Supramolecular assemblies through host-guest interactions of 18-crown-6 with ammonium salts: Geometric effects of amine groups on the hydrogen-bonding architectures

A series of ammonium salts were introduced into the self-assembly with the same host 18-crown-6, yielding five supramolecular salts, that is [(C4H6N3)·(18-crown-6)2]⁺·() (1), [(C6H14N)·(18-crown-6)]⁺·() (2), [(C6H14N)·(18-crown-6)]⁺·() (3), [(C6H10N2)·(18-crown-6)]²⁺·()2 (4) and [(C6H8NO2)·(18-crown-6)]⁺·[(C7H3N2O6)^-]2 (5). Structural analysis indicates that different kinds of guest amines, ranging from chain-like aliphatic amine, annular aliphatic amine to aromatic amine, have a great impact on host-guest interactions and supramolecular architectures. The major driving force in host-guest systems is found to be the strong N-H.O or/and weak C-H.O hydrogen-bonding interactions, with various ring motifs and interesting substructures such as the butterfly-like trimer in 1 and the rotator-stator assembly in 2-5. By analysing and summing up, we can come to the conclusion that the group in 4 exhibits an optimum value of around 0.755 Å from the O-plane and the 18-crown-6 macrocycle displays the minimum distortion. On the whole, ammonium cations show control over supramolecular assemblies, but counter anions that easily form hydrogen bonds will affect crystal structures, for instance, anion in 4 facilitates the formation of the 3D hydrogen-bonding network and helical hydrogen-bonding sheets while deprotonated 3,5-dinitrobenzoic acid assists the formation of discrete subunits.