S. Hayashi
[Clays and Clay Minerals, Vol.45, pp.724-732, 1997]

Motion of the guest molecules in kaolinite/dimethyl sulfoxide (DMSO) intercalation compounds Al₂Si₂O₅(OH)₄�E(CH₃)₂SO has been studied by means of solid-state nuclear magnetic resonance (NMR) in the temperature range between 300 and 380 K, which is just below the evolution temperature. The ¹³C magic angle spinning (MAS) NMR spectra show two inequivalent methyl carbons: one methyl carbon is keyed in the ditrigonal hole of the silicate sheet, while the other is located parallel to the sheet. Above 320 K, the two peaks have different intensities, suggesting that the keyed methyl groups from some of the DMSO molecules are released from the hole. The 2H NMR spectra have been measured for kaolinite/DMSO-d₆ intercalate. The methyl group of the interlayer DMSO molecule undergoes free rotation around its C₃ axis over the temperature range studied. The axis of rotation is fixed at the low temperature (about 160 K), and the methyl group initiates a wobbling motion whose amplitude increases with temperature. The wobbling angles have an anisotropy, estimated from theoretical analysis of the ²H spectral line shapes. The DMSO molecules released from the silicate layer undergo anisotropic rotation of the whole molecule. Fig. 1 shows the motion of the guest molecules schematically.