Liquids lanthanides

For the liquid lanthanide trihalides data from enthalpy-increment measurements and heat capacity (DSC) measurements are available, as summarised in table C. 1 of Appendix C, the recommended values are given in table 14. The majority of the results have been reported by two... 

The properties of the liquid lanthanide trihalides depend strongly on the atomic number of the halide. The variation in the heat capacity of the lanthanide fluorides indicates a strongly ionic behaviour of the melts with a concomittent irregular trend related to the electronic configuration of the lanthanide ions. In the lanthanide chlorides, bromides and iodides the trend becomes systematically more constant, indicating an increasing molecular nature of the melts. 

Experimental results for the enthalpy of fusion and heat capacity of the liquid lanthanide trichlorides... 

Garcia, R. et al., Solid-liquid lanthanide extraction with ionic-imprinted polymers, Sep. Set Technol., 37, 12, 2839, 2002. 

The densities of the liquid lanthanides, at their respective melting temperatures, are shown as a function of atomic number in fig. 1. With the exception of the divalent liquid metals, Eu and Yb, the densities are seen to increase linearly with Z. It is also notable that the density increases at approximately twice the rate that the atomic weight increases, implying a contraction of the atomic core with increasing Z this has been called the lanthanide contraction . 

Fig. 1. Density, p, of the liquid lanthanides at their respective melting temperatures. Data are from table 1.

Kononenko (1983) also uses a combination of pseudopotential theory and a variational method to calculate specifically for the liquid lanthanide metals. These values are then compared with E obtained from measurements of y and dy/dT (eq. 11) for these liquids. The trends in the measured E are reproduced by the calculated values, except for Sm, for which a transition of a small fraction of ions to the divalent state may have substantial effects not addressed in the calculations. 

The resulting values are listed in Tables 25 and 26. Note that the approximation was constructed without including data on LaQa and PrCls (Savin et al., 1979), CeCla and NdQa (Savin and Mikhailova, 1981), and LaFs (Spedding and Henderson, 1971). For comparison. Tables 25 and 26 also contain the results obtained by Kovacs and Konings (2003), who analyzed the heat capacities of liquid lanthanide trifluorides and trichlorides with the assumption that heat capacity changes can be correlated with changes in AV/V. 

Fig. 28. The heat capacity of liie liquid lanthanide trihalides.

Fig. 30. The heat capacity of liquid lanthanide trichlorides as a function of the volume change AV/ Vcr.

The methods listed thus far can be used for the reliable prediction of NMR chemical shifts for small organic compounds in the gas phase, which are often reasonably close to the liquid-phase results. Heavy elements, such as transition metals and lanthanides, present a much more dilficult problem. Mass defect and spin-coupling terms have been found to be significant for the description of the NMR shielding tensors for these elements. Since NMR is a nuclear effect, core potentials should not be used. 

Relativistic effects are cited for changes in energy levels, resulting in the yellow color of gold and the fact that mercury is a liquid. Relativistic effects are also cited as being responsible for about 10% of lanthanide contraction. Many more specific examples of relativistic effects are reviewed by Pyykko (1988). 

Scheme 5.1-43 Three-component reaction of benzaldehyde, aniline, and diethyl phosphonate in ionic liquids, catalyzed by lanthanide triflates and indium(lll) chloride.

Wilson JA (1977) A Generalized Configuration - Dependent Band Model for Lanthanide Compounds and Conditions for Interconfiguration Fluctuations. 32 57-91 Wilson MR (1999) Atomistic Simulations of Liquid Crystals. 94 41-64 Winkler H, see Trautwein AX (1991) 78 1-96... 

What became known as the tetrad effect was first observed in the late 1960s during lanthanide separation experiments [25]. Fig. 1.3 shows a plot of log K, where is the distribution ratio between the aqueous and organic phases in a liquid-liquid extraction system. There are four humps separated by three minima, first at the f /f pair, secondly at the f point, and thirdly at the pair. 

EDTA complexes of trivalent metals can be extracted successively with liquid anion exchangers such as Aliquat 336-S by careful pH control. Mixtures of lanthanides can be separated by exploiting differences in their EDTA complex formation constants. 

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