Using NMR in Structural Studies of Aluminum Hydroxide Intercalation Compounds with Lithium Salts.

The effect of the anion charge on the structure of [LiAl2(OH)6]nX (X = Cl-, Br-, I-, SO42-, C6H8O42-) intercalation compounds and the water effect on the structure of [LiAl2(OH)6]Cl·nH2O have been studied using 1H, 7Li, and 27Al NMR. A change in the charge on the anion leads to significant changes in the asymmetry parameter for the lithium and aluminum nuclei with relatively small changes in the quadrupolar coupling constant and the broadening factor. The structure of the intermediate [LiAl2(OH)6]Cl·0.5H2O hydrate can be represented as a derivative of the structure of the anhydrous [LiAl2(OH)6]Cl intercalate with a slightly increased layer thickness and a minor orthorhombic distortion of the hexagonal cell; the water molecules partially fill the interlayer voids and participate in the diffusion process. Further hydration of the intercalate (x ≥ 1) leads to a minor (0.2Å) increase in the layer thickness and is accompanied by disordering of chloride ions and water molecules in the interlayer space. [ABSTRACT FROM AUTHOR]