EPR spectroscopy of copper and manganese complexes encapsulated in zeolites

Abstract

The structural basis for the enhanced catalytic activities of copper and manganese Schiff base complexes encapsulated in zeolite-Y is investigated by EPR spectroscopy. The study provides an unequivocal evidence for the encapsulation of complexes inside the supercages of zeolite-Y. The EPR spectroscopy distinguishes the encapsulated complexes from the "neat" and surface-adsorbed metal complexes. Neat complexes showed broad EPR spectra corresponding to nearest neighbour spin–spin interactions whereas the zeolite-encapsulated metal complexes showed well resolved metal hyperfine features similar to the spectra in dilute frozen solutions. The spin Hamiltonian parameters reveal a distorted square pyramidal geometry and an increase in the in-plane covalency of metal–ligand bond as a consequence of encapsulation. The observed changes in the molecular electronic structure are correlated to the enhanced catalytic activity of the encapsulated metal complexes.