Importance of an axial Ln(III)-F bond across the lanthanide series and single-molecule magnet behavior in the Ce and Nd analogues

Regincós Martí, Emma and Canaj, Angelos B. and Sharma, Tanu and Celmina, Anna and Wilson, Claire and Rajaraman, Gopalan and Murrie, Mark (2022) Importance of an axial Ln(III)-F bond across the lanthanide series and single-molecule magnet behavior in the Ce and Nd analogues. Inorganic Chemistry, 61 (26). pp. 9906-9917. ISSN 0020-1669 (https://doi.org/10.1021/acs.inorgchem.2c00556)

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Abstract

The recently reported compound [Dy(III)LF](CF3SO3)2·H2O (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-mol. 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](CF3SO3)2·H2O 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) analogs show slow relaxation of the magnetization under an applied d.c. magnetic field, which is modeled using a Raman process. Complete active space SCF theor. calculations are employed to understand the relaxation pathways in 1-Ce and 3-Nd and also reveal a large tunnel splitting for 5-Tb. Addnl. 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.

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