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

Abstract

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 cyclooctatetraenide dianion ([Er(COT)]+), two alkoxide-bridged dinuclear single-molecule magnets displaying ferromagnetic coupling were synthesized: centrosymmetric [Er(COT)(µ-OEt)(THF)]2 (1) and non-centrosymmetric [Er(COT)]2(µ-OtBu)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.