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

Encapsulation of two different Mn(II)salen complexes within the supercavities of zeolite Y was accomplished by means of two established synthetic routes and they were unequivocally characterized by spectroscopic techniques [Fourier transform infrared, diffuse reflectance and electron paramagnetic resonance (EPR)]. In solution it is well established that high-spin Mn(II)salen complexes react spontaneously with molecular oxygen to yield various oxidation products. These include Mn(III) species and several oxy-bridged [Mn(salen)O] n molecules. In the zeolite only the monomeric Mn(III)salen complex can be expected owing to the steric constraints imposed by these inorganic solids. This oxidation reaction from Mn(II) to Mn(III) was easily followed by EPR spectroscopy. According to these EPR measurements, the intrazeolitic oxidation of Mn(II)salen to Mn(III)salen by dioxygen proceeds with difficulty by virtue of a speculative lattice coordination stabilizing effect. This situation can be overcome by using efficient classical oxidants such as tert-butyl hydroperoxide or hypochlorite. Copyright © 2000 John Wiley & Sons, Ltd.