Establishing coordination numbers for the lanthanides in simple complexes

Abstract

This article reviews the development of the understanding of the coordination number in lanthanide complexes, showing how it was realized in the 1960s that lanthanide complexes frequently had much higher coordination numbers than 6, and how it subsequently became possible for chemists to synthesise compounds with coordination numbers as low as 2, 3 and 4. Subsequent sections examine how coordination of solvent can cause uncertainties in coordination numbers; the determination of the coordination number of the aqua ions and in hydrated salts; variations (or not) in coordination number across the lanthanide series; the effect of counter-ion upon coordination number; and agostic interactions and interactions with distant atoms (when is a bond not a bond?).

Raman spectroscopic study of trivalent lanthanides in concentrated aqueous solutions

“…The difference between the Raman spectra of CeCl 3 and LiCl aqueous solutions, having the equal Cl -concentration of 6.35 M, in the case of CeCl 3 solution demonstrates the intensity deficiency in the spectral area belonging to anion-water (H 2 O n )Cl -complexes (ν ~ 3465 cm -1 ) and the intensity excess in To interpret these spectral data we should attract the results obtained by various methods on the coordination of trivalent lanthanide ions (Ln 3+ ) in solutions [2,3,10,11].…”

“…In the Eu-Tb regions of the lanthanide (III) series the intermediate (between 9 and 8) hydrated numbers are proposed [ 10 ].…”

Small Molecule Luminescent Lanthanide Ion Complexes - Photophysical Characterization and Recent Developments

“…Several methods have been described for the process. NMR, UV/vis or fluorescence titrations are routinely utilized [15,[48][49][50], as are competition studies with EDTA by fluorescence spectroscopy [51], as well as high resolution fluorescence spectroscopy through direct excitation of the 5 D 0 7 F 0 transition of Eu(III) and EXAFS [52][53][54].…”

Selective Lanthanides Sequestration Based on a Self‐Assembled Organosilica

“…A coordination number of six is not usual for Ln 3 + , which has a typical coordination number between 8 and 10. [44] However, about 100 structures, in which the lanthanide is six-coordinated, were found in the Cambridge Structural Data (using ConQuest Version 1.8, updated January 2006). [45] It is worth noting that most of these structures orig-inate from molecular species or complexes usually prepared in non-aqueous solutions, the ligands being generally bulky.…”