Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4− Clusters within Highly Insoluble Imine‐Linked Bis‐Guanidinium Crystals |
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| Authors: | Dr Radu Custelcean Neil J Williams Charles A Seipp Dr Alexander S Ivanov Dr Vyacheslav S Bryantsev |
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| Institution: | 1. Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA;2. Department of Chemistry, The University of Tennessee, Knoxville, TN, USA;3. Department of Chemistry, The University of Texas at Austin, Austin, TX, USA |
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| Abstract: | Selective crystallization of sulfate with a simple bis‐guanidinium ligand, self‐assembled in situ from terephthalaldehyde and aminoguanidinium chloride, was employed as an effective way to separate the highly hydrophilic sulfate anion from aqueous solutions. The resulting bis‐iminoguanidinium sulfate salt has exceptionally low aqueous solubility (Ksp=2.4×10?10), comparable to that of BaSO4. Single‐crystal X‐ray diffraction analysis showed the sulfate anions are sequestered as (SO4)2(H2O)4]4? clusters within the crystals. Variable‐temperature solubility measurements indicated the sulfate crystallization is slightly endothermic (ΔHcryst=3.7 kJ mol?1), thus entropy driven. The real‐world utility of this crystallization‐based approach for sulfate separation was demonstrated by removing up to 99 % of sulfate from seawater in a single step. |
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| Keywords: | anions cluster compounds crystallization guanidines self-assembly |
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