title: Calix[4]arenes as selective extracting agents. An NMR dynamic and conformational investigation of the lanthanide(III) and thorium(IV) complexes.
abstract: The lanthanide and Th4+ complexes with calix[4]arene ligands substituted either on the narrow or at the wide rim by four coordinating groups behave totally differently as shown by an NMR investigation of the dia- and paramagnetic complexes. Solutions of complexes were prepared by reacting anhydrous metal perchlorate salts with the ligands in dry acetonitrile (CAUTION). Relaxation time T1 titrations of acetonitrile solutions of Gd3+ by calixarenes indicate that ligands subsituted on the narrow rim form stable 1:1 complexes whether they feature four amide groups (1) or four phosphine oxide functions. In contrast, a ligand substituted by four (carbamoylmethyl)-diphenylphosphine oxide moieties on the wide rim (3) and its derivatives from polymeric species even at a 1:1 ligand/metal concentration ratio. Nuclear magnetic relaxation dispersion (NMRD) curves (relaxation rates 1/T1 vs magnetic field strength) of Gd3+, Gd3+.1 and Gd3+.3 perchlorates in acetonitrile are analyzed by an extended version of the Solomon-Bloembergen-Morgan equations. A comparison of the calculated rotational correlation times tau r shows that ligand 3 forms oligomeric Gd3+ species. The chelates of ligand 1 are axially symmetric (C4 symmetry), and the paramagnetic shifts induced by the Yb3+ ion are accounted for quantitatively. The addition of water or of nitrate ions does not modify the geometry of the complex. The metal chelates of 3 and its derivatives adopt a C2 symmetry, and the paramagnetic shifts are interpreted on a semiquantitative basis only. Water and NO3- ions completely labilize the complexes of the heavy lanthanides. The very high selectivity of ligand 3 through the lanthanide series stems from a complex interplay of factors.
authors.affiliation: University of Liège, Sart Tilman (B6), B-4000 Liège, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Lambert
authors.forename: V
authors.initials: V
authors.lastname: Jacques
authors.forename: A
authors.initials: A
authors.lastname: Shivanyuk
authors.forename: S E
authors.initials: SE
authors.lastname: Matthews
authors.forename: A
authors.initials: A
authors.lastname: Tunayar
authors.forename: M
authors.initials: M
authors.lastname: Baaden
authors.forename: G
authors.initials: G
authors.lastname: Wipff
authors.forename: V
authors.initials: V
authors.lastname: Böhmer
authors.forename: J F
authors.initials: JF
authors.lastname: Desreux