Competition between chalcogen and halogen bonding assessed through isostructural species.

Area of Science:

• Supramolecular Chemistry
• Crystallography
• Organic Synthesis

Background:

• 1,3,4-Chalcogenadiazoles are heterocyclic compounds with diverse applications.
• Halogen bonding and chalcogen bonding are important non-covalent interactions in crystal engineering.
• Understanding these interactions is crucial for designing materials with specific properties.

Purpose of the Study:

• To synthesize a library of novel 2-halo-5-(4-halophenyl)-1,3,4-chalcogenadiazoles.
• To investigate the role and relative strength of chalcogen bonding versus halogen bonding in the solid state.
• To analyze the crystal packing and intermolecular interactions within the synthesized compounds.

Main Methods:

• Synthesis of four new 2-halo-5-(4-halophenyl)-1,3,4-chalcogenadiazole derivatives.
• Single-crystal X-ray diffraction to determine the crystal structures.
• Hirshfeld surface analysis and energy framework calculations to quantify intermolecular interactions.

Main Results:

• Four isostructural compounds were obtained: 2-iodo-5-(4-iodophenyl)-1,3,4-thiadiazole, 2-bromo-5-(4-bromophenyl)-1,3,4-selenadiazole, 2-bromo-5-(4-iodophenyl)-1,3,4-selenadiazole, and 2-bromo-5-(4-iodophenyl)-1,3,4-thiadiazole.
• All compounds exhibited zigzag packing motifs driven by bifurcated chalcogen bonds (Ch...N) and halogen bonds (X...X).
• Chalcogen bonding interactions were found to be preferentially formed over halogen bonding to the nitrogen atom and were collectively stronger and more structurally influential.

Conclusions:

• The study demonstrates the preferential formation and dominant role of chalcogen bonding in halogenated 1,3,4-chalcogenadiazoles.
• Bifurcated chalcogen bonds play a significant role in directing crystal packing and stabilizing the solid-state structures.
• These findings provide valuable insights into the interplay of non-covalent interactions in halogen-substituted heterocyclic systems.