Synthesis and Structure Refinement of [Co-Al 4 -X] LDHs (X = NO 3 - and SO 4 2- ) from Nordstrandite.

[M-Al 4 -X] LDHs (M = divalent metal and X = anion) are a class of aluminum-rich layered double hydroxides synthesized from both the gibbsite and bayerite polymorphs of Al(OH) 3 . Henceforth, "g" and "b" are used to indicate gibbsite and bayerite. Despite the differences in the stacking arrangement of the hydroxyl layers in the precursor polymorphs, [M-Al 4 -X] LDHs whether synthesized from gibbsite or bayerite were seen to be structurally the same. In this work, we report the first ever synthesis of [M-Al 4 -X] LDHs (M = Zn, Ni, and Co and X = NO 3 - and SO 4 2- ) from nordstrandite, which is yet another polymorph of Al(OH) 3 . Hereafter, "n" represents the nordstrandite precursor. We report that n-[M-Al 4 -X] LDHs do not differ structurally from those prepared from gibbsite and bayerite. We also report the structural refinement of n-[Co-Al 4 -X] LDHs, where X = NO 3 - and SO 4 2- . This work is also significant as it gives for the very first time the refined structure of a [Co-Al 4 -NO 3 ] LDH, though there are earlier reports on the synthesis of this LDH from both gibbsite and bayerite. The NO 3 - ion in the interlayer makes an angle of ∼48° with the plane of the metal hydroxide layer, and its symmetry reduces from D 3 h to C 2 v . Similarly, the change in the symmetry of the SO 4 2- ion in the interlayer is from T d to C 3 v .