Oxides, peroxides, superoxides and suboxides

In this last reaction Na can be replaced by the azide NaN3 to give the same products. The normal oxides of the other alkali metals can be prepared similarly. 

The peroxides M2O2 contain the peroxide ion 02 which is isoelectronic with F2. Li202 is prepared industrially by the reaction of Li0H.H20 with hydrogen peroxide, followed by dehydration of the hydroperoxide by gentle heating under reduced pressure  

It is a thermodynamically stable, white, crystalline solid which decomposes to Li20 on being heated above 195°C. 

is prepared as pale-yellow powder by first oxidizing Na to Na20 in a limited supply of dry oxygen (air) and then reacting this further to give Na202  

Preparation of pure K2O2, Rb202 and CS2O2 by this route is difficult because of the ease with which they oxidize further to the superoxides MO2. Oxidation of the metals with NO has been used but the best method is the quantitative oxidation of the metals in liquid ammonia solution (p. 78). The peroxides can be regarded as salts of the dibasic acid H2O2. Thus reaction with acids or water quantitatively liberates H2O2  

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We shall be largely concerned here with the structures of metal oxides in the crystalline state since nearly all these compounds are solids at ordinary temperatures. We shall mention a number of suboxides, but we shall exclude peroxides and superoxides (and ozonates), for these compounds, in which there are 0-0 bonds, are included in Chapter 11. Little is known of the structures of metal oxides in the liquid or vapour states, though several have been studied as vapours (Table 12.1). The structures of the oxides of the semi-metals and of the B subgroup elements are described in other chapters. 

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