Two types of manganese oxides have been prepared by hydrolysis of tetranuclear
Mn(III) complexes in the presence or absence of phosphate ions. The oxides
have been characterized structurally using X-ray absorption spectroscopy and
functionally by O2 evolution measurements. The structures of the oxides
prepared in the absence of phosphate are dominated by di-μ-oxo bridged
manganese ions that form layers with limited long-range order, consisting of
edge-sharing MnO6 octahedra. The average manganese oxidation state is +3.5.
The structure of these oxides is closely related to other manganese oxides
reported as water oxidation catalysts. They show high oxygen evolution
activity in a light-driven system containing [Ru(bpy)3]2+ and S2O82− at pH 7.
In contrast, the oxides formed by hydrolysis in the presence of phosphate ions
contain almost no di-μ-oxo bridged manganese ions. Instead the phosphate
groups are acting as bridges between the manganese ions. The average oxidation
state of manganese ions is +3. This type of oxide has much lower water
oxidation activity in the light-driven system. Correlations between different
structural motifs and the function as a water oxidation catalyst are discussed
and the lower activity in the phosphate containing oxide is linked to the
absence of protonable di-μ-oxo bridges.
500 Naturwissenschaften und Mathematik::540 Chemie
Water oxidation by manganese oxides formed from tetranuclear precursor
Phys. Chem. Chem. Phys. - (2014),16, S. 11965-11975
the influence of phosphate on structure and activity
Biologie, Chemie, Pharmazie