Coordination of trivalent lanthanides with bismalonamide ligands : implications for liquid-liquid extraction

Abstract

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 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 the structures 2 , 3 and 5 and bidentate in 4 only. It was found that the 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 the metal ions with this type of ligands.