NMR-STUDY OF DYNAMICS OF DIMETHYL-SULFOXIDE MOLECULES IN KAOLINITE DIMETHYL-SULFOXIDE INTERCALATION COMPOUND

We have studied molecular motions in kaolinite/dimethyl sulfoxide (DMSO) compounds by means of solid-state NMR. Quantitative analyses of thermogravimetric analysis and C-13 and Si-29 magic-angle-spinning (MAS) NMR spectra reveal the formation of Al2Si2O5(OH)(4) .(CH3)(2)SO. C-13 MAS NMR spectra show two inequivalent methyl carbons for interlayer DMSO molecules over the temperature range similar to 170-330 K, demonstrating that no exchange between the two methyl sites takes place. We have measured C-13 spin-lattice relaxation times T-1 for kaolinite/DMSO, where C-13 spins relax by rotation of the CH3 group around the C-3 axis, Activation energies for the Methyl rotation have been estimated for the two sites, 13.0 and 16.5 kJ/mol for the keyed and unkeyed methyl groups, respectively. H-2 spectra have been measured for kaolinite/DMSO-d(6) between 160 and 330 K, which are composed of resolved doublet (RD) and narrow central (NC) components. NC is a surface-adsorbed species, while RD contains surface and interlayer molecules. Line shapes indicate that RC undergoes rotation of the CD3 group around the C-3 axis and NC does isotropic rotation. H-2 T-1 has been measured also in the above temperature range, and H-2 spins are relaxed by the CD3 rotation around the C-3 axis. Si-29 spins in the kaolinite/DMSO compound relax by the CH3 rotation in addition to the relaxation by paramagnetic impurities, indicating the contribution of C-13-H-1 dipolar interaction between the guest molecule and the host. The H-1 chemical shift of hydroxyl groups in the host was determined by the CRAMPS technique, which is not changed by the intercalation.