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Ruthenium
In 1844, a Russian scientist named Karl Ernst Claus isolated six grams of a metal so unreactive that it had fooled the greatest chemists of his era for nearly two decades. Working within the stone walls of Kazan State University, Claus examined the stubborn residue left behind after dissolving crude platinum from the Ural Mountains in aqua regia, a mixture of nitric and hydrochloric acid known for its ability to dissolve almost any metal. While his predecessors, including the Polish chemist Jędrzej Śniadecki who had claimed to find the element in 1807 under the name vestium, and the German chemist Gottfried Osann who had tentatively identified it in 1827, had all failed to prove their findings, Claus succeeded where they had faltered. He demonstrated that the compounds Osann had prepared contained a new metal, distinct from the known platinum group elements. Claus chose to name this new body ruthenium, deriving the name from the Latin word Ruthenia to honor his motherland, Russia. He declared that he had every right to use the name because Osann had relinquished his claim and the word did not yet exist in the chemical lexicon. This act of naming established a precedent that continues to this day, where elements are named after countries, and it marked the first time a transition metal was successfully isolated from the complex residues of platinum processing.
The Anomalous Electron
Ruthenium possesses a unique electronic configuration that defies the standard rules governing the periodic table, creating an anomaly that persists across the entire range of elements from atomic number 41 to 45. While other elements in group 8, such as iron and osmium, possess two electrons in their outermost shell, ruthenium has only one electron in its outermost shell, with the final electron residing in a lower shell. This structural quirk has no effect on the chemical properties of the metal, yet it distinguishes ruthenium from its lighter congener iron and its heavier congener osmium. The element is the only 4d transition metal that can assume the oxidation state of plus eight, although this state is less stable than the corresponding state in osmium. This difference in behavior marks the first group from the left of the table where second and third-row transition metals display notable chemical distinctions. Furthermore, ruthenium is the first element in a downward trend in 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 contribute less to metallic bonding. Despite these complexities, the metal remains hard, white, and unreactive to most chemicals at ambient conditions, only oxidizing when heated and dissolving in fused alkalis to form ruthenates.
Karl Ernst Claus isolated ruthenium in 1844 at Kazan State University. He successfully demonstrated the existence of the new metal after previous chemists failed to prove their findings.
Why is the name ruthenium derived from Ruthenia?
Karl Ernst Claus named the element ruthenium to honor his motherland Russia using the Latin word Ruthenia. He claimed the right to use the name because the word did not exist in the chemical lexicon and his predecessors had relinquished their claims.
What is the half-life of the most stable radioactive isotope ruthenium-106?
The most stable radioactive isotope ruthenium-106 has a half-life of 371.8 days. This isotope is a fission product of uranium or plutonium and was detected in high concentrations in the atmosphere over Europe in 2017.
How much ruthenium was consumed globally in 2016?
Approximately 30.9 tonnes of ruthenium were consumed globally in 2016. Thirteen point eight tonnes were dedicated to electrical applications and 7.7 tonnes were used for catalysis.
Who won the Nobel Prize in Chemistry for developing ruthenium catalysts?
Ruthenium carbene complex inventors and Ryoji Noyori won the Nobel Prize in Chemistry for their work. Noyori received the award in 2001 for his contributions to asymmetric hydrogenation using ruthenium complexes.
What is the primary health risk associated with ruthenium compounds?
Ruthenium tetroxide is a highly toxic volatile compound that can cause severe damage to human health. It acts as an aggressive oxidizing agent that decomposes to form the dioxide above 100 degrees Celsius.
Beneath the surface of stable ruthenium lies a complex world of radioactive isotopes that have occasionally surfaced in global events, most notably during an alleged undeclared nuclear accident in Russia in 2017. Naturally occurring ruthenium is composed of seven stable isotopes, including ruthenium-96 and ruthenium-104, but the element also exists in thirty-four synthetic radioactive forms. The most stable of these radioisotopes is ruthenium-106, which has a half-life of 371.8 days, followed by ruthenium-103 with a half-life of 39.245 days. Ruthenium-106 is a fission product of uranium or plutonium, and high concentrations of this isotope detected in the atmosphere over Europe in 2017 were linked to a potential nuclear incident. The primary decay mode for isotopes lighter than the most abundant isotope, ruthenium-102, is electron capture to produce technetium, while heavier isotopes undergo beta emission to rhodium. These radioactive forms are not merely theoretical constructs; they are produced in significant quantities in nuclear fission and can be chemically separated from spent nuclear fuel. The element's presence in nuclear waste offers a potential source for commercial-scale nuclear transmutation, as ruthenium-100 has a relatively large neutron cross-section and technetium, its decay product, has no stable isotopes, avoiding the problem of neutron activation of stable isotopes.
