Surface immobilization of Mo6I8 octahedral cluster cores on functionalized amorphous carbon using a pyridine complexation strategy

Tetrahedral amorphous carbon (a-C) films have been grown by pulsed laser deposition to investigate a liquid phase process for surface immobilization of electroactive Mo₆Iⁱ₈]^4 + transition metal cluster cores using a complexation reaction with a pyridine-terminated alkyl monolayer covalently bonded to the a-C surface (Py^S–alkyl/a-C). These films are stable against thermally-assisted grafting of alkene molecules and the covalent CC interface provides a robust monolayer/a-C assembly. Octahedral Mo₆Iⁱ₈]^4 + cluster cores with iodine inner ligands and labile triflate apical ligands Mo₆Iⁱ₈(CF₃SO₃)^a₆]^2 ? have been immobilized through partial complexation in apical positions by surface pyridine groups (Py^S). The remaining CF₃SO₃^? apical ligands of Mo₆Iⁱ₈ (Py^S)^a_y(CF₃SO₃)^a_6 ? y] cluster units were further substituted with bromopyridine (Py-Br) to obtain air stable surface with expected final composition Mo₆Iⁱ₈ (Py^S)^a_y(Py-Br)^a_6 ? y]. The yield of the different reaction steps is followed by X-ray photoelectron spectroscopy, providing cluster coverage Σ_Mo6I8 = 9 × 10¹² cm^? 2. Each Mo₆I₈]^4 + cluster is bound to the carbon surface through multiple anchoring metal sites (N_PYR = 3 or 4), indicating that pyridine-terminated alkyl chains are flexible enough to accommodate four bonds. Electrical transport through Hg//Mo₆I₈–Py^S–alkyl/a-C/p-Si(111) junctions shows rectifying current–voltage characteristics but does not reveal any signature of cluster immobilization.