Thermal Reaction of 2,4-Dibromopyridine on Cu(100)

Abstract

Nitrogen-containing aromatics have potential applications in surface functionalization, corrosion inhibition, and carbon-nitride materials. Reflection–absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and temperature-programmed reaction/desorption (TPR/D) have been employed to study the system of 2,4-C₅NH₃Br₂/Cu­(100). Our experimental results indicate that 2,4-C₅NH₃Br₂ is adsorbed predominantly in molecular form on Cu(100) at 100 K; however, a tiny fraction of the adsorbed molecules is subjected to debromination. The 2,4-C₅NH₃Br₂ undergoes partial C–Br dissociation below 400 K, forming C₅NH₃Br intermediate. Although after breaking both the C–Br bonds (>400 K), 2,4-pyridyne (C₅NH₃) can be formed, the possibility of Ullmann coupling reaction cannot be excluded. The NEXFAS study shows a ∼ 35° average inclination of the aromatic plane, with respect to the surface, in a packed 2,4-pyridyne adsorption layer. Thermal decomposition of the C₅NH₃ or its coupling reaction products on the Br/Cu(100) surface mainly occurs at a temperature higher than 550 K, generating H₂, HCN, HBr, and (CN)₂