Thermal Treatment of Glutamic Acid-Modified Nickle Nanoclusters on Au{111} Leads to the Formation of One-Dimensional Metal-Organic Coordination Networks

The adsorption of glutamic acid onto two-dimensional (2-D) Ni clusters on Au{111} has been investigated by reflection absorption infrared spectroscopy (RAIRS) and scanning tunneling microscopy (STM). Adsorption at 300 K leads to two distinct adsorbate species, which we conclude are zwitterionic species adsorbed either at Ni-like sites in the center of the clusters or at interfacial sites at the edges of clusters. Adsorption of (S)-glutamic acid causes the complete destruction of clusters of initial diameter < 3 nm. We conclude that the Ni islands have been corroded, resulting in the formation of a Ni salt, presumably nickel(II) glutamate. On annealing to 350 K, chains of one-dimensional (1-D) molecular features are observed in STM experiments. We discuss the possible composition and structure of this salt and conclude that the chains most likely consist of nickel(II) pyroglutamate. Pyroglutamate is well-known to be produced by heating of glutamate salts. The intermolecular bonding and azimuthal alignment of the 1-D chains are discussed.