Cationic M2L4 cages for perchlorate removal from aqueous solutions and preferential perchlorate incorporation in hydrophilic solutionsElectronic supplementary information (ESI) available: Fig. S1-S2 show the crystal structures of 1a, 1b, 2a, and 2b; Fig. S3 shows anion removal chart by 1b. CCDC 1451229 (1a), 1451228 (1b), 1451231 (2a), and 1451230 (2b). For crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ce00267f

• Main Authors: Sone, Eriko, Sato, Moeko, Mochizuki, Masaru, Kamio, Chihiro, Yamanishi, Katsunori, Kondo, Mitsuru
• Format: Journal Article
• Published: 28.06.2016
• ISSN: 1466-8033
• DOI: 10.1039/c6ce00267f

Four new cage-type compounds, [A ⊂ Cu 2 ( m -bbitrb) 4 ]A 3 (A = Cl − ( 1a ), Br − ( 1b ), m -bbitrb = 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene), and [SO 4 ⊂ Cu 2 ( m -bbitrb) 4 ]A 2 (A = Cl − ( 2a ), Br − ( 2b )), were synthesized and characterized. These compounds have a M 2 L 4 -type cationic cage, incorporating an anion in the cage. Although the four compounds are insoluble in water, they exhibit ClO 4 − removal activity from aqueous solutions by exchange with anions located outside the cage. The [Cl ⊂ Cu 2 ( m -bbitrb) 4 ] 3+ cage removes ClO 4 − from aqueous solutions preferentially. To study the selective removal process by the cationic cage, the affinity of the [Cu 2 ( m -bbitrb) 4 ] 4+ cage for ClO 4 − was studied by acquiring the solid-state reflectance spectra, absorption spectra, and ESI-TOF mass spectra in solutions of MeCN and MeCN/H 2 O for [SO 4 ⊂ Cu 2 ( m -bbitrb) 4 ](ClO 4 ) 2 ( 2d ). The results indicated that the SO 4 2− in [SO 4 ⊂ Cu 2 ( m -bbitrb) 4 ] 2+ was retained in the MeCN solution, whereas in the MeCN/H 2 O solution the SO 4 2− was exchanged with the ClO 4 − located outside the cage. This is because an increase in the hydrophilicity of the solution promotes the incorporation of hydrophobic ClO 4 − into the hydrophobic cage, meaning that the preferential removal of ClO 4 − from aqueous solutions is due to the higher affinity of the hydrophobic space created outside the M 2 L B 4 cages in the solid state. Four new cationic cage type compounds have been synthesized and characterized. Their compounds successfully removed perchlorate ions from aqueous solutions. The solvent dependent anion inclusion of the cationic cage is described.