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.

Graphical abstractAll the geometric isomers of the nine benzoate derivatives has been intercalated into [LiAl2(OH)6]Cl·H2O in 50% (v/v) water/ethanol solution. Competitive intercalation studies using binary mixtures of the isomeric benzoates suggests that dipole moment may be a good general index for the preference.Figure optionsDownload full-size imageDownload as PowerPoint slide