Influence of acidic media on the supramolecular aggregation of iso-tellurazole N-oxides

Iso-tellurazole N-oxides are promising supramolecular building blocks. While in neutral solutions, they form tetra- and hexameric macrocyclic aggregates linked by Te···O secondary bonding (σ hole interactions or chalcogen bonds), protonation of the oxygen atom in acidic media disrupts such supramolecular association. The process is reversible and, consequently, can be used to switch on and off the self-assembly process. Hammett acidity measurements gave pKa values of –3.2 for the protonated molecules. Adducts with HCl and HBr were isolated and structurally characterized. Protonation in solution led to the crystallization of a new polymorph of 3-methyl-5-phenyl-1,2-tellurazole N-oxide, which features a unique polymeric arrangement.