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

[Image: see text] 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.