Hyperfine parameters of pyridyl-containing iminoxy radicals generated fromoximes by gamma-irradiation and in zeolite lattice: EPR spectroscopy and density functional study

Incorporation of pyridyl oximes into the channels of thermally activated pe ntasil zeolite ZSM-5 gives rise to iminoxy radicals. EPR spectrum of the sp ecies derived by dehydrogenation of di-2-pyridilketone oxime is fully aniso tropic and characteristic for the iminoxy sigma-type neutral radical. The E PR spectra of the radicals derived from 2-pyridinealdoxime and 4-pyridineal doxime exhibit additional splitting due to the azomethine hydrogen. The (g) over cap and (A) over cap tensor parameters were determined on the basis o f EPR spectra. In order to identify a geometric isomer (E or Z) of the imin oxyls obtained in the pores of the zeolite and within gamma-irradiated samp les of solid oximes, hyperfine interaction parameters of the generated radi cals were compared with the parameters calculated using density functional theory (DFT); these calculations allow to characterize the iminoxy radical isomers formed in zeolite and oxime matrices. (C) 1999 Elsevier Science B.V . All rights reserved.