Supramolecular chemistry of chalcogenadiazoles is attracting an increasing attention due to its applications in materials chemistry. Chalcogen bonding allows a fine-tuning of the self-assembly and, therefore, modulation of physical properties when these compounds are employed. Here, we report a facile preparation of a broad scope of 1,2,4-selenadiazoles via coupling of 2-pyridylselenenyl halides with unactivated nitriles, that represent a novel type of supramolecular building blocks which eagerly engage in a variety of chalcogen bonding interactions. The substituent-dependent propensity of novel selenadiazoles for the formation of four-center Se···N chalcogen bonding is analyzed. Other weak interactions, which in some cases outcompete the formation of 2Se-2N squares, are described. The discovery of the adducts derived from α-halogenated nitriles, which form robust dimers featuring a very specific combination of 2Se-2N square, two Hal···Hal, and two Se···Hal noncovalent interactions, is presented. © 2021 American Chemical Society.