Counterion influence on the N-I-N halogen bond

Area of Science:

• Supramolecular Chemistry
• Halogen Bonding
• Computational Chemistry

Background:

• The [N-I-N]+ moiety forms a cationic three-center halogen bond.
• Understanding counterion influence is crucial for designing novel materials and catalysts.

Purpose of the Study:

• To investigate the impact of counterions on the [N-I-N]+ halogen bond.
• To determine if counterions affect the symmetry and nature of the halogen bond.

Main Methods:

• Translational diffusion coefficient measurements in solution.
• Isotopic perturbation of equilibrium Nuclear Magnetic Resonance (NMR) studies.
• Single crystal X-ray crystallography.
• Density Functional Theory (DFT) computations.

Main Results:

• Counterions remain closely associated with the [N-I-N]+ bond in solution.
• The [N-I-N]+ halogen bond symmetry is maintained regardless of counterion coordination strength.
• Weakly coordinating counterions yield behavior similar to silver(I) complexes, while moderately or strongly coordinating anions induce different geometries in silver(I) systems.
• Iodine-centered systems maintain linearity and lack direct charge transfer with counterions.

Conclusions:

• The [N-I-N]+ halogen bond exhibits inherent symmetry unaffected by counterions.
• This halogen bond is better described as a secondary bond with significant charge-transfer character, rather than a pure coordination bond.