Preferential anion exchange intercalation of pyridinecarboxylate and toluate isomers in the layered double hydroxide [LiAl2(OH)6]Cl·H2O

Abstract

All isomers of both pyridinecarboxylate (2-PA; 3-PA and 4-PA) and toluate (o-TA; m-TA and p-TA) can be intercalated into the layered double hydroxide [LiAl2(OH)6]Cl·H2O in water or a water–ethanol mixture at RT to give the fully ion-exchanged first stage intercalation compounds [LiAl2(OH)6]·G·yH2O (G = 2-PA; 3-PA; 4-PA; o-TA; m-TA and p-TA; y = 2.5–3.5). Experiments also showed that using a mixed ethanol–water solvent may improve the crystallinity and decrease the production of Al(OH)3. The observed interlayer separations for the intercalates vary from 14.9 A for [LiAl2(OH)6](4-PA)·3H2O to 16.7 A for [LiAl2(OH)6](p-TA)·2.5H2O. When [LiAl2(OH)6]Cl·H2O is added to a solution containing an equal concentration of two or three isomers of either pyridinecarboxylate or toluate anions, the host exhibits preferential anion-exchange intercalation. Following a series of competitive intercalation reactions involving two or three component mixtures we were able to determine the preference order for intercalation of both PA and TA guests in [LiAl2(OH)6]Cl·H2O. The order was found to be 4-PA > 2-PA > 3-PA and p-TA > m-TA > o-TA in water at both 20 and 80 °C.