Tris compounds lanthanide

Tris(cyclopentadienyl) lanthanide complexes can be used as precursors for the synthesis of lanthanide derivatives via a protonolysis reaction (Figure 8.7) [15,16]. The biggest advantage of this method is that it excludes the formation of lanthanide -ate compounds [17],... 

All the lanthanides have similar outer electronic configuration and display mainly + 3 oxidation state in their compounds, therefore, lanthanides have exceedingly similar chemical properties. Their similarity is much closer than that of ordinary transition elements because lanthanides differ mainly in the number of 4/electrons which are buried deep in the atoms of lanthanides and thus don t influence their properties. Moreover, due to lanthanide contraction there is a very small difference in the size of all the fifteen tri valent lanthanide ions. Thus, for all practical purposes, the size of these ions is almost identical which results in similar chemical properties of these elements. 

Most of the remainder of this section will be organized around the methods of preparation of Z —CO— complexes containing main group III and lanthanide acceptors. These preparative methods are simple adduct formation, protolysis, and redox processes. Simple adduct formation is by far the most common mode of forming these compounds. One example has just been given in which aluminum alkyls were employed. Also to be noted (Table IV) are several complexes formed between transition metal carbonyls and tris(cyclopentadiene)lanthanide acceptors (9,53,54). 

Although the use of shift reagents is well established, the analysis of the factors responsible for the observed shifts continues. The discussion concerns the relative importance of contact (spin delocalized) and pseudocontact (anisotropic) shifts. Substituted adamantanes and bicyclo[2,2,l]heptanes are suitable rigid systems with which to analyse such shifts. With mono-functional subtrates, shifts with most tris(dipivalomethanato)lanthanides were best explained by formation of 1 1 complexes in which the effect of the dominant pseudocontact shift was modified by a contact shift. This contact shift is only important very close to the lanthanide as the magnitude of the shift decreases very greatly with distance. With bifunctional compounds the analysis is more complex. 

Figure 3. The lattice parameter for the family of rock-salt structure actinide-antimonide compounds is shown where the line is for the corresponding lanthanide compounds. The metallic radii for the light actinide elements are plotted. The smooth line simply connects Ac to the heavy actinides. In both cases the smooth line represents the ideal tri-valent behavior.

Reactions of UCI4 with [Li RC(NCy)2 (THF)]2 (R = Me, Bu ) in THF gave the tris(amidinate) compounds [RC(NCy)2]3UCl that could be reduced with lithium powder in THF to the dark-green homoleptic uranium(lll) complexes [RC(NCy)2]3U. Comparison of the crystal structure of [MeC(NCy)2]3U with those of the lanthanide analog showed that the average U-N distance is shorter than expected from a purely ionic bonding model. ... 

A closely related method does not require conversion of enantiomers to diastereomers but relies on the fact that (in principle, at least) enantiomers have different NMR spectra in a chiral solvent, or when mixed with a chiral molecule (in which case transient diastereomeric species may form). In such cases, the peaks may be separated enough to permit the proportions of enantiomers to be determined from their intensities. Another variation, which gives better results in many cases, is to use an achiral solvent but with the addition of a chiral lanthanide shift reagent such as tris[3-trifiuoroacetyl-Lanthanide shift reagents have the property of spreading NMR peaks of compounds with which they can form coordination compounds, for examples, alcohols, carbonyl compounds, amines, and so on. Chiral lanthanide shift reagents shift the peaks of the two enantiomers of many such compounds to different extents. 

Unlike the di-f dihalides, such compounds differ little in energy from both the equivalent quantity of metal and trihalide, and from other combinations with a similar distribution of metal-metal and metal-halide bonding. So the reduced halide chemistry of the five elements shows considerable variety, and thermodynamics is ill-equipped to account for it. All four elements form di-iodides with strong metal-metal interaction, Prl2 occurring in five different crystalline forms. Lanthanum yields Lai, and for La, Ce and Pr there are hahdes M2X5 where X=Br or I. The rich variety of the chemistry of these tri-f compounds is greatly increased by the incorporahon of other elements that occupy interstitial positions in the lanthanide metal clusters [3 b, 21, 22]. 

The synthesis of lanthanide chemical shift reagents has been the objective of many groups owing to their effect on NMR spectra simplification. A drawback of the commonly used reagents is their sensitivity to water or acids. Tris(tetraphenylimido diphosphinatojpraseodymium [Pr(tpip)3] has been developed as a CSR for the analysis of carboxylic acids.17 Furthermore, it has been found that dinuclear dicarboxylate complexes can be obtained through reactions with ammonium or potassium salts of carboxylic acids, and these compounds can be used to determine the enantiomer composition of carboxylic acids.18... 

---