Competing Effects of Chlorination on the Strength of Te...O Chalcogen Bonds Select the Structure of Mixed Supramolecular Macrocyclic Aggregates of Iso-Tellurazole N-Oxides

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the lambda Te-4 dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te...O ChB distances are 2.062 angstrom, the shortest observed to date in aggregates of this type. DFT-D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating lambda Te-4 and lambda Te-2 centers, which calculations identified as the thermodynamically preferred arrangement.

Automated summary

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the lambda Te-4 dichloro derivative. The crystal structure shows that the heterocycle can autoassociate forming macrocyclic tetramers via chalcogen bonding (ChB). DFT-D3 calculations suggest that while the chlorinated molecule is stronger as a ChB donor, it is weaker as a ChB acceptor, resulting in no significant increase in ChB strength in the chlorinated homotetramer. However, partial halogenation or mixing halogenation can selectively yield a more thermodynamically preferred heterotetramer.