Lanthanide ions organic ligands

There exist many mixed complexes of lanthanides of organic ligands and nitrate ions. From their formulae it can be concluded that nitrate ions are coordinated to the lanthanide ions either as a monodentate or as a bidentate ligand. The actual disposition of the nitrate group may be ascertained from the infrared and Raman spectra [155]. The ionic nitrate and bound nitrate differ in symmetry. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

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... 

The synthesis of mononuclear molecular complexes, in which a single ion is wrapped by a shell of organic ligands, provides an alternative method for creating arrays of nearly isolated lanthanide spin qubits. The study of these materials was boosted by Ishikawa and coworkers [94] discovery of magnetic hysteresis in... 

ILs are becoming useful solvenfs to investigate fhe specfroscopic behavior of both organic and inorganic lanthanide complexes in solution, especially of complexes with weakly binding ligands, which otherwise would be unable to compete with the solvent molecules for a binding site on the lanthanide ion [9]. 

A further application of relaxation rate measurements is that similar 1/71 ratios in a series of lanthanide complexes may be taken to indicate an isostructural series. However, this approach has the limitation that if only part of the complex is studied, perhaps an organic ligand, its 71 ratios would be independent of changes, for example changes in the extent of hydration in the remainder of the complex, provided that the conformation of the ligand relative to the lanthanide ion were preserved. An excellent example of the use of 71 data in a quite different way is its use to determine hydration numbers of lanthanide dipicolinate complexes.562... 

Excitation of the Eu3+ or Tb3+ ions has traditionally been indirect, by broad-band UV excitation of a conjugated organic ligand which is followed by intramolecular energy transfer to the lanthanide ion / system, followed in turn by /- / emission.614 However, more recently, following the advent of tunable dye lasers, direct excitation of an excited / level is in many cases preferable. By scanning this frequency, an excitation spectrum can be obtained whose energy values are independent of the resolution of a monochromator and not subject to spectral interferences. 

FIGURE 5.3 The 1 1 complexation of lanthanide ions (M3+) with organic ligands in water standard deviation (s) of Equation 5.2 as a function of the difference between ionic radii r (for CN = 6) of the M3+/Lu3+pairs of lanthanides. 

---