regarding Pseudo/New Space-group

[kuldeepmahiya]

Hi all,
A very Good evening. Last weekend I solved a structure in P21/n space group showing two crystallographically independent unit in the asymmetric unit, but the checkcif alert show an A level alert:
PLAT113_ALERT_2_A ADDSYM Suggests Possible Pseudo/New Space-group. C2/c
I tried with ADDSYM-SHX to overcome this problem but the new space group was P21/c and not C2/c. What can I do. Please help.
Thanking You with best regards.
Kuldeep

[markoru]

Hi,

Try to refine structure in a suggested space group. To transform from P21/c to C2/c in WinGX do Model/TRANSFORM and Chose C 2/c Space group in following dialog:

Capture-1.jpg

and press OK. This will generate new.ins and new.hkl files with transformed cell. Open them in a new project and try solving from beginning.

You can also check Wilson plot, or open current structure in Mercury and measure distance between "equivalent" atoms of two "independent" molecules and see if they intercept in a single point.

[Rudi]

Hi all,
I tried with ADDSYM-SHX to overcome this problem but the new space group was P21/c and not C2/c.

That is odd. ADDSYM implemented in checkCIF should suggest the same new space group like ADDSYM in Platon.

Which space group is suggested when you press just ADDSYM instead of ADDSYM-SHX?

[kuldeepmahiya]

Dear sir Rudi,

when I press just ADDSYM instead of ADDSYM-SHX in PLATON, it suggest the same P21/c space group and not C2/c space group.

Thanks with best Regards,
kuldeep

[Rudi]

Are you sure that you read the same CIF into PLATON/ADDSYM as you had read into checkCIF? Maybe files were confused?

[kuldeepmahiya]

Dear sir Rudi,

Yes, both the CIF are same read into PLATON/ADDSYM and read into checkCIF. Also the method suggested by Mr. Markoru did not work. Then I went one step back, I re-reduce the raw data using CrysAlisPro system into C2/c space group. The were two likely niggli cells (P21/n and C2/c). I choose C2/c space group and interestingly it work and the size of .HKL file is reduced to exactly half of the original file. Then I thought it was probably a twin of equal contribution from P21/n and C2/c. Is it ok, Am I right Sir?

Thank you with best Regards,
Kuldeep

[Rudi]

Then I thought it was probably a twin of equal contribution from P21/n and C2/c. Is it ok, Am I right Sir?

No, I think there is no twin where each domain exhibits different space group symmetry. Such would be in fact a conglomerate of two different structures rather than a twin.

I am afraid I am not able to advise further, as I do not know the structure. You may send me your CIF or RES file via private message.

[markoru]

...Then I went one step back, I re-reduce the raw data using CrysAlisPro system into C2/c space group. The were two likely niggli cells (P21/n and C2/c). I choose C2/c space group and interestingly it work and the size of .HKL file is reduced to exactly half of the original file.

Did you try to refine solve/refine structure in C2/c? Does refinement converged to good R-factor in both space groups?