Complexes of the Heavier Lanthanoid Nitrates with Crown Ethers

Abstract

Crown ethers form stable complexes with lanthanoid (III) ions (2), (3), (4), (5). We have shown, in previous papers of this series, that unsolvated complexes of the lighter lanthanoid nitrates (Ln = La−Gd) can be isolated with 15-crown-5 and 18-crown-6 ethers. The Ln(III)/crown ether ratio is 1:1 for the complexes with ligand 2 whereas complexes of ligand 3 may have two different stoichiometries, 1:1 for Ln = La−Nd and 4:3 for Ln = La−Gd (6). The strength of the Ln(III)/crown ether interaction depends on both the ratio of ionic diameter/ligand cavity diameter and the ligand flexibility. In this communication we discuss the interaction of ligands 2 and 3 with the heavier lanthanoid (III) ions and we report the results of a ¹H-NMR study of the 18-crown-6 complexes with Ln = La, Pr, Nd, Eu, Yb, as well as some preliminary results of our X-ray structural work on the neodymium nitrate 1:1 and 4:3 complexes with 18-corn-6.

Part 3 of the series “Complexes of Lanthanoid Salts with Macrocyclic Ligands”. For part 2 see reference (1).