Structure of Bayerite-Based Lithium−Aluminum Layered Double Hydroxides (LDHs): Observation of Monoclinic Symmetry

Abstract

The double hydroxides of Li with Al, obtained by the imbibition of Li salts into bayerite and gibbsite-Al(OH)(3), are not different polytypes of the same symmetry but actually crystallize in two different symmetries. The bayerite-derived double hydroxides crystallize with monoclinic symmetry, while the gibbsite-derived hydroxides crystallize with hexagonal symmetry. Successive metal hydroxide layers in the bayerite-derived LDHs are translated by the vector ( approximately -1/3, 0, 1) with respect to each other. The exigency of hydrogen bonding drives the intercalated Cl(-) ion to a site with 2-fold coordination, whereas the intercalated water occupies a site with 6-fold coordination having a pseudotrigonal prismatic symmetry. The nonideal nature of the interlayer sites has implications for the observed selectivity of Li-Al LDHs toward anions of different symmetries.

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

“…Given the diversity of polytypes in the precursor Al(OH) 3 , the Li-Al LDHs also crystallize in diverse structures. LDHs obtained from gibbsite crystallize in structures of hexagonal symmetry [6], while those obtained from bayerite, crystallize in structures of monoclinic symmetry [7].…”

Determination of Partition Coefficients of Metals in Natural Tropical Water

“…Figure 1 shows a comparison of the PXRD pattern of the Li‐Al‐Cl LDH prepared by the gel to crystallite conversion route with those obtained by topotactic transformations of crystalline precursors 5. The gibbsite‐derived LDH is indexed to a hexagonal cell [ a = 5.0999(95) Å; c = 15.4053(44) Å; FOM = 34.70; polytype: 2H] and the bayerite‐derived LDH to a monoclinic cell [ a = 5.0994(11) Å; b = 8.8299(17) Å; c = 7.8611(23) Å; β = 102.44(2)°; FOM = 29.38; polytype: 1M 1 ] It can also be indexed to a 3‐layered hexagonal cell as indicated in Figure 1.…”

“…(i) The fit of the DIFFaX simulated pattern with that of the experimental pattern was poor. As the bayerite‐based structure model of 1M symmetry reported later5 was not known to the authors, their analysis was limited to the 2H model.…”

“…The Li‐Al LDHs are generally prepared by a topotactic route through imbibition of lithium salts into either gibbsite or bayerite 3. The former yields the 2H polytype,2 while the latter gives rise to the 1M 1 polytype 5. As Al(OH) 3 often adopts an X‐ray amorphous gel‐like form, we ask the question: What would be the nature of the LDH product obtained from a gel‐like Al(OH) 3 precursor, which does not offer the potential for a topotactic transformation.…”

DFT Study of Polymorphism in Al(OH)3: A Structural Synthon Approach

“…[3] Of these one was known, [7] two were experimentally realized. [4,8] The unrealized polytypes are proposed as legitimate targets for future synthetic efforts. As different polytypes are expected to have different properties, the synthesis and characterization of different polytypic modifications is of interest to the fields of catalysis, ion exchange and sorption.…”