CU-II LOCATION AND ADSORBATE INTERACTION IN CU-II-EXCHANGED SYNTHETICNA-OMEGA GALLOSILICATE - EPR AND ELECTRON-SPIN ECHO MODULATION STUDIES

The location of Cu-II and its interaction with adsorbates in Cu-II-exc hanged synthetic Na-omega gallosilicate have been studied by EPR and e lectron spin echo modulation (ESEM) spectroscopies. These results are compared with those of Cu-II-exchanged Na-omega aluminosilicate and al so those of L and offretite gallosilicates of similar channel type and size, and the differences are discussed. In general, similar results to those for CuNa-omega gallosilicate are obtained for CuNa-omega alum inosilicate. It is concluded that, in fresh hydrated omega material, C u-II is in a main channel coordinating to three water molecules and to framework oxygens in the main channel wall. A minor Cu-II diaquo spec ies not seen in the gallosilicate is observed in the aluminosilicate. Upon evacuation at increasing temperature, Cu-II moves from the main c hannel to a gmelinite cage. Dehydration at 410 degrees C produces one Cu-II species located in a six-ring window of a gmelinite cage, based on a lack of broadening of its EPR lines by oxygen. In L and offretite gallosilicates, there is evidence for back migration of Cu-II from a hexagonal prism into a main channel to coordinate with adsorbates. How ever, in omega the back migration from a gmelinite cage to a main chan nel seems to be blocked, as shown by very slow changes in the EPR spec tra and differing coordination numbers for methanol, ethanol and propa nol to Cu-II when alcohols are adsorbed. Cu-II does not form a complex with propanol or larger adsorbates in omega gallosilicate. It is sugg ested that, in omega, small adsorbates must diffuse into a gmelinite c age where Cu-II is located, to form Cu-II-adsorbate complexes. The slo w changes in the EPR spectra correspond to the time for adsorbate diff usion into a gmelinite cage. Cu-II interacts with one molecule each of ethylene and acetonitrile, based on EPR and ESEM analyses. Cu-II form s a square-planar complex containing four molecules of ammonia, based on resolved nitrogen superhyperfine coupling.