Ionic core–shell dendrimers with a polycationic core: structural aspects and host–guest binding properties

The structural aspects and host–guest binding properties of ionic core–shell dendrimers [1]Br8 and [2]Br4, which bear a polycationic core and a neutral shell of Fréchet-type poly(benzyl aryl ether) dendrons, have been investigated by means of dendritic wedges [3]Br2 and [4]Br, that resemble one of the four wedges of the dendrimers. Alike the dendrimers, dendritic wedges [3]Br2 and [4]Br form discrete stoichiometric assemblies with Methyl Orange anions to give host–guest assemblies [3][MO]2 and [4][MO], respectively. X-Ray crystal structures of dendritic wedge [3]Br2 and host–guest assembly [4][MO] have been resolved and reveal that besides Coulombic interactions additional interactions, such as weak hydrogen bonds and π–π interactions, can also be present between the dendritic host and substrate molecules. The substrate selectivity of the ionic core–shell dendrimers for sulfonato anions over carboxylato anions, as was observed in preliminary competition experiments, can be attributed to these additional binding interactions. These X-ray structures, furthermore, substantiate earlier speculations in literature on the presence of π–π interactions between Fréchet-type poly(benzyl aryl ether) dendritic wedges and aromatic substrate molecules