Stabilisation of Exotic Tribromide (Br₃⁻) Anions via Supramolecular Interaction with A Tosylated Macrocyclic Pyridinophane. A Serendipitous Case.

• Main Authors: Álvaro Martínez-Camarena, Matteo Savastano, Carla Bazzicalupi, Antonio Bianchi, Enrique García-España
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Molecules
• Subjects: N-heterocycles; anion complexes; anion- interactions; crystal structure; Hirshfeld surface analysis
• Online Access: https://www.mdpi.com/1420-3049/25/14/3155

<b> </b>Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a <i>p</i>-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 (Br₃⁻) anions. Indeed, crystals of (H₂L-Ts)(Br₃)_1.5(NO₃)_0.5 unexpectedly grew from an acidic (HNO₃) 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 Br₃⁻ 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.