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The Cobalt Group Metals and their Applications

Lori A. Watson

Department of Chemistry, Indiana University, Bloomington, IN 47405

c430: Inorganic Chemistry

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The Cobalt group

Oxidation states can range from +5 to -1 Rich coordination and organometallic chemistry is

known Used in industrial, catalytic, and biological chemistryThe

Cobalt Group

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All about Cobalt From the German word for goblin or evil spirit: kobald (Co

was thought to be dangerous to silver ores) and the Greek word for mine: cobalos

Discovered by Georg Brandt, a Swedish chemist, in 1739 while he was trying to prove that the blue color in glass was not due to Bismuth.

Ores are present in Zaire, Morocco and Canada. Co is recovered as a byproduct of refining nickel, silver, lead, copper, and iron.

Co is relatively inexpensive (about $10/g). Cobalt-60, a gamma source, is used to treat some cancers. Co is widely used to form alloys, such as Alnico (made of aluminum, nickel, and cobalt used to make powerful permanent magnets.)

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Some colorful uses of cobalt

Cobalt blue, first used as a pigment to color glass, has been known since the Middle Ages.

In 1803, the Minister of the French government appointed a commission to improve artist’s colors; an improved formulation for Cobalt blue, and additional Co based pigements, were the result.

“A modern, improved blue.”“A good substitution for ultramarine blue for painting skies.”

--John J. Varley, “List of Colours,” 1816

CoO·Al2O3 CoO·ZnO Co3(PO4)2 K3[Co(NO2)6]·H2O

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The role of Co in Vitamin B-12

Cobalt containing vitamin B-12, cobolamin, is needed in the manufacture of red blood cells, among other biological processes.

Symptoms of deficiency include a sore tongue, weakness, and fatigue. Severe deficiency may result in pernicious anemia, which is fatal. Excessive alcohol intake impairs the absorption of this vitamin.

Vitamin B-12 is present in liver, muscle meat, shellfish, eggs, cheese, and fish. Marmite (English) and Vegemite (Australian), dark brown-colored “savory” spreads made from the yeast by-product of the brewing industry, are good sources of B12.

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The role of Co in Vitamin B-12: cont.

The crystal structure (1950’s and early 1960’s) was the first determination of the structure of a metalloenzyme.

The independent synthesis took 11 years, and involved 90 separate reactions performed by over 100 people. Information about how to create stereoselective reactions led to the Woodward-Hoffman rules. In total, 3 Nobel prizes in chemistry and one in medicine resulted from B-12.The core of the B-12 molecule is a cobalt containing corrin ring, consisting of 4 pyrrole subunits.

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All about Rhodium

From the Greek word for rose: rhodon Discovered by William Wollaston, a British chemist, in 1803

after removing platinum and palladium from ores. The dark red powder he isolated was a rhodium chloride.

Ores are present in South America, the Ural mountains, and Canada. Rh is recovered as a byproduct of refining platinum.

Rh is expensive (about $500/g). Used to make electrical contacts,

jewelry, catalytic converters, and alloys with platinum and palladium that make furnace coils, spark plugs, and laboratory crucibles. Rh compounds are also used as catalysts for a variety of industrial processes.

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Rh—Making your car cleaner

Catalytic converters reduce car emissions.

Metal catalysts are placed on honeycomb supports to increase the surface area exposed. In a typical converter, the area exposed to the exhaust stream is about the same as two football fields.

The reduction catalyst is a rhodium alloy with platinum and reduces NOx emissions

2NO N2 + O2

2NO2 N2 + 2O2

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All about Iridium

From the Latin word for rainbow: iris Discovered by Smithson Tennant, a British chemist, in

1803 after removing platinum from ores. Ir is silver white, but its salts are highly colored.

Ir is recovered as a byproduct of refining nickel and in platinum ores. It is expensive (about $500/g).

It is the most corrosion resistant metal known. Ir was used to make the standard meter bar of Paris (a 90:10, Pt:Ir alloy), which was the fundamental unit of length for a century. Used primarily as a hardening agent for platinum, Pt/Ir alloys are used for crucibles and high temperature applications. Os/Ir alloys are used for the tips of fountain pens and compasses.

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Proving where the dinosaurs went

Scientists argued that Ir-enriched K-T boundary was caused by the impact of a giant asteroid (~10 km) that put enough dust into the upper atmosphere to darken and cool the Earth for several years.

This would shut off photosynthesis, with the resulting collapse of the global food chain. As a result nothing larger than 25 kg survived the boundary.

Gubbio, Umbria, Italy

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Another view…

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Conclusions

Elements in the cobalt group have a rich chemistry, with many industrial and catalytic applications

Cobalt, in addition to being used for alloys, provides the basis of several common pigments and is necessary for human life.

Rhodium is also alloyed with other metals for a wide variety of applications, including emission control in automobiles.

Iridium, the most corrosive-resistant element known, is used as a hardening agent in metal alloys. Its presence in the K-T boundary helped confirm the impact of an asteroid that probably resulted in the extinction of the dinosaurs.