Entrapment of Cyclic Fluoride–Water and Sulfate–Water–Sulfate Cluster Within the Self-Assembled Structure of Linear meta-Phenylenediamine Based Bis-Urea Receptors: Positional Isomeric Effect

Abstract

meta-Phenylenediamine based two linear bis-urea anion receptors, L1 (meta-nitro) and L2 (para-nitro), have been synthesized which showed strong binding affinities toward halides as well as planar and tetrahedral oxyanions. In the presence of excess fluoride anion, L1 self-assembles to entrap a cyclic fluoride–water tetrameric cluster within its tetrameric pillar-like assembly of each urea arm (complex 1a). In the presence of sulfate anion, L1 self-assembles in an identical fashion to entrap the bigger tetrahedral anion (complex 1b), whereas two urea moieties of two different receptor molecules of L1 have been structurally authenticated to be sufficient to stabilize the simple Y-shaped acetate anion in complex 1c. On the other hand, receptor L2, with a bis(para-nitro urea) functional group, especially in the presence of sulfate anion, self-assembles like long straight pillars entrapping sulfate–water–sulfate cluster {SO42–-(H2O)3-SO42–} (complex 2a). Additionally, L2 forms a host–guest assembly with the ca...