Dangling and Hydrolyzed Ligand Arms in [Mn₃] and [Mn₆] Coordination Assemblies: Synthesis, Characterization, and Functional Activity

Abstract

Two flexible, branched, and sterically constrained di- and tripodal side arms around a phenol backbone were utilized in ligands H₃L1 and H₅L2 to isolate {Mn₆} and {Mn₃} coordination aggregates. 2,6-Bis{(1-hydroxy-2-methylpropan-2-ylimino)methyl}-4-methylphenol (H₃L1) gave trinuclear complex [Mn₃(μ-H₂L1)₂(μ_1,3-O₂CCH₃)₄(CH₃OH)₂](ClO₄)₂·4CH₃OH (1), whereas 2,6-bis[{1-hydroxy-2-(hydroxymethyl)butan-2-ylimino}methyl]-4-methylphenol (H₅L2) provided hexanuclear complex [Mn₆(μ₄-H₂L2)₂(μ-HL3)₂(μ₃-OH)₂(μ_1,3-O₂CC₂H₅)₄](ClO₄)₂·2H₂O (2). Binding of acetates and coordination of {H₂L1}^- provided a linear Mn^IIIMn^IIMn^III arrangement in 1. A Mn^III₆ fused diadamantane-type assembly was obtained in 2 from propionate bridges, coordination of {H₂L2}^3-, and in situ generated {HL3}^2-. The magnetic characterization of 1 and 2 revealed the properties dominated by intramolecular anti-ferromagnetic exchange interactions, and this was confirmed using density functional theory calculations. Complex 1 exhibited field-induced slow magnetic relaxation at 2 K due to the axial anisotropy of Mn^III centers. Both the complexes show effective solvent-dependent catechol oxidation toward 3,5-di-tert-butylcatechol in air. The catechol oxidation abilities are comparable from two complexes of different nuclearity and structure.