General insights into structural evolution of layered double hydroxide: underlying aspects in topochemical...

The topochemical transformation from transition-metal brucite hydroxide (Co(1-x)Fe(x)(OH)(2), Co(OH)(2), Co(1-x)Ni(x)(OH)(2)) to corresponding (Co(2+)-(Co(3+))-Fe(3+), Co(2+)-(Ni(2+))-Co(3+)) LDH under oxidizing halogen agents (iodine, bromine) exhibits different staging phenomena depending on the metallic composition/ratio in starting brucite. A plausible charge hopping mechanism based on valence interchange between redoxable charge center (Fe(3+)/Co(3+)) and neighboring divalent sites in the host sheet is proposed to understand the restoration of electron donor sites at the interface between brucite crystallites and halogen agents, which ensures a continual oxidative reaction, and a staged intercalation/diffusion of in situ reduced halide anions into the interlayer gallery commensurate with the host charge propagation. The discussion on the correlation between staging product and metallic composition/ratio offers a general perspective and new insights into M(2+)/M(3+) ratio and cation ordering, host layer charge, and phase evolution in LDH structure.