Redox-active ligand controlled selectivity of vanadium oxidation on Au(100)

Christopher D Tempas; Tobias W Morris; David L Wisman; Duy Le; Naseem U Din; Christopher G Williams; Miao Wang; Alexander V Polezhaev; Talat S Rahman; Kenneth G Caulton; Steven L Tait

doi:10.1039/c7sc04752e

Redox-active ligand controlled selectivity of vanadium oxidation on Au(100)

Chem Sci. 2018 Jan 4;9(6):1674-1685. doi: 10.1039/c7sc04752e. eCollection 2018 Feb 14.

Authors

Affiliations

¹ Department of Chemistry , Indiana University , Bloomington , IN 47401 , USA . Email: caulton@indiana.edu ; Email: tait@indiana.edu.
² NAVSEA Crane , Crane , IN 47522 , USA.
³ Department of Physics , University of Central Florida , Orlando , FL , USA . Email: Duy.Le@ucf.edu.
⁴ Department of Physics , Indiana University , Bloomington , IN 47401 , USA.
⁵ Donostia International Physics Center (DIPC) , 20018 San Sebastian , Spain.

Abstract

Metal-organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product. We have studied the chemical reactivity of one-dimensional metal-organic vanadium - 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPTZ) chains with O₂. The electron-rich chains self-assemble through an on-surface redox process on the Au(100) surface and are characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory. Reaction of V-DPTZ chains with O₂ causes an increase in V oxidation state from V^II to V^IV, resulting in a single strongly bonded (DPTZ^2-)V^IVO product and spillover of O to the Au surface. DFT calculations confirm these products and also suggest new candidate intermediate states, providing mechanistic insight into this on-surface reaction. In contrast, the oxidation of ligand-free V is less complete and results in multiple oxygen-bound products. This demonstrates the high chemical selectivity of single-site metal centers in metal-ligand complexes at surfaces compared to metal nanoislands.