A method of making a salt of the formula: Mg[Al(R)4]2, where R represents a compound selected from a deprotonated alcohol or thiol; an amine; or a mixture thereof. The method comprising the steps of; combining a Mg(AlH4)2 precursor with an alcohol, thiol or amine of the general formula R—H to create a reaction liquor containing Mg[Al(R)4]2; and washing the reaction liquor in an organic solvent.