= Ruthenium =

======================================================================
= Ruthenium =
======================================================================

Introduction
======================================================================
Ruthenium is a chemical element; it has 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 unreactive to most chemicals. Karl Ernst Claus, a Russian
scientist of Baltic-German ancestry, discovered the element in 1844 at
Kazan State University and named it in honor of Russia. (He used the
Latin name 'Ruthenia', which can have other meanings, but specifically
stated that the element was named in honor of his "motherland".)
Ruthenium is usually found as a minor component of platinum ores; the
annual production has risen from about 19 tonnes in 2009 to some 35.5
tonnes in 2017. 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 chemical catalyst. A new
application of ruthenium is as the capping layer for extreme
ultraviolet photomasks. Ruthenium 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.

Physical properties
=====================
Ruthenium, a polyvalent hard white metal, is a member of the platinum
group and is in group 8 of the periodic table:

Z !! Element !! No. of electrons/shell
26 iron 2, 8, 14, 2
44 ruthenium 2, 8, 18, 15, 1
76 osmium 2, 8, 18, 32, 14, 2
108 hassium 2, 8, 18, 32, 32, 14, 2

Whereas all other group 8 elements have two 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 also observed in
the neighboring metals niobium (41), molybdenum (42), and rhodium
(45).

Chemical properties
=====================
Ruthenium has four crystal modifications and does not tarnish at
ambient conditions; it oxidizes upon heating to 800 C. Ruthenium
dissolves in fused alkalis to give ruthenates (). It is not attacked
by acids (even aqua regia) but is attacked by sodium hypochlorite at
room temperature, and halogens at high temperatures. 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 only
4d transition metal 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 +2 and +3 states.

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 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 usually paramagnetic at room temperature, as iron also is above its
Curie point. However, the metastable tetragonal phase of ruthenium,
created as a thin film on single crystal Mo, is ferromagnetic at room
temperature.

The reduction potentials in acidic aqueous solution for some common
ruthenium species are shown below:
!Potential!!colspan=2|Reaction
0.455 V Ru2+ + 2e− ↔ Ru
0.249 V Ru3+ + e− ↔ Ru2+
1.120 V RuO2 + 4H+ + 2e− ↔ Ru2+ + 2H2O
1.563 V + 8H+ + 4e− ↔ Ru2+ + 4H2O
1.368 V + 8H+ + 5e− ↔ Ru2+ + 4H2O
1.387 V RuO4 + 4H+ + 4e− ↔ RuO2 + 2H2O

Isotopes
==========
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 (90Ru) to 114.928 Da (115Ru). Most of these have
half-lives that are less than five minutes; the exceptions are 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 while the primary mode after is beta emission. The
primary decay product before 102Ru is technetium and the primary decay
product after is rhodium.

106Ru is a product of fission of a nucleus of uranium or plutonium.
High concentrations of detected atmospheric 106Ru were associated with
an alleged undeclared nuclear accident in Russia in 2017.

Occurrence
============
Ruthenium is found in about 100 parts per trillion in the Earth's
crust, making it the 78th most abundant element. It 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). Ruthenium has a relatively high fission product
yield in nuclear fission; and given that its most long-lived
radioisotope has a half-life of "only" around a year, there are often
proposals to recover ruthenium in a new kind of nuclear reprocessing
from spent fuel. An unusual ruthenium deposit can also be found at the
natural nuclear fission reactor that was active in Oklo, Gabon, some
two billion years ago. Indeed, the isotope ratio of ruthenium found
there was one of several ways used to confirm that a nuclear fission
chain reaction had indeed occurred at that site in the geological
past. Uranium is no longer mined at Oklo, and there have never been
serious attempts to recover any of the platinum group metals present
there.

Production
======================================================================
Roughly 30 tonnes of ruthenium are mined each year, and world reserves
are 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 processing of nickel, copper, and
platinum metal ore. 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 (Os), ruthenium (Ru), rhodium (Rh), and iridium (Ir) are
insoluble in aqua regia and readily precipitate, leaving the other
metals in solution. 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, is separated from by precipitation of (NH4)3RuCl6 with
ammonium chloride or by distillation or extraction with organic
solvents of the volatile osmium tetroxide. 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.

Ruthenium is contained in spent nuclear fuel, both as a direct fission
product and as a product of neutron absorption by long-lived fission
product . After allowing the unstable isotopes of ruthenium to decay,
chemical extraction could yield ruthenium for use in all applications
of ruthenium.

