Consistent Binding Aptitude of Halides and Oxyanions via Cooperative vs. Non-Cooperative Binding Modes by Neutral Napthyl Bis-Urea Receptors

Two electron-rich napthyl ring containing bisurea receptor derived from ortho (L-1) and meta (L-2)-phenylenediamine moiety were designed and synthesized for investigating their anion coordination behavior. L-1 self-assembled in presence of organic terephthalate anion into a dimeric pseudo-capsular host-assembly sealed by tetrabutylammonium counter cation (Complex 1c). However, L-2 self-assembled in 2:4 host-guest fashions (Complex 2d) with H-bonded dihydrogenphosphate tetrameric anionic guest in the presence of excess n-TBA (H2PO4). Further, receptor L-1 has been found to self-assembled into unimolecular cooperative 1:1 complex in presence of spherical Chloride anion (Complex 1a) and planar Acetate anion (Complex 1b). Moreover, receptor L-2 forms similar kind of non-capsular host-guest assembly in presence of spherical halides like Cl-, Br-, and F-. To validate the result obtained in the solid state studies, H-1-NMR titration experiments have also been performed using n-TBA salts of anions to inspect the solution state anion binding behavior of isomeric receptors L-1 and L-2.