Chalcogen bonding vs. weakly coordinating anions - a solid state study on halidoselenium cations in an oxoanionic environment.

We present the crystal structure of selenoyl chloride, SeOCl2, for the first time and show that it can be used for the subsequent synthesis of novel compounds with the [SeCl3]+ cation, which we stabilized as disulfate [S2O7]2- and chlorosulfate [ClSO3]- salts, respectively. Both, SeOCl2 as well as the [SeCl3]+ salts show remarkable macromolecular arrangements and packing motifs in the solid state, so far not or only scarcely analyzed. Additionally, we report the stabilization of the dication [Se2I4]2+ in the tetrasulfate salt [Se2I4]2[S4O13]2(SO3). This marks the very first examples of the respective cations in an oxoanionic environment. All compounds show strong and directional non-covalent interactions, i.e. chalcogen bonding, as well as, to a lesser degree, halogen bonding (HaB). These interactions were investigated via Density functional theory (DFT) investigations, i.e. molecular electrostatic potential (MEP) surface plots, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. Overall, this work demonstrates that, while coulombic forces are the primary drivers in these ionic systems, the directionality and specific orbital contributions of σ- and π-hole interactions are essential for fine-tuning the final supramolecular assemblies.