Combining different hydrogen-bonding motifs to self-assemble interwoven superstructures

Abstract

A series of carboxyl-substituted dibenzylammonium salts have been cocrystallized with the macrocyclic polyethers dibenzo[24]crown-8 (DB24C8) and bis-p-phenylene[34]crown-10 (BPP34C10) to effect the noncovalent syntheses of a wide range of interwoven superstructures in the solid state. In all cases, the dibenzylammonium cations thread through the cavities of the macrocyclic polyethers - primarily as a result of N+-H ··· O hydrogen bonds, with occasional secondary stabilization from C - H ··· O and aryl-aryl interactions - to form pseudorotaxane complexes possessing supplementary recognition sites (specifically, carboxyl groups) for further intercomplex association through hydrogen bonding. One unit of each of the dibenzylammonium cations threads through the DB24C8 macrocycle to make single-stranded, carboxyl-containing [2]pseudorotaxanes that interact further with one another to produce novel supramolecular architectures as a result of hydrogen bonding between their carboxyl groups (the carboxyl dimer supramolecular synthon), or between carboxyl groups and polyether oxygen atoms. Elaborate architectures, such as side-/main-chain pseudopolyrotaxanes and a daisy-chain-like supramolecular array, were thus synthesized noncovalently. BPP34C10 can accommodate two cations within its macrocyclic interior to form carboxyl-containing [3]pseudorotaxanes in which BPP34C10 acts as a girdle that helps to control the spatial orientation of the carboxylic acid-containing recognition sites for additional intersupramolecular association through the carboxyl dimer. PF6/- anions were also found to play a role in the self-assembly processes. When the anions interact with the [3]pseudorotaxanes, these recognition sites are oriented in the same direction. This leads to the formation of doubly-encircled multicomponent supermolecules when BPP34C10 is cocrystallized with dibenzylammonium cations bearing only one carboxyl substituent. On the other hand, when BPP34C10 is cocrystallized with an isophthalic acid-substituted ammonium cation, there is no evidence of any anion assistance to self-assembly; the isophthalic acid units are aligned in opposite directions, creating an interwoven supramolecular cross-linked polymer.