It was while studying another transition metal, platinum, that chemists came across osmium: a black residue would always appear when platinum-containing ores were dissolved in aqua regia. Naturally, they wouldn’t rest until they had found out what exactly that residue was — but the amounts available were too small to allow for its full characterization. It was Smithson Tennant who obtained sufficient quantities (while in a business selling platinum metal), and discovered it to be a mixture of two new elements — one with striking and diverse colours, the other possessing a strong and distinctive smell. He named them iridium and osmium, after the goddess Iris (represented by a rainbow) and the Greek word for smell (osme), respectively.
In last month’s ‘in your element’ article (subscription required), Gregory Girolami recounted how the fate of these two elements, discovered together and neighbours in the periodic table, was to be further intertwined: their densities are so close that for decades different techniques gave a different answer as to which one was the densest of the two — a prestigious claim that would also make the winner the densest of all metals. The title of the article might give you a hint as to which one eventually won, by a very small margin.
Osmium has a few other claims to fame; read the article to discover in what way it rivals diamond, and what urban legend it’s involved in. It also exists in eleven oxidation states, up to a (+8) state rather rarely encountered — OsO4 has a few applications, but is most famous (amongst chemists at least) for its involvement in the Nobel Prize work of K. Barry Sharpless.
Yet, as attractive as alkene dihydroxylations are, especially asymmetric ones, osmium tetroxide is both highly volatile and highly toxic so don’t play Nobel-chemistry at home.
Anne Pichon (Associate Editor, Nature Chemistry)