Absorption spectra of lanthanide

There are difficulties associated with the use of ordinary electronic absorption spectra of lanthanide complexes in solution to provide detailed information regarding coordination number and geometry. However, difference spectra versus NdCl3 are reported for Nd3+-ligand (L) solutions for the 4/9/2— -4G5/2, 4G7,2 transitions (L = dipicolinate, oxydiacetate, iminodiacet-ate, malate, methyliminodiacetate and Ar,Ar -ethylenebis Af-(o-hydroxyphenyl)glycinate ). Hypersensitive behaviour was examined and transition dipole strengths were discussed in terms of the nature of the complex species present.431... 

Absolute configuration of complexes. 495-496 Absolute electronegativity, 351 Absolute hardness. 351 Absorption spectra of lanthanide and actinide ions. 604-607 Acceptor number CAN). 370 Achiral molecules, and point groups, 64 Acids. 2... 

Some salient features of the absorption spectra of lanthanide complexes in solutions.635... 

The energy levels of lanthanide free ions in crystals and solutions determined from the absorption spectra differ somewhat from those of gaseous Ln3+ ions and depend on the environment [33-35]. In the presence of ligand fields, the whole 4f" structure appears to shorten as compared to gaseous ions. The mean J level in Pr3+ shifts by 5 percent [33] and by one percent in Er3+ [36]. The red shift observed in the absorption spectra of lanthanides has been termed as the nephelauxetic effect. The nephelauxetic effect has been discussed in detail [34],... 

Methods for obtaining high-purity rare earth salts combined with the availability of high resolution spectrophotometers led to comprehensive studies of the absorption spectra of lanthanides [136-141]. The experimental work on the spectra of single crystals of rare earth salts by Dieke was of immense value in the theoretical interpretation of the energy level structures of the lanthanide ions [142]. 

The absorption spectra of lanthanide ions with an unfilled 4f level will now be examined. Some data on the terms of f configurations for trivalent lanthanide ions are given in Table 8.11. The configurations fq and f14 q are characterized by an identical set of terms. The number of terms becomes large as one goes from f1 (f13) to f7. There is a systematic... 

In aqueous solutions, lanthanide(III) ions are coordinated by water molecules. The hydration sphere of the lanthanide ions plays a vital role in the chemistry of the ion and also in several biochemical reactions involving isomorphous calcium(II) substitution reactions. The interpretation of the absorption spectra of lanthanide(III) ions in aqueous media is difficult because of the variability of the coordination number of the aquo ions along the lanthanide series. Kinetic and thermodynamic studies [206-210] on the lanthanide aquo systems led to the conclusion that the lighter lanthanides have a coordination number of 9, heavy lanthanides are octacoordinated and the middle members exist in a equilibrium mixture of octa and nonacoordinated aquo ions. 

Many studies on the absorption spectra of lanthanides in alcoholic media have been made and the observations and anomalies have been explained in terms of entry of a chloride ion into the coordination sphere of the lanthanide ion. The composition and stability of halide complexes of lanthanides in alcohol and aqueous alcoholic solutions have been studied by spectral techniques. The halide ions have been found to cause marked changes in the spectra of lanthanides in alcoholic and aqueous media. The observed spectral changes may be attributed to changes in the immediate coordination environment of the lanthanide ion [223]. 

Absorption spectra of lanthanides in the 4f-4f region were used in the studies on complexation by haloacetates in DMF, DMSO, methanol and in mixtures of the solvents. Octacoordination in the solvents was inferred. The band intensities in pure solvents were higher than in solvent mixtures. Haloacetate appears to form an inner sphere complex in organic solvents and an outer sphere complex in aqueous media [227-231],... 

At pH 2.0 diols are not ionized and hence complexation occurs with neutral diol molecule. Above pH 2.0 diols are ionized and become bidentate complexing agent. The absorption spectra of lanthanide complexes with the following diols,... 

As noted in Chapter 8 the absorption spectra of lanthanides are characterized by sharp but complicated absorption spectra of low intensity. It is also to be noted that the spectral features are generally not sensitive to the surrounding environment, at least not as much as the transition metals. That is, the f orbitals are well shielded from the environment. 

In lanthanide elements, the 5s and 5p shells are on the outside of the 4f shell. The 5s and 5p electrons are shielded, any force field (the crystal field or coordinating field in crystals or complexes) of the surrounding elements in complexes have little effect on the electrons in the 4f shell of the lanthanide elements. Therefore, the absorption spectra of lanthanide compounds are line-like spectra similar to those of free ions. This is different from the absorption spectra of d-block compounds. In d-block compounds, spectra originate from 3d 3d transitions. The nd shell is on the outside of the atoms so no shielding effect exists. Therefore, the 3d electrons are easily affected by crystal or coordinating fields. As a result, d-block elements show different absorption spectra in different compounds. Because of a shift in the spectrum line in the d-block, absorption spectra change from line spectra in free ions to band spectra in compounds. 

It has been very difficult to unambiguously prove which state is responsible for the energy transfer processes because of the lack of information regarding the emission from the excited states of the coordinated ligand and the difficulties in determining ligand-localized triplet-triplet absorption spectra of lanthanide complexes. All the experimental work conducted seemed to support case (a) in Figure 1.8. 

A recent development of interest in interpreting the absorption spectra of lanthanide ions has been a theory of absorption intensities developed independently by Judd (14) and by Ofelt (21) which represents an important advance from earlier treatments of this problem (3, 25). 

Fig. 7 Solid-state absorption spectra of lanthanide-radical complexes at 5 K (solid lines) and 290 K (dotted lines). From top to bottom [Eu(hfac)3IMPy] (290 K), [Gd(hfac)3IMPy] (290 K, 5 K), [Gd(hfac)3IMBzImH] (290 K, 5 K). [Gd(hfac)3NITBzImH] (290 K, 5 K) and [Gd(NITBzImH)2(N03)2] (5 K). Alphabetical labels denote maxima summarized in Table 2. Traces are offset along the ordinate for clarity...

Comparing the absorption spectra of lanthanide and actinide ions having the same number of f electrons, the most striking differences occur in molar absorptivity at the light end of the actinide series. For example, in fig. 3, approximately 100-fold larger molar-absorptivity values are evident for bands whose widths are comparable to those of Nd. Actinide-ion band molar absorptivities generally decrease across the... 

Fujii, T, Moriyama, H., and Yamana, H. (2003) Electronic absorption spectra of lanthanides in a molten chloride. J. 

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