Arsenate arsenite
An arsenate arsenite is a chemical compound or salt that contains arsenate and arsenite anions (AsO33- and AsO43-). These are mixed anion compounds or mixed valence compounds. Some have third anions. Most known substances are minerals, but a few artificial arsenate arsenite compounds have been made. Many of the minerals are in the Hematolite Group. An arsenate arsenite compound may also be called an arsenite arsenate. Properties 
Some members of this group of materials like mcgovernite has an extremely high unit cell dimension of 204 Å. Related 
Mixed valence pnictide compounds related to the arsenate arsenites include the nitrite nitrates, and phosphate phosphites. List

References

Arsenates
Arsenites
Mixed anion compounds