Structural and Catalytic Characterization of a Heterovalent Mn(II)Mn(III) Complex\ud That Mimics Purple Acid Phosphatases

摘要

The binuclear heterovalent manganese model complex [Mn(II)Mn(III)(L1)(OAc)2] ClO4 3 H2O (H2L1 = 2-(((3-((bis-\ud(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino)-methyl)phenol) has been prepared\udand studied structurally, spectroscopically, and computationally. The magnetic and electronic properties of the\udcomplex have been related to its structure. The complex is weakly antiferromagnetically coupled (J ∼ -5 cm-1,\udH =-2J S1 3 S2) and the electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectra identify\udthe Jahn-Teller distortion of the Mn(III) center as predominantly a tetragonal compression, with a significant rhombic\udcomponent. Electronic structure calculations using density functional theory have confirmed the conclusions derived from\udthe experimental investigations. In contrast to isostructural M(II)Fe(III) complexes (M = Fe, Mn, Zn, Ni), theMn(II)Mn(III)\udsystem is bifunctional possessing both catalase and hydrolase activities, and only one catalytically relevant pKa (= 8.2) is\uddetected. Mechanistic implications are discussed.