Halide Recognition through Diagnostic “Anion–π” Interactions: Molecular Complexes of Cl, Br, and I with Olefinic and Aromatic π Receptors



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Intense colorations and new charge-transfer absorption bands are observed upon addition of a halide (Cl, Br, I) to neutral organic π acceptors with electron-deficient olefinic and aromatic centers. These phenomena results from noncovalent anion–π interactions (shown schematically), which were confirmed by X-ray crystallography.