Proton Magnetic Resonance Coordination Number Study of Al(III), Be(II), Ga(III), In(III), and Mg(II) in Water and Aqueous Solvent Mixtures

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Abstract
Cation coordination number measurements of AlCl3, AlBr3, Al(ClO4)3, Al(NO3)3, BeCl2, GaCl3, GA(ClO4), InCl3, In(Cl)4)3, and Mg(ClO4)2, in water, and in aqueous acetone mixtures have been carried out by a protonmagnetic resonance method. At low temperatures, solutions of these electrolytes exhibit separate proton resonance signals for bulk water, and water molecules in the first solvation shell of the cation. Integration of these signals provides a direct measure of the coordination number of the cation. The Al(III) and Ga(III) are solvated by six water molecules in all solutions, regardless of the anion present. The Be(II) is coordinated by four water molecules in water and in aqueous acetone mixtures. The In(III) and Mg(II) could only be studied in aqueous acetone mixtures, wherein they are each coordinated by six water molecules. With the possible exception of Be(II) no evidence for contact ion pairing was found.