Theoretical identification of key structural factors for strong magnetic anisotropy in Ni(II) complexes

Single-molecule magnets (SMMs) possess a crucial property called magnetic anisotropy (MA), which has an exceedingly delicate correlation with their structures. In recent years, the study on magneto-structural correlations has emerged as a challenging area in singlemolecule science. Understanding the fundamental physical mechanisms underlying the magneto-structural correlations is essential for building excellent high-temperature SMMs. In this work, we screened various four-coordinated nickel(II) SMMs and studied several key structural factors, such as the lengths and angles of the coordination bonds that may be closely associated with MA. Following that, we developed simple molecular models to deduce the evolution trends of MA with coordination bond angles and lengths. The findings on the magneto-structural correlations stimulated our interest to further explore the crystal structure database. We revealed that the magneto-structural correlation can be well described by a logarithmic function. Guided by such a relationship, we discovered a nickel(II) complex with the strongest MA to date among the tetrahedral-coordinated ones. Our work may be helpful for the empirical synthesis of exceptional high-temperature SMMs.