Same question as usual from me...what is the challenge? Structures and images? Colored curves? What?

When you post these can define the explicit challenge you are pointing to? I like reading the post but an generally confused about what the challenges are that you are pointing to. Thanks

Antony, thanks for the question. The question I pose with this item is: how would your cheminformatics tool of choice represent the metallocene moiety in the structure on the left?

It's easy to think of metallocenes as something only organometallic chemists work with, and therefore not relevant to mainstream cheminformatics. However, this example, like the numerous examples posted before it in this series, come from journals used by organic and medicinal chemists.

I try to indicate the challenge by the tags I give these little items: this one is tagged with 'metallocene', for example.

Metallocenes were once exotic, but no longer.

Now I understand the question you might want to take a look this technical note for ACD/ChemSketch that Iw as involved with two years ago..does this address the question?

http://www.acdlabs.com/download/technotes/80/draw_db/organometallic.pdf

Antony, thanks for the link. The document offers an interesting discussion of how chemists can use structure editors (with more or less accuracy) to depict organometallics such as metallocenes.

The problem is that the underlying data formats and software generally have no notion of this kind of bonding. Until that changes, chemists will be left to their own devices and databases will continue to accumulate entries like these.