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.

Graphical abstractA 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 in which M–N–N–M linkage is present. Compound 1 shows catecholase activity in the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by O2. A kinetic treatment on the basis of Michealis–Menten model has been applied. The compound is found to be antiferromagnetic with J = −2.6 cm−1.Figure optionsDownload full-size imageDownload as PowerPoint slide