NMR investigation of the lanthanide and actinide complexes of bis-triazine extracting agents

Abstract

peer reviewedNuclear magnetic resonance spectroscopy (NMR) is applied to unravel the solution structure and the stoichiometry of the complexes formed between bis-triazine extracting agents (BTP and BTBP) and paramagnetic lanthanide ions. Highly rigid lanthanide perchlorate tris-complexes of threefold symmetry are formed by the pyridine bis-triazine BTP¿s while the bipyridine analogues (BTBP) form bis-complexes with a more open structure that leaves enough space for solvent molecules or anions. The nitrate ion is unable to enter the first coordination sphere of the tris-BTP complexes but the structure and stoichiometry of the bis-BTBP chelates are profoundly modified in presence of this ion. The NMR analysis is extended to actinides in various oxidation states despite technical difficulties. The NpO2+ ion is shown to form a 1:1 BTP complex in which the ligand is located in the plane perpendicular to the dioxo unit. No covalency contribution could be detected in the NMR spectra but such a contribution is clearly visible in the case of Am3+ and Cm3+. The latter induces very large paramagnetic shifts with a large contact contribution