l‑Alanine/Nickel-Induced Size Sorting of Lanthanide(III) Ions in 4f–4f′ Heterometallic Complexes

A versatile approach to create a novel class of mixed-lanthanide compounds with predetermined locations of different lanthanides in cationic and anionic positions has been developed. Pure 4f–4f′ heterometallic complexes were constructed from two independent building blocks: the complex cation [Ln­{Ni­(ala)₂}₆]³⁺ (ala = l-alaninate), which can be formed by La³⁺, Ce³⁺, Pr³⁺, and Nd³⁺ exclusively, and the anion [Gd­(NO₃)₃(OH)₃(H₂O)]^3–. The compositions and structures of the complexes were studied by X-ray crystallography, energy-dispersive X-ray spectroscopy, and inductively coupled plasma mass spectrometry. The X-ray structural analysis showed the high rigidity of the l-alanine/Ni­(II) supramolecular unit in the complex cations, which affected immediately its selectivity toward certain lanthanides