Dear JPK,
I think the coordination geometry of Na is a key, normally it adopts octahedral
geometry with Na---O distances of 2.1-2.2 ang, whereas water molecule is
h-bonded with H-acceptor or H-donor with the distances between 2.6-3.3 ang.
I am not sure it is correct, as i used to be small-molecule X-ray worker.
stephen
Quoting "Steiner, Roberto" <[log in to unmask]>:
> Bond valence sum
>
> Muller et al. Acta Cryst. (2003). D59, 32-37 if the resolution is good
> (better than 1.8 A)
>
>
> R
>
> On 16 Nov 2011, at 18:20, Jacob Keller wrote:
>
> > Dear Crystallographers,
> >
> > I have crystals containing 666mM NH4 and 540mM Na, and there appears
> > to be a "water" which is only about 2.2 Ang from some polar atoms. It
> > is currently reasonably happy as a Na, but is there any reasonable way
> > to decide which cation is there?
> >
> > JPK
> >
> > --
> > *******************************************
> > Jacob Pearson Keller
> > Northwestern University
> > Medical Scientist Training Program
> > email: [log in to unmask]
> > *******************************************
>
> Roberto Steiner, PhD
> Randall Division of Cell and Molecular Biophysics Group Leader
> King's College London
>
> Room 3.10A
> New Hunt's House
> Guy's Campus
> SE1 1UL, London, UK
> Tel 0044-20-78488216
> Fax 0044-20-78486435
> [log in to unmask]
>
--
Dr. Stephen Sin-Yin Chui (®}¥ý½å)
Assistant Professor,
Department of Chemistry,
The University of Hong Kong, Pokfulam Road,
Hong Kong SAR, China.
Tel: 22415814 (Office), 22415818 (X-ray Diffraction Laboratory)
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