Ruthenium is a chemical element with symbol Ru and atomic number 44.
It is a rare transition metal belonging to the platinum group of the
periodic table. Like the other metals of the platinum group, ruthenium
is inert to most other chemicals. The Russian-born scientist of
Baltic-German ancestry and a member of the Russian Academy of Science
Karl Ernst Claus discovered the element in 1844 at
Russia and named it after the Latin name of his
Ruthenium is usually found as a minor component of
platinum ores; the annual production is about 20 tonnes. Most
ruthenium produced is used in wear-resistant electrical contacts and
thick-film resistors. A minor application for ruthenium is in platinum
alloys and as a chemistry catalyst. A new application of ruthenium is
as the capping layer for extreme ultraviolet photomasks.
1.1 Physical properties
3 Chemical compounds
3.1 Oxides and chalcogenides
3.2 Halides and oxyhalides
3.3 Coordination and organometallic complexes
5.1.1 Homogeneous catalysis
5.1.2 Heterogeneous catalysis
5.2 Emerging applications
8 External links
Gas phase grown crystals of ruthenium metal.
A polyvalent hard white metal.
Ruthenium is a member of the platinum
group and is in group 8 of the periodic table:
No. of electrons/shell
2, 8, 14, 2
2, 8, 18, 15, 1
2, 8, 18, 32, 14, 2
2, 8, 18, 32, 32, 14, 2
Whereas all other group 8 elements have 2 electrons in the outermost
shell, in ruthenium, the outermost shell has only one electron (the
final electron is in a lower shell). This anomaly is observed in the
neighboring metals niobium (41), molybdenum (42), and rhodium (45).
Ruthenium has four crystal modifications and does not tarnish unless
subject to high temperatures.
Ruthenium dissolves in fused alkalis to
give ruthenates (RuO2−
4), is not attacked by acids (even aqua regia) but is attacked by
halogens at high temperatures. Indeed, ruthenium is most readily
attacked by oxidizing agents. 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. The metal can be plated by
electroplating and by thermal decomposition. A ruthenium-molybdenum
alloy is known to be superconductive at temperatures below 10.6 K.
Ruthenium is the last of the 4d transition metals that can assume the
group oxidation state +8, and even then it is less stable there than
the heavier congener osmium: this is the first group from the left of
the table where the second and third-row transition metals display
notable differences in chemical behavior. Like iron but unlike osmium,
ruthenium can form aqueous cations in its lower oxidation states of +2
Ruthenium is the first in a downward trend in the melting and boiling
points and atomization enthalpy in the 4d transition metals after the
maximum seen at molybdenum, because the 4d subshell is more than half
full and the electrons are contributing less to metallic bonding.
(Technetium, the previous element, has an exceptionally low value that
is off the trend due to its half-filled [Kr]4d55s2 configuration,
though the small amount of energy needed to excite it to a [Kr]4d65s1
configuration indicates that it is not as far off the trend in the 4d
series as manganese in the 3d transition series.) Unlike the
lighter congener iron, ruthenium is paramagnetic at room temperature,
as iron also is above its Curie point.
The reduction potentials in acidic aqueous solution for some common
ruthenium ions are shown below:
Ru2+ + 2e−
Ru3+ + e−
RuO2 + 4H+ + 2e−
↔ Ru2+ + 2H2O
4 + 8H+ + 4e−
↔ Ru2+ + 4H2O
4 + 8H+ + 5e−
↔ Ru2+ + 4H2O
RuO4 + 4H+ + 4e−
↔ RuO2 + 2H2O
Main article: Isotopes of ruthenium
Naturally occurring ruthenium is composed of seven stable isotopes.
Additionally, 34 radioactive isotopes have been discovered. Of these
radioisotopes, the most stable 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 decay
product after is rhodium.
See also: category:
As the 74th most abundant element in Earth's crust, ruthenium is
relatively rare, found in about 100 parts per trillion.
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. The native form of ruthenium is a very rare mineral (Ir
replaces part of Ru in its structure).
