Structures and stability of I₂ and ICl complexes with pyridine: Ab initio and DFT study

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• Pyridine forms complexes with halogens, influencing its electronic properties.
• Understanding these interactions is crucial for designing new materials and catalysts.

Purpose of the Study:

• To theoretically investigate the thermodynamic stability and bonding characteristics of pyridine-iodine complexes.
• To compare DFT methods with high-level ab initio calculations for accuracy.

Main Methods:

• Density Functional Theory (DFT) using the M06-2X functional.
• High-level ab initio calculations (CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz) for benchmark comparisons.
• Analysis of molecular and ionic isomers, including stability and bonding.

Main Results:

• M06-2X DFT accurately predicts bond distances and dissociation energies compared to benchmark calculations.
• Molecular complexes formed by nitrogen lone pair donation to iodine are most stable.
• Ionic isomers, particularly those with [IPy2]+ cations and I3- or ICl2- counterions, become favorable with oligomerization.

Conclusions:

• The M06-2X functional is reliable for studying pyridine-halogen interactions.
• Complex stability is governed by the mode of interaction (lone pair donation vs. T-shaped).
• Ionic structures and oligomerization play significant roles in the complex formation thermodynamics.