Ruthenium

Ruthenium is a hard, brittle, silvery member of the platinum group, sitting in group 8 below iron and above osmium. Its configuration, [Kr] 4d7 5s1, leaves many d electrons available for bonding, and ruthenium shows a wider range of oxidation states than almost any other element, from −2 to +8. In the +8 state it forms ruthenium tetroxide, RuO4, a volatile, powerfully oxidizing yellow solid. Yet the metal itself is notably unreactive: it does not tarnish at room temperature and is barely attacked even by aqua regia.

That combination of a noble surface and flexible electron count makes ruthenium an exceptional catalyst. Ruthenium complexes catalyse olefin metathesis (the Grubbs catalysts, recognised by the 2005 Nobel Prize in Chemistry), hydrogenation, and ammonia synthesis in some modern plants. In electronics, ruthenium dioxide is used in thick-film chip resistors, and a ruthenium layer a few atoms thick couples the magnetic layers in hard-disk platters. Small additions to platinum and palladium harden jewellery alloys, and ruthenium improves the creep resistance of the nickel superalloys used in turbine blades.

Discovery

Ruthenium was the last platinum-group metal to be found. Jędrzej Śniadecki reported a new metal, 'vestium', in 1808 and Gottfried Osann claimed one in 1828, but neither claim held up. In 1844 Karl Ernst Claus at Kazan University isolated ruthenium from the insoluble residue left after platinum ore from the Ural Mountains was dissolved in aqua regia. He kept Osann's proposed name, from Ruthenia, the Latin name for Russia.