Ruthenium (Ru)

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

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 explosively. Ruthenium dissolves in fused alkalis, is not attacked by acids but is attacked by halogens at high temperatures and by hydroxides. 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 highly effective ability to harden platinum and palladium, ruthenium is used in Pt and Pd alloys to make severe 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.


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.


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.


Recently, large metallo-organic complexes of ruthenium have been found to exhibit anti-tumor activity and the first of a new group of anti-cancer medicine are now in the stage of clinical trials.


Some ruthenium complexes absorb light throughout the visible spectrum and are being actively researched in various, potential, solar energy technologies.


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


Ruthenium red, [(NH3)5Ru-O-Ru(NH3)4-O-Ru(NH3)5]6+, is a biological stain used to visualize polyanionic areas of membranes.

 

History

Ruthenium (Latin Ruthenia) was discovered and isolated by Karl Klaus in 1844. 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.


Jons 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.


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

 

Occurrence

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 and in Pyroxenite deposits in South Africa.


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.


It is also possible to extract Ruthenium from spent nuclear fuel, which contains an average of 2 kg of Ruthenium per metric ton. Ruthenium produced in such a way contains radioactive isotopes, some with a half-life of up to 373.59 days. Therefore this ruthenium has to be stored at least for 10 years in a secured area to allow it to become stable. Fission-derived Ruthenium has a specific activity of 8.1 curies of radioactivity per gram. Under health physics safety rules any isotope that emits more than 1 ci of activity is a hazard; however, after 6 years the activity falls to 4.1 ci, after 7 years it is 2.2, after 8 years 1.1, after 9 years .55 ci and after 10 years only .27 ci. After 20 years the activity falls to 2.702E-4 ci, which is under the threshold for low level risk by even the most stringent health physics rules.

 

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.

 

Isotopes

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


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


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

 

Organometallic Chemistry

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


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 highly toxic and may explode. Ruthenium plays no biological role but does strongly stain human skin, may be carcinogenic and bio-accumulates in bone.

 

References

Los Alamos National Laboratory - Ruthenium

Original article at http://en.wikipedia.org/wiki/Ruthenium