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)(2)CO2-) and succinate (-O2C(CH2)(2)CO2-) anions was also investigated. Monitoring the exchange process in siru using energy-dispersive X-ray diffraction revealed the forniation of second-stage internimiates 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. (C) 2004 Elsevier B.V. All rights reserved.