Engineered π⋯π interactions favour supramolecular dimers X@[FeL] (X = Cl, Br, I): solid state and solution structure.

Ditopic bis-pyrazolylpyridine ligands usually react with divalent metal ions (M) to produce dinuclear triple-stranded helicates [ML] or, π⋯π interactions, dimers of monoatomic complexes ([ML]). The introduction of an additional benzene ring at each end of ligand L increases the number of aromatic contacts within the supramolecular aggregate by 40%, driving the self-recognition process in an irreversible manner. Consequently, the mixing of new bis-pyrazolylquinoline L2 with FeX salts leads to crystallization of the tripartite high-spin assemblies (X@[Fe(L2)]) (X = Cl, Br or I). The aggregates exhibit exceptional stability, as confirmed by a combination of paramagnetic H NMR techniques, demonstrating their persistence in solution. Our investigations further reveal that the guests Br and I are retained inside the associate in solution but Cl is immediately released, resulting in the formation of the empty supramolecular dimer ([Fe(L2)]).