One-Step Vs Stepwise Immobilization of 1-D Coordination-Based Rh–Rh Molecular Wires on Gold Surfaces

Reaction of dimeric [RhII2(phen)2(μ-OAc)2(MeCN)2](BF4)2 (phen =1,10-phenanthroline) with pyrazine (pz) in a 1:2 ratio leads to the new 1-D metal–metal-bonded coordination oligomer {[RhII2(phen)2(μ-OAc)2(pz)](BF4)2}n (Rh–Rhpz)n (1), where each Rh atom of the dimeric unit (Rh–Rh) is coordinated in the equatorial plane to a nitrogen atom of a rigid and linear bifunctionalized organic linker (pz). Single X-ray diffraction analysis reveals the 1-D straight oligomeric chain structure (molecular wire, MW) consists of alternating (Rh–Rh) units and pz linking ligands with free BF4– as counteranions, and each metal center has a slightly distorted octahedral arrangement. The presence of accessible labile MeCN groups on both ends of these MWs (“free ends”) enables functionalization of a 4-mercaptopyridine–gold coordinating platform (Au/MP) to form in one step a layer of coordination oligomer (Au/MP(Rh–Rhpz)n; n ≈ 50). Furthermore (Rh–Rhpz)n (n = 1–6) MWs were grafted to Au/MP surfaces by a conventional step-by-step assembly construction involving coordination reactions between the Rh dimer ([Rh2(phen)2(μ-OAc)2(MeCN)2](BF4)2 (2)) and pz. A detailed physicochemical study (UV–vis, RAIR, QCM-D, ellipsometry, contact angle measurements, as well as impedance spectroscopy and cyclic voltammetry) has been made during both assembly methods to characterize the resulting surface-anchored coordination molecular wire (CMW) layers (Au/MP(Rh–Rhpz)n). The results indicate that the immobilized molecular assemblies (MAs) were successfully fabricated using both methods of assembly. The efficiency of the two methods is discussed.