A Theoretical Study of Cu(II) Sites in a Faujasite-Type Zeolite:  Structures and Electron Paramagnetic Resonance Hyperfine Coupling Constants

Calculations using a density functional theory-based methodology have been performed to study the electron paramagnetic resonance (EPR) properties of Cu(II)−faujasite models. Cluster models of sites II and III have been investigated. The calculated spin density is distributed both on Cu and on the framework atoms. Its value for Cu depends on its local bonding interactions with the zeolite framework. The calculated hyperfine coupling constants vary linearly with the calculated Cu spin density, whatever the models and methodologies are. Comparison with experimental results shows that Cu cations in four- and six-membered rings (sites III and II) can be related with the measured EPR signals, although no explicit site−signal correlation could be found.