Sciencemadness Discussion Board

Why are Fe/Co/Ni not considered as 'platinum group metals' ?

metalresearcher - 8-9-2010 at 12:10

The nine transition metals
Fe Co Ni
Ru Rh Pd
Os Ir Pt
all have high melting points, are heavy metals (within the period of the PT) have several oxidation states each, form complex compounds like PtCl6 2- or Fe(CN)6 3-.
But the lower three are not PGM's ? Because Fe/Co/Ni are not precious ? That might be the only reason I think.
What are your ideas on this ?

hissingnoise - 8-9-2010 at 12:28

The Six aren't called the inert (Noble) metals for nothing. . .
Compare reactivities?

DDTea - 8-9-2010 at 17:44

I found this bit from wikipedia in the article about Platinum Group Metals:
Quote:
The platinum metals have outstanding catalytic properties. They are highly resistant to wear and tarnish, making platinum, in particular, well suited for fine jewelry. Other distinctive properties include resistance to chemical attack, excellent high-temperature characteristics, and stable electrical properties. All these properties have been exploited for industrial applications.


That doesn't really say much. I suspect the reasons are more subtle and have to do with the electronic structures and geometries of the six heavier metals you listed. If I recall correctly, Fe, Co, Ni cannot adopt D4h geometry (square planar), which is important in certain catalytic cycles.

[Edited on 9-9-10 by DDTea]

DJF90 - 8-9-2010 at 17:48

Actually Nickel can do that with high field ligands like cyanide...

watson.fawkes - 8-9-2010 at 19:04

Quote: Originally posted by metalresearcher  
But the lower three are not PGM's ? Because Fe/Co/Ni are not precious ? That might be the only reason I think.
Those six are six of the nine rarest elements on earth: http://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements. There's something interesting that they also form a group of chemically similar elements, as the electronic properties are not typically thought of as affecting nucleosynthesis.

DDTea - 8-9-2010 at 20:09

Quote: Originally posted by watson.fawkes  
There's something interesting that they also form a group of chemically similar elements, as the electronic properties are not typically thought of as affecting nucleosynthesis.


On an interesting note, all of those elements are characteristic of meteorites.