Donor Radii in Rare-Earth Complexes

Abstract

We present a set of donor radii for the rare-earth cations obtained from the analysis of structural data available in the Cambridge Structural Database (CSD). Theoretical calculations using density functional theory (DFT) and wave function approaches (NEVPT2) demonstrate that the Ln-donor distances can be broken down into contributions of the cation and the donor atom, with the minimum in electron density (ρ) that defines the position of (3,–1) critical points corresponding well with Shannon’s crystal radii (CR). Subsequent linear fits of the experimental bond distances for all rare earth cations (except Pm 3+) afforded donor radii (r D) that allow for the prediction of Ln-donor distances regardless of the nature of the rare-earth cation and its oxidation state. This set of donor radii can be used to rationalize structural data and identify particularly weak or strong interactions, which has important implications in the understanding of the stability and reactivity of complexes of these metal ions. A few cases of incorrect atom assignments in X-ray structures were also identified using the derived r D values.

Investigation of Ln3+ complexation by a DOTA derivative substituted by an imidazothiadiazole: synthesis, solution structure, luminescence and relaxation properties

“…However, it cannot be excluded that it belongs to a carboxylate function as similar protonations have been evidenced by X-ray structures of a few examples of DOTA-like complexes. 47–49 The presence of the neighbouring heterocycle could stabilize this protonation through hydrogen bonding, which would explain both a higher than expected value for protonation of the carboxylate functions and modification of the UV and fluorescence properties of the complex.…”

“…This is not the case, which means that the second protonation should occur on the carboxylate function, while maintaining a monohydrated complex as previously observed based on the solid state and solution properties of such LnDOTA derivatives. 47…”

A maximally preorganized tetra‐pyridyl ligand. Rigid five‐membered chelate rings enhance selectivity for large metal ions, such as Th(IV), UO22+ and Lanthanides. A DFT and Thermodynamic study

“…The ideal M−N bond lengths (pyridyl nitrogens) were assumed in the calculations to be a constant 0.17 Å longer than the ideal M−O bonds (aqua ligands) [32] . Use of the Shannon cationic radii [48] as a measure of size of lanthanides here conforms well with approaches reported recently [67] using DFT and searches of structures in the CSD for analyzing the bonding of Ln(III) cations in their complexes.…”