Aqueous Sulfate Separation by Crystallization of Sulfate-Water Clusters.

An effective approach to sulfate separation from aqueous solutions is based on the crystallization of extended [SO4(H2O)5(2-)]n sulfate-water clusters with a bis(guanidinium) ligand. The ligand was generated in situ by hydrazone condensation in water, thereby bypassing the need for elaborate syntheses, tedious purifications, and organic solvents. Crystallization of sulfate-water clusters represents an alternative approach to the now established sulfate separation strategies that involve encapsulation of the "naked" anion.