the checkCIF file of one of my compounds is showing an alert PLAT220_ALERT_2_CLarge Non-Solvent C Ueq(max)/Ueq(min) Range 3.4 Ratio. I would like to know whether this is ignorable. If it has to be solved please help me for the same
Hi, Sarah! It is fairly common to get one or more Level C alert(s), especially for certain types of compounds. In essence, this means that you should check your crystal structure solution to make sure that you have not made a mistake in your refinement. If everything checks out, I would go ahead anyway, since the ratio of 3.4 is not particularly high. Is this the only error alert you got?
Regards,
Daniel
Hi Daniel Lundberg,
Thank you for the reply. For one of the compounds this was the only error found in C level. But for another compound more errors in addition to PLAT220_ALERT were found like PLAT147, 148,222,242,245,250,331,340 and 911. I am new to this field and hardly know how to rectify the errors.If you can suggest any good reference for this it will be very helpful for me.
Hi again, Sarah!
As a general remark, Level C errors are "okay" but one should always check to see if they arise from some sort of (simple) mistake. Some can be corrected and some not, but the structure can still be correct.
Once you have run CheckCIF, the report created includes hyperlinks (web links) to a short description of the error. The link to the PLAT147 error, for instance, tells you "su on symmetry restricted cell angle". This means that the estimated standard deviations (esd) on the cell angles that by definition are 90 or 120 degrees are not set to zero. The IUCr link below gives a full list of all the tests currently run by CheckCIF and their brief explanation. For a more detailed description of how to fix certain errors, it may be necessary to see the structure refinement files.
If you use SHELX as your refinement program, I can highly recommend the book "Crystal Structure Refinement - A Crystallographer's Guide to SHELXL". It serves both as a tutorial as well as a dictionary on how to use the program and solve structures. It costs 67 UKP straight from the publisher (Oxford University Press, catalogue link below). If you are wondering what it looks like, the publisher offers the chapter on disorder as a free sample (available on their homepage).
I hope this helps.
Regards,
Daniel
http://journals.iucr.org/services/cif/datavalidation.html
http://ukcatalogue.oup.com/product/9780198570769.do
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