Lanthanide halides solvates

The existence of solvates of lanthanide halides may be taken as an indication of favorable interaction between the halides and solvent in question. Evidence of this type may suggest solvents which could prove useful or interesting for calorimetric or solubility studies. However, the existence of stable solvates is no guarantee of marked solubility for the halide in the solvent in question. One need look no further than lanthanide fluorides and water for cautionary examples, for despite their very low solubility in water these fluorides form a series of stable hemihydrates, LnF3-V H20. 

The lanthanide halides form a wide range of solvates with a variety of organic solvents for a given halide and solvent, a range of stoichiometries may be exhibited. Some idea of the range of solvents involved is given by Table II (108,112,142-166), which gives references to numerous solvates. The collection of citations in this table is illustrative, not comprehensive. 

Ln-Halides. The complexation/solvation criteria is just one reason why lanthanide halides are the most common precursors in organolanthanide chemistry. In this evaluation, lanthanide iodides are often preferred to bromides and chlorides, however the former are more difficult to synthesize and are much more expensive [96f. Waterfree, solid Ln-halides are ionic substances with high melting points which immediately absorb water when exposed to air, forming hydrates (I > Br > Cl ). Therefore, they have to be handled under an inert gas atmosphere. The main use of the halides is for the production of pure metals [96]. Some methods of preparing Ln(III)-chlorides are summarized in Scheme IV [96],... 

Lanthanide halides, nitrates and triflates are not only common reagents in organic synthesis (Fig. 1) but also represent, in dehydrated form, key precursor compounds for the more reactive organometallics (Scheme 2). As a rule, in compounds of strong monobasic acids or even superacids, cation solvation competes with anion complexation, which is revealed by fully or partially separated anions and solvated cations in their solid state structures. The tendency to form outer sphere complexation in coordinating solvents [47] is used as a criterion of the reactivity of inorganic salt precursors in organometallic transformations. 

Stable monomeric benzyls can be made in solvated form, simply by the reaction of lanthanide halides (either in anhydrous form or the THE solvates) with an alkali metal benzyl. Best results are obtained with the iodide. ... 

With the more electropositive metals such as the lanthanides,31 the dissolution of their chlorides into alcohols results only in the formation of solvates such as LaCl3 SPr OH.31 For most of the early J-block elements, only partial replacement of halide ligands occurs on alcoholysis (equations 5 and... 

Therefore, for small-scale laboratory synthesis it seemed promising to develop alternative methods which avoid the inconvenient high temperature and yield the reactive, solvated form. For example, the THF adducts can readily be synthesized by treating lanthanide powders with CHC13 under ultrasonic conditions, as described by Eq. (1) [100], Redox transmetallation between lanthanide metals and mercury(II) halides are carried out in refluxing THF (Eq. 2) [108]. Recently ammonia was employed as an alternative solvent, e.g. in the synthesis... 

---