Ruthenium

Ruthenium is a rare, hard, shiny member of the platinum group metals: the small family of metals including platinum, palladium and rhodium that share remarkable catalytic properties and corrosion resistance. While less famous than platinum, ruthenium is increasingly important in electronics, catalysis and data storage.

• Atomic Number4444 protons, 44 electrons
• Atomic Mass101.1 u44× heavier than hydrogen
• State at Room TempSolidSolid
• Density12.1 g/cm³
• Melting / Boiling2333.8°C / 4149.9°C
• Discovered1827

What is Ruthenium?

Ruthenium is a transition metal in Group 8 of the periodic table, sitting below iron and osmium. With 44 protons and a melting point of 2,334°C, it is one of the hardest and most corrosion-resistant platinum group metals. It can form compounds in oxidation states from −2 to +8, with +2 and +3 being most common. Ruthenium tetroxide (RuO₄) is volatile and highly toxic.

Ruthenium is named after Ruthenia, the Latin name for a region encompassing Russia, Ukraine and Belarus. The name was proposed by Karl Ernst Claus, a Baltic German chemist working in Kazan, Russia, who first isolated it in 1844. He chose the name to honour his homeland.

Fact The Grätzel cell, a type of dye-sensitised solar cell using a ruthenium bipyridyl complex as the light absorber, was invented in 1991 and offers a cheaper alternative to silicon solar cells. Ruthenium's ability to absorb a broad spectrum of visible light makes it exceptionally effective as a photosensitiser.

Where you find Ruthenium

In space

Ruthenium is produced in stars and found throughout the Sun.

On Earth

Ruthenium is one of the rarest elements in the Earth's crust, just approx. 0.001 parts per million.

• Platinum ores. Ruthenium occurs in native platinum alloys and is recovered as a by-product of platinum group metal mining. South Africa, Russia and Canada are the main producers.
• Meteorites. Platinum group metals, including ruthenium, are concentrated in iron meteorites and in Earth's core.

How we use Ruthenium

• Hard disk coatings.. Thin ruthenium layers are deposited on hard disk drive platters to improve magnetic storage density. Ruthenium allowed storage capacities to break through a density barrier in 2000.
• Catalysis.. Ruthenium complexes catalyse important chemical reactions, including the Haber-Bosch ammonia synthesis and olefin metathesis reactions used to make pharmaceuticals and polymers.
• Electrical contacts.. Ruthenium resists wear and corrosion, making it ideal for electrical contacts in relays and switches.
• Solar energy.. Ruthenium-based dye-sensitised solar cells (Grätzel cells) convert sunlight to electricity using a ruthenium complex as the light-absorbing dye.

Did you know? Ruthenium is one of only a handful of elements that can form stable compounds in the +8 oxidation state, giving away all eight of its outer electrons. Ruthenium tetroxide (RuO₄) is one of these exotic compounds, a yellow, volatile solid so powerful an oxidiser that it can set organic materials on fire.

How it was discovered

Ruthenium was definitively isolated and characterised in 1844 by Karl Ernst Claus in Kazan, Russia, who processed the residues of crude platinum from the Ural mountains. Though Jöns Jacob Berzelius and Gottfried Osann had earlier found anomalies in the same residues, Claus was the first to isolate the pure element and recognise it unambiguously as new.

Deeper dive: ruthenium chemistry and applications

Ruthenium is central to a class of catalysts called Grubbs catalysts, used in olefin metathesis, a reaction that exchanges the ends of carbon-carbon double bonds between molecules. This reaction, developed by Robert Grubbs (Nobel Prize 2005), is used to make pharmaceuticals, specialty polymers and fragrance compounds. The remarkable selectivity of ruthenium in these reactions makes it irreplaceable in modern synthetic chemistry.

The use of ruthenium in perpendicular magnetic recording, developed around 2000, allowed hard disk capacities to double in what would otherwise have been an impenetrable density barrier. A one-to-three-atom-thick layer of ruthenium between magnetic layers acts as an antiferromagnetic coupler, aligning the magnetisation of the layers in opposite directions. This dramatically reduced magnetic "noise" and allowed much smaller, more closely packed data bits.

Moving to 45 protons on the periodic table brings us to Rhodium.