Evidence for a Novel Chemisorption Bond: Formate (HCO2) on Cu(100)

Surface extended-x-ray-absorption fine-structure measurements reveal that formate (HC${\mathrm{O}}_2$) groups on Cu(100) chemisorb via the two oxygen atoms in adjacent fourfold hollow sites with an average O-Cu nearest-neighbor bond length of 2.38±0.03 Å. This distance is significantly (∼0.4 Å) longer than typical O-Cu bonds in bulk compounds and all known surface complexes. The unusually large O-Cu distance is attributed to a steric effect involving the C atom in HC${\mathrm{O}}_2$ and the nearest-neighbor Cu surface atoms.