Together with hydrotalcite-like layered double hydroxides, bivalent and trivalent metal hydroxides and their hydroxy salts are actually anionic clays consisting of positively charged hydroxide layers with anions intercalated in the interlayer region. The anionic clays exhibit anion sorption, anion diffusion and exchange properties together with surface basicity making them materials of importance for many modern applications. In this article, we discuss many different ways of making anionic clays and compare and contrast the rich diversity of this class of materials with the better-known cationic clays.

A mixed-metal hydroxysalt of formula Cu_1.6Zn_0.4(OH)₃(OAc)·H₂O has been synthesized by an acetate hydrolysis route. Acetate ions can be exchanged with simple inorganic anions such as chloride and nitrate, and organic anions such as benzoate and large surfactant anions such as dodecyl sulphate. Structures of these hydroxysalts are derived from that of Cu₂(OH)₃NO₃·H₂O with some of the Cu²⁺ ions being replaced by Zn²⁺.

Nickel-zinc hydroxy acetates with varying amounts of octahedral zinc, Ni_(3-x)Zn(_(3-x)(OH)₈(OAc)₂.mH₂ O, with x varying from 0 to 2, have been synthesized. The crystallographic ^'a^' parameter increases linearly with octahedral zinc content in the series. While the thermal stability is almost the same for the entire series of compounds, the stability of the compound in the alkaline medium increases with a decrease in octahedral zinc content. The selectivity for chloride ion from a mixture of chloride and bromide ions increases linearly with an increase in octahedral zinc content.