Anionic clays interlamellar domains

The term "anionic clay" is used to designate synthetic or natural lamellar hydroxides with interlayer domains containing anionic species. This designation refers to the more usual "cationic clays" whose interlamellar domains contain cationic species. The more structural designation of "Lamellar Double Hydroxides" (LDHs) has been used in the last few years (Martin and Pinnavaia 1986) and account for the presence of two kinds of metallic cations in the... 

Although such compounds are reported (Boehm, Steinle, and Vieweger 1977), anionic clays generally present well-resolved (hk reflections that account for a low turbostratic effect. This leads us to consider that, in spite of the interlamellar disorder, "order information" is transmitted through these domains. 

Mostly focused on cationic clays, and particularly on montmorillonite and hectorite, smectite-type layered silicates and clay-based nanofillers have recently been extended to the family of LDH. Hydrotalcite-like LDH materials are described according to the ideal formula, [M1/ xM"l(OH)2]frl(lra [A H20]inter, where Mn and Mm are metallic cations, A the anions, and intra and inter denote the intralayer and interlayer domain, respectively. The structure consists of brucite-like layers constituted of edge-sharing octahedra. The presence of trivalent cations induces positive charges in the layers that are counterbalanced by interlamellar anions (Scheme 15.16). 

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