Catalytic activity of 3d-metal coordination compounds with diphenylthiocarbazide

Article abstract of DOI:10.1023/A:1020855124255

The catalytic activity of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) diphenylthiocarbazide complexes in decomposition of hydrogen peroxide was studied. The activation energies of this reaction were correlated with the strength of ligand bonding

Full text of DOI:10.1023/A:1020855124255

Russian Journal of General Chemistry, Vol. 72, No. 8, 2002, pp. 1181 1182. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 8, 2002,
pp. 1261 1262.
Original Russian Text Copyright
2002 by Koksharova, Khimich.
Catalytic Activity of 3d-Metal Coordination Compounds
with Diphenylthiocarbazide
T. V. Koksharova and I. S. Khimich
Mechnikov Odessa State University, Odessa, Ukraine
Received December 4, 2000
Abstract The catalytic activity of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) diphenylthiocarbazide
complexes in decomposition of hydrogen peroxide was studied. The activation energies of this reaction were
correlated with the strength of ligand bonding to the metal atom in the catalyst molecule.
Previously we studied the catalytic activity of
3d-metal complexes with thiosemicarbazide [1]. We
found that the catalytic activity of the complexes
depends on both the central metal and counterion.
It seemed interesting to study the catalytic activity
of complexes with other ligands structurally similar to
the larger the low-frequency shift of the thioamide IV
band, the stronger the bond of the metal with sulfur
in the complex. Our results show that the activation
energy of catalytic decomposition of hydrogen perox-
ide in the presence of the complexes varies in parallel
with the metal sulfur bond strength in the complex.
thiosemicarbazide, in particular, with thiocarbazide An exception is the Co(II) complex. This may be due
derivatives. In this work, we examined the catalytic
activity of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), and
Cu(II) complexes with diphenylthiocarbazide (H2L) in
decomposition of hydrogen peroxide and correlated
the results with data on chemical bonding in the com-
plexes.
to the fact that Co(II) is first oxidized to Co(III),
which is followed by catalytic decompostion of H2O2
under the action of the Co(III) complex having differ-
ent characteristics (in particular, different M S bond
strength).
The correlation between the low-frequency shift of
the IR absorption bands of the ligand upon coordina-
tion and the catalytic activity of the complex is of
interest. For example, it was shown [2] that, for struc-
turally related Cu(II) thiosemicarbazone and semicar-
bazone complexes, there is a quantitative relationship
We found that, in neutral solutions, the 3d-metal
diphenylthiocarbazide complexes show no catalytic
activity. Therefore, experiments were performed in
alkaline solutions. In an alkaline solution, hydrogen
peroxide fairly vigorously decomposes in the presence
of any of the above complexes even at room tempera- between the specific rate constants of the reactions of
ture. The reaction order with respect to each catalyst the complexes with peroxyl radicals, shifts of the
is unity. From the temperature dependences of the
reaction rate constants (Fig. 1), we calculated the acti-
vation energies and preexponential terms for all the
complexes under consideration (see table).
IR absorption bands of the ligands upon coordination,
and cytotoxic properties of the complexes.
Low-frequency shifts of the thioamide IV absorption
maximum in the IR spectra, activation energies, and pre-
exponential terms of catalytic decomposition of hydrogen
peroxide in the presence of 3d-metal diphenylthiocarbazide
complexes
These data show that the activation energy of hy-
drogen peroxide decomposition in the presence of 3d-
metal diphenylthiocarbazide complexes decreases in
the order Ni2+ > Fe3+ Mn2+ Cu2+ > Co2+ > Cr3+.
1
1
Comparison of this series with the IR data shows
that the activation energy of catalytic decomposition
of hydrogen peroxide decreases in virtually the same
order as the low-frequency shift of the thioamide IV
absorption maximum, with the correlation being linear
(Fig. 2). Since the thioamide IV band is essentially
the (CS) band, a decrease in its frequency is due to a
decrease in the C=S bond multiplicity, characterizing
the strength of the M S bonding. Hence, apparently,
Complex
Ea, kJ mol
log A
, cm
Cr(HL)3
Mn(HL)2
Fe(HL)3
CoL(H2O)2
NiL(H2O)2
CuL(H2O)2
23
43
45
36
77
42
0.1038
5.73
4.70
4.73
9.21
5
10
10
20
17
10
4.03
1070-3632/02/7208-1181$27.00 2002 MAIK Nauka/Interperiodica

1182
KOKSHAROVA, KHIMICH
Cr(III), Mn(II), Fe(III), Co(II), Ni(II), and Cu(II)
ln k
chlorides and diphenylthiocarbazide were of analyti-
cally pure grade.
4
The metal content of the complexes was deter-
mined by complexometric titration [3]; sulfur content,
by the Schoniger method with weighing of barium
sulfate [4]; and the nitrogen content, by the Dumas
method [4].
6
Hydrogen peroxide was of chemically pure grade;
its concentration was determined by permanganato-
metric titration [5]. Decomposition of hydrogen per-
oxide was performed in an alkaline solution (0.01 M
NaOH) at 18 40 C and initial H2O2 concentration of
1.5 wt %; the total solution volume was 10 ml. The
catalyst weight was 0.1 g in all the cases. The reaction
progress was monitored by the volume of evolved
oxygen.
8
10
12
1
2
3
4
5
6
Synthesis of complexes. A 1.29-g portion of H2L
was dissolved on heating in 50 ml of ethanol. To the
hot solution, 0.005 mol of appropriate metal chloride
was added in portions with stirring. In the case of
Cu(II) and Cr(III), the solutions became brown, and
in the other cases, dark red. With Cu(II), a brown
precipitate formed immediately; with the other metals,
brown precipitates formed only after partial evapora-
tion of the solvent in air. The precipitates were sep-
arated, washed with a small amount of ethanol, and
air-dried to constant weight.
1
3.2
3.3
3.4 103/T, K
Fig. 1. Logarithm of the rate constant of hydrogen
peroxide decomposition in the presence of 3d-metal
coordination compounds with diphenylthiocarbazide vs.
reciprocal temperature: (1) Cr(HL) , (2) Mn(HL) ,
(3) Fe(HL) , (4) CoL(H O) , (5) NiL(H O) , and
(6) CuL(H O) .
3
2
3
2
2
2
2
2
2
Ea,
kJ mol
1 70
60
REFERENCES
50
40
30
20
1. Koksharova, T.V. and Seifullina, I.I., Zh. Obshch.
Khim., 1997, vol. 67, no. 2, p. 177.
2. Cao, R., Garcia, A., and Castell, E., Monatsh. Chem.,
1992, vol. 123, nos. 6 7, p. 487.
1
4
6
8
10 12 14 16
, cm
3. Schwarzenbach, G. and Flaschka, H., Die komplexo-
metrische Titration, Stuttgart: Enke, 1965.
4. Klimova, V.A., Osnovnye mikrometody analiza organi-
cheskikh soedinenii (Main Methods for Organic Micro-
analysis), Moscow: Khimiya, 1975.
Fig. 2. Correlation between the activation energy of
hydrogen peroxide decomposition and the low-frequency
shift of the thioamide IV absorption band.
EXPERIMENTAL
5. Babko, A.K. and Pyatnitskii, I.V., Kolichestvennyi
analiz (Quantitative Analysis), Moscow: Vysshaya
Shkola, 1968, pp. 378 379.
The IR spectra were measured with an IKS-29
spectrometer using KBr pellets.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 8 2002