Structural synthon approach has been applied with great success to different class of layered double hydroxides (LDHs) in predicting the complete universe of possible polytypes. A single metal hydroxide layer of Li and Al is identified as a structural synthon, commonly present in all the [Li-Al] LDHs. This layer can be stacked one over another using different stacking vectors, first, by conserving the symmetry element present, followed by their systematic elimination to yield polytypes of different crystal symmetry. Three different polytypes of bayerite derived [Li-Al-Br] LDH have been obtained by reversible hydration-dehydration, represented as phase I (T = 30 °C, RH~50%), phase II (T = 120 °C), and phase III (T = 30 °C, RH~70%). The DIFFaX simulations of the powder X-ray diffraction (PXRD) patterns using the [Li-Al] synthon reveals that the PXRD patterns corresponding to phase I, II, and III are obtained by the stacking vectors (a/6, 0, 1) [1M polytype, β~96°], (0, 0, 1) [1H polytype], and (a/3, 0, 1) [1M polytype, β~102°] respectively. The partial structure models for all the three phases are constructed with the aid of structural synthon approach and their structures are refined.

Structure refinement of bayerite derived Li and Al layered double hydroxides: A structural synthon approach

253rd National Meeting (2017)

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