Lanthanoids oxides

Rare earth oxides and Y203 are more stable than the other additives [267] no change in concentration of yttria or lanthanoide oxides has been found experimentally, even during long sintering times [232, 268, 272, 274]. 

Yoshida, H., Yamamoto, T., Ikuhara, Y., and Sakuma, T., A change in the chemical bonding strength and high-temperature creep resistance in A1203 with lanthanoid oxide doping Phil. Mag, 2002, A82, 511-25. 

Lanthanoid oxide Freezing point (°C) Boiling point (°C)... 

Thus far, we have focused exclusively upon the block metals. For some, the term transition elements defines just these J-block species for others, it includes the rare earth or lanthanoid elements, sometimes called the inner transition elements . In this chapter, we compare the elements with respect to their valence shells. In doing so, we shall underscore concepts which we have already detailed as well as identifying both differences and similarities between certain aspects of main and inner transition-metal chemistry. We make no attempt to review lanthanoid chemistry at large. Instead our point of departure is the most characteristic feature of lanthanoid chemistry the +3 oxidation state. 

Both phenomena attest to the covalency of the chemical bonding in these species. Incidentally, they also highlight the different characters and implications of the spectrochemical and nephelauxetic series. Within either lanthanoid- or (higher oxidation state) J-block species, the ligand orbitals overlap with the metal s functions... 

Numerous compounds adopt the PbFCl structure. These include, apart from fluoride chlorides, oxide halides MOX (M = Bi, lanthanoids, actinoids X = Cl, Br, I), hydride halides like CaHCl and many compounds with metallic properties like ZrSiS or NbSiAs. 

However, the two methods of choice for the oxidations of a, (B-unsaturated ketones are based on lanthanoid-BINOL complexes or a biomimetic process based on the use of polyamino acids as catalysts for the oxidation 1"1. 

In the first of these techniques the lanthanoid complex (33) (5-8 mol%) is used as the organometallic activator in cumene hydroperoxide or tert-butyl hydrogen peroxide-mediated oxidation of chalcone (epoxide yield 99 % 99 % ee) or the ketone (34) (Scheme 20)[1001. 

Figure 18.6 depicts the E-pH diagram for Pu at 10 M. Again, there are notable resemblances to both U and Np, but evidence of a trend to lanthanoid resemblance is present. These include further stabilization of the An ion with an oxide PU2O3 making its appearance, and a decreasing stability of the Pu+ cation. 

The members of the actinoids have a somewhat greater tendency to form complexes than those of the lanthanoids. They also show a wider variety of complexes due to their more numerous oxidation states. The cations of the actinoids display coordination numbers which are often greater than 6. Although not many data are available, M02+ and M02" " ions attach 5 or 6 HOH molecules giving the central atom a coordination number of 7 or 8, and the and ions attach 9 or 10 HOH molecules. The coordination numbers with ligands other than HOH are often of these magnitudes, but sometimes may be somewhat smaller. 

Asymmetric cyanosilylation of ketones and aldehydes is important because the cyanohydrin product can be easily converted into optically active aminoalcohols by reduction. Moberg, Haswell and coworkers reported on a microflow version of the catalytic cyanosilylation of aldehydes using Pybox [5]/lanthanoid triflates as the catalyst for chiral induction. A T-shaped borosilicate microreactor with channel dimensions of 100 pm X 50 pm was used in this study [6]. Electroosmotic flow (EOF) was employed to pump an acetonitrile solution of phenyl-Pybox, LnCl3 and benzal-dehyde (reservoir A) and an acetonitrile solution of TMSCN (reservoir B). LuC13-catalyzed microflow reactions gave similar enantioselectivity to that observed in analogous batch reactions. However, lower enantioselectivity was observed for the YbCl3-catalyzed microflow reactions than that observed for the batch reaction (Scheme 4.5). It is possible that the oxophilic Yb binds to the silicon oxide surface of the channels. 

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