Gadolinium

MELTING POINT: 1,311°C
BOILING POINT: 3,233.0 °C
DENSITY: 7.89 g cm⁻³
MOST COMMON ION: Gd³⁺

Gadolinium is a chemical element. Its ground state electronic configuration is [Xe]4f⁷5d6s². Monazite and bastnasite are the principal gadolinium ores, in which gadolinium occurs together with other members of the rare earth elements or the lanthanides. It can be separated from the other rare earths by ion exchange or solvent extraction techniques. Gadolinia, the oxide of gadolinium, was first extracted from the mineral gadolinite by Jean-Charles-Galissard de Marignac in 1880. (Gadolinite is named after the Finnish chemist Johan Gadolin.) In 1886 Paul-Émile Lecoq de Boisbaudran independently separated the oxide of gadolinium from Carl Mosander's "yttria" (impure yttrium oxide).

Gadolinium is a silver-white, malleable, and ductile metal. Gadolinium metal is ferromagnetic just below room temperature. Gadolinium chemistry is dominated by the trivalent gadolinium(III) ion, Gd³⁺. This ion forms ionic bonds with ligands containing an oxygen or nitrogen donor atom. The ground state electronic configuration of Gd³⁺ is [Xe]4f⁷. In spectroscopic

analysis there are no absorption bands in the visible region of the electromagnetic spectrum, and gadolinium compounds are colorless.

Gadolinium(III) chelates are used as contrast reagents in magnetic resonance imaging (MRI). Due to the high magnetic moment of the paramagnetic Gd³⁺ ion (with its seven unpaired electrons), the relaxation time of water molecules in the proximity of Gd³⁺ ions is greatly reduced and signal intensity is thereby enhanced. MRI is a medical diagnostic technique that depends on the proton nuclear magnetic resonance (NMR) signal from water in its creation of a proton density map. Gadolinium is a major component of x-ray phosphors, such as Gd₂O₂S:Tb³⁺, within which it dilutes the active emitter (Tb³⁺) to avoid concentration quenching. Because gadolinium effectively absorbs neutrons, this element has found some use in control rods for nuclear reactors.

SEE ALSO CERIUM; DYSPROSIUM; ERBIUM; EUROPIUM; GADOLIN, JOHAN; HOLMIUM; LANTHANIDES; LANTHANUM; LUTETIUM; NEODYMIUM; PRASEODYMIUM; PROMETHIUM; SAMARIUM; TERBIUM; YTTERBIUM.

Koen Binnemans

Bibliography

Bünzli, Jean-Claude G., and Choppin, Gregory R., eds. (1989). Lanthanide Probes in Life, Chemical and Earth Sciences. New York: Elsevier.

Cotton, Simon (1991). Lanthanides and Actinides. New York: Oxford University Press.

Kaltsoyannis, Nikolas, and Scott, Peter (1999). The f Elements. New York: Oxford University Press.