Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4- Clusters within Highly Insoluble Imine-Linked Bis-Guanidinium Crystals

Radu Custelcean; Neil J. Williams; Charles A. Seipp; Alexander S. Ivanov; Vyacheslav S. Bryantsev

doi:10.1002/chem.201504651

Aqueous Sulfate Separation by Sequestration of [(SO₄)₂(H₂O)₄]^4- Clusters within Highly Insoluble Imine-Linked Bis-Guanidinium Crystals

Radu Custelcean, Neil J. Williams, Charles A. Seipp, Alexander S. Ivanov, Vyacheslav S. Bryantsev

Research output: Contribution to journal › Article › peer-review

39 Scopus citations

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(H₂O)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.

Original language	English
Pages (from-to)	1997-2003
Number of pages	7
Journal	Chemistry - A European Journal
Volume	22
Issue number	6
DOIs	https://doi.org/10.1002/chem.201504651
State	Published - Feb 5 2016

Funding

This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. We would like to thank the University of North Carolina Wilmington for providing the seawater used in this study. The electronic-structure calculations used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Funders	Funder number
U.S. Department of Energy
Office of Science	DE-AC02-05CH11231
Basic Energy Sciences
University of North Carolina Wilmington
Chemical Sciences, Geosciences, and Biosciences Division

Keywords

anions
cluster compounds
crystallization
guanidines
self-assembly

Access to Document

10.1002/chem.201504651

Cite this

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title = "Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4- Clusters within Highly Insoluble Imine-Linked Bis-Guanidinium Crystals",

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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AU - Custelcean, Radu

AU - Williams, Neil J.

AU - Seipp, Charles A.

AU - Ivanov, Alexander S.

AU - Bryantsev, Vyacheslav S.

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N2 - 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.

AB - 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.

KW - anions

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KW - self-assembly

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