4-NITROHIPPURIC ACID IN LAYERED LITHIUM ALUMINATES - ONSET OF NONLINEAR OPTICAL-PROPERTIES

[LiAl2(OH)6]Cl is a layered compound in which lithium and aluminum atoms are surrounded octahedrally by hydroxyl groups and constitute the two-dimensional framework. Anions, such as Cl-, are positioned between these sheets in order to preserve neutrality. In this study, we have examined the intercalation of 4-nitrohippuric acid (NHA) into the layers from an acetone solution. The gallery height, as measured by X-ray diffraction, is ∼18 Å, indicating that the NHA molecules are stacked perpendicular to the layers. Optical spectroscopic studies have shown that the NHA molecules are held in the interlayers as carboxylic acid and the process of intercalation is not by an ion-exchange process. The orientation of the NHA molecules in the interlayers leads to an ordered arrangement of dipoles, and the material exhibits frequency-doubling characteristics, generating 532-nm radiation from incident 1064 nm. This is particularly interesting, since crystals of pure NHA do not exhibit any nonlinear optical properties due to a centrosymmetric packing in the crystal. © 1990 American Chemical Society.