Role of the Main and Auxiliary Ligands in the Nuclearity of Cu-Ln Complexes
Résumé
Trianionic ligands with an inner N2O2, an outer O2O2 or O2O coordination site and an oxygen atom coming from an amide function not involved in these sites yield dinuclear Cu-Ln complexes that self-assemble into tetranuclear species with an alternate arrangement of Cu and Ln ions. This alternate Cu-Gd arrangement impedes Cu–Cu and Gd-Gd interactions that could be antiferromagnetic and favours ferromagnetic Cu-Gd interactions whose strength depends on the nature of the bridge, the phenoxo bridge made of a single oxygen atom or the amidato bridge made of three NCO atoms. Depending on the ligands, the phenoxo bridges can be single (CuOGd) or double (CuO2Gd), while the amidato bridge is always a single (CuNCOGd) bridge. A particular complex involving a trinuclear Cu-Gd-Cu arrangement through two amidato bridges confirms that the Cu-Gd interaction through the amidato bridge is always weaker than the interaction through the phenoxo bridge. It has been possible to obtain complexes with an alternate Cu-Gd arrangement involving more than two Cu-Gd entities when two amidato bridges are present. These two amidato bridges may come from a main ligand, as in the case of tetraanionic ligands possessing two amide functions, or from two different ligands involving one amide function that are assembled by a Gd ion through their phenoxo functions. Note that the presence of auxiliary ligands with a good chelating ability for the Gd ion, such as the diketonato ligands, allows isolation of tetranuclear species only, regardless of the number of amide functions.