Engineered π⋯π interactions favour supramolecular dimers X@[FeL 3 ] 2 (X = Cl, Br, I): solid state and solution structure.

Ditopic bis-pyrazolylpyridine ligands usually react with divalent metal ions (M 2+ ) to produce dinuclear triple-stranded helicates [M 2 L 3 ] 4+ or, via π⋯π interactions, dimers of monoatomic complexes ([ML 3 ] 2 ) 4+ . 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 2 salts leads to crystallization of the tripartite high-spin assemblies (X@[Fe(L2) 3 ] 2 ) 3+ (X = Cl, Br or I). The aggregates exhibit exceptional stability, as confirmed by a combination of paramagnetic 1 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) 3 ] 2 ) 4+ .