Effective intervalence transfer occurred between the metal centers of ferrocene moieties that were adsorbed onto a ruthenium thin film surface by ruthenium-carbene pi bonds, a direct verification of Hush's four-decade-old prediction. Electrochemical measurements showed two pairs of voltammetric peaks where the separation of the formal potentials suggested a Class II behavior. Additionally, the potential spacing increased with increasing ferrocene surface coverage, most probably as a consequence of the enhanced contribution from through-space electronic interactions between the metal centers. In contrast, the incorporation of a sp(3) carbon spacer into the ferrocene-ruthenium linkage led to the diminishment of interfacial electronic communication. (C) 2009 Elsevier B. V. All rights reserved.