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

Abstract

Abstract The [M 4 −Hal] − (M=the title compound; Hal=Cl, Br, and I) complexes were isolated in the form of salts of [Et 4 N] + 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, [M 4 −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 [Et 4 N] + [M 4 −Hal] − ; very tentatively, species in the solutions are assigned [M−Hal] − . It is supposed that the formation of the [M 4 −Hal] − proceeds during the crystallization of the [Et 4 N] + [M 4 −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.