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Four manganese(III)-Schiff base complexes (1-4) of formula [MnL n (H 2 O) 2 ] 2 (ClO 4 ) 2 ÁmH 2 O (n = 1-4; m = 0, 1) have been prepared. The multidentate H 2 L n Schiff base ligands consist of 3R,5R-substituted N,N 0 -bis(salicylidene)-1,2-diimino-2,2-dimethylethane, where R = OEt, OMe, Br or Cl. The complexes have been thoroughly characterized by elemental analysis, mass spectrometry, magnetic susceptibility measurements, IR, UV, paramagnetic 1 H NMR and EPR spectroscopies. Other properties, including redox studies and molar conductivity measurements, have also been assessed. The crystal structure of 1 was solved by X-ray diffraction, which revealed the dimeric nature of the compound through m-aqua bridges. The ability of these complexes to split water has been studied by water photolysis experiments, with the oxygen evolution measured in aqueous media in the presence of a hydrogen acceptor (p-benzoquinone), the reduction of which was followed by UV-spectroscopy. The discussion of the photolytic behaviour includes advances in the knowledge of the structural motifs and the chemical activity of this type of complex, as revealed by the development of several characterization techniques in the last decade. Parallel-mode Mn III EPR shows that complexes 1-4 not only mimic reactivity but also share some structural characteristics from partially assembled natural OEC clusters.

The condensation of 3-methoxy-2-hydroxybenzaldehyde and the diamines 1,2-diphenylendiamine, 1,2-diamine-2-methylpropane and 1,3-propanediamine yielded the dianionic tetradentate Schiff base ligands N,N -bis(2-hydroxy-4-methoxybenzylidene3 ) respectively. The organic compounds H 2 L 1 and H 2 L 2 have been characterized by elemental analysis, IR, 1 H and 13 C NMR spectroscopies and mass spectrometry electrospray (ES). The crystal structure of H 2 L 2 in solid state, solved by X-ray crystallography, is highly conditioned in the solid state by two N-H•••N intramolecular interactions. The synthesis of three new manganese(III) complexes 1-3, incorporating these ligands, H 2 L 1 -H 2 L 3 , and dicyanamide (DCA), is reported. The complexes 1-3 have been physicochemically characterized by elemental analysis, IR and paramagnetic 1 H NMR spectroscopy, ESI mass spectrometry, magnetic moment at room temperature and conductivity measurements. Complex 1 has been crystallographically characterized. The X-ray structure shows the self-assembly of the Mn(III)-Schiff base-DCA complex through -aquo bridges between neighbouring axial water molecules and also by -stacking interactions, establishing a dimeric structure. The manganese complexes were also tested as peroxidase mimics for the H 2 O 2 -mediated reaction with the water-soluble trap ABTS, showing complexes 1-2 relevant peroxidase activity in contrast with 3. The rhombicity around the metal ion can explain this catalytic behaviour.

The ability to organize functional molecules into higher dimensional arrays with well-defined spatial relationships between the components is one of the major goals in supramolecular chemistry. We report here a new route for the preparation of supramolecular boxes, incorporating two types of metal ions: (i) alkali-metal ions, which induce the supramolecular architecture and essentially play a structural role in the final compounds; (ii) manganese(III) ions, which are redox-active systems and give functionality to the new cages. Our results evidence that the size of the cavity inside the box can be tuned depending on the alkali metal used, a characteristic that gives this new family of compounds the potential to act selectively against different substrates. These compounds behave as active catalysts for disproportionation of H2O2 or for water photolysis, but they catalyze neither catecholase reaction nor peroxidase action upon using bulky organic substrates.

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