Metal Clusters in Minerals?

Metal cluster chemistry constitues a fascinating area of inorganic chemistry that I have recently found to be extremely fascinating. I'm wondering if any metal clusters or even metal-to-metal bonds are found to naturally occur as minerals. If there are any, how are they formed in their respective environments?

[www.mindat.org]
Tillmannsite has an Ag3Hg cluster.
Metal-metal bonds occur in lots of elements, sulphides and sulphosalts.

Jeremy....this has nothing to do with your question....I'm certainly NOT qualified to attempt an answer....I just wanted to say that it's GOOD to see your name on posts again......whereyabeen??!!?

Don S.



Edited 1 time(s). Last edit at 03/18/2010 09:39PM by Don Saathoff.

Hi Don,

It's been a while since I've last posted.I've been pretty busy with college in general. Sadly, I haven't been out much to collect in quite a while and I've had to put my hobby mostly on hold.

I've never heard of Tillmannsite, but it's certainly an interesting species! It definitely makes sense that metal-metal bonds and clusters would occur in sulfides and sulfosalts, and of course, they are abundant in native elements like gold, copper and silver. Non-sulfosalt and sulfide species containing clusters are especially interesting to me though. They seem to be quite uncommon.

The Bohemia gold mine in Oregon has some deep hydrothermal volcanic veins that contain, pyrite, lead, gold, silver, copper,zinc, arsenic, quartz, and a few others I don't remember. The veinso formed on the edge of a large calders that doesnt exist anymore. The rim of the old caldera is at about 5000 ft and has a creek running throught the middle. There are cross sections of the heavy hydrothermal vein that cut through a few of the rim walls. Solid chuncks of metal heavily oxidized on the outside can be found in the mine dumps from the main gold mine called the Musick mine in the Bohemia District, Oregon. the site is open during the summer for anyone.

Ariel

Jeremy - there are many metal-rich sulfides etc that have an anomalously low apparent valence for the metal if you assume that "sulfide" = S^2- and "arsenide" = As^3-, etc. Some "normal"-looking ones are also not so normal in reality,

Quick examples:

The pentlandite group, e.g. (Fe,Ni)₉S₈, contains a cube-shaped cluster of 8 metals and one that is not clustered per formula unit.

Millerite, NiS, actually has triangular Ni₃ clusters, and domeykite, Cu₃As, is actually [Cu₄]₃As₄, with Cu₄ tetrahedra.

Conversely, S, As and so on often form polyanions, with anion-anion bonding. The pyrite and marcasite groups both have dimeric [S₂]_2- etc, and skutterudite, CoAs₃, is actually Co₄[As₄]₃, with As₄ squares.

Enjoy!

Do any of these have interesting magnetic ordering? I'd imagine many of these metal clusters would show "d orbital aromaticity" in many cases! I wonder if the clusters can work as catalysts in organic reactions happening at the biological-geological interface...

What exactly do you mean with "d orbital aromaticity" ?

Aromaticity is a property of polyatomic molecules, or of polyatomic functional groups within a larger molecule. It is a resonance phenomenon and thus, involves at least two orbitals. It therefore cannot be a property of isolated atomic orbitals.

Peter,

I think Jeremy means that the aromaticity in aromatic organic compounds involves electron sharing through 'overlap' of pi orbitals (p electrons) between adjacent atoms, and that an analogous electon sharing may be occurring through 'overlap' of the d orbitals with some of these metal clusters.

Tim

Timothy, you're spot on as to where I'm getting at. Electron sharing and orbital overlap can occur with hybrid d orbitals similar to what happens in conjugated organic molecules. This is not technically sensu stricto aromaticity, but is mechanistically alike. Many 'aromatic' cluster compounds in synthetic chemistry have been observed. I was wondering if similar naturally occurring compounds existing as mineral phases can be found.