Hydrotalcite schematic

Layered crystal stmcture of hydrotalcite-like compounds Figure 27 Layered structure of hydrotalcites (schematic view). 

Figure 1. Schematic representation of terephthalate exchange with heptamolybdate and decavanadate in hydrotalcite. Pillared hydrotalcite d-spacings were calculated from models.

Hydrotalcites, or layered double hydroxides (LDH), are a class of material related to the mineral hydrotalcite which has the formula [Mg6Al2(0H)i6]C03-4H20. They are layered double hydroxides with the general formula M M]l ,(0H)2,A zH20 which have the trivalent and divalent cations contained within the octahedral sites of posihvely charged hydroxide sheets, in a stmcture akin to that of brucite, Mg(OH)2. The anions, A , and water are contained between the layers of sheets and their intercalation and removal can be monitored by the position of the (003) refiection in their powder diffraction patterns [56]. A schematic of the structure is shown in Figure 21.15 [56]. 

Figure 21.15 Schematic of the hydrotalcite structure. (Reproduced from [56] with permission).

Figure 2.39 Schematic representation of a hydrotalcite structure (MggAl2(0H)igC03-4H20).

Fig. 1.10 Schematic illustration of the structure of hydrotalcite-like compounds.

Figure 20.2 Schematic of the double-layered metal hydroxide structure of a typical hydrotalcite. Reproduced with permission from Ref [8].

Fig. 7.3 Schematic representation of hydrotalcite characterized by CO3 anions and H2O molecules intercalated between positively charged [Mg6Al2(OH)6] layers...

Photochemical cycloaddition for several unsaturated carboxylates has been studied in the presence of hydrotalcite (LDH) (223-225). In addition to the antiparallel packing of the guest, the intermolecular distances of two double bonds of adjacent carboxylates were found to affect the stereoselectivity of the photochemical reactions. While cinnamate yielded head-to-head dimers exclusively, stilbenecaroboxylates (Fig. 33) led to a significant amount of head-to-tail dimer in addition to a head-to-head dimer. This difference was explained by molecular packing of the dye anions in the interlayer space of LDH. The proposed molecular packing of stilbenecarboxylate and p-phenylcinnamate ions in the interlays space of Mg/Al LDH is shown schematically in Figure 34. 

Schematic representation of the hydrotalcite three-dimensional structure.

Figure 3 Structure of hydrotalcite left schematic (a) and SEM image (b). (a) is reprinted from Rives, V. Angeles Ulibarri, M. Coord. Chem. Rev. 1999, 181 (1), 61, with permission from Elsevier.

---