Dangling and hydrolyzed ligand arms in [Mn3] and [Mn6] coordination assemblies : synthesis, characterization, and functional activity

Chattopadhyay, Krishna and Craig, Gavin A. and Heras Ojea, María José and Pait, Moumita and Kundu, Animesh and Lee, Junseong and Murrie, Mark and Frontera, Antonio and Ray, Debashis (2017) Dangling and hydrolyzed ligand arms in [Mn3] and [Mn6] coordination assemblies : synthesis, characterization, and functional activity. Inorganic Chemistry, 56 (5). pp. 2639-2652. ISSN 0020-1669 (https://doi.org/10.1021/acs.inorgchem.6b02813)

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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(μ1,3-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(μ1,3-O2CC2H5)4](ClO4)2·2H2O (2). Binding of acetates and coordination of {H2L1}− provided a linear MnIIIMnIIMnIII arrangement in 1. A MnIII6 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 MnIII 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.

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