Boron triel bonding: a weak electrostatic interaction lacking electron-density descriptors.

Area of Science:

• Solid-state chemistry
• Supramolecular chemistry
• Crystallography

Background:

• π-hole interactions are crucial in molecular recognition and crystal engineering.
• Understanding these interactions requires accurate charge density analysis.
• Previous studies have focused on common π-hole donors like carbon and nitrogen.

Purpose of the Study:

• To accurately describe π-hole interactions in selected compounds using high-resolution X-ray diffraction.
• To compare the fundamental characteristics of π-hole interactions involving boron, carbon, and nitrogen atoms.
• To investigate the role of Bader's Atom in Molecules (AIM) theory in characterizing these interactions.

Main Methods:

• High-resolution X-ray diffraction analyses of single crystals.
• Experimental and theoretical charge density mapping.
• Bader's Atom in Molecules (AIM) theory for topological analysis.

Main Results:

• Experimental charge density maps reveal electron density depletion (electrophilic π-holes) in central B, C, and N atoms of -YO2 units.
• These electrophilic π-holes facilitate intermolecular Lewis acid-Lewis base attractive interactions.
• Unexpectedly, AIM analyses of boron-containing groups (-BO2H2) showed no bond paths or bond critical points between electron-rich sites and the π-hole atoms.

Conclusions:

• π-hole interactions are established through electron density depletion in B, C, and N atoms, leading to attractive forces.
• AIM theory successfully identifies topological descriptors for π-hole interactions in nitro and carboxylic groups.
• The absence of AIM bond paths for boron-containing π-holes suggests a different interaction mechanism or requires further investigation.