Lanthanide trichlorides

The major synthetic route leading to homoleptic lanthanide tris(amidinates) and guanidinates, however, is the metathetical reaction between anhydrous lanthanide trichlorides and preformed lithium amidinates or guanidinates, respectively, in a molar ratio of 1 3. This is outlined in Scheme 69, showing a samarium(lll) guanidinate as a typical example. ... 

The chemistry of lanthanide nitridoborates was developed by the more flexible and more efficient solid-state metathesis route by using nitridoborate salts and a lanthanide trichloride, at reaction temperatures as low as 600 °C. This type of reaction has been previously established and studied in some detail for reactions, such as the synthesis of lanthanide nitrides (LnN). Following this concept, lanthanum nitridoborates are obtained from reactions of lanthanum trichloride and lithium nitridoborate (or calcium nitridoborate), performed in a salt-balanced manner with respect to the formation of the co-produced liCl ... 

Figure 7.10 Thermodynamic data (b)-(d) needed in analysis of the enthalpy of formation of the binary lanthanide metal compounds given in (a), (b) Sum of first, second and third ionization enthalpies of lanthanide metals (c) atomization enthalpy of lanthanide metals (d) derived lattice enthalpy of lanthanide trichlorides.

Lanthanide trichlorides can be converted into the corresponding trifluorides by treatment with fluorine (20), or aluminum fluoride (melt) (22). 

The range of enthalpies of solution of anhydrous lanthanide trichlorides in water may be compared with those for other anhydrous chlorides. They are considerably more negative (Table IV) than those for the alkaline-earth metals [MgCl2, -155 kJ mol-1, to BaCl2, -13 kJ mol-1 (196)] and for the alkali metals [LiCl, — 37 kJ mol-1, to CsCl, +18 kJ mol-1 (197)]. 

Fig. 2. The variation of the enthalpies of solution of lanthanide trichlorides and, for comparison, indium trichloride (dashed line), with acid concentration in aqueous hydrochloric acid, at 25°C (182b).

Enthalpies of Solution for Lanthanide Trichloride Hexahydrates in Aqueous Magnesium Chloride Solutions at 25°C ... 

The results in the three preceding subsections conform fairly well to a consistent pattern. However, there are gaps and inconsistencies that require further thermochemical, and in some cases chemical, study. The series of solution enthalpies for the lanthanide trichlorides is satisfactory, but disagreements over the value for the enthalpy of solution of yttrium trichloride in water need resolving, and a modern value for scandium trichloride (at 25°C) would be welcome. The complete absence of enthalpies of solution of tribromides of the lanthanide elements and yttrium is regrettable, as is the lack of a value for scandium triiodide. 

Enthalpies of Solution of Lanthanide Trichlorides in Nonaqueous Solvents... 

Early studies of the temperature variation of the solubilities of lanthanide trichlorides have already been mentioned. More recently, comprehensive data from —15° to + 50°C have been presented (259, 260) a representative selection is given in Table XVIII. Here and elsewhere, the dependence of solubility on temperature does not conform... 

All the solubilities so far mentioned have been presented in weight or concentration units. These may be converted via standard thermodynamic formulas into Gibbs free energies of solution. One group of authors, however, has preferred to present their data in this form, for YC13, LaClj, and six other lanthanide trichlorides (184). 

For qualitative information on relative solubilities of lanthanide trichlorides in ra-butanol and in water, see Asselin et al. (286). 

Solubilities of Lanthanide Trichlorides in Hexamethylphosphoramide (HMPA), Tributyl Phosphate (TBP), and Hexachlorobutadiene (HCB)... 

Strictly, the solubilities of salt hydrates in nonaqueous solvents, and of lanthanide trichlorides in 97% ethanol, mentioned in Section V,B,2,a,... 

By controlling the stoichiometry of the reaction between lanthanide trichlorides and sodium cyclopentadienide it is possible to replace the chloride ions stepwise. Equihbria are rapidly established, so the addition of Ln(C5H5)3 to one or two equivalents of LnCls will produce M(C5H5)2C1 and M(C5H5)Cl2, respectively. The dichlorides are known only for the lanthanides from samarium to lutetium and are obtained from THF solutions as tris-THF adducts. 

The lanthanide trichlorides have three different crystal structures. The trichlorides of the lighter lanthanides (La—Gd) have the UCI3 type (P63/OT) structure, while the trichlorides of the lanthanides heavier than terbium have the YCI3 type (C2/ot) structure 67, 174, 175). Terbium trichloride and a second form of DyCls have a third structure (PuBr3 type, Cmcni) 176). 

Table 15. Comparison of the cell parameters for the lanthanide trichlorides of three structure type...

The lanthanide trichlorides of La to Eu have a hexagonal crystal structure (space group Pf>- /m) at room temperature. For GdCb the hexagonal as well as the orthorhombic structures have been reported at room temperature. There is some uncertainty which of these is the... 

Fig. 10. The variation of Sexp (o, hexagonal O, monoclinic) and Slat ( ) in the lanthanide trichloride series at 298.15 K the broken line shows the lattice contribution (see text).

Table 5 The crystal field energy levels for the lanthanide trichlorides (Morrison and Leavitt, 1982 Carnall, 1982) ...

Carnall, 1982). The experimental standard entropy values thus obtained for the monoclinic lanthanide trichlorides are listed in table 4. 

High temperature heat capacity functions for the solid lanthanide trichlorides... 

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