Formation and evolution of metallocene single-molecule circuits with direct gold-π links
Files
Accepted manuscript
Date
2022-04-13
Authors
Lawson, Brent
Zahl, Percy
Hybertsen, Mark S.
Kamenetska, Maria
Version
Accepted manuscript
OA Version
Citation
B. Lawson, P. Zahl, M.S. Hybertsen, M. Kamenetska. 2022. "Formation and Evolution of Metallocene Single-Molecule Circuits with Direct Gold-π Links" Journal of the American Chemical Society, Volume 144, Issue 14, pp.6504-6515. https://doi.org/10.1021/jacs.2c01322
Abstract
Single-molecule circuits with group 8 metallocenes are formed without additional linker groups in scanning tunneling microscope-based break junction (STMBJ) measurements at cryogenic and room-temperature conditions with gold (Au) electrodes. We investigate the nature of this direct gold-π binding motif and its effect on molecular conductance and persistence characteristics during junction evolution. The measurement technique under cryogenic conditions tracks molecular plateaus through the full cycle of extension and compression. Analysis reveals that junction persistence when the metal electrodes are pushed together correlates with whether electrodes are locally sharp or blunt, suggesting distinct scenarios for metallocene junction formation and evolution. The top and bottom surfaces of the “barrel”-shaped metallocenes present the electron-rich π system of cyclopentadienyl rings, which interacts with the gold electrodes in two distinct ways. An undercoordinated gold atom on a sharp tip forms a donor–acceptor bond to a specific carbon atom in the ring. However, a small, flat patch on a dull tip can bind more strongly to the ring as a whole through van der Waals interactions. Density functional theory (DFT)-based calculations of model electrode structures provide an atomic-scale picture of these scenarios, demonstrating the role of these bonding motifs during junction evolution and showing that the conductance is relatively independent of tip atomic-scale structure. The nonspecific interaction of the cyclopentadienyl rings with the electrodes enables extended conductance plateaus, a mechanism distinct from that identified for the more commonly studied, rod-shaped organic molecular wires.