AVS 63rd International Symposium & Exhibition
    Surface Science Monday Sessions
       Session SS+AS+HC-MoM

Paper SS+AS+HC-MoM1
Study of Metal-Organic Complexation at Metal and Metal Oxide Surfaces by HREELS

Monday, November 7, 2016, 8:20 am, Room 104E

Session: Mechanistic Insights on Surface Reactions in Catalysis and at Novel Interfaces
Presenter: Miao Wang, Indiana University
Authors: M. Wang, Indiana University
C. Williams, Indiana University
S.L. Tait, Indiana University
Correspondent: Click to Email
The ordering of organic molecules at surfaces and the formation of ordered metal nanostructures at surfaces have been extensively studied for the advancement of organic photovoltaics, nanoscale molecular electronics, and catalysts. There are many chemical systems that benefit from the combination of organic ligands with single-site metal centers to design and tune specific chemistries, but metal-organic complexation at surfaces has not yet been significantly studied. Molecular ligands on a surface with specific binding pockets can bind metal centers to achieve uniform oxidation states, as has been shown in prior studies by our group and by other groups. The goal of these studies is to improve selectivity in heterogeneous catalysts and to develop other novel surface chemistries. With that end in mind, we present new experiments with metal-organic coordination on oxide support surfaces. Most of the metal-organic surfaces studies have been done on metal surfaces to facilitate surface analysis. We have studied the redox assembly of 3,6-Di-2-pyridyl-1,2,4,5-tetrazine (DPTZ) and Pt on oxide surfaces, including rutile TiO2(110) using High Resolution Electron Energy Loss Spectroscopy (HREELS), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). HREELS characterizes vibrational modes, which can provide key information about adsorbate interactions and metal-organic interactions at surfaces. DPTZ and Pt were sublimated onto the surface from a Knudsen-type evaporator. Submonolayer DPTZ vibrational modes were observed on Ag(111) (C-H bending modes at 400 cm-1, 618 cm-1 and 772 cm-1; ring deformation modes at 966 cm-1, 1145 cm-1 and 1354 cm-1) and on TiO2(110) (a ring deformation mode at 1580 cm-1 and a C-H stretching mode at 3060 cm-1). To see the vibrational modes of adsorbates on TiO2, a Fourier deconvolution technique was applied to remove multiple excitations of surface phonon. Annealing DPTZ on Ag(111) at 170 °C caused significant changes to the HREEL spectra (C-H bending modes at 400 cm-1 and 740 cm-1, ring deformation modes at 1100 cm-1, 1445 cm-1, 1574 cm-1, a C-H stretching mode at 3080 cm-1), but no observable changes were seen for DPTZ on TiO2(110) until the sample was annealed at 290 °C. Adding equimolar Pt onto submonolayer DPTZ on Ag(111) caused similar vibrational changes to be observed, but at a lower temperature of 140 °C. HREELS studies of the Pt-DPTZ complex on TiO2(110), Au(100), and other surfaces are ongoing. By studying the redox assembly of metal-organic complexes on these surfaces, strategies can be developed to customize and tune the reactivity of novel surface catalysts.