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, caesium, 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−), hydrogenphosphate (HPO42−) or monofluorophosphate (PO3F2−). 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 [M(H2O)6]2+.
Examples and related compounds 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+.
Related to the Tutton's salts are the alums, which are also double salts but with the formula MM'(SO4)2(H2O)12. The Tutton's salts were once termed "false alums".
History Tutton salts are sometimes called Schönites after the naturally occurring mineral called Schönite (K2Mg(SO4)2(H2O)6). 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 M1M2formulanamea Åb Åc Åβ°V Å3colourNαNβNγ Biaxial2VotherKCdK2[Cd(H2O)6](SO4)2Potassium cadmium sulfate hexahydrate (also includes Ni Cu ) CsCdCs2[Cd(H2O)6](SO4)2Caesium cadmium sulphate hexahydrateNH4Cd(NH4)2[Cd(H2O)6](SO4)2Ammonium Cadmium Sulfate Hydrate 9.39512.7766.299106°43'727.63colourlessl.4861.4881.494Biaxial(-f)largedensity=2.05 Slowly loses water in dry air.KCoK2[Co(H2O)6](SO4)2Potassium cobaltous sulfate6.1519.06112.207104.8°657.78reddensity=2.21RbCoRb2[Co(H2O)6](SO4)2Rubidium hexaaquacobalt(II) sulphate6.249.1912.453105.99°686.5ruby-reddesnsity=2.56CsCoCs2[Co(H2O)6](SO4)2Caesium hexaaquacobalt(II) sulphate 9.318(1)12.826(3)6.3650(9)107.13(1)°727.0 dark redNH4Co(NH4)2[Co(H2O)6](SO4)2Cobaltous ammonium sulfate hexahydrate6.2429.25512.549106.98°693.3purpledensity=1.89TlCoTl2[Co(H2O)6](SO4)2Cobaltous thallium sulfate hexahydrate, Thallium hexaaquacobalt(II) sulfate, 9.227(1)12.437(2)6.220(1)106.40(1)°684.7light redTlCoTl2[Co(H2O)6](SO4)2Dithallium cobalt sulfate hexahydrate9.235(1)12.442(2)6.227(1)106.40(1)°yellowish pink1.5991.6131.624biaxial(-)medium largedensity=4.180 g/cm3RbCrRb2[Cr(H2O)6](SO4)2Dirubidium chromium sulfate hexahydrateCsCrCs2[Cr(H2O)6](SO4)2Dicaesium chromium sulfate hexahydrateND4Cr(ND4)2Cr(SO4)2 Dideuterated ammonium chromium sulfate hexahydratebright blue, formed from with ammonium sulfate in minimal water under nitrogen gas. Stable in air from oxidation, but may dehydrate.KCuK2[Cu(H2O)6](SO4)2 Cyanochroite 9.2712.446.30104.47663.0pale green bluedensity=2.21 within unit cell 7.76 between two Cu atomsRbCuRb2[Cu(H2O)6](SO4)2Dirubidium hexaaquacopper sulfate9.26712.3666.228105°19'686.8brilliant greenish blue 1.4881.4911.506biaxial (+)mediumdensity=2.580g/cm3 Cu-O 2.098 Å Rb-O 3.055 Å.CsCuCs2[Cu(H2O)6](SO4)2Dicaesium hexaaquacopper sulfate 9.43912.7626.310106°11'718.5brilliant greenish blue, 1.5041.5061.514 biaxial (+)density=2.864g/cm3NH4Cu(NH4)2[Cu(H2O)6](SO4)2Ammonium hexaaquacopper(II) sulfate6.31 12.389.22106.16°691.25density=1.921; heat of formation=-777.9 kcal/mol Jahn-Teller distortion axis switches under pressure of ~1500 bars, a,b axis shrinks 3.3% and 3.5% and c axis extends 4.5%.TlCuTl2[Cu(H2O)6](SO4)2Thallium copper sulfate hydrate9.26812.3646.216105°33'brilliant greenish blue 1.6001.6101.620biaxial very largedensity=3.740 g/cm3KFeK2[Fe(H2O)6](SO4)2Dipotassium iron sulfate hexahydrateRbFeRb2[Fe(H2O)6](SO4)2Rubidium iron sulfate hydrate9.21812.4976.256105°45' pale green1.4801.4891.501biaxial (+)large, density=2.523g/cm3CsFeCs2[Fe(H2O)6](SO4)2Caesium hexaaquairon(II) sulphate9.357(2)12.886(2)6.381(1)106.94(1)°736.0dark yellow very pale green 1.5011.5041.516biaxial (+)mediumdensity=2.805NH4Fe(NH4)2[Fe(H2O)6](SO4)2Mohrite 6.24(1)12.65(2)9.32(2)106.8(1)704.28vitreous pale greendensity=1.85 named after Karl Friedrich MohrTlFeTl2[Fe(H2O)6](SO4)2Thallium hexaaquairon(II) sulfate 9.262(2)12.497(1)6.235(2)106.15(1)°693.2 light green1.5901.605=1.616biaxial (-)large density=3.662g/cm3KMgK2[Mg(H2O)6](SO4)2 Picromerite9.0412.246.095104° 48' colourless or white 1.4601.4621.472biaxial (+)mediumdensity=2.025g/cm3; expanded second coordination sphere around