Selective anion-exchange intercalation of isomeric benzoate anions into the layered double hydroxide [LiAl2(OH)6]Cl·H2O

All the geometric isomers of the benzoate derivatives, XC6H4CO2− (X=F, Cl, Br, OH, OCH3, NO2, CO2CH3, NH2, N(CH3)2) can be intercalated into the layered double hydroxide [LiAl2(OH)6]Cl·H2O in 50% (v/v) water/ethanol solution at 80 °C to give fully anion-exchanged first stage intercalation compounds [LiAl2(OH)6]G·yH2O (G=a substituted benzoate). The observed interlayer separations of the intercalates vary from 14.3 Å for [LiAl2(OH)6](4-nitrobenzoate)·2H2O to 20.6 Å for [LiAl2(OH)6](3-dimethylaminobenzoate)·3H2O. Competitive intercalation studies using mixtures of isomeric benzoates showed that the 4-isomers and 2-isomers are the most and the least preferred anions, respectively. Comparing the calculated dipole moments of the anions with the observed isomeric intercalation preferences suggests that dipole moment may be a good general index for the preference; however, it should be remembered that the bulkiness and electronegativity of the other substituent could be very important factors that affect the preferential intercalation.