Au-pseudocarbyne – a unusual example of a twelve coordination by carbon.

Derek Lowe tells the story of “carbyne”, a potential further allotrope of carbon, comprising linear chains of carbon atoms, C-C≡C-C≡C-C. Whether such a molecule can exist on its own has long been the the topic of speculation. Now a report has appeared of a “pseudocarbyne”, stabilised by gold atoms.[1]

The now thankfully almost ubiquitous data availability statement includes the DOI: https://doi.org/10.48349/ASU/3TWEI0 [2] as a data repository source of replication data and one of the files found there is a CIF containing the crystal data. Playing with this, I noticed one unusual feature of this structure, which oddly is not apparently mentioned in the article itself and so I thought I would tease it out here – 12 coordination.

Ths simplest unit comprises three eight membered carbon rings, each connected by 4-membered rings to form a local structure with D3h symmetry and hence revealing twelve C-Au bonds of the same length; 2.415Å. Click on the image above to view a 3D model.

A larger section of the (polymeric) structure is shown below, now with D2h symmetry and again with twelve identical C-Au bond lengths

Is such coordination unusual?‡ Well, not for metal clusters, including Au clusters. There are in fact 2014 hits (1985 examples where Y is constrained to be a metal, hence 29 where the central atom is NOT a metal) in the Cambridge crystal structure database for the general search X12Y where X and Y can be any atom, with 244 for X=Au and 576 for X=O but none yet for X=C (the current example has not yet appeared in the distributed database). So certainly Au-pseudocarbyne is a unique and unusual molecule. This also shows that 3D coordinates can always be a useful adjunct to articles to allow quick access for spotting perhaps unexpected features with just a single click!

‡You might be surprised that a similar search finds 138 hits for X14Y and 16 for X16Y

References

  1. J. Wu, P. Tarakeshwar, S.G. Sayres, M. Meneghetti, H. Kim, J. Barreto, and P.R. Buseck, "Crystal structure of Au-pseudocarbyne(C6)", Scientific Reports, vol. 15, 2025. http://dx.doi.org/10.1038/s41598-024-80359-5

This entry was posted on Saturday, February 1st, 2025 at 9:53 am and is filed under Interesting chemistry. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Leave a Reply