Scandium, Yttrium and the Lanthanides: Applications

Abstract

Abstract New applications are increasingly found for scandium, yttrium, and the lanthanides and their compounds. Among reagents in synthetic organic chemistry, LaNi 5 is a versatile hydrogenation catalyst. SmI 2 is an important one‐electron reducing agent, and lanthanide triflates, Ln(CF 3 OSO 3 ) 3 (Ln = Sc, Y, or lanthanide), are recyclable Lewis acid catalysts, which operate in aqueous conditions. Organocerium compounds are valuable, mild alkylating agents, while using cerium chloride in combination with NaBH 4 and LiAlH 4 permits a range of reductions to be carried out. (NH 4 ) 2 [Ce(NO 3 ) 6 ] is an established oxidant for which new applications are being found. The alloys SmCo 5 and Sm 2 Co 17 have been used to produce magnetic materials that are very powerful for their size, though partly superseded by cheaper Nd 2 Fe 14 B material, while strongly paramagnetic salts of Dy 3+ or Gd 3+ permit attainment of extremely low temperatures through adiabatic demagnetization. The mixed metal oxide YBa 2 Cu 3 O 7− x was the first material to superconduct above 77 K, revolutionizing understanding; new materials are being developed, most recently fluoride‐doped oxypnictides LaFeAsO. In addition to gadolinium complexes as MRI contrast agents, other lanthanide compounds find medicinal application, including cerium compounds in wound and burn treatment. In terms of quantity, the most important application of lanthanide compounds is lanthanide‐exchanged zeolites as catalysts in the petrochemical industry, notably in cracking, but cerium oxide is an important component of catalytic converters in automobile exhausts. The ability of LaNi 5 to absorb hydrogen reversibly has been vital to nickel–metal hydride (NiMH) batteries, while yttrium aluminum garnet (Y 3 Al 5 O 12 ) is widely used as a host material in lasers and phosphors. Yttria‐stabilized zirconia (YSZ) is a ceramic material used as the electrolyte material in solid oxide fuel cells (SOFCs) and in sensors in car exhaust systems.