Perchlorate‐Intercalated Layered Double Hydroxide of Ca and Al: Synthesis, Structure Refinement, and Reversible Dehydration

Abstract

Hydrocalumite-like layered double hydroxides are anionic clays comprising positively charged metal hydroxide layers of the composition [Ca 2 Al(OH) 6 (H 2 O) 2 ] + . The water molecules provide the seventh coordination for the Ca 2+ ion. Anions are intercalated in the interlayer space to balance the charge leading to a class of LDHs having the formula [Ca 2 Al(OH) 6 (H 2 O) 2 ]·A (A = Cl, Br, I). Upon dehydration the Ca 2+ ion gets coordinatively unsaturated, and crystal chemical considerations dictate that the layered structure should collapse. When A = ClO 4 -, the LDH dehydrates fully below 80°C, but the layered structure is retained [a]

Synthesis, polytypism, and dehydration behaviour of nitrate-intercalated layered double hydroxides of Ca and Al

“…Hydrocalumite-like LDHs with other anions such as Br À , I À , ClO 4 À , and SO 4 2À -hereinafter abbreviated to the symbol [Ca-Al-A] (A = anion), have also been assigned to the structure of the 3R polytype (space group R% 3). [12][13][14] Among all the anions, the NO 3 À ion is unique in that its orientation depends on the layer charge as well as the degree of hydration.…”