Synthesis and Structure Refinement of [Co-Al₄-X] LDHs (X = NO₃ ^- and SO₄ ^2-) from Nordstrandite

[M-Al₄-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-Al₄-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-Al₄-X] LDHs (M = Zn, Ni, and Co and X = NO₃ ^- and SO₄ ^2-) from nordstrandite, which is yet another polymorph of Al(OH)₃. Hereafter, "n" represents the nordstrandite precursor. We report that n-[M-Al₄-X] LDHs do not differ structurally from those prepared from gibbsite and bayerite. We also report the structural refinement of n-[Co-Al₄-X] LDHs, where X = NO₃ ^- and SO₄ ^2-. This work is also significant as it gives for the very first time the refined structure of a [Co-Al₄-NO₃] LDH, though there are earlier reports on the synthesis of this LDH from both gibbsite and bayerite. The NO₃ ^- ion in the interlayer makes an angle of ∼48° with the plane of the metal hydroxide layer, and its symmetry reduces from D ₃ to C ₂ . Similarly, the change in the symmetry of the SO₄ ^2- ion in the interlayer is from T to C ₃ .