Synthesis, Characterization, and Catalytic Studies of Mn(III)-Schiff Base-Dicyanamide Complexes: Checking the Rhombicity Effect in Peroxidase Studies

Abstract

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-methoxybenzylidene)-1,2-diphenylendiimine (H 2 L 1 ), N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,2-diamino-2-methylpropane (H 2 L 2 ) and N,N′-bis(2-hydroxy-4-methoxybenzylidene)-1,3-diaminopropane (H 2 L 3 ) 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 µ -aquo bridges between neighbouring axial water molecules and also by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>π</mml:mi><mml:mtext>-</mml:mtext><mml:mi>π</mml:mi></mml:math> 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.