Self-assembled monolayer of a peroxo-bridged dinuclear cobalt(iii) complex on Au(111)

Abstract

Densely packed Self-Assembled Monolayers (SAMs) of a peroxide-bridged dicobalt complex, [Co₂(O₂)(bpbp)(O₂CCH₂CH₂S)]²⁺, 3, (bpbp⁻ = 2,6-bis((N,N′-bis-(2-picolyl)amino)-methyl)-4-tert-butylphenolato) have been prepared on atomically planar Au(111) surfaces. Surface voltammetric and interfacial capacitance data, along with electrochemical scanning tunnelling microscopy (in situ STM) imaging, support the formation of a densely packed adlayer of 3 attached via a gold–thiolate bond. In solution, the disulfide linked precursor for 3 reversibly binds dioxygen with high affinity. Electrochemical measurements show that the redox potential of the O₂²⁻/O₂˙⁻ couple of the monolayer of 3 is cathodically shifted by nearly 500 mV compared to the precursor in solution. This is attributed to the close proximity of the O₂ binding site to the gold surface. Since the redox potential of the O₂²⁻/O₂˙⁻ couple reflects tentatively the binding affinity of O₂ to the deoxygenated Co^II₂ binding site, the potential of the O₂²⁻/O₂˙⁻ couple of the SAM of 3 suggests a much higher affinity towards O₂ compared to the solution precursor.