Intercalation of various anions in layered double hydroxides - ion exchange reactions

Layered double hydroxides (LDH) are a family of compounds with a wide range of applications from cementous systems through the immobilization of potentially toxic elements from the environment to catalysts for organic reactions. The root of the LDH structure is a brucite layer, in which one-third of divalent cations are replaced by trivalent cations, generating a positive surcharge according to the scheme [(M2+1-x M3+x)(OH)2]x+ (where M2+ = Mg2+ or Ca2+ ; M3+ = Al3+ ). In order to balance the electrostatic charge in the crystal, anions such as chloride are intercalated between the layers, resulting in enhanced interlayer spacing. Importantly, the negatively charged interlayer species are exchangeable, and neutral molecules such as water may also be inserted between the layers. This results in a huge diversity of complex structures and polytypes with variable compositions. Here, we intend to measure single-crystal X-ray diffraction of ion-exchanged LDH.