Formation of a Methoxy-Modified Interlayer Surface via the Reaction between Methanol and Layered Perovskite HLaNb₂O₇·xH₂O

The reactions between methanol (CH₃OH, CH₃OD, CD₃OD, ¹³CH₃OH) and layered HLaNb₂O₇·xH₂O were investigated. X-ray powder diffraction (XRD) analysis showed that a peak corresponding to the basal spacing of HLaNb₂O₇·xH₂O (1.05 nm) disappeared and a new peak appeared at 1.18 nm. Carbon-13 NMR spectra revealed the presence of two environments of the methyl group; the broad 67 ppm signal is ascribed to the rigid species located in the interlayer space, and the 50 ppm signal is ascribed to mobile methanol on the external surface. The amount of the latter species was negligibly small. Deuterium NMR spectra revealed the presence of a Pake doublet with an effective quadrupole coupling constant (QCC) of 47 kHz and an asymmetry factor (η) of zero, indicating that the CD₃O group was rigidly bound to the interlayer surface. In addition, when both CD₃OD and CH₃OD were used, no signal corresponding to the OD group was observed. Hence, although XRD results can be interpreted as intercalation of methanol, the ²H NMR results indicate that methanol was dissociatively adsorbed to the interlayer surface. The observed very high thermal stability of the methyl group is consistent with methoxy formation. The structure of the product is discussed on the basis of the results with larger n-alcohols.