Next: d. Stereoviews Up: 3. Molecular Dimensions Previous: b. Torsion angles
Hydrogen bonds X--HY are 2.38 to 3.20 Å with the proviso that the HY distance should generally be 2.2 Å or less. The X--HY angle is usually 150-180. Symmetrical OHO hydrogen bonds are very strong and are approximately 2.38 Å long (OO distance).
Van der Waals contacts may be represented by considering van der Waals radii for each atom. These are listed by Pauling in `The Nature of the Chemical Bond'. H 1.2 Å, C 1.7, N 1.5, O 1.4, P 1.9, S 1.85, F 1.35, Cl 1.8, Br 1.95, I 2.15. Half-thickness of aromatic molecule is 1.85 Å. Radius of methyl group CH3 2.0 Å.
Metal coordination . Metal ions tend to gather negatively charged groups, e.g. the oxygen atoms of carboxylate ions, around them. Distances are shorter than van der Waals distances. The values depend on the number of surrounding oxygen atoms. Li+O 2.0 Na+O 2.4 K+O 2.8-2.9 NH+4O 3.0 Mg2+O 2.1 Ca2+O 2.4-2.5 Zn2+O 2.0-2.2 Mn2+O 2.2 Å.
Copyright © 1984, 1997 International Union of CrystallographyIUCr Webmaster