Mg.RbMgRb2[Mg(H2O)6](SO4)2Rubidium magnesium sulphate hexahydrate9.23512.4866.224105°59'colourless1.4671.4691.476biaxialCsMgCs2[Mg(H2O)6](SO4)2Caesium hexaaquamagnesium sulphate9.338(2)12.849(4)6.361(2)107.07(2)°729.6colourless1.4811.4851.492biaxial(+)mediumdensity=2.689NH4Mg(NH4)2[Mg(H2O)6](SO4)2Boussingaultite9.2812.576.2107°6' NH4Mg(NH4)2[Mg(H2O)6](SO4)2Ammonium Magnesium Chromium Oxide Hydrate9.508±.00112.6746.246106°14'bright yellow1.6371.6381.653biaxial(+)smalldensity=1.840 g/cm 3TlMgTl2[Mg(H2O)6](SO4)2 dithallium magnesium sulfate hexahydrate9.22 9.262(2)12.42 12.459(2)6.185 6.207(1)106°30' 106.39(2)°687.1colourlessdensity=3.532 g/cm3RbMnRb2[Mn(H2O)6](SO4)2Dirubidium hexaaquamanganese sulfate(VI) 9.282(2)12.600(2)6.254(2)105.94(2)703.3Å3CsMnCs2[Mn(H2O)6](SO4)2Caesium hexaaquamanganese(II) sulphate9.418(3)12.963(2)6.386(3)107.17(4)°744.9pale pink purplish white1.4951.4971.502biaxial(+)largedensity=2.763NH4Mn(NH4)2[Mn(H2O)6](SO4)2Manganese ammonium sulfate hexahydrate 9.4012.746.26107.0° pale pink1.4821.4561.492biaxial(+)largedensity=1.827 TlMnTl2[Mn(H2O)6](SO4)2Thallium manganese sulfate hexahydrate 9.3276(6), 9.322(2)12.5735(8), 12.565(2)6.2407(4), and 6.233(1)106.310(3)° 106.29(2)°, 700.8light pinkKNiK2Ni(SO4)2 Potassium Nickel Sulfate Hexahydrateused as UV filterRbNiRb2[Ni(H2O)6](SO4)2Rubidium Nickel Sulfate Hexahydrate 6.22112.419.131106.055°677.43001 surface has step growth of 4.6 Å, optical transmission bands at 250, 500 and 860 nm which are the same as nickel sulfate hexahydrate, but UV band transmits more. Heavy absorption 630-720 nm and 360-420 nm3 density 2.596 g cm−3. stable to 100.5 °C solubility in g/100ml=0.178t + 4.735 MW=529.87CsNiCs2[Ni(H2O)6](SO4)2Caesium hexaaquanickel(II) sulphate, Caesium Nickel Sulfate Hexahydrate9.259(2)12.767(2)6.358(1)107.00(2)°718.7greenish blue1.5071.5121.516biaxial(-)very largedensity=2.883 used as UV filterNH4Ni(NH4)2[Ni(H2O)6](SO4)2Nickel-boussingaultite9.18612.4686.424684.0blueish green.density=1.918 cas=51287-85-5TlNiTl2[Ni(H2O)6](SO4)2Thallium hexaaquanickel(II) sulfate9.161(2)12.389(2)6.210(2)106.35(2)°676.3greenish blue1.6021.6151.620biaxial(-)largedensity=3.763KRuK2[Ru(H2O)6](SO4)2Potassium hexaaquaruthenium(II) sulfate8.95012.2686.135105.27644RbRuRb2[Ru(H2O)6](SO4)2Rubidium hexaaquaruthenium(II) sulfate9.13212.5276.351106.30KVK2[V(H2O)6](SO4)2Vanadium(II) potassium sulfate hexahydrate RbVRb2[V(H2O)6](SO4)2Rubidium vanadium(II) sulfateNH4V(NH4)2[V(H2O)6](SO4)2Vanadium(II) ammonium sulfate hexahydrate9.4212.766.22107.2°714.2amethystdensity=1.8 V-O length 2.15ÅKZnK2[Zn(H2O)6](SO4)2Dipotassium zinc sulphate hexahydrate9.04112.3106.182104.777°colourless1.4781.4811.496biaxiallargedensity=2.242g/cm3 Thermal decomposition at 252K.RbZnRb2[Zn(H2O)6](SO4)2 Rubidium Zinc Sulphate Hexahydrate9.18512.4506.242105°54' colourless1.4831.4891.497biaxiallarge CsZnCs2[Zn(H2O)6](SO4)2Zinc caesium sulphate hexahydrate 9.314(2)12.817(2)6.369(2)106.94(2)°727.3colourless1.5071.6101.615biaxial(-)largedensity=2.881 NH4Zn(NH4)2[Zn(H2O)6](SO4)2Ammonium hexaaquazinc(II) sulfate9.20512.4756.225106°52'684.1heat of fusion 285 J/gTlZnTl2[Zn(H2O)6](SO4)2Thallium hexaaquazinc(II) sulfate 9.219(2)12.426(2)6.226(1)106.29(2)°684.6colourlessCsNiCs2[Zn(H2O)6](SeO4)2Dicaesium nickel selenate hexahydrate7.46747.915211.7972106.363669.04light greenRbCuRb2[Cu(H2O)6](SeO4)2Dirubidium copper selenate hexahydrate6.36312.4319.373104.33718.3
Organic salts Some organic bases can also form salts that crystallise like Tutton's salts.
formulanamea Åb Åc Åβ°V Å3colourNαNβNγ Biaxial2Vother(C4H12N2)[Zn(H2O)6](SO4)2Piperazinediium hexaaquazinc(II) bis(sulfate)12.956210.650213.3251114.0321679.30Colourless(C4H8N3O)2[Cd(H2O)6](SO4)2Cadmium creatininium sulfate6.558427.8717.1955110.3711232.99colourless
References
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