Tutton's salt


Tutton's salts are a family of salts with the formula M2M'26 or M2M'26. 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, deuterated ammonium 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, tetrafluoroberyllate, hydrogenphosphate or monofluorophosphate. Tutton's salts crystallize in the monoclinic space group P21/a. The robustness is the result of the complementary hydrogen-bonding between the tetrahedral anions and cations as well their interactions with the metal aquo complex 2+.

Examples and related compounds

Perhaps the best-known is Mohr's salt, ferrous ammonium sulfate 2Fe2.. Other examples include the vanadous Tutton salt 2V26 and the chromous Tutton salt 2Cr26. In solids and solutions, the M'2+ ion exists as a metal aquo complex 2+.
Related to the Tutton's salts are the alums, which are also double salts but with the formula MM'212. The Tutton's salts were once termed "false alums".

History

Tutton salts are sometimes called Schönites after the naturally occurring mineral called Schönite 2. They are named for Alfred Edwin Howard 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.

Table of salts

Organic salts

Some organic bases can also form salts that crystallise like Tutton's salts.
formulanamea Åb Åc Åβ°V Å3colourNαNβNγBiaxial2Vother
2piperazinediium hexaaquazinc bis12.956210.650213.3251114.0321679.30Colourless------
cadmium creatininium sulfate6.558427.8717.1955110.3711232.99colourless------