Charge compensating anions

Thermal treatments induce dehydration, dehydroxylation and loss of the charge-compensating anions, resulting in mixed oxides with the MgO-type structure. Hydrotalcites are consequently a class of precursors useful for the preparation of catalytically active oxides showing basic properties [94], The acid-base properties of Mg-Al mixed oxides are governed by the Mg Al molar ratio, calcination temperature and preparation conditions. The study of the influence of the acid-base properties and chemical composition on the catalytic performance of calcined hydrotalcites is thus of interest. 

Layered double metal hydroxides consist of positively charged bruclte-type layers In which part of the divalent cations are substituted by trivalent cations. This results in a net positive charge In the layers which Is balanced by charge compensating anions In the Interlayer. Upon heating, the hydroxides undergo... 

The concept of self-doped conducting polymers was proposed some years ago with the synthesis of poly(3-thiophene-j8-ethanesulfonate) and poly(3-thiophene 5-butanesulfonate) (61) [278]. In these systems the charge-compensating anion is covalently bound to the polymeric backbone consequently, instead of anion incorporation, charge compensation upon doping involves the expulsion of cationic species. Furthermore, due to the presence of the sulfonate group, these polymers are the first examples of water-soluble PHCs. The polymers described in Ref. 278 were... 

Fig. 7. Electrochromism in polypyrrole thin films. The yellow-green (undoped) form undergoes reversible oxidation to the blue-violet (conductive) form, with insertion of charge-compensating anions (X ).

In self-doped polymers, the charge-compensating anion is covalently bound to the polymeric backbone, so that oxidative doping involves the expulsion of cationic species rather than anion insertion. Poly(3-thiophene-) -ethanesulfonate) and poly(3-thiophene-<5-butanesulfo-nate) (23) [171] were first prepared with the sulfonate group, which makes these polymers water-soluble. The polymers have been prepared by electropolymerization of the corresponding methyl esters, followed by hydrolysis to the polyelectrolytic form [171]. Films cast from water solution exhibited a rather short conjugation (maximum absorption at 425 nm, 3.6 eV) and conductivities of 1—10 S cm after doping [172]. 

Layered double hydroxides (LDH) are a well-known type of ionic clays made up of positively charged brucite-like layers with an interlayer containing charge compensating anions and solvation molecules. LDH are available as both naturally occurring minerals and synthetic materials, whose strucmre is shown in Fig. 29. The general formula of LDH can be represented by nH20, in... 

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