Magnetic interactions in Cu-II-Ln(III) cyclic tetranuclear complexes: Is it possible to explain the occurrence of SMM behavior in Cu-II-Tb-III and Cu-II-Dy-III complexes?.
Fiche publication
Date publication
mai 2007
Auteurs
Membres identifiés du Cancéropôle Est :
Dr GALLANI Jean-Louis
Tous les auteurs :
Hamamatsu T, Yabe K, Towatari M, Osa S, Matsumoto N, Re N, Pochaba A, Mrozinski J, Gallani JL, Barla A, Imperia P, Paulsen C, Kappler JP
Lien Pubmed
Résumé
An extensive series of tetranuclear Cu(2)(II)Ln(2)(III) complexes [Cu(II)LLn(III)(hfac)(2)](2) (with Ln(III) being all lanthanide(III) ions except for the radioactive Pm-III) has been prepared in order to investigate the nature of the Cu-II-Ln(III) magnetic interactions and to try to answer the following question: What makes the (Cu2Tb2III)-Tb-II and (Cu2Dy2III)-Dy-II 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 Cu-II and Ln(III) ions are arrayed alternately via bridges of ligand complex ((CuL)-L-II). 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 Cu(2)(II)Ln(2)(III) and Ni(2)(II)Ln(2)(III) complexes, with the Ni(2)(II)Ln(2)(III) complex containing diamagnetic Ni-II ions being used as a reference for the evaluation of the Cu-II-Ln(III) magnetic interactions. These measurements have revealed that the interactions between Cu-II and Ln(III) 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 (Cu2Tb2III)-Tb-II, (Cu2Dy2III)-Dy-II, and (Ni2Tb2III)-Tb-II 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 (Cu2Tb2III)-Tb-II 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.
Référence
Inorg Chem. 2007 May 28;46(11):4458-68