Magnetic Interactions in CuII−LnIII Cyclic Tetranuclear Complexes: Is It
Possible to Explain the Occurrence of SMM Behavior in CuII−TbIII and
CuII−DyIII Complexes?
posted on 2007-05-28, 00:00authored byTakefumi Hamamatsu, Kazuya Yabe, Masaaki Towatari, Shutaro Osa, Naohide Matsumoto, Nazzareno Re, Andrzej Pochaba, Jerzy Mrozinski, Jean-Louis Gallani, Alessandro Barla, Paolo Imperia, Carley Paulsen, Jean-Paul Kappler
An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions
except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII−LnIII magnetic
interactions and to try to answer the following question: What makes the CuII2TbIII2 and CuII2DyIII2 complexes single
molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic
tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL).
Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent
magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been
measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions
being used as a reference for the evaluation of the CuII−LnIII magnetic interactions. These measurements have
revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln = Ce, Nd, Sm,
Yb, ferromagnetic if Ln = Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln = La, Eu, Pr, Lu. With the same goal of
better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism
(XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges
of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has
received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular
measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K.