Indium(III) sulfate

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| Name = Indium(III) sulfate
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| OtherNames = Indium sulfate
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| TLV TWA = 0.1 Indium is unusual in forming a sulfate complex. The effect on the sulfate ion is revealed in the Raman spectrum. The proportion of sulfate complex increases with temperature showing the reaction that forms it is endothermic. The proportion also increases with concentration of the solution and can be over a half. The Raman spectrum of the solution shows lines at 650, 1000 and 1125 cm−1 due to a sulfur–oxygen bonds in sulfate bound to indium. A line at 255 cm−1 is due to the indium oxygen bond to the sulfate. The water attached to the indium atom causes a band at about 400 cm−1. During extraction of indium, a sulfate solution of mixed metals, including indium sulfate, has trivalent metals partitioned into a kerosene solution of di 2 ethylhexyl hydrogen phosphate. Isododecylphosphetanic and diisooctylphosphinic acids can also be used for this function. The kerosene mixture is then backwashed with an acid to recover the metals in a water solution and regenerate the extracting fluid.

Indium metal reacts with cold concentrated sulfuric acid to produce Indium sulfate and hydrogen gas. If hot concentrated sulfuric acid is used indium will reduce the sulfuric acid to sulfur dioxide. Indium sulfate can also be produced from a reaction of sulfuric acid on indium oxide, indium carbonate, or indium hydroxide.

An acid sulfate, indium hydrogensulfate tetrahydrate with the formula HIn(SO4)2·4H2O crystallises in the orthorhombic system with unit cell dimensions a = 9.997 Å, b = 5.477 Å, c = 18.44 Å, with four of the formula per cell. The density is 2.50 cm−3. In the acid sulfate, two water molecules are linked to the indium atom and a hydronium ion H5O2 takes care of the proton. This is part of an acid sulfate family that includes Al, Ga, In, Tl(III), Fe(III) and Ti(III). HIn(SO4)2 is made by evaporating an indium sulfate in 40% sulfuric acid solution or cooling indium sulfate in a 60% sulfuric acid solution. As the acid tetrahydrate is heated it gives off water yielding a trihydrate, monohydrate, and an anhydrous form at 370, 385 and 482K. Above 505K it gives out more water and sulfur dioxide yielding the neutral indium sulfate. InOHSO4·(H2O)2 has monoclinic crystals with a=6.06 Å b=7.89 Å c=12.66 Å and β=107.5°. Cell volume is 577.6 Å3. This insoluble basic salt also forms if indium sulfate solution is diluted below 0.005 molar. So a precipitate forms from diluted solutions as well as from heated solutions. Most of these have a rhombohedral crystal structure. However, triammonium indium trisulfate, (NH4)3In(SO4)3 converts from rhombohedral to monoclinic as the temperature drops below 80 °C, and converts back into a rhombohedral form with space group R3c as the temperature rises above 110 °C. nameformulamolecular weighta Åc Åαvolume Å3density trisodium indium trisulfate Na3In(SO4)3 471.97 13.970 8.771 109°00′ 494 3.172 tripotassium indium trisulfate K3In(SO4)3 520.30 14.862 8.960 109°45′ 571 3.026 trirubidium indium trisulfate Rb3In(SO4)3 659.41 15.413 9.136 110°03′ 626 3.498 tricesium indium trisulfate Cs3In(SO4)3 801.72 16.068 9.211 110°36′ 687 3.876 triammonium indium trisulfate (NH4)3In(SO4)3 361.06 15.531 9.163 120° 1914.1 1.88 ammonium indium disulfate NH4In(SO4)2 324.98 4.902 8.703 73.643 171.27 3.15 rubidium indium disulfate RbIn(SO4)2 392.41 4.908 8.7862 73.781 173.50 3.75 cesium indium disulfate CsIn(SO4)2 439.85 4.956 9.2567 74.473 187.26 3.90 thallium indium disulfate TlIn(SO4)2 511.33 4.919 8.7882 73.748 174.27 4.87
Another series of anhydrous rhombohedral double salts in the same series of TlFe(SO4)2 exists. These can be made by heating a mixture of anhydrous sulfates at 350 °C, or by dehydrating hydrous double alum type salts at 300 °C. The substances in this series are RbIn(SO4)2, CsIn(SO4)2, TlIn(SO4)2 and NH4In(SO4)2. Although KIn(SO4)2 exists it has a different crystalline form.

