The importance of hydrogen bonding in the complexation of lanthanide ions by polymer-bound malonamide-type ligands

作者：Yang Yijia; Alexandratos Spiro D^*

来源：Inorganica Chimica Acta, 2010, 363(13): 3448-3452.

DOI：10.1016/j.ica.2010.06.059

• Polymer
• Lanthanide
• Binding mechanism
• Malonamide

Polymer-bound malonate ligands modified with diethylenetriamine (DETA-MAm) are prepared and the lanthanide ion affinities from solutions of 0.001-8 M HCl are quantified. A mechanism is proposed. The affinities are not due to the triamine ligand alone or the adjacent carbonyl sites alone: protonation of the carbonyl oxygen triggers formation of an iminium ion and it acts as an ion-exchange site. Two competing reactions occur during binding: electrostatic attraction of [Ln(H(2)O)(x)Cl(4)] by the protonated ligand and (partial) loss of the waters of hydration. The affinity and selectivity are affected by substituents on the iminium (C=NRR'(+)) ion. Research with tetramethylmalonamide showed that its two methyl groups at the iminium site weaken the positive charge and decrease its affinity for the chlorocomplexes of the later lanthanides; DETA-MAm has at its amide nitrogen only one -CH(2)- (and one H) moiety and therefore is a stronger but less selective ligand since electrostatic attraction is more dominant in the overall mechanism. The higher affinities of malonate monoamidated with ethylenediamine (EDA-MAm) and decreased affinities for those amidated with ethanolamine (EA-MAm) suggest that the protonated -NH- stabilizes the lanthanide chlorocomplex.

• 出版日期2010-10-25