Ruthenium

Ruthenium occupies a curious position among the platinum-group metals: rarer than platinum and less celebrated than palladium, yet indispensable in a surprising range of modern technologies. It is a hard, brittle, silvery-white metal that resists corrosion exceptionally well, even at elevated temperatures. Ruthenium was the last of the naturally occurring platinum-group elements to be isolated, and it was found not in South American ore, as many of its siblings were, but in the platinum residues from the Ural Mountains of Russia. Its discovery capped a decades-long effort by Russian chemists to characterize the metals hiding in those residues, and the name chosen for the new element honored the nation where it was found. Today, ruthenium is produced primarily as a byproduct of nickel and copper mining.

Ruthenium's hardness and corrosion resistance make it a valuable alloying agent. Adding just 0.1 percent ruthenium to titanium increases the metal's corrosion resistance a hundredfold, a property exploited in chemical-plant equipment. In the electronics industry, ruthenium dioxide coatings serve as resistive elements in thick-film resistors, and thin ruthenium layers are sputtered onto hard disk platters to enable perpendicular magnetic recording, dramatically increasing data storage density. Ruthenium complexes, particularly tris(bipyridyl)ruthenium(II), are efficient photosensitizers in dye-sensitized solar cells (DSSCs), absorbing sunlight across a broad visible spectrum and injecting electrons into titanium dioxide semiconductors. In catalysis, ruthenium-based systems drive the synthesis of ammonia at lower pressures than traditional iron catalysts and catalyze olefin metathesis reactions central to pharmaceutical and polymer manufacturing.

The platinum residues left after dissolving native platinum in aqua regia puzzled chemists for decades. Polish chemist Jedrzej Sniadecki claimed in 1808 to have isolated a new element from them, which he named vestium, but he later retracted the claim after failing to reproduce his results. Gottfried Osann of the University of Tartu announced three new elements from Ural platinum residues in 1827, naming one of them ruthenium, but his analysis was flawed. It was Karl Karlovich Klaus, a Baltic German chemist working in Kazan, Russia, who finally succeeded in 1844. Klaus treated residues from the platinum refineries with sodium hydroxide fusions and obtained a small quantity of a new metal, which he confirmed was distinct from all known elements. He retained Osann's name ruthenium, from the medieval Latin Ruthenia, meaning Russia, as a tribute to his adopted homeland.

Ruthenium is one of the rarest stable elements in Earth's crust, present at an average concentration of roughly 0.001 parts per million — comparable to rhodium and far scarcer than platinum. Like the other platinum-group metals, it is a siderophile element: during Earth's formation it preferentially sank into the iron-rich core rather than concentrating in the crust. Commercial ruthenium comes almost entirely from the nickel-copper sulfide ores mined in the Sudbury Basin of Canada, the Bushveld Complex of South Africa, and the Norilsk deposits of Russia. It occurs in these ores partly as a native alloy with other platinum-group metals, partly in the mineral laurite (RuS2), and partly as a trace constituent of pentlandite and other sulfides. Global annual production is only around 30 tonnes, making it precious by any industrial standard.

Ruthenium displays a wide range of oxidation states, from -2 to +8, giving it an exceptionally rich coordination chemistry. Ruthenium tetroxide (RuO4) is a volatile, highly oxidizing compound used in organic synthesis to cleave double bonds and oxidize primary alcohols to carboxylic acids; it must be handled with great care due to its toxicity. Ruthenium dioxide (RuO2) is a good electrical conductor used in mixed-oxide electrodes for chlorine production and as a coating in capacitors. Tris(2,2'-bipyridyl)ruthenium(II) chloride is perhaps the most studied ruthenium complex, prized for its long-lived excited state and intense luminescence; it serves as a model photosensitizer and is central to research on artificial photosynthesis. Grubbs catalysts, which contain ruthenium carbene complexes, revolutionized the field of olefin metathesis and earned the 2005 Nobel Prize in Chemistry.

• Adding a fraction of a percent of ruthenium to titanium makes it over 100 times more resistant to corrosion in hydrochloric and sulfuric acid, a disproportionate effect that still surprises materials scientists.
• Ruthenium was the last platinum-group metal to be discovered, completing a set that now includes ruthenium, rhodium, palladium, osmium, iridium, and platinum.
• The thin ruthenium layer sputtered onto modern hard drive platters — just a few atoms thick — was key to increasing hard disk capacity by enabling perpendicular rather than longitudinal recording.
• Ruthenium tetroxide smells faintly like ozone and is so powerfully oxidizing that it can ignite organic materials on contact, which makes storing it a challenge in the laboratory.
• The tris(bipyridyl)ruthenium complex glows an intense orange when illuminated with ultraviolet light and has been used to label DNA strands, probe protein-folding dynamics, and even detect trace explosives.