M^III aqueous chemistry

Al³⁺ is amphoteric and will dissolve in alkaline and acidic solutions. The [Al(H₂O)₆]³⁺ ion is created at low pH but goes through increasing protolysis as the pH rises above four, and polymeric species like [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺ can be identified. The extremely insoluble Al(OH)₃ is created at neutral pH but redissolves above pH 10:

Al³⁺ depicts typically 'hard' complexing behavior and has a especially strong affinity for negative charged and/or chelating ligands, like (C₂O₄^2-)oxalate and EDTA. Ga³⁺ is identical to Al³⁺ but In³⁺ is more basic. Tl³⁺ is different as it is a strong oxidizing agent, readily creating Tl⁺ (see below and Fig. 1). It also depicts strong class b or 'soft' complexing behavior, even though not so marked like that of Hg²⁺.