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New manganese(II) and manganese(III) complexes of substituted N,N 0 -bis(salicylidene)-1,2-diimino-2methylethane have been prepared and characterized. Elemental analysis, IR and EPR spectroscopies, mass spectrometry, magnetic measurements and the study of their redox properties have confirmed their respective formulae as Mn II L(H 2 O) 2 and Mn III L(H 2 O) n (ClO 4 ). Electron-withdrawing substituents on the phenyl rings of the ligand stabilize the oxidation state (II) for manganese, but the electron-donating substituents on the Schiff bases are those that lead to Mn(III) complexes, which behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS. The rate of peroxidase activity of the present complexes is significantly higher than that of other series of Mn-Schiff base compounds, probably due to their versatility in adopting in solution a structure that allows the coordination of the hydrogen peroxide substrate molecule to the manganese.

The synthesis and structural and spectroscopic characterisation of 12 manganese(III)-Schiff-base complexes of the for-n and H 4 L n Schiff-base ligands were obtained by condensation of different diamines (1,2-diaminoethane, 1,2-diamino-2-methylethane, 1,2-diamino-2,2-dimethylethane, 1,3-diamino-2,2-dimethylpropane) and 2,3-dihydroxybenzaldehyde, 3-methoxy-2-hydroxybenzaldehyde or 3-ethoxy-2-hydroxybenzaldehyde.

We have prepared some transition and post-transition metal complexes derived from the pentadentate thiosemicarbazone ligand bis(4-N-ethylthiosemicarbazone)-2,6-diacetylpyridine H(2)L(Et), by both chemical and electrochemical procedures. The complexes have been synthesised and fully characterised, including the crystal structures for the ligand H(2)L(Et) and its manganese, cadmium and lead complexes. We have also performed multinuclear (109)Ag, (113)Cd, (119)Sn and (207)Pb studies for silver, cadmium, tin and lead compounds, respectively. Moreover we present here a comparative study on the different structures found for pentadentate thiosemicarbazonate complexes, trying to check the influence of different factors, such as experimental procedure, size of metal, structure of the ligand, and metal oxidation state, on the final structure of the complex formed. Our aim is gaining a better insight into the coordination trends of pentadentate thiosemicarbazone ligands.

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Abstract:Kraft pulp has to be bleached to eliminate the chromophoric structures, which cause a darkening of the pulp. In Nature, an equivalent role is assumed by ligninolytic enzymes such as lignin peroxidases, manganese peroxidases and laccases. The development of low molecular weight manganese peroxidase mimics may achieve environmentally-safe bleaching catalysts for the industry. Herein we report the synthesis and characterization of six manganese(III) complexes 1-6, incorporating dianionic hexadentate Schiff base ligands (H 2 L 1 -H 2 L 4 ) and different anions. Complex 4, Mn 2 L 2 2 (H 2 O) 2 (DCA) 2 was crystallographically characterized. Complexes 1-4 behave as more efficient mimics of peroxidase in contrast to 5-6. We have studied the use of these complexes as catalysts for the degradation of the lignin model compound veratryl alcohol. The biomimetic catalysts were used in conjunction with chlorine-free inexpensive co-oxidants as dioxygen or hydrogen peroxide. Yields up to 30% of veratryl alcohol conversion to veratraldehyde have been achieved at room temperature in presence of air flow using 0.5% of catalyst.

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