Self-Assembly of a Mononuclear [FeIII(L)(EtOH)2] Complex Bearing ann-Dodecyl Chain on Solid Highly Oriented Pyrolytic Graphite Surfaces

Abstract

The synthesis and structures of the N-[(2-hydroxy-3-methyl-5-dodecylphenyl)methyl]-N-(carboxymethyl)glycine disodium salt (HL) ligand and its neutral mononuclear complex [Fe(III) (L)(EtOH)(2)] (1) are reported. Structural and electronic properties of 1 were investigated by using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) techniques. These studies reveal that molecules of 1 form well-ordered self-assemblies when deposited on a highly oriented pyrolytic graphite (HOPG) surface. At low concentrations, single or double chains (i.e., nanowires) of the complex were observed, whereas at high concentration the complex forms crystals and densely packed one-dimensional structures. In STM topographies, the dimensions of assemblies of 1 found on the surface are consistent with dimensions obtained from X-ray crystallography, which indicates the strong similarities between the crystal form and surface assembled states. Double chains are attributed to hydrogen-bonding interactions and the molecules align preferentially along graphite defects. In the CITS image of complex 1 a strong tunneling current contrast at the positions of the metal ions was observed. These data were interpreted and reveal that the bonds coordinating the metal ions are weaker than those of the surrounding ligands; therefore the energy levels next to the Fermi energy of the molecule should be dominated by metal-ion orbitals.