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

Journal article, 2017

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 [Nd-2(NO3)(6)L-2]center dot(CH3CN)(3) (2), [Nd-2(NO3)(4)L-2]center dot[Nd(NO3)(5)]center dot(CH3CN) 1.5 (3), Ce(NO3)(3)L-2 (4), and [NdL2]center dot(ClO4)(3)center dot 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.