Metal–Ligand Complexation through Redox Assembly at Surfaces Characterized by Vibrational Spectroscopy

Abstract

The formation of metal–organic complexes on metal surfaces is a research topic of high interest to develop tunable functional surfaces. One such focus of this research is the formation of single site metal centers that have uniform ligand environments and thus uniform chemistry. We report the complexation of Pt and Ag with the ligand dipyridyl-tetrazine (DPTZ) on Ag(111) and of Pt with DPTZ on the reconstructed Au(100) surface. Each metal atom binds two DPTZ molecules resulting in one-dimensional supramolecular chains across the surface. Pt complexation occurs immediately after Pt deposition at room temperature on either surface. This complexation is improved with annealing to 170 °C on Au(100). DPTZ forms complexes with Ag atoms from the Ag(111) substrate when annealed to 110 °C. No similar complexation with substrate atoms is seen on Au(100). This metal–organic complexation with substrate atoms on Ag(111) takes place even when the DPTZ is already complexed to Pt, demonstrating a Pt replacement reaction by Ag at 80 °C, which has not been reported previously. The metal–organic complexes are characterized by high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). This research is among the few to use HREELS to characterize the formation of extended metal organic networks on a surface formed through the redox of the organic species into an anionic state.

Multi‐electron Reduction Capacity and Multiple Binding Pockets in Metal–Organic Redox Assembly at Surfaces

“…We attribute the weakening of out‐of‐plane mode intensities relative to in‐plane modes to metal complex formation. Previous HREELS study showed similar drops in peak intensity and a blue shift of the pyridine out‐of‐plane mode of dipyridyl‐tetrazine when coordinated with Pt or Ag on Ag(111), where electron donation from the metal center to N‐containing aromatic rings was confirmed by XPS . IR studies also showed lower relative intensities of out‐of‐plane modes compared to in‐plane modes of anionic polyacene species, in contrast to neutral molecules .…”

“…We attribute the weakening of out-of-plane modei ntensities relative to in-plane modes to metal complex formation.P revious HREELSs tudy showed similard rops in peak intensity and ab lue shift of the pyridine out-of-plane mode of dipyridyl-tetrazine when coordinated with Pt or Ag on Ag (111), where electron donation from the metal center to N-containing aromatic rings was confirmed by XPS. [21] IR studies also showedl ower relative intensities of out-of-plane modes compared to in-plane modes of anionic polyacene species, in contrast to neutralm olecules. [22] Thus, the relative intensityd ecrease of out-of-plane modes compared to in-plane modesi sa ttributedt oe lectron transfer from metal atoms to organic ligands, which is direct evidence of the redox character of metal complexation.…”

Facilitating hydrogen atom migration via a dense phase on palladium islands to a surrounding silver surface

“…HREELS experiments were performed using an LK-2000 spectrometer using a primary energy of 4.5 eV at 60⁰ specular geometry with a specular full width at half maximum of ~ 6.0 meV (~ 48 cm -1 ). The spectra were normalized with respect to the background counts which has been shown to be proportional to the flux of the electron beam (64). The data was further processed by fitting and subtracting the specular peak for each spectrum to remove contributions of the specular peak from the adsorbate features.…”

Synthesis of High Metal Loading Single Atom Catalysts and Exploration of the Active Center Structure

“…The ligand may control the oxidation state, geometry, and d n electron configuration of the metal center, [212] contributing significantly to the activity, selectivity, and stability of catalysts [213–219] . Depending on the ligands and supports attached to the center metal, the performance of prepared SACs may vary substantially [220–221] . Taking Pt SACs as an example, powdered MgO, Al 2 O 3 , and CeO 2 were used as supports to anchor a Pt single atom with a ligand 3,6‐di‐2‐pyridyl‐1,2,4,5tetrazine (DPTZ) [222] .…”