Preferential intercalation of isomeric but-2-enedioate anions into the layered double hydroxides

Intercalation of cis-but-2-enedioate anion or trans-but-2-enedioate anion into the layered double hydroxide (LDH), [Mg0.66Al0.34(OH)2]Cl0.34·0.43H2O was carried out by the method of ion-exchange procedures. Selective reaction was observed in competitive experiments involving an equal concentration pairs of acids. The trans-but-2-enedioate anion is preferentially intercalated into the Mg-Al-LDH. The obtained intercalation compounds were characterized by X-ray diffraction, infrared and thermogravimetry techniques. The charge density on the oxygens of each of the carboxylate groups for both anions was investigated utilizing ab initio (HF/6-31G) method by G98w. From the X-ray diffraction data, the guest size and the charge density of the oxygen of the guest, the orientation of both anions between the layers was determined and the preferential intercalation mechanism was studied. These results indicate the possibility of a molecular recognition ability of LDHs.