Staging of organic and inorganic anions in layered double hydroxides

The layered double hydroxides (LDHs) Zn-Al-2(OH)(6)Cl(.)nH(2)O, Zn2Cr(OH)(6)Cl(.)nH(2)O, and Cu2Cr(OH)(6)Cl(.)nH(2)O have been shown to undergo staged intercalation reactions with succinate and tartrate anions. Monitoring the process in situ using energy-dispersive X-ray diffraction reveals the formation of second-stage intermediates caused by the filling of every second layer. Depending on the nature of the organic anion, the Bragg peaks of the second-stage intermediates and the fully organic exchanged materials emerge in two distinct sequences indicating two exchange pathways. For tartrate exchange, the fully exchanged material is not observed until the intermediate has gone through its maximum and the chloride precursor has disappeared completely, while for succinate exchange, the final state of intercalation and the second-stage intermediate simultaneously appear. Similar staging has previously been reported only for LiAl2(OH)(6)Cl(.)2H(2)O. These results demonstrate that staging in the intercalation of LDH does not involve a structural order of the host and cannot be explained by a tactoid mechanism.