Quantitative EPR study of Mn(II)salen oxidation within zeolite Y

Encapsulation of two different Mn(II)salen complexes within the supercaviti es of zeolite Y was accomplished by means of two established synthetic rout es and they were unequivocally characterized by spectroscopic techniques [F ourier transform infrared, diffuse reflectance and electron paramagnetic re sonance (EPR)]. In solution it is well established that high-spin Mn(II)sal en complexes react spontaneously with molecular oxygen to yield various oxi dation products. These include Mn(III) species and several oxy-bridged [Mn( salen)O](n) molecules. In the zeolite only the monomeric Mn(III)salen compl ex can be expected owing to the steric constraints imposed by these inorgan ic solids. This oxidation reaction from Mn(II) to Mn(III) was easily follow ed by EPR spectroscopy. According to these EPR measurements, the intrazeoli tic oxidation of Mn(II)salen to Mn(III)salen by dioxygen proceeds with diff iculty by virtue of a speculative lattice coordination stabilizing effect. This situation can be overcome by using efficient classical oxidants such a s tert-butyl hydroperoxide or hypochlorite. Copyright (C) 2000 John Wiley & Sons, Ltd.