Ruthenium can also be produced by deliberate nuclear transmutation
from . Given its relatively long half-life, high fission product yield
and high chemical mobility in the environment, is among the most
often proposed non-actinides for commercial-scale nuclear
transmutation. has a relatively large neutron cross section, and
because technetium has no stable isotopes, there would not be a
problem of neutron activation of stable isotopes. Significant amounts
of are produced in nuclear fission. They are also produced as a
byproduct of the use of in nuclear medicine, because this isomer
decays to . Exposing the target to strong enough neutron radiation
will eventually yield appreciable quantities of ruthenium, which can
be chemically separated while consuming .

Chemical compounds
======================================================================
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. RuO4 is mostly used as an intermediate
in the purification of ruthenium from ores and radiowastes.

Dipotassium ruthenate (K2RuO4, +6) and potassium perruthenate (KRuO4,
+7) are also known. Unlike osmium tetroxide, ruthenium tetroxide is
less stable, 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 ruthenate () 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, which are
diamagnetic semiconductors crystallizing in the pyrite structure.
Ruthenium sulfide (RuS2) occurs naturally as the mineral laurite.

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
oxidation state. 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
orange ruthenate. Potassium ruthenate may be synthesized by reacting
ruthenium metal with molten potassium hydroxide and potassium nitrate.

Some mixed oxides are also known, such as MIIRuIVO3, Na3RuVO4, NaRuO,
and MLnRuO.

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. Ruthenium pentafluoride
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 fluorides.

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,
tribromide 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) oxyfluoride, RuOF4.

Coordination and organometallic complexes
===========================================
Ruthenium forms a variety of coordination complexes. Examples are the
many pentaammine 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
tris(bipyridine)ruthenium(II) chloride.

Ruthenium forms a wide range compounds with carbon-ruthenium bonds.
Grubbs' catalyst is used for alkene metathesis. Ruthenocene is
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
dodecacarbonyl. 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
chlorohydridotris(triphenylphosphine)ruthenium(II) (RuHCl(PPh3)3).

History
======================================================================
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
discovery.

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.

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." The name itself derives from the Latin word 'Ruthenia'.
In doing so, Claus started a trend that continues to this day - naming
an element after a country.

Applications
======================================================================
Approximately 30.9 tonnes of ruthenium were consumed in 2016, 13.8 of
them in electrical applications, 7.7 in catalysis, and 4.6 in
electrochemistry.

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 its similar properties to and lower cost than
rhodium, electric contacts are a major use of ruthenium. The ruthenium
plate is applied to the electrical contact and electrode base metal by
electroplating or sputtering.

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 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. 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. 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.

Electronics
=============
Electronics is the largest use of ruthenium. Ru metal is particularly
nonvolatile, which is advantageous in microelectronic devices. Ru and
its main oxide RuO2 have comparable electrical resistivities. Copper
can be directly electroplated onto ruthenium, particular applications
include barrier layers, transistor gates, and interconnects. Ru films
can be deposited by chemical vapor deposition using volatile complexes
such as ruthenium tetroxide and the organoruthenium compound
(cyclohexadiene)Ru(CO)3.

Catalysis
===========
Many ruthenium-containing compounds exhibit useful catalytic
properties. 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 similar reactivity but are only
used on small-scale. The Grubbs' catalysts for example have been
employed in the preparation of drugs and advanced materials.

Some ruthenium complexes are highly active catalysts for transfer
hydrogenations (sometimes referred to as "borrowing hydrogen"
reactions). Chiral ruthenium complexes, introduced by Ryoji Noyori,
are employed for the enantioselective hydrogenation of ketones,
aldehydes, and imines. A typical catalyst is (cymene)Ru(S,S-TsDPEN): A
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
synthesis.

Emerging applications
=======================
Ruthenium-based compounds are components of dye-sensitized solar
cells, which are proposed as low-cost solar cell system.

Health effects
======================================================================
Little is known about the health effects of ruthenium and it is
relatively rare for people to encounter ruthenium compounds. Metallic
ruthenium is inert (is not chemically reactive). Some compounds such
as ruthenium tetroxide (RuO4) are highly toxic and volatile.

See also
======================================================================
* Airborne radioactivity increase in Europe in autumn 2017

External links
======================================================================
* [http://www.periodicvideos.com/videos/044.htm Ruthenium] at 'The
Periodic Table of Videos' (University of Nottingham)
*
[http://www.brightsurf.com/news/headlines/32014/Nano-layer_of_ruthenium_stabilizes_magnetic_sensors.html
Nano-layer of ruthenium stabilizes magnetic sensors]

License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL: http://creativecommons.org/licenses/by-sa/3.0/
Original Article: http://en.wikipedia.org/wiki/Ruthenium