Layered double hydroxide intercalated with p-methylbenzoate and p-bromobenzoate: molecular simulations and XRD analysis

Abstract

Samples of Mg4Al2 layered double hydroxide (LDH) intercalated with p-methylbenzoate and p-bromobenzoate anions were prepared by reconstruction of calcined LDH. The interlayer arrangement of guests was investigated by molecular modeling combined with X-ray powder diffraction and thermogravimetry. Molecular modeling was carried out in a Cerius2 modeling environment. In both structures the guest anions adopt a nearly perpendicular arrangement of their long axis with respect to the host layers and they are anchored to the OH groups of the layers through COO− groups via electrostatic interactions. Molecular modeling revealed that both structures of the intercalates exhibit a certain disorder of guest anions in the interlayer space. In the case of LDH–p-methylbenzoate intercalate the anions tend to be situated in disordered rows, and the LDH–p-bromobenzoate intercalate exhibits a total disorientation of guest anions. A good agreement between calculated and measured X-ray diffraction patterns and between experimental and calculated basal spacings was obtained. In the LDH–p-methylbenzoate intercalate dexp=16.96 Å and dcalc=16.97 Å, and in the case of LDH–p-bromobenzoate intercalate dexp=17.19 Å and dcalc=17.40 Å.