Arsenite
In chemistry, an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. IUPAC have recommended that arsenite compounds are to be named as arsenate(III), for example ortho-arsenatite is called trioxidoarsenate(III). Ortho-arsenite contrasts to the corresponding anions of the lighter members of group 15, phosphite which has the structure HPO2−
3 and nitrite, NO−
2 which is bent.
A number of different arsenite anions are known:
In all of these the geometry around the AsIII centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active. Well known examples of arsenites include sodium meta-arsenite which contains a polymeric linear anion, [AsO−
2]
n, and silver ortho-arsenite, Ag3AsO3, which contains the trigonal AsO3−
3 anion.
Some arsenite salts can be prepared from an aqueous solution of As2O3. Examples of these are the meta-arsenite salts and at low temperature, hydrogen arsenite salts can be prepared, such as Na2(H2As4O8), NaAsO2·4H2O, Na2(HAsO3)·5H2O and Na5(HAsO3)(AsO3)·12H2O
A number of minerals contain arsenite anions: reinerite, Zn3(AsO3)2;finnemanite, Pb5Cl(AsO3)3;paulmooreite, Pb2As2O5;stenhuggarite, CaFeSbAs2O7 (contains a complex polymeric anion);schneiderhöhnite, FeII
FeIII
3(As2O5)2AsO3;magnussonite, Mn5(OH)(AsO3)3;trippkeite, CuAs2O4;trigonite, Pb3Mn(AsO3)2(HAsO3);tooeleite, Fe6(AsO3)4SO4(OH)4·4H2O.
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