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Re: [sdpd] Seminars raining about SDPD

>This is an interesting point - are you sure your database
>of structures solved from Powder diffraction is up to date
>and might not be missing some organic style journals?

For the SDPD Database, bibliography is verified once each year
by using the ISI Current Contents CD-ROM (annual) with
appropriate keywords. Of course papers not listed by ISI are missing,
and some listed ones may escape to the screening. But I would say
that the list of references is probably complete at >80% up to
the end of 1999. You will have to wait for February 2001 for a
longer list of papers published in the year 2000.

>When you compare the graph at:
>   http://www.cristal.org/iniref.html 
>
>With the numbers of structures submitted into the
>Cambridge database:
>   http://www.ccdc.cam.ac.uk/about/annrep99/Report.html
>
>There does seem to be a miss-match here.

Why ? The continuous increase in the CSD database
will be reflected in the SDPD one only when organic
chemists will really add powder diffraction to the list
of their analysis methods. Up to now, published structures
really determined from powder diffraction data are 
mainly inorganic ones. In my University, there are many
organic chemistry laboratories. Sometimes researchers in these
labs are interested in determining a crystal structure and they
come with a single crystal in an inorganic chemistry lab (the
lab in which I have a desk...), but never, never they think
to come with a powder, and they even think less to buy
a powder diffractometer... Is that not a mondial
phenomenon ? Powder diffraction is simply not in the
majority of the organician minds. We need > 10 years for
changing that. This will need more than 400 structures in the
SDPD Database, of which <100 are inorganic ones. Almost
nothing. Our specialty is quite beautiful but too small and
anecdotal... 

>One point is whether the literature is missing a big
>proportion of structures that don't make it to press?

A point hard to give an answer. But probably yes, many big
(pharmaceutical) companies are determining exactly
the same structures and never publish them. This may change
with patent problems due to the lack of characterization of
polymorphs ;-).

>   http://srs.dl.ac.uk/xrd/9.8/
>
>   82 publications so far in 3.5 years (35 publications in 1999)
>   But is is estimated by Simon Teat that the Bruker CCD on 9.8
>    has solved around 1000 to 1500 structures in its
>    so far quite recent history.

This may explain the stabilization at 50 SDPDs per year...
The size of usable single crystals has decreased. And it is
so easier to determine a structure from single crystal data.
Remember the SDPD Round Robin : a small crystal of 
tetracycline hydrochloride was taken from the powder and
mounted on the 9.8 diffractometer. I would say that all the
Round Robin participants would have easily determine
the structure from the single crystal data (push the TREF
button in SHELXS...), but only 2 of them could solve the
structure from the powder diffraction data (2nd generation
synchrotron powder data).

Anyway, the SDPD database excludes studies from any single
crystal data, even from very small crystals ;-). And we have
already discussed why people would still use powders in spite
of having crystals as large as 20 microns. 

>Minor self citation alert:  
>  Notes for the Bayreuth Powder Diffraction Workshop are
>   on-line:
>   Freely Available Software tools to aid in Structure Solution 
>   from Powder Diffraction
>     http://www.ccp14.ac.uk/poster-talks/powd2000/ 

Can we expect from the 134 participants to the Bayreuth workshop
at least one SDPD per year after the workshop end ? This would be
a success proof.

>Though before you can solve with all these new 
>solution tools - you still have to index and 
>assign a cell - or is this still considered an
>after-thought?

Certainly not, this should be considered as of primary importance.
But the Bayreuth workshop focuses on the two last steps in the
SDPD sequence, solving and refining... Nothing about what has
to be done before.

Best,

Armel Le Bail
http://www.cristal.org/course/


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