Molecular Adsorption Bond Lengths at Metal Oxide Surfaces: Failure of Current Theoretical Methods

New experimental structure determinations for molecular adsorbates on NiO(100) reveal much shorter Ni-C and Ni-N bond lengths for adsorbed CO and NH3 as well as NO (2.07, 1.88, 2.07 Å) than previously computed theoretical values, with discrepancies up to 0.79 Å, highlighting a major weakness of current theoretical descriptions of oxide-molecule bonding. Comparisons with experimentally determined bond lengths of the same species adsorbed atop Ni on metallic Ni(111) show values on the oxide surface that are consistently larger (0.1–0.3 Å) than on the metal, indicating somewhat weaker bonding.