Introduction group VIIIB

Group VIIIB includes following elements: Iron - [Fe], Ruthenium - [Ru], Osmium - [Os], Cobalt - [Co], Rhodium - [Rh], Iridium - [Ir], Nickel - [Ni], Palladium - [Pd], Platinum - [Pt].

Iron. Ruthenium. Osmium.

The nine elements: Fe, Ru, Os; Co, Rh, Ir; Ni, Pd and Pt, together formed Group VIII of Mendeleev’s periodic table. They will be treated, like the other transition elements, in “vertical” triads, but because of the marked “horizontal” similarities it is not uncommon for Fe, Co and Ni to be distinguished from the other six elements (known collectively as the “platinum” metals) and the two sets of elements considered separately.

The triad Fe, Ru and Os is dominated, as indeed is the whole block of transition elements, by the immense importance of iron. This element has been known since prehistoric times and no other metal has played a more important role in man’s material progress. Iron beads dating from around 4000 BC were no doubt of meteoric origin, and later samples, produced by reducing iron ore with charcoal, were not cast because adequate temperatures were not attainable without the use of some form of bellows. Instead, the spongy material produced by low-temperature reduction would have had to be shaped by prolonged hammering. It seems that iron was first smelted by the Hittites in Asia Minor sometime in the third millennium BC, but the value of the process was so great that its secret was carefully guarded and it was only with the eventual fall of the Hittite empire around 1200 BC that the knowledge was dispersed and the “Iron Age” began. In more recent times the introduction of coke as the reductant had farreaching effects, and was one of the major factors in the initiation of the Industrial Revolution. The name “iron” is Anglo-Saxon in origin (iren, cf. German Eisen). The symbol Fe and words such as “ferrous” derive from the Latin ferrum, iron.

Biologically, iron plays crucial roles in the transport and storage of oxygen and also in electron transport, and it is safe to say that, with only a few possible exceptions in the bacterial world, there would be no life without iron. Again, within the last forty years or so, the already rich organometallic chemistry of iron has been enormously expanded, and work in the whole field given an added impetus by the discovery and characterization of ferrocene.

Ruthenium and osmium, though interesting and useful, are in no way comparable with iron and are relative newcomers. They were discovered independently in the residues left after crude platinum had been dissolved in aqua regia; ruthenium in 1844 from ores from the Urals by K. Klaus who named it after Ruthenia, the Latin name for Russia; and osmium in 1803 by S. Tennant who named it from the Greek word for odour (Greek-osme) because of the characteristic and pungent smell of the volatile oxide, OsO4.

Cobalt. Rhodium. Iridium.

Although hardly any metallic cobalt was used until the twentieth century, its ores have been used for thousands of years to impart a blue colour to glass and pottery. It is present in Egyptian pottery dated at around 2600 BC and Iranian glass beads of 2250 BC. The source of the blue colour was recognized in 1735 by the Swedish chemist G. Brandt, who isolated a very impure metal, or “regulus”, which he named “cobalt rex”. In 1780 T. O. Bergman showed this to be a new element. Its name has some resemblance to the Greek word for “mine” but is almost certainly derived from the German word Kobold for “goblin” or “evil spirit”. The miners of northern European countries thought that the spitefulness of such spirits was responsible for ores which, on smelting, not only failed unexpectedly to yield the anticipated metal but also produced highly toxic fumes (As4O6).

In 1803 both rhodium and iridium were discovered, like their preceding neighbours in the periodic table, ruthenium and osmium, in the black residue left after crude platinum had been dissolved in aqua regia. W. H. Wollaston discovered rhodium, naming it after the Greek word “rose” because of the rose-colour commonly found in aqueous solutions of its salts. S. Tennant discovered iridium along with osmium, and named it after the Greek goddess Iris, whose sign was the rainbow, because of the variety of colours of its compounds.

Nickel. Palladium. Platinum.

An alloy of nickel was known in China over 2000 years ago, and Saxon miners were familiar with the reddish-coloured ore, Ni-As, which superficially resembles Cu2O. These miners attributed their inability to extract copper from this source to the work of the devil and named the ore “Kupfernickel” (Old Nick’s copper). In 1751 A. F. Cronstedt isolated an impure metal from some Swedish ores and, identifying it with the metallic component of Kupfernickel, named the new metal “nickel”. In 1804 J. B. Richter produced a much purer sample and so was able to determine its physical properties more accurately.

Impure, native platinum seems to have been used unwittingly by ancient Egyptian craftsmen in place of silver, and was certainly used to make small items of jewellery by the Indians of Ecuador before the Spanish conquest. The introduction of the metal to Europe is a complex and intriguing story. In 1736 A. de Ulloa, a Spanish astronomer and naval officer, observed an unworkable metal, platina (Spanish, little silver), in the gold mines of what is now Colombia. Returning home in 1745 his ship was attacked by privateers and finally captured by the British navy. He was brought to London and his papers confiscated, but was fortunately befriended by members of the Royal Society and was indeed elected to that body in 1746 when his papers were returned. Meanwhile, in 1741, C. Wood brought to England the first samples of the metal and, following the eventual publication of de Ulloa’s report in 1748, investigation of its properties began in England and Sweden. It became known as “white gold” (a term now used to describe an Au-Pd alloy) and the “eighth metal” (the seven metals Au, Ag, Hg, Cu, Fe, Sn and Pb having been known since ancient times). Great difficulty was experienced in working it because of its high melting point and brittle nature (due to impurities of Fe and Cu). Powder metallurgical techniques of fabrication were developed in great secrecy in Spain by the Frenchman P. F. Chabeneau, and subsequently in London by W. H. Wollaston, who in the years 1800-21 produced well over 1 tonne of malleable platinum. These techniques were developed because the chemical methods used to isolate the metal produced an easily powdered spongy precipitate. Not until the availability, half a century later, of furnaces capable of sustaining sufficiently high temperatures was easily workable, fused platinum commercially available.

In 1803, in the course of his study of platinum, Wollaston isolated and identified palladium from the mother liquor remaining after platinum had been precipitated as (NH4)2PtCl6 from its solution in aqua regia. He named it after the newly discovered asteroid, Pallas, itself named after the Greek goddess of wisdom (palladion, of Pallas).