Self-assembled monolayers of ruthenium and osmium bis-terpyridine complexes -: Insights of the structure and interaction energies by combining scanning tunneling microscopy and electrochemistry

Self-assembled monolayers of [Ru(terpy)(terpy-py)](2+) and [Os(terpy)(terpy-py)](2+) salts (terpy is 2,2':6',2"-terpyridine and terpy-py is 4'-(4-pyridyl)-2,2':6',2"-terpyridine) on platinum were investigated by means of STM and electrochemistry. The STM experiments reveal that the species within the monolayer are ordered in a hexagonal array. This information was utilized together with the scan rate dependency of the peak current density (j(p)) of potential sweep experiments to calculate interaction energies within the monolayer. Significantly, the repulsive interactions within the monolayers of 2,2':6',2"-terpyridine complex are greater than those observed with analogous 2,2'-bipyridine species. This results in a lower overall surface coverage, an ordered structure where each particle has 6 closest neighbors, and a shift of the redox potentials toward more positive values with the terpy complexes. Also, a correlation between the solvent dielectric constant and the interaction energies could be established, reflecting the different ability of the solvent to screen charges depending upon its polarity.