Iso-Tellurazolium<i>-N</i>-Phenoxides: A Family of Te···O Chalcogen-Bonding Supramolecular Building Blocks

Abstract

Formal substitution of the oxygen atom of an iso-tellurazole <i>N</i>-oxide with deprotonated (<i>ortho</i>, <i>meta</i>, and <i>para</i>)-hydroxyphenyl groups generated molecules that readily aggregate through Te···O chalcogen bonding (ChB) interactions. The molecules undergo autoassociation in solution, as shown by variable temperature (VT) ¹H NMR experiments and paralleling the behavior of iso-tellurazole <i>N</i>-oxides. Judicious adjustment of crystallization conditions enabled the isolation of either polymeric or macrocyclic aggregates. Among the latter, the <i>ortho</i> compound assembled a calixarene-like trimer, while the <i>para</i> isomer built a macrocyclic tetramer akin to a molecular square. The Te···O ChB distances in these structures range from 2.13 to 2.17 Å, comparable to those in the structures of iso-tellurazole <i>N</i>-oxides. DFT calculations estimate that the corresponding Te···O ChB energies are between -122 and -195 kJ mol^-1 in model dimers and suggest that macrocyclic aggregation enhances these interactions.