Magically Magnetic Gadolinium Pekka Pyykkö Discusses the History and Characteristics of Gadolinium
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in your element Magically magnetic gadolinium Pekka Pyykkö discusses the history and characteristics of gadolinium. he lanthanides run from lanthanum Gd3+ is somewhat toxic, the gadolinium ion is to lutetium across the periodic table, surrounded by chelating ligands that prevent Tand together with the chemically it from entering tissues. New ligands are similar yttrium and scandium they form under development to improve safety. a family dubbed the rare-earth elements. Both gadolinium and some of its alloys An unspecified mixture of their oxides or salts play a prominent role in magnetic was isolated in 17941–3 by Johan Gadolin cooling. In this refrigeration process, a (1760–1852) from a mineral that had been magnetic substance becomes hotter when discovered in Ytterby, near Stockholm, placed under certain external magnetic field, Sweden by Carl Axel Arrhenius, and owing to the orientation of its magnetic described in 1788 by Geijer4. Gadolin dipoles. Inversely when the field is removed, cautiously stated that this oxide, or ‘earth’, and the substance thermally isolated, it cools could contain a new element. This would be down. By varying the magnetic field, and a pity he said1–3, because the elements were the sample’s insulation, one shuffles entropy already “becoming far too numerous” — an between the material’s electronic spin system interesting twist for an element that would and other degrees of freedom. be named after him. Gadolin’s analysis was The conspicuous luminescence colours confirmed in 1797 by A. G. Ekeberg5, and the of certain other lanthanides are used in original mineral was soon named gadolinite. fluorescent lamps and in displays — both SCOTT CAMAZINE / ALAMY CAMAZINE SCOTT The oxide of gadolinium (symbol Gd) the old-style picture tubes, and the current was discovered by repeated recrystallization trivalent Gd3+ ion can organize its seven 4f flat screens. The compounds of element 64 by Marignac6, who also determined its electrons in a half-filled shell with all spins itself are colourless, but they can be used atomic weight, but it was Boisbaudran parallel — a magic number, as it were. This to absorb UV radiation and to transfer (with Marignac’s approval) who suggested gives Gd(iii) the largest possible total spin its energy to other lanthanides that have the name in 18807. Although it is not known S = 7/2, and a correspondingly very large emissions in the desired optical range. whether he was thinking of the mineral spin magnetic moment. This characteristic Moreover, the 155Gd and 157Gd nuclei have or the man, or both, gadolinium remains can be used to improve permanent magnets. unusually large neutron absorption cross the only element with a name derived The 4f shell of lanthanides has electron sections, which can be used in nuclear from Hebrew. Its root ‘gadol’ (pictured), binding energies in the valence range, technology for reactor control rods. meaning ‘great’, was chosen by Gadolin’s making it possible to chemically vary the 4f Gadolin may have wished for fewer grandfather as his surname and comes from occupation, but the compact 4f radial size elements to exist, but gadolinium offers a a translation of Maunula, the name of the is typical of the outermost core electrons rich history spanning over two centuries, Finnish farm he lived on. and prevents most 4f electrons from directly intriguing characteristics, and a variety of participating in bond formation. practical applications. ❐ Despite their name, the rare earths are not particularly rare; €111 per 10 g of metallic PEKKA PYYKKÖ is professor emeritus in gadolinium (99.9% purity) is the going the Department of Chemistry, University of rate, though in metallurgy a much cheaper, Helsinki, POB 55, 00014 Helsinki, Finland. The chemical behaviour of most unseparated mischmetal is normally used. His former position as ‘the parallel chair of lanthanides is fairly similar, which explains An important current use is in medicine, chemistry’ was split from Gadolin’s chair of why, in all, it took more than a century to as a ‘contrast agent’ in magnetic resonance chemistry in 1908. split them into the individual elements. imaging (MRI). The MRI signal comes from e-mail: [email protected] Despite their chemical similarities, their certain nuclear spins, such as the ubiquitous optical and magnetic properties are distinct. protons. That nuclear spin system, however, References 1. Gadolin, J. Kungl. Svenska Vetenskapsak. Handl. 15, 137–155 (1794). The magnetic properties of gadolinium in is heated by the radiofrequency field used for 2. Gadolin, J. Crells Ann. 313–329 (1796). particular are unique, and underscore many the magnetic resonance. This heating typically 3. Pyykkö, P. & Orama, O. in Episodes from the History of the Rare of its applications. Element 64 is located half- weakens the MRI signal. The large electronic Earth Elements (ed. Evans, C. H.) 1–12 (Kluwer, 1996). way through the lanthanide 4f series and the magnetic moment of Gd(iii) helps to couple 4. Geijer, B. R. Crells Ann. 229–230 (1788). 5. Ekeberg, A. G. Kungl. Svenska Vetenskapsak. Handl. the nuclear spin system to the ‘lattice’ and to 18, 156–164 (1797). keep it cool. This is called nuclear spin–lattice 6. de Marignac J.‑C. G. Arch. Sci. (Genève) 3, 413–418 (1880). relaxation. To avoid health hazards, because 7. Lecoq de Boisbaudran, P.-E. C. R. Acad. Sci. 102, 902 (1886). Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl 680 NATURE CHEMISTRY | VOL 7 | AUGUST 2015 | www.nature.com/naturechemistry © 2015 Macmillan Publishers Limited. All rights reserved.