The surface and intercalate chemistry of the layered silicates. Part IV. Crystallographies electron-spectroscopic, and kinetic studies of the sodium montmorillonite–pyridine system

Abstract

Neutron-diffraction studies of the stable pyridine (py) intercalate of Na⁺-exchanged montmorillonite [basal-spacing 14.8 Å, idealized formula Na⁺ _0.5(Al_3.5Mg_0.5)Si₈O₂₀(OH)₄·py·2H₂O] have been carried out. It is shown that the plane of the guest aromatic molecule is perpendicular, and the long (C–N) axis inclined at 60°, to the aluminosilicate sheets. The kinetics of the conversion of the initially formed less-stable intercalate [basal-spacing 23.3 Å, idealized formula Na⁺ _0.5(Al_3.5Mg_0.5)Si₈O₂₀(OH)₄·(py)₂·H₂O] to the more stable 14.8 Å intercalate has been followed by X-ray diffraction. X-Ray induced photoelectron spectroscopy (x.p.s.) has also been used to probe electronic changes in the environment of the Na⁺ ions following intercalation. X.p.s. shows that the pyridine is retained even in vacua of 10^–6 N m^–2 at room temperature, and that the nitrogen atoms are situated within essentially one type of environment.