Structure of the Chloride‐ and Bromide‐Intercalated Layered Double Hydroxides of Li and Al – Interplay of Coulombic and Hydrogen‐Bonding Interactions in the Interlayer Gallery

Abstract

AbstractRietveld refinement of the structures of the [LixAl(OH)3]Xx·yH2O (X = Br, Cl; y ≈ 1/2, 2/3) layered double hydroxides (LDHs) shows that the halide ion occupies two distinct positions in each phase. One position (2a), promoted by Coulombic attraction, is proximal to the Li+ ion, which is the seat of the positive charge in the metal hydroxide layer. The other position (6h) is within a close hydrogen‐bonding distance from the hydroxy group of the metal hydroxide layer as well as the intercalated water molecule. The LDH with intercalated Br– ions crystallizes in two different structures, one of which is isostructural with the Cl– analogue. In the other structure obtained at a higher relative humidity (≥76 %; y ≈ 2/3), the Br– ion occupies a site proximal to the Al3+ ion (2b), and intercalated water molecules are proximal to the Li+ ion. In this structure, the hydration of the Li+ ion in a distant coordination shell overcomes Coulombic interactions with Br– ions. On partial dehydration (ambient humidity 29 %; y ≈ 1/2), this Br– ion reversibly reverts back to the site (2a) proximal to the Li+ ion, which results in a humidity‐induced structure change without any variation in the basal spacing. Thereby, the position of the halide ion in the interlayer gallery is determined by the interplay of Coulombic and hydrogen‐bonding interactions.