Lanthanide high symmetry

Tamao K, Miyaura N (2002) Introduction to Cross-Coupling Reactions. 219 1-9 Tanaka M (2003) Homogeneous Catalysis for H-P Bond Addition Reactions. 232 25-54 Tanner PA (2004) Spectra, Energy Levels and Energy Transfer in High Symmetry Lanthanide Compounds. 241 167-278 ten Cate MGJ, see Crego-Calama M (2005) 249 in press ten Holte P,see Zwanenburg B (2001) 216 93-124 Thiem J,see Werschkun B (2001) 215 293-325... 

In contrast to the situation with the 3d transition metals in particular, the 4f-4f transitions in the electronic spectra of lanthanide complexes rarely serve any diagnostic purpose. It may be noted, however, that the spectra of the octahedral [LnXe] " ions (X = Cl, Br) have particularly small extinction coefficients, an order of magnitude lower than the corresponding aqua ions, due to the high symmetry of the environment. 

Although we have treated the hyperfine interaction as an interaction between the nuclear spin I and the intrinsic spin s of the electron, it is in reality the interaction of I with the total angular momentum of the electron. Most lanthanide and actinide ions and some transition metal ions in high symmetry do not have their orbital momentum quenched by the crystal fields. In these cases a complete treatment of the hyperfine interaction must include the following term... 

We therefore developed a much simplified, but mathematically exact, version of a shell model which is particularly suitable for the analysis of cross relaxation in high symmetry systems such as the lanthanide elpasolites. Since the vibronic structure in the emission and absorption spectra of these compounds is both intense and broad (relative to the electronic origins), there are many cases where the vibronic structure of one electronic transition in emission overlaps with the vibronic structure of another electronic transition of a chemically identical ion in absorption. The emission of the excited ion may then be partially quenched by energy transfer. Implicit in this formulation is the assumption that the interionic coupling is weak compared with the vibronic coupling this is certainly true for the lanthanide elpasolites where the lanthanide ions are separated by distances of more than 0.7 nm. We refer to this process as cross relaxation by the electric dipole vibronic-electric dipole vibronic (EDVEDV) mechanism. 

Spectra, Energy Levels and Energy Transfer in High Symmetry Lanthanide Compounds... 

Such terms are equivalent to those obtained by Satten et al. (1983) in their study of the excitations of the T,u vibrational mode of the octahedral complex UCI5 at 260 cm L They were aware that their approach would work in a similar way for lanthanide complexes their choice of an actinide was partly determined by their familiarity with the UClj complex. Another important consideration was the high symmetry of the uranium site, which greatly reduces the number of intensity parameters required in the analysis. To assess the situation we note first that the possible pairs (k,t) in expression (94) are (1,2), (3,2), (3,4), (5,4), (5,6) and (7,6). The number of Ti representations of 0(, that occur in the representations of 0(3) are 1, 1,2 and 2 for /c = 1, 3, 5 and 7, so we expect 9 parameters in all. Satten et al. (1983) reduced that number to 6 by carrying out a complete closure over all virtual electronic states, which has the effect of fixing the ratio of the two operators (94) for which t = /c 1. They were able to account quite well for the relative intensities of some 20 or so transitions of the type Aig( H4)-> T, ( Lj), where is a... 

Tanner PA (2004) Spectra, energy levels and energy transfer in high symmetry lanthanide compormds. Top Curr Orem 241 167-278... 

The local structure of a molten lanthanide trichloride was studied for the first time by Maroni et al. (1974) who investigated the LaCl3-KCl binary mixture. The conclusion of the existence of at least one highly symmetrical associated species in this melt based on the analysis of Raman spectra was soon substantiated in the case of yttrium trichloride (Papatheodorou, 1977). In the latter work, the high-symmetry structural unit was identified as the octahedral hexachloride (YCle) . Next, a comparison of the Raman spectra of liquid and solid yttrium trichloride samples led the authors to conclude that lattice-type vibrations occurred in melts. 

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