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⁺ .
Competing Interests: There are no conflicts to declare.
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