Systematics of Lanthanide Coordination

Abstract

This article discusses the general trends of lanthanide coordination in solution. The bonding in these compounds is best described by an ionic model. Minor covalent interactions are inferred from spectral measurements; however, these probably involve the 5d or 6s rather than the 4/ orbitals. The enthalpy and entropy of these reactions are largely compensatory. Nevertheless, deviations are observed for systems involving strong metal-donor interactions such as the polyaminocarboxylates. The kinetics of complexation of these polyaminocarboxylates are interpreted in terms of a dissociative interchange mechanism. The rate-determining step probably involves the formation of a distorted LnY* complex (low AH* and negative AS*). The use of NMR and chiroptical methods to study the conformational preference and mode of coordination in these complexes are also discussed.

139La NMR Kinetic Study of Lanthanum(III) Complexation with Acetohydroxamic Acid

“…The closeness of this value to the water-exchange rate constant seems reasonable considering that both ligands are uncharged, i.e. H 2 O and HA molecules, and considering the electrostatic nature of the ligandϪLa III bond, [27] which also accounts for a much smaller value calculated for k Ϫ12 than k Ϫ11 .…”

New tris-3,4-HOPO lanthanide complexes as potential imaging probes: complex stability and magnetic properties

“…The compensation of these two effects is reflected in the observed wavy trend of the log β MH i L values. 22,23 Spectrophotometric titrations were carried out to help the identification of the specific donor groups of the ligand involved in the metal chelation. The marked differences § of the spectra in the absence (Fig.…”

Structural Characterization, Magnetic and Luminescent Properties of Praseodymium(III)-4,4,4-Trifluoro-1-(2-Naphthyl)Butane-1,3-Dionato(1-) Complexes

“…The high surface positive charge density of Ln 3+ ions (charge/ionic radius) makes them behave as hard acids and consequently they prefer the coordination to hard Lewis bases. Although the intermolecular interaction forces of Ln 3+ with chelated ligand(s) are electrostatic in nature, steric factors rather than electronic ones [44] dominate the geometry of the complexes and as a result, the Ln 3+ complexes containing the same ligand are usually all isostructural. The interactions of β-diketonato ligands with Ln 3+ produces thermodynamically stable complexes [9,17,40,41,43,[45][46][47][48], where the coordinated βdiketonates act as efficient antenna ligands for lanthanides emitting in the visible and NIR region [1][2][3][4]6,17,36].…”