# Gallium(III) sulfate

Gallium(III) sulfate refers to the chemical compound, a salt, with the formula Ga$_2$(SO$_4$)$_3$, or its hydrates Ga$_2$(SO$_4$)$_3$·xH$_2$O. Gallium metal dissolves in sulfuric acid to form solutions containing [Ga(OH$_2$)$_6$]$^{3+}$ and SO$_4$$^{2−}$ ions. The octadecahydrate Ga$_2$(SO$_4$)$_3$·18H$_2$O crystallises from these solutions at room temperature. This hydrate loses water in stages when heated, forming the anhydrate Ga$_2$(SO$_4$)$_3$ above 150 °C and completely above 310 °C. Anhydrous Ga$_2$(SO$_4$)$_3$ is isostructural with iron(III) sulfate, crystallizing in the rhombohedral space group R3.

## Preparation

Gallium(III) sulfate is prepared from the reaction of hydroxygallium diacetate and sulfuric acid. The two reactants were mixed at 90 °C and left for 2 days which produced the octadecahydrate. Then, it was dried in a vacuum for 2 hours which created the extremely hygroscopic anhydrous form. The overall reaction is below:
    2 Ga(CH$_3$COO)$_2$OH + 3 H$_2$SO$_4$ → Ga$_2$(SO$_4$)$_3$ + 4 CH$_3$COOH + 2 H$_2$O
After the production, it was confirmed to be the simple salt, Ga$_2$(SO$_4$)$_3$, by x-ray diffraction.

## Properties

When heated over 680 °C, gallium sulfate gives off sulfur trioxide, yielding gallium(III) oxide. A gallium sulfate solution in water mixed with zinc sulfate can precipitate ZnGa$_2$O$_4$.

## Derivatives

Basic gallium sulfate is known with the formula (H$_3$O)Ga$_3$(SO$_4$)$_2$(OH)$_6$.
Double gallium sulfates are known with composition NaGa$_3$(SO$_4$)$_2$(OH)$_6$, KGa$_3$(SO$_4$)$_2$(OH)$_6$, RbGa$_3$(SO$_4$)$_2$(OH)$_6$, NH$_4$Ga$_3$(SO$_4$)$_2$(OH)$_6$. These compounds are isostructural with jarosite and alunite. Jarosite and alunite can contain a small amount of gallium substituted for iron or aluminium. Organic base double gallium sulfates can contain different core structures, these can be chains of [Ga(SO$_4$)$_3$]$^{3-}$, [Ga(OH)(SO$_4$)$_2$]$^{2-}$ or [Ga(H$_2$O)$_2$(SO$_4$)$_2$]$^−$ or sheets of [Ga(H$_2$O)$_2$(SO$_4$)$_2$]$^−$ units.
| | formula | crystal system | space group | unit cell Å | volume | density | properties |
| | (H$_3$O)Ga$_3$(SO$_4$)$_2$(OH)$_6$ | | R3m | a=7.18 c=17.17 z=1.5 | 766 | | |
| | Ga$_4$(OH)$_{10}$SO$_4$ | | | | | | |
| | NH$_4$Ga$_3$(SO$_4$)$_2$(OH)$_6$ | | | | | | |
| trisodium gallium sulfate | Na$_3$Ga(SO$_4$)$_3$ | tetragonal | | a = 9.451 c = 7.097 | | | |
| | NaGa$_3$(SO$_4$)$_2$(OH)$_6$ | | | | | | |
| | KGa$_3$(SO$_4$)$_2$(OH)$_6$ | | | | | | |
| | RbGa$_3$(SO$_4$)$_2$(OH)$_6$ | | | | | | |
| Caesium gallium sulfate dodecahydrate | CsGa(SO$_4$)$_2$•12H$_2$O | cubic | Pa3 | Z=4 | | 2.127 | refractive index=1.461 |
| dimethylammonium gallium sulfate hexahydrate | (CH$_3$)$_2$NH$_2$Ga(SO$_4$)$_2$·6H$_2$O | | | | | | ferroeelastic |
| guanidinium gallium sulfate | [C(NH$_2$)$_3$]Ga(SO$_4$)$_2$·6H$_2$O | hexagonal | P31m | a=11.82 c=9.13 | | | ferroelectric |
| Ethylenediammonium acid gallium sulfate | [C$_2$H$_{10}$N$_2$][H$_3$O][Ga(SO$_4$)$_3$] | | | | | | |
| Ethylenediammonium basic gallium sulfate | [C$_2$H$_{10}$N$_2$][Ga(OH)(SO$_4$)$_2$]·H$_2$O | | | | | | |
| Tetramethylenediammonium gallium sulfate | [C$_4$H$_{14}$N$_2$][Ga(H$_2$O)$_2$(SO$_4$)$_2$]$_2$ | | | | | | |
| Hexamethylenediammonium gallium sulfate | [C$_6$H$_{18}$N$_2$][Ga(H$_2$O)$_2$(SO$_4$)$_2$]$_2$ | | | | | | |