
629.35
20.5
15.8
21.2
6.0
C20H26Br2MnN6O2
MnðHL1Þ2SO4
C20H26MnN6O6S
MnðHL2Þ2Cl2
C20H26MnCl2N6S2
MnðHL2Þ2Br2
C20H26Br2MnN6S2
thiosemicarbazide the bands at 1643 and 1617 cmÀ1 are assigned, respec-
tively, to the deformation bands of the NH2 group in the hydrazine residue
and to the amide II band of the primary amine. In the thiosemicarbazones,
the former band disappears and the amide II band (1617 cmÀ1) is shifted
towards lower wave numbers (1603 cmÀ1) which may be due to the electron-
withdrawing nature of this group14,15
.
16
A band at 795 cmÀ1 is mainly due to vðC›SÞ . In the IR spectra of the
complexes this band shifted towards lower frequencies by ca. 30 cmÀ1. A
medium band at 1310 cmÀ1 in HL2 also contains contributions from vðC›SÞ
and includes contribution from vðN À C À NÞ stretching vibrations17 and the
N-C-N deformation vibration. This band has shifted to higher frequency in the
complexes as also observed in the spectra of other thiosemicarbazone com-
plexes18. The strong vðC›NÞ bandinHL2 hasbeen observed at1520 cmÀ1. The
band shifted towards higher wave numbers by ca. 40 cmÀ1. This observation
indicates that bothligands act as bidentate coordinating throughN of vðC›NÞ
and O=S of the semicarbazone=thiosemicarbazone moieties.
Far-InfraredSpectra
The far-IR spectral bands in the ligands are unchanged in the com-
plexes but shownewbands in the region 350 7344 cmÀ1 and 3177306 cmÀ1
which, tentatively, may be assigned to vðM-NÞ and vðM-SÞ modes, respec-
tively. Halide sensitive bands appear at 2507220 cmÀ1 for M-C1 and
2207210 cmÀ1 for M-Br19 (Table IV).

MANGANESE(II) COMPLEXES
1763

1764
CHANDRA ET AL.
Electronic Spectra
In the high-spin, octahedrally coordinated Mn(II) complex, the lowest
3
2
configuration ðt2gÞ ðegÞ gives rise to the ground state 6A1g. Since this is the
only sextet level present, all of the absorption bands must therefore be spin-
forbidden transitions.
The electronic spectra of the complexes display weak absorption
bands in the ranges 19,608719,920, 23,810724,981, 28,571729,850,
29,850731; 746 cmÀ1 characteristic of octahedral geometry20. These bands
4
4
6
4
6
4
are assigned as A1g ! A1g ð GÞ (10Bþ5C), A1g ! Eg;4 A1gð GÞ,
4
4
6
4
6
4
(10Bþ5C) A1g ! Egð DÞ (17Bþ5C) and A1g ! T1gð PÞ (7Bþ5C) tran-
sitions, respectively (Table II). The experimentally observed transition en-
ergies and calculated values for the parameters B, C, Dq and b are shown in
Table III. The values obtained for the parameters B and C using the tran-
4
4
6
4
6
4
sitions A1g; ! T1gð GÞ and A1g ! T1gð PÞ are negative which has no
physical significance, while the transitions Alg ! Eg; 4Algð GÞ and
6
4
4
6Alg ! Tlgð PÞ yield absurd values for parameter B and hence these values
4
4
are not included in Table III. The best set of values for the parameters B and
6
C could be obtained using the transitions Alg ! Eg; 4Algð GÞ and
4
4
6Alg ! Egð DÞ. This is due to the fact that the energies of these two tran-
sitions are independent of the crystal field splitting energy and only depend21
on the parameters B and C. The values for the parameter Dq could be
evaluated with the help of curve transition energies vs. Dq given by Orgel22,
4
4
using the energy level due to the transition 6Alg ! Algð GÞ. The parameters
B and C are linear combinations of certain Coulomb and exchange integrals
and are generally treated as empirical parameters obtained from the spectra
of free ions. The Slater, Condon-Shortly parameters F2 and F4 are related to
the Racah inter-electronic repulsion parameters B and C as follows23:
B ¼ (F2À5F4) and C ¼ 35 F4. By using values of the Racah parameters B and
C, values for the parameters F2 and F4 have been calculated (Table III).
4
4
Table III. Ligand Field Parameters
Complex
Dq (cmÀ1
)
B (cmÀ1
)
C (cmÀ1
)
b
F4
F2
hx
MnðHL1Þ Cl2
MnðHL1Þ2Br2
MnðHL1Þ2SO4
MnðHL2Þ2Cl2
MnðHL2Þ22Br2
934
970
1002
898
707
735
759
680
696
3394
3314
3301
3402
3605
0.89
0.94
0.97
0.87
97 1192 1.42
95 1210 0.85
94 1229 0.43
97 1165 1.86
919
0.84 103 1211 2.28

