Anion coordination selective [Mn3] and [Mn4] assemblies: synthesis, structural diversity, magnetic properties and catechol oxidase activity

Abstract

Syntheses, crystal structures, magnetic properties and catechol oxidation behavior are presented for [Mn₃] and [Mn₄] aggregates, [Mn^III₂Mn^II(O₂CMe)₄(dmp)₂(H₂O)₂]·2H₂O (1·2H₂O), [Mn^III₂Mn^II(O₂CCH₂Cl)₄(dmp)₂(H₂O)₂]·H₂O·MeOH (2·H₂O·MeOH), [Mn^III₄(μ₃-O)(dmp)₄(μ-DMSO)(N₃)(DMSO)(H₂O)]ClO₄·DMSO (3·ClO₄·DMSO), and [Mn^III₄(μ₃-O)(dmp)₄(μ-DMSO)(ClO₄)(DMSO)(H₂O)]ClO₄·DMSO (4·ClO₄·DMSO), developed with single type ligand H₂dmp, 2-[(2-hydroxy-1,1-dimethyl-ethylimino)-methyl]-phenol. The successful isolation of 1–4 resulted from a systematic exploration of the effect of Mn^II salts, added carboxylates, Mn/H₂dmp ratio, presence of azide, and other reaction conditions. The cores of 1 and 2 are similar and consist of a linear Mn^IIIMn^IIMn^III unit in a carboxylate and H₂dmp environment, revealing a central Mn^II ion in a different environment and terminal Mn^III ions available for the introduction of structural and magnetic anisotropy to the system. The cores of 3 and 4 are also similar and consist of a distorted incomplete-adamantane type Mn₄ coordination assembly in a carboxylate-free environment built on a triangular [Mn^III₃(μ₃-O)] unit. The magnetic behavior of complexes 1–3 is dominated by antiferromagnetic exchange coupling that results in ground state spin values of S = 3/2 for 1 and 2 and S = 0 for 3. In solution, all four complexes 1–4 show catechol oxidation activity towards 3,5-DTBC. The catalytic activity for the oxidation of 3,5-DTBC in air followed the order 4 < 3 < 1 < 2.