title: Lanthanide(III) Complexes of Tripodal N-Donor Ligands: Structural Models for the Species Involved in Solvent Extraction of Actinides(III).
abstract: The complexation of lanthanides(III) by the tripodal ligands tpa (tris[(2-pyridyl)methyl]amine) and tpza (tris[(2-pyrazinyl)methyl]amine) has been investigated by solution NMR studies and by X-ray crystallography. The crystallographic studies show that both tpa and the new ligand tpza form complexes with a 1:1 metal:ligand ratio in which the tripodal amine acts as a tetradentate ligand. For the tpa complexes the remaining coordination sites are occupied by chloride counterions to give 7-coordination (Eu, Tb, Lu) or by chloride counterions and a methanol molecule to give 8-coordination (Nd). In [Nd(tpza)(H(2)O)(3)(CH(3)CN)(3)](ClO(4))(3).3H(2)O the remaining coordination sites are occupied by water and acetonitrile molecules to give 10-coordination while the perchlorate counterions remain non coordinating. Tpza complexes have been isolated from acetonitrile solution and dissociate completely in methanol, while the complexes of the more basic tpa can be isolated from methanol and exist in water in equilibrium with the free ligand. Solvent extraction studies of lanthanides(III) and actinides(III) from nitric acid solutions show that the new ligand tpza is, unlike tpa, a selective complexant of actinides(III). Considering their structural analogy, this difference could be explained in terms of the electronic differences between the two ligands resulting in a stronger affinity of actinides(III) for the softer donor tpza.
authors.affiliation: Laboratoire de Reconnaissance Ionique, and Laboratoire de Chimie de Coordination, Service de Chimie Inorganique et Biologique Département de Recherche Fondamentale sur la Matière Condensée, CEA-Grenoble, 38054 Grenoble Cedex 09, France, and the Département de Recherche en Retraitement et Vitrification/SEMP, Commissariat à l'Energie Atomique, Bat. 399, B.P. 171, 30207 Bagnols-sur-Cèze Cedex, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Wietzke
authors.forename: Marinella
authors.initials: M
authors.lastname: Mazzanti
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Latour
authors.forename: Jacques
authors.initials: J
authors.lastname: Pécaut
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Cordier
authors.forename: Charles
authors.initials: C
authors.lastname: Madic