High R1 Value and wR2

Please use this forum to post questions on general small molecule X-ray crystallography from theory to practical.
vivekanand
Sealed Tube
Posts: 13
Joined: 05 Apr 2017, 10:41

High R1 Value and wR2

Post by vivekanand » 11 Jun 2019, 18:53

Hello everyone, I have a crystal data in which everythings seems to be fine but still observing high R1 and wR2. I have tried to check spacegroup error through platon but suggesting that no need to change space group (P21/c). It contains two units of same molecule. The parameters are R1 = 20.28, wR2 = 56.15, I/sigma = 13.5, Rint = 10.95, Max. peak = 1.8, GooF = 1.059, d min (Mo) = 0.75. There is no metal atoms present in it. Kindly suggest the possible reason to this proble. Thanks a lot.

User avatar
markoru
Sealed Tube With Optics
Posts: 66
Joined: 03 Oct 2010, 19:22

Re: High R1 Value and wR2

Post by markoru » 11 Jun 2019, 19:52

Well, I'd disagree that "everything is fine with the crystal data", as you have quite large Rint (11%, compared to 2-4% which I find in most datasets). Also, I'd prefer I/sigma > 20. So, with information available, I think that problem may be in low quality data. What is the diffraction limit of the dataset?

User avatar
Helge
Rotating Anode With Optics
Posts: 255
Joined: 26 Jan 2012, 16:04

Re: High R1 Value and wR2

Post by Helge » 13 Jun 2019, 13:30

What markoru means with his last question: At which resolution does the crystal stop to diffract? I would be very surprised indeed if the crystal diffracted to 0.75 Angstroem with light atoms only. If you have access to either the raw data of XPrep then check where the average I/sigma value drops below 4 (or 2, depending on what you are used to; I believe that a shell with an average I/sigma of below 4 is mostly noise, others put that limit at 2) and cut the data there. I would check the raw data anyway; Perhaps cutting off the noise does the job already, but an Rint of 11% speaks for something being wrong other than including noise shells.

vivekanand
Sealed Tube
Posts: 13
Joined: 05 Apr 2017, 10:41

Re: High R1 Value and wR2

Post by vivekanand » 13 Jun 2019, 17:13

Hello Markoru and Helge. I don't have a fundamental understanding of the various terms but as the discussion proceeds, I conclude that the diffraction limit of the dataset is related to I/sigma value? Please correct me if I am wrong. Also, suggest how to know the diffraction limit of the dataset and what exactly it means? Is any other possible source of errors? Thank you all for your valuable suggestions and time. :)

dkratzert
Rotating Anode
Posts: 125
Joined: 08 Mar 2011, 22:50

Re: High R1 Value and wR2

Post by dkratzert » 13 Jun 2019, 17:23

Hi,

I think Peter Müller gave a good overall explanation about your questions in this publication:

http://web.mit.edu/pmueller/www/own_pap ... stions.pdf

Regards
Daniel

User avatar
Helge
Rotating Anode With Optics
Posts: 255
Joined: 26 Jan 2012, 16:04

Re: High R1 Value and wR2

Post by Helge » 14 Jun 2019, 10:00

Except that particular problem, as I gather from reading the document (a very good one to read, nonetheless! I have downloaded it myself).

When you collect data then at the end of the data reduction you should get a table which looks something like the table in the middle of this post. In XPrep, option S (Display Intensity Statistics), any suboption you will get a similar table. There you can see at which resolution there is only noise measured.

Return to “General SMX”