ON H...H DISTANCES AND THE VANDERWAALS RADIUS OF HYDROGEN IN INORGANIC AND ORGANIC-COMPOUNDS

The short H...H contacts of the head-to-side type of about 2.05 angstrom described recently as having been found in carbohydrates [Steiner & Saenger (1991). Acta Cryst. B47, 1022-1023] complement nicely the observations on inorganic hydroxides and hydrates, which led to a revision of the van der Waals radius of hydrogen to 1.0 angstrom [Baur (1972). Acta Cryst. B28, 1456-1465]. For the case of side-to-side contacts a different behaviour is diagnosed for organic and inorganic crystal structures: side-on contacts in inorganic compounds can be shorter than the head-on contacts are, while in organic compounds the opposite is true.