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

A new macrocyclic hexanuclear manganese(III) 18-azametallacrown-6 compound, [Mn₆(ashz)₆(CH₃OH)₃(H₂O)₃] · 3H₂O · 3DMF (1), has been prepared using a trianionic pentadentate ligand N-acetylsalicylhydrazide (ashz³⁻) and characterised by various techniques such as elemental analysis, IR, UV-vis and fluorescence spectroscopy, cyclic voltammetry and X-ray diffraction. Six ashz³⁻ 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 stereochemistry of the Mn³⁺ ions as a propeller configuration with alternating Δ/Λ forms. The kinetic studies on catecholase activity of 1 for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by O₂ were done using UV-Vis absorption spectra method. Compound 1 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.