Synthon Approach to Structure Models for the Bayerite-Derived Layered Double Hydroxides of Li and Al

Area of Science:

• Materials Science
• Crystallography
• Inorganic Chemistry

Background:

• Layered double hydroxides (LDHs) are versatile materials with tunable properties.
• The synthesis precursor (bayerite vs. gibbsite) influences LDH crystal structure.
• LDHs can undergo reversible structural changes in response to environmental stimuli.

Purpose of the Study:

• To investigate the crystal structure of bromide ion intercalated Li-Al LDH derived from bayerite.
• To elucidate the temperature- and humidity-induced interpolytype transformations in this LDH.
• To model and refine the structures of different hydration states.

Main Methods:

• Synthesis of Li-Al LDH intercalated with bromide ions using a bayerite precursor.
• X-ray diffraction (XRD) for structural analysis under varying temperature and humidity.
• Structure modeling using the structural synthon approach and refinement (space groups P3̅1m and C2/m).

Main Results:

• The bayerite-derived LDH crystallizes in a hexagonal symmetry (P3̅1m) when dehydrated.
• Upon cooling and rehydration, the LDH transitions to monoclinic symmetry (C2/m) through two distinct steps.
• Interpolytype transitions are attributed to rigid translations of metal hydroxide layers by specific vectors.

Conclusions:

• The precursor type significantly impacts LDH structure and transformation behavior.
• Reversible interpolytype transformations in LDHs are governed by layer stacking dynamics.
• Understanding these transformations is crucial for designing functional LDH materials.