Lanthanide ions ligands

Many lanthanides in the form of complexes emit fluorescence when excited with light absorbed by ligands. Lanthanide ions in crystals or in solution also exhibit fluorescence. The fluorescence observed due to energy transfer from the triplet state of the ligand to excited state of Ln3+ is known as enhanced fluorescence. The fluorescence emission spectra of Tb3+ aquo ion in the absence and presence of porcine trypsin at pH 6.3 is shown in Fig. 11.3. 

The reason why lanthanides of high atomic number emerge first is that the stability of a lanthanide ion-citrate ion complex increases with the atomic number. Since these complexes are formed by ions, this must mean that the ion-ligand attraction also increases with atomic number, i.e. that the ionic radius decreases (inverse square law). It is a characteristic of the lanthanides that the ionic radius... 

Complexes of lanthanide ions with N-donor ligands. J. H. Forsberg, Coord. Chem. Rev., 1973,10, 195-226 (129). 

Let us now consider MMCT for the case in which the donating ion is a lanthanide ion with a partly filled 4/ shell M(/")M(d°)CT. The trivalent lanthanide ions with a low fourth ionization potential are Ce, Pr ", Tb ". Their optical absorption spectra show usually allowed 4f-5d transitions in the ultraviolet part of the spectrum [6, 35]. These are considered as MC transitions, although they will undoubtedly have a certain CT character due to the higher admixture of ligand orbitals into the d orbitals. In combination with M(d°) ions these M(/") ions show MMCT transitions. An early example has been given by Paul [36] for Ce(III)-Ti(IV) MMCT in borosilicate glasses. The absorption maximum was at about 30000 cm ... 

When not complexed, lanthanide ions have a high affinity for bone in vivo because they act as calcium ion mimics. Because the lanthanides undergo hydrolysis above a pH of 4, they readily form radiocolloids when not complexed, and are then taken up by the liver. This bone and liver uptake results in non-specific radiation doses to non-target (normal) tissues and organs and is undesirable.91 The polyaminocarboxylate class of ligands are considered to be the optimal choice for the basis of BFCAs for the+3 metal cations, including the lanthanides. It is essential that the... 

Electronic Structure of Lanthanide Ions in a Ligand Field 7... 

When a lanthanide ion is placed in a ligand environment with symmetry lower than spherical, the energies of its partly filled 4f orbitals are split by the electrostatic field of the ligand. The result is a splitting of the 2/ + 1 degeneracy of the free ion states (see Figure 1.2). 

Figure 1.2 Energetic structure of a Kramers lanthanide ion in a ligand field evidencing the effect of progressively weaker perturbation. The magnetic field effect is estimated assuming a 1T field.

The structures and dynamic magnetic behaviours of 31-Dy4 and 31-Tb4 have been presented in Figure 3.22. Four lanthanide ions are aggregated in the grid-like metal core by a central p4-S and eight peripheral i2-S atoms from ethanethiol ligands [38]. The individual lanthanide centres occupy distorted six-coordinate [LnNS5] octahedral coordination environments. Ac susceptibilities measurements reveal pronounced temperature dependence with a series of maxima below 28 K, typical for SMM behaviour, in complex 31-Dy4. Furthermore, an... 

In this sub-chapter, selected examples of lanthanide-based chains are described. We have chosen to comment on only systems with structural characterization and significant dynamic properties. Chains with a sole lanthanide ion as spin carrier are described first. 3d-4f and 3d-3d -4f heterometallic chains follow. Finally, chains comprising lanthanide and radical ligands conclude this chapter. 

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