Efficient separation of pyridinedicarboxylates by preferential anion exchange intercalation in [LiAl2(OH)6]Cl·H2O

Abstract

All six isomers of pyridinedicarboxylate (2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA) can be intercalated by the layered double hydroxide [LiAl2(OH)6]Cl·H2O in water at 100 °C to give the fully ion-exchanged first stage intercalation compounds [LiAl2(OH)6]G0.5·xH2O (G = 2,3-PDA; 2,4-PDA; 2,5-PDA; 2,6-PDA; 3,4-PDA; 3,5-PDA; x = 2–3.5) . The observed interlayer separations for the intercalates vary from 10.9 A for the high temperature form of [LiAl2(OH)6](3,5-PDA)0.5·2H2O to 14.8 A for [LiAl2(OH)6](2,3-PDA)0.5·3H2O. When a solution containing an equal concentration of two or more of the pyridinedicarboxylate anions is added to a suspension of [LiAl2(OH)6]Cl·H2O in water then the host exhibits preferential anion-exchange intercalation. Following an extensive series of competitive intercalation reactions involving two component through to six component mixtures we were able to determine the preference order for intercalation of all six PDA guests in [LiAl2(OH)6]Cl·H2O. The order was found to be 2,5-PDA > 2,3-PDA > 2,4-PDA > 2,6-PDA ≈ 3,5-PDA ≈ 3,4-PDA in water at 100 °C.