Roughly 12 tonnes of ruthenium are mined each year with world reserves
estimated at 5,000 tonnes. The composition of the mined platinum
group metal (PGM) mixtures varies widely, depending on the geochemical
formation. For example, the PGMs mined in
South Africa contain on
average 11% ruthenium while the PGMs mined in the former USSR contain
only 2% (1992). Ruthenium, osmium, and iridium are considered
the minor platinum group metals.
Ruthenium, like the other platinum group metals, is obtained
commercially as a by-product from nickel, and copper, and platinum
metals ore processing. During electrorefining of copper and nickel,
noble metals such as silver, gold, and the platinum group metals
precipitate as anode mud, the feedstock for the extraction.
The metals are converted to ionized solutes by any of several methods,
depending on the composition of the feedstock. One representative
method is fusion with sodium peroxide followed by dissolution in aqua
regia, and solution in a mixture of chlorine with hydrochloric
acid. Osmium, ruthenium, rhodium, and iridium are insoluble in
aqua regia and readily precipitate, leaving the other metals in
Rhodium is separated from the residue by treatment with
molten sodium bisulfate. The insoluble residue, containing Ru, Os, and
Ir is treated with sodium oxide, in which Ir is insoluble, producing
dissolved Ru and Os salts. After oxidation to the volatile oxides, RuO
4 is separated from OsO
4 by precipitation of (NH4)3RuCl6 with ammonium chloride or by
distillation or extraction with organic solvents of the volatile
Hydrogen is used to reduce ammonium ruthenium
chloride yielding a powder. The product is reduced using hydrogen,
yielding the metal as a powder or sponge metal that can be treated
with powder metallurgy techniques or argon-arc welding.
See also: Category:
The oxidation states of ruthenium range from 0 to +8, and −2. The
properties of ruthenium and osmium compounds are often similar. The
+2, +3, and +4 states are the most common. The most prevalent
precursor is ruthenium trichloride, a red solid that is poorly defined
chemically but versatile synthetically.
Oxides and chalcogenides
Ruthenium can be oxidized to ruthenium(IV) oxide (RuO2, oxidation
state +4) which can in turn be oxidized by sodium metaperiodate to the
volatile yellow tetrahedral ruthenium tetroxide, RuO4, an aggressive,
strong oxidizing agent with structure and properties analogous to
osmium tetroxide. Like osmium tetroxide, ruthenium tetroxide is a
potent fixative and stain for electron microscopy of organic
materials, and is mostly used to reveal the structure of polymer
samples. Dipotassium ruthenate (K2RuO4, +6), and potassium
perruthenate (KRuO4, +7) are also known. Unlike osmium tetroxide,
ruthenium tetroxide is less stable and is strong enough as an
oxidising agent to oxidise dilute hydrochloric acid and organic
solvents like ethanol at room temperature, and is easily reduced to
4) in aqueous alkaline solutions; it decomposes to form the dioxide
above 100 °C. Unlike iron but like osmium, ruthenium does not
form oxides in its lower +2 and +3 oxidation states. Ruthenium
forms dichalcogenides only when reacted directly with the chalcogens,
which are diamagnetic semiconductors crystallizing in the pyrite
structure and thus must contain ruthenium(II).
Like iron, ruthenium does not readily form oxoanions, and prefers to
achieve high coordination numbers with hydroxide ions instead.
Ruthenium tetroxide is reduced by cold dilute potassium hydroxide to
form black potassium perruthenate, KRuO4, with ruthenium in the +7
Potassium perruthenate can also be produced by
oxidising potassium ruthenate, K2RuO4, with chlorine gas. The
perruthenate ion is unstable and is reduced by water to form the
Potassium ruthenate may be synthesized by reacting
ruthenium metal with potassium hydroxide and potassium nitrate.
