ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION STUDIES OF THE INCORPORATION OF MACROCYCLIC-COMPLEXED CUPRIC IONS INTO SILICEOUS MCM-41

A novel complexation method to control the incorporation of Cu(II) within silica tubes of siliceous MCM-41 is developed. Complexation of the cupric ions with a surfactant macrobicyclic cage compound in the reaction gel has been used for this purpose. Electron spin resonance and electron spin echo modulation techniques are used to monitor the coordination of Cu(II) in as-synthesized, calcined, and dehydrated MCM-41 as well as its interaction with polar absorbates such as NH3, and D2O. Cupric ions are found to be coordinated to four framework oxygens in dehydrated CuMCM-41. Adsorption of ammonia and water results in the formation of [CU(NH3)(4)](2+) and [CU(H2O)(6)](2+) complexes. The results of this complexation method are compared with experiments on CuMCM-41 where uncomplexed Cu(II) is directly added to the reaction gel. No major differences in the dehydration behavior and adsorbate interaction were found. Therefore, both complexed and uncomplexed Cu(II) ions introduced during synthesis are incorporated inside the silica tubes of the MCM-41 structure.