Hi Charlie,
Maybe it is not P43.
What about your real symmetry being lower than tetragonal? (For
example, twinning in an orthorhombic space group with a more or less
equal to b)
What about the h00 reflections? Any trend there?
Signs of pseudo-translation?
Roberto
On 4 Oct 2007, at 04:40, Charlie Bond wrote:
Hi All,
I'm trying to understand what's going on in one of our crystals:
Merging and sysabs clearly indicate P42212. Looking at the
intensities, 00l=2n are absolutely clearly present and are not
systematically weaker than 004n.
Intensity stats show clear signs of twinning. The structure can be
solved and refined in P43212 (and not in any P4,P41,P42
spacegroup), although refining in P43 with twice as many molecules
and a h,-k,-l twin fraction of 0.48 produces a better R-factor
(0.24 vs 0.30 - still high as I'd expect 0.1-0.15 based on other
crystal forms).
What I cannot understand is how we see 00l=2n reflections for a
structure that is apparently P43.
Any explanation of this phenomenon and why it may contribute to the
R-factor not going down despite excellent, informative, atomic
electron density would be gratefully received.
Cheers,
Charlie
--
Charlie Bond
Professorial Fellow
University of Western Australia
School of Biomedical, Biomolecular and Chemical Sciences
M310
35 Stirling Highway
Crawley WA 6009
Australia
[EMAIL PROTECTED]
+61 8 6488 4406
---
Dr. Roberto Steiner
Randall Division of Cell and Molecular Biophysics
New Hunt's House
King's College London
Guy's Campus
London, SE1 1UL
Phone +44 (0)20-7848-8216
Fax +44 (0)20-7848-6435
e-mail [EMAIL PROTECTED]
