Mononuclear Dysprosium(III) Complexes with Triphenylphosphine Oxide Ligands: Controlling the Coordination Environment and Magnetic Anisotropy

Stuart Langley,Sophie Benjamin,Wasinee Phonsri,Gary Hix,Gopalan Rajaraman,Boujemaa Moubaraki,Keith Murray,Kuduva Vignesh,Kerey Holton

doi:10.3390/inorganics6020061

Abstract

We report the synthesis, structural and magnetic characterization of five mononuclear DyIII ion complexes using triphenylphosphine oxide as a monodentate ligand. They have formulae [DyIII(OPPh3)3(NO3)3] (1), [DyIII(OPPh3)4(NO3)2](NO3) (2), [DyIII(OPPh3)3Cl3] (3), [DyIII(OPPh3)4Cl2]Cl (4) and [DyIII(OPPh3)4Cl2](FeCl4) (5). These complexes are characterized using single crystal X-ray diffraction, which revealed that each complex has a unique coordination environment around the DyIII ion, which results in varying dynamic magnetic behavior. Ab initio calculations are performed to rationalize the observed magnetic behavior and to understand the effect that the ligand and coordination geometry around the DyIII ion has on the single-molecule magnet (SMM) behavior. In recent years, seven coordinate DyIII complexes possessing pseudo ~D5h symmetry are found to yield attractive blocking temperatures for the development of new SMM complexes. However, here we show that the strength of the donor ligand plays a critical role in determining the effective energy barrier and is not simply dependent on the geometry and the symmetry around the DyIII ion. Seven coordinate molecules possessing pseudo D5h symmetry with strong equatorial ligation and weak axial ligation are found to be inferior, exhibiting no SMM characteristics under zero-field conditions. Thus, this comprehensive study offers insight on improving the blocking temperature of mononuclear SMMs.

Highlights

The magnetic properties of mononuclear lanthanide ion coordination complexes have come to the forefront of research in the field of molecular magnetism due to the observation of slow relaxation of magnetization [1,2]
The results reveal the ground state Kramers doublet (KD) of complexes 1–5 has strong transverse components, suggesting strong mixing of the wavefunction and not the ideal Ising type anisotropy desired for slow relaxation of the magnetization
We find three or four “strong donor” ligands are not beneficial towards stabilizing an Ising type anisotropy

Summary

Introduction

The magnetic properties of mononuclear lanthanide ion coordination complexes have come to the forefront of research in the field of molecular magnetism due to the observation of slow relaxation of magnetization [1,2] Complexes that exhibit this behavior have been termed single-molecule magnets. Long, Ruiz and their co-workers have used simple electrostatic models to predict the ideal coordination geometry/environment for DyIII that would result in a SMM with a considerable magnetic anisotropy [7,8,9]. This “ideal” coordination environment involves negatively charged ligands coordinating along a single axis due to the prolate nature of the f electron density around the DyIII ion. This design approach has provided spectacular recent results for a dysprosium metallocene complex with cyclopentadienyl ligands situated above and below the

Methods

Results

Conclusion