Stabilisation of reactive intermediates in molecular sieves

This paper presents studies on paramagnetic intermediates, free atoms and radicals produced in γ-irradiated molecular sieves and their reactions with adsorbate molecules or exchangeable cations. Four different systems have been investigated using EPR spectroscopy, Na-A/CH₄, AgNa-A/CH₃OH, Ag-SAPO-11/C₂H₄ and AgCs-rho/NH₃. It was found that methyl radicals are formed in two different sites in Na-A/CH₄ and in one of them they are stable at room temperature. The formation of Ag·CH₂OH⁺ radical cation with one-electron bond between silver and carbon has been established in AgNa-A/CH₃OH by EPR experiments with ¹³C]CH₃OH and DFT calculations. In Ag-SAPO-11/C₂H₄ the stabilisation of biligand silver/ethylene complex, Ag⁰(C₂H₄)₂ was postulated based on EPR and DFT results. Tetrameric silver clusters (Ag ₄ ³⁺ ) produced radiolytically in AgCs-rho/NH₃ strongly interact with two ammonia molecules as was deduced from the changes in superhyperfine structure of high-field EPR line of Ag ₄ ³⁺ pentet for zeolite exposed to ¹⁴N]NH₃ and ¹⁵N]NH₃. The presented examples clearly show that the combination of radiation methods with EPR technique is very useful to study the structure and reactivity of paramagnetic intermediates.