Novel peroxidase mimics: μ-Aqua manganese–Schiff base dimers

The interaction of manganese(II) carboxylate salts [Mn(O2CR)2, where R = ethane, pentane] with H2L1 [N,N′-bis(3-methoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] and H2L2 [N,N′-bis(3-ethoxy-2-hydroxybenzaldehyde)-1,2-phenylenediamine] was studied. MnL1(O2CEt)(H2O) (1), MnL1(O2CPen)(H2O) (2), MnL2(O2CEt)(H2O)2 (3) and MnL2(O2CPen)(H2O)2 (4) were isolated and thoroughly characterised by elemental analysis, FAB mass spectrometry, infrared and 1H NMR spectroscopy, magnetic susceptibility measurements, molar conductivities, and cyclic and normal pulse voltammetry. Compounds 1 and 2 were crystallographically characterised revealing a tetragonally elongated octahedral geometry for the manganese coordination sphere and also a dimeric nature through μ-aqua bridges. Complexes 1–4 behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS, probably due to their ease to coordinate the substrate molecule. A correlation between rhombicity of the complexes and peroxidase activity has also been established.