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Updated: Feb 21, 2026

Sulfate Separation by Selective Crystallization with a Bis-iminoguanidinium Ligand
Published on: September 8, 2016
Selective Binding of Spherical and Linear Anions by Tetraphenyl(thio)urea-Based Dihomooxacalix[4]arene Receptors
Filipa A Teixeira1, Paula M Marcos1,2, José R Ascenso3
1Centro de Química Estrutural, Faculdade de Ciências da Universidade de Lisboa , Edifício C8, 1749-016 Lisboa, Portugal.
Abstract:
Three novel tetra(thio)ureido dihomooxacalix[4]arene anion receptors (phenylurea 4a, phenylthiourea 4b, and tert-butylurea 4c) were synthesized and obtained in the cone conformation in solution, as shown by NMR studies. The X-ray crystal structure of 4c is reported. The host-guest properties of these receptors toward several anions were investigated by 1H NMR titrations. Phenylurea 4a displayed a very efficient binding toward the spherical F- and Cl- anions, and the linear CN- (log Kass = 3.46, 3.50, and 4.02, respectively). In comparison to related bidentate phenylurea dihomooxacalix[4]arenes, tetraphenylurea 4a is more preorganized and the higher number of hydrogen bond donor sites provides a remarkable enhancement of its binding efficiency.
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