A structural study of formate on Cu(111)

We have performed the first structural study of formate adsorbed on Cu(111). The local registry of formate has been determined using normal incidence X-ray standing wavefield absorption (NIXSW). The oxygen atoms of the formate were located in atop sites, with NIXSW measurements made using the (1̄11) planes suggesting that they could be statically displaced by up to 0.33 Å, and with the formate bridging two copper atoms. This adsorption site is identical to that found for formate on Cu(110) and Cu(100) by Woodruff and co-workers. The oxygen–(111) plane separation determined by NIXSW was 1.89 Å. This would, assuming that the oxygen atoms are displaced by 0.33 Å from a perfect atop position and no relaxation of the underlying substrate, infer a upper limit for the CuO separation of 1.92±0.04 Å. This value compares with CuO separations of 1.98±0.04 Å for formate on both Cu(100) and Cu(110), and the average value of 1.97 Å observed for all known μ2-formate–copper complexes.