Substituent Effects on the [N-I-N](+) Halogen Bond

Area of Science:

• Supramolecular Chemistry
• Halogen Bonding
• Organic Synthesis

Background:

• The [N-I-N](+) halogen bond is a key interaction in various chemical systems.
• Understanding electronic effects on halogen bonds is crucial for designing synthetic reagents.

Purpose of the Study:

• To investigate how electron density influences the [N-I-N](+) halogen bond.
• To explore the relationship between substituent effects and halogen bond properties.

Main Methods:

• Synthesis of substituted [bis(pyridine)iodine](+) and related complexes.
• Spectroscopic studies including (15)N NMR and UV-kinetics.
• Computational methods (DFT) and single crystal X-ray diffraction.

Main Results:

• Systematic variation of pyridine nitrogen electron density confirmed by (15)N NMR and computational analysis.
• Formation of [N-I-N](+) halogen bonds resulted in significant (15)N NMR coordination shifts.
• Increased electron density at the halogen bond acceptor stabilizes the [N···I···N](+) bond, while electron deficiency reduces stability.

Conclusions:

• The [N-I-N](+) halogen bond is static and symmetric, irrespective of electron density.
• Electron density primarily affects the stability of the halogen bond, not the N-I bond length.
• Modulating electron density offers a method to control the reactivity of [bis(pyridine)halogen](+)-type reagents.