Hydrogen-bridged chelate ring-assisted π-stacking interactions

Area of Science:

• Crystal Engineering
• Supramolecular Chemistry
• Organic Chemistry

Background:

• Salicylideneaniline (SA) derivatives exhibit unique hydrogen-bridged chelate rings with enhanced aromaticity due to NH character.
• Nonconventional π-stacking interactions, termed hybrid π-stacking, occur between quasiaromatic chelate rings and ordinary aromatic rings.
• Pure π-stacking interactions are observed between two hydrogen-bridged quasiaromatic chelate rings.

Purpose of the Study:

• To investigate and characterize novel π-stacking interactions in salicylideneaniline derivatives.
• To explore the influence of aromaticity on the stacking arrangements of these molecular crystals.
• To differentiate these interactions from conventional π···π interactions.

Main Methods:

• Crystal structure analysis of a specific salicylideneaniline derivative.
• Computational analysis of π-stacking interactions.
• Conformational Search (CSD) of molecular crystals.

Main Results:

• Observed hybrid π-stacking interactions between quasiaromatic chelate rings and ordinary aromatic rings.
• Identified pure π-stacking interactions between hydrogen-bridged quasiaromatic chelate rings.
• Demonstrated that aromaticity levels of SA derivative fragments significantly impact stacking arrangements.
• Characterized pure interactions as having more pronounced σ- and π-deficient character compared to hybrid ones.

Conclusions:

• The study elucidates the formation and characteristics of hybrid and pure π-stacking interactions in salicylideneaniline derivatives.
• Aromaticity is a critical factor governing the observed stacking patterns in these molecular crystals.
• These findings expand the understanding of non-covalent interactions in organic materials.