Coordination of Trivalent Lanthanides with Bismalonamide Ligands: Implications for Liquid-Liquid Extraction.

The complexation of the bismalonamide ligand 2,2'-[1,2-phenylenebis(methylene)]bis(N,N,N',N'-tetraethylmalonamide) (L), bearing two C-alkylated N,N,N',N'-tetraethylmalonamide groups, onto an ortho-xylylene [C6H4(CH2)2] platform with trivalent lanthanides was investigated, both in solid and solution states. The crystal structures [Nd2(NO3)6L2]·(CH3CN)3 (2), [Nd2(NO3)4L2]·[Nd(NO3)5]·(CH3CN)1.5 (3), Ce(NO3)3L2 (4), and [NdL2]·(ClO4)3·C2H5OH (5) were analyzed by single-crystal X-ray diffraction. The ortho-bismalonamide (L) is tetradentate in structures 2, 3, and 5 and bidentate in 4 only. It was found that structures 2 and 3 are composed of dimeric species. According to electrospray-ionization mass spectrometry, the dimers are prevailing in acetonitrile solutions. The polydentate coordination of the ortho-bismalonamide (L) with trivalent lanthanides suggests that an entropy effect favors liquid-liquid extraction of metal ions with this type of ligand. [ABSTRACT FROM AUTHOR]