Solution-State Anion Recognition, and Structural Studies, of a Series of Electron-Rich meta-Phenylene Bis(phenylurea) Receptors and Their Self-Assembled Structures

meta-Phenylene bis­(phenylurea) receptors 1–4 were designed and synthesized to investigate the association between receptor shape, anion-selective binding and anion-directed self-assembly processes. Solution studies, performed through 1H NMR titrations with a variety of tetra-N-butylammonium salts, demonstrated strong binding of 2 equiv of H2PO4–, AcO–, BzO– anions and comparatively weak binding of Cl–, HSO4–, and SO42– anions. Binding modes and stability constants (log β) were determined by regression analysis of the obtained 1H NMR titration data in DMSO-d6, and the cooperativities of the binding interactions were probed. Host–guest complexes of receptors 1 and 2 were studied in the crystalline phase to further probe the anion-binding behavior of this motif. This included a triple-stranded helicate consisting of three strands of receptor 2 arranged around a mixed-phosphate anionic core, which was characterized by using X-ray crystallography.