Some mixed oxides are also known, such as MIIRuIVO3, Na3RuVO4, Na
7, and MII
Halides and oxyhalides
The highest known ruthenium halide is the hexafluoride, a dark brown
solid that melts at 54 °C. It hydrolyzes violently upon contact
with water and easily disproportionates to form a mixture of lower
ruthenium fluorides, releasing fluorine gas.
is a tetrameric dark green solid that is also readily hydrolyzed,
melting at 86.5 °C. The yellow ruthenium tetrafluoride is
probably also polymeric and can be formed by reducing the
pentafluoride with iodine. Among the binary compounds of ruthenium,
these high oxidation states are known only in the oxides and
Ruthenium trichloride is a well-known compound, existing in a black
α-form and a dark brown β-form: the trihydrate is red. Of the
known trihalides, trifluoride is dark brown and decomposes above
650 °C, tetrabromide is dark-brown and decomposes above
400 °C, and triiodide is black. Of the dihalides, difluoride
is not known, dichloride is brown, dibromide is black, and diiodide is
blue. The only known oxyhalide is the pale green ruthenium(VI)
Coordination and organometallic complexes
Main article: Organoruthenium chemistry
Grubbs' catalyst, which earned a Nobel Prize for its inventor, is used
in alkene metathesis reactions.
Ruthenium forms a variety of coordination complexes. Examples are the
many pentammine derivatives [Ru(NH3)5L]n+ that often exist for both
Ru(II) and Ru(III). Derivatives of bipyridine and terpyridine are
numerous, best known being the luminescent
Ruthenium forms a wide range compounds with carbon-ruthenium bonds.
Grubbs' catalyst is used for alkene metathesis.
analogous to ferrocene structurally, but exhibits distinctive redox
properties. The colorless liquid ruthenium pentacarbonyl converts in
the absence of CO pressure to the dark red solid triruthenium
Ruthenium trichloride reacts with carbon monoxide to
give many derivatives including RuHCl(CO)(PPh3)3 and Ru(CO)2(PPh3)3
(Roper's complex). Heating solutions of ruthenium trichloride in
alcohols with triphenylphosphine gives
tris(triphenylphosphine)ruthenium dichloride (RuCl2(PPh3)3), which
converts to the hydride complex
Though naturally occurring platinum alloys containing all six
platinum-group metals were used for a long time by pre-Columbian
Americans and known as a material to European chemists from the
mid-16th century, not until the mid-18th century was platinum
identified as a pure element. That natural platinum contained
palladium, rhodium, osmium and iridium was discovered in the first
decade of the 19th century.
Platinum in alluvial sands of Russian
rivers gave access to raw material for use in plates and medals and
for the minting of ruble coins, starting in 1828. Residues from
platinum production for coinage were available in the Russian Empire,
and therefore most of the research on them was done in Eastern Europe.
It is possible that the Polish chemist
Jędrzej Śniadecki isolated
element 44 (which he called "vestium" after the asteroid Vesta
discovered shortly before) from South American platinum ores in 1807.
He published an announcement of his discovery in 1808. His work
was never confirmed, however, and he later withdrew his claim of
Jöns Berzelius and
Gottfried Osann nearly discovered ruthenium in
1827. They 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, which
he called pluranium, ruthenium, and polinium. This discrepancy led to
a long-standing controversy between Berzelius and Osann about the
composition of the residues. As Osann was not able to repeat his
isolation of ruthenium, he eventually relinquished his claims.
The name "ruthenium" was chosen by Osann because the analysed samples
stemmed from the
Ural Mountains in Russia. The name itself derives
from Ruthenia, the Latin word for Rus', a historical area that
included present-day western Russia, Ukraine, Belarus, and parts of
Slovakia and Poland.
In 1844, Karl Ernst Claus, a Russian scientist of Baltic German
descent, showed that the compounds prepared by Gottfried Osann
contained small amounts of ruthenium, which Claus had discovered the
same year. Claus isolated ruthenium from the platinum residues of
rouble production while he was working in
Kazan University, Kazan,
the same way its heavier congener osmium had been discovered four
decades earlier. Claus 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. Choosing the name for
the new element, Claus stated: "I named the new body, in honour of my
Motherland, ruthenium. I had every right to call it by this name
because Mr. Osann relinquished his ruthenium and the word does not yet
exist in chemistry."
