Rhodium Roles Lars Öhrström Relates the Various Roles Played by Rhodium in Our Daily Lives, Ranging from Car Components to Drugs

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in your element Rhodium roles Lars Öhrström relates the various roles played by rhodium in our daily lives, ranging from car components to drugs.

nce the thin electroplated rhodium information to be extracted by 2D NMR coating that makes new pieces spectroscopy techniques. Oof jewellery extra bright and Several artificial radioactive isotopes are shiny wears off, most of us are likely to also known, including meta-stable nuclear come across rhodium mainly as a crucial isomers. One of those, 103mRh — produced component in catalytic converters for by decay from 103Ru — has been investigated cars. In these devices, metallic particles of as a cancer therapy agent2. In light of its element 45 are embedded in the porous short half-life (59 min) and the slow ligand ceramic structure of the catalyst, and its exchange rates for Rh(iii) complexes, specific role is to help break down nitrogen however, the synthesis and use of 103mRh

oxides to innocuous O2 and N2. compounds require careful planning. 4+ In 1988, a year before catalytic converters A variety of complexes based on the Rh2 became compulsory for new cars in Sweden, core have also shown promise as anticancer I encountered this otherwise silver-white compounds. Recently, in an exciting noble metal in a very different form: development, a dirhodium(ii) compound 50 grams of a purple powder, worth half a featuring a ligand endowed with an organic year’s pay for a graduate student. This price 3, ACS REF. FROM REPRODUCED fluorophore has been shown to be taken up reflected both the fact that element 45 is for applications, and the reason behind by cancer cells in a different manner than the typically the most expensive of the platinum William S. Knowles and Ryoji Noyori free ligand3 (the dirhodium compound shows group metals (PGMs), as well as the difficulty sharing half of the 2001 Nobel Prize a scattered distribution in the cytoplasm, of oxidizing it into a molecular compound. in Chemistry. pictured). This points to new possibilities Rhodium’s price fluctuates according to A notable feature of coordination for these kinds of M–M bonded compounds external factors, increasing for example if compounds containing rhodium in and may encourage big pharmaceutical car sales go up or environmental legislation oxidation state +3 is their slow release companies to step outside their organic gets tougher. Moreover, as its production is and recapture of ligands. For example, for comfort zone, just as they did 40 years ago dominated by a few countries, notably South rhodium(iii) chloride dissolved in water, with the development of cisplatin-type drugs Africa, mining strikes or local politics may ten different species may form and the based on rhodium’s diagonal neighbour in also significantly affect the world market. interchange in the octahedral coordination the periodic table, platinum. The purple powder was rhodium(iii) environment around the rhodium centre — Although it may be in the shadow of + chloride, the compound that incidentally say between cis-[RhCl2(H2O)4] and its better-known PGM cousins, palladium + also gave the element its name, from rhodon trans-[RhCl2(H2O)4] — is very slow. So slow and platinum, on the road of chemical (Greek for rose). I used it over the next in fact that it may take a year or more for such applications, rhodium is gaining ground and five years to make various coordination a solution to reach chemical equilibrium. shows no signs of slowing down. ❐ compounds, including catalysts, a main use This is in sharp contrast to, for example, the + for this metal in laboratories — new organic Fe(iii) analogue cis-[FeCl2(H2O)4] for which LARS ÖHRSTRÖM author of The Last reactions catalysed by rhodium complexes the corresponding cis–trans isomerization Alchemist in Paris & Other Curious Tales are reported every year. takes milliseconds. From Chemistry is in the Department of Such rhodium catalysts are also used There is a peculiar way to observe this: Chemistry and Chemical Engineering, industrially, notably for making menthol rhodium NMR spectroscopy1. Rhodium Chalmers University of Technology, (found in many consumer products is one of the few elements that comes with SE-412 96 Gothenburg, Sweden. such as lip balm, cough remedies, only one isotope in nature, 103Rh. This e-mail: [email protected] toothpaste and aftershave), as well as isotope has the same nuclear spin (½) as Twitter: @Larsohrstrom l-DOPA (l-3,4-dihydroxyphenylalanine) that of protons, and is thus excellent for used to treat Parkinson’s disease. A NMR studies. Its poor sensitivity means References 1. Carr, C., Glaser, J. & Sandström, M. Inorg. Chim. Acta noteworthy aspect of these catalysts is that impractical amount of sample and 131, 153–156 (1987). their enantioselectivity, which is crucial time are often required to get a signal, 2. Nilsson, J., Bernhardt, P., Skarnemark, G., Maecke, H. which has hampered widespread use, yet it & Forssell-Aronsson, E. Eur. J. Nucl. Med. Mol. Imaging 33, S149 (2006). is not without proponents as Rh-coupling 3. Pena, B., Barhoumi, R., Burghardt, R. C., Turro, C. with other nuclei can allow valuable & Dunbar, K. R. J. Am. Chem. Soc. 136, 7861–7864 (2014). Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm 90 NATURE CHEMISTRY | VOL 8 | JANUARY 2016 | www.nature.com/naturechemistry