EPR spectroscopy of copper and manganese complexes encapsulated in zeolites

The structural basis for the enhanced catalytic activities of copper and ma nganese Schiff base complexes encapsulated in zeolite-Y is investigated by EPR spectroscopy. The study provides an unequivocal evidence for the encaps ulation of complexes inside the supercages of zeolite-Y. The EPR spectrosco py distinguishes the encapsulated complexes from the "neat" and surface-ads orbed metal complexes. Neat complexes showed broad EPR spectra correspondin g to nearest neighbour spin-spin interactions whereas the zeolite-encapsula ted metal complexes showed well resolved metal hyperfine features similar t o the spectra in dilute frozen solutions. The spin Hamiltonian parameters r eveal a distorted square pyramidal geometry and an increase in the in-plane covalency of metal-ligand bond as a consequence of encapsulation. The obse rved changes in the molecular electronic structure are correlated to the en hanced catalytic activity of the encapsulated metal complexes. (C) 2001 Els evier Science B.V. All rights reserved.