Pnictide Oxide Comparisons

The oxides of nitrogen bear little resemblance to those of the other pnictides, but arsenic, antimony and bismuth form oxides with the same empirical formulae as those of phosphorus  

The trioxides can all be obtained by reacting the elements or their sulphides in air (Table 4.13). They show increasing thermal stability and basic character, but reluctance to oxidise to the pentava-lent state, on progressing from P to Bi. Although less soluble in water than its phosphorus analogue (Table 4.11), AS4O6 eventually produces arsenous acid As(OH)3 Unlike phosphorous acid, however, the latter compound does not exist in tetrahedral form with an As-H linkage. 

In addition to the cubic forms based on discrete AS4O6 and Sb40 molecules, there are alternative crystalline forms of (As203 and (Sb203) which are highly polymerised structmes. In all of these, the pnictide atoms form pyramidal configurations of three bonds to O atoms, which are linked to give two-dimensional sheet structures as in (4.82). 

The P4O10 and P4O6 structures were the first examples found in phosphorus chemistry to have the adamantane, (CH)4(CH2)6, or hexamethylene tetramine, (NH2)4(CH2)6-type tetrahedral structures. Many examples of this type of structure are now known (Table 4.14). 

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