Langmuir, Vol.28, No.32, 11788-11798, 2012
One-Step Vs Stepwise Immobilization of 1-D Coordination-Based Rh-Rh Molecular Wires on Gold Surfaces
Reaction of dimeric [Rh-2(II)(phen)(2)(mu-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 {[Rh-2(II)(phen)(2)(mu-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 MW's ("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 approximate to 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 ([Rh-2(phen)(2)(mu-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.