Ruthenium

Ruthenium (pronounced /ruːˈθiːniəm/) is a chemical element that has the symbol Ru and atomic number 44. A rare transition metal of the platinum group of the periodic table, ruthenium is found associated with platinum ores and used as a catalyst in some platinum alloys.

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Notable characteristics

A polyvalent hard white metal, ruthenium is a member of the platinum group, has four crystal modifications and does not tarnish at normal temperatures, but does oxidize readily on exposure to air to form ruthenium tetroxide, RuO₄, a strong oxidising agent with properties analogous to those of osmium tetroxide. Ruthenium dissolves in fused alkalis, is not attacked by acids but is attacked by halogens at high temperatures. Small amounts of ruthenium can increase the hardness of platinum and palladium. The corrosion resistance of titanium is increased markedly by the addition of a small amount of ruthenium.

This metal can be plated either through electrodeposition or by thermal decomposition methods. One ruthenium-molybdenum alloy has been found to be superconductive at 10.6 K. The oxidation states of ruthenium range from +1 to +8, and -2 is known, though oxidation states of +2, +3, and +4 are most common.

Applications

Due to its ability to harden platinum and palladium, ruthenium is used in platinum and palladium alloys to make wear-resistant electrical contacts. It is sometimes alloyed with gold in jewelry. 0.1% ruthenium is added to titanium to improve its corrosion resistance a hundredfold.^[2]

Ruthenium is also used in some advanced high-temperature single-crystal superalloys, with applications including the turbine blades in jet engines.

Fountain pen nibs are frequently tipped with alloys containing ruthenium. From 1944 onward, the famous Parker 51 fountain pen was fitted with the "RU" nib, a 14K gold nib tipped with 96.2% ruthenium and 3.8% iridium.

Ruthenium is also a versatile catalyst. Hydrogen sulfide can be split by light by using an aqueous suspension of CdS particles loaded with ruthenium dioxide. This may be useful in the removal of H₂S from oil refineries and from other industrial processes.

Ruthenium is a component of mixed-metal oxide (MMO) anodes used for cathodic protection of underground and submerged structures, and for electrolytic cells for chemical processes such as generating chlorine from saltwater.

Organometallic ruthenium carbene and allenylidene complexes have recently been found as highly efficient catalysts for olefin metathesis with important applications in organic and pharmaceutical chemistry.

Some ruthenium complexes absorb light throughout the visible spectrum and are being actively researched in various, potential, solar energy technologies. Ruthenium-based dyes have been used as the electron providers in dye-sensitized solar cells, a promising new low-cost solar cell system.

The fluorescence of some ruthenium complexes is quenched by oxygen, which has led to their use as optode sensors for oxygen.

Ruthenium red, [(NH₃)₅Ru-O-Ru(NH₃)₄-O-Ru(NH₃)₅]⁶⁺, is a biological stain used to stain polyanionic molecules such as pectin and nucleic acids for light microscopy and electron microscopy.

Ruthenium-centered complexes are being researched for possible anticancer properties. Ruthenium, unlike traditional platinum complexes, show greater resistance to hydrolysis and more selective action on tumors. NAMI-A and KP1019 are two drugs undergoing clinical evaluation against metastatic tumors and colon cancers.

In 1990, IBM scientists discovered that a thin layer of ruthenium atoms created a strong anti-parallel coupling between adjacent ferromagnetic layers, stronger than any other nonmagnetic spacer-layer element. Such a ruthenium layer was used in the first giant magnetoresistive read element for hard disk drives. In 2001, IBM announced a three-atom-thick layer of the element ruthenium, informally referred to as pixie dust, which would allow a quadrupling of the data density of current hard disk drive media.^[3]

History

Ruthenium was discovered and isolated by Russian scientist Karl Klaus in 1844 in Kazan University, Kazan. Klaus showed that ruthenium oxide contained a new metal and obtained 6 grams of ruthenium from the part of crude platinum that is insoluble in aqua regia.

Jöns Berzelius and Gottfried Osann nearly discovered ruthenium in 1827. The men examined residues that were left after dissolving crude platinum from the Ural Mountains in aqua regia. Berzelius did not find any unusual metals, but Osann thought he found three new metals and named one of them ruthenium.

The name derives from Ruthenia, the Latin word for Rus', a historical area which gave birth to the Russian nation and includes present-day western Russia, Ukraine, Belarus, and parts of Slovakia and Poland. Karl Klaus named the element in honour of his birthland, as he was born in Tartu, Estonia, which was at the time a part of the Russian Empire.

It is also possible that Polish chemist Jędrzej Śniadecki isolated element 44 (which he called vestium) from platinum ores in 1807. However his work was never confirmed, and he later withdrew his claim of discovery.

