Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

Abstract

A diphenoxido-bridged dinuclear copper (II) complex, [Cu₂L₂(ClO₄)₂] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper (II) complex, [Cu₂L₂(OH)]ClO₄ (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements and spectroscopic methods. In 1, the two phenoxido bridges are equatorial–equatorial and the species shows strong antiferromagnetic coupling with J = −615.6 (6.1) cm^–1. The inclusion of the equatorial–equatorial hydroxido bridge in 2 changes the Cu•••Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial–equatorial, and the magnetic coupling to ferromagnetic with J = 50.1 (1.4) cm^–1. Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k_cat = 233.4 h^–1) than compound 1 (k_cat = 93.6 h^–1). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.