in your element V for vanadium Andrea Taroni shares his experience with vanadium — a colourful element with a rich chemistry (and physics!) that is emblematic of all transition metals.

uite why I chose to study chemistry changing the colour of the complex. The at university is a mystery, even to me. rest of my undergraduate practical required QI mostly got the general principles, but me to determine the oxidation states of it was as if its details — oxidation, reduction; vanadium upon reducing my solution cis, trans; R, S — or rather which way around with various agents. I vividly recall the those details went, had been designed to sudden changes in colour that came with consistently make me feel like I couldn’t tell each oxidation state switch, and I like to my right hand from my left. It is fair to say I think this gave me a greater appreciation wasn’t a natural at the subject. for the inspired decision to name the One of the first elements I remember element after Vanadis, the Norse goddess encountering in the lab — by attempting more commonly known as Freyja, whose

to work with it, as opposed to simply attributes include beauty. PHOTOGRAPHY/ ANDREW LAMBERT LIBRARY PHOTO SCIENCE acknowledging its existence — is vanadium. In fact, many transition metal My inorganic chemistry lab practical compounds have spectacular colours (earning Albert Fert and Peter Grünberg involved the synthesis and analysis of the (pictured), making them ideal for pigments. the 2007 Nobel Prize in Physics in the

five-coordinate complex VO(acac)2 (where Their rich redox chemistry is also key to process). All of these properties arise from acac is acetylacetone) and I soon got a their application in biological systems the different choreographies that the electrons vivid demonstration of just how colourful (think manganese in photosynthesis). of these systems can be made to arrange chemistry could be. Redox reactions are also, of course, central in — a seemingly limitless set that material in electrochemistry, and vanadium flow scientists are becoming ever more adept The fascinating chemical batteries have been devised that store at manipulating. energy in liquid electrolytes instead of Naturally, element 23 also displays its own and physical properties of electrodes. These work using 4+V /V5+ set of intriguing, yet useful, properties in the vanadium all stem from the rich and V2+/V3+ aqueous sulfate solutions solid state. Vanadium dioxide, for instance, as cathode- and anode-side electrolytes is the textbook example of an oxide that behaviour of its d electrons. separated by an ion-exchange membrane. undergoes a transition from a conducting Transition metals give rise to exciting metal to a non-conducting insulator as it is Like most transition metals, vanadium physics too. When bound together in cooled below room temperature. In fact, this exists in a wide range of oxidation states — the solid state, forming what condensed- metal–insulator transition can be controlled most commonly from +2 to +5, but all states matter physicists call a strongly correlated using a range of external parameters such as from –1 to +5 exist and even the rare –3 is electron system, remarkable properties pressure, doping and applied electric fields, 3– known, in V(CO)5 — and can therefore become manifest. and as it is accompanied by huge changes in take part in all manner of electron-transfer The conductivity and ferromagnetic nature resistivity and opacity, VO2 is widely used in processes. In a coordination complex, these of iron — an element that has been exploited coatings and sensors. can occur in the form of charge-transfer to the extent that an entire epoch of human Like the rest of the transition metal transitions from the metal ion to the ligand history is named after it — are two examples elements, the fascinating chemical and (or vice versa). As the excitation energies of that have been used since antiquity; for physical properties of vanadium all stem these transitions occur in the visible region example in magnetite-based compass needles. from the rich behaviour of its d electrons. of the electromagnetic spectrum, absorption In the mid-1980s, it was realized that certain Back in my undergraduate chemistry days, of light produces a characteristic intense copper oxides can be made to superconduct where I got a small, albeit spectacular

colour — blue in the case of VO(acac)2. when cooled with liquid nitrogen, a demonstration of this, I never would have Changing a metal’s oxidation state, discovery for which J. Georg Bednorz and guessed that these strongly correlated typically by adding or swapping a ligand, K. Alex Müller were awarded the 1987 electron systems would go on to dominate affects its coordination environment, in Nobel Prize in Physics. In the same decade, my own research interests as a physicist. ❐ turn altering the energetics of the charge- thin Fe–Cr films were found to display a transfer transitions it is involved in, thereby giant electrical response to applied magnetic ANDREA TARONI is the Chief Editor of fields, an effect now known as giant Nature Physics. magnetoresistance, which underpins much of the memory storage technology in use today Corrected after print: 21 June 2017 Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr 602 NATURE CHEMISTRY | VOL 9 | JUNE 2017 | www.nature.com/naturechemistry ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.

Correction A sentence in the fifth paragraph of the In Your Element article ‘V for vanadium’ (Nat. Chem. 9, 602; 2017) incorrectly mentioned magnesium, it should have read: “Their rich redox chemistry is also key to their application in biological systems (think manganese in photosynthesis)”. This has been corrected after print 21 June 2017.

©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.