Switching the anisotropy barrier of a single-ion magnet by symmetry change from quasi-D5h to quasi-Oh

A reversible single-crystal-to-single-crystal transformation is used to dramatically change the relaxation behavior of a single-ion magnet. The coordination geometry of the DyIII site of a [Zn–Dy–Zn] complex changes from pentagonal–bipyramid (quasi-D5h) to octahedron (quasi-Oh), inducing an energy barrier change from 305 cm−1 (439 K) to a negligible value, respectively. Ab initio calculations reveal that the ideal D5h–DyIII is of perfect axiality with a substantial energy barrier in accordance with the experimental result.