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 center dot H2O in 50% (v/v) water/ethanol Solution at 80 degrees C to give fully anion-exchanged first stage intercalation compounds [LiAl2(OH)(6)]G center dot yH(2)O (G = a substituted benzoate). The observed interlayer separations of the intercalates vary from 14.3 angstrom for [LiAl2(OH)(6)](4-nitrobenzoate) center dot 2H(2)O to 20.6 angstrom for [LiA](2)(OH)(6)](3-dimethylaminobenzoate) 3H(2)O. 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. (C) 2005 Elsevier Inc. All rights reserved.