Stability constants and some other properties of the lanthanoid nitrate complexes with tri-, tetra-, and pentaethylene glycols

The lanthanoid nitrate complexes of tri-, tetra-, and pentaethylene glycols (EO3, EO4, and EO5) exhibited anomalous stability trends attributed to structures similar to those of crown complexes. The stability constants of the EO4 and the EO5 complexes decreased with an increase in the atomic number of the lanthanoid in contrast to the lanthanoid complexes with most other ligands. A maximum stability was found at europium for EO3 complexes. The decomposition temperatures of EO3 complexes were higher than those of the corresponding EO4 and EO5 complexes. The yields of the solid complexes in reactions of the lanthanoids with EO5 decreased with an increase in the atomic number of the lanthanoid (with some exceptions). The separation factors observed for fractional precipitation using EO5 as the separating reagents were comparable to those reported regarding reagents practically used for lanthanoid separation. (author)