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

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 CoII2 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.