Importance of an Axial Ln III -F Bond across the Lanthanide Series and Single-Molecule Magnet Behavior in the Ce and Nd Analogues.

The recently reported compound [Dy III LF](CF 3 SO 3 ) 2 ·H 2 O (L = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane) displays a strong axial magnetic anisotropy, due to the short axial Dy-F bond, and single-molecule magnet (SMM) behavior. Following our earlier [Dy III LF] 2+ work, herein we report the systematic structural and magnetic study of a family of [Ln III LF](CF 3 SO 3 ) 2 ·H 2 O compounds (Ln(III) = 1 -Ce, 2 -Pr, 3 -Nd, 4 -Eu, 5 -Tb, 6 -Ho, 7 -Er, 8 -Tm, and 9 -Yb). From this series, the Ce(III) and Nd(III) analogues show slow relaxation of the magnetization under an applied direct current magnetic field, which is modeled using a Raman process. Complete active space self-consistent field theoretical calculations are employed to understand the relaxation pathways in 1 -Ce and 3 -Nd and also reveal a large tunnel splitting for 5 -Tb. Additional computational studies on model compounds where we remove the axial F - ligand, or replace F - with I - , highlight the importance of the F - ligand in creating a strong axial crystal field for 1 -Ce and 3 -Nd and for promoting the SMM behavior. Importantly, this systematic study provides insight into the magnetic properties of these lighter lanthanide ions.