Polytype Selection by Intercalated Anions: Design and Synthesis of the 3R₂ Polytype of the Layered Double Hydroxide of Zn and Al

Abstract

The layered double hydroxides are obtained by the stacking of metal hydroxide layers one above another. The stacking sequence is determined by the molecular symmetry of the intercalated anion. Anions select for those stacking sequences which provide interlayer sites having a local symmetry compatible with their own molecular symmetry. Oxoanions, XO3 n– (X = S, I), are unique in that their molecular symmetry, C 3v , is compatible with two different polytypes of rhombohedral symmetry. The SO3 2– ion selects for the more ubiquitous 3R1 polytype, whereas the IO3 – ion selects for the much rarer 3R2 polytype. Structure refinement shows that neither anion departs significantly from the structure of the free species on intercalation. The higher charge-to-size ratio of the SO3 2– ion compared to the IO3 – ion and its consequent stronger basicity is responsible for the nucleation of the 3R1 polytype, wherein the trigonal prismatic interlayer sites facilitate the superior hydrogen bonding capacity of the SO3 2– ion. The poorer basicity of the IO3 – ion and its consequent poorer proclivity to form hydrogen bonds select for the 3R2 polytype wherein the IO3 – ion is lodged in interlayer sites of octahedral symmetry.

Electrochemical characterization of carbon paste electrodes modified with MgZnGa and ZnGaAl hydrotalcite-like compounds

“…1; all diffraction patterns exhibit the characteristic reflections (003), (006), (012), (015), (018), (110), and (113), indicating that the phase formed is the 3R 1 polytype [22]. The results suggest that synthesized HTs were crystallized with wellordered layered structures.…”

Synthesis, polytypism, and dehydration behaviour of nitrate-intercalated layered double hydroxides of Ca and Al

“…These polytypes differ from one another in the manner in which successive metal hydroxide layers are translated relative to each other. Known structures of mineral, as well as laboratory-synthesized LDHs, were found to belong to 2H 1 (space group P6 3 /mcm), 2 3R 1 , 3 and 3R 2 4 (space group R% 3m) polytypes.…”

Morphology controlled growth of ZnAl-layered double hydroxide and ZnO nanorod hybrid nanostructures by solution method

“…[9][10][11][12] ZnO nanorods (NRs) have gained much attention because their crystal structure possesses the intrinsic potential to grow along with the c-axis under controlled growth factors such as the selection of a hydroxide anion generating agent, the pH of the solution, the zinc ion precursor, and the type of seed layer. [15][16][17][18][19][20] The general formula of LDH compounds is [Zn (1- , CH 3 COO -). [15][16][17][18][19][20] The general formula of LDH compounds is [Zn (1- , CH 3 COO -).…”

“…9,13,14 In addition, when Zn 2+ cations are isomorphously substituted by trivalent cations, layered double hydroxide (LDH) structures are obtained. [15][16][17][18][19][20] The general formula of LDH compounds is [Zn (1Àx) M III (x) (OH) 2 ][A nÀ x/n $mH 2 O] (M III ¼ Al, Cr, Ga; A nÀ ¼ CO 3 2À , Cl À , NO 3 À , CH 3 COO À ). 21,22 The excess charges of the trivalent cation produce an overall positive charge in brucite-type structures, which is balanced by the intercalation of anions between LDHs.…”