Anion-Induced Assembly of Hexacoordinate Rare-Earth(III) Complexes

Rare-earth(III) complexes of the general formula [RE{(Hsal)(3)-tren)(2)](CF(3)SO(3))(3)center dot nCH(3)CN, where RE is Eu (1), Gd (2), and Tb (3), and (Hsal)(3)tren is tris[2-(salicylideneimino)ethyl]amine, have been synthesized and structurally characterized. X-ray crystallographic studies show that the rare-earth(III) center is coordinated by six oxygen atoms that belong to the phenolato groups of two (Hsal)3tren ligand molecules to give an unusual hexacoordinate geometry. The molecular structure is stabilized by strong intramolecular interactions established between the hydrogen atoms located on the three imino nitrogen atoms and the deprotonated phenol oxygen atoms of each ligand. Luminescence studies have indicated the presence of efficient nonradiative deactivation pathways in 1-3, and only a weak ligand emission was observed (lambda(exc) = 275 nm, lambda(em) = 545 nm) in all cases. Temperature-dependent magnetic susceptibility studies have shown that crystal field effects are dominant for complex 3, whilst small antiferro-magnetic interactions have been observed in 2.