Air-Stable Hexagonal Bipyramidal Dysprosium(III) Single-Ion Magnets with Nearly Perfect D6h Local Symmetry

Local eight-coordination of the Dy(III) with D_6h symmetry receives much expectation for high-performance single-molecule magnets (SMMs) due to the simultaneous fulfillment of the magnetic axiality and high coordination number (a requisite for the air stability). But the experimental realization is challenging due to the required restriction of six coordination atoms in the equatorial plane of the hexagonal-bipyramid, which is usually too crowded for the central Dy(III) ion. Here we show by using the hexaaza macrocyclic Schiff base ligand and fine-tuning the axial alkoxide/phenol type ligands, a family of hexagonal-bipyramidal Dy(III) complexes, namely [Dy^III(L)(Cl)₂(H₂O/CH₃OH)]Cl 1, [Dy^III(L)(C₆F₅O)₂(H₂O)](BPh₄)·2, [Dy^III(L)(PhO)₂](BPh₄) 3, [Dy^III(L)(4-MeO-PhO)₂](BPh₄) 4, [Dy^III(L)(naPhO)₂](BPh₄) 5 and [Dy^III(L)(Ph₃SiO)₂](BPh₄) 6 , can be isolated. Among them, complexes 3, 4 and 5 possess nearly perfect D_6h local symmetry. Complex 4 shows the highest effective magnetic reversal barrier 1338 K and an open hysteresis temperature 6 K at the field sweeping rate of 1.2 mT/s, which represents a new record for D_6h SMMs.