Cation-π interaction:: a case for macrocycle-cation π-interaction by its ureidoarene counteranion

We report the solid state structures of homocomplex [1.K](+)[I](-) and of heterocomplexes [1.K](+)[3.I](-) and [1.K](+)[4.I]. In the [1.K](+)[I](-) complex the apical position of the K 1 in the macrocycle is occupied by a -CH2- moiety of a neighboring 18-crown-6, consistent with a close contact and corresponding to 'agostic' interactions between K+ and -CH2- moieties. In the [1.K](+)[3.I](-) complex the second apical site of the cation is coordinated by a bridging water molecule which is simultaneously H-bonded to both the phenol hydroxyl and the iodide anion. In the [1.K](+)[4.I](-) complex the second apical site of the cation is occupied by the indole moiety. Moreover, the new heterocomplex system [1.K](+)[4.I](-) presented here, despite the multiple possibilities of K+-pi contacts with the sterically available phenyl, phenyl-indole and pyrrole-indole rings of 4, shows that the pyrrolo C2=C3 double bond is a versatile pi-donor. H-1 NMR results led us to conclude that the complexes adopt similar conformations in solution to those observed in the solid state.