A reinterpretation of the EPR spectra of Cu(II) in zeolites A, Y and ZK4, based on ab initio cluster model calculations

• DOI: 10.1039/b100531f
• Publication Date: 2002-07-26T09:05:30Z
• Authors: Kristine Pierloot; Annelies Delabie; Marijke H. Grooth...; Robert A. Schoonh...
• Keywords: Coordination sphere

A theoretical study is presented of the EPR spectra dehydrated Cu(II)-A, Cu(II)-Y and Cu(II)-ZK4 zeolites. B3LYP-DFT geometry optimizations were performed on cluster models representing six-ring sites with different Al contents, as observed for All calculated structures indicated a strong preference Cu(II) ion coordination to oxygens bound rather than Si, together striving planar four-fold oxygen in six-rings. Depending number relative positions aluminiums ring two distinct modes distinguished, containing either only one or several "competing" position both their first sphere. The electronic g-tensors all optimized by means CASPT2 method (multiconfigurational perturbation theory based complete-active-space reference wavefunction), inclusion spin–orbit coupling. These calculations pointed appearance EPR-signals connection modes. Based close correspondence between g-factors experimental three zeolites under investigation, new interpretation latter signals suggested. According this occurrence zeolite Y opposed signal connected higher Si/Al ratio former zeolite, topology (as was suggested earlier assignments spectra). Our corroborated obtained Cu-ZK4: same A, but closer Y, indeed observed. Finally, our also indicate that, six-rings more aluminium, likely undergo hopping process at room temperature.