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" <[email protected]>: > 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: [email protected] > > ******************************************* > > 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 > [email protected] > -- Dr. Stephen Sin-Yin Chui (徐先賢) Assistant Professor, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China. Tel: 22415814 (Office), 22415818 (X-ray Diffraction Laboratory)
