Lanthanides halides

Table 30.4 Properties of lanthanide halides colour, mprc and coordination ...

Systematic features in the structural chemistry of the uranium halides, oxyhalides and related transition metal and lanthanide halides, J. C. Taylor, Coord. Chem. Rev., 1976, 20,197-273 (205). 

Metathetical routes using bulky lithium guanidinates as starting materials have also been employed to synthesize bis(guanidinato) lanthanide halides as well as reactive alkyls and hydrides. Scheme 63 shows as a typical example the formation of the lutetium chloro precursor, which was isolated in 76% yield. ... 

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. 

Cerium, samarium, and other lanthanide halides promote addition of ketene silyl enol ethers to aldehydes.54 Imines react with ketene silyl acetals in the presence of Yb(03SCF3)3. Preferential addition to the imine occurs even in the presence of aldehyde... 

Interesting chemical and structural phenomena can occur when radioactive materials are stored in the solid state Extensive studies have been made of both the chemical and physical status of progeny species that result from the a or 3" decay of actinide ions in several different compounds The samples have been both initially pure actinide compounds—halides, oxides, etc.—and actinides incorporated into other non-radioactive host materials, for example lanthanide halides. In general, the oxidation state of the actinide progeny is controlled by the oxidation state of its parent (a result of heredity). The structure of the progeny compound seems to be controlled by its host (a result of environment). These conclusions are drawn from solid state absorption spectral studies, and where possible, from x-ray diffraction studies of multi-microgram sized samples. 

The crystal structures of the various lanthanide halides into which einsteinium trihalides were incorporated are summarized in Table IV. Both bromides and chlorides were prepared. The crystal... 

Table IV. Crystal Structures of Lanthanide Halides Used as Hosts for Einsteinium Halide Decay Studies...

This work was undertaken as a part of a study of divalent lanthanide halides in an effort to obtain more accurate thermal data on EuC12 and to determine if the close similarity of the high-temperature thermodynamic properties of divalent europium and alkaline earth compounds emphasized earlier (13-16) could be extended. 

In absence of more detailed information we suggest therefore that for practical reasons the enthalpies of dimerisation are treated constant in the different lanthanide halides series -233 kJ-mol 1 for the trifluorides, —213 kJ mol-1 for the trichlorides, —185 kJmol-1 for the tribromides, and —165 kJmol-1 for the triiodides. 

Vapor Phase Spectroscopy of Complex Lanthanide Halide-Aluminum Halide Molecular Species, W.T. Camall, J.P. Hessler, C.W. Williams, and H.R. Hoekstra, J. Mol. Struct. 46, 269-284 (1978). 

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],... 

As a rule, lanthanide bromides, and more especially the iodides, are more reactive because of their often higher solubility (Table 5), and also show enhanced thermodynamic lability (Scheme III). Moreover, reactivities different from those of the chloride analogues should be expected because of, for example, the softer Lewis basicity of the iodide anion and different solubility properties of the eliminated alkali salts. Table 5 gives an arbitrary sample of solubilities for lanthanide halides in various standard-laboratory donating solvents [97f]. 

Table 5. Solubility of lanthanide halides in nonaqueous coordination solvents (g/100 g solvent) [96f]...

As can be seen from Scheme III, lanthanide halides are suitable precursors for the synthesis of homoleptic derivatives such as silylamides [114], cyclopen-tadienyls [115] and aryloxides [116]. Such organometallies can be readily obtained in a pure form by sublimating them from the reaction mixture. They themselves are important precursors in organometallic transformations (vide infra). Heteroleptic complexes of the type CpxLn(halide)y (x + y = 2,3) are important synthetic precursors with respect to formation of various Ln-X bonds via simple metathesis reactions [2-29]. Fig. 4 indicates the lanthanide element bonds which are involved in these ubiquitous heteroleptic cyclopentadienyl systems. 

In particular the redox stability of lanthanide cations makes the route superior to, e.g., the usual metathesis reaction involving lanthanide halides. The advantages are evident ... 

Lanthanide halide complexes free of coordinated Lewis bases, such as alcohols, phosphates, amines, dimethylsulfoxide, or THF, suffer from low solubilities in non-coordinating solvents. Therefore, catalytic systems based on LnCl3 generally require preformation or aging in order to reach maximum activities. In contrast, lanthanide tetrahalogenoaluminate complexes are soluble in aromatic solvents. Such simple Ln/Al heterobimetallic halide... 

Because of the low solubilities of lanthanide halides in aliphatic and aromatic solvents catalytic activities of the initially reported binary systems LnCl3/R3 A1 were rather low. Pseudohalogen borohydride ligands [BH4] , sue-... 

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