A one-dimensional polymeric mixed-valent Mn(II)Mn(III) complex with a macrocyclic compartmental ligand: Structure, properties and catecholase like activity

Abstract

Reaction of 2,6-diformyl-4-methylphenol, 1,3-diaminopropane, Mn(ClO4)2∙6H2O and CH3COONa∙3H2O in 1:1:1:1 mole ratio in methanol afford a linear coordination polymer of formula {[MnIIMnIIIL(OAc)2]ClO4}n (L2− represents the Robson-type ligand) in 64% yield. The complex has been characterized by elemental (CHN) analysis, magnetic susceptibility, spectroscopic (IR, UV–Vis and EPR) and solution electrical conductivity measurements. The linear polymeric structure and the mixed-valent character of the complex have been confirmed by single crystal X-ray crystallography. In the repetitive dinuclear unit, both metal centers are in N2O4 coordination spheres assembled by the compartmental macrocyclic N2O2N2-donor L2−, an intra-dinuclear bridging acetate and an inter-dinuclear bridging acetate. The coordination geometry around the manganese(II) center (S = 5/2) is severely distorted octahedral, while that around the manganese(III) center (S = 2) is tetragonally elongated octahedral. Variable temperature magnetic susceptibility measurements indicate a weak intra-dinuclear ferromagnetic (J = 1.12(3) cm−1) interaction as well as a weak inter-molecular antiferromagnetic (zJ′ = −0.679 (3) cm−1) interaction. Cyclic voltammogram of the complex displays a metal centered quasi-reversible reduction at −0.03 V and an irreversible ligand centered reduction at −1.16 V (vs Ag/AgCl). The complex efficiently catalyzes the aerobic oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzoquinone with a turnover number (kcat) 1.2 × 104 h−1.