Synthesis and Structure of the Gibbsite Intercalation Compounds [LiAl₂(OH)₆]X {X = Cl, Br, NO₃} and [LiAl₂(OH)₆]Cl·H₂O Using Synchrotron X-ray and Neutron Powder Diffraction

Abstract

Treatment of gibbsite {γ-Al(OH)3} with the lithium salts LiX {X = Cl, Br, NO3} in water leads to intercalation of both the cations and anions into the host structure to give [LiAl2(OH)6]X·H2O {X = Cl, Br, NO3}. Thermogravimetric analysis indicates that these materials can be readily dehydrated to give highly hydroscopic, crystalline layered phases [LiAl2(OH)6]X {X = Cl, Br, NO3}. The structures of these dehydrated phases have been determined by synchrotron X-ray and neutron powder diffraction. The dehydrated intercalates with {X = Cl, Br} are isomorphous and crystallize in the P63/mcm space group. [LiAl2(OH)6]NO3 adopts a similar structure but crystallizes in space group P63/m due to disorder of the intercalated nitrate anions in the crystallographic ab plane. All the intercalates consist of eclipsed Al(OH)3 layers stacked along the c-axis with the halide or nitrate ions located at the cell edges and midway between the Al(OH)3 layers. The lithium ions have been located in the unfilled octahedral sites within the Al(OH)3 layers. The structure of the hydrated phase [LiAl2(OH)6]Cl·H2O has also been determined, it adopts a similar structure with eclipsed [LiAl2(OH)6]+ layers stacking along the c-axis. However the intercalated Cl- ions and water molecules were found to be disordered over five sites located midway between the Al(OH)3 layers.

A kinetic and mechanistic study into the formation of the Cu–Cr layered double hydroxide

“…The spectrum of the latter displays the 4 A 2g -4 T 1g and 4 A 2g -4 T 2g transitions at 410 nm and 575 nm respectively, with an intensity ratio of I 410 /I 575 = 1.18, in excellent agreement with the literature values. 51 However, for the aliquots removed from the reaction gel, the 4 51 This dimer has previously been reported over the pH range 2.8-5.0, the same range as seen in these experiments. The formation of such oligomeric species en route to LDH formation has previously been observed by Briois and co-workers.…”

“…This is consistent with the results of AES (such hydrolysis releases one third of the total number of copper ions in the CuO, as seen by AES) and UV-visible spectroscopy, which shows Cu being released into the reaction medium as its hexaaqua complex. This yields Cu(OH) 2 , a 1D material containing edge-sharing Cu(OH) 4 squares. The formation of this material is evidenced by XRD data, and is also supported by the SEM images (which contain irregular 1D-like particles at intermediate reaction times) together with the increase in OH content shown in IR spectroscopy.…”

“…Next, the unsaturated Cu 2+ ions in the chains increase their coordination number from 4 to 6 by condensing with aqueous Cr 3+ species. Each Cr 3+ ion can join with two Cu(OH) 4 squares, and in this way two chains are connected together. This must happen twice for every Cu in the chains, linking them together in two dimensions to form infinite planes.…”

Synthesis, structure refinement and chromate sorption characteristics of an Al-rich bayerite-based layered double hydroxide

“…As a consequence of the anisotropy in bonding, the layers can be stacked one above the other in different ways giving rise to a range of polytypes known as bayerite [1], gibbsite [2], nordstrandite [3] and doyleite [4]. The vacancies in the [Al 2 □(OH) 6 ] layer can be filled with Li þ ions to yield positively charged layers of the composition [Al 2 Li(OH) 6 ] þ . Simultaneous incorporation of anions in the interlayer region restores charge neutrality, yielding a layered double hydroxide (LDH) of the composition [LiAl 2 (OH) 6 ][A nÀ ] 1/n Á yH 2 O (A¼anion) [5].…”

“…The vacancies in the [Al 2 □(OH) 6 ] layer can be filled with Li þ ions to yield positively charged layers of the composition [Al 2 Li(OH) 6 ] þ . Simultaneous incorporation of anions in the interlayer region restores charge neutrality, yielding a layered double hydroxide (LDH) of the composition [LiAl 2 (OH) 6 ][A nÀ ] 1/n Á yH 2 O (A¼anion) [5]. Given the diversity of polytypes in the precursor Al(OH) 3 , the Li-Al LDHs also crystallize in diverse structures.…”