Cationic ordering and second-staging structures in copper-chromium and zinc-chromium layered double hydroxides

Extended X-ray absorption fine structure (EXAFS) was used to evidence a cationic order within the sheets of the layered double hydroxide (LDH) [Cu2Cr-Cl]. The influence of the synthesis mode, coprecipitation or oxide-salt method, on the cation ordering was demonstrated. Indeed, EXAFS simulations concluded unambiguously for a local order in a longer range for the coprecipitated phase. The exchange of chloride anions in this lamellar host as well as in [Zn2Cr-Cl] by tartrate (−O2C(CHOH)2CO2−) and succinate (−O2C(CH2)2CO2−) anions was also investigated. Monitoring the exchange process in situ using energy-dispersive X-ray diffraction revealed the formation of second-stage intermediates caused by the filling of every second layer in both cases. We infer that staging phenomena in LDH system is a peculiarity of mixed organic-inorganic ion exchanged forms resulting from the hydrophobic binding effect of the organic part.