ELECTRON SPIN RESONANCE STUDY OF DONOR- ACCEPTOR SITES IN ZR-MONTMORILLONITE

nite of different grain size pillared with Zr by interaction with perylene (Pe) and tetracyanoethylene (TCNE) has been studied. These smectites are strongly affected by the exchange ofZr and appear to be strong electron acceptors and weak donors. The ESR results how that heir ability to form charge transfer radicals i related to the details of preparation, which most probably control the accessibility of Pe and TCNE to the internal surface. Various properties of materials containing a paramagnetic cation as a local probe can be studied by electron spin resonance (ESR): geometry, type of active sites, transformation by various treatments. The cation can be introduced on purpose as a paramagnetic probe and does not disturb the behaviour of the compound studied. In some favourable cases, the paramagnetic on is already present within the structure and is an integral part of the material with the result that the methodology and investigation are simplified as insertion of a foreign substance may lead to additional problems. It is well known that the adsorption of aromatic amines or hydrocarbons on alumina or silica-aluminas produces radical ions detectable by ESR (Terenin et al., 1963). The formation of these ions is attributed to a transfer of charge occurring between the organi