Notiz zur Präparation von wasserfreien Lanthaniden-Haloge-niden, Insbesondere von Jodiden

This chapter discusses the thermodynamic properties of the lanthanide (III) halides. The melting points in all four lanthanide trihalide series exhibit aminimum that shift from the heavy lanthanides to the light lanthanides as the atomic number of the halide increases. The variation in the heat capacity and entropy of the solid lanthanide trihalides can be described by a lattice contribution that linearly varies with the atomic number within each crystallographic class of compounds and an excess contribution that depends on the electronic configuration (crystal field) of the lanthanide ions. A distinct difference is observed between the heat capacity, and entropy of the hexagonal and monoclinic lanthanide trichlorides that clearly correlates with a distinct difference in molar volume between the two modifications. Both the effects are absent in the lanthanide trifluoride series. The properties of the liquid lanthanide trihalides depend strongly on the atomic number of the halide. The molecular parameters of the gaseous lanthanide trihalide molecules exhibit simple linear trends, with decreasing bond length and increasing vibrational frequencies, as the atomic number of the lanthanide ion increases.

The primary aim of this review is to collect together information on the solution thermochemistry of the trihalides of the lanthanides¹, yttrium, and scandium. There is a meager amount of published work relating to nonaqueous solvents, rather than more relating to aqueous solutions. One shall deal with both types of solvent, in both cases, concentrating on enthalpies of solution and on solubilities. The determination of many thermodynamic solution properties of these trihalides, especially enthalpies of solution, requires the use of anhydrous materials. These are by no means always readily available for this group of compounds. Therefore, the discussion of thermochemical results with a section on preparative methods are preceded, in which one deal summarily with many of the relevant papers published since Taylor's extensively referenced review, published in 1962. However, the radioactive nature of these compounds has prevented any calorimetric or solubility investigations so far, and they make only one fleeting appearance in this review