Tutton's salt

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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.[1] 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 monofluorophosphate (PO3F2−).

Examples and related compounds[edit]

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.[2] 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".[3]

History[edit]

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.[4]
Such salts were of historical importance because they were obtainable in high purity and served as reliable reagents and spectroscopic standards.

Table of salts[edit]

M1 M2 formula name a Å b Å c Å β° V Å3 colour Biaxial 2V other
K Cd K2Cd(SO4)2·6H2O Potassium cadmium sulfate[5]
Cs Cd Cs2Cd(SO4)2·6H2O caesium cadmium sulphate hexahydrate[6]
NH4 Cd (NH4)2Cd(S04)2.6H 20 Ammonium Cadmium Sulfate Hydrate 9.395 12.776 6.299 106°43' 727.63 colourless l.486 1.488 1.494 Biaxial(-f) large[7] density=2.05[8]
K Co K2Co(SO4)2·6H2O [9] Potassium cobaltous sulfate[10] 6.151 9.061 12.207 104.8° 657.78[11] density=2.21
Rb Co Rb2[Co(H2O)6](SO4)2[12] Rubidium cobalt sulfate ruby-red[12]
Rb Co Rb2[Co(H2O)6](SO4)2 Rubidium hexaaquacobalt(II) sulphate 6.24 9.19 12.453 105.99° 686.5[13] desnsity=2.56
Cs Co Cs2[Co(H2O)6](SO4)2 Caesium hexaaquacobalt(II) sulphate 9.318(1) 12.826(3) 6.3650(9) 107.13(1)° 727.0[14] dark red
NH4 Co (NH4)2Co(SO4)2·6 H2O[15] Cobaltous ammonium sulfate hexahydrate 6.242 9.255 12.549 106.98° 693.3[16] purple[17] density=1.89
Tl Co Tl2[Co(H2O)6](SO4)2 Cobaltous thallium sulfate hexahydrate, Thallium hexaaquacobalt(II) sulfate, 9.227(1) 12.437(2) 6.220(1) 106.40(1)° 684.7 light red[18]
Tl Co Cs2[Co(H2O)6](SO4)2 dithallium cobalt sulfate hexahydrate 9.235(1) 12.442(2) 6.227(1) 106.40(1)° yellowish pink 1.599 1.613 1.624 biaxial(-) medium large[19] density=4.180 g/cm3
Rb Cr Rb2Cr(SO4)2.6H2O[20] dirubidium chromium sulfate hexahydrate
Cs Cr Cs2Cr(SO4)2.6H2O[20] dicaesium chromium sulfate hexahydrate
ND4 Cr (ND4)2Cr(SO4)2.6H2O[20] dideuterated ammonium chromium sulfate hexahydrate bright blue, formed from CrSO4.3H2O with ammonium sulfate in minimal water under nitrogen gas. Stable in air from oxidation, but may dehydrate.[21]
K Cu K2[Cu(H2O)6](SO4)2 cyanochroite[10] 9.27 12.44 6.30 104.47[22] 663.0[22] pale green blue density=2.21[22] within unit cell 7.76 between two Cu atoms[23]
Rb Cu Rb2[Cu(H2O)6](SO4)2 Dirubidium hexaaquacopper sulfate 9.267 12.366 6.228 105°19' 686.8 brilliant greenish blue 1.488 1.491 1.506 biaxial (+)[24] medium density=2.580g/cm3[7] Cu-O 2.098 Å Rb-O 3.055 Å.[24]
Cs Cu Cs2[ Cu(H2O)6](SO4)2[24] dicaesium hexaaquacopper sulfate 9.439 12.762 6.310 106°11' 718.5 brilliant greenish blue, 1.504 1.506 1.514 biaxial (+) density=2.864g/cm3[25]
NH4 Cu (NH4)2[Cu(H2O)6](SO4)2 ammonium hexaaquacopper(II) sulfate[26] 6.31 12.38 9.22 106.16° 691.25[27] density=1.921;[27] heat of formation=-777.9 kcal/mol[27] 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%.[26]
Tl Cu Tl2[Cu(H2O)6](SO4)2 Thallium copper sulfate hydrate 9.268 12.364 6.216 105°33' brilliant greenish blue 1.600 1.610 1.620 biaxial very large[28] density=3.740 g/cm3
K Fe K2Fe(SO4)2·6 H2O dipotassium iron sulfate hexahydrate[10]
Rb Fe Rb2Fe(S04)2.6H20 Rubidium iron sulfate hydrate 9.218 12.497 6.256 105°45' pale green 1.480 1.489 1.501 biaxial (+) large, density=2.523g/cm3[29]
Cs Fe Cs2[Fe(H2O)6](SO4)2 Caesium hexaaquairon(II) sulphate 9.357(2) 12.886(2) 6.381(1) 106.94(1)° 736.0 dark yellow[14] very pale green 1.501 1.504 1.516 biaxial (+) medium[30] density=2.805
NH4 Fe (NH4)2Fe(SO4)2·6 H2O mohrite[10] 6.24(1) 12.65(2) 9.32(2) 106.8(1) 704.28 vitreous pale green density=1.85 named after Karl Friedrich Mohr[31]
