(a) Molecular structures for tetrapodal ligands EDTA (ethylenediaminetetraacetic acid) and its pyridine and pyrazine derivatives. (b) Percentage of stripped cations and separation factors for the back-extraction of Eu(III) and Am(III) by 0.5 M water solution of ligand 20 and 21 at pH of 3 comparing to HEDTA (ligand 14, Figure 6). (c) Evolution of stability constants logβ for ML complexes as an inverse function of the cation ionic radii for La(III), Nd(III), Eu(III), Dy(III) and Lu(III). Data in panel (b) and (c) are recreated from Ref [115].