Ordering a rhenium catalyst on Ag(001) through molecule-surface step interaction

Abstract

Atomic scale studies of the anchoring of catalytically active complexes to surfaces may provide valuable insights for the design of new catalytically active hybrid systems. In this work, the self-assembly of 1D, 2D and 3D structures of the complex fac-Re(bpy)(CO)3Cl (bpy = 2,2′-bipyridine), a CO2 reduction catalyst, on the Ag(001) surface are studied by a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Infrared and sum frequency generation spectroscopy confirm that the complex remains chemically intact under sublimation. Deposition of the complexes onto the silver surface at 300 K leads to strong local variations in the resulting surface coverage on the nanometer scale, indicating that in the initial phase of deposition a large fraction of the molecules is desorbing from the surface. Low coverage regions show a decoration of step edges aligned along the crystal’s symmetry axes <110>. These crystallographic directions are found to be of major importance to the binding of the complexes to the surface. Moreover, the interaction between the molecules and the substrate promotes the restructuring of surface steps along these directions. Well-aligned and decorated steps are found to act as nucleation point for monolayer growth (2D) before 3D growth starts.

Testing functional anchor groups for the efficient immobilization of molecular catalysts on silver surfaces

“…The goal of this work is to evaluate the effect of the sulfur anchors at the ligand periphery of fac-Re( S-S bpy)(CO) 3 Cl ( S-S bpy = 3,3′-disulfide-2,2′bipyridine), short Rebpy S-S , on the molecule-surface interaction as compared to the parent complex fac-Re(bpy)(CO) 3 Cl (bpy = 2,2′-bipyridine), short Rebpy, on the Ag(001) surface, which we have studied earlier 23 . For the sulfurated complex, we used very similar sample preparation and investigation methods for direct comparison (see 'Methods'), which allows us to attribute observed differences in the growth behavior to the sulfur anchors.…”

Making and breaking of chemical bonds in single nanoconfined molecules

“…1A, demonstrates the high quality of the long-range ordered self-assembled molecular pattern. The alignment of the molecules on the surface has recently been clarified ( 33 ). The energetically most favorable configuration is with the Cl ligand facing the surface, as depicted in the side view in Fig.…”

“…A second option is the single-bond breaking dissociation of a CO ligand from the metal center. With the help of density functional theory (DFT) calculations, the energetically favorable alignment of the molecules with respect to the surface is with the Cl ligand facing the surface, i.e., one CO group is facing the tip and the other two are aligned in parallel to the surface ( 33 ). If one CO was split off, then this would likely attach at some random position (on tip or sample) or desorb into vacuum, which stands in direct contrast to the experimental observation of a reversible reaction and the electrochemical findings on the complex in solution ( 36 ).…”

“…To study the local excitation of nanoconfined molecules, a monolayer-covered silver crystal was prepared by in situ thermal evaporation of fac -Re(bpy)(CO) 3 Cl (bpy = 2,2′-bipyridine) onto the clean Ag(001) surface, resulting in the self-assembly of long-range ordered molecular monolayers on the length scale of hundreds of nanometers. Details on the preparation process and on the multifaceted growth behavior of the complex can be found elsewhere ( 33 ).…”

“…S9). This is a simplified model because the experimental monolayer has very large periodicity in one direction [14.4 nm; ( 33 )]. Thus, the full monolayer is too large to model with DFT, and to avoid a mismatch between the periodic images of the four rows of molecules, they were separated by roughly 6 Å in the long direction.…”