Zinc orthoarsenate

Zinc Arsenates.—Zinc Orthoarsenate, Zng(As04)2, has been obtained in the anhydrous form by heating zinc carbonate with aqueous arsenic acid to 200° C.6 or by fusing a mixture of zinc chloride and arsenic pentoxide.7 The latter process yields prismatic crystals of density 4-913 at 15° C. The trihydrate, Zn3(As04)2.3H20, is precipitated... 

Zinc Metarsenate, Zn(As03)2, has been described as a heavy white powder formed by allowing zinc orthoarsenate trihydrate to remain in contact with aqueous arsenic acid for more than a year and then filtering the solution.13... 

There are many compounds in which As and Sb form tetrahedral bonds (valence group 8) as, for example, GaAs, GaSb, InAs, and InSb which, like the corresponding phosphides, crystallize with the zinc-blende structure. Tetrahedral bonds are formed by As in the ASO4 ion in orthoarsenates (and arsine oxides) but note the quite different behaviour of Sb in its oxy-compounds (see later). 

---