Adjusting the balance between hydrogen and chalcogen bonds

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Chemical Physics

Background:

• Hydrogen bonds (HB) and chalcogen bonds (ChB) are crucial non-covalent interactions.
• Understanding and controlling these interactions is key for designing molecular materials.

Purpose of the Study:

• To investigate the interplay between hydrogen bonds and chalcogen bonds in a novel molecular complex.
• To explore how substituents influence the strength of these bonds.
• To correlate bond characteristics with NMR spectroscopic properties.

Main Methods:

• Assembly of a molecular complex pairing a carboxyl group (X1COOH) with a 1,2,5-chalcogenadiazole ring.
• Systematic variation of substituents on the acid and the ring.
• Analysis of hydrogen bond (OH⋯N) and chalcogen bond (Y⋯O, Y=S, Se, Te) formation.
• Characterization using NMR spectroscopy to probe chemical shielding and nuclear coupling.

Main Results:

• A hydrogen bond (OH⋯N) and a chalcogen bond (Y⋯O) were successfully formed.
• Chalcogen bond strength increases with the size of the chalcogen atom (S < Se < Te).
• Electron-withdrawing groups on the acid strengthen HB but weaken ChB, while EWGs on the ring have the opposite effect.
• A balance between HB and ChB strengths can be achieved by strategic substituent selection.
• NMR chemical shielding and coupling constants reflect the strengths of the formed bonds.

Conclusions:

• The study demonstrates precise control over hydrogen and chalcogen bond strengths through substituent effects.
• A tunable balance between these two interactions is achievable in the designed molecular system.
• NMR spectroscopy provides valuable insights into the nature and strength of these non-covalent interactions.