The diiodine basicity scale: toward a general halogen-bond basicity scale

Area of Science:

• Chemistry
• Supramolecular Chemistry
• Chemical Physics

Background:

• Lewis basicity is crucial for understanding chemical interactions.
• Existing basicity scales (hydrogen-bond, dative-bond, cation) offer different perspectives.
• A comprehensive scale is needed to capture diverse bonding interactions.

Purpose of the Study:

• Introduce and validate a new diiodine basicity scale (pK(BI2)).
• Explore the orthogonality of the diiodine basicity scale with existing scales.
• Quantify substituent effects and classify various organic functional groups based on diiodine basicity.

Main Methods:

• Development of the diiodine basicity scale (pK(BI2)).
• Analysis of substituent effects using linear free energy relationships.
• Calculation of individual complexation constants for polybases.
• Classification of aromatic compounds as specific types of bases.

Main Results:

• The pK(BI2) scale is quasi-orthogonal to established Lewis basicity scales.
• Established sequences for diiodine basicity across different atomic sites and functional groups.
• Quantified substituent effects and classified aromatic ethers, amines, thioethers, and selenoethers.
• Identified unique bonding interactions including superbasic nitriles and hydrogen-bond-assisted iodine bonds.

Conclusions:

• The diiodine basicity scale provides a novel and complementary measure of Lewis basicity.
• The scale is applicable to both inorganic and organic systems, with potential for family-dependent adjustments.
• It offers valuable insights into the nature of halogen bonding and the behavior of complex molecules.