Synthesis and characterisation of some new manganese(II) and manganese(III) complexes of tetradentate Schiff-base ligands and their reaction with molecular oxygen

Abstract

Some new manganese complexes containing tetradentate Schiff -base ligands (H₂L) derived from 1-hydroxy-2-naphthaldehyde and aliphatic diamines, H₂N(CH₂)_nNH₂[n= 2,3,4, or 10; H₂L =NN′-ethylene-, propane-1,3-diyl-, butane-1,4-diyl-, and decane-1, 10-diyl-bis(1-hydroxy-2-naphthylmethyleneimine)], have been synthesised. The structure and reactivity of the manganese(II) complexes critically depends on n. Thus, planar [MnL] are formed for n= 2,4, or 10, but for n= 3 the pseudo-octahedral [MnL(H₂O)₂] is obtained. These manganese (II) species absorb approximately 0.5 mol O₂ per mol of Mn to form dimeric di-µ-oxo manganese (IV) complexes [{MnL(O)}₂], but this reaction in NN-dimethylformamide is surprisingly much faster for the complex [MnL(H₂O)₂] than for the planar species. In addition some manganese(III) complexes [MnL(H₂O)] ClO₄ have been obtained.