Occurrence

Normal mining

This element is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, Canada, and in pyroxenite deposits in South Africa.

Ruthenium is exceedingly rare and is the 74th most abundant metal on earth [Nature's Building Block, John Emsley, Oxford University Press,2001]. Roughly 12MT of Ru is mined each year with world reserves estimated to be 5000mt [Nature's Building Block, John Emsley, Oxford University Press,2001].

This metal is commercially isolated through a complex chemical process in which hydrogen is used to reduce ammonium ruthenium chloride yielding a powder. The powder is then consolidated by powder metallurgy techniques or by argon-arc welding.

From used nuclear fuels

It is also possible to extract ruthenium from used nuclear fuel. Each kilo of fission products of ²³⁵U will contain 63.44 grams of ruthenium isotopes with halflives longer than a day. Since a typical used nuclear fuel contains about 3% fission products, one ton of used fuel will contain about 1.9 kg of ruthenium. The ¹⁰³Ru and ¹⁰⁶Ru will render the fission ruthenium very radioactive. If the fission occurs in an instant then the ruthenium thus formed will have an activity due to ¹⁰³Ru of 109 TBq g^-1 and ¹⁰⁶Ru of 1.52 TBq g^-1. Ru 103 has a half life of about 39 days meaning that within 390 days it will have effectively decayed to ground state, well before any reprocessing is likely to occur. Ru 106 has a half life of about 373 days meaning that if the fuel is let to cool for 5 years before reprocessing only about 3% of the original quantity will remain, the rest will have decayed to ground state.

See also Ruthenium minerals.

Compounds

Ruthenium compounds are often similar in properties to those of osmium and exhibit at least eight oxidation states, but the +2, +3, and +4 states are the most common. Examples are ruthenium(IV) oxide (Ru(IV)O₂, oxidation state +4), dipotassium ruthenate (K₂Ru(VI)O₄, +6), potassium perruthenate (KRu(VII)O₄, +7) and ruthenium tetroxide (Ru(VIII)O₄, +8). Compounds of ruthenium with chlorine are ruthenium(II) chloride (RuCl₂) and ruthenium(III) chloride (RuCl₃).

See also Ruthenium compounds.

Isotopes

Main article: isotopes of ruthenium

Naturally occurring ruthenium is composed of seven isotopes. The most stable radioisotopes are ¹⁰⁶Ru with a half-life of 373.59 days, ¹⁰³Ru with a half-life of 39.26 days and ⁹⁷Ru with a half-life of 2.9 days.

Fifteen other radioisotopes have been characterized with atomic weights ranging from 89.93 u (⁹⁰Ru) to 114.928 u (¹¹⁵Ru). Most of these have half-lives that are less than five minutes except ⁹⁵Ru (half-life: 1.643 hours) and ¹⁰⁵Ru (half-life: 4.44 hours).

The primary decay mode before the most abundant isotope, ¹⁰²Ru, is electron capture and the primary mode after is beta emission. The primary decay product before ¹⁰²Ru is technetium and the primary mode after is rhodium.

Organometallic chemistry

It is quite easy to form compounds with carbon ruthenium bonds, as these compounds tend to be darker and react more quickly than the osmium compounds. Recently, Professor Anthony Hill and his co-workers have been making compounds of ruthenium in which a boron atom binds to the metal atom^[4].

The organometallic ruthenium compound that is easiest to make is RuHCl(CO)(PPh₃)₃. This compound has two forms (yellow and pink) that are identical once they are dissolved but different in the solid state.

An organometallic compound similar to ruthenocene, bis(2,4-dimethylpentadienyl)ruthenium, is readily synthesized in near quantitative yields and has applications in vapor-phase deposition of metallic ruthenium, as well as in catalysis, including Fischer-Tropsch synthesis of transportation fuels.

Important catalysts based on ruthenium are Grubbs' catalyst and Roper's complex.

Precautions

The compound ruthenium tetroxide, RuO₄, similar to osmium tetroxide, is volatile, highly toxic and may cause explosions if allowed to come into contact with combustible materials.^[5] Ruthenium plays no biological role but does strongly stain human skin, may be carcinogenic^[6] and bio-accumulates in bone.

References

1. ^ Ruthenium: ruthenium(I) fluoride compound data. OpenMOPAC.net. Retrieved on 2007-12-10.
2. ^ It's Elemental - Ruthenium
3. ^ Brian Hayes, Terabyte Territory, American Scientist, Vol 90 No 3 (May-June 2002) p. 212
4. ^ - Professor Anthony Hill - Current Research
5. ^ Ruthenium Tetroxide and Other Ruthenium Compounds?
6. ^ INHALATION OF RADIONUCLIDES AND CARCINOGENESIS

• Los Alamos National Laboratory – Ruthenium