Interplay between Halogen Bonding and Lone Pair-π Interactions: A Computational and Crystal Packing Study.

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Crystallography

Background:

• Halogen bonding (XB) is a key non-covalent interaction driving molecular self-assembly.
• Modified thiophenes offer versatile scaffolds for creating complex supramolecular structures.
• Understanding the interplay of different non-covalent interactions is crucial for designing functional materials.

Purpose of the Study:

• To investigate the supramolecular organization of modified thiophenes driven by N⋅⋅⋅I halogen bonding.
• To elucidate the synergistic effects between halogen bonding and lone pair-orbital (lp⋅⋅⋅π) interactions.
• To experimentally and computationally validate the observed structural arrangements.

Main Methods:

• X-ray diffraction analysis of two polymorphs of a supramolecular complex.
• Quantum mechanical calculations (ωB97X-D/6-31+G(d,p)) in the gas phase.
• Dispersion-corrected Density-Functional Theory (DFT) calculations.

Main Results:

• Two polymorphs exhibited distinct supramolecular arrangements controlled by halogen-bonded pyridyl and tetrafluoroiodobenzene rings.
• One polymorph featured additional O⋅⋅⋅pyridyl and I⋅⋅⋅tetrafluoroiodobenzene lone pair-orbital (lp⋅⋅⋅π) interactions, while the other did not.
• Quantum mechanical calculations confirmed the interplay of these interactions and corroborated longer N⋅⋅⋅I distances in the absence of lp⋅⋅⋅π interactions.

Conclusions:

• This work presents the first experimental and computational evidence for synergy between lone pair-orbital (lp⋅⋅⋅π) interactions and halogen bonding (XB).
• The findings highlight the importance of considering multiple non-covalent interactions for controlling supramolecular architecture.
• This research provides insights into the rational design of ordered structures using modified thiophenes.