Lanthanide ions applications

Equation (S6.1) is applicable to the salts of lanthanide ions. These have a partly filled 4f shell, and the 4f orbitals are well shielded from any interaction with the surrounding atoms by filled 5.9, 5p, and 6.9 orbitals, so that, with the notable exceptions, Eu3+ and Sm3+, they behave like isolated ions. For the transition metals, especially those of the 3d series, interaction with the surroundings is considerable. Because of this, the 3d transition-metal ions often have magnetic dipole moments corresponding only to the electron spin contribution. The orbital moment is said to be quenched. In such materials Eq. (S6.1) can then be replaced by a spin-only formula ... 

Trivalent lanthanide cations have luminescent properties which are used in a number of applications. The luminescence of the lanthanide ions is unique in that it is long-lasting (up to more than a millisecond) and consists of very sharp bands. Lanthanide emission, in contrast to other long-lived emission processes, is not particularly sensitive to quenching by oxygen because the 4f electrons found within the inner electron core... 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

A number of non-podand (i.e., those without an apical atom or group) acyclic ligand systems have been developed for lanthanide luminescence applications. Many of these are designed as helicating ligands such that the lanthanide ion is well encapsulated despite the linearity of the ligand. 

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... 

For the application of lanthanide complexes in medical diagnosis and therapy, a general requirement is that the ion Ln3+ and the ligand should remain associated while the complex is in the body, i. e. their dissociation should be minimal, since the free ligand and Ln3+ are toxic. For the dissociation to be negligible, the complexes must be kinetically inert under physiological conditions. Since the complexation properties of the lanthanide ions and Y3+ are quite similar, it is of interest to compare the results obtained as concerns the kinetic behavior of Gd3+ complexes with those known for the complexes of other lanthanides and Y3+. 

The basis for applying the LIS quantitatively to problems in stereochemistry depends upon expressions including the term (3 cos2 — l)r-3, where r is the distance from the carbon to the lanthanide ion and the angle d is defined by the symmetry axis of the complex and the vector from the lanthanide ion to the carbon in question. This application depends on a LIS imposed entirely by the pseudocontact mechanism. It has been shown that the contact mechanism is important for europium and praseodymium complexes in 13C NMR for distances up to four bonds from the site of complexation, and that ytterbium complexes interact with 13C nuclei largely, if not entirely, by the pseudocontact process. (12, 13)... 

Within solution inorganic chemistry, there would be no apparent reason to obtain NMR spectra at high pressures in structural characterization studies. It prevails that most applications of hp NMR spectroscopy relate to solvent exchange reactions on solvated metal ions their mechanisms often have direct bearing upon the kinetics and mechanisms of substitution of one or more solvent molecules from a metal center by other ligands. The first part of the results section provides ample illustration of the value of high-pressure measurements on transition metal and lanthanide ions, fully... 

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