SIMDAVIS 1.2: Phosphonates are outstanding SIM ligands. Crown ethers are not.

This study presents SIMDAVIS 1.2, an updated dataset and analysis tool for lanthanide-based single-ion magnets (Ln-SIMs), focusing on the role of various ligands in influencing their magnetic properties. The revised dataset, accessible via a user-friendly online dashboard, encompasses over 10,000 data points on chemical and physical properties derived from more than 400 publications. Notably, the study redefines ligand classifications, introducing phosphonate-based ligands as a distinct family and highlighting their superior performance as SIM ligands compared to less effective alternatives such as crown ethers. Phosphonates exhibit promising pentagonal bipyramidal geometries that enhance magnetic stability by minimizing low-energy vibrational interactions. Comparative analysis reveals that while phosphonates may have moderate U_eff values compared to other leading ligands, their magnetic memory and hysteresis properties are comparable to those of bis-phthalocyaninato or metallocene sandwiches. This work emphasizes the importance of rational ligand selection and frugal data-driven approaches in the design of effective Ln-SIMs, contributing valuable insights into the optimization of single-ion magnet design strategies.