in your element Brief encounters with dubnium Lars Öhrström tells of the fleeting, but still tangible, chemistry of dubnium, the heaviest of the group 5 elements.

ow you see me, now you don’t, this system for the separation of dubnium from might be a fitting exit line for a its group 4 neighbour rutherfordium4. Ndubnium atom slipping through our One has to be aware that a simple hands as it decays by sending out an alpha extrapolation from the properties of the particle. However, the chemist gets the last lighter group members (Nb and Ta in this laugh, as it is this very vanishing act that case) is not an adequate way of predicting the makes the one-atom-at-a-time chemistry properties of the 6d elements. As the nucleus experiments on element 105, a heavier gets heavier, relativistic effects come into play, analogue of tantalum, feasible. so the experiments need to be complemented As one of the most hotly disputed elements by advanced quantum chemistry. In this during the transfermium name dispute, case, such calculations suggest an increased when the Cold War cast a dark shadow on stability of the +5 oxidation state and an science, dubnium initially went under many electron configuration of [Rn]5f 146d37s2, names. It was synthesized by groups in the Legendary transuranium and transactinide concurrent with Db being the heaviest Soviet Union and the United States in the scientists Georgy Flerov (1913–1990), member of group 5 (ref. 1). late 1960s, starting in Dubna — the science Yuri Oganessian (1933–) and Glenn Seaborg This intricate interplay between theory city outside Moscow that was to eventually (1912–1999) on the Volga River bank in Dubna, and experiment is of interest and importance give its name to the element. There, scientists Russia. Photo reproduced with permission from not only to chemists, but also to nuclear smashed 243Am with 22Ne producing a the Joint Institute for Nuclear Research, Dubna. physicists trying to establish the identity 260 261 mixture of Db and Db (t1/2 = 1.5–1.8 s) of new elements. When these decay into after the loss of five and four neutrons, unknown isotopes, as for elements 113, respectively, and announced the discovery of about atoms per week. Thus with current 115 and 117 where many alpha-decay nielsbohrium. Around the same time, their technology, the chances of accumulating chains ended in 268Db, it is vital to establish principal rivals from Berkeley used 15N to hit any meaningful amount of dubnium is nil. the identity of these isotopes so that the a 249Cf target and formed 260Db, proposing the So, we cannot expect to prepare back-calculation will give the right atomic name hahnium1. The dispute was eventually dinuclear compounds characteristic of the number of the new element5. resolved2 and the name dubnium was adopted group 5 elements, such as the analogues So, in this borderland where chemistry

by the International Union of Pure and of the dimeric Ta2Cl10. Luckily, the gas- meets physics, nothing should be taken for Applied Chemistry (IUPAC) in 1997. phase chemistry of Ta2Cl10 is that of the granted and one does well to remember One often meets with the opinion that pentacoordinated mononuclear complex. As that even after a new superheavy element

the transfermium elements are of limited a result DbCl5, DbBr5, and also DbOCl3 — has obtained its place in the periodic use on account of their short lifetimes. On the latter of which is expected from the table, isotopes with higher stability may the contrary, take radiopharmaceuticals reaction with traces of oxygen in the carrier yet be discovered, as indeed was the case used in diagnostics for example. These must gas — have been inferred from one-atom-at- for dubnium. ❐ decay relatively quickly to provide an image a-time experiments. for the physician in a timely manner. For These techniques are becoming LARS ÖHRSTRÖM, author of The Last this purpose, the 99mTc isotope is routinely increasingly sophisticated such that Alchemist in Paris and Other Curious Tales employed; it has a half-life of 6 hours, which is investigation of dubnium’s aqueous From Chemistry, is in the Department of 3 − approximately four times shorter than that of chemistry is now possible . Both [DbOCl4] Chemistry and Chemical Engineering, 268 − Db — the longest-lived Db isotope known. and [Db(OH)2Cl4] , and even complexes Chalmers University of Technology, The real problem for dubnium use is its with the chelating α-hydroxyisobutyric SE-412 96 Gothenburg, Sweden. slow production rate. One atom of the most acid, have been suggested, based on where e-mail: [email protected]; 262 studied dubnium isotope, Db (t1/2 = 34 s), in the chain of chromatography, extraction Twitter: @Larsohrstrom can be prepared in less than 1 minute, and surface detection a characteristic Db whereas for the 268Db isotope — the final alpha decay is observed. Crucial for these References 1. Schädel, M. & Shaughnessy, D. Chemistry of the Superheavy alpha-decay product from the synthesis of experiments is comparison with lighter Elements 2nd edn (Springer, 2014). elements 113, 115 and 117 — we are talking analogues under the same circumstances. 2. Garcia, M. A. Nat. Chem. 2, 66 (2010). For example, radioactive isotopes of Hf 3. Nagame, Y., Kratz, J. V. & Schädel, M. Nucl. Phys. A 944, 614–639 (2015). and Ta, produced by neutron activation, 4. Schumann, D. & Dressler, R. Radiochim. Acta 104, 41–49 (2016). were recently used to develop an extraction 5. Dmitriev, S. N. et al. Mendeleev Commun. 15, 1–4 (2005). No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn 113 Fl 115 Lv 117 118 119 120 121 122 986 NATURE CHEMISTRY | VOL 8 | OCTOBER 2016 | www.nature.com/naturechemistry ©2016 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.