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

Abstract

The binuclear heterovalent manganese model complex [Mn(II)Mn(III)(L1 )(OAc)2] CIO4-H2O (H2L1 = 2-(((3-((bis(pyrldin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl) (pyridin-2-ylmethyl)amino)-methyl)phenol) has been prepared and studied structurally, spectroscopically, and computationally. The magnetic and electronic properties of the complex have been related to its structure. The complex is weakly antiferromagnetically coupled (J ∼ -5 cm-1, H = -2J S1 • S2) and the electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectra identify the Jahn-Teller distortion of the Mn(III) center as predominantly a tetragonal compression, with a significant rhombic component. Electronic structure calculations using density functional theory have confirmed the conclusions derived from the experimental Investigations. In contrast to isostructural M(II)Fe(III) complexes (M = Fe, Mn, Zn, Ni), the Mn(II)Mn(III) system is afunctional possessing both catalase and hydrolase activities, and only one catalytically relevant pKa (= 8.2) is detected. Mechanistic Implications are discussed.