Hydrated double salts of indium in an alum structure exist with formula MIIn(SO4)2·12H2O. All alums have a cubic crystal structure with space group Pa3. has formula weight 656.0, unit cell width 12.54 Å, cell volume 1972 Å3 and density 2.20 g/cm3. It has the β alum structure. The cesium alum can be used in the analysis of indium. It precipitates when cesium nitrate is added to indium sulfate solution with extra sulfuric acid added. Indium ammonium alum NH4In(SO4)2·12H2O is fairly unstable at room temperature and must be crystallised below 5 °C. It decomposes at 36 °C to a tetrahydrate. It changes to a ferroelectric phase below 127K. The alum methyl ammonium indium sulfate dodecahydrate CH3NH3In(SO4)2·12H2O becomes ferroelectric below 164K. Potassium indium alum has not been crystallised. Rubidum indium alum is highly efflorescent very easily losing its water. Another series of monoclinic hydrated double salts have four water molecules MIn(SO4)2·4H2O, with five formulae per unit cell, where M is NH4, K or Rb and the point group is P21/c. The prototype substance for the series is (NH4)Sm(SO4)2(H2O)4.

formulaweighta Åb Åc Åβvolume Å3densityref NH4In(SO4)2•4H2O 397.04 10.651 10.745 9.279 102.67° 1036.08 3.182 KIn(SO4)2•4H2O 418.10 10.581 10.641 9.224 101.93° 1016.1 3.416 RbIn(SO4)2•4H2O 464.47 10.651 10.745 9.279 102.67° 1036.1 3.722

Cadmium can also form a double sulfate, Cd3In2(SO4)6·26H2O. Crystals with less water also exist like KIn(SO4)2·H2O.

Organic base double sulfates of indium include the guanidinium salt [C(NH2)3][In(H2O)2(SO4)2], which crystallises in a monoclinic system with space group P21/c a = 4.769 Å, b = 20.416 Å, c = 10.445 Å, β = 93.39°, cell volume 1015.3 Å3, 4 formulas per cell and density 2.637. [H2(4,4' bi py)][In2(H2O)6(SO4)4]·2H2O crystallises in the triclinic system with a = 7.143 Å, b = 7.798 Å, c = 12.580 Å, α = 107.61°, β = 98.79°, γ = 93.89°, cell volume 655.2 Å3, one formula per cell and density 2.322. [H(2,2' bipy)][In(H2O)(SO4)2]·2H2O, the hexamethylenediamine salt [H3N(CH2)6NH3][In(H2O)2(SO4)2]2·2H2O and [H2(Py(CH2)3Py)][In(H2O)2(SO4)2]2·2H2O also exist. and amylammonium. Dimethylindium sulfate [(CH3)2In]2SO4 can be made by reacting trimethylindium with dry sulfuric acid.

A double indium sulfate chloride salt has formula In2(SO4)3·InCl3·(17±1)H2O.

Indium(I) sulfate, In2SO4 can be made in a solid state by heating indium metal with indium(III) sulfate, but when dissolving in water or sulfuric acid, In+ reacts to produce hydrogen gas. The mixed valence salt InIInIII(SO4)2 is also made by heating indium metal with indium(III) sulfate.

Indium sulfate is a commercially available chemical. It can be used to electroplate indium metal, as a hardening agent in gold electroplating or to prepare other indium containing substances such as copper indium selenide. It has been sold as a health supplement, even though there is no evidence of benefit to humans, and it is toxic. The first high frequency transistor was the surface barrier germanium transistor developed by Philco in 1953, capable of operating up to 60 MHz. These were made by etching depressions into an N type germanium base from both sides with jets of indium sulfate until it was a few ten thousandths of an inch thick. Indium electroplated into the depressions formed the collector and emitter.