RE: [sdpd] XRDU:RIET: Review references for refining structures in too high a symmetry?

[Armel Le Bail <alb...@cristal.org>]

 >Other papers similar to the situation in the ACA 2004 abstract of
 >Clearfield, Bestaoui, Ouyang, Fredoueil, Bujoli appreciated.
 >
 >"Crystal Structure of Cd3(O3PC2H4CO2)2.2H2O : Influence of the Solid
 >State NMR in the Structure Determination"
 > http://www.hwi.buffalo.edu/ACA/ACA04/abstracts/text/W0313.pdf
 >
 >Lachlan

In the abstract, one can find :
"The systematic absences were consistent with P21 /c and P21"

Is there not a typo ? This would be understandable if the statement
was instead :
"The systematic absences were consistent with P21 /m and P21"

Because there is not any consistency between the systematic absences
of the P21 /c and P21 spacegroups...

So, if there was a typo, this is just the presence or not of an
inversion center which is in question.

If there is not a typo, then this would mean that the h0l with l=2n+1
which are unambiguous (with no overlapping) on the powder
pattern have zero intensity, explaining that first choice of the P21/c
space group. But, when selecting P21, it would be surprising if
all h0l with l=2n+1 wero fortuitously null.

In that later explanation telling that :
"The systematic absences were consistent with P21 /c and P21"
is too short (would need more explanation) and remains a nonsense.

Armel




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