The structure of acetate and trifluoroacetate on Cu(111)

The structure of acetate and 1,1,1-trifluoroacetate on Cu(111) has been determined using normal incidence X-ray standing wavefield absorption (NIXSW). Our results show that the carboxylate groups of both species bond in a bidentate form, with oxygen atoms adopting displaced atop positions on neighbouring copper atoms, and their heights above a non-relaxed copper surface measuring 1.81 +/- 0.03 and 1.91 +/- 0.05 Angstrom for acetate and trifluoroacetate, respectively. These distances are very similar to those found in previous studies employing other surface structural techniques, Tn the case nf trifluoroacetate the NIXSW data are consistent with a freely rotating CF3 group. The structure of chemisorbed trifluoroacetate is identical, within experimental error, to that found in inorganic trifluoroacetate mu (2)-copper complexes, that display considerable ionic bonding character. From the similarity between the structures of the observed surface species and the inorganic complexes we infer the existence of a significant ionic component in the chemisorption bonds. (C) 2001 Elsevier Science B.V. All rights reserved.