Synthesis, characterization and catalytic activity toward dye decolorization by manganese (II) mononuclear complexes

Manganese(II) perchlorate reacts with L1 = N,N,N′-tris(2-methylpyridyl)-N′-hydroxyethyl-ethylenodiamine and L2 = N-(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)-N′-hydroxyethyl-ethylenodiamine in ethanol to form the corresponding complexes [MnL1(H2O)](ClO4)2 and [MnL2]ClO4. Both complexes crystallize in the monoclinic system and space group P 21/n. In [MnL1(H2O)]2+ and [MnL2]+ the manganese(II) ion is heptacoordinated and hexacoordinated, respectively. FTIR, elemental analysis and conductance measurements were all in accordance with the molecular structures of [MnL1(H2O)](ClO4)2 and [MnL2]ClO4. The ability of [MnL1(H2O)](ClO4)2 and [MnL2]ClO4 to catalyze the oxidation of the dyes methyl orange and reactive orange 16 was studied in aqueous alkaline solution (carbonate/bicarbonate buffer). Both complexes were active catalysts promoting significant enhancement of dye solution decolorization in comparison to control reactions.

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► Dye decolorization reactions using manganese complexes as catalysts.
► Complete structural characterization of the catalysts.
► Radical scavenger tert-BuOH reduces reaction rates indicating a radical mechanism.
► MnIV and MnIIIMnIV species detected in reaction medium by EPR spectroscopy.