E0015
What is a Routine Crystal Structure
Determination? A.L.Spek, Utrecht University, 3584 CH Utrecht,
The Netherlands
Really routine crystal structures can be
determined nowadays by experts on a one-hour basis or often less, given
access to a state-of-the-art CCD-detector based diffractometer system.
For one, we have solved structures from 10 minute KappaCCD/rotating
anode datasets.
However, contrary to what some vendors claim,
the real world problem is that many samples made available for
structural analysis are far from standard; at least not within our
National facility for single crystal structure determination (e.g.
poorly reflecting, small, twinned, disorder, losing solvent etc.).
Fact is that there are many pitfalls on the
road to a reliable structure determination suitable for publication.
The catch is that one needs to be an experienced crystallographer to
recognize possible trouble.
Unfortunately, the literature is contaminated
with publications of false structural results due to the fact that all
warning signals were ignored.
Disorder can be real or an artifact. Atoms can
be assigned the wrong element type. The space group assigned may be
wrong. Essential hydrogen atoms may have been missed resulting in false
conclusions about the chemistry.
Tools are now under development aiming at the
automated analysis of the results of a crystal structure determination
(at least generating warning signals).
A large number of tests have now been
implemented in the checking/validation software that is run routinely
for structures submitted for publication in Acta Cryst.
This talk will present a few interesting
non-standard structures/problems and their solution from the over 2000
structures we studied.