Cation recognition by benzene sandwich compounds - a DFT perspective.

Area of Science:

• Computational Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Cation-π interactions are crucial in various chemical and biological systems.
• Sandwich compounds, featuring metal ions coordinated between aromatic rings, offer unique electronic properties.
• Understanding these interactions is key to designing novel molecular receptors.

Purpose of the Study:

• To investigate and quantify cation-π interactions between various cations and benzene/cyclopentadienyl (Cp) sandwich compounds.
• To compare the interaction strengths of different types of sandwich compounds and cations.
• To explore the correlation between interaction strength and geometric changes in sandwich compounds.

Main Methods:

• High-level quantum chemical calculations, specifically CCSD(T)/CBS and DFT (B3LYP/def2-TZVP).
• Systematic study of alkali, alkaline earth, and ammonium cations with benzene and Cp sandwich compounds.
• Analysis of interaction energies and geometric parameters.

Main Results:

• Sandwich compounds exhibit significantly stronger cation-π interactions than uncoordinated benzene.
• Benzene sandwich compounds display the strongest interactions, with a maximum energy of -196.8 kcal mol⁻¹ for Mg²⁺/W(benzene)₂.
• Interaction strength increases in the order: benzene < Cp sandwich < benzene sandwich.
• Geometrical changes in sandwich compounds strongly correlate with cation-π interaction strength.
• Variations in interaction energy across different transition metals (3d, 4d, 5d) were minimal.

Conclusions:

• Benzene sandwich compounds are exceptionally effective in cation-π interactions.
• The strength of cation-π interactions follows a clear trend based on the sandwich compound structure.
• Sandwich compounds, especially those with C₆ aromatic rings, show promise as new receptors for metal cations.