Catalytic oxidation of 3,5-di-tert-butylcatechol by a manganese(III) 18-azametallacrown-6 compound: Synthesis, crystal structure, fluorescence, magnetic and kinetic investigation

摘要

A new macrocyclic hexanuclear manganese(III) 18-azametallacrown-6 compound, [Mn-6(ashz)(6)(CH3OH)(3)(H2O)(3)]- 3H(2)O - 3DMF (1), has been prepared using a trianionic pentadentate ligand N-acetylsalicylhydrazide (ashZ(3-)) and characterised by various techniques such as elemental analysis, IR, LJ-V-vis and fluorescence spectroscopy, cyclic voltarnmetry and X-ray diffraction. Six ashz(3-) ligands connect six metal ions to form the cyclic skeleton based on the M-N-N-M linkage. Due to the meridional coordination of the ligand to the Mn3+ ion, the ligand enforces the stereochentistry of the Mn3+ ions as a propeller configuration with alternating A/A forms. The kinetic studies on catecholase activity of 1 for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by O-2 were done using UV-Vis absorption spectra method. Compound I has been evaluated as a model system for the catechol oxidase enzyme and it is found that the compound shows high catecholase activity. It exhibits the activity with a turnover number of 270 h(-1). A kinetic treatment on the basis of the Michaelis-Menten model has been applied. The magnetic susceptibility (300-5 K) study indicates antiferromagnetic exchange interactions with J = -2.6 cm(-1) between the adjacent Mn3+ ions. (c) 2006 Elsevier B.V. All rights reserved.