Encapsulation of [X2(H2O)4]2? (X = F/Cl) clusters by pyridyl terminated tripodal amide receptor in aqueous medium: single crystal X-ray structural evidence?

Dalton Transactions Pub Date: 2013-11-26 DOI: 10.1039/C3DT52694A

Abstract

A new tris-amide receptor L based on 1,3,5-methyl substituted benzene platform and pyridyl as an attached unit is synthesized and explored towards anion recognition in aqueous environment. The presence of pyridyl terminal in L facilitates its aqueous solubility. The binding of halides and oxyanions towards L are examined by 1H-NMR technique in solution and by single crystal X-ray crystallography in solid state studies. Crystallization of fluoride and chloride with L is carried out in acetone–water (1?:?1, v/v) binary solvent mixture that yields crystals for respective host–guest complexes, [L]2·[F2(H2O)4]·[TBA]2 (1) and [L]2·[Cl2(H2O)4]·[TBA]2 (2) suitable for single crystal X-ray diffraction studies. On the other hand, complexation of L with fluoride in dioxane–acetone (1?:?1, v/v) solvent mixture, results the formation of SiF62? encapsulated complex, [L]2·[SiF6(H2O)2]·[TBA]2 (3). Crystallographic result shows the formation of [F2(H2O)4]2? and [Cl2(H2O)4]2? zipped 1D-polymeric tweezer-like assemblies of L in acetone–water (1?:?1, v/v) binary solvent mixture in complexes 1 and 2 respectively. Solution state 1H-NMR studies in D2O–acetone-d6 (1?:?19, v/v) support 1?:?4 (host–guest) binding stoichiometry of F?, Cl?, Br?, NO3?, HSO4? and H2PO4? with L. Binding constants of these investigated anions with L by 1?:?1 binding model are calculated which show the following binding order: NO3? ≈ HSO4? > F? ≈ Cl? ≈ Br? > H2PO4?. Further, solution state 19F-NMR studies are also carried out to establish the F? binding with L in DMSO-d6.

Graphical abstract: Encapsulation of [X2(H2O)4]2? (X = F/Cl) clusters by pyridyl terminated tripodal amide receptor in aqueous medium: single crystal X-ray structural evidence
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