Oxides of Ga, In and Tl

     The oxides and related compounds of the heavier group 13 metals call for less attention than those of Al. Gallium, like Al, forms more than one polymorph of Ga₂O₃, GaO(OH) and Ga(OH)₃, and the compounds are amphoteric. This contrasts with the basic nature of In₂O₃, InO(OH) and In(OH)₃. Thallium is unique among the group in exhibiting an oxide for the M(I) state: Tl₂O forms when Tl₂CO₃ is heated in N₂, and reacts with water.

    Thallium(III) forms the oxide Tl₂O₃, but no simple hydroxide. Tl₂O₃ is insoluble in water and decomposes in acids. In concentrated NaOH solution and in the presence of Ba(OH)₂, the hydrated oxide Tl₂O₃.xH₂O forms Ba₂[Tl(OH)₆]OH. In the solid state, the [Tl(OH)₆]^3- ions are connected to Ba²⁺‏ and [OH]^- ions to give a structure that is related to that of K₂PtCl₆ .