  Here we describe the design, single-molecule transport measurements, and
theoretical modeling of a ferrocene-based organometallic molecular wire, whose
bias-dependent conductance shows a clear Lorentzian form with magnitude
exceeding 70% of the conductance quantum G_0. We attribute this unprecedented
level of single-molecule conductance to a manifestation of the low-lying
molecular resonance and extended orbital network long-predicted for a
conjugated organic system. A similar-in-length, all-organic conjugated
phenylethynyl oligomer molecular framework shows much lower conductance.
