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.