Stabilisation of Exotic Tribromide (Br) Anions via Supramolecular Interaction with A Tosylated Macrocyclic Pyridinophane. A Serendipitous Case.

Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a -toluenesulfonyl (tosyl; Ts) group, appear to be a useful tool to provide evidence on how the interplay of various supramolecular forces can help stabilise exotic anionic species such as tribromide (Br) anions. Indeed, crystals of (HL-Ts)(Br)(NO) unexpectedly grew from an acidic (HNO) aqueous solution of L-Ts in the presence of Br anions. The crystal structure of this compound was determined by single crystal XRD analysis. Hydrogen bonds, salt-bridges, anion-, - stacking, and van der Waals interactions contribute to stabilising the crystal lattice. The observation of two independent Br anions stuck over the π-electron densities of pyridine and tosyl ligand groups, one of them being sandwiched between two pyridine rings, corroborates the significance of anion-π interactions for N-containing heterocycles. We show herein the possibility of detecting anion-π contacts from fingerprint plots generated by Hirshfeld surface analysis, demonstrating the effective usage of this structural investigation technique to further dissect individual contributions of stabilising supramolecular forces.