Using SHELXL, restraints can be applied to symmetry equivalent atoms
so one can easily restrain the sulphate to be a regular tetrahedron by
restraining the S-O distances to be equal and the O1..O2, O1'..O2 etc.
distances to be equal (with or without target values). For details of
a similar example see Acta Cryst. A64 (2008) 112-122. From Eleanor's
comment it appears that REFMAC can now do this too, though I was not
aware of the facility. If you then wish to refine S anisotropically
SHELXL will also automatically generate and apply the constraints
required for the special position (in any space group), this can be
very useful for high-resolution refinements.
George
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
On Fri, 11 Jan 2008, Charlie Bond wrote:
> Eleanor Dodson wrote:
> > It should be more or less equivalent, but better I think to put 1S at
> > 0.5 occ and 2O at occ = 1
> >
> > At least in REFMAC the restraints to the symmetry atoms should be set up
>
> But if you do that, some of the bond angles will be unrestrained, won't
> they?: O1-S-O2 will be OK, but O1-S-O1' and O2-S-O2' will not. Or is
> refmac cleverer than I think?
>
> 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
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> +61 8 6488 4406
>
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