The adsorption of (S)-proline on Au(111) at 300 K was studied by low-temperature scanning tunnelling microscopy, X-ray photoelectron spectroscopy, and high resolution electron energy loss spectroscopy. (S)-proline adsorbs to produce a 2-D gas phase at 300 K, which can be condensed to form ordered molecular assemblies on cooling to 77 K. The chemical nature of the self-assembled structures is discussed in light of the information provided by photoelectron and vibrational spectroscopies.
Nickel nanoparticles modified by the adsorption of chiral amino acids are known to be effective enantioselective heterogeneous catalysts. The leaching of nickel by amino acids has a number of potential effects including the induction of chirality in the nickel atoms left behind in the nanoparticle and the creation of catalytically active nickel complexes. The adsorption of (S)-proline onto Au(111) precovered by two dimensional nickel nanoclusters was investigated by scanning tunnelling microscopy, X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy. Adsorption of (S)-proline at 300 K resulted in the corrosion of the nickel clusters, the oxidation of the leached nickel and the on-surface formation of bioinorganic complexes, which are concluded to contain three prolinate species in an 2 octahedral arrangement around the central Ni ion. Two distinguishable forms of nickel prolinate complexes were identified. One form self-assembles into 1-D chains and the other form gives rise to porous 2-D islands. Octahedral complexes of the type M(AB) 3 are intrinsically chiral resulting in two pairs of enantiomers. The mirror symmetry of each pair of enantiomers is broken when, as in this study, the bidentate ligand itself possesses a chiral center. DFT calculations are used to examine the relative energies of each Ni(prolinate) 3 complex as isolated gas phase species and isolated adsorbed species.
Metal carbonyl complexes have been widely investigated for use in heterogeneous catalysis as a method for the formation of metal clusters. However, their use as a metal source for metallosupramolecular assemblies has not been widely considered. In this study, the combination of Cr(CO)6 with p-terphenyldinitrile on Au(111) creates ordered 1D chains, which are thermally stable up to 423 K. The bond between the nitrile linkers and metal nodes undergoes a unique π-interaction, which thus far has been observed only in a small set of organometallic complexes. The structure and composition of the metal–organic coordination network have been elucidated and characterized using scanning tunnelling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory calculations.
The reaction of (S)-proline with two-dimensional Ni nanoclusters on Au(111) results in the formation of ordered structures constructed from two distinct types of nickel prolinate complex. Scanning tunnelling microscopy and density functional theory are combined to analyze the supramolecular arrangements produced as a function of annealing temperature. Octahedral Ni(pro) 3 complexes are the fundamental building blocks of multiple phases identified by the formation of hexagonal pores of 1 nm diameter. Coexisting with the hexagonal porous phases is a honeycomb phase constructed from Ni(pro) 2 complexes. In contrast to the thermal stability of the hexagonal porous phases, the honeycomb phase transforms on heating to a mesh phase which is concluded to be constructed from pro-pro dipeptide species coordinated to Ni ions. At even higher temperature, more extensive oligomerization occurs to produce an ordered rose phase whose structure is consistent with the formation of oligoproline species.
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