The Spectroscopic Study on the Dimerization of Pyridine Derivatives on the Surfaces of MgO, CaO and SrO

The adsorption and dimerization of pyridine derivatives on MgO, CaO, and SrO were studied by ESR and visible absorption spectrometries. Adsorbed pyridine on the oxides was found to give an ESR signal of five lines and 580 nm absorption spectrum which were attributed to dipyridyl anion radical. The deuterium isotope effects for the formation of dipyridyl anion radicals were observed on MgO and CaO, but not on strong basic oxide, SrO. Methylpyridines adsorbed on MgO gave the same species as pyridine by the irradiation of light (λ>370 nm). From these facts, the surface intermediates for the dimerization reaction were discussed. When the adsorbed species were exposed to oxygen molecule, the dipyridyl anion radicals faded away and the ESR spectra attributed to the O2− ion were observed.