COVALENT ATTACHMENT OF NICKEL CLUSTERS TO GOLD ELECTRODE SURFACES - FORMATION OF RECTIFYING MOLECULAR LAYERS

Attachment of electroactive triangular nickel clusters to gold electro des was accomplished with 4-isocyanophenyl thiolate linkages. The disu lfide linked ''dimer of trimers'' cluster )(mu(2)-dppm)(3)(mu(3),eta(1 )-C=NC6H4S-)}(2)](2+), 5, was prepared by reaction of 2 equiv of [Ni-3 (mu(3)-I)(2)(mu(2)-dppm)(3)], 2, with 1 equiv of 4,4'-bis(isocyano)dip henyl disulfide, 4. Films of 3(mu(3)-I)(mu(2)-dppm)(3)(mu(3),eta(1)-C= NC6H4S-)] 6, On gold electrodes were formed by electrochemical deposit ion or by immersing the electrode in a methylene chloride solution of 5. After deposition, persistent oxidation and reduction of the adsorbe d cluster was observed via cyclic voltammetry with peak current (i(p)) proportional to the scan rate. The electron accepters methyl viologen (MV(2+)) and the methyl ester of cobaltocenium carboxylate [CoCpCpCOO Me][PF6] were used to demonstrate rectification in the interfacial ele ctron transfer from nickel cluster modified gold electrodes to the ele ctron accepters. Surface coverage was estimated by both electrochemist ry and reflection-absorption infrared spectroscopy(RAIR). Both RAIR an d electrochemical measurements indicated surface coverages of cluster 6 of approximately one monolayer or 2 x 10(14) molecules/cm(2).