Surface coordination of nitric oxide to a self-assembled monolayer of a triruthenium cluster: An in situ infrared spectroscopic study

Coordination of nitric oxide (NO) to a self-assembled monolayer (SAM) of a triruthenium (Ru₃) cluster, [Ru₃(μ₃-O)(μ- CH₃COO)₆(CO)(L₁)(L₂)]⁰ (L₁ = [(NC₅H₄)CH₂NHC(O)(CH ₂)₁₀S-]₂, L₂ = 4-methylpyridine), on a gold electrode surface has been studied by electrochemical and in situ infrared (IR) spectroscopic measurements. Ligand substitution reaction of NO for carbon monoxide (CO) ligands in the SAM strongly depends on the oxidation state of the terminal Ru₃ cluster. NO can be introduced into the Ru3 cluster in the SAM with a high yield after one-electron oxidation of the Ru3 core to a (III,III,III) oxidation state, while no coordination reaction occurs at the initial oxidation state (II,III,III) of the Ru₃ cluster. The kinetics of the NO coordination and desorption processes is also evaluated by time-resolved in situ IR spectroscopy. Finally, we demonstrate that the SAM with NO/CO randomly mixed ligands at a desired ratio can be constructed on the gold surface by tuning a suitable oxidation state of the Ru₃ cluster under electrochemical control.