Cis-trans isomerism modulates the magnetic relaxation of dysprosium single-molecule magnets

Geometry and magnetic relaxation modulations in a series of mononuclear dysprosium complexes, [DyLz₂(o-vanilin)₂]·X·solvent (Lz = 6-pyridin-2-yl-[1,3,5]triazine-2,4-diamine; X = Br^- (1), NO₃^- (2), CF₃SO₃^- (3)), were realized by changing the nature of the counter-anion. The Dy^III ions in all complexes are eight-coordinate and in approximate D_4d symmetry environments. The magnetic relaxation and anisotropy of these complexes were systematically investigated, both experimentally and from ab initio calculations. All complexes exhibit excellent single-molecule magnetic behavior. Remarkably, magneto-structural studies show that the rotation of the coordinating plane of the square-antiprismatic environment in complex 2 induces a magnetic relaxation path through higher excited states, yielding a high anisotropy barrier of 615 K (696 K for a diluted sample). Additionally, obvious opening of the hysteresis loop is observed up to 7 K, which is the highest blocking temperature ever reported for dysprosium single-molecule magnets.