ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION STUDIES OF CU(II) ION COORDINATION AND ADSORBATE INTERACTION IN ION-EXCHANGED ALMCM-41 MESOPOROUS MATERIALS

Cu(II) ions have been ion-exchanged into AlMCM-41 mesoporous material by a liquid state reaction. The coordination of Cu(II) in dehydrated (L)Cu-AlMCM-41 and its interaction with various polar and nonpolar adsorbate molecules were studied by electron spin resonance and electron spin echo modulation spectroscopy. In comparison to Cu(II) ions ion-exchanged into pure siliceous (L)Cu-MCM-41, a substantial higher ion-exchange capacity and stronger bonding of the Cu(II) ions to the framework were found in (L)Cu-AlMCM-41. Cupric ions are coordinated to six framework oxygens in dehydrated (L)Cu-AlMCM-41. Cupric ions coordinate directly to two molecules of water, methanol, or ammonia. But Cu(II) is also still coordinated to framework oxygens in these complexes, indicating a strong bonding of the Cu(II) to the framework. Bulky adsorbate molecules such as pyridine, benzene; and ethylene do not directly coordinate to the cupric ions. This suggests that the ion-exchange sites are located within the walls of the AlMCM-41 structure.