Dominance of Cyclobutadienyl Over Cyclopentadienyl in the Crystal Field Splitting in Dysprosium Single‐Molecule Magnets
James P. Durrant, Benjamin M. Day, Jinkui Tang, Akseli Mansikkamäki, Richard A. Layfield
Abstract
Abstract Replacing a monoanionic cyclopentadienyl (Cp) ligand in dysprosium single‐molecule magnets (SMMs) with a dianionic cyclobutadienyl (Cb) ligand in the sandwich complexes [(η 4 ‐Cb′′′′)Dy(η 5 ‐C 5 Me 4 t Bu)(BH 4 )] − ( 1 ), [(η 4 ‐Cb′′′′)Dy(η 8 ‐Pn † )K(THF)] ( 2 ) and [(η 4 ‐Cb′′′′)Dy(η 8 ‐Pn † )] − ( 3 ) leads to larger energy barriers to magnetization reversal (Cb′′′′=C 4 (SiMe 3 ) 4 , Pn † =1,4‐di(tri‐isopropylsilyl)pentalenyl). Short distances to the Cb′′′′ ligands and longer distances to the Cp ligands in 1 – 3 are consistent with the crystal field splitting being dominated by the former. Theoretical analysis shows that the magnetic axes in the ground Kramers doublets of 1 – 3 are oriented towards the Cb′′′′ ligands. The theoretical axiality parameter and the relative axiality parameter Z and Z rel are introduced to facilitate comparisons of the SMM performance of 1 – 3 with a benchmark SMM. Increases in Z and Z rel when Cb′′′ replaces Cp signposts a route to SMMs with properties that could surpass leading systems.