Arsenic catenation

NaAs03 has an infinite polymeric chain anion similar to that in diopside (pp. 349, 529) but with a trimeric repeat unit LiAs03 is similar but with a dimeric repeat unit whereas /6-KASO3 appears to have a cyclic trimeric anion As309 which resembles the cyc/o-trimetaphosphates (p. 530). There is thus a certain structural similarity between arsenates and phosphates, though arsenic acid and the arsenates show less tendency to catenation (p. 526). The tetrahedral As 04) group also resembles PO4) in forming the central unit in several heteropoly acid anions (p. 1014). 

Arsenic forms a large number of compounds with other Group 5 members. These are dealt with element by element down the group. However, in the case of arsenic only its catenated and jr-bonded compounds are dealt with. 

Both phosphorus and arsenic show a significant tendency to catenation, forming a series of cyclic compounds (RP) and (RAs) where n = 3-6, as well as some R2PPR2 and R2AsAsR2 compounds. 

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