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

Abstract

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.

Thin Films of Conjugated Chalcogenadiazole: Growth, Structure, and Optical Properties of Substituted Selenadiazoloquinoxaline

“…The unique molecular structure of 1,2,5-selenadiazoles enables these molecules to aggregate into supramolecular synthons forming characteristic Se···N square motifs through chalcogen bonding, which has received, among other secondary bonding interactions, growing attention in the last two decades. , This bonding originates from the interaction of the σ-holes (regions of positive electrostatic potential) centered on selenium atoms with the lone pairs of nitrogen atoms acting as a Lewis base . The strength and directionality of this bonding allow the formation of dimers and polymers, with the possibility of electron transfer between molecules and the formation of well-ordered structures. ,,− This aspect is important, as the molecular ordering within the material critically determines charge transport, energy transfer, and optical properties and, consequently, defines and controls the overall performance of the device. − To additionally strengthen this feature, the self-association of π-conjugated molecules through effective π–π stacking interactions can be employed to achieve morphological organization and structural order at mesoscopic length scales . In this regard, a rational design strategy to achieve perfect crystallinity within the material involves extending the conjugated framework by incorporating aromatic systems into the chalcogenadiazole moiety.…”