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. Crystalline complexes of 5,6‐dicyano‐2,1,3‐benzoselenadiazole with [Hal]− (Hal=Cl, Br and I) feature unprecedented 4 : 1 stoichiometry caused by cooperative interplay of chalcogen and hydrogen bondings. Solution UV‐Vis spectra of the complexes contain [Hal]−‐dependent charge‐transfer bands allowing identification of the individual [Hal]−, and the parent selenadiazole can be considered as a chromogenic receptor and prototype sensor of [Hal]−.