Because it hardens platinum and palladium alloys, ruthenium is used in
electrical contacts, where a thin film is sufficient to achieve the
desired durability. With similar properties and lower cost than
rhodium, electric contacts are a major use of ruthenium.
The plate is applied to the base by electroplating or
Ruthenium dioxide with lead and bismuth ruthenates are used in
thick-film chip resistors. These two electronic
applications account for 50% of the ruthenium consumption.
Ruthenium is seldom alloyed with metals outside the platinum group,
where small quantities improve some properties. The added corrosion
resistance in titanium alloys led to the development of a special
alloy with 0.1% ruthenium.
Ruthenium is also used in some advanced
high-temperature single-crystal superalloys, with applications that
include the turbines in jet engines. Several nickel based superalloy
compositions are described, such as EPM-102 (with 3% Ru), TMS-162
(with 6% Ru), TMS-138, and TMS-174, the latter two
containing 6% rhenium.
Fountain pen nibs are frequently tipped
with ruthenium alloy. 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 a component of mixed-metal oxide (MMO) anodes used for
cathodic protection of underground and submerged structures, and for
electrolytic cells for such processes as generating chlorine from salt
water. The fluorescence of some ruthenium complexes is quenched by
oxygen, finding use in optode sensors for oxygen.
[(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. The beta-decaying isotope 106
of ruthenium is used in radiotherapy of eye tumors, mainly malignant
melanomas of the uvea. Ruthenium-centered complexes are being
researched for possible anticancer properties. Compared with
platinum complexes, those of ruthenium show greater resistance to
hydrolysis and more selective action on tumors.
Ruthenium tetroxide exposes latent fingerprints by reacting on contact
with fatty oils or fats with sebaceous contaminants and producing
brown/black ruthenium dioxide pigment.
Many ruthenium-containing compounds exhibit useful catalytic
properties. The catalysts are conveniently divided into those that are
soluble in the reaction medium, homogeneous catalysts, and those that
are not, which are called heterogeneous catalysts.
Solutions containing ruthenium trichloride are highly active for
olefin metathesis. Such catalysts are used commercially for the
production of polynorbornene for example. Well defined ruthenium
carbene and alkylidene complexes show comparable reactivity and
provide mechanistic insights into the industrial processes. The
Grubbs' catalysts for example have been employed in the preparation of
drugs and advanced materials.
RuCl3-catalyzed ring-opening metathesis polymerization reaction giving
Ruthenium complexes are highly active catalyst for transfer
hydrogenations (sometimes referred to as "borrowing hydrogen"
reactions). This process is employed for the enantioselective
hydrogenation of ketones, aldehydes, and imines. This reaction
exploits using chiral ruthenium complexes introduced by Ryoji
Noyori.For example, (cymene)Ru(S,S-TsDPEN) catalyzes the
hydrogenation of benzil into (R,R)-hydrobenzoin. In this reaction,
formate and water/alcohol serve as the source of H2:
[RuCl(S,S-TsDPEN)(cymene)]-catalysed (R,R)-hydrobenzoin synthesis
(yield 100%, ee >99%)
Nobel Prize in Chemistry
Nobel Prize in Chemistry was awarded in 2001 to
Ryōji Noyori for
contributions to the field of asymmetric hydrogenation.
Ruthenium-promoted cobalt catalysts are used in Fischer-Tropsch
Some ruthenium complexes absorb light throughout the visible spectrum
and are being actively researched for solar energy technologies. For
example, Ruthenium-based compounds have been used for light absorption
in dye-sensitized solar cells, a promising new low-cost solar cell
Many ruthenium-based oxides show very unusual properties, such as a
quantum critical point behavior, exotic superconductivity, and
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