W0089

A Comparison of Transition Metal-Bound Halogens as Hydrogen Bond Acceptors. Eric A. Bruton, and Lee Brammer, Dept. of Chemistry, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121-4499

Hydrogen bonds comprised of transition metal-bound halogens as the acceptor and C-H, N-H, and O-H donors were studied using the Cambridge Structural Database. A comparison of the normalized H^ÖX distance and the normalized Y-H^ÖX and H^ÖX-M angles will be discussed for both single and bifurcated H-bonds, where X = F, Cl, Br, or I and Y = C, N, or O. The distances were normalized with a spatial correction in order to make a semi-direct comparison between the different halogens. The two angles were normalized using a conical correction.

In previous work M-Cl as an H-bond acceptor was compared to C-Cl and Cl^- acceptors. It was seen that the M-Cl is a much better acceptor than the C-Cl acceptor due most likely to the polarity of M-Cl bond being much greater. The trends that were observed for the different halogens, with respect to the normalized H^ÖX distance, again reflects that the more polar X-M bonds have shorter H^ÖX distances. The mean normalized Y-H^ÖX and H^ÖX-M angles will be discussed in terms of the X-M polarity and the hybridization of the halogen X. The differences observed between the single and bifurcated H-bonds are as would be expected. The mean H^ÖX bond distances for the bifurcated cases are longer than the single cases. The two normalized angles are smaller in most cases for the bifurcated case than the single cases.

These results are consistent with an electrostatic model for H-bonds. The observations here are now being applied in the area of supramolecular inorganic chemistry.