Structure lanthanide halides

Since the structural modification adopted by the trihalides changes systematically with ionic radius and since the relatively soft halide ions undergo compression rather easily, lanthanide halide structures are pressure sensitive. Most lanthanide, numerous actinide, and several mixed lanthanide/actinide systems have been examined under elevated pressures, the typical effect of which is transformation to a more densely packed structure. 

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). 

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...

The early lanthanide fluorides adopt the LaFs structure (Figure 3.3) based on a metal ion surrounded by a trigonal prism of fluorides with two additional capping fluorides, giving 11 coordination (9 + 2), whilst the later fluorides have the YF3 structure. This is based on tricapped trigonal prismatic 9 coordination, in which the prism is somewhat distorted. The structure adopted by UCI3 and several of the lanthanide halides is again a tricapped... 

The actinide trihalides display a similar pattern of structure to those of the lanthanide trihalides. However, comparing the coordination numbers for Ln + and An + ions with the same number of f electrons ( above one another in the Periodic Table ), it can be seen that the coordination number of the lanthanide halides decreases sooner than in the actinide series, a reflection of the fact that the larger actinide ions allow more halide ions to pack around them. Table 10.3 gives comparative coordination numbers for the trihalides of the lanthanides and actinides. 

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. 

Various lanthanide halides (ScCR, YCI3, LaCl3,Ndl3) react with K2[3-(C3H3SiMe3-l)2SiMe2] to form a/ 5a-bis(allyl) complexes. The lanthanum derivative has been structurally authenticated as a coordination polymer (14), in which allyl anions interleave alternating lanthanum and potassium ions the latter display K- -MeSi contacts of 2.79(3) and 2.96(4) kd... 

Culberson et al. (1987) used their INDO/1 method to investigate equilibrium structures and ionization potentials of selected lanthanide halides RX (n=2,3,4). The overall accuracy for bond lengths is usually better than 0.05 A, the values calculated for the... 

The formation and disruption of M-M bonds through chemical reactions can be performed reversibly with the hydride halides of the trivalent lanthanides whose structures are closely related to that of Gd2Q2C2. 

Additional areas of lanthanide halide chemistry that have been reviewed include the synthesis, phase studies, and structures of complex lanthanide halides - compounds formed between one or more group 1 cation and lanthanide element halides (Meyer 1982). Halides in combination with lanthanide elements in the II, III, and IV oxidation states were considered with the chemistry of the heavier halides being emphasized. More recently the reduced ternary lanthanide halides (Meyer 1983) and the reduced halides of the lanthanide elements were reviewed (Meyer 1988). The latter review considered lanthanides in which the formal oxidation state of the cation was 2 and included hydride halides, oxide halides, mixed-valence ternary halides, and reduced halide clusters. Corbett et al. (1987) discussed the structures and some bonding aspects of highly reduced lanthanide halides and compounds stabilized by a second-period element bound within each cluster, e.g., SC7CIJ2B, SC5CI5B, YjCljC. 

The synthesis of lanthanide and actinide compounds is the topic of a book edited by Meyer and Morss (1991). Topics that relate to halides, with the author(s) in brackets, include Lanthanide fluorides [B.G. Muller], Actinide fluorides [N.P. Freestone], Binary lanthanide(III) halides, RX3, X = Cl, Br, and I [G. Meyer], Complex lan-thanide(III) chlorides, bromides and iodides [G. Meyer], Conproportionation routes to reduced lanthanide halides [J.D. Corbett], and Action of alkali metals on lanthanide(III) halides an alternative to the conproportionation route to reduced lanthanide halides [G. Meyer and T. Schleid]. Meyer and Meyer (1992) reviewed lanthanide halides in which the valence of the lanthanide was considered unusual, with unusual being defined as compounds in which the localized valence of an atom differs from its oxidation number. A metallic halide such as Lalj [oxidation number (0)= -1-2 valence (V)= -l-3, since the 5d electron is delocalized in the conduction band] or a semiconducting halide such as PrjBtj (O = -t- 2.5 V = -I- 3) is unusual by this definition, but Tmlj (O = -1-2 V = +2) is not. In this review synthesis, properties, and calculated electronic structures are considered with emphasis on praseodymium halides and hydrogen intercalation into lanthanide dihalides and monohalides . 

Homogeneous Catalysis Lanthanide Halides Organometallic Chemistry Fundamental Properties Tetravalent Chemisiry Inoiganic Tetravalent Chemistry Organometallic The Divalent State in Solid Rare Earth Metal Halides The Electronic Structure of the Lanthanides. 

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