COORDINATION OF CUPRIC IONS TO WATER AND TO METAL-OXIDE PILLARS IN COPPER(II)-DOPED, AL-13-PILLARED AND ZR-4-PILLARED MONTMORILLONITE CLAYS STUDIED BY ELECTRON-SPIN ECHO MODULATION SPECTROSCOPY

The location and coordination of Cu(II) cations exchanged into Al-13- and Zr-4-pillared natural montmorillonite has been studied by electron spin resonance and electron spin echo modulation (ESEM) spectroscopies. For the first time, ESEM spectroscopy was applied successfully to Cu(II)-doped pillared montmorillonite. When copper cations are exchanged before introduction of the alumina pillars, they are directly coordinated to two water molecules and four oxygens of an alumina pillar. When copper cations are exchanged after introduction of the alumina pillars, they are directly coordinated to one water molecule and five oxygens of an alumina pillar. Thus in both cases the cupric ion is strongly bound to the alumina pillars. In Zr-4-pillared montmorillonite, cupric ion directly coordinates to three water molecules and to only three oxygens of a zirconia pillar. Thus the cupric ion binds less strongly to zirconia pillars. Also, in Zr-4-pillared montmorillonite, but not in Al-13-pillared montmorillonite, part of the Cu(II) is freely tumbling between the clay pillars and is suggested to be hexacoordinated to water.