The Industrial Backbone
Ruthenium serves as the unsung hero of modern electronics, accounting for the majority of global consumption in the form of thick-film resistors and wear-resistant electrical contacts. Approximately 30.9 tonnes of ruthenium were consumed in 2016, with 13.8 tonnes dedicated to electrical applications and 7.7 tonnes to catalysis. The metal is used to harden platinum and palladium alloys, creating thin films that provide the durability required for electrical contacts and electrodes. Ruthenium dioxide, combined with lead and bismuth ruthenates, forms the basis of thick-film chip resistors, which account for 50% of the ruthenium consumed worldwide. In the semiconductor industry, ruthenium has emerged as a critical capping layer for extreme ultraviolet photomasks, enabling the precise lithography required for advanced microelectronic devices. The metal's non-volatile nature makes it particularly advantageous for microelectronic devices, where copper can be directly electroplated onto ruthenium to create barrier layers, transistor gates, and interconnects. Despite its scarcity, with annual production rising from about 19 tonnes in 2009 to 35.5 tonnes in 2017, the metal is essential for the functionality of modern technology, from the fountain pen nibs of the Parker 51, which were tipped with 96.2% ruthenium and 3.8% iridium from 1944 onward, to the complex alloys used in jet engine turbines.
The Catalyst of Life
Ruthenium has revolutionized the field of organic chemistry through its ability to catalyze reactions that were previously impossible or inefficient, earning its inventors the Nobel Prize in Chemistry. The Grubbs' catalyst, a ruthenium carbene complex, is used for alkene metathesis reactions, a process that has been employed in the preparation of drugs and advanced materials. This catalyst, along with others developed by Ryoji Noyori, has enabled the enantioselective hydrogenation of ketones, aldehydes, and imines, earning Noyori the Nobel Prize in 2001 for his contributions to asymmetric hydrogenation. Ruthenium complexes are also used in transfer hydrogenations, sometimes referred to as borrowing hydrogen reactions, and in Fischer-Tropsch synthesis to convert coal and natural gas into liquid fuels. Beyond industrial applications, ruthenium-based compounds are being researched for their potential anticancer properties, with piano-stool ruthenium compounds showing promise to replace current platinum-based anti-tumor drugs. The element's ability to form a variety of coordination complexes, including the luminescent tris(bipyridine)ruthenium(II) chloride, has also found use in optode sensors for oxygen detection and in the fluorescence quenching that allows for the detection of oxygen in biological systems.
The Toxic Shadow
While metallic ruthenium is inert and poses little threat to human health, its volatile compounds, particularly ruthenium tetroxide, are highly toxic and capable of causing severe damage. Ruthenium tetroxide is an aggressive, strong oxidizing agent that can oxidize dilute hydrochloric acid and organic solvents like ethanol at room temperature, and it decomposes to form the dioxide above 100 degrees Celsius. This compound is mostly used as an intermediate in the purification of ruthenium from ores and radiowastes, but its volatility makes it a significant hazard. The metal's ability to expose latent fingerprints by reacting on contact with fatty oils or fats with sebaceous contaminants and producing brown or black ruthenium dioxide pigment has been utilized in criminal justice, yet the same reactivity that makes it useful for detection also makes it dangerous. Ruthenium red, a biological stain used to stain polyanionic molecules such as pectin and nucleic acids for light microscopy and electron microscopy, is another example of the element's dual nature. The beta-decaying isotope ruthenium-106 is used in radiotherapy of eye tumors, mainly melanomas of the uvea, demonstrating how the element's radioactive properties can be harnessed for medical treatment despite the risks associated with its toxicity.