Do solid-state structures reflect Lewis acidity trends of heavier group 13 trihalides? Experimental and theoretical...

Area of Science:

• Inorganic Chemistry
• Materials Science
• Computational Chemistry

Background:

• Understanding Lewis acidity is crucial for predicting reactivity in chemical synthesis and catalysis.
• Group 13 element trihalides (MX(3)) exhibit varying Lewis acid strengths.
• The influence of solid-state packing and intermolecular interactions on observed Lewis acidity is not fully understood.

Purpose of the Study:

• To determine the Lewis acidity trends of aluminum (Al) and gallium (Ga) halides.
• To investigate the impact of solid-state effects on Lewis acidity measurements.
• To establish reliable methods for assessing Lewis acidity in both gas and solid phases.

Main Methods:

• X-ray diffraction studies were employed to determine the structures of metal halide complexes.
• Density Functional Theory (DFT) calculations at the B3LYP/TZVP level were performed.
• Analysis of experimental and theoretical data for complexes with various nitrogen, phosphorus, arsenic, and oxygen donors.

Main Results:

• Established Lewis acidity trends: Al > Ga and Cl ≈ Br > I.
• Observed that solid-state packing effects can mask intrinsic Lewis acidity trends of aluminum halides.
• Demonstrated that shorter donor-acceptor bond distances in solid complexes do not always correlate with higher Lewis acidity due to intermolecular interactions.

Conclusions:

• The intrinsic Lewis acidity order Al > Ga and Cl ≈ Br > I was confirmed.
• Solid-state intermolecular (H···X) interactions significantly influence the observed donor-acceptor bond distances in adducts.
• Donor-acceptor bond distance in solid complexes is not a universally reliable criterion for assessing Lewis acidity.