Halide Complexes of 5,6‐Dicyano‐2,1,3‐Benzoselenadiazole with 1:4 Stoichiometry: Cooperativity between Chalcogen and Hydrogen Bonding

The [M₄−Hal]⁻ (M=the title compound; Hal=Cl, Br, and I) complexes were isolated in the form of salts of [Et₄N]⁺ cation and characterized by XRD, NMR, UV‐Vis, DFT, QTAIM, EDD, and EDA. Their stoichiometry is caused by a cooperative interplay of σ‐hole‐driven chalcogen (ChB) and hydrogen (HB) bondings. In the crystal, [M₄−Hal]⁻ are connected by the π‐hole‐driven ChB; overall, each [Hal]⁻ is six‐coordinated. In the ChB, the electrostatic interaction dominates over orbital and dispersion interactions. In UV‐Vis spectra of the M+[Hal]⁻ solutions, ChB‐typical and [Hal]⁻‐dependent charge‐transfer bands are present; they reflect orbital interactions and allow identification of the individual [Hal]⁻. However, the structural situation in the solutions is not entirely clear. Particularly, the UV‐Vis spectra of the solutions are different from the solid‐state spectra of the [Et₄N]⁺[M₄−Hal]⁻; very tentatively, species in the solutions are assigned [M−Hal]⁻. It is supposed that the formation of the [M₄−Hal]⁻ proceeds during the crystallization of the [Et₄N]⁺[M₄−Hal]⁻. Overall, M can be considered as a chromogenic receptor and prototype sensor of [Hal]⁻. The findings are also useful for crystal engineering and supramolecular chemistry.