Gallium perchlorate is an inorganic compound with the chemical formula . It is the gallium salt of perchloric acid. Gallium perchlorate is strongly deliquescent and highly soluble in water, and several hydrated forms are known, including the hexahydrate and nonahydrate.
Preparation Hydrated gallium perchlorate can be prepared by reacting gallium(III) oxide with aqueous perchloric acid. Crystals of the nonahydrate have been obtained by treating gallium(III) oxide with 70% perchloric acid, followed by recrystallization from water and evaporation of the solution at room temperature.
Ga2O3 + 6 HClO4 -> 2 Ga(ClO4)3 + 3 H2O
The hexahydrate can also be prepared directly from metallic gallium. Gallium dissolves rapidly in constant-boiling 72% perchloric acid, and cooling the resulting solution causes gallium perchlorate hexahydrate to crystallize.
Anhydrous solutions of gallium perchlorate in methanol can be prepared by metathesis of anhydrous gallium trichloride with silver perchlorate. The precipitation of silver chloride drives the reaction:
GaCl3 + 3 AgClO4 -> Ga(ClO4)3 + 3 AgCl v
Properties and structure Gallium perchlorate is very deliquescent and highly soluble in water. The hexahydrate is difficult to dehydrate directly; attempts to remove its water of crystallization by heating produce a basic salt instead. Gallium perchlorate decomposes at approximately 155 °C under vacuum and 175 °C in air. The nonahydrate, , crystallizes in the trigonal crystal system in space group Rc. Its structure contains octahedral ions. These aqua complexes are linked through additional water molecules by hydrogen bonding, while the columns of hydrated gallium ions are separated by approximately tetrahedral perchlorate ions. Hydrogen bonding involving both coordinated and uncoordinated water molecules and the perchlorate ions produces a three-dimensional structure. In aqueous gallium perchlorate solutions, gallium(III) occurs predominantly as the hexaaqua ion . Raman spectroscopic studies found no significant inner-sphere complex formation between gallium(III) and perchlorate over the investigated concentration and temperature ranges.
Applications Gallium perchlorate has been investigated as a Lewis acid catalyst in organic synthesis. It catalyzes the formation of substituted quinoxalines by reaction of α-hydroxy ketones with o-phenylenediamines. In the reported procedure, 10 mol% gallium perchlorate in ethanol at room temperature gave the quinoxaline products in good yields.
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