Proton Magnetic Resonance Studies of Al(III) and Ga(III) Hydration Numbers in Aqueous Solution

Schweitzer and Stephens have recently suggested that the hydration numbers of Al³⁺ and Ga³⁺ and Ga³⁺ in aqueous solutions containing a considerable excess of chloride ion are probably less than six. Hydration numbers as low as 4.64 (in 1.44 M AlCl₃+ 2.15 M CaCl₂) or 4.61 (in 0.645 M GaCl₃+ 3.32 M CaCl₂) were obtained.¹ That Ga³⁺ forms chloro-complexes under these conditions is well known though interaction between Al³⁺ and chloride is considered unlikely in aqueous solution.^2–4