The monomer-to-dimer transition and bimodal growth of Co–salen on NaCl(001): a high resolution atomic force microscopy study

Abstract

Molecules of Co-salen, a paramagnetic metal-organic Schiff base complex, self-assemble into two different well ordered morphologies on a NaCl(001) substrate: nanowires, which form networks, and compact nanocrystallites. Their growth can be controlled by adjusting the deposition parameters. It turns out that the nanowires are metastable. Molecular resolution images suggest that the packing in both morphologies is the same as in bulk Co-salen single crystals. Only the orientation of the c-axis with respect to the substrate is different. The origin of this intriguing bimodal growth is associated with a monomer-to-dimer transition, which probably takes place during initial nucleation at step edges.

Recent Trends in Surface Characterization and Chemistry with High‐Resolution Scanning Force Methods

“…The second approach has been used in nc‐AFM studies of individual molecules of Co‐Salen (Figure 10b), a small chiral paramagnetic metal‐organic Schiff base complex, on the NaCl (001) surface using Cr‐coated tips at 30 K 240, 241. The obtained images simultaneously exhibit both the position and the orientation of the adsorbed molecules and the atomic structure of the surface, enabling the determination of the exact adsorption site.…”

“…Copyright 2009, American Physical Society. Panel (b) reproduced with permission 240. Copyright 2009, Institute of Physics.…”

Tuning Molecular Self‐Assembly on Bulk Insulator Surfaces by Anchoring of the Organic Building Blocks

“…This structure, however, has been shown to be metastable as a dewetting49 transition of the molecular film to bulk‐like crystals is observed at coverages higher than ≈0.85 monolayer. Another example for this so‐called bimodal growth has been revealed for cobalt‐salen molecules on the NaCl(001) surface, where metastable nanowires transform into stable nanocrystallites upon annealing the sample 50. Molecular dewetting has also been observed for PTCDA molecules on KBr(001) (Figure 1b)51 and KCl(001)52 surfaces as well as for 3,4,9,10‐perylene tetracarboxylic diimide (PTCDI) molecules on KBr(001)53 and NaCl(001) substrates 53, 54.…”

“…For the adsorption of cobalt‐salen molecules on NaCl(001) surfaces, a pure electrostatic interaction between the cobalt metal atom and the surface chloride anions has been found 78. The adsorption energy has been calculated by means of DFT to be of the order of 0.6 to 0.7 eV 50. Along this line, molecules bearing a large dipole moment have been explored for increasing the electrostatic interaction with the surface 37, 69, 74, 79–81.…”

Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces

“…In the former case, the structures mostly grow in three-dimensional crystallites [7–10]. Only for systems in which the MM interaction was directional, as for example by H-bonding [11] or by covalent bonding [12–13], layer-by-layer growth or even one-dimensional growth [14] was observed.…”