The ordered and controlled location of molecular compounds on electrode surfaces is essential for the nanometer-scale design of electrochemical interfaces in view of fundamental electron-transfer studies and several lines of applications, such as molecular electronic devices, optical devices, and sensors.[1] Furthermore, layer-by-layer deposition of molecular units onto preorganized self-assembled monolayers (SAMs) has proven to be useful in preparing layered architectures with enhanced properties.[2] Although a significant progress has been made for atomic-scale depositions (such as underpotential deposition and atomic layer epitaxy) [3] or molecular 2D assembly, [4] an "electrochemicalcontrol strategy" to prepare layer-by-layer 3D structures from molecular building blocks is currently unavailable. Herein we report on the successful construction of layer-by-layer nanostructures on a gold electrode by using a redox-active metalcluster molecule, [5] in which the electrode potential modulation precisely controls the multilayer growth. We show that the series of multilayers display extensive electronic coupling between the linked molecular units, thus allowing facile multielectron transport to occur at interfaces.

The ordered and controlled location of molecular compounds on electrode surfaces is essential for the nanometer-scale design of electrochemical interfaces in view of fundamental electron-transfer studies and several lines of applications, such as molecular electronic devices, optical devices, and sensors.[1] Furthermore, layer-by-layer deposition of molecular units onto preorganized self-assembled monolayers (SAMs) has proven to be useful in preparing layered architectures with enhanced properties.[2] Although a significant progress has been made for atomic-scale depositions (such as underpotential deposition and atomic layer epitaxy) [3] or molecular 2D assembly, [4] an "electrochemicalcontrol strategy" to prepare layer-by-layer 3D structures from molecular building blocks is currently unavailable. Herein we report on the successful construction of layer-by-layer nanostructures on a gold electrode by using a redox-active metalcluster molecule, [5] in which the electrode potential modulation precisely controls the multilayer growth. We show that the series of multilayers display extensive electronic coupling between the linked molecular units, thus allowing facile multielectron transport to occur at interfaces.

An in situ approach for rapid growth of multilayers of redox-active triruthenium cluster complexes has been developed under electrochemical potential control of the gold electrode, the formation process being successfully probed by cyclic voltammetry and AFM images.

Densely packed redox-active self-assembled monolayers (SAMs) of monocarbonyl triruthenium complexes [Ru3(μ3-O)(μ-CH3COO)6(CO)(mpy)(C10PY)] (1) (mpy, 4-methylpyridine; C10PY, {(NC5H4)CH2NHC(O)(CH2)10S–}2), [Ru3(μ3-O)(μ-CH3COO)6(CO)(μ-C10PY)] (2), and [{Ru3(μ3-O)(μ-CH3COO)6(CO)(mpy)}2(μ-C10PY)] (3) have been constructed on an Au(111) electrode surface. They were characterized by infrared reflection absorption spectroscopy (IRRAS), spectroscopic ellipsometry, and contact angle measurement as well as cyclic voltammetry. Redox potential of the SAMs of 1 at the interface of aqueous electrolyte solutions shifted negatively as the concentration of HClO4 increased from 0.01 to 1.0 mol dm−3 with the slope of 0.059 V/decade and as the electrolyte was changed from H2SO4 (0.79 V vs. Ag|AgCl) to HNO3 (0.69 V) and HClO4 (0.59 V) at a fixed concentration of 0.1 mol dm−3. No significant difference in the redox potential was observed between the acid and its sodium salt. The effect is explained, as previously reported for the ferrocenylalkanethiol and non-carbonyl triruthenium SAMs, in terms of the effective ion pair formation in the order ClO4− > NO3− > SO42−. The rate of the CO dissociation reaction of the complex in the SAMs (complete within a few minutes at room temperature) that occurs in the oxidation state of Ru3III,III,III was not very sensitive to the applied electrode potential (0.6–0.8 V), but increased by ca. 2.5 times as the concentration of HClO4 (0.01–1.0 mol dm−3) was lowered, and by ca. one-order of magnitude as the electrolyte anions was changed from ClO4− to SO42− and NO3−.

Infrared photodissociation spectra of CH 3 NH 3 +-Ar and (CH 3 NH 2) n H + with n = 2-4 are measured in the 2600-3500 cm-1 region and analyzed with the aid of ab initio calculations. The intensities of the CH-stretching transitions relative to the NH-stretching transitions increase with increasing n, suggesting the change of the binding features of an excess proton in the clusters. Two CH 3 NH 2 molecules in (CH 3 NH 2) 2 H + equally share the proton. On the other hand, the proton is localized on the central molecule in (CH 3 NH 2) 4 H + , forming the CH 3 NH 3 + core solvated by three CH 3 NH 2 molecules.