Imperial College London

Henry Rzepa

I am completing my survey of the
[vote](http://yearinreview.cenmag.org/molecules-of-the-year/) for
molecule of the year candidates, which this year seems focused on
chemical records of one type or another.

The first article\[cite\]10.1002/chem.201601916\[/cite\] reports
striving towards creating a molecule covering a complete column of the
period table. In this case, group 7, containing N, P, As, Sb, Bi and
Mc. Only the first four of these were incorporated, although the
prospects of extending this to five seem good (and to six extremely
unlikely).  The structure of this pnictogen chain is referenced here:
DOI:
[10.5517/CCDC.CSD.CC1LHPJ9](http://doi.org/10.5517/CCDC.CSD.CC1LHPJ9) and
I have demurred from a calculation.

The second article\[cite\]10.1021/jacs.6b02590\[/cite\] relates to what
might be called hypercoordination, and the achievement of what is felt
is a maximum value of 16 to a single metal. I thought I might approach
this one by searching the Cambridge structure database (CSD) by
specifying **any metal with a coordination number 16** as the search
query. However, I was foiled in this query because the search software
(Conquest) allows a maximum value of only 15! So instead I list the
total number of hits retrieved for coordination numbers
of 10-15:** 25224, 4753, 8856, 2492, 839, 348** respectively.  

These totals have to be taken with some caution; the coordination number
of what may often be very weak interactions may be often determined by
human chemical perception rather than hard and fast rules. Nevertheless,
the assignment of 348 molecules to having a coordination number of 15 is
still a remarkably high number. If I can persuade CCDC to allow searches
with 16, who knows what other candidates might emerge to rival this one,
DOI: [CCDC.CSD.CC1KFCQ2](https://doi.org/10.5517/CCDC.CSD.CC1KFCQ2)

The final candidate\[cite\]10.1039/C6SC01726F\[/cite\] is the only one
where no measured coordinates are reported, with the title "Preparation
of an ion with the highest calculated proton
affinity: *ortho*-diethynylbenzene dianion". There high level
theoretical and computational modelling is reported to which I cannot
add anything useful.

The common theme emerging of my review is that most of the candidates
have crystal structures to which I have been able to occasionally add
some computed quantum mechanical properties to try to tease out some
other aspects of their character. It is also nice to be able to cite a
persistent identifier (DOI) that leads directly to the 3D coordinates
for the structures. My [first ever
post](http://www.ch.imperial.ac.uk/rzepa/blog/?m=200804) to this blog in
2008 addressed one solution on how such immediacy might be achieved and
it is nice to see this now as a mainstream aspect of chemical
publishing.

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I am completing my survey of the vote for molecule of the year candidates, which this year seems focused on chemical records of one type or another. The first article[cite]10.1002/chem.201601916[/cite] reports striving towards creating a molecule covering a complete column of the period table.

Messaggi di Rogue Scholar

Molecules of the year? Pnictogen chains and 16 coordinate Cs.