Probing axial anisotropy in dinuclear alkoxide-bridged Er-COT single-molecule magnets

Developing well-coupled lanthanide-based magnetic materials via a building block approach has proven difficult since few systems exists that are able to simultaneously maintain anisotropy and promote adequate coupling. Employing the anisotropic building block consisting of Er3+ bound to the cyclooctate-traenide dianion ([Er(COT)](+)), two alkoxide-bridged dinuclear single-molecule magnets displaying ferromagnetic coupling were synthesized: centrosymmetric [Er(COT)(mu-OEt)(THF)](2) (1) and non-centrosymmetric [Er(COT)](2)(mu-(OBu)-Bu-t)(2)(THF) (2). AC relaxation studies reveal that both systems have similar weak temperature dependence of their relaxation, despite anisotropy axes being parallel in 1 and nearly perpendicular in 2. Due to the strong crystal field provided by the alkoxide ligands, both complexes display enhanced mixing of the total angular momentum states, which provides a fast relaxation pathway even with conserved single-ion anisotropy and ferromagnetic coupling. (C) 2019 Elsevier Ltd. All rights reserved.