Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4− Clusters within Highly Insoluble Imine‐Linked Bis‐Guanidinium Crystals. Issue 6 (8th December 2015)

• Record Type: Journal Article
• Authors: Custelcean, Radu; Williams, Neil J.; Seipp, Charles A.; Ivanov, Alexander S.; Bryantsev, Vyacheslav S.
• Is Part Of: Chemistry. Volume 22:Issue 6(2016)
• Page Start: 1997
• Page End: 2003
• Publication Date: 2015-12-08
• Subjects: anions -- cluster compounds -- crystallization -- guanidines -- self-assembly; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201504651
• Languages: English
• ISSNs: 0947-6539

Abstract

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 ( K sp =2.4×10 −10 ), comparable to that of BaSO4 . Single‐crystal X‐ray diffraction analysis showed the sulfate anions are sequestered as [(SO4 )2 (H2 O)4 ] 4− clusters within the crystals. Variable‐temperature solubility measurements indicated the sulfate crystallization is slightly endothermic ( ΔH cryst =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. Abstract : Out of the blue : The highly hydrophilic sulfate anion can be effectively crystallized from water as [(SO4 )2 (H2 O)4 ] 4− clusters with a bis‐guanidinium ligand self‐assembled in situ from terephthalaldehyde and aminoguanidinium chloride, by forming an exceptionally insoluble salt, on a par with BaSO4 . The real‐world utility of this approach was demonstrated by effective separation of sulfate from seawater.