Tutton's salts are a family of salts with the formula M2M'(SO4)2(H2O)6 (sulfates) or M2M'(SeO4)2(H2O)6 (selenates). These materials are double salts, which means that they contain two different cations, M+ and M'2+ crystallized in the same regular ionic lattice. The univalent cation can be potassium, rubidium, cesium, ammonium NH4, deuterated ammonium ND4 or thallium. Sodium or Lithium ions are too small. The divalent cation can be magnesium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc or cadmium. In addition to sulfate and selenate, the divalent anion can be chromate (CrO42-), tetrafluoroberyllate (BeF42-) or fluorophosphate (PO3F2-).
Perhaps the best-known is Mohr's salt, ferrous ammonium sulfate (NH4)2Fe(SO4)2.(H2O)6). Other examples include the vanadous Tutton salt (NH4)2V(SO4)2(H2O)6 and the chromous Tutton salt (NH4)2Cr(SO4)2(H2O)6. In solids and solutions, the M'2+ ion exists as a metal aquo complex [M'(H2O)6]2+.
Tutton salts are sometimes called Schönites after the naturally occurring mineral called Schönite (K2Mg(SO4)2(H2O)6). They are named for A. E. H. Tutton, who identified and characterised a large range of these salts around 1900.
Such salts were of historical importance because they were obtainable in high purity and served as reliable reagents and spectroscopic standards.
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- A. E. Tutton (1900–1901). "A Comparative Crystallographical Study of the Double Selenates of the Series R2M(SeO4)2.6H2O.--Salts in Which M Is Zinc". Proceedings of the Royal Society of London 67 (435–441): 58–84. doi:10.1098/rspl.1900.0002.