Tl Fe Tl2Fe(SO4)2·6H2O Thallium hexaaquairon(II) sulfate 9.262(2) 12.497(1) 6.235(2) 106.15(1)° 693.2[18] light green 1.590 1.605 =1.616 biaxial (-) large density=3.662g/cm3[32]
K Mg K2Mg(SO4)2·6H2O picromerite 9.04 12.24 6.095 104° 48'[10][10] colourless 1.460 1.462 1.472 biaxial (+) medium density=2.025g/cm3;[33] expanded second coordination sphere around Mg.[10]
Rb Mg Rb2Mg(SO4)2 · 6H2O rubidium magnesium sulphate hexahydrate[34] 9.235 12.486 6.224 105°59' colourless 1.467 1.469 1.476[35] biaxial
Cs Mg Cs2[Mg(H2O)6](SO4)2 Cesium hexaaquamagnesium sulphate 9.338(2) 12.849(4) 6.361(2) 107.07(2)° 729.6 colourless[14] 1.481 1.485 1.492 biaxial(+) medium density=2.689[36]
NH4 Mg (NH4)2Mg(SO4)2 · 6H2O boussingaultite 9.28 12.57 6.2 107°6'[10][15]
NH4 Mg (NH4)2Mg(Cr04)2.6H20 Ammonium Magnesium Chromium Oxide Hydrate 9.508±.001 12.674 6.246 106°14' bright yellow 1.637 1.638 1.653 biaxial(+) small density=1.840 g/cm 3[7]
Tl Mg Tl2Mg(SO4)2·6H2O[37] dithallium magnesium sulfate hexahydrate 9.22 9.262(2) 12.42 12.459(2) 6.185 6.207(1) 106°30' 106.39(2)° 687.1 colourless[18] density=3.532 g/cm3
Rb Mn Rb2[Mn(H2O)6](SO4)2 Dirubidium hexaaquamanganese sulfate(VI) 9.282(2) 12.600(2) 6.254(2) 105.94(2) 703.3Å3[38][39]
Cs Mn Cs2[Mn(H2O)6](SO4)2 Caesium hexaaquamanganese(II) sulphate 9.418(3) 12.963(2) 6.386(3) 107.17(4)° 744.9 pale pink[14] purplish white[40] 1.495 1.497 1.502 biaxial(+) large density=2.763[40]
NH4 Mn (NH4)2[Mn(H2O)6](SO4)2 manganese ammonium sulfate hexahydrate 9.40 12.74 6.26 107.0°[41] pale pink 1.482 1.456 1.492 biaxial(+) large density=1.827 [42]
Tl Mn Tl2[Mn(H2O)6](SO4)2 Thallium 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)°[43] 106.29(2)°, 700.8[18] light pink
K Ni K2Ni(SO4)2·6H2O[9] Potassium Nickel Sulfate Hexahydrate[10] used as UV filter[44]
Rb Ni Rb2Ni(SO4)2·6H2O Rubidium Nickel Sulfate Hexahydrate 6.221 12.41 9.131 106.055° 677.43 001 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.[44] stable to 100.5 °C solubility in g/100ml=0.178t + 4.735 MW=529.87
Cs Ni Cs2[Ni(H2O)6](SO4)2 Caesium hexaaquanickel(II) sulphate, Cesium Nickel Sulfate Hexahydrate 9.259(2) 12.767(2) 6.358(1) 107.00(2)° 718.7[14] greenish blue 1.507 1.512 1.516 biaxial(-) very large density=2.883 [45] used as UV filter[44]
NH4 Ni (NH4)2Ni(SO4)2·6 H2O nickel-boussingaultite[10][46] 9.186 12.468 6.424 684.0 blueish green.[47][48] density=1.918 cas=51287-85-5
Tl Ni Tl2Ni(SO4)2·6 H2O Thallium hexaaquanickel(II) sulfate 9.161(2) 12.389(2) 6.210(2) 106.35(2)° 676.3 greenish blue[18] 1.602 1.615 1.620 biaxial(-) large density=3.763[49]
K V K2V(SO4)2·6 H2O Vanadium(II) potassium sulfate hexahydrate [50]
Rb V Rb2V(SO4)2·6 H2O Rubidium vanadium(II) sulfate 硫酸钒(II)铷
NH4 V (NH4)2V(SO4)2·6 H2O Vanadium(II) ammonium sulfate hexahydrate 9.42 12.76 6.22 107.2° 714.2 amethyst density=1.8 V-O length 2.15Å[51]
K Zn K2Zn(SO4)2 · 6H2O [9][10] dipotassium zinc sulphate hexahydrate 9.041 12.215 6.156 104°49' colourless 1.478 1.481 1.496 biaxial large density=2.242g/cm3[52]
Rb Zn Rb2[Zn(H2O)6](SO4)2 Rubidium Zinc Sulphate Hexahydrate[53] 9.185 12.450 6.242 105°54' colourless 1.483 1.489 1.497 biaxial large [54]
Cs Zn Cs2[Zn(H2O)6](SO4)2 zinc cesium sulphate hexahydrate [55] 9.314(2) 12.817(2) 6.369(2) 106.94(2)° 727.3 colourless[14] 1.507 1.610 1.615 biaxial(-) large density=2.881 [56]
NH4 Zn (NH4)2Zn(SO4)2·6H2O 9.205 12.475 6.225 106°52'[15] 684.1 heat of fusion 285 J/g[57]
Tl Zn Tl2Zn(SO4)2 · 6H2O Thallium hexaaquazinc(II) sulfate [58] 9.219(2) 12.426(2) 6.226(1) 106.29(2)° 684.6 colourless[18]

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