MANGANESE(II) COMPLEXES
1765
Table IV. Infrared Spectral Bands (cmÀ1) of HL1 and Mn(HL1)2X2
n(C ¼ O)
Compound
HL1
n(C ¼ N) n(NHþCH) Amide I Amide II Amide III n(MÀX)
1520
3380 s, 3238 s, 1680 ns 1618 s
3152 s, 3050 s
3400 m, 3270 s, 1645 ns 1550 s
3120 s
3400 m, 3280 s, 1650 ns 1550 s
3125 m
3405 m, 3080 m, 1645 ns 1545 s
3120 m
1300 m
1320 m
1310 m
1320 m
MnðHL1Þ2Cl2 1550 s
MnðHL1Þ2Br2 1545 s
MnðHL1Þ2SO4 1550 s
220 m
210 m
The electron-electron repulsion in the complexes is less than that in the
free ion, resulting in an increased distance between electrons and, thus, an
effective increase in the size of the orbitals. On increasing delocalization, the
value of b decreases and is less than one in the complex. An estimate of b has
been obtained from the nephelauxetic parameter for the ligand (hx) and the
nephelauxetic parameter of the metal ion KM as (1-b) ¼ hxKM12. The values
of the parameter hx for the complexes have been calculated using the cov-
alency contribution of Mn(II) ion (0.07) while the numerical value 786 cmÀ1
for B of the free Mn(ll) ion24 has been used to calculate the value for b.
ESR Spectra
The ESR spectra of the complexes have been recorded as polycrystal-
line samples and in aqueous solutions. Polycrystalline samples give one
isotropic signal centered around the approximate free electron g value (Table
II). In polycrystalline samples, Mn(II) complexes usually give broad signals
attributed to forbidden transitions where DM ¼ Æ1 (M ¼ electron spin
Table V. Infrared Spectral Bands (cmÀ1) of HL2 and Mn(HL2)2X2
d(NH2) and Mainly n(CN) n(C ¼ S)
Mainly
þNH2 n(CN) n(C ¼ S) n(MÀX)
Compound
Amide II band
and NH2
HL2
1603 ns
1630 ns
1630 ns
1520 s
1565 s
1565 s
1480 m 1310 m 790 s
1470 m 1360 m 760 s
1470 m 1360 m 762 s
MnðHL2Þ Cl2
250 m
220 m
MnðHL2Þ22Br2

1766
CHANDRA ET AL.
quantum number) and Dm ¼ 0 (where m ¼ nuclear spin quantum number).
The broadening of the spectrum in the powdered sample is analogous to that
observed in the case of immobilised free radicals (e.g. Mn(II) complexes of
conconvalin)25. Broadening due to immobilization of Mn(II) ion in the li-
gand results because the motion of Mn(II) is highly restricted. Another origin
of line broadening is spin-relaxation25 which is temperature dependent. The
intensity of forbidden25 transitions is inversely proportional to the square of
the applied magnetic field, hence, their intensities should be reduced in the K-
band spectrum with consequent enhancement of the intensities of the allowed
signals. This aspect, however is not covered in the present studies.
In aqueous solutions, all of the complexes give ESR spectra containing
six lines arising from the hyperfine interaction between the unpaired electron
with the 55Mn nucleus (1 ¼ 5=2) The nuclear magnetic quantum number
m (MI) corresponding to these lines are À5=2, À3=2, À1=2, þ1=2, þ3=2, and
þ5=2 from lowto high field.
All the complexes give similar ESR spectra in aqueous solution and so
do all thiosemicarbazone complexes. It is obvious that in aqueous solution,
the complexes exist as common complex ion [Mn(HL1)2(H2O)2]2þ, respec-
tively. The observations in the light of the above discussion are suggestive of
near octahedral geometry of these aquo species. The line width attributed to
Figure 2. Structure of the complexes.

MANGANESE(II) COMPLEXES
1767
Figure 3. Structure of the aqueous complexes.
the 1=2 $ À1=2 transition is only slightly higher ( ꢁ 115 G) than that for
Mn(H2O)62þ( ꢁ 93 G)26.
On the basis of the above studies, the following structures (Figs. 2 and
3) may be suggested for the complexes.
ACKNOWLEDGMENTS
Thanks are due to the Department of Science and Technology,
Technology Bhawan, New Delhi, for financial assistance and the Indian
Institute of Technology, Mumbai for recording ESR spectra.
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1768
CHANDRA ET AL.
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Received December 20, 2000
Accepted August 22, 2001
Referee I: G. N. Holder
Referee II: R. A. Faltynek