THE CRYSTAL STRUCTURE OF PALLADIUM DIPHENYLGLYOXIME; AN ANALYSIS OF STRONG HYDROGEN BONDS IN PALLADIUM-DIGLYOXIME COMPOUNDS. Ronald F. See, Christopher Curtis and William M. Strub, Department of Chemistry, Saint Louis University, St. Louis, MO 63103, Joseph W. Ziller, Department of Chemistry, University of California at Irvine, Irvine CA 927l7

When the 2+ ions of group 10 metals, such as palladium, react with bidentate glyoxime-type ligands, the result is a four-coordinate, square-planar compound where the glyoxime moieties are linked by intramolecular strong hydrogen bonds of the O^..H^..0 type. The nature of these strong hydrogen bonds has long been of interest, in as much as they offer a serious challenge to theories of chemical bonding. Palladium(II)-diglyoxime complexes provide an excellent opportunity to compare strong hydrogen bonds, as changes in the hydrogen bonds can be measured against the electronic effects of the substituent groups on the glyoxime backbone. The structure of the title compound, Pd(dpgH)₂ (dpg = diphenylglyoxime), was refined to R = 4.46% for 4[[sigma]] data and 7.90% for all data. The distance between the oxygen atoms involved in the intramolecular hydrogen bond is 2.550(10) Å. There is strong evidence that the hydrogen atom involved in this hydrogen bond is in a nearly-centered (though asymmetric) position. This structure can be compared with those previously reported structures of palladiumdiglyoxime compounds, which have the substituents -H, -NH₂, -CH₃ and [[alpha]]-furyl. Use of the Hammett parameters allows one to quantify the electronic effects of the substituent groups, and thus to investigate the response of the intramolecular hydrogen bond to changing electronic environments. These results indicate that electron-withdrawing groups tend to strengthen the hydrogen bond; it may be possible to explain this observation with reference to bond valence theory.