ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P126. Preparation and Characterization of Manganese Schiff Base
Complexes as Models for PSII
T. Matsushita, H. Imagawa, H. Asada, M. Kasuno, and M. Fujiwara
Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University,
Seta, Otsu 520-2194 Japan
e-mail: matusita@chem.ryukoku.ac.jp
Manganese ions are believed to function dioxygen generation from water in PSII of green plants. So far many
model manganese compounds have been prepared and characterized to mimic this process. However, a few
artificial photosynthetic dioxygen generation using higher-valent manganese complexes has been reported.
Previously we have reported on the preparation of a series of dichloromanganese(IV) Schiff base complexes,
their molecular structures and reactions with water, which can generate dioxygen [1-4].
In this study we have prepared and characterized dinucleating Schiff base ligands, which were obtained by the
reaction of triethylenetetramine and salicylaldehyde derivatives, and their manganese(III) complexes(Fig.1).
Moreover, novel dinucleating ligands, which were derived from 5, 5’-methylene-bis-salicylaldehyde and
alkylesters of 1 : 1 condensation product of 5-carboxysalicylaldehyde and ethylenediamine, and their
manganese(III) complexes have been prepared. All the manganese complexes were identified by several
physico-chemical measurements. These manganese(III) Schiff base complexes have been allowed to react with
chlorine to form the corresponding manganese(IV) complexes and then with water molecules. The reactions of
the manganese(III) complexes with Cl2 and then water have been monitored by measuring the changes in UVvisible
spectra and cyclic voltammograms. In the visible spectra, new intense bands around 600 nm were
observed by the addition of Cl2 to the solutions of manganese(III) complexes, which can be assigned to charge
transfer transitions from Cl - to Mn. These bands decreased in intensity by the addition of water. In addition, in
the CV, new cathodic waves appeared near -0.9 V vs. SCE by the addition of water after addition of Cl2 to the
solutions of manganese(III) complexes, which disappeared by passing through argon. These results indicate that
the present manganese(III) complexes can be oxidized by Cl2 to yield dichloromanganese(IV) complexes, which
can react with water to generate dioxygen. Moreover, amounts of dioxygen generated by the reactions of the
manganese(IV) complexes with water have been monitored by using an oxygen electrode. We have confirmed
dioxygen evolved from water, but their yields are low: about 3 to 5% based on the manganese complexes, which
may be caused by some decomposition of the complexes. In addition, heterodinuclear complexes which include
both manganese(III) and copper(II) ions have been prepared and characterized.
X X
N N
X
N N
Y OH
OH HO
Y
Y
Mn(OAc)3･2H2O
or
X = H, CH3, Y = H, 5-Cl, 5-Br, 5-NO2, 5-COOEt, 5-SO3Na, Z = Cl - , OAc - Fig. 1. Dinuclear manganese(III) complexes
studied.
References:
[1] T. Matsushita, M. Fujiwara, and T. Shono, Chem. Lett., 1981(5), 631.
[2] T. Matsushita, H. Kono, and T. Shono, Bull. Chem. Soc. Jpn., 54(9), 2646 (1981).
[3] M. Fujiwara, T. Matsushita, and T. Shono, Polyhedron, 4(11), 1895 (1985).
[4] H. Asada, M. Fujiwara, and T. Matsushita, Polyhedron, 19 (18), 2039 (2000).
X X
N Z N
X
N
Z
N
Y O Z
O O
Y
_____________________________________________________________________
245
Mn
Y
Mn