Covalent Attachment of Nickel Clusters to Gold Electrode Surfaces. Formation of Rectifying Molecular Layers

Attachment of electroactive triangular nickel clusters to gold electrodes was accomplished with 4-isocyanophenyl thiolate linkages. The disulfide linked “dimer of trimers” cluster [{Ni 3 (μ 3 -I)(μ 2 -dppm) 3 (μ 3,η 1 -C⋮NC 6 H 4 S-)} 2 ] 2+, 5, was prepared by reaction of 2 equiv of [Ni 3 (μ 3 -I) 2 (μ 2 -dppm) 3 ], 2, with 1 equiv of 4,4‘-bis(isocyano)diphenyl disulfide, 4 . Films of [Ni 3 (μ 3 -I)(μ 2 -dppm) 3 (μ 3,η 1 -C⋮NC 6 H 4 S-)], 6, on gold electrodes were formed by electrochemical deposition or by immersing the electrode in a methylene chloride solution of 5 . After deposition, persistent oxidation and reduction of the adsorbed cluster was observed via cyclic voltammetry with peak current ( i p ) proportional to the scan rate. The electron acceptors methyl viologen (MV 2+ ) and the methyl ester of cobaltocenium carboxylate [CoCpCpCOOMe][PF 6 ] were used to demonstrate rectification in the interfacial electron transfer from nickel cluster modified gold electrodes to the electron acceptors. Surface coverage was estimated by both electrochemistry and reflection−absorption infrared spectroscopy (RAIR). Both RAIR and electrochemical measurements indicated surface coverages of cluster 6 of approximately one monolayer or 2 × 10 14 molecules/cm 2 .