HIGH-RESOLUTION SOLID-STATE NMR OF EXCHANGEABLE CATIONS IN THE INTERLAYER SURFACE OF A SWELLING MICA - NA-23, CD-111, AND CS-133 VERMICULITES

The isotropic chemical shift of 23Na, 111Cd, or 133Cs in cation-exchanged Llano vermiculites is directly related to the hydration states. This swelling mica undergoes phase transitions easily detectable from the X-ray reflections along the C axis, perpendicular to the basal plane, the d001 reflections. The reference states are the corresponding dilute salt solutions. With respect to this reference, the chemical shift can be accounted for by a general equation obtained by considering the configuration of the lattice and water oxygen ligands and the electron back-donation from the ligand to the cation. The quadrupole coupling constant (QCC) of 23Na at all hydration states and in the dehydrated state is small (QCC < 1 MHz), whereas in the dehydrated state the 111Cs QCC is about 6.7 MHz (vQ ≃ 0.48 MHz). For all three cations the asymmetry parameter (either quadrupolar or chemical shift) is close to one. © 1990 American Chemical Society.